Melatonin enhancement of [3H]-gamma-aminobutyric acid and [3H]muscimol binding in rat brain.

The pineal hormone, melatonin, enhanced the sodium-independent binding of [3H]-gamma-aminobutyric acid ([3H]GABA) and [3H]muscimol in the rat cerebral cortex in vitro. This effect was augmented by preincubation of synaptic membranes with melatonin but was abolished by preincubation with Triton X-100. Saturation binding studies using [3H]GABA (2.5 to 1000 nM) indicated that the melatonin-induced enhancement of binding is due to an increase in low-affinity GABAA binding sites. These findings suggest that the central effects of melatonin involve modulation of GABAergic function.