FACTORS CONTROLLING THE DENDRITIC ARBORIZATION OF RETINAL GANGLION-CELLS

The effects of changing retinal ganglion cell (RGC) density and availa bility of presynaptic sites on the development of RGC dendritic arbor in the developing chick retina were contrasted. Visual form deprivatio n was used to induce ocular enlargement and expanded retinal area resu lting in a 20-30% decrease in RGC density. In these retinas, RGC dendr itic arbors increased in a compensatory manner to maintain the inner n uclear layer to RGC convergence ratio in a way that is consistent with simple stretching; RGC dendritic arbors become larger with increased branch lengths, but without change in the total number of branches. In the second manipulation, partial optic nerve section was used to prod uce areas of RGC depletion of approximately 60% in the central retina. This reduction in density is comparable to the density of locations i n the normal peripheral retina. In RGC-depleted retinas, dendritic arb or areas of RGCs in the central retina grow to match the size of norma l peripheral arbors. In contrast to the expanded case, two measures of intrinsic arbor structure are changed in RGC-depleted retinas; the br anch density of RGC dendrites is greater, and the relative areas of th e two arbors of bistratified cells are altered. We discuss the potenti al roles of retinal growth, local RGC density, and availability of pre synaptic terminals in the developmental control of RGC dendritic arbor .