DIFFERENTIAL-EFFECTS OF DOPAMINE ANTAGONISTS ON EVOKED DOPAMINE RELEASE FROM SLICES OF STRIATUM AND NUCLEUS-ACCUMBENS IN RATS

The effects of dopamine-receptor antagonists on electrically-evoked do pamine release were compared in the nucleus accumbens and striatal sli ces of rats. (-)-Sulpiride induced a concentration-dependent increase in the evoked dopamine release from both regions, the increase in the nucleus accumbens being significantly greater than that in the striatu m. Clozapine also increased evoked dopamine release from the nucleus a ccumbens, but not from the striatum. The haloperidol-induced increase in evoked dopamine release from the nucleus accumbens was less than th at from the striatum. These findings indicate that, in terms of dopami ne transmission, (-)-sulpiride and clozapine, but not haloperidol, pre dominantly affect the nucleus accumbens rather than the striatum. We h ave previously reported that the contribution of D-3 receptors to the regulation of dopamine release from dopamine nerve terminals is much g reater in the nucleus accumbens than that in the striatum. (-)-Sulpiri de and clozapine have relatively higher affinity for D-3 receptors tha n does haloperidol. The regional differences in responsiveness of dopa mine release to dopamine antagonists could be due to the different aff inities to D-2 or D-3 receptors of the dopamine antagonists.