Inhibitory action of various 5-HT1B receptor agonists on rat masculine sexual behaviour

The systemic administration of the 5-HT1B receptor agonists, RU 24969 (0.25 and 0.5 mg/kg), TFMPP (0.25 and 0.5 mg/kg) and mCPP (0.75 and 1.0 mg/kg) resulted in an inhibition of rat masculine sexual behaviour reflected as a reduction in the proportion of copulating animals. Additionally, the analysis of the sexual behaviour of the animals obtaining ejaculation revealed that RU 24969 and TFMPP administration resulted in an increase in the number of mounts and in a prolongation of the intromission and ejaculation latencies and of the postejaculatory interval. Administration of mCPP increased the number of mounts preceding ejaculation. None of these changes could be attributed to a motor coordination impairment since none of these drugs, at the doses tested, produced changes in a treadmill test. The administration of the 5-HT1A agonist, ipsapirone (2.5, 5 and 10 mg/kg) resulted in a facilitation of the sexual behaviour expressed as a reduction in the number of intromissions preceding ejaculation accompanied by a shortening of the ejaculation latency. Present data show a differential action of 5-HT1A and 5-HT1B receptor subtypes in the control of rat masculine sexual behaviour. The hypothesis that the endogenous serotonin inhibitory action on copulation is mediated via the 5-HT1B receptor subtype is proposed.