Evidence for a tonic facilitatory influence of substance P on dopamine release in the nucleus accumbens.

Microinjections of a monoclonal antibody against substance P (SP) into the nucleus accumbens (NAS) increased the concentrations of dopamine (DA) and its metabolite 3,4-dihydroxyphenylacetic acid (DOPAC) in the NAS but not in neuroanatomically adjacent areas. SP immunoneutralization in the NAS also reduced the locomotor response to systemically administered D-amphetamine. Microinjections of control antibody did not significantly alter either DA metabolism or D-amphetamine-induced locomotion. These data are consistent with the hypothesis that endogenous SP modulates the release of DA in the NAS.