p-Chlorophenylalanine and Copulatory Behaviour in the Male Rat

Abstract

EVIDENCE has accumulated that copulatory behaviour in the female and male rat is inhibited by increased central nervous serotoninergic tone^1–4. One approach to the study of the specificity of the antagonistic relationship between serotonin and copulatory behaviour has been selectively to increase serotonin by the combination of a monoamine oxidase inhibitor and the serotonin precursor 5-hydroxytryptophane (5-HTP). B. J. M. has shown that this treatment inhibits the copulatory response (lordosis reflex) in the female rat⁴ and we have also shown³ it to decrease the number of male rats mounting oestrous females. Analogous experiments with the catecholamine precursor dihydroxyphenylalanine (DOPA) revealed no inhibitory effect of increased catecholamine concentrations. According to the studies of Shillito^5,6 and Tagliamonte et al.⁷, a selective decrease of serotonin by the serotonin synthesis inhibitor p-chlorophenylalanine⁸ augmented sexual and social interaction between male rats, and in our work this agent also facilitated sexual receptivity in oestrogen-treated ovariectomized females⁹. Increased copulatory behaviour after p-chlorophenylalanine treatment has recently been shown in the male and female cat^10,11, although contradictory results are also available^12–14. The purpose of the experiments described here was to study the effect of p-chlorophenylalanine on heterosexual mounting behaviour in castrated males, which had been given a dose of testosterone adjusted to maintain a submaximal mounting response.