Melatonin increases in vivo GABA accumulation in rat hypothalamus, cerebellum, cerebral cortex and pineal gland.

The effect of melatonin on in vivo gamma-aminobutyric acid (GABA) accumulation in several brain regions was determined by measuring the increase of GABA levels following inhibition of GABA transaminase. A single melatonin injection (25-300 micrograms/kg) augmented significantly, by 17-20%, GABA accumulation in the hypothalamus and caused a dose-dependent increase of this parameter in the pineal gland. Significant rises of GABA accumulation were found in the cerebellum and cerebral cortex after administering 100-300 and 300 micrograms/kg of melatonin, respectively.