Abstract
This study investigated the interaction of the undecapeptide, substance P (SP), on basal and potassium-stimulated release of endogenous dopamine (DA) from rat striatal slices in vitro. Addition of substance P (0.5–50 μM) to the incubation medium produced a dose-dependent increase in basal or spontaneous DA release and inhibited potassium-stimulated dopamine release. These effects of SP could be antagonized with 20 μM naloxone. The selective delta opiate receptor antagonist, ICI 174864 (10μM) antagonized the SP-induced changes in basal dopamine release, but did not alter the SP-induced reduction of stimulated DA release. Naloxone and ICI 174864 alone did not change either basal or potassium-stimulated dopamine release. The data is consistent with SP modulation of spontaneous and stimulated dopamine release from rat striatum through an interaction with endogenous opiate peptides. Further, the SP-induced change in basal dopamine release may involve, in part, an endogenous delta-opiate receptor ligand; while the SP-induced reduction of potassium-stimulated dopamine release may involve mu-type opiate ligand.
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