Opposite effects of γ1- and γ2-melanocyte stimulating hormone on regulation of the dopaminergic mesolimbic system in rats

By use of the brain microdialysis technique we show that administration of gamma(1)-melanocyte stimulating hormone (gamma(1)-MSH) into the ventral tegmental area of anaesthetized rats causes an increase in the release of extracellular dopamine and its metabolite 3,4-dihydroxyphenylacetic acid in the nucleus accumbens, while gamma(2)-MSH causes the opposite effect. Moreover, gamma(2)-MSH pre-treatment considerably reduced the gamma(1)-MSH-induced effects. Our findings suggest an opposing action of two gamma-MSH-activated pathways on the mesolimbic dopaminergic system, which could be important in the maintenance of a balanced psychoactivation state.