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Retinal projection to the nucleus of the optic tract in the cat as revealed by retrograde transport of horseradish peroxidase
Neuroscience Letters, 26 (1981) 197-202
197
Elsevier/North-Holland Scientific Publishers Ltd.
R E T I N A L P R O J E C T I O N TO T H E N U C L E U S OF THE OPTIC T R A C T IN THE C A T AS R E V E A L E D BY R E T R O G R A D E T R A N S P O R T OF H O R S E R A D I S H PEROXIDASE
I. BALLAS, K.P. HOFFMANN* and H.-J. WAGNER** A bteilung Vergleichende Neurobiologie and **A bteilung Klinische Morphologie, Postfach 4066, D- 7900 UIm (F.R.G.)
(Received July 13th, 1981; Accepted July 29th, 1981)
Key words: cat - horseradish peroxidase - nucleus of the optic tract - optokinetic nystagmus - retina
Retrograde transport of horseradish peroxidase injected iontophoretically into the nucleus of the optic tract of cats revealed that the direction-selective cells in this pretectal nucleus receive direct retinal projections from small retinal ganglion cells, the so-called 3,-cells. These cells from a horizontal band on the contralateral retina. Few labeled cells are found in the ipsilateral temporal retina. The input from the contralateral retina is 10 times more numerous than from the ipsilateral one. In both retinae the highest concentration of labeled cells is near the area centralis.
The nucleus o f the optic t r a c t ( N O T ) in the p r e t e c t u m o f m a m m a l s has been i d e n t i f i e d as the link between the retina a n d p r e m o t o r nuclei in the p a t h w a y mediating the o p t o k i n e t i c reflex [2, 4, 9]. W e w a n t e d to i d e n t i f y the retinal g a n g l i o n cells t h a t p l a y a role in the h o r i z o n t a l o p t o k i n e t i c n y s t a g m u s ( O K N ) o f the cat by injecting h o r s e r a d i s h p e r o x i d a s e ( H R P ) into the N O T . T h r e e m o r p h o l o g i c a l classes o f g a n g l i o n cells have been d e s c r i b e d in the c a t ' s retina [1, 11, 14]. a - C e l l s h a v e large cell b o d i e s with a d i a m e t e r o f a b o u t 30 ~zm, very thick a x o n s , a n d 5 - 6 large d e n d r i t e s which b r a n c h out s t r o n g l y into the p e r i p h e r y . / 3 - C e l l s have m e d i u m - s i z e d cell b o d i e s with a d i a m e t e r o f a b o u t 30 #m, very thick a x o n s , a n d 5 - 6 large r a m i f i e d d e n d r i t i c trees, which a r e m u c h less e x t e n d e d . 3,-Cells constitute a heterog e n o u s p o p u l a t i o n o f retinal g a n g l i o n cells, which all have a very thin a x o n in c o m m o n . M o s t o f t h e m have very small cell b o d i e s with a d i a m e t e r o f less t h a n 16 # m a n d a sparsely b r a n c h i n g , b u t f a r - r e a c h i n g , d e n d r i t i c tree. 3,-Cells with m e d i u m sized cell b o d i e s [1, 11] have a d e n d r i t i c p a t t e r n similar to t h a t o f the a-cells. The following d a t a will s h o w , that o n l y 3,-cells p r o j e c t to the N O T . F o r this s t u d y , t h r e e a d u l t cats were a n e s t h e t i z e d with K e t a n e s t (i.v. 1 0 - 2 0 m g / k g ) , i m m o b i l i z e d with F l a x e d i l a n d a r t i f i c i a l l y r e s p i r a t e d with a m i x t u r e o f *To whom correspondence should be addressed 0304-3940/81/0000-0000/$ 02.50 © Elsevier/North-Holland Scientific Publishers Ltd.
198 N 2 0 : O 2 (70°70:30%). The head was fixed in a stereotaxic apparatus for electrophysiological recording and iontophoresis of H R P . The NOT in the pretectum was identified neurophysiologically on the basis of its characteristic response to visual stimulation [4, 10]. We considered the recording tip of the micropipette to be located in the NOT when large patterns rich in contour were more effective visual stimuli than single spots or lines, when cells were direction-selective and preferred movement from the periphery to the center of the visual field, and when these cells could be activated antidromically by electrical stimulation of the inferior olive. H R P (30% in 2% dimethylsulfoxide, DMSO was injected iontophoretically from the recording micropipette in l-sec long pulses at a frequency of 0.5 Hz over a period of 30 min. After 36 h survival time, the animals were deeply anesthetized with an overdose of Nembutal and sacrified by vascular perfusion of 0.9% NaC1 in 0.1% Novocain; followed by 3 liters of 1% paraformaldehyde and 2% glutaraldehyde in 0.1 M phosphate buffer pH 7.4, 650 mOsm. The retinae were kept in 0.1 M phosphate buffer pH 7.4, while the brain was placed in phosphate buffer containing 20% sucrose at 4°C for 12 h or at least until it had sunk. The site of injection was cut into 80 t~m frontal sections on a freezing microtome. The retina was removed from the eye cup and freed from the pigment epithelium. The retina and the sections of the injection site were incubated in H a n k e r - Y a t e s reagent at room temperature. (Incubation solution: 150 mg H a n k e r - Y a t e s reagent in 100 ml Tris (hydroxymethylaminomethane) buffer pH 7.6, 650 m O s m , 33 t~l 30°70 H202) [3]. The sections were incubated until they showed a general light brown tinge, but for no longer than 20 min. Subsequently they were rinsed twice with phosphate buffer pH 7.4, mounted with chromalum gelatine, left to dry overnight at room temperature, counterstained with 0.1070 cresyl violet and covered with malinol. Whole mounts were made from the retinae [13]. Once the labeled retinal ganglion cells were plotted ( X - Y recorder attached to the stage of a microscope), drawn (drawing mirror, light microscope) and measured (MOP AMO2), the retinae were uncovered, rehydrated and counter-stained with cresyl violet, because the sizes o f ganglion cell bodies of unlabeled ganglion cells could only be measured from stained retinae. The results from one of the three experiments are shown in Fig. 1. (1) The injection site (see Fig. 1, top). The 80 ~m frontal sections of the injection into the N O T are displayed in the anterior posterior direction. The black area represents the region containing the brown reaction product, indicating the presence of H R P . The site of the greatest H R P concentration stretches from anterior 3.3 to anterior 3.5, the total injection area from anterior 3.2 to anterior 4. I. The injection site lies superficially. Nuclei other than the NOT are not affected; however, fibers which border the region of the injection site could have absorbed H R P . (2) The retina (Fig. 1, bottom). The retinal m a p of the contralateral retina is shown. Each dot represents a retrogradely labeled y-cell, dots with circles are labeled s-cells. Blood vessels serve as orientation landmarks. The star marks the
199
~---~
a 4.1
Injection site
f j
3.2
I
5mm ,-dq
! /.11"'7,,'-',. ~-.-~retina f .. ,, / ,,'j--z,~CY e ~.-cells / ,'?,',.,~')- -Y ~ .1I • y~ells
Fig. 1. Top: The injection site into the nucleus of the optic tract (NOT). The sections (80 #m) are laid out in anterior posterior direction from anterior 3.2 to anterior 4.1. The black area indicates the extension of the injection site. LGB, lateral geniculate body; MGB, medial geniculate body. Bottom: The retinal distribution of labeled cells in the contralateral retina. Every dot indicates a labeled -r-cell; dots in circles show labeled a-cells. Blood vessels serve for better orientation; the star indicates the area centralis, the circle the blind spot. Between the inner dotted line and the edge of the retina lies the area of intact pigment epithelium. This area could only be interpreted to a limited extent, but ganglion cell density is very low there.
a r e a centralis, the circle i n d i c a t e s the b l i n d s p o t . B e t w e e n the i n n e r b r o k e n line a n d the e d g e o f t h e r e t i n a lies a n a r e a o f r e t i n a , w h e r e the p i g m e n t e p i t h e l i u m c o u l d n o t be r e m o v e d . In this p e r i p h e r a l p a r t , t h e g a n g l i o n cell d e n s i t y is, h o w e v e r , v e r y l o w . M o s t o f t h e 119 l a b e l e d cells in t h e c o n t r a l a t e r a l r e t i n a lie o n a h o r i z o n t a l b a n d s t r e t c h i n g o u t i n t o t h e u p p e r p a r t o f t h e r e t i n a . O f t h e 6 l a b e l e d u - c e l l s , 5 lie in t h e p e r i p h e r y o f t h e r e t i n a l field. In t h e ipsilateral t e m p o r a l r e t i n a o n l y 13 cells a r e l a b e l e d . T h e y a r e s i t u a t e d n e a r t h e a r e a centralis.
200
The histograms in Fig. 2 show the size/frequency distribution of the total population of retinal ganglion cells and of the labeled cell bodies of all cats in the central (upper) and peripheral retina (lower part). With exception of a few labeled ~-cells, all retinal ganglion cells projecting into the NOT were identified as y-cells due to their small cell bodies and thin, long dendrites. -17 Hi
100 p.m 'X
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.
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.......:'
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,
, -":",
3L.,-
,-"/
, *
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Fig. 2. The histograms sho,.~ the frequency dis[ribufion of ceil body sizes in the area cmltralis (upper par[) and peripheral retina (lowm parl) o1' fllrec cases. [he abscissa indicates the cell body sizes in/m~ z. Each bar represents a 10/~m 2 class. Labeled cells are indicated by arrows and lheir number can be read on the left ordinate. The righ[ ordinate indicates the percentage o( all cells in that relina! area within a given class o f cell body size. Camera lucida drawings o f labeled cells are shown as insets. The lower part is an example o f a labeled ~-cell; lhe upper part shows labeled small y-calls on the left and one medium-sized
y-cell on the righL
201
Examples of the morphology of retrogradely labeled retinal ganglion cells are also drawn in Fig. 2. The granules are H R P vesicles stained with H a n k e r - Y a t e s reagent. The cells were identified according to the previous descriptions [1, 11, 14]. "/-Cells (Fig. 2 top, left hand) have small cell bodies with a few sparsely branching, farreaching dendrites and thin axons. The small caliber of the axons may be the reason why only a small amount of H R P is transported into their cell bodies. -,/-Cells with medium-sized cell bodies (Fig. 2 top, right hand) and the same dendritic branching pattern as a-cells (Fig. 2 bottom) were also identified. They also have thin axons and therefore are only sparsely filled with HRP when compared to o~-cells, c~-Cells have large cell bodies and 3-5 main far-reaching, branching dendrites. Due to their thick axons they are densely filled with H R P granules. No ~-cells were labeled. The reaction according to Hanker-Yates for demonstration of the presence of H R P is not as sensitive as the TMB method [7, 8]. The Hanker-Yates method is, however, very simple to use, the product of the reaction is not carcinogenic, it does not fade, and the process is sensitive enough to allow a clear identification of retrogradely labeled ceils. The best of the 3 injections into the NOT of cats was presented, the other two experiments show the same results. Deviations were present in so far as the possibility existed in one experiment that the nucleus pretectalis posterior (NPP), and in the other the pulvinar, were also contaminated with HRP from the injection sites in the NOT. Corresponding control experiments must still demarcate the retinal projections into these regions from tt~at into the NOT. Electrophysiologically, the excitatory retinal input to the NOT in the cat has been identified as W-type [4, 5]. Almost all of the cells labeled by H R P injections into the NOT wer e -r-cells. The few labeled c~-cells may result from injury of o~-fibers in the brachium of the superior colliculus or from H R P diffused into the NPP [10]. Our anatomical results thus fully confirm our electrophysiological finding. W-Cells are the physiological counter part of 7-cells and they provide the input to the NOT. The results do not, however, allow the definition of a clear subpopulation of .y-cells as the W-cells involved in OKN. This work was supported by Grant DFG H. 450/12 to K.P. Hoffmann.
1 Boycott, B.B. and W~ssle, H., The morphological types of ganglion cells of domestic cat's retina, J. Physiol. (Lond.), 24 (1974) 397-419. 2 Collewijn, H., Sensory control of optokinetic nystagmus in the rabbit, Trends Neurosci., 29 (1980) 277-280. 3 Hanker, J.S., Yates, P.E., Metz, C.B. and Rustioni, A., A new specific, sensitive and noncarcinogenic reagent for the demonstration of horse-radish peroxidase, J. Histochem., 9 (1977) 789-792. 4 Hoffmann, K.P. and Schoppmann, A., Retinal input to direction selective cells in the nucleus tractus opticus of the cat, Brain Res., 99 (1975) 359 366. 5 Hoffmann, K.P. and Schoppmann, A., A quantitative analysis of the direction-specific response of neurons in the cat's nucleus of the optic tract, Exp. Brain Res., 42 (1981) 146-157.
202 6 Levick, W.R., Form and function of cat retinal ganglion cells, Nature (Lond.), 254 (1975) 659-662. 7 Mesulam M.-M., Tetramethylbenzidine for horse-radish peroxidase neurochemistry: a noncarcinogenic blue reaction-product with superior sensitivity for visualizing neuronal afferents and efferents, J. Histochem. Cytochem., 26 (1978) 106 117. 8 Mesulam, M.-M. and Mufson, E.J., The rapid anterograde transport of horse-radish peroxidase, Neuroscience, 5 (1980) 1277 1286. 9 Precht, W. and Strata, P., On the pathway mediating optokinetic responses in vestibular nuclear neurons, Neuroscience, 5 (1980) 777-787. 10 Schoppmann, A. and Hoffmann, K.P., A comparison of visual responses in two pretectal nuclei in the superior colliculus of the cat, Exp. Brain Res., 35 (1979)495-510. I1 Stone, J. and Clarke, R., Correlation between soma size and dendritic morphology in cat retinal ganglion cells: evidence of further variation in gamma-cell class, J. comp. Neurol., 19 (1980) 11-17. 12 Stone, J. and Keens, J., Distribution of small and medium-sized ganglion cells in cat's retina, J. comp. Neurol., 19 (1980) 35 46. 13 Wassle, H., Levick, W.R. and Cleland, B.G., The distribution of the alpha type of ganglion cells in the cat's retina, J. comp. Neurol., 159 (1975) 419-437. 14 W~issle, H., Illing, R.-B. and Peichl, L., Morphologische Klassen und zentrale F'rojektion von Ganglienzellen in der Retina der Katze. Verh. Dtsch. Zool. Ges., (1979) 180 193.
197
Elsevier/North-Holland Scientific Publishers Ltd.
R E T I N A L P R O J E C T I O N TO T H E N U C L E U S OF THE OPTIC T R A C T IN THE C A T AS R E V E A L E D BY R E T R O G R A D E T R A N S P O R T OF H O R S E R A D I S H PEROXIDASE
I. BALLAS, K.P. HOFFMANN* and H.-J. WAGNER** A bteilung Vergleichende Neurobiologie and **A bteilung Klinische Morphologie, Postfach 4066, D- 7900 UIm (F.R.G.)
(Received July 13th, 1981; Accepted July 29th, 1981)
Key words: cat - horseradish peroxidase - nucleus of the optic tract - optokinetic nystagmus - retina
Retrograde transport of horseradish peroxidase injected iontophoretically into the nucleus of the optic tract of cats revealed that the direction-selective cells in this pretectal nucleus receive direct retinal projections from small retinal ganglion cells, the so-called 3,-cells. These cells from a horizontal band on the contralateral retina. Few labeled cells are found in the ipsilateral temporal retina. The input from the contralateral retina is 10 times more numerous than from the ipsilateral one. In both retinae the highest concentration of labeled cells is near the area centralis.
The nucleus o f the optic t r a c t ( N O T ) in the p r e t e c t u m o f m a m m a l s has been i d e n t i f i e d as the link between the retina a n d p r e m o t o r nuclei in the p a t h w a y mediating the o p t o k i n e t i c reflex [2, 4, 9]. W e w a n t e d to i d e n t i f y the retinal g a n g l i o n cells t h a t p l a y a role in the h o r i z o n t a l o p t o k i n e t i c n y s t a g m u s ( O K N ) o f the cat by injecting h o r s e r a d i s h p e r o x i d a s e ( H R P ) into the N O T . T h r e e m o r p h o l o g i c a l classes o f g a n g l i o n cells have been d e s c r i b e d in the c a t ' s retina [1, 11, 14]. a - C e l l s h a v e large cell b o d i e s with a d i a m e t e r o f a b o u t 30 ~zm, very thick a x o n s , a n d 5 - 6 large d e n d r i t e s which b r a n c h out s t r o n g l y into the p e r i p h e r y . / 3 - C e l l s have m e d i u m - s i z e d cell b o d i e s with a d i a m e t e r o f a b o u t 30 #m, very thick a x o n s , a n d 5 - 6 large r a m i f i e d d e n d r i t i c trees, which a r e m u c h less e x t e n d e d . 3,-Cells constitute a heterog e n o u s p o p u l a t i o n o f retinal g a n g l i o n cells, which all have a very thin a x o n in c o m m o n . M o s t o f t h e m have very small cell b o d i e s with a d i a m e t e r o f less t h a n 16 # m a n d a sparsely b r a n c h i n g , b u t f a r - r e a c h i n g , d e n d r i t i c tree. 3,-Cells with m e d i u m sized cell b o d i e s [1, 11] have a d e n d r i t i c p a t t e r n similar to t h a t o f the a-cells. The following d a t a will s h o w , that o n l y 3,-cells p r o j e c t to the N O T . F o r this s t u d y , t h r e e a d u l t cats were a n e s t h e t i z e d with K e t a n e s t (i.v. 1 0 - 2 0 m g / k g ) , i m m o b i l i z e d with F l a x e d i l a n d a r t i f i c i a l l y r e s p i r a t e d with a m i x t u r e o f *To whom correspondence should be addressed 0304-3940/81/0000-0000/$ 02.50 © Elsevier/North-Holland Scientific Publishers Ltd.
198 N 2 0 : O 2 (70°70:30%). The head was fixed in a stereotaxic apparatus for electrophysiological recording and iontophoresis of H R P . The NOT in the pretectum was identified neurophysiologically on the basis of its characteristic response to visual stimulation [4, 10]. We considered the recording tip of the micropipette to be located in the NOT when large patterns rich in contour were more effective visual stimuli than single spots or lines, when cells were direction-selective and preferred movement from the periphery to the center of the visual field, and when these cells could be activated antidromically by electrical stimulation of the inferior olive. H R P (30% in 2% dimethylsulfoxide, DMSO was injected iontophoretically from the recording micropipette in l-sec long pulses at a frequency of 0.5 Hz over a period of 30 min. After 36 h survival time, the animals were deeply anesthetized with an overdose of Nembutal and sacrified by vascular perfusion of 0.9% NaC1 in 0.1% Novocain; followed by 3 liters of 1% paraformaldehyde and 2% glutaraldehyde in 0.1 M phosphate buffer pH 7.4, 650 mOsm. The retinae were kept in 0.1 M phosphate buffer pH 7.4, while the brain was placed in phosphate buffer containing 20% sucrose at 4°C for 12 h or at least until it had sunk. The site of injection was cut into 80 t~m frontal sections on a freezing microtome. The retina was removed from the eye cup and freed from the pigment epithelium. The retina and the sections of the injection site were incubated in H a n k e r - Y a t e s reagent at room temperature. (Incubation solution: 150 mg H a n k e r - Y a t e s reagent in 100 ml Tris (hydroxymethylaminomethane) buffer pH 7.6, 650 m O s m , 33 t~l 30°70 H202) [3]. The sections were incubated until they showed a general light brown tinge, but for no longer than 20 min. Subsequently they were rinsed twice with phosphate buffer pH 7.4, mounted with chromalum gelatine, left to dry overnight at room temperature, counterstained with 0.1070 cresyl violet and covered with malinol. Whole mounts were made from the retinae [13]. Once the labeled retinal ganglion cells were plotted ( X - Y recorder attached to the stage of a microscope), drawn (drawing mirror, light microscope) and measured (MOP AMO2), the retinae were uncovered, rehydrated and counter-stained with cresyl violet, because the sizes o f ganglion cell bodies of unlabeled ganglion cells could only be measured from stained retinae. The results from one of the three experiments are shown in Fig. 1. (1) The injection site (see Fig. 1, top). The 80 ~m frontal sections of the injection into the N O T are displayed in the anterior posterior direction. The black area represents the region containing the brown reaction product, indicating the presence of H R P . The site of the greatest H R P concentration stretches from anterior 3.3 to anterior 3.5, the total injection area from anterior 3.2 to anterior 4. I. The injection site lies superficially. Nuclei other than the NOT are not affected; however, fibers which border the region of the injection site could have absorbed H R P . (2) The retina (Fig. 1, bottom). The retinal m a p of the contralateral retina is shown. Each dot represents a retrogradely labeled y-cell, dots with circles are labeled s-cells. Blood vessels serve as orientation landmarks. The star marks the
199
~---~
a 4.1
Injection site
f j
3.2
I
5mm ,-dq
! /.11"'7,,'-',. ~-.-~retina f .. ,, / ,,'j--z,~CY e ~.-cells / ,'?,',.,~')- -Y ~ .1I • y~ells
Fig. 1. Top: The injection site into the nucleus of the optic tract (NOT). The sections (80 #m) are laid out in anterior posterior direction from anterior 3.2 to anterior 4.1. The black area indicates the extension of the injection site. LGB, lateral geniculate body; MGB, medial geniculate body. Bottom: The retinal distribution of labeled cells in the contralateral retina. Every dot indicates a labeled -r-cell; dots in circles show labeled a-cells. Blood vessels serve for better orientation; the star indicates the area centralis, the circle the blind spot. Between the inner dotted line and the edge of the retina lies the area of intact pigment epithelium. This area could only be interpreted to a limited extent, but ganglion cell density is very low there.
a r e a centralis, the circle i n d i c a t e s the b l i n d s p o t . B e t w e e n the i n n e r b r o k e n line a n d the e d g e o f t h e r e t i n a lies a n a r e a o f r e t i n a , w h e r e the p i g m e n t e p i t h e l i u m c o u l d n o t be r e m o v e d . In this p e r i p h e r a l p a r t , t h e g a n g l i o n cell d e n s i t y is, h o w e v e r , v e r y l o w . M o s t o f t h e 119 l a b e l e d cells in t h e c o n t r a l a t e r a l r e t i n a lie o n a h o r i z o n t a l b a n d s t r e t c h i n g o u t i n t o t h e u p p e r p a r t o f t h e r e t i n a . O f t h e 6 l a b e l e d u - c e l l s , 5 lie in t h e p e r i p h e r y o f t h e r e t i n a l field. In t h e ipsilateral t e m p o r a l r e t i n a o n l y 13 cells a r e l a b e l e d . T h e y a r e s i t u a t e d n e a r t h e a r e a centralis.
200
The histograms in Fig. 2 show the size/frequency distribution of the total population of retinal ganglion cells and of the labeled cell bodies of all cats in the central (upper) and peripheral retina (lower part). With exception of a few labeled ~-cells, all retinal ganglion cells projecting into the NOT were identified as y-cells due to their small cell bodies and thin, long dendrites. -17 Hi
100 p.m 'X
" ,
-10
,4,
!
N
--~Irl
F
.
,/,_
30
i, / ~
2C
II1~
n
II
nn
".4.
b i
,
,__,__,__,_ ,__ :,,:....
.......:'
IIIll'lno ",..
~io' 16o ' 2 ~ '3d
,
, -":",
3L.,-
,-"/
, *
-lo
,:
~'x
~!-
'
i[
2
Fig. 2. The histograms sho,.~ the frequency dis[ribufion of ceil body sizes in the area cmltralis (upper par[) and peripheral retina (lowm parl) o1' fllrec cases. [he abscissa indicates the cell body sizes in/m~ z. Each bar represents a 10/~m 2 class. Labeled cells are indicated by arrows and lheir number can be read on the left ordinate. The righ[ ordinate indicates the percentage o( all cells in that relina! area within a given class o f cell body size. Camera lucida drawings o f labeled cells are shown as insets. The lower part is an example o f a labeled ~-cell; lhe upper part shows labeled small y-calls on the left and one medium-sized
y-cell on the righL
201
Examples of the morphology of retrogradely labeled retinal ganglion cells are also drawn in Fig. 2. The granules are H R P vesicles stained with H a n k e r - Y a t e s reagent. The cells were identified according to the previous descriptions [1, 11, 14]. "/-Cells (Fig. 2 top, left hand) have small cell bodies with a few sparsely branching, farreaching dendrites and thin axons. The small caliber of the axons may be the reason why only a small amount of H R P is transported into their cell bodies. -,/-Cells with medium-sized cell bodies (Fig. 2 top, right hand) and the same dendritic branching pattern as a-cells (Fig. 2 bottom) were also identified. They also have thin axons and therefore are only sparsely filled with HRP when compared to o~-cells, c~-Cells have large cell bodies and 3-5 main far-reaching, branching dendrites. Due to their thick axons they are densely filled with H R P granules. No ~-cells were labeled. The reaction according to Hanker-Yates for demonstration of the presence of H R P is not as sensitive as the TMB method [7, 8]. The Hanker-Yates method is, however, very simple to use, the product of the reaction is not carcinogenic, it does not fade, and the process is sensitive enough to allow a clear identification of retrogradely labeled ceils. The best of the 3 injections into the NOT of cats was presented, the other two experiments show the same results. Deviations were present in so far as the possibility existed in one experiment that the nucleus pretectalis posterior (NPP), and in the other the pulvinar, were also contaminated with HRP from the injection sites in the NOT. Corresponding control experiments must still demarcate the retinal projections into these regions from tt~at into the NOT. Electrophysiologically, the excitatory retinal input to the NOT in the cat has been identified as W-type [4, 5]. Almost all of the cells labeled by H R P injections into the NOT wer e -r-cells. The few labeled c~-cells may result from injury of o~-fibers in the brachium of the superior colliculus or from H R P diffused into the NPP [10]. Our anatomical results thus fully confirm our electrophysiological finding. W-Cells are the physiological counter part of 7-cells and they provide the input to the NOT. The results do not, however, allow the definition of a clear subpopulation of .y-cells as the W-cells involved in OKN. This work was supported by Grant DFG H. 450/12 to K.P. Hoffmann.
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202 6 Levick, W.R., Form and function of cat retinal ganglion cells, Nature (Lond.), 254 (1975) 659-662. 7 Mesulam M.-M., Tetramethylbenzidine for horse-radish peroxidase neurochemistry: a noncarcinogenic blue reaction-product with superior sensitivity for visualizing neuronal afferents and efferents, J. Histochem. Cytochem., 26 (1978) 106 117. 8 Mesulam, M.-M. and Mufson, E.J., The rapid anterograde transport of horse-radish peroxidase, Neuroscience, 5 (1980) 1277 1286. 9 Precht, W. and Strata, P., On the pathway mediating optokinetic responses in vestibular nuclear neurons, Neuroscience, 5 (1980) 777-787. 10 Schoppmann, A. and Hoffmann, K.P., A comparison of visual responses in two pretectal nuclei in the superior colliculus of the cat, Exp. Brain Res., 35 (1979)495-510. I1 Stone, J. and Clarke, R., Correlation between soma size and dendritic morphology in cat retinal ganglion cells: evidence of further variation in gamma-cell class, J. comp. Neurol., 19 (1980) 11-17. 12 Stone, J. and Keens, J., Distribution of small and medium-sized ganglion cells in cat's retina, J. comp. Neurol., 19 (1980) 35 46. 13 Wassle, H., Levick, W.R. and Cleland, B.G., The distribution of the alpha type of ganglion cells in the cat's retina, J. comp. Neurol., 159 (1975) 419-437. 14 W~issle, H., Illing, R.-B. and Peichl, L., Morphologische Klassen und zentrale F'rojektion von Ganglienzellen in der Retina der Katze. Verh. Dtsch. Zool. Ges., (1979) 180 193.