MICROGLIAL INVASION AND ACTIVATION IN RESPONSE TO NATURALLY-OCCURRINGNEURONAL DEGENERATION IN THE GANGLION-CELL LAYER OF THE POSTNATAL CATRETINA

Retinae of kittens between postnatal (P) days 2 and 10 were examined f or the presence of degenerating neuronal profiles, normal nucleoli and microglia. Comparison of the numbers of degenerating profiles with nu mbers of axons lost from the optic nerve suggest that the majority of these profiles result from the degeneration of retinal ganglion cells. Analysis of local densities of the different profiles revealed differ ent rates of cell loss, occurring at different times in central and pe ripheral retina. The period of rapid cell loss occurred between P2 and P3 in central retina compared to between P8 and P10 in peripheral ret ina. At both locations, these periods of rapid cell loss were accompan ied by a decrease in the ratio of microglia to dying cells even though the absolute densities of microglia increased. However, calculation o f the clearance times of cellular debris indicate that the speed of re moval of degeneration products is greater during rapid cell loss, whic h suggests that cellular degeneration serves to activate the phagocyti c process.