Abstract
In this study, we examined the interaction of 5‐HT~1A~ and 5‐HT~2A~ receptors in the rat medial prefrontal cortex (mPFc) using the techniques of extracellular single unit recording and microiontophoresis. The iontophoresis of the selective 5‐HT~1A~ 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‐HT~2A~/5‐HT~2C~ receptor antagonist ritanserin and the selective 5 HT~2A~ receptor antagonist MDL 28727 significantly potentiated and prolonged 8‐OHDPATs suppressant action. In addition, the systemic administration of another selective 5‐HT~2A~ antagonist MDL 100907, but not its less active enantiomer MDL 100009, also potentiated and prolonged 8‐OHDPATs action. The potentiating effect of the 5‐HT~2A~ 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‐HT~3~ 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‐HT~3~ 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‐HT~2A,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‐HT~1A~ and 5‐HT~2A~ receptors in the mPFc at the neuronal level. © 1994 Wiley‐Liss, Inc.