Consistency of the tracer coupling pattern of amacrine and ganglion cell types in the rabbit retina

Purpose. To study the consistency of the tracer coupling pattern of amacrine and ganglion cell types in the rabbit retina. Methods. Intracellular recordings were obtained from cells in the superfused, isolated rabbit retina-eyecup. Following physiological measures, cells were injected iontophoretically with Neurobiotin. Results. We studied the tracer coupling pattern of 90 amacrine and ganglion cells. This included 55 amacrine cells with dendritic arbors ranging from about 50-4000 μm across; most of these cells were identifiable as AII, S1, DAPI-3 or starburst amacrine cells. With the exception of starburst cells, all amacrine cells showed tracer coupling to other amacrine cells. Moreover, for amacrine cells within any particular class, the pattern of tracer coupling remained consistent across retinas (under the same light adaptation conditions). We studied 35 ganglion cells with dendritic arbors ranging from about 50-600 μm across. Al ganglion cells with arbors <300 μm showed tracer coupling to other ganglion cells and/or amacrine cells. Again, ganglion cells with similar soma-dendritic morphology showed consistent coupling patterns across retinas. However, larger ganglion cells (arbors >300 μm) showed more varied coupling patterns. Of 22 large-field ganglion cells, 10 showed tracer coupling to amacrine and/or ganglion cells, whereas the remainder showed no tracer coupling. We carried out a morphometric analysis of these large-field cells, quantifying several parameters including: soma size, arbor size, number of dendritic branches, branchpoints and terminal endings, arbor symmetry and level of stratification. We found that large-field ganglion cells with indistinguishable morphology showed different patterns of tracer coupling. Conclusions. The majority of amacrine and ganglion cell types in the rabbit retina show consistent patterns of tracer coupling. An exception is a class of large-field ganglion cells which, though showing similar morphology, displays different tracer coupling patterns. It is presently unclear whether this difference reflects a functional subdivision of large-field ganglion cells within a single morphological class.