Electrophysiological evidence for a functional interaction between 5‐HT1A and 5‐HT2A receptors in the rat medial prefrontal cortex: An lontophoretic study

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Abstract
In this study, we examined the interaction of 5-HT1A and 5-HT2A receptors in the rat medial prefrontal cortex (mPFc) using the techniques of extracellular single unit recording and microiontophoresis. The iontophoresis of the selective 5-HT1A receptor agonist (±)-8-hydroxy-2-(di-n-propylamino) tetralin (8-OHDPAT) produced a current-dependent suppression (2.5-20 nA) of the basal firing rate of spontaneously active mPFc cells. The iontophoretic (5-10 nA) and systemic administration (0.1-0.5 mg/kg, i.v. ) of the 5-HT2A/5-HT2C receptor antagonist ritanserin and the selective 5 HT2A receptor antagonist MDL 28727 significantly potentiated and prolonged 8-OHDPATs suppressant action. In addition, the systemic administration of another selective 5-HT2A antagonist MDL 100907, but not its less active enantiomer MDL 100009, also potentiated and prolonged 8-OHDPATs action. The potentiating effect of the 5-HT2A receptor antagonists on the action of 8-OHDPAT is specific in that neither the iontophoresis of ritanserin nor MDL 28727 altered the suppressant action produced by the iontophoresis of the 5-HT3 receptor agonist 2-methylserotonin onto mPFc cells. Moreover, the suppressant action of 8-OHDPAT was not altered by the systemic administration of the selective 5-HT3 receptor antagonist granisetron (0.1-0.5 mg/kg, i.v.). On the other hand, the iontophoresis of a low current (0.5 nA) of the 5-HT2A,2C receptor agonist (±)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) potentiated the excitation induced by the iontophoresis of 1-glutamate on quiescent mPFc cells. The iontophoresis of 8-OHD-PAT at a current that had no effect on the firing rate of 1-glutamate activated when administered alone significantly attenuated the excitatory action produced by the iontophoresis of DOI. Overall these results confirm and extend the hypothesis that there is an interaction between 5-HT1A and 5-HT2A receptors in the mPFc at the neuronal level.