Opposite control of mesocortical and mesoaccumbal dopamine pathways by serotonin receptor blockade: Involvement of medial prefrontal cortex serotonin receptors.

Recent studies have shown that serotonin receptor (5-HTR) antagonists exert opposite facilitatory and inhibitory effects on dopamine (DA) release in the medial prefrontal cortex (mPFC) and the nucleus accumbens (NAc), respectively, thereby leading to the proposal that these compounds could provide an interesting pharmacological tool for treating schizophrenia. Although the mechanisms underlying these effects remain unknown, several data in the literature suggest that 5-HTRs located into the mPFC could participate in this interaction. The present study, using in vivo microdialysis and electrophysiological recordings in rats, assessed this hypothesis by means of two selective 5-HTR (WAY 100635) and 5-HTR (RS 127445) antagonists. WAY 100635, administered either subcutaneously (0.16 mg/kg, s.c) or locally into the mPFC (0.1 μM), blocked the changes of mPFC and NAc DA release induced by the intraperitoneal administration of RS 127445 (0.16 mg/kg, i.p.). The administration of RS 127445 (0.16 mg/kg, i.p.) increased both dorsal raphe nucleus (DRN) 5-HT neuron firing rate and 5-HT outflow in the mPFC. Likewise, mPFC 5-HT outflow was increased following the intra-DRN injection of RS 127445 (0.032 μg/0.2 μl). Finally, intra-DRN injection of RS 127445 increased and decreased DA outflow in the mPFC and the NAc, respectively, these effects being reversed by the intra-mPFC perfusion of WAY 100635. These results demonstrate the existence of a functional interplay between mPFC 5-HTRs and DRN 5-HTRs in the control of the DA mesocorticolimbic system, and highlight the clinical interest of this interaction, as both receptors represent an important pharmacological target for the treatment of schizophrenia.