| Summary: | Many neurochemical and behavioral functions mediated by dopamine require the dynamic interaction between dopamine receptors. We examined the behavioral effects evoked by microinjections of drugs with relative selectivity for specific dopamine receptors into the nucleus accumbens (Acb). The results showed that, at behaviorally inactive doses, the dopamine D1-class receptor agonist SKF 38393 switched the behavioral profile induced by injections of the dopamine D2-class receptor agonist quinpirole into the Acb, from sedation, yawning, and motor inhibition to hyperactive-like behavior. Further, the effects of injections of the dopamine D2-class receptor agonist (+)-PD 128907 into the shell of Acb, including suppression of rearing, locomotion, and grooming, and induction of oral dyskinesia, yawning, and sedation, could not be distinguished from those elicited by (+)-PD 128907 following infusions into the core of Acb. However, the behavioral effects elicited by coadministration of SKF 38393 and (+)-PD 128907 into the core or the shell of Acb showed a striking anatomical specificity. The infusion of SKF 38393 plus (+)-PD 128907 into the core, but not into the shell, of Acb modified the pattern of responses induced by (+)-PD 128907, inducing behavioral hyperactivity. These results suggest critical differences in the functional interaction between dopamine receptors in the core and the shell of the Acb and reveal a mechanism of behavioral switching in the core of Acb by virtue of which dopamine D1-class receptors regulate the transition from states of behavioral suppression to states of heightened psychomotor arousal.
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