EXTRAHYPOTHALAMIC EFFECTS OF MELATONIN ADMINISTRATION ON SEROTONIN AND NOREPINEPHRINE SYNTHESIS IN FEMALE SYRIAN-HAMSTERS

The effects of daily late afternoon injections of melatonin for 10 wee ks on the metabolism of serotonin (5-HT) and norepinephrine (NE) were examined in regional brain extracts of intact and ovariectomized (GX) Syrian hamsters. Accumulation of 5-HT and NE after administration of t he monoamine oxidase inhibitor pargyline was used as a measure of the rate of neurotransmitter synthesis - with concentrations determined by HPLC with electrochemical detection. Daytime 5-HT synthesis was signi ficantly decreased in the amygdala of melatonin-treated hamsters that had been GX (to 50% of GX controls). No significant effect on 5-HT syn thesis could be detected in the mediobasal hypothalamus (MBH), however , a significant increase was demonstrated in the pontine brain stem of both intact and GX hamsters treated with melatonin Daytime NE synthes is was decreased to levels not significantly different from zero in th e amygdala of GX hamsters treated with melatonin, while in the brain s tem, melatonin reduced NE synthesis in both intact and GX animals. The present data demonstrate that these melatonin effects on 5-HT and NE metabolism are not limited to the MBH and are not secondary to melaton in-induced changes in circulating levels of the ovarian steroids.