The Roles of Different Types of Serotonin Receptors in Activation of the Hypophyseal-Testicular Complex Induced in Mice by the Presence of a Female

Abstract

Placing of receptive females in the sector of a cage separated by a partition preventing physical contact but allowing sight and olfaction induced increases in blood testosterone levels in male mice. The selective agonist of 5-HT_1A receptors 8-OH-DPAT (0.1 mg/kg) and the mixed 5-HT_1A/1B receptor agonist eltoprazine (3.0 and 10.0 mg/kg) blocked the activatory effect of presentation of females on the hypothalamo-hypophyseal-testicular complex (HHTC) in males, while the 5-HT_1A receptor antagonist p-MPPI (0.2 mg/kg) prevented the inhibitory effects of 8-OH-DPAT and eltoprazine. The 5-HT_1B receptor agonist CGS-12066A (1.0 and 2.0 mg/kg) had no effect, while the mixed 5-HT_1B/2C agonist TFMPP (5.0 mg/kg) blocked the increase in blood testosterone in males in response to presentation of females. The 5-HT_2A receptor antagonist ketanserin (1.0 and 2.0 mg/kg) prevented the increase in testosterone induced by the presence of females. The 5-HT₃ receptor antagonist ondansetron (0.05 and 0.1 mg/kg) increased the initial plasma testosterone level but blocked activation of the HHTC induced by the presence of receptive females. These results led to the conclusion that 5-HT receptors are involved in controlling the sexual activation of males. Different types and even subtypes of the same type of 5-HT receptor had different effects, both inhibitory and activatory, on activation of the HHTC by receptive females. Blockade of HHTC activation induced by the presence of females appears to involve 5-HT_1A and 5-HT_2C receptors, while activation involves 5-HT_2A and 5-HT₃ receptors.