$142

VOLTAGE-CLAMP STUDY OF HORIZONTAL CELLS IN CARP RETINA. J.C. ~ #YAMADA t M. t LOW t AND DJAMGOZ r M.B.A. Neurobioloqy Groupr Imperial Colleqe t London SW7

2BB t U.K. & #Electrotechnical Lab. t Tsukuba t Ibaraki 305 t Japan.

The electromotive force (emf) of light-evoked synaptic currents and passive membrane proper-

ties of horizontal cells (HCs) were studied by a voltage-clamp method. By using double-barrelled

micro-electrodes cone- and rod-driven HCs in dark-adapted carp retina were voltage-clamped whilst

perfusing 5 ~M dopamine which uncoupled the gap junctions. Current-voltage (I-V) relationships

were measured using both rectangular and ramp functions of command voltage. Input impedances of

HCs in darkness were 28 ~ 12 M~ (mean ~ s.d., n=72); the resting potentials were -37 ~ Ii mV

(n=72). The I-V curve for some cells of all types showed a region of negative resistance consis-

tent with the involvement of a Ca 2+ current. The I-V curves did not seem to correlate with par-

ticular cell types. Synaptic currents (I s) evoked by monochromatic stimuli (460, 533, 688 nm)

were measured at various clamped voltages. A reversal potential of I s to bright red background

light was 9 mV more positive than the resting potential. In every type of HC the reversal

potentials to brief light flashes of every colour were estimated by extrapolation of the Is-V

curves and were consistently 9 mV more positive than resting potentials. Thus, the emfs of

light-evoked synaptic currents of HCs are probably derived from K + and Na + and/or Ca 2+ gradients.

MACROMOLECULAR O R G A N I Z A T I O N OF DISK AND PLASMA MEMBRANES OF ROD O U T E R SEGMENT IN THE R A T R E T I N A .KATSUYUKI MIYAGUCHI* , T A K A H I R O GOTOW* AND P A U L O H I T O N A R I H A S H I M O T O , D e p a r t m e n t of A n a t o m y , O s a k a U n i v e r s i t y Medica l S c h o o l , 3 -57 N a k a n o s h i m a 4, K i t a k u , O s a k a 530, J a p a n .

D i s k a n d p l a s m a m e m b r a n e s o f r o d o u t e r s e g m e n t w e r e e x a m i n e d w i t h a r a p i d - f r e e z e a n d d e e p - e t c h t e c h n i q u e u s i n g f r e s h r a t r e t i n a to k n o w h o w m e m b r a n e p r o t e i n s , r h o d o p s i n a n d o t h e r c o m p o n e n t s , a r e m a c r o m o l e c u l a r l y o r g a n i z e d . P a i r e d d i s k m e m b r a n e s in t h e s ame d i s k w e r e a lmos t a l w a y s a t t a c h e d to e a c h o t h e r e x c e p t a t m a r g i n a l a r e a s w h e r e t h e i n t r a d i s c a l s p a c e a p p e a r e d . O w i n g to s u c h m e m b r a n e a t t a c h m e n t , p a r t i c l e s w i t h i n o p p o s i t e m e m b r a n e s a p p e a r e d to b e f u s e d w i t h e a c h o t h e r . On c y t o p l a s m i c s u r f a c e s (CS) o f t h e d i s k a n d p l a s m a m e m b r a n e s , two t y p e s of p a r t i c l e w e r e o b s e r v e d : o n e is s m a l l e r (7 -12 nm in d i a m e t e r ) a n d l o w e r , t h e o t h e r i s l a r g e r (11-15 nm in d i a m e t e r ) a n d t a l l e r . T h e r e w e r e n o d e t e c t a b l e p a r t i c l e p r o f i l e s , h o w e v e r , o n t h e i n t r a d i s c a l s u r f a c e of t h e d i s k m e m b r a n e s as well a s o n t h e e x t r a c e l l u l a r s u r f a c e s o f t h e p l a s m a m e m b r a n e s . Some o f t h e i n t r a m e m b r a n e p a r t i c l e s ( IMPs) on t h e P f a c e o f t h e d i s k m e m b r a n e f o r m s t r a n d - l i k e p r o f i l e s a n d c o r r e s p o n d i n g g r o o v e s w e r e d e t e c t a b l e on t h e E f a c e . Small p a r t i c l e s on t h e CS w e r e s i m i l a r in d i s t r i b u t i o n d e n s i t y to t h e IMPs o n t h e P f a c e , a n d t h e y a p p e a r e d to b e c o n t i n u o u s in s t r u c t u r e , wh i l e CS l a r g e p a r t i c l e s s e e m e d to b e a t t a c h e d to t h e d i s k m e m b r a n e . T h e s e o b s e r v a t i o n s s u g g e s t s t r o n g l y t h a t CS smal l p a r t i c l e s r e p r e s e n t t h e c y t o p l a s m i c p o r t i o n o f t h e m e m b r a n e p r o t e i n , r h o d o p s i n , a n d t h e l a r g e p a r t i c l e s a r e e x t r i n s i c m e m b r a n e c o m p o n e n t s . T h u s , smal l p a t i c l e s m i g h t b e t h e COOH t e r m i n a l d o m a i n o f r h o d o p s i n , a n d l a r g e o n e s c o u l d b e G T P - b i n d i n g p r o t e i n s a n d p h o s p h o d i e s t e r a s e .

45. Visual system II. Anatomy and physiology THE OPTIC TECTUM OF THE SPARROW--A COX-GOLGI STUDY. TAKAO RYU, Department of Anatomy, dichi

Medical School, Minamikawachi, Tochigi 329-04, Japan.

To achieve an understanding of the cytoarchitecture of the sparrow optic tectum, this experi-

ment was conducted using a series of IO brains from young house sparrows. Each sparrow brain was

surgically removed, and then fixed in 10% neutral formalin (PBS) for at least 2 weeks. Following

the COX-GOLGI method (Van der Lees, ]956), serial coronal 6O~m celloidin sections were carefully

examined.

Findings obtained concerning the neurons and fiber structures in the sparrow optic tectum were

clearly confined in the following particular tectal laminae: l) Stratum opticum, 2) Stratum

griesum et fibrosum superficiale, 3) Stratum griesum centrale, 4) Stratum album centrale, 5) Stra-

tum griesum periventriculare, and 6) Stratum fibrosum periventriculare.

Apart from the synaptic organization in the tectum, the present study of the morphology of the

sparrow optic tectum is in general accord with some reports such as Jungherr (]945), Karten and

Hodos (1967), LaVail and Cowan (Ig7]), and Stokes et al. (1974).