GABA_C receptor-mediated inhibition in the retina

Inhibition at bipolar cell axon terminals regulates excitatory signaling to ganglion cells and is mediated, in part, by GABA_C receptors. We investigated GABA_C receptor-mediated inhibition using pharmacological approaches and genetically altered mice that lack GABA_C receptors. Responses to applied GABA showed distinct time courses in various bipolar cell classes, attributable to different proportions of GABA_A and GABA _C receptors. The elimination of GABA_C receptors in GABA_C null mice reduced and shortened GABA-activated currents and light-evoked inhibitory synaptic currents (L-IPSCs) in rod bipolar cells. ERG measurements and recordings from the optic nerve showed that inner retinal function was altered in GABA_C null mice. These data suggest that GABA_C receptors determine the time course and extent of inhibition at bipolar cell terminals that, in turn, modulates the magnitude of excitatory transmission from bipolar cells to ganglion cells.