The present study was designed to compare the effects of typical and atypical antipsychotic drugs on extracellular dopamine (DA) levels in the medial prefrontal cortex (mPFC) and the nucleus accumbens (NAC), using in vivo microdialysis with dual probe implantation in awake, freely moving rats. Amperozide (2 and 10 mg/kg), clozapine (5 and 20 mg/kg), and olanzapine (10 mg/kg), all of which are atypical antipsychotics, produced greater increases in extracellular DA levels in the mPFC than in the NAG. Olanzapine (1 mg/kg), risperidone (0.1 and 1 mg/kg), also an atypical antipsychotic, and S-(-)-sulpiride (25 mg/kg), a typical antipsychotic, produced comparable increases in extracellular DA levels in the mPFC and the NAG. S-(-)-sulpiride (10 mg/kg) and haloperidol (0.1 and 1 mg/kg), another typical antipsychotic, significantly increased extracellular DA levels in the NAC but not in the mPFC. The effects of the six antipsychotic drugs to increase extracellular DA levels in the mPFC relative to those in the NAC was positively correlated with the difference between their pKi values for serotonin (5-hydroxytryptamine, 5-HT2A) and DA-D-2 receptors and was inversely correlated to their pKi values for D-2 or D-3 receptors, but was not for 5-HT2A receptors alone. These results are consistent with the hypothesis that the ability of antipsychotic drugs to produce a greater increase in prefrontal compared with NAC extracellular DA levels may be related, in part, to weak D-2 and D-3 receptor affinity relative to 5-HT2A receptor antagonism.
