Bistratified ganglion cells of rabbit retina: Neural architecture for contrast-independent visual responses

Bistratified (BS) ganglion cells have long been recognized in vertebrate retina. Thirty years ago, it became clear that bistratification allows the integration of ON and OFF retinal pathways to produce contrast-independent responses in ganglion cells. Best studied is the type 1 bistratified (BS1) ganglion cell of rabbit retina, the physiologically well-characterized ON-OFF directionally selective (DS) ganglion cell, which is co-stratified with the two types of starburst amacrine (SA) cells in sublaminae a and b of the inner plexiform layer (IPL). DS responses have recently been documented in the latter. In this report, BS1 cells are further studied and are used as ʹʹfiducialsʹʹ to characterize a second type of BS ganglion cell. An example of a possible third type is shown to be distinct from examples of BS1 and BS2 cells. All three have two distinct, narrowly stratified arborizations, one in sublamina a and one in sublamina b. All have similar dimensions, except for their dendritic trees, differing also in branching pattern. BS1 cells have compact, regular, highly branched trees; BS2 cells have significantly larger, more sparsely branched, irregular, radiate trees; the proposed BS3 type is intermediate in field size, and its branching pattern is different from the first two. BS2 and BS3 cells are co-stratified, branching nearer to the margins of the IPL, out of range of SA cells. In a previous report by others, illustrating the morphology of intracellularly stained ganglion cells, one example each of both ʹʹorientation-selectiveʹʹ ganglion cells and ʹʹuniformity detectorsʹʹ resembles the BS2 cell. A rationale is presented for correlating BS2 cells with uniformity detectors.