'Coronate' amacrine cells in the rabbit retina have the 'starburst' dendritic morphology

Acetylcholine-synthesizing cells in the rabbit retina are symmetrically distributed about the inner plexiform layer: one population of cholinergic amacrines has cell bodies in the inner nuclear layer and an equivalent population of displaced amacrines has cell bodies in the ganglion cell layer. It has been suggested that the morphological correlates of the acetylcholine-synthesizing cells are either coronate amacrine cells or starburst amacrine cells. Coronate cells have a characteristic nuclear morphology and can be selectively labelled by neurofibrillar methods or with the fluorescent dye4',6-diamidino-2-phenyl-indole (DAPI). Starburst cells have a characteristic dendritic morphology but have only been described from Golgi-stained retinae. This paper bridges the gap between the previous studies. DAPI-labelled coronate cells were impaled with a micropipette under microscopic control and filled with Lucifer yellow by iontophoresis. The results show that the coronate amacrines in the ganglion cell layer are type b starburst cells, and that those DAPI-labelled neurones in the inner nuclear layer with a coronate-like nuclear morphology are type a starburst cells. At a given eccentricity the dendritic field diameter of type a starburst cells is about 1.13 times larger than that of type b starburst cells. The dendritic field coverage of coronate (type b starburst) cells increases linearly with decreasing coronate cell density and ranges from 25 on the peak visual streak to 70+ in the superior periphery.