Substance P modulation of the mesolimbic dopamine system.

It has been shown previously that microinjection with substance P into the ventral tegmental area of the rat produces an increase in locomotor activity that is dependent upon an intact mesolimbic dopamine (DA) system. In this study substance P was microinjected into subnuclei of the ventromedial mesencephalon and an increase in motor activity was observed in all nuclei corresponding to the A-10 dopamine region. Following behavioral measurements, rats were given substance P and levels of DA and its metabolites measured in the nucleus accumbens. In contrast with the behavioral response, an increase in DA metabolites was observed only after injection made into the nucleus paranigralis or nucleus parabrachialis pigmentosus. Injections made along the midline (nucleus linearis and nucleus interfascicularis) did not elevate DA metabolites in the nucleus accumbens.