5‐HT2A and D2 receptor blockade increases cortical DA release via 5‐HT1A receptor activation: a possible mechanism of atypical antipsychotic‐induced cortical dopamine release

Atypical antipsychotic drugs (APDs), all of which are relatively more potent as serotonin (5‐HT) 2A than dopamine D 2 antagonists, may improve negative symptoms and cognitive dysfunction in schizophrenia, in part, via increasing cortical dopamine release. 5‐HT 1A agonism has been also suggested to contribute to the ability to increase cortical dopamine release. The present study tested the hypothesis that clozapine, olanzapine, risperidone, and perhaps other atypical APDs, increase dopamine release in rat medial prefrontal cortex (mPFC) via 5‐HT 1A receptor activation, as a result of the blockade of 5‐HT 2A and D 2 receptors. M100907 (0.1 mg/kg), a 5‐HT 2A antagonist, significantly increased the ability of both S (–)‐sulpiride (10 mg/kg), a D 2 antagonist devoid of 5‐HT 1A affinity, and R (+)‐8‐OH‐DPAT (0.05 mg/kg), a 5‐HT 1A agonist, to increase mPFC dopamine release. These effects of M100907 were abolished by WAY100635 (0.05 mg/kg), a 5‐HT 1A antagonist, which by itself has no effect on mPFC dopamine release. WAY100635 (0.2 mg/kg) also reversed the ability of clozapine (20 mg/kg), olanzapine (1 mg/kg), risperidone (1 mg/kg), and the R (+)‐8‐OH‐DPAT (0.2 mg/kg) to increase mPFC dopamine release. Clozapine is a direct acting 5‐HT 1A partial agonist, whereas olanzapine and risperidone are not. These results suggest that the atypical APDs via 5‐HT 2A and D 2 receptor blockade, regardless of intrinsic 5‐HT 1A affinity, may promote the ability of 5‐HT 1A receptor stimulation to increase mPFC DA release, and provide additional evidence that coadministration of 5‐HT 2A antagonists and typical APDs, which are D 2 antagonists, may facilitate 5‐HT 1A agonist activity.