596
Speeialia
t h e 2 n d c-wave s e e m i n g l y b e h a v e s j u s t like a p o s i t i v e off-response u n d e r some s t i m u l u s c o n d i t i o n s , s u c h as all t r a c e s of t h e r i g h t c o l u m n in F i g u r e 2 as well as t h e t r a c e s of 10 sec a n d 20 sec of t h e left c o l u m n . I t is well k n o w n t h a t a p p r o p r i a t e a p p l i c a t i o n s of e t h e r are effective for isolation of P~, P ~ a n d P m c o m p o n e n t s in E R G a. Therefore, we s t u d i e d o n t h e m o v e m e n t s of t h e 2nd c - w a v e u n d e r t h e e t h e r a n e s t h e s i a sufficient t o a b o l i s h t h e c - w a v e (PI) a n d t h e l i g h t p e a k . F i g u r e 3 shows t h a t t h e 2rid c-wave was r e p l a c e d b y a large slow p o s i t i v e p o t e n t i a l following t h e e n h a n c e d fall of t h e b - w a v e (Pn), a n d its p e a k t i m e was b e t w e e n 140 sec a n d 180 sec. T h i s v a l u e w a s f a r longer t h a n t h a t of t h e 2 n d C-wave.
A t t e n t i o n m u s t b e p a i d t o t h e s h a p e of t h e p o t e n t i a l v a r i a t i o n p r o d u c e d d u r i n g a p e r i o d f r o m t h e b e g i n n i n g of t h e l i g h t s t i m u l u s to t h e p e a k of t h e large slow p o s i t i v e p o t e n t i a l . T h e s h a p e of t h e b-wave, w h i c h shows a r e d u c e d rise a n d a n e n h a n c e d fall, infers t h a t a c t i v i t y of P n , c o m p o n e n t p r e d o m i n a t e s o v e r t h a t of P n c o m p o n e n t . If we ignore t h e s m a l l rise of t h e b - w a v e , t h e r e m a i n i n g
EXPERIENTIA
32]5
p o t e n t i a l v a r i a t i o n seems to b e s i m i l a r in s h a p e to a n isolated l a t e r e c e p t o r p o t e n t i a l (Pro) of retina, p i c k e d u p b y m i c r o e l e c t r o d e t e c h n i q u e s . T h u s t h e 2 n d c - w a v e seems to c o r r e s p o n d in c o n f i g u r a t i o n to t h e tail of t h e isolated late r e c e p t o r p o t e n t i a l . This working hypothesis may be supported by the r e p o r t of KNAVE e t al. 4,5. T h e y r e c o r d e d a slow cornean e g a t i v e p o t e n t i a l in s h e e p b y c o n v e n t i o n a l electror e t i n o g r a p h y , a n d t h e y c o n s i d e r e d i t to b e a late r e c e p t o r p o t e n t i a l . A l t h o u g h t h e i r r e c o r d i n g p e r i o d was n o t long enough, t h e i r p o t e n t i a l closely r e s e m b l e s in m o v e m e n t s o u r r e m a i n i n g p o t e n t i a l . Therefore, we h a v e a s t r o n g i m pression t h a t t h e 2nd c - w a v e is b a s e d o n t h e t a i l of t h e late r e c e p t o r p o t e n t i a l of t h e r e t i n a . W e h a v e c o n f i r m e d t h e 2nd c - w a v e also in t h e h u m a n a n d c h i c k e n eye as well as in t h e cat, b u t n o t in t h e frog. a i . GRANIT, J. Physiol., Loud. 77, 207 (1933). 4 B. KNAVE, A. ~V[OLLER and H. E. PERSSON, Vision Res. 72, 1669 (1972). 5 B. K N A V E and H. E. PERSS0N, Acta physiol, scand. 91, 187 (1974).
I n t e r a c t i o n s B e t w e e n T w o Identified Cells in t h e V i s c e r a l G a n g l i o n of the Snail, Helix pomatia S. E. JUDGE 1, G. A. I~ERKUT a n d R.
j.
WALKER
Department o/ Physiology and Biochemistry, University o/ Southampton, Medical and Biological Sciences Building, Southampton S09 5 N H (England), 7d November 1975. Summary. A n i n t e r n e u r o n e , m a k i n g e x c i t a t o r y s y n a p t i c c o n n e c t i o n s w i t h a second n e u r o n e h a s b e e n i d e n t i f i e d in t h e b r a i n of Helix pomatia. T h e r e s u l t s s u g g e s t t h a t t h e c o n n e c t i o n is m o n o s y n a p t i c . I n t e r n e u r o n e s m e d i a t i n g a v a r i e t y of s y n a p t i c a c t i o n s t o several p o s t s y n a p t i c cells h a v e b e e n i d e n t i f i e d in Aplysia 2, a, Helix 4, a n d Planorbis ~. T h e s e s y s t e m s are a n a d v a n t a g e in t h e s t u d y of s y n a p t i c t r a n s m i s s i o n as well as for d e t a i l e d p h a r m a c o l o g i c a l s t u d i e s once t h e t r a n s m i t t e r c o m p o u n d s h a v e b e e n identified. F o r t h i s reason, a t t e m p t s were m a d e to i d e n t i f y a n i n t e r n e u r o n e in t h e s u b o e s o p h a g e a l ganglia of t h e snail, m a k i n g m o n o s y n a p t i c c o n n e c t i o n s w i t h o t h e r ceils. T h i s r e p o r t describes t h e i n t e r a c t i o n b e t w e e n 2 i d e n t i f i e d cells in t h e visceral g a n g l i o n of Helix pomatia%
4 Fig. 1. Diagram of the ventral surface of the visceral ganglion showing the positions of the 2 cells postulated to be in monosynaptic connection. Ev denotes the ventral surface (v) of the visceral ganglion (E).
Materials and methods. S t a n d a r d e l e c t r o p h y s i o l o g i c a l m e t h o d s were used. T h e snail b r a i n was r e m o v e d f r o m the animal together with the attached nerve trunks and p i n n e d o n t o a ' S i l a s t i n ' block. T h e p r e p a r a t i o n was p l a c e d in a n o r g a n b a t h c o n t a i n i n g 10 m l of R i n g e r (NaCI: 8 0 m M ; KCI: 4 m M ; CaCI~: 8 m M ; 3/IgC~: 5 m M ; Tris b u f f e r : 5 r a M ; p H : 7.4). T h e n e u r o n e s t o b e i m p a l e d were exposed b y d i s s e c t i n g a w a y t h e o u t e r c o n n e c t i v e tissue. S i m u l t a n e o u s r e c o r d i n g s were m a d e f r o m cell p a i r s u s i n g glass m i c r o e l e c t r o d e s c o n t a i n i n g 1 M KAc. A T e t r o n i x 502A oscilloscope was u s e d a n d p e r m a n e n t r e c o r d i n g s were o b t a i n e d o n a W a t a n a b e p e n recorder. E a c h cell could b e d e p o l a r i z e d b y t h e b r i d g e or s t i m u l a t e d i n t r a c e l l u l a r l y w i t h a s t i m u l a t o r i n d e p e n d e n t l y of t h e second cell. Results and discussion. C h e m i c a l l y m e d i a t e d s y n a p t i c p a t h w a y s were d e m o n s t r a t e d in a p p r o x i m a t e l y 4 % of t e s t e d d i f f e r e n t cell p a i r s in t h e c e n t r a l ganglia. O v e r 300 cell p a i r s were t e s t e d . One c o n s i s t e n t i n t e r a c t i o n was d e m o n s t r a t e d w h i c h s h o w e d t h e c h a r a c t e r i s t i c s of a m o n o s y n a p t i c - l i k e c o n n e c t i o n . A s t r o n g 'one for one' conn e c t i o n w a s d e m o n s t r a t e d b e t w e e n 2 s m a l l cells o n t h e v e n t r a l surface of t h e v i s c e r a l ganglion. T h e l o c a t i o n of t h e cells w i t h i n t h e g a n g l i o n is i n d i c a t e d in F i g u r e 1. E v d e n o t e s t h e v e n t r a l surface (v) of t h e v i s c e r a l g a n g l i o n ( E ) t T h e p r e s y n a p t i c cell w a s d e s i g n a t e d E v 9 . T h e p r o p e r t i e s of t h e p o s t s y n a p t i c cell, E v 8 , h a v e b e e n s t u d i e d p r e v i o u s l y 6. 1 We thank the .hi.R.C. for a Training Grant to S.E.J. 2 E. R. KANDEL,W. T. th'RAZIER,R. WAZIRI and R. E. COGGESHALL, J. Neurophysiol. 30, 1352 (1967). a D. GARDNER and E. R. KANDEL,Science 176, 675 (1972). 4 G. A. COTTRELL,Nature, Loud. 225, 1060 (1970). 5 ~/[.S. BERRYand G. A. COTTRELL,J. Physiol. Loud. 244, 589 (1975). S. E. JUDGE, Ph. D. Thesis, University of Southampton (1976).
15.5. 1976
597
Specialia
S t i m u l a t i o n of t h e p r e s y n a p t i c cell elicited a s t e a d y t r a i n of spikes w h i c h r e s u l t e d in t h e a p p e a r a n c e of s m a l l d e p o l a r i z i n g p o t e n t i a l s in t h e p o s t s y n a p t i c cell. T h e i n t e r a c t i o n was one way. H y p e r p o l a r i z a t i o n of t h e p o s t s y n a p t i c cell b y 50-60 m V g r e a t l y i n c r e a s e d t h e a m p l i t u d e of t h e p o t e n t i a l s i n d i c a t i n g t h a t t h e l a t t e r are e x c i t a t o r y post-
A) 10t mV 5O Ev8
0/m'
/
lsec - Fig. 2. Responses recorded in the postsynaptie cell (upper traces) when the. presynaptic cell (lower traces) is stimulated to fire spikes. A) Each presynaptic spike gives rise to 1 EPSP. EPSP's summate if they are evoked close enough together. B) Facilitation and summation of EPSP's produced by a train of presynaptic spikes. C) EPSP's summate to cause the postsynaptic cell to fire an action potential.
s y n a p t i c p o t e n t i a l s ( E P S P ' s ) . I n F i g u r e 2A t h e s t r i c t one for one r e l a t i o n s h i p b e t w e e n t h e p r e s y n a p t i c spikes a n d t h e E P S P ' s c a n b e seen. T h e r e was a d e l a y of 20 msec b e t w e e n t h e p r e s y n a p t i c spike a n d t h e o n s e t of t h e E P S P . T h e d u r a t i o n of t h e E P S P was b e t w e e n 200 a n d 250 msec. T h e a m p l i t u d e of t h e E P S P w a s 1 m V a t a m e m b r a n e p o t e n t i a l of --100 mV. T h e one for one r e l a t i o n s h i p was m a i n t a i n e d as t h e f r e q u e n c y of firing in t h e d r i v e r celt was i n c r e a s e d (Figure 2A). T h e E P S P ' s b e g a n t o s u m m a t e as soon as t h e f r e q u e n c y of firing in t h e d r i v e r cell was i n c r e a s e d to 2 spikes p e r sec. F i g u r e 2 A shows s u m m a t i o n of t h e E P S P ' s d e p o l a r i z e d t h e m e m b r a n e b y 5 mV. D u r i n g t h e d e p o l a r i z a t i o n i n d i v i d u a l E P S P ' s c o u l d b e seen clearly. Often, s u m m a t i o n of E P S P ' s c a u s e d t h e p o s t s y n a p t i c cell t o fire a n a c t i o n p o t e n t i a l (Figure 2C). W i t h r e p e t i t i v e s t i m u l a t i o n of t h e d r i v e r cell t h e E P S P ' s were f a c i l i t a t e d as well as s u m m a t e d (Figure 2 B). A f t e r p r o l o n g e d periods of firing in t h e d r i v e r cell, E P S P ' s i n c r e a s e d in b o t h a m plitude and duration. Unitary PSP's reached an amplitude of 2 m V a n d i n c r e a s e d in d u r a t i o n t o as long as 1 sec f r o m a n i n i t i a l d u r a t i o n of 200 msec. T h e d e l a y b e t w e e n s t i m u l a t i o n a n d r e s p o n s e r e m a i n e d c o n s t a n t a t 20 msec. T h e r e s u l t s suggest t h a t t h e i n p u t o n t o t h e follower cell is m o n o s y n a p t i c . P r e l i m i n a r y i n v e s t i g a t i o n s h a v e suggested t h a t a c e t y l c h o l i n e or g l u t a m a t e could b e t h e t r a n s m i t t e r c o m p o u n d released b y t h e p r e s y n a p t i c cell o n t o t h e follower cell 6. I t t h e r e f o r e a p p e a r s t h a t t h e p r e s y n a p t i c cell is a n i n t e r n e u r o n e . E x p e r i m e n t s s h o w t h a t it receives a n e x c i t a t o r y i n p u t f r o m t h e a n a l n e r v e s. This system requires further investigation into the m o n o s y n a p t i c n a t u r e of t h e synapse, b u t a l r e a d y p r o m i s e s t o b e useful for t h e s t u d y of cell-cell i n t e r a c t i o n s .
G. A. KERKUT, J. D. C. LAMBERT, R. J. GAYTON, J. g. LOKER and R. J. WALKER, Comp. Biochem. Physiol. 50A, 1 (1975).
U l t r a s t r u c t u r a l C h a n g e s in the D o r s a l R o o t G a n g l i a E v o k e d by T h a l i d o m i d e in R a b b i t s I P. A. STOKES, A. W. J: LYKIr
a n d W. G. McBRIDE 2
The University o / N e w South Wales, School o/Pathology, P.O. Box 7, Kensington (N.S.W., Australia 2033), ld November 1975. Summary. A d m i n i s t r a t i o n of t h e t e r a t o g e n i c d r u g t h a l i d o m i d e t o p r e g n a n t does p r o d u c e s u i t r a s t r u c t u r a l c h a n g e s in foetal g a n g l i o n ceils, S c h w a n n ceils a n d a x o n s in t h e p o s t e r i o r r o o t g a n g l i a c o r r e s p o n d i n g to f o r e l i m b s e g m e n t s d e f o r m e d b y t h e drug. U l t r a s t r u c t u r a l c h a n g e s in g a n g l i a a p p e a r o n t h e 1 3 t h d a y of g e s t a t i o n , i.e., p r e c e d i n g t h e a p p e a r a n c e of limb malformation. A m o n g t e r a t o g e n i c s u b s t a n c e s c a p a b l e of p r o d u c i n g d e f o r m i t i e s in t h e m a j o r s y s t e m s of t h e h u m a n b o d y , t h e m a x i m u m a c t i v i t y is e x h i b i t e d b y • 3, 4. N e v e r t h e l e s s , t h e v a r i o u s m e c h a n i s m s of d y s m o r p h o genesis a n d in p a r t i c u l a r t h a l i d o m i d e t e r a t o g e n e s i s are p o o r l y u n d e r s t o o d . McBRIDE 5, 8 r e p o r t e d t h a t t h a l i d o m i d e t o x i c i t y is a s s o c i a t e d w i t h d e r a n g e m e n t a n d d e c r e a s e d n u m b e r s of g a n g l i o n cells of t h e d o r s a l r o o t a n d p o s t u l a t e s t h a t i t is t h e d i m i n u t i o n in n u m b e r of s e n s o r y n e r v e fibres which interferes with peripheral organ development, To seek c o n f i r m a t i o n of t h i s h y p o t h e s i s , t h e u l t r a s t r u c t u r e of s e n s o r y n e u r o n s of t h e dorsal r o o t g a n g l i a of New Zealand White Rabbits deformed by thalidomide w a s c o m p a r e d w i t h t h a t of u n t r e a t e d controls. S e n s o r y n e u r o n s were e x a m i n e d on t h e 13th, 15th, 1 7 t h a n d 21st
d a y s of g e s t a t i o n b e c a u s e t h e s e d a y s c o r r e s p o n d t o i m p o r t a n t stages i n d e v e l o p m e n t of l i m b s : o n d a y 15 d i g i t a l tissues b e g i n t o c o n d e n s e in t h e f o r e p a w s a n d b y d a y 17 s e p a r a t i o n h a s o c c u r r e d of t h e digits of t h e forepaws, as well as c o m p l e t e r e d u c t i o n of t h e w e b b i n g . D a y 21 m a r k s t h e e n d of o r g a n o g e n e s i s in t h e r a b b i t (EDWARDST). 1 This work was supported by a grant from Foundation 41. We are grateful to Miss C. ELLIS and Mr. P. ~VVESTPHALfor technical assistance. a W. G. McBRIDE, Lancet 2, 1358 (1961). 4 W. LENZ, Lancet 1, 45 {1962). W. G. McBRIDE, Int. Res. Commun. Syst. 73-7, 5-5-4 (1973). W. G. MCBRIDE, Teratology 10, 283 (1974). 7 j. A. EDWARDS, in Advances in Teratology (Ed. WOLLAM; Logos, London i968), vol. 3, p. 243.
Speeialia
t h e 2 n d c-wave s e e m i n g l y b e h a v e s j u s t like a p o s i t i v e off-response u n d e r some s t i m u l u s c o n d i t i o n s , s u c h as all t r a c e s of t h e r i g h t c o l u m n in F i g u r e 2 as well as t h e t r a c e s of 10 sec a n d 20 sec of t h e left c o l u m n . I t is well k n o w n t h a t a p p r o p r i a t e a p p l i c a t i o n s of e t h e r are effective for isolation of P~, P ~ a n d P m c o m p o n e n t s in E R G a. Therefore, we s t u d i e d o n t h e m o v e m e n t s of t h e 2nd c - w a v e u n d e r t h e e t h e r a n e s t h e s i a sufficient t o a b o l i s h t h e c - w a v e (PI) a n d t h e l i g h t p e a k . F i g u r e 3 shows t h a t t h e 2rid c-wave was r e p l a c e d b y a large slow p o s i t i v e p o t e n t i a l following t h e e n h a n c e d fall of t h e b - w a v e (Pn), a n d its p e a k t i m e was b e t w e e n 140 sec a n d 180 sec. T h i s v a l u e w a s f a r longer t h a n t h a t of t h e 2 n d C-wave.
A t t e n t i o n m u s t b e p a i d t o t h e s h a p e of t h e p o t e n t i a l v a r i a t i o n p r o d u c e d d u r i n g a p e r i o d f r o m t h e b e g i n n i n g of t h e l i g h t s t i m u l u s to t h e p e a k of t h e large slow p o s i t i v e p o t e n t i a l . T h e s h a p e of t h e b-wave, w h i c h shows a r e d u c e d rise a n d a n e n h a n c e d fall, infers t h a t a c t i v i t y of P n , c o m p o n e n t p r e d o m i n a t e s o v e r t h a t of P n c o m p o n e n t . If we ignore t h e s m a l l rise of t h e b - w a v e , t h e r e m a i n i n g
EXPERIENTIA
32]5
p o t e n t i a l v a r i a t i o n seems to b e s i m i l a r in s h a p e to a n isolated l a t e r e c e p t o r p o t e n t i a l (Pro) of retina, p i c k e d u p b y m i c r o e l e c t r o d e t e c h n i q u e s . T h u s t h e 2 n d c - w a v e seems to c o r r e s p o n d in c o n f i g u r a t i o n to t h e tail of t h e isolated late r e c e p t o r p o t e n t i a l . This working hypothesis may be supported by the r e p o r t of KNAVE e t al. 4,5. T h e y r e c o r d e d a slow cornean e g a t i v e p o t e n t i a l in s h e e p b y c o n v e n t i o n a l electror e t i n o g r a p h y , a n d t h e y c o n s i d e r e d i t to b e a late r e c e p t o r p o t e n t i a l . A l t h o u g h t h e i r r e c o r d i n g p e r i o d was n o t long enough, t h e i r p o t e n t i a l closely r e s e m b l e s in m o v e m e n t s o u r r e m a i n i n g p o t e n t i a l . Therefore, we h a v e a s t r o n g i m pression t h a t t h e 2nd c - w a v e is b a s e d o n t h e t a i l of t h e late r e c e p t o r p o t e n t i a l of t h e r e t i n a . W e h a v e c o n f i r m e d t h e 2nd c - w a v e also in t h e h u m a n a n d c h i c k e n eye as well as in t h e cat, b u t n o t in t h e frog. a i . GRANIT, J. Physiol., Loud. 77, 207 (1933). 4 B. KNAVE, A. ~V[OLLER and H. E. PERSSON, Vision Res. 72, 1669 (1972). 5 B. K N A V E and H. E. PERSS0N, Acta physiol, scand. 91, 187 (1974).
I n t e r a c t i o n s B e t w e e n T w o Identified Cells in t h e V i s c e r a l G a n g l i o n of the Snail, Helix pomatia S. E. JUDGE 1, G. A. I~ERKUT a n d R.
j.
WALKER
Department o/ Physiology and Biochemistry, University o/ Southampton, Medical and Biological Sciences Building, Southampton S09 5 N H (England), 7d November 1975. Summary. A n i n t e r n e u r o n e , m a k i n g e x c i t a t o r y s y n a p t i c c o n n e c t i o n s w i t h a second n e u r o n e h a s b e e n i d e n t i f i e d in t h e b r a i n of Helix pomatia. T h e r e s u l t s s u g g e s t t h a t t h e c o n n e c t i o n is m o n o s y n a p t i c . I n t e r n e u r o n e s m e d i a t i n g a v a r i e t y of s y n a p t i c a c t i o n s t o several p o s t s y n a p t i c cells h a v e b e e n i d e n t i f i e d in Aplysia 2, a, Helix 4, a n d Planorbis ~. T h e s e s y s t e m s are a n a d v a n t a g e in t h e s t u d y of s y n a p t i c t r a n s m i s s i o n as well as for d e t a i l e d p h a r m a c o l o g i c a l s t u d i e s once t h e t r a n s m i t t e r c o m p o u n d s h a v e b e e n identified. F o r t h i s reason, a t t e m p t s were m a d e to i d e n t i f y a n i n t e r n e u r o n e in t h e s u b o e s o p h a g e a l ganglia of t h e snail, m a k i n g m o n o s y n a p t i c c o n n e c t i o n s w i t h o t h e r ceils. T h i s r e p o r t describes t h e i n t e r a c t i o n b e t w e e n 2 i d e n t i f i e d cells in t h e visceral g a n g l i o n of Helix pomatia%
4 Fig. 1. Diagram of the ventral surface of the visceral ganglion showing the positions of the 2 cells postulated to be in monosynaptic connection. Ev denotes the ventral surface (v) of the visceral ganglion (E).
Materials and methods. S t a n d a r d e l e c t r o p h y s i o l o g i c a l m e t h o d s were used. T h e snail b r a i n was r e m o v e d f r o m the animal together with the attached nerve trunks and p i n n e d o n t o a ' S i l a s t i n ' block. T h e p r e p a r a t i o n was p l a c e d in a n o r g a n b a t h c o n t a i n i n g 10 m l of R i n g e r (NaCI: 8 0 m M ; KCI: 4 m M ; CaCI~: 8 m M ; 3/IgC~: 5 m M ; Tris b u f f e r : 5 r a M ; p H : 7.4). T h e n e u r o n e s t o b e i m p a l e d were exposed b y d i s s e c t i n g a w a y t h e o u t e r c o n n e c t i v e tissue. S i m u l t a n e o u s r e c o r d i n g s were m a d e f r o m cell p a i r s u s i n g glass m i c r o e l e c t r o d e s c o n t a i n i n g 1 M KAc. A T e t r o n i x 502A oscilloscope was u s e d a n d p e r m a n e n t r e c o r d i n g s were o b t a i n e d o n a W a t a n a b e p e n recorder. E a c h cell could b e d e p o l a r i z e d b y t h e b r i d g e or s t i m u l a t e d i n t r a c e l l u l a r l y w i t h a s t i m u l a t o r i n d e p e n d e n t l y of t h e second cell. Results and discussion. C h e m i c a l l y m e d i a t e d s y n a p t i c p a t h w a y s were d e m o n s t r a t e d in a p p r o x i m a t e l y 4 % of t e s t e d d i f f e r e n t cell p a i r s in t h e c e n t r a l ganglia. O v e r 300 cell p a i r s were t e s t e d . One c o n s i s t e n t i n t e r a c t i o n was d e m o n s t r a t e d w h i c h s h o w e d t h e c h a r a c t e r i s t i c s of a m o n o s y n a p t i c - l i k e c o n n e c t i o n . A s t r o n g 'one for one' conn e c t i o n w a s d e m o n s t r a t e d b e t w e e n 2 s m a l l cells o n t h e v e n t r a l surface of t h e v i s c e r a l ganglion. T h e l o c a t i o n of t h e cells w i t h i n t h e g a n g l i o n is i n d i c a t e d in F i g u r e 1. E v d e n o t e s t h e v e n t r a l surface (v) of t h e v i s c e r a l g a n g l i o n ( E ) t T h e p r e s y n a p t i c cell w a s d e s i g n a t e d E v 9 . T h e p r o p e r t i e s of t h e p o s t s y n a p t i c cell, E v 8 , h a v e b e e n s t u d i e d p r e v i o u s l y 6. 1 We thank the .hi.R.C. for a Training Grant to S.E.J. 2 E. R. KANDEL,W. T. th'RAZIER,R. WAZIRI and R. E. COGGESHALL, J. Neurophysiol. 30, 1352 (1967). a D. GARDNER and E. R. KANDEL,Science 176, 675 (1972). 4 G. A. COTTRELL,Nature, Loud. 225, 1060 (1970). 5 ~/[.S. BERRYand G. A. COTTRELL,J. Physiol. Loud. 244, 589 (1975). S. E. JUDGE, Ph. D. Thesis, University of Southampton (1976).
15.5. 1976
597
Specialia
S t i m u l a t i o n of t h e p r e s y n a p t i c cell elicited a s t e a d y t r a i n of spikes w h i c h r e s u l t e d in t h e a p p e a r a n c e of s m a l l d e p o l a r i z i n g p o t e n t i a l s in t h e p o s t s y n a p t i c cell. T h e i n t e r a c t i o n was one way. H y p e r p o l a r i z a t i o n of t h e p o s t s y n a p t i c cell b y 50-60 m V g r e a t l y i n c r e a s e d t h e a m p l i t u d e of t h e p o t e n t i a l s i n d i c a t i n g t h a t t h e l a t t e r are e x c i t a t o r y post-
A) 10t mV 5O Ev8
0/m'
/
lsec - Fig. 2. Responses recorded in the postsynaptie cell (upper traces) when the. presynaptic cell (lower traces) is stimulated to fire spikes. A) Each presynaptic spike gives rise to 1 EPSP. EPSP's summate if they are evoked close enough together. B) Facilitation and summation of EPSP's produced by a train of presynaptic spikes. C) EPSP's summate to cause the postsynaptic cell to fire an action potential.
s y n a p t i c p o t e n t i a l s ( E P S P ' s ) . I n F i g u r e 2A t h e s t r i c t one for one r e l a t i o n s h i p b e t w e e n t h e p r e s y n a p t i c spikes a n d t h e E P S P ' s c a n b e seen. T h e r e was a d e l a y of 20 msec b e t w e e n t h e p r e s y n a p t i c spike a n d t h e o n s e t of t h e E P S P . T h e d u r a t i o n of t h e E P S P was b e t w e e n 200 a n d 250 msec. T h e a m p l i t u d e of t h e E P S P w a s 1 m V a t a m e m b r a n e p o t e n t i a l of --100 mV. T h e one for one r e l a t i o n s h i p was m a i n t a i n e d as t h e f r e q u e n c y of firing in t h e d r i v e r celt was i n c r e a s e d (Figure 2A). T h e E P S P ' s b e g a n t o s u m m a t e as soon as t h e f r e q u e n c y of firing in t h e d r i v e r cell was i n c r e a s e d to 2 spikes p e r sec. F i g u r e 2 A shows s u m m a t i o n of t h e E P S P ' s d e p o l a r i z e d t h e m e m b r a n e b y 5 mV. D u r i n g t h e d e p o l a r i z a t i o n i n d i v i d u a l E P S P ' s c o u l d b e seen clearly. Often, s u m m a t i o n of E P S P ' s c a u s e d t h e p o s t s y n a p t i c cell t o fire a n a c t i o n p o t e n t i a l (Figure 2C). W i t h r e p e t i t i v e s t i m u l a t i o n of t h e d r i v e r cell t h e E P S P ' s were f a c i l i t a t e d as well as s u m m a t e d (Figure 2 B). A f t e r p r o l o n g e d periods of firing in t h e d r i v e r cell, E P S P ' s i n c r e a s e d in b o t h a m plitude and duration. Unitary PSP's reached an amplitude of 2 m V a n d i n c r e a s e d in d u r a t i o n t o as long as 1 sec f r o m a n i n i t i a l d u r a t i o n of 200 msec. T h e d e l a y b e t w e e n s t i m u l a t i o n a n d r e s p o n s e r e m a i n e d c o n s t a n t a t 20 msec. T h e r e s u l t s suggest t h a t t h e i n p u t o n t o t h e follower cell is m o n o s y n a p t i c . P r e l i m i n a r y i n v e s t i g a t i o n s h a v e suggested t h a t a c e t y l c h o l i n e or g l u t a m a t e could b e t h e t r a n s m i t t e r c o m p o u n d released b y t h e p r e s y n a p t i c cell o n t o t h e follower cell 6. I t t h e r e f o r e a p p e a r s t h a t t h e p r e s y n a p t i c cell is a n i n t e r n e u r o n e . E x p e r i m e n t s s h o w t h a t it receives a n e x c i t a t o r y i n p u t f r o m t h e a n a l n e r v e s. This system requires further investigation into the m o n o s y n a p t i c n a t u r e of t h e synapse, b u t a l r e a d y p r o m i s e s t o b e useful for t h e s t u d y of cell-cell i n t e r a c t i o n s .
G. A. KERKUT, J. D. C. LAMBERT, R. J. GAYTON, J. g. LOKER and R. J. WALKER, Comp. Biochem. Physiol. 50A, 1 (1975).
U l t r a s t r u c t u r a l C h a n g e s in the D o r s a l R o o t G a n g l i a E v o k e d by T h a l i d o m i d e in R a b b i t s I P. A. STOKES, A. W. J: LYKIr
a n d W. G. McBRIDE 2
The University o / N e w South Wales, School o/Pathology, P.O. Box 7, Kensington (N.S.W., Australia 2033), ld November 1975. Summary. A d m i n i s t r a t i o n of t h e t e r a t o g e n i c d r u g t h a l i d o m i d e t o p r e g n a n t does p r o d u c e s u i t r a s t r u c t u r a l c h a n g e s in foetal g a n g l i o n ceils, S c h w a n n ceils a n d a x o n s in t h e p o s t e r i o r r o o t g a n g l i a c o r r e s p o n d i n g to f o r e l i m b s e g m e n t s d e f o r m e d b y t h e drug. U l t r a s t r u c t u r a l c h a n g e s in g a n g l i a a p p e a r o n t h e 1 3 t h d a y of g e s t a t i o n , i.e., p r e c e d i n g t h e a p p e a r a n c e of limb malformation. A m o n g t e r a t o g e n i c s u b s t a n c e s c a p a b l e of p r o d u c i n g d e f o r m i t i e s in t h e m a j o r s y s t e m s of t h e h u m a n b o d y , t h e m a x i m u m a c t i v i t y is e x h i b i t e d b y • 3, 4. N e v e r t h e l e s s , t h e v a r i o u s m e c h a n i s m s of d y s m o r p h o genesis a n d in p a r t i c u l a r t h a l i d o m i d e t e r a t o g e n e s i s are p o o r l y u n d e r s t o o d . McBRIDE 5, 8 r e p o r t e d t h a t t h a l i d o m i d e t o x i c i t y is a s s o c i a t e d w i t h d e r a n g e m e n t a n d d e c r e a s e d n u m b e r s of g a n g l i o n cells of t h e d o r s a l r o o t a n d p o s t u l a t e s t h a t i t is t h e d i m i n u t i o n in n u m b e r of s e n s o r y n e r v e fibres which interferes with peripheral organ development, To seek c o n f i r m a t i o n of t h i s h y p o t h e s i s , t h e u l t r a s t r u c t u r e of s e n s o r y n e u r o n s of t h e dorsal r o o t g a n g l i a of New Zealand White Rabbits deformed by thalidomide w a s c o m p a r e d w i t h t h a t of u n t r e a t e d controls. S e n s o r y n e u r o n s were e x a m i n e d on t h e 13th, 15th, 1 7 t h a n d 21st
d a y s of g e s t a t i o n b e c a u s e t h e s e d a y s c o r r e s p o n d t o i m p o r t a n t stages i n d e v e l o p m e n t of l i m b s : o n d a y 15 d i g i t a l tissues b e g i n t o c o n d e n s e in t h e f o r e p a w s a n d b y d a y 17 s e p a r a t i o n h a s o c c u r r e d of t h e digits of t h e forepaws, as well as c o m p l e t e r e d u c t i o n of t h e w e b b i n g . D a y 21 m a r k s t h e e n d of o r g a n o g e n e s i s in t h e r a b b i t (EDWARDST). 1 This work was supported by a grant from Foundation 41. We are grateful to Miss C. ELLIS and Mr. P. ~VVESTPHALfor technical assistance. a W. G. McBRIDE, Lancet 2, 1358 (1961). 4 W. LENZ, Lancet 1, 45 {1962). W. G. McBRIDE, Int. Res. Commun. Syst. 73-7, 5-5-4 (1973). W. G. MCBRIDE, Teratology 10, 283 (1974). 7 j. A. EDWARDS, in Advances in Teratology (Ed. WOLLAM; Logos, London i968), vol. 3, p. 243.
