Regeneration of cat's optic nerve and its functional recovery

The optic nerve of adult mammals can regenerate when a permissive environment is provided with a peripheral nerve (PN) graft. Using this method of PN transplantation, we have studied regeneration of the optic nerve in adult cats. Number of retinal ganglion cells (RGCs) which regenerated their axons through the PN graft corresponds to 3-4% of the total RGC population. The RGCs with regenerated axons distributed widely from central to peripheral retinas. Of the known cell types of cat's RGCs, alpha, beta, gamma and other cells, alpha cells revealed the greatest capacity to regenerate their axons. Dendritic field diameters of most RGCs with regenerated axons were preserved. These regenerated axons were, however, mostly unmyelinated when surveyed by electron microscopy at two months after the transplantation surgery. The regenerated axons revealed normal physiological properties in response to visual stimuli and were classifiable into Y, X or W cells. In accordance with morphological data, Y cells (morphological alpha cells) were more frequently sampled than in normal retinas, whereas the occurrences of X cells (morphological beta cells) and other cells were unchanged or decreased. These results suggest that RGCs retain their physiological function during axonal regeneration, and RGCs with large soma and large dendritic field (Y or alpha cells) have the greatest capacity to regenerate their axons.