DOPAMINE GLUTAMIC-ACID INTERACTION IN THE ANTERIOR HYPOTHALAMUS - MODULATORY EFFECT OF MELATONIN

THE aim of the present study was to investigate the role of melatonin as neuromodulator. For that, the effects of melatonin on the extracell ular concentrations of excitatory amino acids, glutamic and aspartic a cids, were investigated in the anterior hypothalamus and parieto-tempo ral cortex of the conscious rat using an intracerebral perfusion syste m. Melatonin at doses of 250 nM and 1 mu M produced no effects on extr acellular glutamate and aspartate concentrations in these two areas of the brain. Since amphetamine releases dopamine we perfused melatonin into the anterior hypothalamus and parieto-temporal cortex after a pre vious injection of amphetamine. Interestingly, we found a release of g lutamic acid (p < 0.01) and aspartic acid (p < 0.01) produced by melat onin only when the increase (157%) of the extracellular dopamine conce ntration evoked by amphetamine was inhibited by melatonin in the anter ior hypothalamus. The possibility is discussed of melatonin exerting i ts effects when the dopaminergic system is activated.