Participation of 5-HT1B receptors in the inhibitory actions of serotonin on masculine sexual behaviour of mice: Pharmacological analysis in 5-HT1B receptor knockout mice

Abstract

1. The role of the 5-Hydroxytryptamine1B (5-HT1B) receptor subtype in masculine sexual behaviour in mice was analysed in both 5-HT1B receptor knockout (KO1B) and wild-type (WT) animals. 2. Comparison of male copulatory behaviour of WT and KO1B strains revealed that KO1B mice become interested earlier in sexual behaviour, but require more stimulation to achieve ejaculation than its corresponding WT strain. 3. The pharmacological manipulation of male sexual activity in the WT strain showed that the serotonin precursor 5-Hydroxytryptophan (5-HTP), the 5-HT1B agonist (1-(m-trifluoromethylphenyl) piperazine (TFMPP) and the 5-Hydroxytryptamine1A (5-HT1A) receptor agonist 8-hydroxy-2-di-n-propylamino-tetralin (8-OH-DPAT) all inhibited male copulatory behaviour in mice. 4. In KO1B mice, TFMPP lacked an effect, 5-HTP exerted a mild inhibitory effect while 8-OH-DPAT provoked only a tendency towards a reduction in the percentage of animals that achieved ejaculation. In general, KO1B mice were less sensitive to the inhibitory actions of 5-HTP and 8-OH-DPAT than the WT strain. 5. Based on these results, we can suggest that serotonin plays a general inhibitory role in the sexual behaviour of male mice and that both 5-HT1B and 5-HT1A receptor subtypes participate in the inhibitory actions of this neurotransmitter. 6. The absence of the 5-HT1B receptor subtype affected both components of mouse masculine sexual behaviour, motivation and execution, further confirming the involvement of this receptor subtype in the control of this behaviour. In addition, the diminished sensitivity to serotonergic stimulation exhibited by KO1B mice suggests the occurrence of compensatory changes as a consequence of the absence of the 5-HT1B receptor subtype.