Role of different monoamine receptors controlling MK-801-induced release of serotonin and glutamate in the medial prefrontal cortex: relevance for antipsychotic action.

Several studies have demonstrated that systemically administered N-methyl-d-aspartate (NMDA) receptor antagonists increase serotonin (5-HT) and glutamate release in the medial prefrontal cortex (mPFC). Previously we showed that the perfusion of clozapine in the mPFC prevented the MK-801-induced increase in extracellular glutamate and 5-HT whereas haloperidol blocked only the effect of MK-801 on glutamate. To study the contribution of different monoaminergic receptors (for which clozapine and haloperidol exhibit distinct affinities) to these effects, here we used in-vivo microdialysis to examine the role of local blockade of dopamine D2, 5-HT2A and alpha1-adrenergic receptors as well as agonism at dopamine D1 and 5-HT1A receptors in the mPFC on the increased efflux of glutamate and 5-HT elicited by MK-801. The results show that M100907 (5-HT2A antagonist), BAY x 3702 (5-HT1A agonist) and prazosin (alpha1-adrenergic antagonist) blocked the MK-801-induced increase of 5-HT and glutamate in the mPFC. However, raclopride, eticlopride (dopamine D2 antagonists) and SKF-38393 (dopamine D1 agonist) were able to prevent the increased efflux of glutamate (but not that of 5-HT) elicited by MK-801. We propose that D2 receptor antagonists and D1 agonists would act predominantly on a subpopulation of GABAergic interneurons of the mPFC, thus leading to an enhanced cortical inhibition that would prevent an excessive glutamatergic transmission. On the other hand, atypical antipsychotic drugs might further act upon 5-HT2A, 5-HT1A and alpha1-adrenoceptors present in pyramidal cells (including those projecting to the dorsal raphe nucleus), which would directly inhibit an excessive excitability of these cells.