Dendritic architecture of ON-OFF direction-selective ganglion cells in the rabbit retina.

ON-OFF direction-selective ganglion cells in rabbit retina have bistratified dendritic arbors that are formed by contributions from three or four primary dendrites and their dependent branches (dendritic systems). Most dendritic systems contribute to both branching planes, but some are confined to a single plane. The way in which dendritic systems combine to form the branching planes varies from cell to cell, but the dendritic systems always produce a non-overlapping tiling of the planes having a distinctive mesh-like appearance. This mesh-like pattern appears to be produced primarily by a large number of branches that terminate close to the cell somata. Despite clear differences in the detailed construction of the dendritic arbors, quantitative morphological attributes vary primarily with overall size, and the variation is nearly isometric. We therefore regard these cells as isomorphic, in the sense that they have developed according to the same rather liberal rules for dendritic growth. More importantly, however, we have not found any morphological feature that is correlated with the cells' preferred response directions. We conclude that the distinctive dendritic architecture of these cells is related to general requirements for dense, uniform sampling from specific input arrays, and not direction-selectivity per se. The most important rules governing the branching pattern of the ON-OFF direction-selective cells may be related to territoriality, wherein dendrites, dendritic systems, and cells of the same type establish non-overlapping domains.