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 extracellular concentrations of excitatory amino acids, glutamic and aspartic acids, were investigated in the anterior hypothalamus and parieto-temporal cortex of the conscious rat using an intracerebral perfusion system. Melatonin at doses of 250 nM and 1 microM produced no effects on extracellular 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 previous injection of amphetamine. Interestingly, we found a release of glutamic acid (p < 0.01) and aspartic acid (p < 0.01) produced by melatonin only when the increase (157%) of the extracellular dopamine concentration evoked by amphetamine was inhibited by melatonin in the anterior hypothalamus. The possibility is discussed of melatonin exerting its effects when the dopaminergic system is activated.