330
Brain Research, 5~) (1991) 330-333 © 1991 Elsevier Science Publishers B.V. All rights reserved. (KX)6-8993/91/$03.50 A DONIS 000689939124855kl
BRES 24855
Axonal regeneration of retinal ganglion cells in the cat geniculocortical pathway Masami Watanabe ~, Hajime Sawai 2 and Yutaka Fukuda z 1Department of Physiology, Institute for Developmental Research, Aichi Prefectural Colony, Kasugai (Japan), and 2Department of Physiology, Osaka University Medical School, Suita, Osaka (Japan) (Accepted 2 July 1991)
Key words: Optic nerve regeneration; Retinal ganglion cell; Geniculocortical system; lntracellular injection; Morphology; Cat
The optic nerve of anesthetized cats was completely cut and the autologous sciatic nerve was transplanted. Sixty days later some populations of retinal ganglion cells were shown to regenerate the axon with retrograde HRP labeling. We verified that ganglion cells that had projected to the lateral geniculate nucleus (LGN) were able to regenerate through the transplant with a double-labeling method: diI was injected into the LGN prior to the transplantation, and dextran-fluorescein was injected into the graft after axonal regeneration. Intracellular injection of HRP into regenerating ganglion cells in an in vitro preparation revealed that the two major cell types projecting to the LGN, a and r, regenerated axons and showed normal dendritic morphology. The transected axons of retinal ganglion cells elongate a long distance along the autografted sciatic nerve in adult rats l ' n and hamsters 6. Regenerating retinal axons make normal synaptic contacts in the superior colliculUS3'13 and the synapses formed with their terminals manifest physiological function 7. Since extensive information is available on the morphology, physiology and central connections of cat retinal ganglion cells, it is worth asking whether the retinal ganglion cells can also regenerate their axons by the autografted peripheral nerve. If they do, the following question can be addressed which type of ganglion cells can regenerate their axon in terms of a, fl and 7 cells2. It would be especially important to clarify whether ganglion cells projecting to the lateral geniculate nucleus (LGN) can regenerate. We performed the present experiments to answer these questions. Surgical procedures for the transplantation of peripheral nerve were essentially the same as those used for rats and hamsters 3'6'n'13. Fourteen adult cats of either sex, weighing 2-3.5 kg, were anesthetized with an intramuscular injection of 57.6 mg ketamine HC1, then with a gas mixture of 1-2% halothane, nitrous oxide (1 liter/ min) and oxygen (1 liter/min). The heart rate and rectal temperature were monitored during anesthesia. The left optic nerve was completely cut at 2 - 6 mm from the eyeball. The anterior branch of the sciatic nerve (30-50 mm) was sutured to the optic stump with microsurgery thread, and the other end of the grafts was bur-
ied into the temporalis muscle. Retrograde labeling o f regenerating ganglion cells'. Fifty-five to 80 days later the cats were anesthetized with the above mentioned drug and gas, and the graft was exposed. A mixture of H R P (10% final) and dextranconjugated tetramethylrhodamine (Molecular Probes, M W = 10,000, 10% final) was injected into the graft at a point of 10 m m or more distal to the original cut. Forty to 72 h later the cats were deeply anesthetized with an overdose of Nembutal, and were perfused transcardially with 0.5% paraformaldehyde/l% glutaraldehyde in 0.1 M phosphate buffer, p H = 7.4. The retinas were dissected, and labeled cells were quickly observed under an epifluorescence microscope. The retinas were then reacted with diaminobenzidine to visualize HRP-labeled cells, and were counter-stained with 0.01% Cresyl violet. In two cats 6/zl of sonicated suspension of a carbocyanine dye, di114 (10 mg/ml), in saline containing 1% Triton-X were stereotaxically injected into the right L G N with a microsyringe 7 days before the transplantation, to prelabel ganglion cells projecting to the L G N . Sixty days after the transplantation 10% dextran-fluorescein (Molecular Probes, M W = 10.000) in water was injected into the graft. Two days later the cats were deeply anesthetized, the retina was dissected from the enucleated eye in the oygenated (95% 02/5% CO2) Ames medium, and double-labeled cells were photographed under an epifluorescence microscope. The retinas were then used for
Correspondence: M. Watanabe, Department of Physiology, Institute for Developmental Research, Aichi Prefectural Colony, Kasugai, Aichi 480-03, Japan.
331
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Fig. 1. Distribution of regenerating retinal ganglion cells retrogradely labeled with HRP in one retina (cat 6L). The area centralis (*) was determined from blood vessel pattern, and it was situated between 3.2 and 4.2 mm away from the optic disk in all 4 retinas. S, superior; I, inferior; N, nasal; T, temporal.
HRP-intracellular injection.
HRP-intracellular injection in in vitro preparation. The method was described in detail elsewhere 4'15. Regenerating ganglion cells were labeled with dextran-fluorescein (10% in water) injected into the graft in 5 cats. Two days later the operated eye was enucleated from the cats anesthetized with an overdose of Nembutal. The retina was dissected in the oxygenated A m e s medium, affixed in a chamber and superfused with the medium. Rhodamine-conjugated H R P (Sigma, 1000 U in 130/~1 of 50 mM M O P S solution, p H = 7.0) was injected into labeled cells ad libitum with glass microelectrodes. Positive currents, 3-10 n A 1 s on, 1 s off, were applied through the tip under an epifluorescence microscope. The retina was fixed with 1% glutaraldehyde and reacted with diaminobenzidine. In 8 cats regeneration of axons of retinal ganglion cell was verified with retrograde labeling with H R P - d y e mixture. Fig. 1 shows the distribution of HRP-labeled ganglion cells in one representative retina (cat 6L) in which 663 cells were labeled. Numbers of HRP-labeled ganglion cells in 3 other retinas were 593 (cat 17L), 513 (cat 19L) and 992 (cat 20L). These were less than 1% of total numbers of ganglion cells, 105,000-140,500 (ref. 12), or of fibers of the cat optic nerve, 193,000 (ref. 9). However, we observed many unlabeled cells which had similar cytological features in Nissl staining compared to
Fig. 2. A: fluorescence photomicrograph under excitation filter, 450--490 nm; barrier filter, 510 nm long pass. Two regenerating cells were retrogradely labeled with dextran-conjugated fluorescein injected into the graft. B: fluorescence photomicrograph of the same field of (A) under excitation filter, 510-560 nm and barrier filter, 590 nm long pass. One cell was labeled with diI which had been injected into the LGN 7 days prior to the transplantation.
those of HRP-labeled cells. The unlabeled cells possibly regenerated their axon which was too short to be labeled retrogradely with tracers. Therefore numbers of actually regenerating cells could be more than those of HRP-labeled ones. It might be claimed that some surviving cells without the regenerated axon took up dye and H R P diffusing from the injection site, and numbers of HRP-labeled cells included these cells. However, this did not appear to occur because the distance between injection sites of H R P - d y e mixture in the graft and the suture point of graft to the sectioned optic nerve was greater than 10 mm in each case. In fact there was no evidence for diffusion of rhodamine or H R P at the optic disk in whole mount retinas. Soma diameters of regenerating ganglion cells ranged from 8 to 55/~m (mean ___ S.D. = 29.0 -+ 6.6/~m, n = 1769) in 3 retinas (cats 6L, 17L, 19L). The range of soma size was slightly larger than in normal retinas, 8-45/~m (ref. 8), but the distribution of soma size of regenerating cells shifted to significantly larger sizes. Enlarged somata have been reported as a characteristic feature of regenerating ganglion cells in rodents 6'13.
332
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Fig. 3. Drawings of regenerating cells revealed with HRP intracellular injection. A, B, and C were in the upper retina, D was in the lower retina. Open arrows, axon. Numbers in parentheses, eccentricity in mm. A, B: ct cells. The axon of cell A had a finer 'collateral' (closed arrow), which branched at the same plane of other dendrites. Cell B had projected to the LGN before transplantation (see text). C: fl cell. Dendritic branches spread densely in a small field at a diameter of 104 am. D: one of non-a non-fl cells. The thin dendrites spread widely and the axon was very fine.
Using a double-labeling method with two fluorescent dyes we then verified that ganglion cells that had projected to the L G N regenerated the axon into the peripheral nerve graft. In two retinas, many of regenerating cells labeled with dextran-fluorescein (Fig. 2A) were also labeled with diI (Fig. 2B) that had been injected into the LGN. In a restricted area of the upper retina of cat 21L, 15 (65%) cells out of 23 regenerating cells were labeled with both diI and dextran-fluorescein. Nineteen cells showed a distinguishable profile from
intracellular injection of rhodamine-HRP. The morphology of 4 representative ganglion cells is illustrated in Fig. 3. Cells A and B have the large soma and thick primary dendrites branching symmetrically, which are characteristic of a-Y cells 2"5. Cell B had originally projected in the L G N since it was double labeled with diI and dextranfluorescein. Cell C is an example of regenerating fl-X cells within the normal range for this cell type 2'5. Eight ct cells and 4 fl cells were identified. One of 7 cells which do not appear a nor fl is shown in Fig. 3D. It shares
333 features of Y cells: the widely spreading (up to 800/~m),
ganglion cells in the cat retina regenerated their axon. It
sparsely branching dendrites and the very fine axon. Six
also remains to be clarified whether these regenerating
other recovered cells also revealed a different morphology from that of a or t , and their c o m m o n features were
axons can re-establish functional synapses in cat visual centers such as the L G N and superior colliculus as proven in rodents 3'13.
fewer dendritic ramifications and the thin dendrites and finer axon. F r o m these results we conclude that ganglion cells of the cat retina can regenerate the axon along the peripheral nerve graft. A n especially important finding was that ganglion cells involved in the geniculocortical pathway 1° are capable of regenerating axons long into the peripheral nerve graft. A t present only a small proportion of
1 Agnayo, A.J., Axonal regeneration from injured neurons in the adult mammalian central nervous system. In C.W. Cotman (Ed.), Synaptic Plasticity, Guilford, New York, 1985, pp. 457484. 2 Boycott, B.B. and W~issle,H., The morphological types of ganglion cells of the domestic cat's retina, J. Physiol., 240 (1974) 397-419. 3 Carter, D.A., Bray, G.M. and Aguayo, A.J., Regenerated retinal ganglion cell axons can form well-differentiated synapses in the superior colliculus of adult hamsters, J. Neurosci., 9 (1989) 4042-4060. 4 Dacey, D.M., Monoamine-accumulating ganglion cell type of the cat's retina, J. Comp. Neurol., 288 (1989) 59-80. 5 Fukuda, Y., Hsiao, C.-F., Watanabe, M. and Ito, H., Morphological correlates of physiologically identified Y-, X- and W-cells in the cat retina, J. Neurophysiol., 52 (1984) 999-1013. 6 Fukuda, Y., Sasaki, H., Adachi, E., Inoue, T. and Morigiwa, K., Optic nerve regeneration by peripheral nerve transplant, Neurosci. Res. (Suppl)., 13 (1990) $24-$30. 7 Keirstead, S.A., Rasminsky, M., Fukuda, Y., Carter, D.A., Aguayo, A.J. and Vidal-Sanz, M., Electrophysiologic responses in hamster superior colliculus evoked by regenerating retinal axons, Science, 246 (1989) 255-257. 8 Hughes, A., Population magnitude and distribution of the major classes of cat retinal ganglion cell as estimated from HRP
We thank Dr. D.M. Dacey for his critical reading of manuscript and valuable comments and Drs. M. Ito and I. Uramoto for their encouragement and support throughout the study. Supported by Collaboration Grant of National Institute for Physiological Sciences, Okazaki, and by Grant-in-Aid for Scientific Research of Priority Area (02220212) from Ministry of Education and Science.
9 10 11 12 13
14
15
filling and a systematic survey of the modal soma diameter spectra for classical neurons, J. Comp. Neurol., 197 (1981) 303-339. Hughes, A. and W~issle, H., The cat optic nerve: fibre total count and diameter spectrum, J. Comp. Neurol., 169 (1976) 171-184. Rodieck, R.W. and Watanabe, M., Morphologic diversity in the ganglion cell projection to different zones within the cat lateral geniculate nucleus, Soc. Neurosci. Abstr., 12 (1986) 1038. So, K.-E and Aguayo, A.J., Lengthy regrowth of cut axons from ganglion cells after peripheral nerve transplantation into the retina of adult rats, Brain Research, 328 (1985) 349-354. Stone, J., The number and division of ganglion cells in the cat's retina, J. Comp. Neurol., 180 (1978) 753-772. Vidal-Sanz, M., Bray, G.M., Villegas-Prrez, M.P., Thanos, S. and Aguayo, A.J., Axonal regeneration and synaptic formation in the superior colliculus by retinal ganglion cells in the adult rat, J. Neurosci., 7 (1987) 2894-2909. Vidal-Sanz, M., Villegas-Prrez, M.P., Bray, G.M. and Aguayo, A.J., Persistent retrograde labeling of adult retinal ganglion cells with carbocyanine dye diI, Exp. Neurol., 102 (1988) 92101. Watanabe, M. and Rodieck, R.W., Parasol and midget ganglion cells of the primate retina, J. Comp. Neurol., 289 (1989) 434454.
Brain Research, 5~) (1991) 330-333 © 1991 Elsevier Science Publishers B.V. All rights reserved. (KX)6-8993/91/$03.50 A DONIS 000689939124855kl
BRES 24855
Axonal regeneration of retinal ganglion cells in the cat geniculocortical pathway Masami Watanabe ~, Hajime Sawai 2 and Yutaka Fukuda z 1Department of Physiology, Institute for Developmental Research, Aichi Prefectural Colony, Kasugai (Japan), and 2Department of Physiology, Osaka University Medical School, Suita, Osaka (Japan) (Accepted 2 July 1991)
Key words: Optic nerve regeneration; Retinal ganglion cell; Geniculocortical system; lntracellular injection; Morphology; Cat
The optic nerve of anesthetized cats was completely cut and the autologous sciatic nerve was transplanted. Sixty days later some populations of retinal ganglion cells were shown to regenerate the axon with retrograde HRP labeling. We verified that ganglion cells that had projected to the lateral geniculate nucleus (LGN) were able to regenerate through the transplant with a double-labeling method: diI was injected into the LGN prior to the transplantation, and dextran-fluorescein was injected into the graft after axonal regeneration. Intracellular injection of HRP into regenerating ganglion cells in an in vitro preparation revealed that the two major cell types projecting to the LGN, a and r, regenerated axons and showed normal dendritic morphology. The transected axons of retinal ganglion cells elongate a long distance along the autografted sciatic nerve in adult rats l ' n and hamsters 6. Regenerating retinal axons make normal synaptic contacts in the superior colliculUS3'13 and the synapses formed with their terminals manifest physiological function 7. Since extensive information is available on the morphology, physiology and central connections of cat retinal ganglion cells, it is worth asking whether the retinal ganglion cells can also regenerate their axons by the autografted peripheral nerve. If they do, the following question can be addressed which type of ganglion cells can regenerate their axon in terms of a, fl and 7 cells2. It would be especially important to clarify whether ganglion cells projecting to the lateral geniculate nucleus (LGN) can regenerate. We performed the present experiments to answer these questions. Surgical procedures for the transplantation of peripheral nerve were essentially the same as those used for rats and hamsters 3'6'n'13. Fourteen adult cats of either sex, weighing 2-3.5 kg, were anesthetized with an intramuscular injection of 57.6 mg ketamine HC1, then with a gas mixture of 1-2% halothane, nitrous oxide (1 liter/ min) and oxygen (1 liter/min). The heart rate and rectal temperature were monitored during anesthesia. The left optic nerve was completely cut at 2 - 6 mm from the eyeball. The anterior branch of the sciatic nerve (30-50 mm) was sutured to the optic stump with microsurgery thread, and the other end of the grafts was bur-
ied into the temporalis muscle. Retrograde labeling o f regenerating ganglion cells'. Fifty-five to 80 days later the cats were anesthetized with the above mentioned drug and gas, and the graft was exposed. A mixture of H R P (10% final) and dextranconjugated tetramethylrhodamine (Molecular Probes, M W = 10,000, 10% final) was injected into the graft at a point of 10 m m or more distal to the original cut. Forty to 72 h later the cats were deeply anesthetized with an overdose of Nembutal, and were perfused transcardially with 0.5% paraformaldehyde/l% glutaraldehyde in 0.1 M phosphate buffer, p H = 7.4. The retinas were dissected, and labeled cells were quickly observed under an epifluorescence microscope. The retinas were then reacted with diaminobenzidine to visualize HRP-labeled cells, and were counter-stained with 0.01% Cresyl violet. In two cats 6/zl of sonicated suspension of a carbocyanine dye, di114 (10 mg/ml), in saline containing 1% Triton-X were stereotaxically injected into the right L G N with a microsyringe 7 days before the transplantation, to prelabel ganglion cells projecting to the L G N . Sixty days after the transplantation 10% dextran-fluorescein (Molecular Probes, M W = 10.000) in water was injected into the graft. Two days later the cats were deeply anesthetized, the retina was dissected from the enucleated eye in the oygenated (95% 02/5% CO2) Ames medium, and double-labeled cells were photographed under an epifluorescence microscope. The retinas were then used for
Correspondence: M. Watanabe, Department of Physiology, Institute for Developmental Research, Aichi Prefectural Colony, Kasugai, Aichi 480-03, Japan.
331
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.--____..~..
N ~--
~'~-~.
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... " % 2". . ; , . • \
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.; :
: .
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5mm
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Fig. 1. Distribution of regenerating retinal ganglion cells retrogradely labeled with HRP in one retina (cat 6L). The area centralis (*) was determined from blood vessel pattern, and it was situated between 3.2 and 4.2 mm away from the optic disk in all 4 retinas. S, superior; I, inferior; N, nasal; T, temporal.
HRP-intracellular injection.
HRP-intracellular injection in in vitro preparation. The method was described in detail elsewhere 4'15. Regenerating ganglion cells were labeled with dextran-fluorescein (10% in water) injected into the graft in 5 cats. Two days later the operated eye was enucleated from the cats anesthetized with an overdose of Nembutal. The retina was dissected in the oxygenated A m e s medium, affixed in a chamber and superfused with the medium. Rhodamine-conjugated H R P (Sigma, 1000 U in 130/~1 of 50 mM M O P S solution, p H = 7.0) was injected into labeled cells ad libitum with glass microelectrodes. Positive currents, 3-10 n A 1 s on, 1 s off, were applied through the tip under an epifluorescence microscope. The retina was fixed with 1% glutaraldehyde and reacted with diaminobenzidine. In 8 cats regeneration of axons of retinal ganglion cell was verified with retrograde labeling with H R P - d y e mixture. Fig. 1 shows the distribution of HRP-labeled ganglion cells in one representative retina (cat 6L) in which 663 cells were labeled. Numbers of HRP-labeled ganglion cells in 3 other retinas were 593 (cat 17L), 513 (cat 19L) and 992 (cat 20L). These were less than 1% of total numbers of ganglion cells, 105,000-140,500 (ref. 12), or of fibers of the cat optic nerve, 193,000 (ref. 9). However, we observed many unlabeled cells which had similar cytological features in Nissl staining compared to
Fig. 2. A: fluorescence photomicrograph under excitation filter, 450--490 nm; barrier filter, 510 nm long pass. Two regenerating cells were retrogradely labeled with dextran-conjugated fluorescein injected into the graft. B: fluorescence photomicrograph of the same field of (A) under excitation filter, 510-560 nm and barrier filter, 590 nm long pass. One cell was labeled with diI which had been injected into the LGN 7 days prior to the transplantation.
those of HRP-labeled cells. The unlabeled cells possibly regenerated their axon which was too short to be labeled retrogradely with tracers. Therefore numbers of actually regenerating cells could be more than those of HRP-labeled ones. It might be claimed that some surviving cells without the regenerated axon took up dye and H R P diffusing from the injection site, and numbers of HRP-labeled cells included these cells. However, this did not appear to occur because the distance between injection sites of H R P - d y e mixture in the graft and the suture point of graft to the sectioned optic nerve was greater than 10 mm in each case. In fact there was no evidence for diffusion of rhodamine or H R P at the optic disk in whole mount retinas. Soma diameters of regenerating ganglion cells ranged from 8 to 55/~m (mean ___ S.D. = 29.0 -+ 6.6/~m, n = 1769) in 3 retinas (cats 6L, 17L, 19L). The range of soma size was slightly larger than in normal retinas, 8-45/~m (ref. 8), but the distribution of soma size of regenerating cells shifted to significantly larger sizes. Enlarged somata have been reported as a characteristic feature of regenerating ganglion cells in rodents 6'13.
332
. ,
, t
--~" ." , .
,
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rs
t' ,f
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~;
/~' V ....
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....
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,;
"
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A (3.2)
Fig. 3. Drawings of regenerating cells revealed with HRP intracellular injection. A, B, and C were in the upper retina, D was in the lower retina. Open arrows, axon. Numbers in parentheses, eccentricity in mm. A, B: ct cells. The axon of cell A had a finer 'collateral' (closed arrow), which branched at the same plane of other dendrites. Cell B had projected to the LGN before transplantation (see text). C: fl cell. Dendritic branches spread densely in a small field at a diameter of 104 am. D: one of non-a non-fl cells. The thin dendrites spread widely and the axon was very fine.
Using a double-labeling method with two fluorescent dyes we then verified that ganglion cells that had projected to the L G N regenerated the axon into the peripheral nerve graft. In two retinas, many of regenerating cells labeled with dextran-fluorescein (Fig. 2A) were also labeled with diI (Fig. 2B) that had been injected into the LGN. In a restricted area of the upper retina of cat 21L, 15 (65%) cells out of 23 regenerating cells were labeled with both diI and dextran-fluorescein. Nineteen cells showed a distinguishable profile from
intracellular injection of rhodamine-HRP. The morphology of 4 representative ganglion cells is illustrated in Fig. 3. Cells A and B have the large soma and thick primary dendrites branching symmetrically, which are characteristic of a-Y cells 2"5. Cell B had originally projected in the L G N since it was double labeled with diI and dextranfluorescein. Cell C is an example of regenerating fl-X cells within the normal range for this cell type 2'5. Eight ct cells and 4 fl cells were identified. One of 7 cells which do not appear a nor fl is shown in Fig. 3D. It shares
333 features of Y cells: the widely spreading (up to 800/~m),
ganglion cells in the cat retina regenerated their axon. It
sparsely branching dendrites and the very fine axon. Six
also remains to be clarified whether these regenerating
other recovered cells also revealed a different morphology from that of a or t , and their c o m m o n features were
axons can re-establish functional synapses in cat visual centers such as the L G N and superior colliculus as proven in rodents 3'13.
fewer dendritic ramifications and the thin dendrites and finer axon. F r o m these results we conclude that ganglion cells of the cat retina can regenerate the axon along the peripheral nerve graft. A n especially important finding was that ganglion cells involved in the geniculocortical pathway 1° are capable of regenerating axons long into the peripheral nerve graft. A t present only a small proportion of
1 Agnayo, A.J., Axonal regeneration from injured neurons in the adult mammalian central nervous system. In C.W. Cotman (Ed.), Synaptic Plasticity, Guilford, New York, 1985, pp. 457484. 2 Boycott, B.B. and W~issle,H., The morphological types of ganglion cells of the domestic cat's retina, J. Physiol., 240 (1974) 397-419. 3 Carter, D.A., Bray, G.M. and Aguayo, A.J., Regenerated retinal ganglion cell axons can form well-differentiated synapses in the superior colliculus of adult hamsters, J. Neurosci., 9 (1989) 4042-4060. 4 Dacey, D.M., Monoamine-accumulating ganglion cell type of the cat's retina, J. Comp. Neurol., 288 (1989) 59-80. 5 Fukuda, Y., Hsiao, C.-F., Watanabe, M. and Ito, H., Morphological correlates of physiologically identified Y-, X- and W-cells in the cat retina, J. Neurophysiol., 52 (1984) 999-1013. 6 Fukuda, Y., Sasaki, H., Adachi, E., Inoue, T. and Morigiwa, K., Optic nerve regeneration by peripheral nerve transplant, Neurosci. Res. (Suppl)., 13 (1990) $24-$30. 7 Keirstead, S.A., Rasminsky, M., Fukuda, Y., Carter, D.A., Aguayo, A.J. and Vidal-Sanz, M., Electrophysiologic responses in hamster superior colliculus evoked by regenerating retinal axons, Science, 246 (1989) 255-257. 8 Hughes, A., Population magnitude and distribution of the major classes of cat retinal ganglion cell as estimated from HRP
We thank Dr. D.M. Dacey for his critical reading of manuscript and valuable comments and Drs. M. Ito and I. Uramoto for their encouragement and support throughout the study. Supported by Collaboration Grant of National Institute for Physiological Sciences, Okazaki, and by Grant-in-Aid for Scientific Research of Priority Area (02220212) from Ministry of Education and Science.
9 10 11 12 13
14
15
filling and a systematic survey of the modal soma diameter spectra for classical neurons, J. Comp. Neurol., 197 (1981) 303-339. Hughes, A. and W~issle, H., The cat optic nerve: fibre total count and diameter spectrum, J. Comp. Neurol., 169 (1976) 171-184. Rodieck, R.W. and Watanabe, M., Morphologic diversity in the ganglion cell projection to different zones within the cat lateral geniculate nucleus, Soc. Neurosci. Abstr., 12 (1986) 1038. So, K.-E and Aguayo, A.J., Lengthy regrowth of cut axons from ganglion cells after peripheral nerve transplantation into the retina of adult rats, Brain Research, 328 (1985) 349-354. Stone, J., The number and division of ganglion cells in the cat's retina, J. Comp. Neurol., 180 (1978) 753-772. Vidal-Sanz, M., Bray, G.M., Villegas-Prrez, M.P., Thanos, S. and Aguayo, A.J., Axonal regeneration and synaptic formation in the superior colliculus by retinal ganglion cells in the adult rat, J. Neurosci., 7 (1987) 2894-2909. Vidal-Sanz, M., Villegas-Prrez, M.P., Bray, G.M. and Aguayo, A.J., Persistent retrograde labeling of adult retinal ganglion cells with carbocyanine dye diI, Exp. Neurol., 102 (1988) 92101. Watanabe, M. and Rodieck, R.W., Parasol and midget ganglion cells of the primate retina, J. Comp. Neurol., 289 (1989) 434454.
