University of Southern California Dissertations and Theses

Some aspects of the metabolism of nervous tissue

(USC Thesis Other)

Some aspects of the metabolism of nervous tissue

PDF

Download

Open document

Flip pages

Download a page range

Download transcript

Copy asset link

Request this asset

Transcript (if available)

Content SOME ASPECTS OF THE METABOLISM OF
NERVOUS TISSUE
A T h esis
P re se n te d to
th e F a c u lty o f th e D epartm ent o f
B io ch em istry and N u tr itio n
U n iv e r s ity o f S o u th ern C a lif o rn ia
]
I n P a r t i a l F u lf illm e n t
o f th e R equirem ents f o r th e Degree
- M aster o f A rts
Dy
C h arles McGaughey
J u ly 1952
UM I Number: EP41328
All rights reserved
INFORMATION TO ALL USERS
The quality of this reproduction is dependent upon the quality of the copy submitted.
In the unlikely event that the author did not send a complete manuscript
and there are missing pages, these will be noted. Also, if material had to be removed,
a note will indicate the deletion.
Dlssartatibn Publishing
UMI EP41328
Published by ProQuest LLC (2014). Copyright in the Dissertation held by the Author.
Microform Edition © ProQuest LLC.
All rights reserved. This work is protected against
unauthorized copying under Title 17, United States Code
ProQuest LLC.
789 East Eisenhower Parkway
P.O. Box 1346
Ann Arbor, Ml 48106-1346
B , o S i M l * * *
This thesis, written by
.............
under the guidance of h-J.&....Facuity Committee,
and approved by all its members, has been
presented to and accepted by the Council on
Graduate Study and Research in partial fullfill-
ment of the requirements for the degree of
A . t t * ......................
D ate............. S . A . Q ...
Faculty Com m ittee
..L coauM l
Chairman
TABLE OF CONTENTS
PACE
INTRODUCTION........................ . ........................................................... 1
THE ENERGY METABOLISM OF BRAIN AND NERVE . . . . . . . 5
G en eral Comparison w ith O ther T issu e s . . . . . .. 5
S u b s tr a te D e g ra d a tio n and O x id a tio n • . • • • . . 8
A naerobic g ly c o ly s is . . . . .................................. 8
Some r e g u la to r s o f g ly c o ly s is 10
The p o s s i b i l i t y o f n o n -carb o h y d rate
s u b s t r a t e s ............................ 13
The unknown f a t e o f hexose ........................ 15
P o s s ib le pathways o f g lu c o se o x id a tio n
and d e g r a d a t i o n ....................... 16
The t r i c a r b o x y l i c a c id (TCA) c y c l e ............. 20
Some r e g u la to r s o f a e ro b ic m etabolism . . . 26
R e la tio n s betw een th e a e ro b ic and a n a e ro b ic
energy so u rc e s . . . . . . .................................. 28
THE CHEMICAL AND METABOLIC NATURE OF ELECTRICAL
' PHENOM ENA IN NERVE ............................. 31
The R e stin g P o t e n t i a l . . . . . ...................................... 31
The A ce ty l C holine P r o b l e m ....................... 34
The r o l e o f a c e t y l c h o lin e i n th e nerve
im pulse .............................. . ...................... 34
The s y n th e s is of a c e t y l c h o l i n e ........................ .... 38
iv
PAGE'
The A ctiv e Nerve . . . . . . ........................................... 43
THE FUNCTION OF GLUTAMIC ACID IN NERVOUS TISSUE . . . 47
The E l e c t r i c a l A c tiv ity o f th e B ra in . . . . . . 47
P o s s ib le Key R oles o f G lutam ic A cid i n Nerve
M e ta b o lis m ................................................................................. 49
Ammonia m e t a b o l i s m ..................................... 50
A c e ty lc h o lin e s y n th e s is • 53
A d ren erg ic a c t i o n ................................ 56
M aintenance o f c a tio n b a la n c e • .................... 57
Carbon d io x id e m etabolism • ••• .. ..• 58
A DESIRABLE EXPERIMENT IN BRAIN METABOLISM . . . . . 64
I n tr o d u c tio n . • • « . • • • . . . . . . . . . . 64
The E xperim ent: The N ature o f th e Pathway o f
M ethyl G lyoxal S y n th e s is i n R at Cortex
Homogenates . . . . . . . . ...................................... 65
BIBLIOGRAPHY- .......................................................................................... 69
. 1
SOME ASPECTS OF THE METABOLISM OF NERVOUS TISSUE
INTRODUCTION
The stu d y o f b r a in and nerve m etabolism has developed
c o n c u rre n tly w ith t h a t of o th e r organs and t i s s u e s . Two
more o r l e s s s e p a r a te avenues have b een fo llo w ed , one b ein g
t h a t o f p r a c t i c a l problem s o f m e n tal and nervous d is o rd e r^
and th e o th e r more academ ic i n t e r e s t s i n com parative i n t e r
m ediary, m etabolism .
The i n i t i a l approach to problem s o f m ental d is o r d e r
was th e g ro s s c l i n i c a l one, where le v e l s o f b i o l o g i c a l
su b sta n c e s i n b lood and t i s s u e s were d eterm in ed i n la r g e
numbers o f norm al and abnorm al p a t i e n t s and th e r e s u l t s
an aly zed s t a t i s t i c a l l y . T his ap p ro ach has proved n o t too
f r u i t f u l , one re a s o n b ein g th e s e l e c t i v e p e rm e a b ility o f
th e blood b r a in b a r r i e r . The r e s o l u t i o n o f th e s e problem s
w i l l th e r e f o r e be l e f t , f o r th e m ost p a r t , to th e more
q u a n t i t a t i v e and b e t t e r c o n tr o lle d b io c h e m ic a l and p h y s io
l o g i c a l a p p ro ac h es, and even th e s e approaches a re so f a r
lim ite d by th e e f f ic ie n c y o f m ethods o f study such a s
e x t r a c t i o n , a n a l y s i s , developm ent o f s u i t a b l e b u ffe re d
media f o r o b se rv in g i s o l a t e d b io c h e m ic a l system s i n v i t r o ,
developm ent o f p e r f u s io n media f o r stu d y in g organs i n v iv o ,
d is c o v e ry o f enzyme i n h i b i t o r s e t c .
2
The stu d y o f th e m etabolism o f nervous t i s s u e has
o ffe re d some s p e c ia l d i f f i c u l t i e s of i t s own. B ra in and
» . ’
n erve have l e n t th em selv es to d i f f e r e n t ty p e s o f in v e s tig a -
I
t i o n . P e r ip h e r a l nerve has been more am endable to th e
stu d y of e l e c t r i c a l phenomena th a n b r a i n and has b een th e
s u b je c t of more d e t a i l e d i n v e s t i g a t i o n o f th e r e l a t i o n s h i p s
o f m etabolism to nerve tr a n s m is s io n . I n d iv id u a l nerve
f i b e r s can be p re p a re d , p la c e d i n s u s ta in in g media and
examined f o r r e l a t i v e l y long p e rio d s o f tim e. The c l a s s i c a l
example o f t h i s p ro c e d u re i s th e use o f th e g i a n t axohe of
th e sq u id , w hich n erve has been c a lle d ”God* s g i f t to th e
n e u r o l o g i s t .w B ra in has been th e o b je c t o f more s tu d ie s
where m etabolism o n ly , and n o t n e c e s s a r ily i t s r e l a t i o n to
th e nerve im pulse i s s tu d ie d . T his has been b ecau se o f th e
read y a v a i l a b i l i t y o f b r a i n t i s s u e i n la r g e q u a n t i t i e s from
a v a r i e t y o f a n im a ls. T his advantage i s somewhat m o d ifie d ,
however, by th e f a c t t h a t th e r e i s more th a n one c e l l type
p r e s e n t e .g . c o r t i c a l and g l i a l , and th e s e have d i f f e r e n t
chem ical p r o p e r t i e s . Because of t h e i r sm all s iz e and
i n t r i c a c y , in d iv id u a l nervous u n its of th e b r a i n have not
been s tu d ie d e i t h e r w ith re g a rd to m etabolism o r th e n a tu re
o f th e nerve im p u lse. Some s tu d ie s of e f f e c t s , m e ta b o lic
and o th e rw ise , o f e l e c t r i c a l s tim u la tio n o f i n t a c t b r a in
i n v iv o have been c a r r ie d o u t.
3
The s u b s t r a te u t i l i z a t i o n , and b e a t p ro d u c tio n o f
p e r ip h e r a l nerve i s v e ry s m a ll, a f a c t w hich has n e c e s s i
t a te d th e developm ent o f v e ry a c c u r a te methods f o r m easuring
th e s e to d eterm in e t h e i r r e l a t i o n to m etabolism and to th e
n erve im p u lse.
Much modern work i s based on i n v i t r o s tu d ie s o f
b r a in s l i c e s o r hom ogenates. I t may, however, be d i f f i c u l t
to g e n e r a liz e from such i n v i t r o work to i n v iv o s i t u a t i o n s .
I n homogenates th e c e l l u l a r a r c h i t e c t u r e i s d is r u p te d and
i n b o th homogenates and s l i c e s , th e absence o f th e n a t u r a l
b lo o d - b r a in b a r r i e r must be ta k e n in t o c o n s id e r a tio n . T his
b a r r i e r , composed o f c a p i l l a r i e s and e p i t h e l i a l t i s s u e , has
a v e ry marked e f f e c t on th e k in d s and amounts o f su b sta n c e s
a v a i l a b l e to th e b r a i n c e l l s . F or example i t e x h i b its a
r e l a t i v e im p e rm e a b ility to n e g a tiv e ly charged io n s , and
su b sta n c e s w ith ca rb o x y l groups seem to be le s s s u ite d to
p assag e th a n o th e r s . M oreover, th e p re se n c e o f v a rio u s
su b sta n c e s i n th e b lo o d stre am may a f f e c t th e p e r m e a b ility
( 1 ) . This b a r r i e r may be r e s p o n s ib le a ls o f o r th e freedom
from en d o c rin e c o n tr o l e x h ib ite d by th e b r a in i n v iv o . I t
may be imperm eable to hormones o f p r o t e i n n a tu re ( 2 ) . Thus,
i n v i t r o s tu d ie s g iv e an i n d i c a t i o n o f th e c a p a b i l i t i e s o f
th e enzyme system s o f th e b r a in , b u t do not d iv u lg e w ith
c e r t a i n t y what th e system s a c t u a l l y do i n v iv o a s determ ined
4
by th e s u b s t r a t e s p r e s e n t and th e amounts I n w hich th e y a re
p r e s e n t.
The p u rp o se o f t h i s p ap e r i s to p r e s e n t a g e n e ra l
review o f v a r io u s a s p e c ts o f th e ' m etabolism o f b r a in and
p e r ip h e r a l n e rv e , to g e th e r w ith p o s s ib le r e l a t i o n s o f
m etabolism to th e nerve im pulse and to th e r e s t i n g p o te n
t i a l , Concerning b r a in , ev id en ce w i l l be p re s e n te d from
homogenates and e x t r a c t s a s w e ll a s s l i c e s , m inces and in
v iv o work. A lthough th e l a s t th r e e a r e u s u a lly o f more
v a lu e i n ap p ro x im atin g a c t u a l p h y s io lo g ic a l c o n d itio n s i n
t
v iv o th a n th e f i r s t two, a l l methods may o f f e r c lu e s to th e
m e ta b o lic p i c t u r e . In th e ca se of n e rv e , m ost work has
been done w ith i n t a c t f i b e r s . I n some c a s e s , such a s th e
s y n th e s is o f a c e ty l c h o li n e , g e n e r a liz a ti o n s can p r o f i t a b l y
be made from n erve to b r a i n and v ic e v e r s a . Some evidence
from e le c tro e n c e p h a lo g ra p h !c s tu d ie s w i l l be p re s e n te d
when i t i s f e l t t h a t th e c o r r e l a t i o n s o b ta in e d betw een
m e ta b o lic c o n d itio n s and ty p e s o f waves observed a re s t r i k
in g enough to w a rra n t d is c u s s io n .
5
THE ENERGY METABOLISM OF BRAIN AND NERVE
G en eral Comparison w ith O ther T issu e s
I n o rg a n iz in g t h i s m a t e r i a l , i t seemed d e s i r a b l e
f i r s t to p r e s e n t a g e n e r a liz e d p i c t u r e o f th e m e ta b o lic
p ro c e s s e s o f nervous t i s s u e and some o f th e d i f f e r e n c e s
betw een nervous and o th e r tis s u e s * This w i l l be fo llo w ed
by a more d e t a i l e d d is c u s s io n o f th e v a r io u s p h ases o f
m etabolism *
B ra in and p e r ip h e r a l nerve seem to e x h i b i t some
i n t e r e s t i n g v a r i a t i o n s from th e g e n e r a l m e ta b o lic scheme a s
i t i s commonly v i s u a l i z e d . T his a p p a re n tly i s th e r e s u l t
• ’ ^ i
o f th e re q u ire m e n ts imposed upon t h e i r chem ical m achinery
by t h e i r s p e c ia liz e d f u n c tio n : t h a t o f r a p id ly t r a n s
m ittin g th e nerve im pulse.
There a r e c e r t a i n fundam ental p r o p e r t i e s o f m etabolism
w hich a r e common to a l l tis su e s'.- C arbohydrate breakdown o f
two p h a s e s, a e ro b ic and a n a e ro b ic , i s c a r r ie d on by a l l ,
though th e prepo n d eran ce o f one o r th e o th e r may v a ry from
t i s s u e to t i s s u e and a t d i f f e r e n t tim es w ith in th e same
t i s s u e . More s p e c i f i c a l l y , a l l t i s s u e s in c lu d in g n erv e (2 )
have now b een shown to c a rry on th e s e two p h ases in c lu d in g
a t l e a s t th e p ro c e s s e s o f p h o s p h o ry la tio n o f g lu c o se and
i t s breakdown to p y ru v a te or phosphoenol p y ru v a te (3 )> and
6
th e e n tra n c e o f a t l e a s t one o f th e l a t t e r In to a t r i c a r
b o x y lic a c id c y c le . Meyerhof (4) f i r s t d e f i n i t e l y
e s ta b lis h e d th e e x is te n c e o f th e p h o s p h o ry la tiv e g l y c o l y t i c
pathway f o r b r a i n i n 1958. This has b een s u b s ta n tia te d ( 2 ).
That a c y c le a t l e a s t s im ila r to th e t r i c a r b o x y l i c a c id
c y c le o ccu rs i n b r a i n seems to have been u n c e r ta in u n t i l
r e c e n tly (5 ) b ecause o f f a i l u r e to observ e th e o x id a tio n o f
c i t r a t e .
The e x is te n c e o f v a rio u s mechanisms o th e r th a n th e
Embden-Meyerhof p la n f o r th e breakdown o f g lu c o se p r i o r to
e n tra n c e in to th e t r i c a r b o x y l i c a c id c y c le have been p o s tu
la te d f o r b r a in . That one o r more o f th e s e e x i s t seems to
be e s ta b li s h e d , b u t e i t h e r th e im portance or th e e x is te n c e
o f a l l has been d e b a te d .
The P a s te u r e f f e c t (s u p p re s s io n o f g ly c o ly s is under
a e ro b ic c o n d itio n s ) has been r e p o r te d a b s e n t f o r b r a in
homogenates ( 6 ) b u t i t i s q u e s tio n a b le w hether t h i s la c k o f
s u p p re s s io n o ccu rs to a la r g e e x te n t i n s l i c e s (7 *8 )* The
b r a in does seem to be a b le to c a l l upon an a e ro b ic p ro c e s s e s
to a id th e a e ro b ic ones in c e r t a i n c o n d itio n s e l i c i t i n g a
la c k o f oxygen ( 9 ) . W hether t h i s p ro p e r ty i s sh ared by
o th e r t i s s u e s i s u n c e r ta in .
The oxygen consum ption (QO2 ) o f p e r ip h e r a l nerve
b o th a t r e s t and d u rin g a c t i v i t y i s u s u a lly v e ry sm all ( 10) .
7
That o f b r a i n seems to he n e a re r to o th e r t i s s u e s . E x p e ri
m ents perform ed i n v iv o u sin g a c a p i l l a r y re s p ir o m e te r
y i e l d v a lu e s o f around 5 cu. m m ./hr./m g. (1 1 ). V alues o f
around 15 have been o b ta in e d f o r s l i c e s by Burk (7 ) . This
does n o t d i f f e r m arkedly from o th e r t i s s u e s l i c e s .
The r e s p i r a t o r y q u o tie n t (R .Q .) o f p e r ip h e r a l nerve
seems to below u n ity e x c e p t d u rin g a c t i v i t y (1 2 ). The R.Q.
o f b r a i n seems c o n s i s t e n t l y to be 1 .0 b o th i n v iv o ( 15) and
i n v i t r o (7 ) . B ra in th u s ap p e a rs to o x id iz e c a rb o h y d ra te
o r i t s d e r i v a t i v e s v e ry n e a rly e x c lu s iv e ly under norm al
c o n d itio n s . However i n em erg en cies, b r a in can p ro b a b ly
o x id iz e f a t s and p erh ap s o th e r su b sta n c e s a s evidenced by an
R.Q. o f O.76-O.8 7 i n th e th ia m in d e f i c i e n t c e r e b r a l c o rte x
o f th e p ig e o n and dog (1 4 ). B reusch and Tulus (15) have
r e p o r te d t h a t an enzyme e x i s t s i n th e b r a in o f c a ts and
p ig eo n s which o x id iz e s a l l "the 0 hydroxy f a t t y a c id s from ,
C i|_ to 0jZ |. •
W ith th e e x c e p tio n o f th e e f f e c t o f th y ro id hormone,
th e b r a i n seems to e x h i b it e x tr a o rd in a ry freedom from
e n d o c rin e c o n tr o l e x c e p t i n d i r e c t l y ( 2 ,1 6 ) . The b lood b r a in
b a r r i e r may have in f lu e n c e h e re .
B ra in seems n o t to u t i l i z e g lycogen a s a f u e l (17)
b u t only sim ple su g a rs such a s g lu c o s e , f r u c to s e ( 18) and
g a la c to s e (1 9 ). However, under c e r t a i n c o n d itio n s , as i n
8
c o n v u lsio n s induced i n m ice by e x t e r n a l s tim u li such a s
j i n g l i n g o f m e ta l tu b e s , o r by d ru g s such a s p ic r o to x in ,
m e tra z o l, am phetam ine, n ik eth am id e e t c . , g lycogen s y n th e s is
can o ccu r (2 0 ) .
B ra in la c k s th e f u e l r e s e rv e s o f o th e r t i s s u e s . In
v i t r o , w ith o u t added s u b s t r a t e , m ost t i s s u e s can c o n tin u e
to r e s p i r e f o r q u i t e some tim e, w hereas w ith b r a in , th e
Q O 2 goes down r a p id ly from th e s t a r t ( 10) .
Some o f th e p o s s ib le d if f e r e n c e s i n c a rb o h y d ra te
m etabolism betw een nervous and o th e r t i s s u e s w i l l be
d is c u s s e d i n th e n e x t s e c tio n .
S u b s tr a te D e g ra d a tio n and O x id a tio n
A naerobic g l y c o l y s i s . That g ly c o ly s is o ccu rs i n
nervous t i s s u e a c c o rd in g to th e Embden-Meyerhof p la n seems
to be w e ll e s ta b lis h e d (4) and a l l th e in te rm e d ia te s have
been i d e n t i f i e d (2 1 ). There seems no re a s o n to b e lie v e
t h a t th e chem ical p ro c e s s e s o f t h i s pathway d i f f e r h e re i n
any o u ts ta n d in g way from thoas o c c u rrin g i n o th e r t i s s u e s .
T here has b een some d e b a te a s to th e im portance o f t h i s
pathway w ith r e l a t i o n to o th e r p o s s i b le mechanisms o f
ca rb o h y d ra te d e g ra d a tio n i n b r a in , and t h i s w i l l be d i s
cussed l a t e r .
G ly c o ly s is i n nerve seems to produce a q u ic k , a n a e r
o b ic so u rce o f energy f o r th e e v e n ts o f a c t i v i t y , to f u r n is h
9
s u b s t r a te f o r f u r t h e r energy m etabolism when oxygen i s
a v a i l a b l e and p o s s ib ly to f u r n is h p a r t o f th e energy f o r
m aintenance o f th e r e s t i n g p o t e n t i a l (2 2 ). The a n a e ro b ic
energy i s u t i l i z e d by means o f a n e t s y n th e s is o f h ig h
energy p h o sp h ate bonds i n a d e n o s in e trip h o s p h a te (ATP) and
c r e a tin e p h o sp h a te . The s to ra g e and r e l e a s e sequence of
th e s e bonds seems to be s im ila r to t h a t i n m uscle. Darwin
and R ic h te r (23) have shown t h a t e l e c t r i c a l s ti m u la tio n of
r a t b r a in cau ses a r a p id f a l l i n p h o sp h o c re a tin e le v e l and
a co rresp o n d in g t r a n s i e n t r i s e i n th e hexose p h o sp h a te .
t
The i n i t i a l changes a r e fo llo w ed by th e r e t u r n o f th e
hexose p h o sp h ate to normal le v e ls accom panied by th e l i b e r
a t i o n of in o rg a n ic p h o sp h a te . These events- i n d i c a t e a
breakdown o f c r e a t i n e p h o sp h ate and ATP f o r energy pro d u c
t i o n and a re e v id e n t up to t e n seconds a f t e r s tim u la tio n .
At 15 to 45 seconds a f t e r s ti m u la tio n , th e b r a in shows a
r e t u r n o f p h o sp h o c re a tin e and in o rg a n ic p h o sp h ate to normal
l e v e l s . ATP showed o n ly a s l i g h t f a l l and r e t u r n to normal
i n 25 seconds. These changes a r e q u a l i t a t i v e l y com parable
to th o se o c c u rrin g i n m uscle c o n tr a c tio n .
One o u ts ta n d in g d if f e r e n c e betw een b r a i n and m uscle
is. t h a t th e form er seems un ab le to b re a k down g ly co g en ,
f o r u t i l i z a t i o n a s a. r e s e rv e f u e l (2 4 ). I t seems only a b le
to s y n th e s iz e gly co g en under th e s p e c ia l c o n d itio n s o f
1 G
c o n v u lsio n s e l i c i t e d by e l e c t r i c shock ( 2 5 ) or by th e d ru g s
i n s u l i n , n ik e th am id e, s tr y c h n in e , p ic r o to x i n , m e tro z o l,
amphetomine e t c . (2 6 ). The re a s o n f o r t h i s i s o b sc u re .
Some r e g u la to r s o f g l y c o l y s i s . S u b s tr a te c o n c e n tra
t i o n . I f b r a in s l i c e s a r e in c u b a te d a n a e r o b ic a lly i n th e
absence o f g lu c o se f o r a few m inutes a t 3 7° c e n tig r a d e , they
lo s e , a t l e a s t i n p a r t , t h e i r a b i l i t y to c a rr y on th e
a n a e ro b ic breakdown o f g lu c o se (2 7 ). I f , however, th e
s l i c e s a r e a g a in exposed to oxygen, th ey r e g a in t h e i r power
to b rin g ab o u t g ly c o ly s is (2 8 ). The p o s s i b i l i t y th e r e f o r e
e x i s t s t h a t su b sta n c e s produced a n a e r o b ic a lly e x e r t an
e f f e c t i n i n h i b i t i n g a n a e ro b ic p r o c e s s e s . I t i s known t h a t
l a c t a t e i n h i b i t s a n a e ro b ic g l y c o l y s i s , a s do D and L
g lu ta m a te and hydroxy g lu ta m ic a c id . T his may be due to
c o m p e titio n f o r enzymes needed i n g ly c o ly s is (2 9 ). In th e
c a se o f th e l a s t two compounds, th e i n h i b i t i o n i s found to
be re v e rs e d by p y ru v a te and i t i s su g g e ste d by W eil-M alherbe
(2 9 ) t h a t t h i s may be due to a r e a c t i o n betw een,them and
p y ru v a te .
A d e n o sin e trip h o sp h a te (ATP) , ad e n o sin e d ip h o sp h a te
(ADP) and a p y ra s e . Meyerhof and W ilson (ty) have found t h a t
f r e e g lu c o se and f r u c to s e a r e m e ta b o liz e d more r a p id ly i n
b r a i n hom ogenates w ith h ig h c o n c e n tr a tio n s o f ATP, w hereas
hexose d ip h o sp h a te i s m e ta b o liz e d more r a p id ly w ith h ig h con-
c e n tr a tio n s o f a p y ra se (ad e n y lp y ro p h o sp h ata se) and t h e r e f o r ts,
11
presum ably, w ith h ig h c o n c e n tr a tio n s o f ADP. I t seems,
t h e r e f o r e , i n co n c u rren ce w ith th e h y p o th e s is o f th e s e
a u th o rs , t h a t th e r a t e o f g ly c o ly s is i s p a r t i a l l y governed
by th e r e l a t i v e c o n c e n tra tio n s o f ATP, ADP and a p y ra s e .
The p o r tio n o f g ly c o ly s is up to hexose d ip h o sp h a te i s
dependent upon ATP f o r th e fo rm a tio n o f g lu c o s e - 6-p h o sp h ate
and o f f r u c t o s e - 1, 6-d ip h o sp h a te and would be a c c e le r a te d by
ATP. The su b seq u en t p o r tio n i s d ependent upon th e p re se n c e
o f ADP a s an a c c e p to r o f h ig h energy bonds s in c e d u rin g th is
phase th ey a r e s y n th e s iz e d and t r a n s f e r r e d to an a c c e p to r
from p h o sp h o g ly c e ric and phosphopyruvic a c id s . Meyerhof and
W ilson found t h a t 9/10 o f th e ap y ra se a c t v i t y i s bound to
th e s t r u c t u r a l elem en ts o f b r a i n hom ogenates. A cc o rd in g ly ,
th e tu rn o v e r o f hexose d ip h o sp h a te i s h ig h when th e s t r u c
t u r a l elem ents a re p r e s e n t and low when e x t r a c t s a r e used
w ith th e s t r u c t u r a l elem ents c e n tr ifu g e d o u t. T his p o in ts
up th e im portance o f c o n s id e r a tio n s of l o c a t i o n o f compounds
w ith in th e c e l l and o f th e r e l a t i v e q u a n t i t i e s p r e s e n t when
i n t e r p r e t i n g e x p e rim e n ta l r e s u l t s .
A denosine-5 -p h o sp h o ric a c id (AMP-5) . G reenberg (30)
has found t h a t a n a e ro b ic g ly c o ly s is i n homogenates i s
i n h i b i t e d s p e c i f i c a l l y by a d e n o sin e - 5 -p h o sp h o ric a c id .
A denosine, AMP3, and ATP do n o t produce I n h i b i t i o n . The
e f f e c t d e c re a s e s a s g ly c o ly s is p ro ceed s i f . t h e i n i t i a l
12
I n h i b i t i o n i s h o t g r e a t . Hexosedipb.osph.ate r a p id ly o v e r
comes th e i n h i b i t i o n . The s u g g e s tio n i s made by G reenberg
t h a t th e p ro d u c tio n and rem oval o f AM P5 may be one o f th e
f a c t o r s c o n t r o ll in g g l y c o l y t i c r a t e i n b r a in .
Ammonium io n . There a r e a t l e a s t fo u r r e a c tio n s i n
th e g l y c o l y t i c system p r e s e n t i n e x t r a c t o f r a t b r a in a c e
to n e powder t h a t a r e s tim u la te d by ammonium io n s . They a r e
th e tra n s p h o s p h o ry la tio n from phosphopyruvic a c id to
a d e n y lic a c id , th e tra n s p h o s p h o ry la tio n to ADP, th e hexo-
k in a se r e a c t i o n and th e phosphohexokinase r e a c tio n . Munz
and H urw itz (31) have shown t h a t th e s e r e a c tio n s w i l l p ro
ceed slow ly i n sodium b u f f e r s when ammonium and p o ta ssiu m
io n s have been removed. They a r e r a p id when,ammonium ion. i s
added. A rch ib ald (32) s t a t e s t h a t ammonium io n f u n c tio n s
a n a lo g o u sly to p o ta ssiu m io n , s tim u la tin g a e ro b ic m etabolism
and i n h i b i t i n g a n a e ro b ic . W ei1-M alherbe (2 9 ) has p erh ap s
r e c o n c ile d th e s e c o n f l i c t i n g o b s e rv a tio n s by fin d in g t h a t in
sm a ll c o n c e n tra tio n s ammonium io n s tim u la te s a n a e ro b ic
g ly c o ly s is w hereas i n l a r g e r amounts i t i s in h i b i t o r y .
P o tassiu m io n . A shford and Dixon (33) have found
t h a t a lth o u g h a e r o b i c a l ly , p o ta ssiu m io n s s tim u la te r e s p i r a
t i o n , l a c t i c a c id p ro d u c tio n and g lu c o se consum ption by
s l i c e s o f r a b b i t c e r e b r a l c o r te x , p o ta ssiu m ex cess combined
w ith an o x ia d e p re s s e s th e l a c t i c a c id p ro d u c tio n and
13
g lu c o se d is a p p e a ra n c e . .P o ta ssiu m th u s seems to s tim u la te
a e ro b ic m etabolism and to i n h i b i t a n a e ro b ic g l y c o l s i s .
Amides and amino a c id e s t e r s . I t has been found (3*0
t h a t mouse b r a in homogenates c o n ta in a f a c t o r i n h i b i t o r y to
a g l y c o ly tic enzyme, p o s s ib ly g ly c e ra ld e h y d e p h o sp h a te
dehydrogenase. C e rta in am ides and amino and e s t e r s p r o te c t
th e g ly c o l y t i c mechanism from t h i s i n a c t i v a t i o n . The
mechanism f o r th e s e p ro c e s s e s seems n o t 't o be c l e a r .
The p o s s i b i l i t y o f n o n -carb o h y d rate s u b s t r a t e s .
There may be some r a t h e r marked d if f e r e n c e s i n pathways o f
g lu c o se d e g ra d a tio n between nervous and o th e r t i s s u e s . I f
th e e x p e rim e n ta l ev id en ce to be c i te d does n o t r e f l e c t th e
developm ent o f unique m e ta b o lic pathw ays i n n erv e, i t a t
l e a s t im p lie s im p o rta n t q u a n t i t a t i v e d e v ia tio n s from o th e r
t i s s u e s .
Evidence i n d ic a t e s t h a t p e r ip h e r a l nerve may use
some s u b s t r a te o th e r th an c a rb o h y d ra te f o r energy m etabo
lism w h ile keeping th e r e s p i r a t o r y q u o tie n t (IQ) n ea r u n ity .
The RQ o f r e s t i n g nerve i s below u n ity . However, when th e
nerve i s te t a n l z e d , th e RQ in c r e a s e s to u n ity , y e t th e
in c re a s e d o x id a tiv e a c t i v i t y seems n o t to be a s s o c ia te d
w ith in c re a s e d lo s s o f c a rb o h y d ra te (35)* M oreover,
acco rd in g to G erard (19)> th e e x tr a o x id a tio n i s not
su p p o rted by added c a rb o h y d ra te . Holmes, e t . a l . (35)
14
an a ly ze d g ly co g en , f r e e su g a r and l a c t i c a c id by two
d i f f e r e n t methods i n b o th r e s t i n g and a c tiv e fro g s c i a t i c
n erv es suspended i n n u t r i e n t media f o r p e rio d s up to n in e
h o u rs. A lthough o x id a tio n in c re a s e d m arkedly in th e a c tiv e
n erv es a s evidenced by a r i s e i n oxygen consum ption, th e re
was no d e t e c t a b le d if f e r e n c e betw een r e s t i n g and a c tiv e
n erv es i n amounts o f g ly co g en , l a c t i c a c id and f r e e sugar
d is a p p e a rin g . C u rio u sly , th e RQ r o s e to u n ity d u rin g
a c t i v i t y . G lucose and g a l a c t o s e , however, p ro lo n g th e
p e rio d d u rin g which i s o l a t e d , non s tim u la te d , mammalian
n erve ta k e s up oxygen a t a ste a d y r a t e ( 19) J th u s t h i s s h i f t
i n s u b s t r a te u t i l i z a t i o n seems to be a s s o c ia te d w ith
a c t i v i t y . I t i s s ta te d by G erard (19) t h a t b r a in may a ls o
e x h i b i t a s h i f t i n s u b s t r a te u t i l i z a t i o n though no f u r t h e r
ev id en ce could be found i n su p p o rt o f t h i s . The RQ o f b ra in
seems c o n s ta n tly to be n e a r u n ity , though more oxygen i s
p ro b ab ly used on s tim u la tio n (3 6 , 3 7 )•
I f such a s h i f t i n s u b s t r a te u t i l i z a t i o n a c t u a l l y
o c c u rs , i t seems p ro b a b le t h a t th e new s u b s t r a te i s d e riv e d
from c a rb o h y d ra te . I t was observed by Holmes, e t . a l . (35)
t h a t d u rin g th e e a r ly p e rio d s o f o x id a tio n by i s o l a t e d b u l l
fro g s c i a t i c n e rv e , more c a rb o h y d ra te was used th a n could
be acco u n ted f o r by oxygen u p ta k e . A fte r a la p s e o f tim e ,
however, oxygen uptake exceeded t h a t which co u ld r e s u l t
15
from o x id a tio n o f th e c a rb o h y d ra te d is a p p e a rin g . P o s s ib ly ,
a su b sta n c e i s s to r e d which has a c a rb o h y d ra te p r e c u r s o r .
The unknown f a t e o f h ex o se. There i s o th e r ev id en ce
t h a t c a rb o h y d ra te can be m e ta b o liz e d w ith o u t com plete
o x id a tio n i n ways o th e r th a n th ro u g h a c c e p te d pathw ays.
R e in er ( 6 ) observed t h a t in b r a i n homogenates only
betw een 78 and 91 p e r c e n t re c o v e ry o f g lu c o se a d m in is te re d
was o b ta in e d a s l a c t i c a c id e s t e r i f i e d p h o sp h ate and C O 2 .
The r e s t m ust have ta k e n some o th e r r o u te o f m etabolism and
p erh ap s have been p a r t i a l l y degraded to some su b stan ce
f u r t h e r u t i l i z a b l e under th e p ro p e r c o n d itio n s .
G eiger and Magnes (37) have i s o l a t e d th e e e r e b r a l
c i r c u l a t i o n and p e rfu s e d th e b r a i n o f th e liv in g c a t w ith
d e f i b r i n a t e d , h e p a rin iz e d ox b lo o d . The v a s o c o n s tr ic to r
su b sta n c e s were removed by p re v io u s p e r f u s io n th ro u g h an
i s o l a t e d l i v e r . They found t h a t oxygen consum ption was
r e l a t e d to c e r e b r a l a c t i v i t y a s ev id en ced by spontaneous
movements o f th e an im al, b u t t h a t g lu c o se d isa p p e a ra n c e was
o f te n g r e a t l y i n ex cess o f what could be accounted f o r by
oxygen consum ption and l a c t i c a c id p ro d u c tio n . The v a lu e s
ranged betw een 5 and 68 p e r c e n t ex c ess g lu c o se d is a p p e a r
ance from a r t e r i a l blood w ith an av e ra g e o f ab o u t 30 p e r
c e n t i n a s e r i e s o f 12 e x p e rim e n ts. I t i s b ro u g h t o u t by
th e a u th o rs t h a t changes in p e r m e a b ility to g lu c o se may
16
be r e s p o n s ib le , b u t t h i s i s n o t a c e r t a i n t y .
E xcess use o f g lu c o se o ver and above o x id a tio n r a t e
has been observed f o r s l i c e s o f s e v e ra l t i s s u e s by O lson
e t . a l . (3 8 ).
The p o s s i b i l i t y e x i s t s t h a t g lu ta m a te and g lu ta m in e
a r e form s i n w hich r e s e r v e o x id izab le: m a te r ia l i s s to r e d by
th e b r a in . T ay lo r and W aelseh (18) have found t h a t a s long
a s g lu c o se i s p r e s e n t i n th e i n t a c t c a ts b r a i n i n v iv o ,
th e r e i s no u t i l i z a t i o n o f f r u c t o s e , and t h a t d u rin g t h i s
p e rio d g lu c o se u t i l i z a t i o n can ro u g h ly be acco u n ted f o r by
oxygen u p ta k e . When th e g lu c o se i s d e p le te d , however,
f r u c to s e can be u sed , and a t t h i s . t i m e , more oxygen i s
ta k e n up th a n can be acco u n ted f o r by f r u c to s e d is a p p e a r
an c e. T his oxygen can, ,however, be accounted f o r by th e
d isa p p e a ra n c e o f g lu ta m in e and g lu ta m ic a c id .
P o s s ib le pathw ays o f g lu c o se o x id a tio n and d e g ra d a
t i o n . G lucose c a n ,p ro b a b ly be o x id iz e d i n b r a i n p r i o r to
th e t r i c a r b o x y l i c a c id c y c le . The use o f d i f f e r e n t i a l
i n h i b i t o r s has in d ic a te d t h a t th e u t i l i z a t i o n o f oxygen i n
b r a i n does n o t n e c e s s a r ily in v o lv e th e o x id a tio n o f p y ru v a te .
T his i n d i c a t e s pathways o f g lu c o se breakdown o th e r th a n th e
com plete Embden-Meyerhof p la n , p re c e d in g th e K re ls c y c le
i
and in v o lv in g th e u t i l i z a t i o n o f oxygen. Thus i n h i b i t o r s
such a s n ic o tin e and hydroxym oionate d im in is h oxygen
17
consum ption o f b r a in s l i c e s i n th e p re se n c e , o f l a c t a t e to a
g r e a t e r e x te n t th a n i n th e p re se n c e o f g lu c o se (39*40). I n
f u r t h e r su p p o rt o f t h i s , i t has been f o u n d .(41) t h a t I n th e
p re se n c e o f s u f f i c i e n t n ic o tin e tb co m p letely i n h i b i t
p y ru v a te o x id a tio n , th e oxygen consum ption o f r a t c o rte x
s l i c e s could be acco u n ted f o r by g lu c o se u t i l i z a t i o n . On
th e o th e r hand, i n kidney and t e s t i s s l i c e s , g lu c o se o x id a
t i o n was co m p letely p re v e n te d by n ic o tin e , in d ic a t in g th e
absence o f e x tr a o x id a tiv e p ro c e s s e s h e re . N ic o tin e and
hydroxym alonate b lo c k th e fo rm a tio n o f p y ru v a te from l a c t a t e
as w e ll a s th e su b seq u en t o x id a tio n o f p y ru v a te .
One p o s tu la te d scheme o f o x id a tiv e g lu c o se u t i l i z a
t i o n f o r which th e re i s evidence n o t o n ly i n b r a in b u t in
o th e r t i s s u e s and y e a s t a s w e ll was uncovered by D ickens
(42) i n 1956. Hexose i s f i r s t e s t e r i f i e d to h e x o se -6-p h o s-
p h a te , th e n o x id iz e d to 2 -heto p h o sp h o h ex o n ate and f i n a l l y
degraded to p e n to se p h o sp h o ric a c id by o x id a tiv e d e c a r
b o x y la tio n . Then, presum ably by a c o n tin u a tio n o f t h i s
p r o c e s s , th e d e g ra d a tio n i s co n tin u ed down to a th r e e
carbon frag m en t i n g u in e a p ig a n d , r a t b r a in s l i c e s . I t was
found l a t e r (43) t h a t t h i s p ro c e s s co u ld y i e l d 0Q 2 and
e th a n o l i n b e e r y e a s t. T hat an enzyme o ccu rs i n b r a i n a s
w e ll a s most o th e r t i s s u e s which c a ta ly z e s th e fo rm a tio n o f
p e n to s e - 6-p h o sp h a te and which has TPN a s i t s coenzyme has
18
been shown by H orecker (4 4 ). T his mechanism has s in c e been
r e f e r r e d to a s th e hexose p h o sp h ate sh u n t.
The e x is te n c e o f t h i s mechanism seems to be w e ll
e s ta b li s h e d . I t would ac co u n t f o r some o f th e o x id a tiv e
d e s t r u c t i o n o f g lu c o s e , y e t n e i th e r th e q u e s tio n o f w hether
i t i s th e s o le pathway f o r t h i s d e s t r u c t i o n nor i t s impor
ta n c e w ith r e l a t i o n to o th e r p ro c e s s e s o f g lu c o se b re a k
down has been d e te rm in e d .
E xperim ents by A shford and Holmes (17) have in d ic a te d .
t h a t an a n a e ro b ic mechanism o f g lu c o se breakdown o th e r th a n
th e Embden-Meyerhof p la n i s q u a n t i t a t i v e l y m ost im p o rta n t.
They observed t h a t im m o b iliz a tio n of p h o sp h ate by calcium
d id n o t p re v e n t th e fo rm a tio n o f l a c t i c a c id from g lu c o s e ,
and t h a t th e v e l o c i t y of th e l a c t i c a c id fo rm a tio n was not
in c re a s e d by th e re p la cem en t o f th e p h o sp h a te . A shford (45)
th e n showed t h a t when hexose monophosphate o r d ip h o sp h a te
and g lu c o se a r e p r e s e n t to g e th e r , th e g ly c o ly s is produced
i s th e sum o f th e g ly c o ly s is o f th e p h o sp h ate e s t e r s and o f
th e g lu c o s e . These ex p erim en ts were perform ed w ith b r a in
m inces. E u le r, e t . a l . (4 6 ), u sin g c e l l f r e e b r a i n
e x t r a c t s , th e n found s i m i l a r i t i e s i n g ly c o ly s is betw een
th e s e and s im ila r m uscle p r e p a r a t io n s . T his a s c r ib e d a
g r e a t e r im portance to g ly c o l y s i s . I t was th e n found by
Johnson (47) t h a t a p p r e c ia b le q u a n t i t i e s o f 4 g ly c e r o l
19
p h o sp h ate were m e ta b o liz e d o n ly in th e p re se n c e o f oxygen,
and by A shford (48) t h a t l a c t a t e was form ed only to a sm all
e x te n t from p y ru v a te and oC g ly c e r o l p h o sp h ate i n b r a in
m in ces. B oth o f th e s e o b s e rv a tio n s le s s e n th e im portance
o f com plete g l y c o l y s i s . R ecent o p in io n seems to h old t h a t
g ly c o ly s is p la y s a n im p o rta n t p a r t i n a l l n erve m etabolism ,
b u t i t seems n o t to be th e only pathw ay o f g lu c o se d eg rad a
ti o n . The r e l a t i o n s betw een th e v a r io u s mechanisms o f
breakdown i s n o t f u l l y u n d e rsto o d .
The p o s s i b i l i t y e x i s t s , though u n s u b s ta n tia te d , t h a t
one o f th e mechanisms of g lu c o se breakdown o th e r th a n th e
Embden-Meyerhof p la n depends upon th e fo rm a tio n o f m ethyl
g ly o x a l from g lu c o s e . M ethyl g ly o x a l can be formed from
p h o sp h o g ly cerald eh y d e (49), and i n l i v e r homogenates from
hexose d ip h o sp h a te (50) where i t i s c o n v e rte d in t o L
l a c t i c a c id by g ly o x a la s e and red u ced g lu ta th io n e (5 1 )*
B ra in t i s s u e su sp e n sio n s have been found to form l a c t i c
'
a c id fo u r tim es as r a p id ly from m eth y l g ly o x a l as from
g lu c o s e , w hereas m uscle su sp e n sio n s form l a c t i c a c id fo u r
to f i v e tim es as r a p id ly from g ly co g en a s from m ethyl
g ly o x a l (5 2 ). I t i s c o n c e iv a b le a ls o t h a t m ethyl g ly o x a l
may be formed I n Dickens* hexose p h o sp h a te sh u n t.
L a c tic a c id w i l l n o t overcome e n t i r e l y th e io d o -
a c e t a t e I n h i b i t i o n o f g lu c o se d e s t r u c t i o n (5 3 ). T his p o in ts
20
to th e p o s s i b i l i t y o f a n o th e r pathway o f d e g r a d a tio n which
i s a ls o in h ib i te d by io d o a c e ta te , y e t which does n o t need
to p ass th ro u g h th e in te r m e d ia te s o f l a c t a t e o r p y ru v a te i n
o rd e r to e x h i b it th e u t i l i z a t i o n o f oxygen. More work i s
needed i n o rd e r t h a t th e n a tu re o f th e s e o x id a tio n s and
d e g ra d a tio n s be more c l e a r l y e lu c id a te d . T hat pathways
e x i s t in b r a in o th e r th a n th e c l a s s i c a l g ly c o ly s is and th e
o x id a tiv e Krebs c y c le seems e s ta b li s h e d . M oreover, a t
l e a s t one o f th e s e u se s oxygen and p ro b a b ly one does n o t.
F i n a l l y , i t i s in d ic a te d t h a t one o r more o f th e s e pathw ays,
i f n o t unique f o r b r a i n t i s s u e , i s a t l e a s t more im p o rta n t
h ere' th a n i n o th e r t i s s u e s .
The t r i c a r b o x y l i c a c id ( TOA) c y c le . U n til r e c e n tly
i t had n o t been c o n c lu s iv e ly d em o n strated t h a t th e o x id a tio n
o f p y ru v a te i n b r a i n in v o lv e d a t r i c a r b o x y l i c a c id c y c le
(5 ^ ). One re a s o n f o r q u e s tio n n in g th e o p e r a tio n o f th e TCA
c y c le i s b r a in was th e o b s e rv a tio n t h a t th e in c re a s e d oxy
gen uptake observed on a d d itio n o f fu m arate w ith p y ru v a te
was n o t observed w ith c i t r a t e , which supposedly could n o t,
t h e r e f o r e , be an in te rm e d ia te (55)• Coxon e t . a l . (5 )
found, however, t h a t c i t r a t e and a su b sta n c e e s tim a te d a s
k e t o g lu ta r a t e accum ulate d u rin g th e o x id a tio n o f p y ru
v a te i n th e p re se n c e o f fu m arate and m a lo n ate. T his sub
s t a n t i a t e d th e e x is te n c e o f a Krebs c y c le . U n lik e kidney
21
p r e p a r a tio n s , b r a i n homogenates dp n o t o x id iz e c i t r a t e ,
a c c o rd in g to th e s e w o rk e rs, and c i s a c o n i t a t e i s o x id iz e d
only to a sm a ll e x te n t. They advanced th e view t h a t c i t r i c
a c id i s n o t on th e c y c le , b u t e x i s t s a s a s id e p ro d u c t.
The d i r e c t p a r t i c i p a t i o n o f e i t r a t e i n th e TCA c y c le i n
p ig eo n l i v e r was th e n made v e ry l i k e l y by th e work o f S te r n
and Ochoa (5 6 ) who found c i t r a t e fo rm a tio n i n homogenates
v i a th e c o n d e n sa tio n o f a c e t a t e and o x o la c e ta te i n th e
p re se n c e o f ATP, Goenzyme A and magnesium io n . The
a c o n ita s e c o n c e n tr a tio n s i n th e s e ex p erim en ts were k e p t so
low t h a t fo rm a tio n o f c i t r a t e from a c o n i t a t e was p re c lu d e d .
M oreover, O gstons co n cep t o f enzymic s p e c i f i c i t y f o r a
c e r t a i n p a r t o f th e sym m etrical c i t r a t e m olecule (57) has
been s u b s t a n tia te d by P o t t e r and H e id e lb e rg e r (5 8 ) . They
showed a symm etric l a b e l l i n g o f th e ca rb o x y l o f c^-ketoglu-
t a r a t e formed e n z y m a tic a lly from i s o l a t e d ca rb o x y l l a b e ll e d
c i t r a t e . T his c i t r a t e had been s y n th e s iz e d by a r a t l i v e r
homogenate o x id iz in g o x a la c e ta te and p y ru v a te . The o ld
argum ents w hich p la c e d c i t r a t e o f f th e c y c le th u s seem to
be in v a l i d a t e d , a t l e a s t f o r l i v e r . I t rem a in s, however,
d i f f i c u l t to e x p la in th e f a i l u r e o f Coxon e t . a l . (5) to
observe th e o x id a tio n o f c i t r a t e i n t h e i r b r a in p r e p a r a t i o n s .
S t i l l a n o th e r anomaly i s t h a t , w hereas i n th e p re se n c e o f
p o ta ssiu m , magnesium, in o rg a n ic p h o sp h a te , cytochrom e C,
22
o x a la c e ta te and ATP, c i t r a t e accu m u lates i n l i v e r and kidney
hom ogenates, i t does n o t do so i n b r a in and h e a r t ( 169) .
The e s ta b li s h in g o f e i t r a t e as th e i n i t i a l co n d e n sa tio n
p ro d u c t i n l i v e r makes re a s o n a b le a t e n t a t i v e s u p p o s itio n
t h a t t h i s may a ls o o ccu r i n b r a in , b u t i n view o f th e
o th e r d e v ia tio n s o f nerve m etabolism from t h a t o f o th e r
t i s s u e s , th e re i s d an g er i n making g e n e r a liz a ti o n s o f t h i s
ty p e . E xperim ents such a s th o se o f S te r n and Ochoa (5 6 )
(above) should be perform ed w ith b r a in to e s t a b l i s h c i t r a t e
a s an in te rm e d ia te h e re .
I t was found by Coxon e t . a l . (5 ) t h a t when fum arate
i s a b s e n t, th e o x id a tio n o f p y ru v a te i s a s s o c ia te d w ith th e
fo rm a tio n o f a c e t a t e . T his o b s e rv a tio n had been en la rg e d
upon by Long (59) i n 19^6. He found t h a t th e a d d itio n o f a
d ie a r b o x y lie a c id does n o t in c r e a s e th e a e ro b ic rem oval of
p y ru v a te by b r a i n hom ogenates. In th e absence o f a d ic a r -
boxy l i e a c id , th e r e a c tio n .c o r r e s p o n d s to p y ru v a te i~ G .5
acetate-f-CGg w hereas i n i t s p re se n c e n e a rly com plete o x id a
t i o n ta k e s p la c e a s shown by p y r u v a te - t2 .5 O 2
a lth o u g h some a c e t a t e i s s t i l l form ed. T his a g a in su p p o rts
Coxon e t . a l . (5 ) who found l e s s a c e t a t e and more c i t r a t e
and k e t o g lu ta r a t e i n th e p re se n c e o f la r g e amounts o f
fu m arate and o x a l a c e ta t e . I n some t i s s u e s such a s h e a r t ,
25
t h i s re q u ire m e n t o f a d ic a r b o x y lic a c id seems to he a
' r e q u i s i t e f o r any o x id a tio n a t a l l , even th e o x id a tiv e
d e c a rb o x y la tio n of p y ru v a te , w hich means t h a t th e d e c a r
b o x y la tio n o f p y ru v a te and th e c o n d e n sa tio n a r e in te rd e p e n
d e n t h e re (6 0 ). Such dependence could a ls o e x i s t i n b r a i n
and co u ld be m ediated th ro u g h th e Go. A system (6 0 ).
Because o f th e im m ediate and s e rio u s n a tu re o f th e
nervous symptoms evidenced i n d e f i c i e n c i e s o f th ia m in e a
g r e a t amount o f i n t e r e s t has c e n te re d around i t s r o l e i n
b r a i n and nerve m etabolism . T hat p o l y n e u r i t i s m ight be due
to a v ita m in d e f ic ie n c y was f i r s t su g g e sted by S h a ttu c k i n
1928 and M inot i n 1926 ( 6 l , 6 2 ) • J o l l i f f e and C o lb e rt ( 6 5)
showed t h a t th e d isa p p e a ra n c e o f n e u r i t i s i n th e a lc o h o lic
a d d ic t upon th e i n s t i t u t i o n of v ita m in B -l th e ra p y depended
upon th e v ita m in s c a l o r i c r a t i o . That e o c a rb o x y la s e ils
in d is p e n s a b le f o r th e o x id a tio n o f l a c t i c a c id i n th e
c e n tra l^ n e rv o u s system was f i r s t shown by Galvao and
P e r e ir a (6 ^ )• There i s a l a r g e r r e l a t i v e in c r e a s e i n
co c a rb o x y la se o f b r a i n th a n o f o th e r organs when a v i t a
m in o tic p ig e o n s a r e dosed w ith th ia m in e ( 65)5 th u s th e
compound may be o f s p e c ia l im portance h e re . The o b s e rv a tio n
o f R e in er (6) t h a t p y ru v a te o x id a tio n may be a t l e a s t one
o f th e r a t e d ete rm in in g s te p s i n th e c a rb o h y d ra te o x id a tio n
o f b r a i n homogenates may e x p la in th e c r u c i a l im p o rtan ce o f
24
c o c arb o x y lase e s p e c i a lly i n b r a in , where o x id a tio n s a re
c a r r ie d on so r a p id ly and where c a rb o h y d ra te and i t s
d e r i v a t i v e s a r e p r a c t ic a lly , th e s o le s u b s t r a t e s , n o rm ally .
L ip s e tt and O r e s c i t e l l i (3) have r e c e n tly produced
evidence t h a t p h o sp h o en o lp y ru v ate r a t h e r th a n p y ru v a te
e n te r s d i r e c t l y in to th e o x id a tiv e c y c le i n r a t c e r e b r a l
c o rte x s l i c e s and t h a t p o ta ssiu m io n c a ta ly z e s th e r e a c t i o n
phosphopyruvate -t~ ADP -^ C -2 fragm ent -f- ATP. I t was found
t h a t th e r e was a marked s tim u la tio n o f oxygen uptake when
g lu c o s e , p y ru v a te o r l a c t a t e were used a s s u b s t r a t e s , con
firm in g p re v io u s w o rk e rs' r e s u l t s . The amount o f s tim u la
t i o n o f QO 2 by KG1 v a r ie d d i r e c t l y w ith th e c o n c e n tr a tio n
o f p y ru v a te . T his would n o t be ex p ected i f p y ru v a te i t s e l f
were e n te r in g th e c y c le d i r e c t l y , s in c e t h i s r e a c t i o n i s
n o t c a ta ly z e d by p o ta ssiu m io n . .The e x tr a QO 2 when g lu c o se
was used a s s u b s t r a te was th u s e x p la in e d by th e g r e a t e r
p ro d u c tio n o f ATP th ro u g h th e breakdown o f phosphopyruvate
a s in d ic a te d above. I f t h i s h y p o th e s is i s t r u e , th e n th e re
should be a c e r t a i n r a t i o o f g lu c o se to p y ru v a te c o n c e n tra
ti o n s w hich would p re v e n t th e in c r e a s e i n Q02 produced by
p y ru v a te i n a p o ta ssiu m c o n ta in in g medium. T his was found
to be t r u e . I t was e x p la in e d th a t th e s e r e s u l t s d id not
remove th e p o s s i b i l i t y t h a t p o ta ssiu m Io n was c a ta ly z in g a
r e a c t i o n f u r t h e r up th e g ly c o l y t i c c y c le , b u t such a
(r*
25
h y p o th e sis was th o u g h t to he u n n ec essary i n view o f th e
r e s u l t s .
As concerns th e r e s t o f th e TGA c y c le i n b r a i n , th e
p ro c e s s e s a s r e p o r te d so f a r seem to be s im ila r to th o se
o c c u rrin g i n o th e r o rg a n s. P y ru v a te i s co m p letely o x id iz e d
and t h i s r e q u ir e s th e p re se n c e o f d ip h o sp h o p y rid in e
n u c le o tid e (DPN), in o rg a n ic p h o sp h a te , magnesium io n , ATP,
cytochrom e 0 and a.C -4 d ic a r b o x y lic a c id ( 6 6) . In c e n t r a l
nervous system hom ogenates, o x id a tiv e enzyme a c t i v i t y i s
found to be a s s o c ia te d w ith th e m ito c h o n d ria l f r a c t i o n (21)
and a l l o f th e TGA I n te r m e d ia te s seem to have b een i d e n t i
f i e d i n nervous t i s s u e . I n r e s t o r i n g r e f l e x re s p o n s e s , i n
i s o l a t e d p e rfu s e d r a t s p in a l co rd , w hich had d is a p p e a re d on
w ith h o ld in g g lu c o se f o r two to fo u r m in u te s, p y ru v a te ,
i s o c l t r a t e , k e t o g l u t a r a t e , g lu ta m a te , g lu ta m in e and p a r t i
a l l y o x a la c e ta te were e f f e c t i v e . T his was n o t t r u e , however
o f a c e t a t e , l a c t a t e , s u c c in a te , fu m a ra te , and ra a la te ( 6 2).
I t was s t a t e d to be o b scu re why some members and n o t o th e rs
o f th e TGA c y c le w ere e f f e c t i v e . I t i s known t h a t s u c c in a te
m arkedly ( 6 7) , l a c t a t e (3 ) , a c e to a c e ta te s l i g h t l y ( 6 8) , and
g lu ta m a te ( 69) in c r e a s e r e s p i r a t i o n of b r a in s l i c e s and
t h a t s u c c in a te goes q u a n t i t a t i v e l y to X . fu m arate and 1
m a la te (7 0 ). I t has b een found (7 1 ) t h a t C02 from la b e le d
b ic a r b o n a te i s f ix e d s o le ly in th e t e r t i a r y c a rb o x y l o f
26
c i t r a t e , showing a pathway from c i t r a t e th ro u g h o tk e to g lu -
t a r a t e s im ila r to o th e r t i s s u e s . B ra in s l i c e s have "been
r e p o r te d n o t to c a ta ly z e th e d e c a r b o x y la tio n o f o x a la c e ta te
to p y ru v a te a p p r e c ia b ly (7 0 ) ; however t h i s i s a spontaneous
r e a c t i o n w hich o ccu rs r e l a t i v e l y r a p i d l y a t p h y s io lo g ic a l
pH v a lu e s and i s c a ta ly z e d by m e ta l c a tio n s and amino a c id s
( 6 0) .
As re g a rd s 002 f i x a t i o n , i t seems t h a t th e o nly
pathway f o r t h i s uncovered so f a r i s t h a t v i a oC k e to g lu tu r a t
as m entioned above (7 1 )* Ho f i x a t i o n by t h i s o r any o th e r
pathway was observed by S t e r n (7 2 ) f o r g u in e a p ig , p ig e o n
o r sheep c o rte x s l i c e s a n a e r o b ic a lly . CO 2 f ix in g c a p a c ity
i s low f o r h e a r t and p ig e o n b r e a t m uscle a e r o b i c a l ly (7 3 )
and p erh ap s lo w est f o r b r a i n (7 2 ). T his low G O 2 f ix in g
a b i l i t y o f b r a i n , p erh ap s e f f e c t e d o nly th ro u g h th e one
pathway m entioned, could have a r e l a t i o n to grand mal
e p ile p s y , i n w hich g r a d u a lly m ounting CO 2 v a lu e s a r e
observed p r i o r to th e s e iz u r e s (7* 0 *
Some r e g u la to r s o f a e ro b ic m etab o lism . In o rg a n ic
p h o sp h a te . T his su b sta n c e o c c u rs i n norm al b r a in i n con-
c e n tr a tio n s o f ab o u t 5 x 10 - M (75)* I t i s i n t e r e s t i n g ,
t h e r e f o r e , t h a t r e s p i r a t i o n o f b r a i n s l i c e s has been
observed to in c r e a s e w ith in c r e a s e i n p h o sp h ate c o n c e n tra
t i o n w ith in th e same ra n g e , f o r in s ta n c e l - 20x l 0- 3M. a s
27
found by Banga, Ochoa and P e te r s (7 5 ) . O ther ev id en ce a ls o
e x i s t s f o r t h i s (7 6 ) . D ecreases i n in o rg a n ic p h o sp h ate
a r e caused by g lu ta m a te and may be r e l a t e d to th e e f f e c t s
of t h i s compound on b r a i n r e s p i r a t i o n . G lutam ate I n h i b i t s
a n a e ro b ic g ly c o ly s is ( 2 9 ) , and a g lu ta m y l p h o sp h a te has
been p o s tu la te d a s an in te rm e d ia te i n th e s y n th e s is o f
g lu ta m in e by E l l i o t (77)* T his i n h i b i t i o n may th e r e f o r e
be th e r e s u l t o f c o m p e titio n f o r in o r g a n ic p h o sp h a te .
Ammonium i o n . T his io n may have an i n h i b i t o r y e f f e c t
on a e ro b ic m etabolism a s found by P o tte r and R ecknagel (78),
These w orkers were a b le to s h i f t p y ru v a te m etabolism i n a
p r e d ic ta b le manner from one pathway to a n o th e r a s a conse
quence o f th e c o m p e titio n o f ammonium io n s f o r at- k e to g lu -
t a r i c a c id and a p r e v e n tio n of o x a la c e ta te fo rm a tio n .
A rc h ib a ld (32) s t a t e s to th e c o n tra ry t h a t ammonium io n
fu n c tio n s a n a lo g o u sly to p o ta ssiu m io n , s tim u la tin g a e ro b ic
m etabolism and i n h i b i t i n g a n a e ro b ic . The t r u t h p ro b ab ly i s
t h a t th e io n can a c t b o th a s a s tim u la tin g and i n h i b i t o r y
a g e n t depending upon th e e x i s tin g c o n d itio n s . I t w i l l be
r e c a l l e d from th e d is c u s s io n o f th e e f f e c t o f ammonium io n
on g ly c o ly s is t h a t s ti m u la tio n o r i n h i b i t i o n may depend on
c o n c e n tr a tio n (2 9 ). Ammonium io n seems to i n h i b i t carbon
d io x id e f i x a t i o n a s found by Crane and B a ll (73) and by
W eil-M alherbe (2 9) .
28
P otassium io n * T his io n seems to s tim u la te a e ro b ic
m etabolism w h ile i n h i b i t i n g a n a e ro b ic g ly c o ly s is (3 3 ,7 9 ) as
a lre a d y d is c u s s e d i n c o n n e c tio n w ith g l y c o l y t i c r e g u l a t o r s .
I t i s p ro b a b le t h a t j u s t a s i n g l y c o ly s is , a e ro b ic
m etabolism i s a ls o r e g u la te d by d e g re e o f c o m p e titio n f o r
enzymes by v a rio u s s u b s t r a t e s , r e l a t i v e c o n c e n tr a tio n s o f
ATP, ADP and a p y ra s e , and o th e r su b sta n c e s o r c o n d itio n s .
Those m entioned h e re a r e th e ones upon w hich some r a t h e r
d e f i n i t i v e work h a s .b e e n done.
R e la tio n s betw een th e a e ro b ic and a n a e ro b ic energy
s o u r c e s . The b r a i n seems to be a b le to c a l l upon th e
a n a e ro b ic p ro c e s s e s to a i d th e a e ro b ic ones i n p a r t i a l
an o x ia and i n re sp o n se to th e a c t i o n o f c e r t a i n d ru g s and
p h y s ic a l p ro c e s s e s w hich produce a n i n d i r e c t a n o x ia o r i t s
e q u iv a le n t. A gents w hich e x e r t t h i s e f f e c t and t h e i r
mechanisms o f a c tio n a r e a s fo llo w ss Cyanide p o iso n s th e
cytoehrom e o x id a se system . N itro g e n d is p la c e s oxygen.
M e tra zo l p ro d u ces c o n v u lsiv e s e iz u r e s , sim u lta n e o u sly i n t e r
r u p tin g r e s p i r a t i o n and d e c re a s in g th e s a t u r a t i o n o f hemo-
. « f c
g lo b in i n a r t e r i a l b lo o d . E l e c t r i c , shock produces co n v u l
sio n s w ith a n e f f e c t s i m i l a r - t o t h a t o f m e tra z o l (9)*
I n th e ca se o f cy an id e f o r exam ple, i t i s known t h a t
t h i s su b sta n c e has a s tim u la tin g e f f e c t when g iv e n i n sm a ll
d o s e s . Loewenhart jet. a l . (80) found t h a t sm all d o ses o f
29
sodium cyanide caused a la r g e in c re a s e i n p h y s ic a l and
m e n tal a c t i v i t y i n a stu p o ro u s ca se o f s c h iz o p h re n ia . I t
i s known t h a t d e p r iv a tio n o f oxygen in c r e a s e s b o th th e
d e s t r u c t i o n o f g lu c o se (81) and th e p ro d u c tio n o f l a c t i c
a c id (82) i n c e r e b r a l c o rte x s l i c e s o f th e r a b b i t and r a t .
More r e c e n tly th e s e r e s u l t s were o b ta in e d w ith human
c o rte x (7 9 ). t h i s ca se enormous I n c r e a s e s i n th e r a t e
o f l a c t i c a c id p ro d u c tio n and g lu c o se consum ption were
o b ta in e d -in an o x ia and i t i s su g g e sted by Dixon (79) t h a t
many o f th e i r r i t a t i v e phenomena en c o u n tered a s a r e s u l t o f
p a th o lo g ic a l p ro c e s s e s i n th e human b r a i n may be due to th is
s tim u la tio n o f m etabolism consequent upon oxygen sh o rta g e
i n nerve c e n te r s .
The r e l a t i o n betw een th e a n a e ro b ic and a e ro b ic
so u rce s o f energy i n th e phylogeny o f m etabolism a re
p a r t i c u l a r l y I n t e r e s t i n g i n , t h e b r a i n . The a b i l i t y o f
b r a in t i s s u e to w ith s ta n d anoxia seems to depend upon th e
amount o f energy w hich can be o b ta in e d a n a e r o b ic a lly . In
a l l an im als s tu d ie d , c o r r e l a t i o n s have been o b ta in e d be
tween a b i l i t y to su rv iv e la c k o f oxygen and th e d eg ree to
w hich energy i s f u rn is h e d a n a e r o b ic a lly . T his a b i l i t y
v a r i e s w ith age and s p e c ie s . I t i s found t h a t th e newborn
an im al e x h i b its an e x tr a o rd in a r y to le r a n e e to an o x ia i n
many d i f f e r e n t s p e c ie s . As th e an im al grow s, b o th th e
a e ro b ic and a n a e ro b ic energy so u rce s in c r e a s e , b u t th e
30
a e ro b ic so u rce does so more r a p i d l y (83*84). T his i s
r e f l e c t e d i n d e c re a se d a b i l i t y to s u rv iv e an o x ia a s th e
an im al grows o ld e r . T his s h i f t from a n a e ro b ic to a e ro b ic
o x id a tio n system s which o ccu rs w ith grow th may be th e
r e s u l t o f enzym atic changes. Mew enzyme system s may a p p e ar
such a s cytochrom e G (8 5 ) , and a l l enzymes may in c r e a s e i n
c o n c e n tr a tio n (86)•
31
THE CHEMICAL AM) METABOLIC NATURE OF
ELECTRICAL PHENOMENA IN NERVE
The R e stin g P o t e n t i a l
The com plete m e ta b o lic scheme a s s o c ia te d w ith th e
e l e c t r i c a l c h a r a c t e r i s t i c s o f nerv% e i t h e r a c t i v e o r r e s t
in g , has n o t b e e n -e lu c id a te d . I t i s known t h a t th e r e s t i n g
p o t e n t i a l i s m a in ta in e d by o x id a tiv e m etabolism . I t depends
upon th e i n t e g r i t y o f th e d eh y d ro g en ase-cy to ch ro m e-cy to -
chrome o x id a se system ( 8 7 )• Some e l u c i d a t i v e work has been
done by Shanes and Brown (22) a s to th e r e l a t i o n s betw een
m etabolism and th e r e s t i n g p o t e n t i a l . A d e c lin e i n r e s t i n g
p o t e n t i a l o ccu rs i n th e absence o f Qg, and th e r i s e i n r e s t
in g p o t e n t i a l w hich o r d i n a r i l y o cc u rs w ith a r i s e i n tem per
a t u r e does n o t ta k e p la c e in a n o x ia . O x id a tiv e m etabolism
seems to be c a p ab le o f e n t i r e l y m a in ta in in g th e r e s t i n g
p o t e n t i a l , however th e r e I s a more r a p id f a l l of r e s t i n g
p o t e n t i a l I n an lo d o a c e tic a c id -p o is o n e d fro g nerve in
R inger s o lu t io n w ith p y ru v a te added th a n o cc u rs i n R inger
s o lu tio n d u rin g a n o x ia and w ith o u t added s u b s t r a t e . T his
i n d ic a t e s t h a t d u rin g a n o x ia , a t l e a s t , g ly c o ly s is p la y s an
emergency p a r t i n m a in ta in in g th e r e s t i n g p o t e n t i a l , which
i s I n acco rd an ce w ith th e p r e v io u s ly d is c u s s e d emergency
in c o r p o r a tio n o f a n a e ro b ic p ro c e s s e s i n b r a in d u rin g an o x ia
(se e page 3 0 ) . Because th ey observed a more r a p id f a l l o f
32
p o t e n t i a l w ith f l u o r i d e p lu s a n o x ia th a n w ith an o x ia a lo n e ,
Shanes and Brown p o s t u l a t e t h a t th e r e a c t i o n phosphoenol-
p y ru v a te p y ru v a te w ith th e l i b e r a t i o n o f a h ig h energy
p h o sp h ate bond i s somehow d i r e c t l y concerned w ith th e m ain
te n an ce of th e r e s t i n g p o t e n t i a l , and t h a t t h i s i s o n ly an
a u x i l i a r y mechanism s in c e p y ru v a te r e s t o r e s th e r e s t i n g
p o t e n t i a l to norm al. At h ig h c o n c e n tra tio n s o f f l u o r i d e ,
however, p y ru v a te f a i l s to r e s t o r e th e r e s t i n g p o t e n t i a l
and i t i s su g g ested t h a t t h i s may be an i n d i c a t i o n o f a
d i f f e r e n t s i t e o f a c tib n j© f f l u o r i d e , p o s s ib ly th e b re a k
down o f ATP under th e a c t i o n o f ATPase w hich i s known to be
i n h i b i t e d by f l u o r i d e .
S e v e ra l id e a s have been advanced i n e x p la n a tio n o f
th e mechanism f o r m aintenance o f th e r e s t i n g p o t e n t i a l .
Shanes and Brown (22) su g g e st t h a t p h o s p h o ry la tio n may be
d i r e c t l y r e s p o n s ib le f o r th e o r i e n t a t i o n o f p r o t e i n m olecule
a t th e n e u ro n a l s u r fa c e and th u s may gov ern p o l o r i z a t i o n .
They th e o r iz e f u r t h e r t h a t a p o t e n t i a l g r a d ie n t may be
e s ta b li s h e d by th e o x id a tio n - r e d u c ti o n - r e a c tio n s ta k in g
p la c e i n n e rv e . T his p ro c e s s may o r may n o t be d ependent
upon p h o s p h o ry la tio n s . These a u th o rs found o nly p a r t i a l
r e d u c tio n i n th e r e s t i n g p o t e n t i a l w ith a n o x ia , and b rin g
o u t t h a t th e r e s i d u a l p o t e n t i a l may be p u re ly p h y s ic a l or
may be th e r e s u l t of a n a e ro b ic m etabolism . T hat i t i s a t
s
35
l e a s t p a r t l y p h y s ic a l i s in d ic a te d by th e work o f Ling and
G erard (91) who observed two components making up th e r e s t
ing p o t e n t i a l i n th e fro g s a r t o r i u s muscle* One, o f ab o u t
50 m v., was d e s tro y e d by io d o a c e tic a c id , b u t could be
r e s to r e d a g a in . The o th e r , o f a b o u t 65 m v., depended upon
th e i n t e g r i t y o f th e c e l l membrane and could be d e s tro y e d
only i r r e v e r s i b l y . I t i s n o t c e r t a i n , o f c o u rse , t h a t t h i s
work can be extended to n e rv e , b u t i t i s i n d i c a t i v e .
S te in b a c h (88) s u g g e sts t h a t th e a c t i v i t y o f p o ta ssiu m i n
th e c e l l may be d eterm in ed by i t s d isp la c e m e n t by p h o sp h a te .
Hober and A ndersch ( 8 9 ) b e lie v e , w ith Shanes and Brown (2 2 ),
t h a t se m ip e rm e a b ility i s m a in ta in e d by p h o s p h o ry la tio n . An
o th e r p o s s ib le f a c t o r , though p erh ap s a m inor one r e l a t i v e l y
sp e ak in g , i s th e com plete o x id a tio n o f g lu c o se to 00% and th e
fo rm a tio n o f c a rb o n ic a c id . Hydrogen io n s would th u s be
produced and th e s e would presum ably be in v o lv e d i n m a in ta in
in g th e p o t e n t i a l (9 0 ). I t i s o f i n t e r e s t i n t h i s re g a rd to
n o te th e r e l a t i o n s h i p betw een th e enzyme, ca rb o n ic a n h y d ra se ,
and c e n t r a l nervous system m etabolism a s found by Ashby and
S c h u s te r (9 2 ,9 5 ,9 4 ,1 1 8 ). T his w i l l be d is c u s s e d l a t e r (se e
page #
The p r o b a b i l i t y e x i s t s t h a t m etabolism i s more
d i r e c t l y and sim ply concerned w ith th e m aintenance of th e
r e s t i n g p o t e n t i a l by in f lu e n c in g th e d i s t r i b u t i o n o f c a tio n s
3 *
o u ts id e and w ith in th e c e l l . . When blood su g a r i s used up or
when g ly c o ly s is i s i n h i b i t e d by f l u o r i d e , i n t r a c e l l u l a r
p o ta ssiu m d i f f u s e s b u t o f e r y th r o c y te s (95*)* Moreover
p o ta ssiu m p e n e tr a te s i n t o e r y th r o c y te s o r le u c o c y te s on th e
a d d i tio n o f g lu c o se ( 9 6 ) . C arbohydrate m etabolism i s th u s
r e s p o n s ib le f o r th e i n t r a and e x t r a c e l l u l a r d i s t r i b u t i o n o f
p o ta ssiu m in th e s e c e l l s . The same phenomenon has been
observed i n s l i c e s o f c e r e b r a l c o rte x by D ixon (9 7 ), and i t
was shown t h a t g ly c o ly s is i s p r im a r ily r e s p o n s ib le f o r th e
r e t e n t i o n o f p o ta ssiu m , s in c e leak ag e was observed only
under sim u ltan eo u s a n a e ro b ic c o n d itio n s and ab sen ce o f
g lu c o s e . I n th e p re se n c e o f g lu c o se th e r e was no leak ag e
a n a e r o b ic a lly . Shanes and Brown (22) o bserved no le ak ag e o f
p o ta ssiu m i n a n .io d o a c e ta te -p o is o n e d fro g n e rv e , and b e lie v e
t h a t m etabolism i s concerned w ith th e r e s t i n g p o t e n t i a l i n
ways o th e r th a n th ro u g h c a tio n b a la n c e . I t a p p e a rs t h a t
more th a n one mechanism may e x i s t f o r m a in ta in in g th e r e s t
in g p o t e n t i a l i n n e rv e .
The A ce ty l C holine Problem
The r o l e o f a c e t y l c h o lin e i n th e n erv e im p u lse .
The f u n c tio n o f a c e t y l c h o lin e (ACh) i n th e tr a n s m is s io n o f
t h e “n erv e im pulse i s a s u b je c t b road enough to c o n s t i t u t e a
t h e s i s i n i t s e l f , and i n view o f t h i s no a tte m p t w i l l be
made h e re to cover th e s u b je c t c o m p le te ly . A s h o r t
55
d is c u s s io n o f th e p r e s e n t s t a t u s o f knowledge, however, i s
i n o r d e r , so t h a t a n id e a may be g a in e d o f p o s s ib le r e l a
tio n s h ip s o f ACh to m e ta b o lic p ro c e s s e s i n nerve and con
se q u en t i n d i r e c t c o n n e c tio n s o f th e s e p ro c e s s e s to th e
nerve im p u lse.
The a r t e r i a l i n j e c t i o n o f ACh in to a m uscle ca u ses
t e t a n i c c o n t r a c tio n o f th e m uscle f i b e r s ; in to a g a n g lio n ,
r e p e t i t i v e f i r i n g o f th e p o s tg a n g lio n ic f i b e r s . S im ila r ly ,
waves o f 'e x c i t a t i o n a r e i n i t i a t e d from the- c e l l s o f th e
\
c e n t r a l nervous system upon th e l o c a l a p p l ic a tio n o f
a c e ty lc h o lin e (9 8 ), I f e s e r in e ; a c h o lin e e s t e r a s e i n h i b i
t o r , i s i n j e c t e d i n sm a ll am ounts, m u sc a rin ic parasym pathe
t i c a c t i v i t y i s observed which depends upon th e ex cess ACh
pro d u ced . P u p illa r y c o n s t r i c t i o n , c a rd ia c slow ing, u r in a r y
b la d d e r c o n tr a c tio n , and g a s tr o i n t e s t i n a l s tim u la tio n o c c u r.
I f la r g e d o se s a r e g iv e n , n i c o t i n i c e f f e c t s a r e o b serv ed ,
such a s in c o o rd in a te d m u scu lar movements, tv i t c h i n g s and
c o n v u lsio n s (100)• These e f f e c t s may be due to th e d e p o la r
iz in g p ro p e r ty o f a c e ty lc h o lin e (9 8 ). I t i s d e p re s s a n t i n
la rg e q u a n t i t i e s , s in c e i t now p ro d u ces co n tin u o u s d e p o l a r i
z a tio n .
C e rta in ly th e e f f e c t s o f t h i s p o te n t and n a t u r a l l y
o
o c c u rrin g drug a r e n o t to be d is p u te d . W hether th e p re se n c e
o f ACh i s m erely f o r t u i t o u s w ith r e s p e c t to co n d u c tio n , o r
0
36
w hether i t i s e s s e n t i a l f o r norm al co n d u c tio n i n nerve h a s,
however, b een disputed*. There a r e two rev iew s on t h i s
s u b je c t co v e rin g th e l i t e r a t u r e to 1946: . one by Nachman-
sohn (102) th e c h i e f p ro p o n en t o f t h e .id e a t h a t ACh i s
d i r e c t l y and in d is p e n s ib ly In v o lv ed i n . th e tr a n s m is s io n of
th e n erve im pulse,--and th e o th e r'b y ^ O e ra rd (103)# who m ain
t a i n s t h a t t h i s compound i s o nly i n d i r e c t l y concerned w ith
th e im p u lse, b e in g more o f a r e s u l t th a n a cause o f th e
co n d u c tio n sequence. The c o n c lu s io n w hich one i s le d to
draw a f t e r re a d in g th e s e rev ie w s i s t h a t a lth o u g h ACh may
n o t f u n c tio n i n p ro p a g a tin g th e a c t i o n c u r r e n t alo n g th e
axone, i t seems to f u n c tio n v i t a l l y i n th e p ro d u c tio n of
th e a c tio n p o t e n t i a l , p erh ap s by means o f d e p o l a r iz a tio n o f
th e n erve membrane. The l o c a l i z a t i o n o f c h o lin e e s t e r a s e
a t th e n e u ro n a l s u r fa c e i n c o n c e n tr a tio n s p r o p o r tio n a l to
th e d eg ree o f nervous a c t i v i t y , th e speed 'o f d e s t r u c t i o n o f
ACh, th e energy r e l a t i o n s h i p s o b ta in in g e t c . o f f e r an
enormous amount o f ev id en ce i n su p p o rt o f an im p o rta n t
p rim ary f u n c tio n o f ACh i n tr a n s m is s io n . G erard (103) con
te n d s t h a t many su b sta n c e s a s s o c ia te d w ith th e n erv e im pulse
have a c tio n s s im ila r to ACh c i t i n g a s exam ples e p in e p h rin e ,
w hich m a in ta in s th e a c t i o n p o t e n t i a l o f i s o l a t e d c a t nerve ,
and ATP, w hich s tim u la te s smooth a s w e ll a s s t r i p e d m uscle.
C arbonic an h y d rase and C O 2 p o s s ib ly have some f u n c tio n .
37
T hiam ine, which a f f e c t s ACh a c tio n and s y n th e s is , i s
l i b e r a t e d i n la rg e amounts from s tim u la te d fro g n e rv e , and
i s lo c a li z e d l i k e ACh a t th e n e u ro n a l s u r f a c e . Nachmansohn
m a in ta in s t h a t none o f th e s e compounds and system s shows
th e t y p i c a l f e a t u r e s o f th e ACh system , such a s th e h ig h
speed, e x c lu s iv e l o c a l i z a t i o n a t th e s u rfa c e and p a r a l l e l
ism o f v o lta g e . R e c e n tly B u llo c k e t . a l . (104) have
observed th e p re se n c e o f s p e c i f i c c h o lin e e s t e r a s e i n
T u r b e lla r ia and P la o a r ia . They s t a t e t h a t i t s o cc u rren c e
i n th e s e , th e lo w est an im als to p o s s e s s a nervous system
com parable w ith t h a t o f h ig h e r a n im a ls, th e u b iq u ity o f
s p e c i f i c c h o lin e e s t e r a s e i n co n d u ctin g t i s s u e , and th e
dependence o f c o n d u c tio n on th e a c t i v i t y o f th e enzyme
p e rm it th e c o n c lu s io n t h a t th e r o l e of ACh i n c o n d u c tio n i s
a g e n e ra l one.
From o b s e rv a tio n s o f b ir e f r i n g e n c e i n p o la r iz e d
l i g h t , i t has b een d e te rm in e d t h a t th e m e d u lla ry s h e a th i n
nerve i s composed o f c o n c e n tric la y e r s o f l i p i d ch a in s
a rra n g e d r a d i a l l y and a l t e r n a t i n g w ith c o n c e n tric la y e r s o f
p r o t e i n s . The p o la r h y d r o p h ilic groups o f th e l i p i d s a r e
p ro b a b ly lin k e d .t o th e p r o t e i n s , w h ile th e hydrophobic
p a r a f f i n c h a in s ad h e re to one a n o th e r (105)• S in c e th e
l i p i d s c o n ta in n e g a tiv e ly charged p h o sp h o ric a c id groups
and p o s i t i v e l y charged q u a te rn a ry ammonium groups o f
58
l e c i t h i n , two o p p o s ite ly charged la y e r s a r e supposedly
formed a t th e p r o t e i n - l i p i d i n t e r f a c e . These la y e r s may be
p a r t l y r e s p o n s ib le f o r th e r e s t i n g p o t e n t i a l o f n erve (1 0 6 ).
ACh i s s o lu b le i n w a te r a s w e ll a s l i p i d s , and i t s p re se n c e
w i l l g iv e r i s e to a p o t e n t i a l a t th e o il- w a te r i n t e r f a c e
(1 0 7 ). A ll o f th e s e o b s e rv a tio n s can be woven in to an
e n tic in g p a t t e r n o f ACh mechanism. T hat i t i s indispensable*
f o r norm al nervous a c t i v i t y seems to be w e ll e s ta b li s h e d .
P o s s ib ly i t p la y s a r o l e i n in t e n s i f y i n g o r d im in ish in g
nerve e x c i t a t i o n (1 0 8 ). ' „
The s y n th e s is o f a c e t y l c h o l i n e . I n 1945 an enzyme,
c h o lin e a c e ty l a s e , which forms ACh i n th e p re se n c e o f ATP,
was e x tr a c te d from b r a i n (1 0 9 ). S h o r tly a fte rw a rd s i t was
found t h a t t h i s enzyme i s r a p id ly i n a c ti v a te d on d i a l y s i s
(1 1 0 ). L g lu ta m ic a c id and c i t r i c a c id i n 0.02M c o n c e n tra
t io n s may r e a c t i v a t e i t p a r t l y . S tro n g e r b u t n o t y e t
com plete r e a c t i v a t i o n was o b ta in e d w ith c y s te in e . I t was
f i n a l l y found (111) t h a t a coenzyme a c t i v a t e d more power
f u l l y th a n any o f th e s e compounds and was a p p a re n tly non
s p e c i f i c , s in c e th e coenzyme, i n c o n t r a s t to th e enzyme,
was found i n a v a r i e t y o f t i s s u e s : h e a r t , l i v e r , k id n e y ,
s k e l e t a l m uscle and b r a in . This f a c t o r has been found to
be I d e n t i c a l w ith coenzyme A, n e c e ss a ry f o r a c e t y l a t i o n s
g e n e r a lly , and was d eterm in ed by Lipmann .et. a l . (112) to be
39
a p a n to th e n ie a c id d e r i v a t i v e . This has been confirm ed by
d i e t a r y s tu d ie s i n w hich th e w ith o ld in g o f p a n to th e n ic a c id
r e s u l t e d i n a d e p l e ti o n o f coenzyme A i n d i f f e r e n t an im als
(1 1 3 ).
R e c e n tly i t has been p o s tu la te d by Korey (114) t h a t
th e enzym atic a c e t y l a t i o n o f c h o lin e i n nervous t i s s u e
in v o lv e s a t l e a s t two s te p s , th e t r a n s f e r o f an a c y l group
to coenzyme A o r to an enzyme, a c e t y l k in a s e , and th e sub
se q u en t e s t e r i f l c a t i o n o f c h o lin e by c h o lin e a c e ty l a s e .
T r a n s - a c e ty la tio n from o - a c y l e s t e r s and a c e t y l amino a c id s
has been shown to o ccu r i n th e p re se n c e o f th e com plete
system . When b r a i n s l i c e s o r p u lp a r e in c u b a te d i n a s a lin e
medium, a e ro b ic c o n d itio n s a r e r e q u ir e d f o r th e s y n th e s is of
AGh, and th e s y n th e s is i s i n h i b i t e d by cy an id e and a z id e .
However, when hom ogenates o r e x t r a c t s o f a c e to n e d r ie d powder
a r e used, th e s y n th e s is can ta k e p la c e a n a e r o b ic a lly p r o
v id e d e i t h e r ATP o r c i t r a t e , p lu s b o ile d s a l i n e e x t r a c t s o f
a c e to n e d r ie d powder, a r e added. I f b o th ATP and th e
b o ile d e x t r a c t a r e added, more s y n th e s is i s o b ta in e d (1 1 5 ).
I t i s su g g ested by P e ld b e rg (98) t h a t r e s p i r a t i o n i n s l i c e s
i s a s s o c ia te d w ith th e r e l e a s e o f ACh w hich o c c u rre n c e may
be n e c e ssa ry f o r more s y n th e s is , and so a f f e c t s s y n th e s is
i n d i r e c t l y . I t i s p o s tu l a te d f u r t h e r th a n i n v iv o th e
s y n th e s is may occur i n two s ta g e s , th e f i r s t a n a e ro b ic ,
40
in v o lv in g ATP, and th e second a e r o b ic .
I t has been observed t h a t p o ta ssiu m io n a c c e le r a te s
and calcium io n i n h i b i t s th e s y n th e s is o f ACh (9 8 ,1 1 6 ). I t
i s su g g e sted by F eld b e rg (98) t h a t th e m o b iliz a tio n o f
p o ta ssiu m a t th e n erv e membrane d u rin g th e im pulse may
f a c i l i t a t e th e r e l e a s e o f ACh and prom ote more s y n th e s is .
P o tassiu m s tim u la te s a e ro b ic m etabolism m arkedly (7 9 ); th u s
i t s e f f e c t on. ACh s y n th e s is may be th ro u g h t h i s mechanism.
D ecreased r e s p i r a t i o n (117) and d im in ish e d ACh s y n th e s is
(116) has been observed a ls o w ith low ered calcium c o n c e n tra
t i o n . Very sm a ll amounts o f calciu m s tim u la te ACh s y n t h e s i s .
The optimum c o n c e n tr a tio n o f calciu m f o r th e s y n th e s is o f
ACh i s a b o u t 1.3 raM. Above t h i s c o n c e n tr a tio n i s i s marked
ly i n h i b i t e d ( H 6 ) . L a s n itz k i (117) found t h a t a t l e a s t one
o f th e a c tio n s o f calcium i s i t s e f f e c t on th e d i f f u s i o n o f
p o ta ssiu m . A s im ila r b u t le s s marked dependence o f ACh
s y n th e s is on magnesium has been found (1 1 6 ). C i tr a te has
been found to have a p a r t i c u l a r l y s tro n g a c t i v a t i n g i n
flu e n c e on th e fo rm a tio n o f ACh ( 9 8 ) b u t i t has been
observed by McLennan and E l l i o t (116) to i n h i b i t s y n th e s is
i n a calciu m c o n ta in in g medium. These w orkers found f u r t h e r
t h a t b ic a rb o n a te C02 was e v id e n tly e s s e n t i a l and ex p erim en ts
in d ic a te d an o p tim a l b ic a rb o n a te c o n c e n tr a tio n a t around
25mM a t c o n s ta n t pH. B ic a rb o n a te could n o t be re p la c e d by
41
o x a la c e ta te ; th u s th e l a t t e r ■w as n o t a c tin g as a COg d o n o r.
When b o th g lu c o se and b ic a r b o n a te were p r e s e n t, o x a la c e ta te
and. p y ru v a te even caused some i n h i b i t i o n . I t has been found
r e c e n tly ( 170) t h a t b ic a rb o n a te i s a n e c e ss a ry c o f a c to r f o r
c i t r a t e s y n th e s is w hich may e x p la in th e s e r e s u l t s . I t I s
i n t e r e s t i n g i n t h i s re g a rd t h a t Ashby (118) has o b ta in e d -
some c o r r e l a t i o n betw een c a rb o n ic an h y d rase c o n te n t and
speed o f tr a n s m is s io n i n n e rv e .
G lucose prom otes s y n th e s is o f ACh i n g lu c o se
d e f ic ie n c y , b u t a n e x c ess seems to i n h i b i t s y n th e s is (9 8) .
L a c tic a c id and a c e to a c e tic a c id have a ls o b ee n found to
in c re a s e th e s y n th e s is (1 1 9 ). A c c e le ra tio n o f s y n th e s is i n
c o rte x s l i c e s has b een o bserved when p y ru v a te i s used as
s u b s t r a t e , and th e ACh c o n te n t o f th e c e r e b r a l c o rte x was
d e c re a se d i n th ia m in e d e f i c i e n t r a t s (1 2 0 ). Thiam ine and
co c a rb o x y la se a c c e l e r a t e ACh s y n th e s is i n a c e to n e e x t r a c t s
up to a p o in t a e r o b i c a l l y , b u t i n h i b i t th e a n a e ro b ic syn
t h e s i s i n th e p re se n c e o f ATP (9 8 ). I n c o n s id e rin g v a rio u s
a c c e le r a ti n g and i n h i b i t i n g a g e n ts , i t m ust be remembered
t h a t p o ta ssiu m , a d r e n a lin e , p i t u i t r i n , a s p h y x ia , e t c .
f a c i l i t a t e th e r e l e a s e o f ACh from th e n erv e membrane and
may th u s prom ote more s y n th e s is ( 9 8 )•
ACh e x i s t s i n b r a i n i n b o th f r e e and bound form
(9 8 ,1 0 2 ,1 1 6 ). F re e ACh I s formed when an e s e r in e c o n ta in in g
42
b r a i n su sp e n sio n i s dropped in to l i q u i d a i r , w h ile a
d e c re a s e i n t o t a l ACh o ccu rs under th e same c o n d itio n s u sin g
a n o n e s e rin iz e d b r a in , s in c e now th e ACh r e le a s e d from bound
form i s d e s tro y e d (1 1 6 ). A r a p id r i s e i n bound ACh i s m ani
f e s t e d on in c u b a tio n i n a E in g e r -b ic a rb o n a te - g lu c o s e medium,
and i t i s su g g e sted by E l l i o t and H enderson (116) t h a t th e
l i m i t o f t h i s r i s e may r e p r e s e n t th e maximum p o t e n t i a l ACh
c o n te n t o f th e t i s s u e s .
I t seems p o s s ib le t h a t th e c o n c e n tr a tio n of f r e e or
bound ACh i n th e t i s s u e s may i t s e l f be a r e g u la to r y a g e n t in
th e s y n th e s is . B u lb erin g (121) has r e c e n t l y made a com pari
son betw een a c e to n e powder o f a u r i c l e s f r e s h l y e x c is e d ,
a u r i c l e s which had stopped b e a tin g i n 24 hours a f t e r e x b is io n
and powder from a u r i c l e s i n w hich th e b e a t had been s t a r t e d
a g a in w ith ACh. These powders w ere a l l in c u b a te d w ith
c h o lin e , c i t r a t e , ATP and o th e r s u b s ta n c e s . The stopped
a u r i c l e s l o s t most o f th e ACh s y n th e tic power b u t th e r e
s t a r t e d a u r i c l e s re g a in e d i t . F u r th e r , j u s t as ACh d e p re s s e s
the- c o n tr a c tio n o f f r e s h a u r i c l e s i n a b a th , so th e a d d i tio n
o f ACh to tu b e s c o n ta in in g powder from f r e s h a u r i e l e s d e
p r e s s e s th e a d d itio n s o f ACh to powder from stopped a u r i c l e s
V
in c re a s e d th e s y n th e s is in p r o p o r tio n to th e amount added,
e x e r tin g an a u t o c a t a l y t l c e f f e c t . The f a c t t h a t th e
a d d i t i o n o f ACh to c o n d u c tiv e t i s s u e i s I n h ib ito r y to th e
43
s y n th e s is , w h ile to n o n -co n d u ctiv e t i s s u e i t i s a u to c a ta ly -
t i c , and t h a t co rresp o n d in g , e f f e c t s a r e observed on c o n tra c
t i o n , su p p o rts th e id e a t h a t ACh i s i t s own r e g u l a t o r . ACh
seems to be r e le a s e d from bound form a s i t i s needed, a f t e r
which i t i s im m ediately d e s tro y e d . I t i s c o n s ta n tly being
r e s y n th e s iz e d to com pensate f o r lo s s e s (9 8 ,1 0 2 ).
The ACh c o n te n t o f th e b r a i n a p p a r e n tly d e c re a s e s
w ith th e p h y lo g e n e tic a lly h ig h e r developm ent o f th e s p e c ie s ,
and a low s to r e o f ACh w ith a g r e a t a b i l i t y to s y n th e s iz e
«
i t may be a c h a r a c t e r i s t i c f e a t u r e o f a t i s s u e w hich, lik e
th e CHS, e x h i b its co n tin u o u s a c t i v i t y ( 9 8 ) .
The A ctiv e Nerve
The m e ta b o lic p ro c e s s e s a s s o c ia te d w ith th e a c t i v e l y
con d u ctin g nerve a p p e a r to be d i f f e r e n t from th o se o f th e
r e s t i n g s t a t e ( 168) b u t t h e i r n a tu re i s a s y e t somewhat
o b sc u re . The breakdown and s y n th e s is o f h ig h energy phos
p h a te bonds i s s im ila r to t h a t o f m u scle, th e r e l a t i o n s h i p s
o f c r e a tin e .p h o s p h a te , ATP and in o rg a n ic p h o sp h a te being
a l i k e (2 3 ). A c ti v ity i s a s s o c ia te d w ith th e breakdown o f
a s c o rb ic a c id (122) and o f n u c le o p ro te in ( 123) w hich a re
l a t e r r e s y n th e s iz e d . D uring p h y s io lo g ic a l e x c i t a t i o n th e r e
i s a d i s t i n c t in c r e a s e i n th e consum ption o f oxygen in
s in g le nerve f i b e r s and, ac c o rd in g to th e a l l o r none law,
44
i t i s in d e p en d en t o f th e i n t e n s i t y o f s tim u la tio n (1 2 4 ). The
RQ o f a c t i v e n erv e i s n ea r u n ity , y e t some s u b s t r a te o th e r
th a n c a rb o h y d ra te seems to be used (19,35) (s e e page / 3 ) .
Oxygen, n e v e r th e le s s , i s n o t n e c e s s a ry f o r th e c o n d u c tio n of
n e rv e , though i t i s e v e n tu a lly r e q u ir e d f o r th e m aintenance
o f norm al e x c i t a b i l i t y (8 7 ) . I n t h i s r e s p e c t i t i s s im ila r
to m u scle. The energy p r o d u c tio n i n n e rv e , however, i s
much low er th a n t h a t o f m uscle (1 2 5 ). As i n m uscle th e r e i s
an ^ in c re a s e i n h e a t p ro d u c tio n d u rin g a c t i v i t y and an even
g r e a t e r in c r e a s e d u rin g re c o v e ry , b u t b o th a r e m in u te.
C onduction o f an im pulse i s accom panied by an outw ard
d i f f u s i o n o f p o ta ssiu m io n s p r e s e n t i n h ig h c o n c e n tr a tio n
w ith in th e f i b e r which i s b a la n c e d by an Inward d i f f u s i o n o f
sodium io n s (1 2 6 ). T his exchange seems to be th e f a c t o r
l a r g e l y r e s p o n s ib le f o r th e a c t i o n p o t e n t i a l , as has been
evidenced by th e r e c e n t work o f Hodgkin and Katz (1 2 7 ).
They have shown beyond re a s o n a b le doubt t h a t d u rin g a c t i v i t y
th e r e i s a r e v e r s a l o f p e r m e a b ility to sodium and p o ta ssiu m .
The n erve membrane becomes a lm o st s e l e c t i v e l y perm eable to
sodium, w hereas a t r e s t i t i s alm o st im perm eable to t h i s
s u b sta n c e , a llo w in g only th e e n tra n c e of p o ta ssiu m . These
a u th o rs s t a t e t h a t th e r e i s l i t t l e re a s o n to b e lie v e t h a t
th e p r o c e s s e s d i r e c t l y concerned w ith th e a c t i o n p o t e n t i a l
a r e o f an o x id a tiv e n a tu re ; though o x id a tiv e p ro c e s s e s may
45
be concerned w ith th e mechanism of sodium t r a n s p o r t . I f
t h i s i s t r u e , th e n th e p re v e n tio n o f th e e n tra n c e o f sodium
would be th e b u rd en b o rn by th e m e ta b o lic p r o c e s s e s , and
changes i n m etabolism would more l o g i c a l l y be th e r e s u l t o f
a c t i v i t y r a t h e r th a n i t s c a u se.
A ctiv e m etabolism has r e c e n t l y b een s e p a ra te d from
r e s t i n g p ro c e s s e s by G erard and Doty (168) u sin g th e i n
h i b i t o r s a z id e and m e th y lf lu o r a c e ta te . The form er can
a b o lis h th e e x tr a oxygen consum ption o f a c t i v e fro g n erv e,
b u t has p r a c t i c a l l y no e f f e c t on r e s t i n g r e s p i r a t i o n or
c o n d u c tio n . M e th y lf lu o ra c e ta te can re d u c e th e r e s t i n g
oxygen consum ption to 50 p e r c e n t below norm al w h ile having
no e f f e c t on th e a c t i v e n e rv e . Thus a change i n o x id a tiv e
m etabolism seems to occur norm ally when th e n erve becomes
a c t i v e , y e t t h i s change seems n o t to be e s s e n t i a l f o r
c o n d u c tio n .
Im m ersion o f s p in a l cord i n R in g ers s o l u t i o n con
ta in in g a c e ty l c h o li n e ca u ses th e l i b e r a t i o n o f p o tassiu m
io n s and i t has b een su g g e ste d t h a t t h i s may be th e
mechanism o f a c t i o n o f a c e ty lc h o lin e (1 2 9 ). The p o s s i b i l i t y
e x i s t s t h a t in c re a s e d p ro d u c tio n o f a c e ty lc h o lin e i s
r e s p o n s ib le f o r d e p o l a r i z a t i o n and t h a t an in c re a s e d aerobic;
m etabolism f u n c tio n s i n r e p o l a r i z a t i o n a f t e r th e phenomena
a s s o c ia te d w ith a c t i v i t y .
46
P o tassiu m ion. seems to have a d e p o la r iz in g e f f e c t and
t h i s may have i t s b a s is p a r t l y i n an in c r e a s e of a c e t y l
c h o lin e p r o d u c tio n th ro u g h th e e f f e c t o f p o ta ssiu m upon
m etab o lism . P o tassiu m s tim u la te s antoaom ie g a n g lia (128)
and has been shown to have n e u ro n a l s tim u la tin g e f f e c t s i n
many o th e r in s t a n c e s . I t a ls o s tim u la te s a e ro b ic m etabolisrr
and th e a e ro b ic p ro d u c tio n o f l a c t i c a c id (7 9 )» c o n c u rre n tly
in c r e a s in g th e s y n th e s is o f a c e ty l c h o li n e .
I t has been d em o n strate d (130) t h a t th e monomolecular
la y e r s o f charged l i p i d s undergo a n a l t e r a t i o n i n t h e i r
s t r u c t u r e when th e r e c i p r o c a l d i f f u s i o n s o f sodium and
p o ta ssiu m o c c u rs .
»
4?
THE FUNCTION OF GLUTAMIC ACID IN NERVOUS TISSUE
The E l e c t r i c a l A c ti v ity o f th e B ra in
S in ce ev id en ce w i l l be c i t e d i n t h i s s e c tio n which
in v o lv e s e le c tro e n c e p h a lo g ra p h lc (EEG) re c o rd s o f b r a in
p o t e n t i a l s and t h e i r changes under c e r t a i n c o n d itio n s , a
b r i e f e x p la n a tio n w i l l be g iv e n o f th e n a tu re o f th e EEG and
o f th e p ro b a b le ca u ses u n d e rly in g th e phenomenon o f b r a i n
waves.
The EEG i s a chym ographie r e c o rd o f th e c y l ic changes
i n p o t e n t i a l o f v a r io u s a re a s o f th e b r a i n which can be
s e le c te d by a l t e r i n g th e p o s i t i o n o f th e e l e c t r o d e s . The
e le c tr o d e s can e i t h e r b o th be a p p lie d to th e s c a lp a t
d i f f e r e n t l o c a ti o n s , i n which ca se th e y r e c o rd and am p lify
d i f f e r e n c e s i n p o t e n t i a l betw een d i f f e r e n t a r e a s i n th e
i
c o r te x , o r one can be a p p lie d to a n o th e r a r e a o f th e body,
e .g . th e e a r lo b e , where a b s o lu te v a lu e s w ith r e s p e c t to
body p o t e n t i a l a r e o b ta in e d . The form er i s u s u a lly used to
l o c a l i z e abnorm al e l e c t r i c a l phenomena t h a t do n o t In v o lv e
synchronous d is c h a r g e s , w hereas th e l a t t e r a r e used i n th e
stu d y o f e p ile p s y and normal b r a in s where synchrony o f
d i f f e r e n t a r e a s i s a p t to be en c o u n te re d (1 3 1 ).
There a r e v a r io u s d i s t i n c t rhythm s which a r e mani
f e s te d under d i f f e r e n t c o n d itio n s such a s norm al re p o s e ,
s le e p , h y p n o sis e t c . The c u r r e n t : tr e n d in. b r a i n wave_______
48
r e s e a r c h i s to c o n s id e r th e s e th e r e s u l t o f la r g e m asses o f
neurones o s c i l l a t i n g e l e c t r i c a l l y and f a l l i n g in to s te p or
synchrony w ith each o th e r , th e re b y c r e a tin g a la r g e o s c i l l a
to r y c u r r e n t a r e a i n th e c o r te x (1 3 2 ). The neurone i s con
s id e re d by Olken (132) a s e q u iv a le n t to a m u l t i v i b r a t o r
c i r c u i t a s i s en c o u n tered i n e l e c t r o n i c s . Such a c i r c u i t
w i l l s h i f t r e a d i l y from one ty p e o f e l e c t r i c a l o p e r a tio n to
a n o th e r w ith s l i g h t changes i n v o lta g e , r e s i s t a n c e and
c a p a c ita n c e ,, and i t i s su g g e ste d t h a t such s h i f t s co u ld ta k e
p la c e w ith s l i g h t changes i n m e ta b o lic c o n d itio n s .
The oC waves o r th e waves o f norm al q u i e t r e p o s e , a re
th o s e s tu d ie d i n m ost abnorm al b r a i n c o n d itio n s . A th e o ry
o f th e o r i g i n and f u n c tio n o f ©c waves which seems to be i n
h ig h r e p u te i s t h a t th e y a r i s e from a c t i v i t y i n v a r io u s
a r e a s o f th e c o rte x w hich i s s i g n i f i c a n t o f a scan n in g o f
th e p r o j e c t i o n a r e a s f o r in fo rm a tio n . F or in s t a n c e , th e
i
rhythm o f th e v i s u a l a r e a s i s supposed to sweep o ver th e
p r o j e c t i o n and a s s o c i a t i o n a r e a s to p ic k up, re c o r d , and
i n t e r p r e t incom ing v i s u a l s t i m u l i . F u n c tio n in g i n t h i s
fa s h io n , th e b r a in would be an alogous to a t e l e v i s i o n s e t .
Opening th e e y e s, c lo se d d u rin g th e r e c o rd in g , r e s u l t s i n
a b lo c k in g o f th e oC rhythm . T his i s e x p la in e d -b y th e f a c t
t h a t th e sweep i s stopped when i t e n c o u n te rs a r e g io n o f
a c t i v i t y (1 3 3 ). O ther t h e o r ie s more o r l e s s s im ila r a r e
49
g iv e n i n th e review c i t e d .
The EEG has n o t so f a r proved to be a v e ry s e n s i t i v e
o r d is c r im in a tin g method f o r d is c o v e r in g b io c h e m ic a l e f f e c t s
s in c e s im ila r changes a r e produced under a v a r i e t y o f
c o n d itio n s w hich v e ry l i k e l y have d i f f e r e n t c a u se s. F or
exam ple, a s h i f t tow ard low fre q u en cy i s observed s i m i l a r l y
i n a n o x ia , a lc o h o l i n t o x i c a t i o n and hypoglycem ia (1 3 3 ). I t
i s t r u e , however, t h a t changes i n e l e c t r i c a l a c t i v i t y a r e
r e f l e c t e d by changes i n c a rb o h y d ra te m etabolism which may
a f f e c t n erve tr a n s m is s io n i n d i f f e r e n t ways, p o s s ib ly
th ro u g h changes i n s y n th e s is o f su b sta n c e s which have a
p rim ary r o l e i n tra n s m is s io n e .g . ACh (1 3 4 ). In some c a se s
th e EEG can be p r o f i t a b l y used i n th e i n t e r p r e t a t i o n o f
m e ta b o lic changes, a s w i l l be seen .
I t may be o f h e lp i n c l a r i f y i n g th e impending d i s
c u s s io n to m ention t h a t i n g ran d mal e p ile p s y th e EEG
r e g i s t e r s f a s t waves o f la r g e a m p litu d e , w hereas i n p e t i t
m al, slow waves s t i l l o f la rg e am p litu d e a r e re c o rd e d .
P o s s ib le Key R oles o f G lutam ic Acid i n Nerve M etabolism
Many c l i n i c a l w orkers have observed t h a t g lu ta m ic
a c id i n la r g e d o ses e x h i b its th e p r o p e r ty o f a l l e v i a t i n g
th e symptoms o f p e t i t mal e p ile p s y (135) and o f I n c re a s in g
m e n tal a b i l i t y i n c a se s o f m e n ta l d e f ic ie n c y (1 3 6 ).
A lthough some r e c e n t work has c a s t some d o u b lt on th e i n i t i a
i
I o b s e rv a tio n s . There has been much s p e c u la tio n w ith re g a rd <
i i
i to p o s s ib le s p e c i f i c mechanisms o f a c t i o n o f t h i s su b sta n c e I
I
! and as to w hether th e mechanisms i n each o f th e s e m a lad ies
|
may be th e same o r d i f f e r e n t .
G lutam ic a c id and g lu ta m in e com prise an e x t r a
o r d i n a r i l y la r g e p o r t i o n (40-80 p e r c e n t) o f th e f r e e t o t a l
amino a c id n itr o g e n i n th e b r a i n (137)* T his i s rem ark ab le
b ecau se b r a in m e ta b o liz e s c a rb o h y d ra te f o r th e m ost p a r t
and i s supposedly n o t concerned w ith n itr o g e n m etabolism
nor w ith t i s s u e breakdown and r e p a i r (137)* C ortex s l i c e s
a r e a b le to ab so rb g lu ta m ic a c id a g a in s t a c o n c e n tr a tio n
g r a d ie n t, p ro v id e d g lu c o s e i s p r e s e n t (1 3 8 ). I t may b e, j
I
however, t h a t f r e e g lu ta m ic a c id o r g lu ta m a te i s n o t j
, absorbed a s such i n v iv o . I t i s known t h a t th e b lo o d - b ra in j
* ' i
; b a r r i e r i s n o t v e ry perm eable to g lu ta m a te io n s . Schw erin
j
' e t . a l , ( 139) have n o ted no s i g n i f i c a n t in c r e a s e i n g lu ta m ic
a c id u p tak e by th e whole b r a in s o f r a t s and m ice on i n t r a
venous i n j e c t i o n o f t h i s s u b sta n c e . I n je c te d g lu ta m in e ,
however, p ro d u ces a marked in c r e a s e in g lu ta m in e c o n c e n tra
t i o n o f b r a in b o th i n t r a p e r i t o n e a l l y and in tr a v e n o u s ly ;
(139,140) and i t a p p e a rs t h a t th e m ajor p o r t i o n o f th e
g lu ta m ic a c id o f b r a i n m ust come e i t h e r from blood g lu ta m in e
i
o r from s y n th e s is w ith in th e organ.
I
Ammonia m etab o lism . In c re a s e d ammonia fo rm a tio n has
i 51 '
i 1
I '
been o b serv ed v e ry g e n e r a lly on s ti m u la tio n o f nervous J
i
t i s s u e . I t i s l i b e r a t e d on s tim u la tio n of b r a i n (157) * !
n erve (5 2 ), and d u rin g c o n v u lsio n s (157)• Ammonia i n h i b i t s j
t
ACh fo rm a tio n b u t in c r e a s e s f r e e ACh a t th e expense of
combined ACh. I t s tim u la te s a e ro b ic m etabolism and a p p a r
e n tly may s tim u la te o r i n h i b i t a n a e ro b ic g l y c o ly s is ,
depending upon i t s c o n c e n tr a tio n (1 5 7 ). There seems to be
no d o ubt t h a t th e r e i s some im p o rta n t r e l a t i o n o f ammonia
|to nerve m etabolism , and in view o f t h i s , g lu ta m ic a c id may
e x e r t an im p o rta n t I n flu e n c e by i t s c a p a c ity to r e g u la te
th e c o n c e n tr a tio n o f t h i s s u b s ta n c e . Grey c o rte x and r e t i n a
can b in d ammonia a t th e r a t e o f 0 .8 p e r c e n t o f th e t i s s u e
d ry w eig h t p e r hour in th e p re s e n c e o f g lu ta m ic a c id ( l 4 l ) .
S a p i r s t e i n (142) has evoked c o n v u lsio n s i n r a t s w ith j
.ammonium c h lo r id e and has o b ta in e d com plete p r o te c tio n from
i
!t h e s e c o n v u ls io n s by p r e lim in a r y i n j e c t i o n s o f g lu ta m ic
a c i d . A s p a r t ic a c id f a i l e d t o o f f e r t h i s p r o t e c t i o n . The
u n iq u e c o n v u ls io n -p r o d u c in g p r o p e r t i e s o f ammonia and i t s
e f f e c t s on m e ta b o lis m , com bined w it h th e s in g u la r am m onia-
b in d in g c a p a c it y o f g lu ta m ic a c i d , h a s le d some w o r k e rs t o
p o s t u l a t e t h a t t h i 3 i s th e p rim a ry m echanism by w h ic h g l u
ta m ic a c id e x e r t s i t s t h e r e p e u t i c e f f e c t s i n p e t i t m al
j ' i
je p ile p s y . G lutam ic dehydrogenase may be found u n iq u e ly J
jamong amino a c id o x id a se s i n b r a i n ( 157)* sin c e g lu ta m ic I
• 52
a e id seems to be th e o nly amino a c id o x id iz e d a p p r e c ia b ly .
The g lu ta m ic a c id system c o u ld a c t a s e i t h e r a donor o r
a c c e p to r o f amino g ro u p s, depending upon th e a v a i l a b i l i t y
o f f r e e ammonia, a c c o rd in g to th e fo llo w in g e m p iric a l
e q u a tio n s which have b een o bserved to h o ld tr u e i n v i t r o :
2 g lu ta m ic a c id — > g lu ta m in e -f« * k e to g lu ta ric a c id (147)
o C k e to g lu ta ric a c id + NH-^—^ g l u t a m i c acid-*- 0 .5 02 (146)
A lso , a d is m u ta tio n r e a c t i o n can ta k e p la c e :
2 o< k e t o g l u t a r a t e — > ■ s u c c in a te - tCOg”*"glutam ate (149)
T his f u n c tio n o f g lu ta m ic a c id i s im p o rta n t f o r m etab o lism ,
b u t w hether i t i s r e s p o n s ib le f o r th e s u b s ta n c e 1s c u r a tiv e
t
p r o p e r t i e s i s n o t c e r t a i n . G lutam ic a c id a f f e c t s only
p e t i t mal and n o t g ran d mal e p ile p s y ( 150) , th u s i f d is r u p
t i o n i n ammonia m etabolism i s r e s p o n s ib le f o r p e t i t m al, i t
can n o t be f o r g ran d m al, p ro v id e d g lu ta m ic a c id a c ts h e re
by v i r t u e o f i t s f u n c tio n i n ammonia m etab o lism . So f a r , nc
r i s e r i n g lu ta m ic a c id o r g lu ta m in e i n b r a i n has been
observed w ith a d m in is t r a tio n , by any m eans, o f g lu ta m ic
a c id i t s e l f . I n c r e a s e s have been o b ta in e d o nly w ith g l u t a
mine (1 5 9 ,1 4 0 ), w hich would f u n c tio n i n in tr o d u c in g ammonia
in to th e b r a in , &jmone e t . a l . (145) have f o u n d .t h a t i n t r a
venous i n j e c t i o n s o f ammonium c h lo rid e caused no i n d i c a t i o n
o f e p i l e p t i c a l c o r t i c a l d is c h a rg e i n th e EEG o f d o g s,
i n d ic a t in g a s p in a l r a t h e r th a n a e o r t i c a l o r i g i n o f th e s e
53
c o n v u ls io n s . I t i s known t h a t e p i l e p t i c c o n v u lsio n s a r e
c o r t i c a l i n o r i g i n . A lthough ammonia i s o b v io u sly a sub
s ta n c e o f h ig h p h a rm a c o lo g ic a l a c t i v i t y and though c e r t a i n l y
g lu ta m ic a c id f u n c tio n s i n m a in ta in in g ammonia b a la n c e ,
w hether i t s c u r a t iv e p r o p e r t i e s a r e m ed iated th ro u g h t h i s
mechanism i s s t i l l open to q u e s tio n . R ic h te r and Dawson
(144) have r e c e n t l y r e p o r te d t h a t no change i n th e b r a in
g lu ta m in e le v e l o ccu r e i t h e r w ith a d e c re a s e i n ammonia
b ro u g h t a b o u t by nem butal n a r c o s is o r w ith an in c r e a s e i n
ammonia produced by changes in c r e a s in g c e r e b r a l i r r i t a b i l i t y
A c e ty lc h o lin e s y n t h e s i s . W hether g lu ta m ic a c id can
a c t a s a coenzyme i n v iv o f o r th e a c t i v a t i o n o f th e c h o lin e
a c e ty l a s e system i s a t p r e s e n t u n c e r ta in . I t has r e c e n tly
been found (141) t h a t th e a d d i t i o n o f g lu ta m ic a c id to th e
coenzyme A a c t i v a t e d system has no e f f e c t i n v i t r o . Glu
tam ic a c id does have an e f f e c t , however, i n a c t i v a t i n g cho
l i n e a c e ty l a s e when OoA i s a b s e n t ( l i o ) . M oreover, i t
seems to have a c t i v i t y i n r a t b r a i n e x t r a c t s (145)* Glu
tam ine has o n ly ab o u t h a l f th e a c t i v i t y o f g lu ta m ic a c id
h e re . The ammonium io n , a s p r e v io u s ly m entioned, i n h i b i t s
ACh fo rm a tio n w h ile ca u sin g i t s l i b e r a t i o n from bound form
( 157) , th u s g lu ta m ic a c id may e x e r t a n i n d i r e c t e f f e c t on
ACh s y n th e s is and a v a i l a b i l i t y by c o n t r o l l i n g ammonium io n
c o n c e n tr a tio n . There i s some ev id en ce t h a t ACh i r r e g u l a r i -
lti.e s may b e a f a c to r in v o lv e d i n th e e p i l e p t i c d is c h a rg e
54
(1 4 6 ,1 4 7 ). The r e s u l t s o f Bubin e t . a l . (148) su p p o rt th e
view t h a t a q u a n t i t a t i v e r e l a t i o n s h i p e x i s t s betw een
c a rb o h y d ra te m etabolism and th e fre q u en cy o f b r a in w aves.
Luminal slows th e r a t e o f c o r t i c a l waves. H yperglycem ia'
p re v e n ts th e slow p e t i t m al w aves, w h ile hypoglycem ia cau ses
them to become a lm o st c o n tin u o u s (1 5 6 ). The slowed waves
produced by hypoglycem ia may be in c re a s e d in r a p i d i t y by
g lu c o s e , mannose and m a lto se g iv e n in tr a v e n o u s ly to
e v i s c e r a te d , h e p a tec to m ized an im als (1 4 9 ). ACh depends on
g lu c o se m etabolism ( 105) , b u t g lu c o se a t th e norm al-blood
su g a r le v e l i s supposed to su p p re ss ACh s y n th e s is 'b e lo w th e
optimum. When th e l e v e l d ro p s , th e s y n th e s is o f ACh i s
in c re a s e d f o r a tim e and c o n v u lsio n s a r e e l i c i t e d (9 8 ) . I t
may be t h a t ex cess g lu c o s e removes ATP, w hich i s n e c e ss a ry
f o r a n a e ro b ic ACh s y n th e s is (9 8 ). Thus th e changes i n
c o r t i c a l a c t i v i t y o b serv ed w ith hypogiycem ia may be only
i n d i r e c t l y r e l a t e d to t h i s c o n d itio n th ro u g h ACh. E x p e ri
m e n ta lly in c re a s e d c o n c e n tr a tio n s o f ACh ca n produce
g e n e r a liz e d s e iz u r e s . I t i s th u s c o n c e iv a b le t h a t increased,
ACh p ro d u c tio n i s r e s p o n s ib le f o r p e t i t mal e p ile p s y . I n
c o n t r a s t to t h i s , o th e r ex p erim en ts p o in t to th e p o s s i b i l i t y
t h a t th e r e may be a d e f ic ie n c y i n th e s y n th e s is o f ACh i n
p a t i e n t s w ith p e t i t m al, and In c r e a s e s o n ly i n g ran d m al.
G lutam ic a c id I s e f f e c t i v e o nly i n p a t i e n t s w ith p e t i t mal
• 55
( 150) , w h ile c h o lin e e s t e r a s e i n h i b i t o r s m odify th e c o a rse
o f p e t i t m al e p ile p s y (1 5 1 ). I n g ran d m al, n o t o n ly i s
g lu ta m ic a c id i n e f f e c t i v e b u t i t sometim es a c t u a l l y i n
c re a s e s th e number o f s e iz u r e s ( 150) and a c e ty lc h o lin e
seems to have p a r a l l e l e f f e c t s . . D iis o p ro p y lflu o ro p h o s p h a te
(DPP), a c h o lin e e s t e r a s e i n h i b i t o r , when i n j e c t e d in to th e
common c a r o t i d a r t e r y o f th e c u r a r iz e d r a b b i t , p ro d u ces
b r a i n wave p a t t e r n s rese m b lin g th o s e o f g rand mal e p ile p s y
i n man (1 4 4 ). These abnorm al b r a i n waves a r e a s s o c ia te d
w ith a p ro fo u n d f a l l i n c h o lin e e s t e r a s e a c t i v i t y and th e
p re su m p tiv e ac cu m u latio n o f a c e ty l c h o li n e . ACh i n h i b i t o r s
such a s a tr o p in e and a t r o p i n e - l i k e d ru g s c o r r e c t th e ab
norm al b r a i n waves (1 5 2 ). I f g lu ta m ic a c id could be shown
to have a c a t a l y t i c e f f e c t on th e s y n th e s is o f ACh i n v iv o ,
th e n a n a t t r a c t i v e h y p o th e s is o f th e th e r e p e u tic e f f e c t s o f
t h i s su b sta n c e m ight be in d u c e d . ACh, when a p p lie d i n
s tr e n g th s o f from two to tw enty p e r c e n t, pro d u ces a l o c a l
iz e d d e p r e s s io n of e le c t r o c o r ti c o g r a p h ic a c t i v i t y ; The
d e p r e s s a n t a c t i o n may be fo llo w ed by l o c a l , h ig h fre q u e n c y ,
la r g e am p litu d e sp ik e s re se m b lin g g rand mal a c t i v i t y . One
p e r c e n t e s e r in e s u l f a t e a c c e n tu a te s t h i s and a t r o p in e
i n h i b i t s i t (1 5 3 ). Ajmone and F u o rte s (99) however, f in d
t h a t in tra v e n o u s i n j e c t i o n s o f sm a ll amounts o f ACh a r e
a lm o st w ith o u t e f f e c t on e l e c t r i c a l a c t i v i t y o f th e b r a i n
56
and s p in a l oord o f d o g s, and t h a t no m otor phenomena a p p e a r.
Large d o ses r e s u l t i n h e a r t a r r e s t , fo llo w ed by d e c re a se d
c o r t i c a l a c t i v i t y and in c re a s e d s p in a l a c t i v i t y . S in c e th e
changes a r e s im ila r to th o se o f a s p h y x ia , i t i s p o s tu la te d
t h a t th e c o n v u lsiv e movements fo llo w in g a c e ty lc h o lin e a r e
n o t c o r t i c a l i n o r i g i n , b u t a r e due to i n s u f f i c i e n t oxy
g e n a tio n secondary to c i r c u l a t o r y changes. I t may th u s be
t h a t ex p erim en ts em ploying th e method o f in tra v e n o u s i n j e c
t io n s o f ACh i n th e stu d y o f b r a i n wave p a t t e r n s m ust be
d is c o u n te d .
A d ren erg ic a c t i o n . In tra v e n o u s i n j e c t i o n o f 20 g o f
L g lu ta m ic a c id r e s t o r e d c o n sc io u sn e ss to s u b je c ts i n
hypoglycem ic eoma i n 26 o f 45 ex p e rim en ts and m o d ifie d th e
d e p th o f coma i n th e re m a in d e r. S im ila r e f f e c t s were
o b se rv e d , however, w ith g ly c in e and p-am inobenzoic a c id . In
a l l c a se s th e r e was a r i s e i n b lood g lu c o s e w hich was not
i t s e l f s u f f i c i e n t f o r th e r e s t o r a t i o n of c o n sc io u sn e ss (154)
A r i s e i n b lood g lu c o se was n o t found i n non-hypoglycem ic
p a t i e n t s on i n j e c t i o n . o f la r g e amounts o f g lu ta m ic a c id
(154) b u t i n norm al r a b b i t s , th e ^hyperglycem ia has been
found, w ith b o th g lu ta m ic a c id and g ly c in e , to exceed t h a t
produced by g lu c o s e , t h i s b ein g p re v e n te d by ad renalectom y
(1 5 7 ). G lutam ic a c id in d u c e s th e c l a s s i c a l t r i a d of
a d r e n a lin e a c t i o n ( r i s e i n b lood s u g a r, b lo o d p r e s s u r e and
57
p u ls e r a t e ) . Moreover> -blood ta k e n from hypoglycem ic
p a t i e n t s a f t e r i n j e c t i o n s o f g lu ta m ic a c id showed in c re a s e d
' a d r e n e rg ic a c t i v i t y compared w ith a p r e i n j e c t i o n sam ple,
and a r g in in e , g ly c in e and p-am inobenzoic a c id have a c tio n s
s im ila r to a d r e n a lin e i n hypoglycem ia. On th e b a s is o f
th e s e f a c t s , W eil-M alherbe ( 1*0 su g g e s ts t h a t th e a c t i o n o f
g lu ta m ic a c id i n m e n ta l d e f ic ie n c y may be th ro u g h an
a d r e n e rg ic a c t i o n s im ila r to t h a t o bserved c l i n i c a l l y w ith
am phetam ine. T his i s c o n te s te d by th e f a c t th a t g ly c in e
does n o t seem to have th e e f f e c t s o f g lu ta m ic a c id i n
In c r e a s in g th e i n t e l l i g e n c e o f r a t s ( 155)« The ev id en ce
p o in ts f a i r l y c o n c lu s iv e ly to th e a d re n e rg ic e f f e c t s o f
g lu ta m ic a c id i n hypoglycem ia. I t seems d i f f i c u l t , however,
to ex ten d th e s e o b s e rv a tio n s to i t s e f f e c t s i n m en tal
d e f ic ie n c y , though i t may e x e r t some in f lu e n c e th ro u g h
th e s e c h a n n e ls .
M aintenance o f c a tio n b a la n c e . . There i s ev id en ce
t h a t g lu ta m ic a c id has a s p e c i f i c f u n c tio n i n m a in ta in in g
th e c a tio n b a la n c e i n n e rv e . K rebs (157) has found t h a t
b r a i n s l i c e s ta k e up b o th g lu ta m ic a c id and p o ta ssiu m io n
v e ry r a p i d l y a g a in s t a c o n c e n tr a tio n g r a d i e n t . I f th e
/
s l i c e s a r e p la c e d i n a medium w ith o u t s u b s t r a t e , th e y lo s e
p o ta ssiu m , and n e i th e r g lu c o se nor g lu ta m ic a c id a lo n e w i l l
r e s t o r e i t . However, i f b o th g lu c o se and g lu ta m ic a c id
-a re-ad d ed T — th e -p o ta s s iu m — is-n o t-o n -ly - r e s t o r e d , — b u t— th e ---------
58
amount o f p o ta ssiu m ta k e n up i s e q u iv a le n t on a m olar b a s is
to th e up tak e o f g lu ta m ic a c id . N e ith e r, g lu ta m in e ,
a s p a ra g in e nor oC k e t o g l u t a r i e and would p erfo rm t h i s
f u n c tio n .
Carbon d io x id e m e tab o lism . The EEG a c t i v i t y o f th e
c o rte x o f norm al s u b je c ts can be a l t e r e d by v a ry in g th e
c o n c e n tr a tio n s o f in h a le d C02 . Ten p e r c e n t C02 w i l l speed
up th e c< rhythm . In p e t i t mal e p ile p s y , r e s p i r i n g 10 p e r
c e n t C02 i s b e n e f i c i a l i n i n h i b i t i n g s e iz u r e s and i n norm al
iz in g th e EEG p a t t e r n ( 158) . Gibbs e t . a l . (159) found th a t
i n g e n e r a l, p a t i e n t s w ith p e t i t mal had an ab n o rm ally low
c e r e b r a l C02 l e v e l w h ile th o s e w ith g rand m al had a h ig h
l e v e l . Darrow e t . a l . ( 160) observed t h a t th e C 02 v a lu e s
w ent even low er i n p e t i t mal im m ediately p re c e d in g an
a t t a c k and t h a t th e y r o s e s t e a d i l y f o r s e v e r a l days b e fo re
c o n v u lsio n s i n g rand m al. C 02 could be r e s p o n s ib le f o r
th e phenomena c h a r a c t e r i s t i c o f e p ile p s y i n s e v e r a l
d i f f e r e n t ways. W ith a d e p l e ti o n o f C02 th e d e s t r u c t i o n o f
a c e ty lc h o lin e i s a id e d b e c a u s e .a lk a lo s is enhances c h o lin e
e s t e r a s e a c t i v i t y r( l 6 l ) . T his would be i n agreem ent w ith
- i T
many o f th e o b s e rv a tio n s o f ACh a c t i v i t y i n e p ile p s y and
EEG a c t i v i t y .
A nother mechanism in v o lv e s changes i n th e oxygen
su p p ly to th e b r a i n a s a n i n d i r e c t r e s u l t o f r e f l e x
59
c i r c u l a t o r y a l t e r a t i o n , Bain, and K le in ( 162) an a ly ze d th e
b r a in s o f norm al and c o n v u lsin g c a ts u nder c o n d itio n s
d e sig n e d to a l t e r th e C C ^ -b ic a rb o n a te -c a rb o n ic a c id system s.
I n norm al a n im a ls, b re a th in g 10 to 30 p e r c e n t C O 2 m ix tu re s
r e s u l t e d i n a low ering o f p y ru v a te and l a c t a t e le v e ls and
had l i t t l e i f any e f f e c t on g lu c o se o r p h o sp h a te l e v e l s .
In co n vulsed an im als th e s e c o n d itio n s m arkedly lim ite d th e
ex p ected r i s e i n l a c t a t e , p y ru v a te and in o rg a n ic p h o sp h a te
and p re v e n te d th e f a l l i n h ig h energy p h o sp h a te , a l l o f
which o r d i n a r i l y accompany c o n v u ls io n s . The e x p la n a tio n
ad o p ted as m ost p ro b a b le by th e s e w orkers was ..that in creasec.
blood flow and oxygen te n s io n i n re sp o n se to in c re a s e d C O 2
c o n c e n tr a tio n en ab led b r a in to more n e a rly b a la n c e energy
demands w ith o x id a tiv e p r o c e s s e s ,, rem oving th e need f o r
l a c t a t e fo rm a tio n from p y ru v a te , and g iv in g an in c re a s e d
su p p ly o f h ig h energy bonds.
I t seems, however t h a t I n a d d i t i o n to th e c i r c u l a t o r y
e f f e c t s , G G 2 i s more s p e c i f i c a l l y concerned w ith nerve
m etabolism . P o llo c k ( 163) s tu d ie d th e e f f e c t s o f v a r io u s
c o n c e n tr a tio n s o f CO 2 and ©2 b o th to g e th e r w ith o u t n itr o g e n
and s e p a r a te ly w ith n itr o g e n , on th e norm al c a t EEG. High
c o n c e n tr a tio n s o f CO 2 w ere more e f f e c t i v e th a n low a t b o th
hig h and low O 2 p a r t i a l p r e s s u r e s i n in c r e a s in g th e f r e
quency and d e c re a s in g th e am p litu d e o f th e EEG. Pure 02
6o
and h ig h p a r t i a l p r e s s u r e s o f O 2 i n N 2 enhance th e convul-
*
s io n s induced by e l e c t r i c shock, w hereas low p a r t i a l
p r e s s u r e s , b o th w ith and w ith o u t C ©2 show an tag o n ism . C O 2
a n ta g o n iz e s s e iz u r e s produced by b o th e l e c t r i c shock and
m e tra z o l, b o th o f w hich c r e a te an an o x ic c o n d itio n w hich i s
supposedly d i r e c t l y r e s p o n s ib le f o r th e s e iz u r e s , i n t h a t
th e a n a e ro b ic so u rc e s o f energy a r e o v e r s tim u la te d . I n
th e s e c a se s th e p rim ary e f f e c t o f C O 2 c e r t a i n l y can n o t be
e i t h e r a c i r c u l a t o r y o r a r e s p i r a t o r y one in c r e a s in g th e n e t
o x y g en atio n o f th e b r a i n , s in c e p u re oxygen and h ig h p a r t i a l
p r e s s u r e s of oxygen a g g re v a te th e s e iz u r e s w h ile C O 2 a n ta g
o n iz e s them. H ere, as i n p e t i t m al, th e e f f e c t o f th e C O 2
i s to r a i s e th e fre q u e n c y o f th e la r g e a m p litu d e , slow EEG
waves induced by m e tra z o l.
L o re n te de Ho (164) showed t h a t 5 p e r c e n t CO 2 a c tin g
on i s o l a t e d fro g n erve r a i s e d th e th r e s h o ld o f s tim u la tio n
and in c re a s e d th e membrane p o t e n t i a l . Because o f a d e la y
o f f a t i g u e , th e n erve tr a n s m itte d t r a i n s o f im p u lses more
r e a d i l y . H igher c o n c e n tr a tio n s o f CO 2 up to 100 p e r c e n t
produce c o rresp o n d in g in c r e a s e s i n membrane p o t e n t i a l . The
low ered e x c i t a b i l i t y e f f e c t may e a s i l y be a t l e a s t i n
p a r t , r e s p o n s ib le f o r th e a n ta g o n is t ic e f f e c t s tow ard
m e tra z o l c o n v u ls io n s . O O 2 when in h a le d i n th e p ro p e r con
c e n tr a tio n s i s a l s o a b le to in d u ce c o n v u lsio n s i n humans
6 l
( 1 7 2 ) b u t t h e s e a r e d i f f e r e n t from t h e e p i l e p t i c - l i k e
s e i z u r e s o b s e r v e d w it h e l e c t r i c s h o c k .
The a b o v e , c o u p le d w it h t h e o b s e r v a t io n s o f A shby and
S c h u s te r (9 2 ,9 3 * 9 4 ) on c a r b o n ic a n h y d r a se r e l a t i o n s h i p s i n .
th e c e n t r a l n e r v o u s sy ste m o f a n im a ls i n d i c a t e s t h a t C02
h a s a p l a c e o f p rim a ry im p o r ta n c e i n n e r v e m e ta b o lis m .
C arb on ic a n h y d r a se o c c u r s i n a p a t t e r n o f q u a n t it a
t i v e d i s t r i b u t i o n i n t h e c e n t r a l n e r v o u s sy ste m r a n g in g
from 0 t o 10 p e r c e n t o f t h a t fo u n d i n b lo o d . The c o n t e n t
h as b e e n fo u n d t o p a r a l l e l th e ©2 u p ta k e f o r d i f f e r e n t
l e v e l s o f th e c e n t r a l n e r v o u s sy s te m and t h e d i s t r i b u t i o n
show s a r o s t r a l p r o g r e s s io n (9 5 ). Maximum am ounts a r e
a lw a y s fo u n d i n th e c e r e b r a l c o r t e x and i n th e m otor c o r t e x
o f man and m on k eys. An abn orm al d i s t r i b u t i o n seem s t o b e
fo u n d i n c e r t a i n o r g a n ic m e n t a l.d is o r d e r s ( 9 ^ ) . I t has
b e e n fo u n d f u r t h e r by Ashby and S c h u s t e r . ( 9 2 ) t h a t c a r b o n ic
a n h y d r a se c o n c e n t r a t io n i n th e c e n t r a l n e r v o u s sy ste m i s
r e l a t e d t o th e d e g r e e o f m a tu r ity i n a n im a ls and humans
and t h a t i t s o c c u r r e n c e may b e r e l a t e d t o th e o n s e t o f
s e n s e f u n c t i o n s and th e a p p e a r a n c e o f e le c t r o e n c e p h y a lo -
g r a p h ic w a v e s. No c a r b o n ic a n h y d r a se w as fo u n d , c u r i o u s l y ,
i n t h e p e r ip h e r a l n e r v o u s sy s te m o f a n im a ls .
W h atever th e f u n c t i o n o f C02 may b e , g lu ta m ic a c id
c o u ld e a s i l y p la y a r o l e I n s u p p ly in g t h i s s u b s t a n c e .
62
G lutam ic a c id f u r n is h e s < * . k e t o g l u t a r i c a c id which i s th e n
d e c a rb o x y la te d to s u c c in ic a c id (6 0 ). T his co u ld p o s s ib ly
make up f o r C02 d e f i c i e n c i e s when g lu ta m ic a c id was p r e s e n t
i n e x c e s s . R e ce n tly a p ro b a b le new mechanism f o r 002 f o r
m a tio n v i a g lu ta m ic a c id has b e e n uncovered by Awapara (166)
and R o b erts ( 167) . Both o f th e s e w orkers have found
am in o b u ty ric a c id i n la r g e q u a n t i t i e s i n th e b r a i n of
humans, r a b b i t s , g u in e a p ig s , p ig e o n s , b e e f and f i s h .
Awapara showed sim u lta n eo u s G02 l i b e r a t i o n , d e c re a s e s i n
g lu ta m ic a c id and in c r e a s e s i n *£ a m in o b u ty ric a c id , which
was i d e n t i f i e d by p a p e r chrom atography. R o b e rts has f u r t h e r
s u b s t a n tia te d t h i s by showing la b e lin g o f th e am in o b u ty ric
a c id when u n ifo rm ly la b e le d g lu ta m ic a c id i s in c u b a te d w ith
b r a i n e x t r a c t s . T hat t h i s r e a c t i o n i s o f im p o rtan ce i n
b r a i n i s upheld by th e la r g e e x te n t to w hich i t ta k e s p la c e .
The fo rm a tio n o f 002 may, however, be o f o n ly secondary
im p o rta n ce. I t has b een found (32) t h a t ammonia i s formed
f \ «
by i s o l a t e d b r a i n from b u t y l , am yl, iso am y l and h e p ty l
am ines. M oreover, am ines d e c re a s e th e oxygen consum ption
o f b r a i n (1 3 4 ). I n view o f th e p o te n t a c t i o n o f b o th
ammonia and am ines and th e a p p a re n t im p o rtan ce o f ammonia
i n n erv e m etab o lism , g lu ta m ic a c id may a c t p a r t l y i n t h i s
f a s h io n i n th e r e g u l a t i o n o f nervous f u n c tio n . The sub
s ta n c e i s c e r t a i n l y o f key im portance in many w ays. I t
rem ains f o r l a t e r work to d e c id e th e s p e c i f i c manner
w hich i t i s a c tin g i n e p ile p s y and m e n ta l d e f ic ie n c y ,
c u r a tiv e mechanisms a r e p r oh a b ly n o t th e same.
64
A DESIRABLE EXPERIMENT IN BRAIN METABOLISM
I n t r o d u c t io n
None o f th e pathw ays o f c a rb o h y d ra te breakdown i n
b r a i n t i s s u e o th e r th a n g ly c o ly s is and th e t r i c a r b o x y l i c
a c id c y c le has b een s tu d ie d v e ry e x te n s iv e ly . T h at a t
l e a s t one pathway in v o lv e s, th e u t i l i z a t i o n o f oxygen has
been shown by th e u se o f d i f f e r e n t i a l i n h i b i t o r s (3 9 > 4 0 ,4 l)
(s e e page / ? ) . ^h© hexose p h o sp h a te sh u n t, w h erein g lu c o se
i s o x id iz e d to th r e e ca rb o n frag m en ts v i a s u c c e s s iv e ly
low er su g a r a c id s o r t h e i r d e r i v a t i v e s seems f a i r l y w e ll
s u b s t a n tia te d f o r b r a i n (4 2 ,4 4 ) (s e e page /7 ) , though i t s
im p o rtan ce i s u n c e r ta in .
M ethyl g ly o x a l i s a u t i l i z a b l e s u b s t r a t e when added
to su sp e n sio n s o f b o th b r a i n and m uscle (5 2 ) , seem ingly
b e in g u t i l i z e d by b r a i n f a r more r a p id ly th a n by m uscle.
N e ith e r i t s f a t e nor i t s o r i g i n i s known i n i t s e n t i r e t y ,
though i t can be formed i n l i v e r from hexose d ip h o sp h a te
(5 0 ) and i n b r a i n from p h o sp h o g ly cerald eh y d e (49)* l a
view o f t h i s , i t would seem p r o f i t a b l e to p erfo rm more
e x te n s iv e ex p erim en ts to d e te rm in e th e r o l e o f t h i s sub
s ta n c e i n b r a i n m etabolism and p erh ap s to g a in more i n s i g h t
in t o v a r io u s pathw ays o f c a rb o h y d ra te breakdown i n b r a in .
65
The E x p e r im e n t: The N a tu re o f t h e P athw ay o f M eth y l G ly o x a l
S y n t h e s is i n R at C o rtex H om ogenates
S im p le i s o t o p i c t e c h n iq u e s m ig h t f i r s t b e em ployed,
to c o n fir m th e fo r m a tio n o f m e th y l g l y o x a l by b r a in t i s s u e
and t o g a i n some id e a o f t h e ty p e o f r o u t e in v o lv e d . U n i
fo r m ly la b e le d g lu c o s e and a n u n la b e le d m e th y l g l y o x a l
p o o l w ou ld b e added t o a s u s p e n s io n o f r a t c o r t e x h oraogen ate.
The e x t e n t o f l a b e l i n g o f th e g l y o x a l p o o l f o r v a r io u s
p e r io d s o f in c u b a t io n a t 3 7 ° c e n t ig r a d e u n der b o th a e r o b ic
and a n a e r o b ic c o n d it io n s w ou ld b e d e te r m in e d b y p r e c i p i t a
t i o n w it h sod ium b i s u l f i t e , i s o l a t i n g th e p r e c i p i t a t e and
d e te r m in in g s p e c i f i c r a d i o a c t i v i t y o f th e b i s u l f i t e a d d it io n
p r o d u c t. A p p r e c ia b le l a b e l i n g o f th e p o o l w ou ld i n d i c a t e
a p ath w ay f o r th e p r o d u c tio n o f m e th y l g l y o x a l from g lu c o s e
o r i t s d e r i v a t i v e s . An id e a o f t h e r a t e o f tu r n o v e r o f th e
p o o l w ou ld b e g a in e d by a s tu d y o f t h e tim e c u r v e so
o b t a in e d .
I t h a s b e e n fo u n d (50) t h a t i n l i v e r h o m o g e n a te s,
m e th y l g l y o x a l i s form ed u n der a n a e r o b ic c o n d it io n s from
h e x o s e d ip h o s p h a te ( s e e p a g e A lso m e th y l g l y o x a l
form s * l a c t i c a c id w it h th e a c id o f r e d u c e d g l u t a t h i n e
and th e enzym e, g l y o x a l a s e . T h is s y s te m h a s b e e n i s o l a t e d
and s t u d ie d ( 5 1 ) . I t i s c o n c e i v a b l e , a l s o , t h a t m e th y l
g l y o x a l m ig h t b e form ed a e r o b i c a l l y , f o r in s t a n c e v i a th e
66
h e x o s e p h o sp h a te sh u n t* S in c e i t may b e t h a t i n b r a in
h o m o g en a tes ( 6 ) , a s o p p o sed t o s l i c e s (7)f l a c t i c a c id form a
t i o n i s n o t s u p p r e s s e d u n d er a e r o b ic c o n d i t i o n s , i t c o u ld
n o t b e assum ed t h a t o n ly o x y g en u t i l i z i n g p r o c e s s e s w ere
o c c u r r in g u n der a e r o b ic c o n d i t i o n s . H ow ever, a n a ly s e s o f
l a c t i c a c id c o u ld b e u s e d t o i n d i c a t e th e d e g r e e t o w h ich
p r o c e s s e s n o t u s in g o x y g en w ere e n t e r in g i n under a e r o b ic
c o n d i t i o n s . I n t h i s m anner, a w o r th w h ile am ount o f i n f o r
m a tio n m ig h t b e g a in e d from su ch a s tu d y .
I f , f o r i n s t a n c e , m e th y l g l y o x a l w ere form ed i n
a p p r e c ia b le q u a n t i t i e s o n ly u n der a n a e r o b ic c o n d i t i o n s , i t
c o u ld b e assum ed t h a t o n ly a p r o c e s s n o t u s in g o x y g e n i s
i n v o lv e d . I f th e s y n t h e s i s to o k p la c e o n ly a e r o b i c a l l y ,
th e n two p o s s i b i l i t i e s w ou ld e x i s t . E it h e r a n o x y g e n
u t i l i z i n g pathw ay o n ly i s b e in g e m p lo y ed , o r , f o r some
r e a s o n , a e r o b ic c o n d i t i o n s m ig h t b e r e q u ir e d f o r th e non
o x y g e n u s in g fo rm a tio n , o f m e th y l g l y o x a l , th o u g h t h i s w ou ld
b e u n l i k e l y . I f t h e s y n t h e s i s o c c u r r e d u n d er b o th a e r o b ic
and a n a e r o b ic c o n d i t i o n s , th e n e i t h e r b o th o x i d a t i v e and
n o n o x id a t iv e p a th w a y s m ig h t e x i s t , o r th e a n a e r o b ic path w ay
m ig h t b e m a n if e s t in g i t s e l f under b o th a e r o b ic and a n a e r o b ic
c o n d i t i o n s . I n fo r m a tio n a s t o th e c h o ic e b e tw e e n t h e s e l a s t
two p o s s i b i l i t i e s m ig h t b e o b ta in e d by a c o m p a riso n b e tw e en
m e th y l g l y o x a l s y n t h e s i s and l a c t i c a c id fo r m a tio n u n der
67
a e ro b ic and a n a e ro b ic c o n d itio n s . F or in s ta n c e , i f th e
m ethyl g ly o x a l / l a c t i c a c id r a t i o w ent up under a e ro b ic
c o n d itio n s , th e n b o th an oxygen u sin g and a p ro c e s s not
u sin g oxygen would be in d ic a te d f o r m eth y l g ly o x a l syn
t h e s i s . I f i t s ta y e d r e l a t i v e l y c o n s ta n t, th e n a p r o c e s s ,
n o t u sin g oxygen, p e rh a p s a n a d ju n c t o f g ly c o ly s is would be
l i k e l y .
To f u r t h e r e l u c i d a t e th e n a tu re o f th e pathway i n
v o lv e d , io d o a e e ta te co u ld be employed a s a n I n h i b i t o r o f
l a c t i c a c id fo rm a tio n v i a g l y c o l y s i s . T his su b sta n c e
p re v e n ts th e fo rm a tio n o f p h o sp h o g ly c e ric a c id from phos-
p h o g ly c e ra ld e h y d e by i n h i b i t i n g g ly c e ro p h o sp h a te dehydro
g e n a se . I f the fo rm a tio n o f m eth y l g ly o x a l were observed
under a n a e ro b ic c o n d itio n s i n th e p re s e n c e o f enough
i n h i b i t o r to co m p letely p re v e n t th e fo rm a tio n o f l a c t i c
a c id v i a th e Embden-Meyerhof pathw ay, th e n th e s y n th e s is
would p ro b a b ly be o c c u rrin g e i t h e r from p h o sp h o g ly e ra ld e -
hyde o r from hexose d ip h o s p h a te . I f th e s y n th e s is to o k
p la c e only under a e ro b ic c o n d itio n s i n th e p re se n c e o f th e
i n h i b i t o r , th e n a n oxygen u t i l i z i n g pathw ay o f m ethyl
g ly o x a l fo rm a tio n s from g lu c o se co u ld j u s t i f y a b l y be
p o s tu l a te d . I f th e s y n th e s is took p la c e under b o th a e ro b ic
and a n a e ro b ic c o n d itio n s i n th e p re s e n c e o f th e i n h i b i t o r ,
th e n t o t a l amounts found under th e two c o n d itio n s would be
6 8
compared. I f more w ere formed under a e ro b ic th a n a n a e ro b ic
c o n d itio n s , th e n c e r t a i n l y an a e ro b ic and a n a n a e ro b ic
pathw ay would b o th be in v o lv e d . I f th e same amount o r l e s s
were formed under a e ro b ic th a n a n a e ro b ic c o n d itio n s , th e n
e i t h e r b o th ty p e s o f p athw ays, o r a n a n a e ro b ic pathway o nly
co u ld e x i s t . Comparisons o f r e s u l t s w ith and w ith o u t th e
i n h i b i t o r co u ld y i e l d in f o rm a tio n which would h e lp to
f u r t h e r e l u c id a te th e n a tu re o f th e pathw ays in v o lv e d .
BIBLIOGRAPHY
69
1. Hirawich, H0 E ., B ra in M etabolism and C e re b ra l
D is o r d e r s , pp. 117-119"> (1951}V The W illiam s and
W ilk in s Co., B a ltim o re , M aryland. #51 pp.
2 . I b i d . , p . 90.
3 . L ip s e t, M. W . and C r e s c i t e l l i , P ., A rch. B lochem .,
28, 329 (1950).
4 . M eyerhof, 0 . and W ilson, J . R ., A rch. Biochem ., 14,
71, (1 9 ^ 7 ).
5 . Coxon, R. V ., L ieb ecq , C. and P e t e r s , R. A .,
Biochem. J . , 4£, 320 (1949).
6 . R e in e r, J . M., Arch. B iochem ., 12, 327 (1947).
7 . Burk, D ., Cold S p rin g H arbor Symposia on Q u a n tita tiv e
B i o l . , 1 , 420 (1939).
8 . Burk, D ., O c c a sio n a l P u b l. Amer. A ssoc. Advancement
o f S c ie n c e , 4 , 121 (1937).
9 . Himwich, H. E. (se e r e f . l ) , pp. 240-252.
10. G erard , R. W., P h y s io l. Rev. 12, 469 (1932).
11. G erard , R. W., Ann. Rev. Biochem. 6 , 419 (1937).
12. Holmes, E. G ., G erard , R. W ,. and Solomon, E. J . ,
Am. J . P h y s i o l ., 9 3 > 342 (1930).
13. Himwich, H. E. (s e e r e f . l ) , p . 25.
14. G a u rile s c u , Bf., M eik lejo h n , A .P ., Passm ore, R and
P e te r s , R. A ., P ro c. Royal Soc. London B110, 431 (1932).
15. B reu sch , F. L. and T u lu s, R ., Enzym ologia, 11, 352
(1 9 4 5 ).
16. Himwich, H. E. (s e e r e f . 1 ), pp. 236-240.
17. A shford, C. A. and Holmes, E. G ., Biochem. J . 2 3 .
748, (1929).
70
18. T a y lo r, R. M. and W aelsch, H ., Fed. P r o c ., 8 , 55
(1949).
1 9. G erard , B. W., Ann. New York Acad. S c i . , 4 7 , 575
(1 9 4 6 -4 7 ).
20. Chance, M. R. and Y axley, D. C ., J . Exp. B io l. Med.,
21, 311 (1 9 5 0 ).
21. Abood, L ., Cavanaugh, M., T s h ir g i, R. D. and G erard,
R. W., Fed. P ro c . 10, 3 (1 9 5 1 ).
22. S hanes, A. M. and Brown, D. E. S ., J . C e ll. Comp.
P h y s i o l ., 1£, 1 (1 9 4 2 ).
2 3 . Darwin, R. M. C. and R ic h te r , D ., B io l. A b st. 24,
23402 ( 1950) .
24. A shford, C. A. and Holmes, E. J . , Biochem. J . 2 3 ,
748 (1929).
2 5 . Chance, M. R. and Y axley, D, C ., J . Exp. B io l. Med.,
21, 311 (1950).
26. Chance, M. R. and Y axley, D. C ., I b i d . , 6 ,1 (1951).
2 7 . D ickens, F. and G r e v ille , G. D ., Biochem. J . 2 7 ,
1138 (1 9 5 3 ).
28. Q u a s te l, j . H. and W heatly, A. H. M., J . B io l. Chem.
119, LXXX (1 9 3 7 ).
2 9 . W eil-M alherbe, H ., Biochem. J . , 22* 2257 (1 9 3 6 ).
3 0 . G reenberg, R. G ., J . B io l. Chem. 181, 781 (1949).
3 1 . Munz, J . A. and H u rw itz, J . , Arch. Biochem. B io p h y s.,
2 2 , 137 (1 9 5 0 ). :
32. A rc h ib a ld , R. M., Chem. Revs. 37 > 161 (1 9 4 5 ).
3 3 . A shford, C. A. and Dixon, K. C ., Biochem J . 2£, 157
(1 9 3 5 ).
3 4 . Krim sky, J . and R acker, E.., J . B io l. Chem., 179, 903
(1 9 4 9 ).
35. Holmes, E. G ., G erard , R. W. and Solomon, E. J , , Am.
J . P h y s io l. 9 2 , 342 (1 9 3 0 ).
•71
3 6 . Kahn, I . L. and Chekoun, L ., Compt. R end., 201. 505
(1 9 3 1 ).
37* G e ig e r, A. and Magnes, M., Am. J . P h y s io l. 149. 517
(1 9 4 7 ). i
■38. O lson, R. E ., Robson, J . S . , R ic h a rd s , H. and H irsc h ,
E. G ., Fed. P ro c . £ , 211 (1 9 5 0 ).
39* B ak er, Z . , F azek as, J . F. and Himwich, H. E ., J . B io l.
Chem. 1 2 £ ,.545 (1938).
40. J o w e tt, M. and Q u a s te l, J . H ., Biochem. J . , 31# 275 ’
(1 9 3 7 ). - - ■
41. B aker, Z ., F azek as, J . F. and Himwich, H. E ., J . B io l.
Chem. 12£, 557 (1938).
42. D ick en s, F . , N a tu re , 138. 1057 (1 9 3 6 ).
43. D ick en s, F . , Biochem. J . , ]52, 1645 (1 9 3 8 ).
44. H okecker, B. L ., Fed. P ro c . £ , 185 (1 9 5 0 ).
4 5 . A sh fo rd , G. A ., Biochem. J . , 2 J , 903 (1933).
46. E u le r , H. v . , G unther, G. and V e s tin , R ., Z e i t . P h y s io l.
Ghem. 240, 265 (1 9 3 3 ).
4 7 . Jo h n so n , R. E ., Biochem. J . , 33 (1936).
48. A sh fo rd , G. A ., Biochem. J . , 28, 2229 (1934).
4 9 . B a rren sh een , H. K. and B enesehovsky, H ., Biochem. Z e i t .
2 6 5 . 159 (1 9 3 3 ).
5 0 . Salem . H. M. and Crook, E. M., Biochem. J . 46, XXXVII
(1950).
5 1 . Crook, E. M. and Law, K ., I b id .
5 2 . G e ig e r, A ., Biochem. J . 29, 811, (1 9 3 5 ).
5 3 . Page, I . H ., C hem istry o f th e B r a in , p . 163, (1937) j
» C h arles C. Thomas, S p r in g f ie ld 111. and B a ltim o re , Md. [
444 pp.
5 4 . K rebs, H. A. and Johnson, W. A ., Enzym ologia, 4 , 148 :
7 2
55. K rebs, H. &. and E g g le s to n , L. V ., Biochem. J . , 54,
442 (1 9 4 4 ).
5 6 . S te r n . J . R. and Ochoa, S ., J . B io l. Chem., 179. 491
(1 9 4 9 ).
5 7 . O gston, .A. G ., N a tu re , 162. 965 (1 9 4 8 ).
5 8 . P o t t e r , V. R. and H e id e lh e rg e r, C ., N a tu re , 164, 181
(1949).
5 9 . Long, 0 ., Biochem. J . 40, 278 (1946)
6 0 . Ochoa, S ., P h y s io l. Rev. 31, 56 (1 9 5 1 ).
6 1. S h a ttu c k , G. C ., J . Am. Med. A ssn ., I l l , 1729 (1938).
62. M inot, G. R ., Ann. I n t . Med., 2 , 216 ( 1929- 3 0 ) .
6 3 . J o l l i f f e , N. and C o lb e rt, C. N ., J . Am. Med. A ssn ., 107.
„ 642 (1936).
64. G alvao, P. E. and P e r e i r a , J . , Arg. I n s t . B io l. ( B r a z il)
£ , 25 (1930).
6 5 . Ochoa, S. and P e t e r s , R. A ., Biochem. J . 3 2 . 1501 (1938).
66. L a rn e r, J . and Jandokf*, B. J . , J . B io l. Chem. 178, 373
(1949).
6 7 . F u rc h g o tt, R. F« and Shoks, E ., J , B io l. Chem. 175»
201 (1 9 4 8 ).
68. McGowan, D, K. and P e t e r s , R. A ., Biochem. J . 31, 772
(1937).
6 9 . F r a n k lin , A. J . , Regan, M., Lew is, D ., S to k s ta d , E. L.
R* and Ju k e s , T. H ., P ro c . Soc. Exp. B io l. M ed., 6 7 ,
523 (1 9 4 8 ).
7 0 . E l l i o t , K. A. C ., G rie g , M. G ., and Benoy, M. P .,
Biochem.. J . 3 1 , 1003 (1 9 3 7 ).
7 1 . F lu to , N ., Medes, G. and W einhouse, S . , J . B io l. Chem.
171, 633 U 9 4 7 ). ,
72. S te r n , J . R ., Biochem. J . 42, 616 (1 9 4 8 ).
73-. C rane, R.K. and B a ll, E .G ., J . B io l. Chem., 188, 819 1
73
7 4 . Darrow, C. W., G reen, R ., D av is. E. W. and G a ro l, H.
W., N e u ro p h y s io l., £ , 217 (1 9 4 4 ).
7 5 . Banga, I . , Ochoa, S. and P e t e r s , R. A ., Biochem. J . ,
2 1 , H 0 9 (1939).
7 6 . Long, 0 ., Biochem. J-. , 39* 143 (1 9 4 5 ).
77. E l l i o t , W. H ., N a tu re , 161, 128 (1 9 4 8 ).
7 8 . P o t t e r , V. R. and R ecknagel, R. 0 . , Fed. P ro c . £ , 205
(1 9 5 0 ).
7 9 . D ixon, K. G., B ra in , 62* 191 (1 9 4 0 ).
80. L o ev e n h art, A. S .,. L orenz, ¥ . F . and W aters, R. M.,
J . Am. Med. A ssn ., £ 2 , 880 (1 9 2 9 ).
81. Dixon, K. G ., Biochem. J , 2Q.* 1479 (1938).
82. W arburg, 0 . , P o se n e r, K. and N e g e le in , E . , Biochem. 2 ,
152. 309 (1924).
83. G h e sle r, A. and Himwich, H. E ., Am. J . P h y s i o l ., 142,
544 (1 9 4 4 ).
84. Himwich, H. E. and F a z e k a s, J . F . , I b i d . , 132. 454
(1 9 4 1 ).
8 5 . DuBois, K. P . , J . B io l. Ghem. 142, 417 (1942).
8 6 . K och, W. and K och, M. L ., I b i d . , 1£, 423 (1 9 1 3 ).
8 7 . Freedman, B ., J . N europath. Exp. N e u ro l., £ , 204 (1 9 5 0 ).
88. S te in b a c h , H. B ., J . B io l. Chem. 133. 695 (1 9 4 0 ).
8 9 . H ober, R ., A ndersch, M. and H ober, J . J . C e ll. Comp.
P h y s i o l ., 12, 195 (1 9 3 9 ).
9 0 . T e o r e ll, T ., P ro c . Soe. Exp. B io l. Med. 22# 282 (1 9 3 5 ).
91. L ing, G. and G erard , R. W., J . C e ll. Comp, P h y s i o l .,
3 4 , 413 (1 9 4 9 ).
92. Ashby, W. and S c h u s te r, E. M*, J . B io l. Ghem. 184,
109 (1 9 5 0 ).
93.
94.
95.
96.
97.
98.
99.
100.
101.
102.
103.
104.
105.
106.
107.
108.
109.
110.
111.
112.
74
Ashby, ¥ . , J . Nerv. Ment. D is. 1 0 5 (2 ). 107 (1947).
Ashby, ¥ . , J . B io l. Ghem. 15^ , 167 (1 9 4 4 ).
Danowski, T. S . , J . B io l. Chem. 139, 693 (1941).
H a r r is , J . , I b i d . , 141, 579 (1 9 4 1 ).
Dixon, K. G ., Biochem. J . 44, 187 (1 9 4 9 ).
P e ld b e rg , ¥ . , P h y s io l. Rev. 2 £ , 596 (1 9 4 5 ).
Ajmone, M. C. and P u o r te s , M. 0 . P . , E le c tro e n c e p h .
C lin . N eu ro p h y sio l. 1, 283 (1 9 4 9 ).
Himwich, H. E ., (s e e r e f . 1 ) , p . 251.
S te r n , J . R ., S h a p iro , B. and Ochoa, S . , N atu re,
166, 403 ( 1950).
Nachmansohn, D ., Ann. New York Acad. S c i. 4 7 * 395
(1 9 4 6 ).
G erard , R. ¥ . , Ann. New York Acad. S c i. 41, 575 (1946).
B u llo c k , T. H ., G ru n d fe s t, H ., Nachmanshohn, D. and
R othenberg, M.A., J . N e u ro p h y sio c ., 10, 11, (1947).
S c b m itt, P. 0 . , Adv. P r o t. Chem. 1, 44 (1 9 4 4 ).
Hober, R ., Ann. New York Acad. S c i. 4 j , 381 (1946).
B arn es, T. and B e u tn e r, R ., S c ie n c e , 104. 569 (1946).
S o z e r, P. and W in te r s te in , H ., Arch. I n t e r n a t . P h y s io l.
I I , 159 (1 9 4 6 ).
Nachmanshohn. D. and Machado, A. L ., J . N eu ro p h y sio l.
6, 397 (1 9 4 3 ).
Nachmanshohn, John, H. M. and ¥ a e ls c h , H ., J . B io l.
Chem. 1£0, 485 (1 9 4 3 ).
Nachmanshohn and Berman, M., J . B io l. Chem. 165, 551
(1 9 4 6 ). — ^
Lipman, F . , K aplan, N. 0 . , N o v e ll!, G. D ., T u t t l e ,
and G u ira rd , B .. M., J . B io l. Chem., 167, 869
75
113. O lson, R. E. and K aplan, N. 0 . , J . B io l. Chem. 175,
515 (1 9 4 8 ).
114. K orey, S. K ., Fed. P ro c . 10* 75 (1951).
115. F e ld b e rg , W. and Mann, T ., J , P h y s io l. 104, 17 (1945).
116. McLennan, H. and E l l i o t , K. A. C ., Am. J . P h y s io l.
165, 605 (1 9 5 0 ).
117. L a s n itz k l, A ., Compt. Rend. S oc. B io l. 145, 697 (1 9 4 9 ).
118. Ashby, ¥ . , J . B io l. Chem. 156, 323 , 331 (1 9 4 5 ).
119. B a lb i,. R ., B u ll. Soc. I t a l . B i o l . , 18, 285 (1943).
120. Egana, E ., U galde, F . , S a la z a , J . , S choeierm an, S. and
C elhay, J . , Rev. Med. y A lim e n ta cio n 11, 14, 19,
28, 44, 5 6 , 72 (1 9 4 7 ).
121. Anonymous, N a tu re , 165. 506 (1 9 5 0 ).
. 122. S u lk in , N. M. and K untz, A ., A nat. Ree. 101. 33 (1 9 4 8 ).
123. Nachmansohn, D ., C o ates, C. and Machado, H ., J .
N e u ro p h y s io l.,,6, 383 (1 9 4 3 ).
*
124. W in te r s te in , H. and B aso g lu , M., Arch. I n t e r n a t .
P h y s io l. 2 2 , 159 (1 9 4 6 ). ,
125. Nachmansohn, D ., V itam in s and Hormones 2> 337 (1 9 4 5 ).
126. Hodgkin, A. L. and H uxley, A. F . , N atu re, 158, 376
(1 9 4 6 ).
127. Hodgkin, A, L. and K atz, B. J . P h y s io l. 108, 37 (1949)►
128. F e ld b e rg , ¥ . and V a rtia n e n , A ., J . P h y s io l. 82, 103
(1 9 3 4 ).
129'* D u ll e r e , W., and Loewi, 0 . , N a tu re , 144, 244 (1939).
130. H a rk in s, W ., M attso n , R ., and C orin, M., J . Am. Chem.
Soc. 6Q, 220 (1 9 4 6 ).
131. G ibbs, F. A. and G ibbs. E. L . , " A tla s o f E ncephalo
g r a p h y ,” 2nd Ed. (1945)# Addison and W esley P re s s I n c . ,
Cambridge, Mass. 221 pp. ,
76
132. O lken, H ., F ed. P r o c ., £ , 305 (1 9 5 0 ).
135* Grey, W. W. and W a lte r, V. J , , Ann. Rev. P h y s io l. 11,
- 199 (1949).
134. Q u a s te l, J . H ., Ann. Rev. Biochem. 8,435 (1 9 3 9 ).
135. P r ic e , J . G ., W aelsch, H. and Putnam, T ., J . , J . Am.
Med. A ssoc. 122. 1153 (1 9 4 3 ).
136. A lb e r t, K ., Hoch, P. and W aelsch, H ,, J . Nerv. Ment.
DS -s « 104. 263 (1 9 4 6 ).
137. W ei1-M alherb, H ., P h y s io l. R e v ., 2 0 , 549 (1 9 5 0 ).
138. S te r n , J . R ., E g g le s to n , L. V ., H erns, R. and K rebs,
H. A ., Biochem. J . , 44, 410 (1949).
139* S chw erin, P . , Bessman, S. P. and W aelsch, H ., J . B io l.
Ghem. 184, 37 (1 9 5 0 ).
140. Tigerm an, H. and M acVicar, R ., J . B io l. Ghem. 189.
793 (1951).
141. W ei1-M alherb, H ., Biochem. J . 2 0 , 665 (1 9 3 6 ).
142. S a p i r s t e i n , M. R ., P ro c . Soc. Exp. B io l. Med. 52, 334
(1943).
143. Ajmone, M. C ., F u o r te s , M. G. F. and M arossero, F . ,
E le c tro e n c e p h . C lin . N eu ro p h y sio l. 1, 291 (1949).
144. R ic h te r , D ,. and Dawson, R. M, G. - R ef. L o s t.
145. Nachmansohn, D. and W eiss, M. S . , J . B io l. Chem. 172,
627 ( 1 9 4 8 ) .
146. F o r s t e r , F. M,, A rch. N eu ro l. P s y e h i a t ., 5 4 , 391 (1946).
147. B ren n e r, G. and M e rit, H. H ., I b id . 48, 382 (1 9 4 2 ).
148. Rubin, M. A ., Cohen, M. H. and H oagland, H ., Endo
c rin o lo g y 2 1 , 536 (1939*) .
149. G ibbs, F . A ., G ibbs, E. L. and Lennox, W. G ., T ran s.
Am. N eu ro l. A ssoc. 62, 129 (1 9 3 7 ).
150.
151.
152.
153.
1 5 4.
155.
156.
157.
158.
159.
160.
161.
1 62.
165.
164.
165.
166.
167.
77
P r i c e , J . G ., W a e lsc h , H. and. Putnam , T. J . , J . Jim.
Med. A s s o c . 122. 1153 (1 9 4 3 ).
Pope, A ., M o rris, A. A ., J a s p e r , H ., E l l i o t , K. A. C.
and P e u f ie ld , W., A R esearch N erv. Ment. D is. P ro c .
2 6 , 218 (19473.
Hampson, J . L ., E s s ig , 0 . F . , W i l l i s , A. and Himwich,
H. E ., C lin . N e u ro p h y s io l., 2 , 41 (1 9 5 0 ).
E s s ig , C. F . , F ed. P ro c . 10, 40 (1 9 5 1 ).
Meyer^ G. W. and W alker, J . W., Biochem. J . , 44, 92
Zimmerman, F. T. and R oss, S . , A rch. N eu ro l. P s y e h ia t.
5 1 , 446 (1 9 4 4 ).
Dawson, R. M. C ., N ature 164, 1097 (1 9 4 9 ).
K rebs, H. A ., Biochem. J . , 4X, (1 9 5 0 ).
Himwich, H. E. (s e e r e f . l ) , p . 106.
G ibbs, E. L . , Lennox, W. G. and G ibbs, F. A ., Arch.
N eu ro l, and P s y e h ia t. 42., 223 (1 9 4 0 ).
Darrow, C. W., G reen, R ., D av is, E. W. and G a ro l, H.
W., J . N e u ro p h y sio l. 217, ( l§ 4 4 ) .
G e s e ll, R ., Am. J . P h y s io l. 6 6, 5 (1 9 2 3 ).
B ain , J . A. and K le in , J . R ., Am. J . P h y s io l. 158.
478 (1 9 4 9 ).
P o llo c k , G. H ., J . N e u ro p h y sio l. 12, 315 (1 9 4 9 ).
L o re n te De No, S t u d . ;R o c k e f e lle r I n s t . Q l , 148 (1 9 4 7 ).
G y a r f a s ,.K ., P o llo c k , G. H. and S te in , S. N ., P ro c .
Soc. Exp. B io l. Med., £ 0 , 292 (1 9 4 9 ).
Awapara, J . , Texas R e p ts. B io l, and Med. 8 , 443 (1950)
R o b e rts, E. and F ra n k e l, S . , J . B io l. Chem. 187. 55
(1 9 5 0 ).
78
168. G erard , B. W. and D oty, R. W., Biochem. I t . B iophys.
A cta, 4 , 113 (1 9 5 0 ).
169* P o t t e r , V. K ., P a rd e e , A. B. and L y le, G. G„, J , B io l.
Ghem., J J 6 , 1075 (1 9 4 8 ).
170. M eduski, « X . W., Biochem. E t. B iophys, A cta , 5 , 138
(1 9 5 0 ).
Ulilveralty of S o u th e rn CalifornJa Library

Linked assets

University of Southern California Dissertations and Theses

Conceptually similar

PDF

Glycoproteins in saline extracts of tissues of normal adult rats

PDF

Synthetic pyrimidine nucleosides as potential inhibitors of nucleic acid metabolism

PDF

The metabolism of the hexitols

PDF

Some enzymes and inhibitors of human pancreas

PDF

The effects of the non-dialyzable products of pepsin digested serum proteins on the growth of tissue cells in vitro

PDF

Determination of protein-bound and unbound calcium in serum using dextran gel

PDF

Some aspects of the metabolism of Endamoeba histolytica

PDF

A comparative study of the utilization of jojoba and cottonseed oil in the rat

PDF

A comparative study of halodeoxyuridines

PDF

Porphyrin biosynthesis by microorganisms

PDF

The effect of lutein on carotene utilization as measured by growth of the rat

PDF

Some aspects of the carbohydrate metabolism of Endamoeba histolytica

PDF

Studies on metabolism of tissues. I. The polarographic measurement of cytochrome oxidase in liver homogenates. II. Studies on the effect of thyroxine on respiration of isolated rat diaphragm

PDF

The synthesis of niacin from tryptophan in rat liver slices

PDF

The comparative nutritional value of foodstuffs under stress conditions

$The effect of L-thyroxine on oxidation and phosphorylation in a subcellular particulate fraction of baking yeast$

PDF

The effect of L-thyroxine on oxidation and phosphorylation in a subcellular particulate fraction of baking yeast

PDF

The sites of alkaline phosphatase in Dentinogenesis

PDF

The effect of neoplastic tissue on the metabolism of formic acid by the host

PDF

The synthesis and biological activity of compounds structurally related to thyroxine

PDF

Effects of sources of dietary protein on collagen biosynthesis

Asset Metadata

Creator McGaughey, Charles (author)

Core Title Some aspects of the metabolism of nervous tissue

Degree Master of Science

Degree Program Biochemistry and Nutrition

Publisher University of Southern California (original), University of Southern California. Libraries (digital)

Tag chemistry, biochemistry,OAI-PMH Harvest

Language English

Contributor Digitized by ProQuest (provenance)

Permanent Link (DOI) https://doi.org/10.25549/usctheses-c17-777921

Unique identifier UC11347931

Identifier EP41328.pdf (filename),usctheses-c17-777921 (legacy record id)

Legacy Identifier EP41328.pdf

Dmrecord 777921

Document Type Thesis

Rights McGaughey, Charles

Type texts

Source University of Southern California (contributing entity), University of Southern California Dissertations and Theses (collection)

Access Conditions The author retains rights to his/her dissertation, thesis or other graduate work according to U.S. copyright law. Electronic access is being provided by the USC Libraries in agreement with the au...

Repository Name University of Southern California Digital Library

Repository Location USC Digital Library, University of Southern California, University Park Campus, Los Angeles, California 90089, USA