Clozapine blocks dopamine, 5-HT2 and 5-HT3 responses in the medial prefrontal cortex:: an in vivo microiontophoretic study

Clozapine is an atypical antipsychotic drug active on both positive and negative symptoms of schizophrenia which has a unique serotonergic and dopaminergic profile. Given the putative role of the medial prefrontal cortex (mPFC) in negative symptoms of schizophrenia, the aim of this study was to assess the effects of clozapine on the dopamine- and serotonin-responsive neurons in that particular brain structure. D-1 and D-2 agonists (SKF 38393 and quinpirole) as well as 5-HT2 and 5-HT3 agonists (1-(2,5-dimethoxy-4iodophenyl)-2-aminopropane, DOI, and phenylbiguanide) were applied by microiontophoresis alone and concurrently with clozapine while recording extracellularly mPFC neurons. Dopamine ejections inhibited firing activity while D-1 and D-2 agonists were ineffective. Clozapine did not change basal firing by itself, but was able to suppress the inhibition produced by dopamine and by the 5-HT2/5-HT3 receptor agonists. It is concluded that clozapine at the mPFC level exerts a complex modulatory activity on dopamine receptors, that is directly at the dopaminergic receptors and through 5-HT receptors on the same neurons. (C) 1999 Elsevier Science B.V. All rights reserved.