Dopamine in the rat ventral pallidum/substantia innominata: biochemical and electrophysiological studies

Recent anatomical literature suggests that dopaminergic projections ascending from the midbrain terminate within the ventral pallidum/substantia innominata (VP/SI). The present investigation evaluated this possibility using standard biochemical and electrophysiologic approaches. Biochemical studies revealed that dopamine and its major metabolites are present within the rat VP/SI. Concentrations of these compounds were diminished greatly when dopaminergic neurons of the substantia nigra were destroyed. Electrophysiologic studies demonstrated that VP/SI neurons often respond to local applications of dopamine with a decrease in firing rate. These observations support the contention that dopamine regulates neuronal activity within the VP/SI and that cells of origin for at least a portion of this projection lie within the substantia nigra.