DENDRITIC ARCHITECTURE OF ON OFF DIRECTION-SELECTIVE GANGLION-CELLS IN THE RABBIT RETINA

ON-OFF direction-selective ganglion cells in rabbit retina have bistra tified dendritic arbors that are formed by contributions from three or four primary dendrites and their dependent branches (dendritic system s). Most dendritic systems contribute to both branching planes, but so me 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 plan es having a distinctive mesh-like appearance. This mesh-like pattern a ppears to be produced primarily by a large number of branches that ter minate close to the cell somata. Despite clear differences in the deta iled construction of the dendritic arbors, quantitative morphological attributes vary primarily with overall size, and the variation is near ly isometric. We therefore regard these cells as isomorphic, in the se nse that they have developed according to the same rather liberal rule s for dendritic growth. More importantly, however, we have not found a ny morphological feature that is correlated with the cells' preferred response directions. We conclude that the distinctive dendritic archit ecture of these cells is related to general requirements for dense, un iform sampling from specific input arrays, and not direction-selectivi ty 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 est ablish non-overlapping domains.