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 γ₁-melanocyte stimulating hormone (γ₁-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 γ₂-MSH causes the opposite effect. Moreover, γ₂-MSH pre-treatment considerably reduced the γ₁-MSH-induced effects. Our findings suggest an opposing action of two γ-MSH-activated pathways on the mesolimbic dopaminergic system, which could be important in the maintenance of a balanced psychoactivation state.