The cholinergic amacrine cells of rabbit retina receive on and off input: An analysis of [H]-ACh release using 2-amino-4-phosphonobutyric acid (APB) and chloride free medium

Using thein vitro rabbit eye-cup we have examined the light-evoked release of ACh from cholinergic amacrine cells under conditions known to eliminate On responses in the retina. APB (100 μM), which blocks the photoreceptor/depolarizing bipolar cell synapse, reduced the light-evoked release of ACh by 80% but a small light-evoked response remained, which was potentiated by bicuculline. Depolarizing bipolar cells are also Cl⁻ dependent. Cl⁻ free medium caused a tenfold Ca²⁺-dependent increase in the release of ACh but some small light evoked release remained. These results indicate that the cholinergic amacrine cells receive On and Off input. Our findings are consistent with anatomical and electrophysiological evidence which suggests that the displaced cholinergic amacrine cells are On cells and the conventionally placed cholinergic amacrine cells are Off cells.