Term: retinal ganglion cell A1

Definition: Subgroup RGA1 cells (Figs. 2A, 3-5, Table 1) have a morphology similar to that of the giant cells of Bunt (1976). They have large somata, often polygonal in shape, from which a medium- to large-gauge axon emerges (Figs. 2A, 3). In one instance, a bifucarting axon was seen to exit the soma (see Fig. 3A). The large dendritic fields of RGA1 cells consist of three to seven stout dendrites that emerge radially from a centrally placed soma. The dendrites are smooth and overlap infrequently (Figs. 2, 3). RGA1 cells are found across the retina (Figs. 5, 6)and, on average, have the largest dendritic fields of all the RGCs labelled. RGA1 cells exhibited tracer coupling...they were strongly coupled to at least ten neurons (large-bodied gnalgion cells and some presumed amacrine cells-the latter gad very small somata and were found both the GCL and the INL; Fig.5). We classified cells with a large soma and a large dendritic field as RGA, cells with a small- to medium-sized soma and a small- to medium-sized dendritic field as RGB, and cells with a small- to medium-sized soma but a medium-to-large dendritic field RGC. Seventy five RGA cells were identified. RGA cells had an average soma diameter of 23.4 micrometers, an average dendritic-field diameter of 300.0 micrometers, and a radial pattern of branching. They are similar to Perry type I cells (Perry, 1979).