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Reproductive behaviour in the male rat: importance of 5-HT2 receptor activity and relation to 5-HT2-dependent serotonergic stereotypy Watson, Neil Verne


It is well established that the neurotransmitter serotonin participates in the control of sexual behaviour in the male rat. Recently, it has been found that serotonergic activity may either inhibit or facilitate sexual behaviour, depending on the subtypes of serotonin receptors involved. However, the participation of 5-HT2 receptors in the control of male rat copulation has received little experimental attention, and the published data are equivocal. In Experiments 1-4, it was established that the 5- HT2/1C agonist DCI inhibits sexual behaviour in male rats; this inhibition is effectively reversed by the antagonists ritanserin, pirenperone, and ketanserin. Comparison of these effects , with reference to the binding profiles of each drug, provided strong evidence that 5-HT2/1C receptors mediate an inhibitory influence on sexual behaviour in male rats. In addition, a tentative claim may be made that the effects of these drugs may be more attributable to 5-HT2 activity than 5-UT1C activity. ‘Wet dog shake’ behaviour in rats is known to be 5-HT2- dependent. Experiments 5—7 evaluated the novel proposition that the incidence of spontaneous wet dog shaking (WDS) by male rats in mating tests may provide a behavioural assay of concurrent 5—HT2 activity. WDS was found to be associated with copulatory inhibition in noncopulating males, compared to normal copulators, and this relationship was specific to mating situations. Activating 5-HT2/1C receptors with DOl simultaneously induced WDS and inhibited copulation. Thus, the incidence of spontaneous WDS in untreated males may reflect the function of a 5—HT2—mediated neural mechanism that tonically inhibits copulation in male rats. In Experiment 8, DOl microinjection in the nucleus raphe obscurus/inferior olivary complex also induced WDS and inhibited copulation. This suggests that the hypothesized 5- flT2-dependent inhibitory mechanism is vested in the ventromedial brainstem. Recent anatomical findings support this suggestion: cells in this region have bifurcating axons, projecting collaterally to both the medial preoptic area (implicated in sexual behaviour) and to the ventral cervical spinal cord (implicated in WDS). Overall, the results of the eight experiments provide strong evidence that 5-HT2 receptors mediate some of the inhibitory effects of serotonin on male rat sexual behaviour.

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