SYNAPTOLOGY OF PHYSIOLOGICALLY IDENTIFIED GANGLION-CELLS IN THE CAT RETINA - A COMPARISON OF RETINAL X-CELLS AND Y-CELLS

It has long been known that a number of functionally different types o f ganglion cells exist in the cat retina, and that each responds diffe rently to visual stimulation. To determine whether the characteristic response properties of different retinal ganglion cell types might ref lect differences in the number and distribution of their bipolar and a macrine cell inputs, we compared the percentages and distributions of the synaptic inputs from bipolar and amacrine cells to the entire dend ritic arbors of physiologically characterized retinal X- and Y-cells. Sixty-two percent of the synaptic input to the Y-cell was from amacrin e cell terminals, while the X-cells received approximately equal amoun ts of input from amacrine and bipolar cells. We found no significant d ifference in the distributions of bipolar or amacrine cell inputs to X - and Y-cells, or ON-center and OFF-center cells, either as a function of dendritic branch order or distance from the origin of the dendriti c arbor. While, on the basis of these data, we cannot exclude the poss ibility that the difference in the proportion of bipolar and amacrine cell input contributes to the functional differences between X- and Y- cells, the magnitude of this difference, and the similarity in the dis tributions of the input from the two afferent cell types, suggest that mechanisms other than a simple predominance of input from amacrine or bipolar cells underlie the differences in their response properties. More likely, perhaps, is that the specific response features of X- and Y-cells originate in differences in the visual responses of the bipol ar and amacrine cells that provide their input, or in the complex syna ptic arrangements found among amacrine and bipolar cell terminals and the dendrites of specific types of retinal ganglion cells. (C) 1994 Wi ley-Liss, Inc.