gamma-Aminobutyric acid-mediated inhibition at cholinergic synapses formed by cultured retinal neurons

The purpose of this study was to investigate the effect of gamma-aminobutyric acid (GABA) on the function of synapses formed by cholinergic neurons derived from the chick retina. We used an experimental culture system in which striated muscle cells served as postsynaptic targets for cholinergic neurons of the retina. This cell culture system permitted the physiological monitoring of acetylcholine release at synapses formed by retinal neurons. By plating a low density of dissociated retinal cells with myotubes, it was possible to study relatively isolated, presynaptic cholinergic neurons. We found that GABA and its agonists, muscimol and isoguvacine, inhibited spontaneous transmission at retina-muscle synapses. These inhibitory effects were reversibly blocked by bicuculline, a GABA receptor antagonist. The benzodiazepine, flurazepam, potentiated GABA-mediated inhibition. Overall, our findings suggest a direct inhibitory action of GABA on the cholinergic retinal neurons studied in our cell culture system.