THE GANGLION-CELL RESPONSE TO OPTIC-NERVE INJURY IN THE CAT - DIFFERENTIAL RESPONSES REVEALED BY NEUROFIBRILLAR STAINING

The early responses of cat retinal ganglion cells to axotomy have been examined using neurofibrillar and Nissl-stained wholemounts. We were interested to learn whether the enhanced neurofilament expression, see n in a number of neuronal systems, was also present in different neuro nal populations of the cat retina and could be used to study the distr ibution of these cells. We found that beta ganglion cells degenerate v ery rapidly after axotomy with the nuclei becoming pyknotic within a f ew days. Few beta cells showed increased neurofibrillar staining of th e dendrites. The cell body degenerated prior to any visible degenerati ve changes in the axon. A proportion of the alpha and gamma ganglion c ells degenerated in the first two to three weeks after axotomy. The al pha cells underwent markedly enhanced neurofibrillar staining of their dendrites prior to degeneration. The Nissl material of the cell bodie s diminished as the cells degenerated but we have not observed pyknoti c nuclei. The dendritic trees of some axotomised gamma cells were also revealed by the neurofibrillar stain three weeks after axotomy. These results show that retinal ganglion cells do not degenerate by a dying back process. We suggest that the rapid degeneration of the beta gang lion cell population comes about by excitotoxic cell death, a conseque nce of their large glutamatergic input from bipolar cells. The degener ating beta ganglion cells have the morphological appearance of cells u ndergoing apoptosis.