Electrophysiological and molecular biological studies on axotomized and regenerating cat retinal ganglion cells

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1. Visual functions of regenerated cat optic nerve fibers : A piece of peripheral nerve (PN) was grafted to the sectioned optic nerve of adult cats. 60-90 days later, single unit recordings were made from regenrated RGCs axons in the PN graft and their receptive field properties were examined. Most of these unit recordings could be identified as Y, X or W cells, though Y cells were being most frequently sampled. 2. Morphological identifications of regenerated cat RGCs into ON center or OFF center types : After intracellular HRP injections and vertical sections of regenerated RGCs, we identified them into ON center or OFF center types according to the level of their dendritic extensions within the IPL. Proportions of ON center types were higher than OFF center types among β and γ cells, as expected from physiological samplings. However, in the sample of a cells OFF center cells outnumbered, which was quite unexpected. 3. Effects of environmental light on survival and regeneration of cat … More RGCs : In PN grafted cats, reared in complete darkness, we found that the number of regenerated RGCs were less than those reared in normal light/dark environment and that dying or degenerating RGCs were frequently encountered, indicating that environmental light is essential for the survival and regeneration of cat RGCs. 4. Facilitatory effects of neurotrophins on the survival and axonal regeneration of cat RGCs : After intraocular injections of each of the BDNF, CNTF and GDNF, the survival of cat RGCs, evaluated at 14 days after axotomy, increased as compared with the untreated controls, the effect being most significant among β cells. Addition of forskolin to BDNF and CNTF further facilitated regeneration ratios of axotomized RGCs after PN graft. 5. Cell survival and receptive field properties of axotomized cat RGCs within 2 weeks after optic nerve sections : In morpohological studies with intracellular dye injections we noted that almost 80% of β cells died at 7 days after axotomy, while even 70% of a cells survived at 14 days after axotomy. In physiological recordings from axotomized RGCs at 5 days survival, we recorded X cells as well as Y cells though some of them having smaller receptive fields than normal, at 14 days survival, on the other hand, almost exclusively Y cells were sampled, indicating again that Y cells are more resistant to axotomy than X cells in the cat retina. Less