Melatonin modulates glycine currents of retinal ganglion cells in rat.

Melatonin is a hormone participating in the modulation of various physiological functions via binding to specific melatonin receptors. In the retina, melatonin is synthesized and released by photoreceptors and may play a neuromodulatory role. By using patch clamp techniques, we demonstrate for the first time that glycine-induced currents from a population of isolated ganglion cells in the rat retina are potentiated by melatonin of nanomolar concentrations by increasing the efficacy and the channel conductance of the strychnine-sensitive glycine receptor. The melatonin effect is blocked by 4-P-PDOT, indicating the mediation of the MT2 receptor. These results suggest that melatonin, along with the MT2 receptor, may be involved in retinal information processing by modulating glycine receptor-mediated inhibition.