Changes in visual response properties of cat retinal ganglion cells within two weeks after axotomy

Abstract

After optic nerve transection beta cells of cat retinal ganglion cells (RGCs) suffer from rapid cell death from 3 to 7 days, whereas alpha cells gradual cell death until 14 days. Here we report electrophysiological properties of Y- (morphological alpha) and X- (morphological beta) cells at 5 and 14 days after axotomy in comparison with those of intact Y- and X-cells. Most of the axotomized RGCs revealed characteristic visual response properties that enable us to classify them into Y- or X-cells. Physiological sampling ratio of X-cells sharply decreased from day 5 to 14 after axotomy, corresponding to the previous morphological results. As compared with intact RGCs, axotomized RGCs of both Y- and X-type revealed the following abnormalities: smaller receptive field centers, weaker visual responses and lower spontaneous activities. Intracellular injections of Lucifer yellow into axotomized and intact RGCs at eccentricities 0-6 mm from the area centralis revealed no sign of shrinkage in dendritic field size of either alpha or beta cells on day 5 and day 14 after axotomy, revealing that observed smaller receptive field centers of axotomized RGCs on day 5 were not due to the change of dendritic field sizes. These results suggest that the major events occurring shortly after axotomy are significant loss of synaptic inputs from afferent neurons in the retina and/or changes of membrane properties of axotomized RGCs. These events can also explain lower spontaneous activities and weaker visual responses of axotomized RGCs.