Effect of 5-HT 1C and 5-HT 2 receptor stimulation on excessive grooming, penile erection and plasma oxytocin concentrations

Abstract

Serotonin (5-HT) receptor agonist-induced excessive grooming, penile erection and oxytocin secretion were studied in chronically cannulated freely moving rats. The 5-HT 1C receptor agonists, m-chlorophenylpiperazine (m-CPP), which also binds to other 5-HT receptors, produced dose-dependent excessive grooming, penile erection and increases in circulating oxytocin concentrations. Maximal responses for excessive grooming and penile erection occured at 0.3–0.6 mg/kg i.v. m-CPP. Higher doses (0.9–2.5 mg/kg i.v.) caused further increases in oxytocin concentrations, but attenuated both behavioral responses. All three responses to m-CPP (0.6 mg/kg) were attenuated by antagonist with high affinity for the 5-HT 1C receptor site (mianserin, LY-53857 and metergoline), but not by the 5-HT 2 receptor antagonist ketanserin. The 5-HT 2/5-HT 1C agonist, 1-(2,5-dimenthoxy-4-iodophenyl)-2-aminopropane (DOI), increased plasma oxytocin concentrations only. After katanserin pretreatment, DOI caused penile erection and diminished the oxytocin response. All responses to DOI were blocked completely by pretreatment with LY-53857 plus ketanserin. Excessive grooming and penile erection showed significant bimodal correlations with the oxytocin response. These data suggest that stimulation of 5-HT 1C receptors induces excessive grooming, penile erection and increased oxytocin secretion. Stimulation of 5-HT 2 receptors causes a further increase in plasma oxytocin concentration, but inhibits both behavioral responses.