Parachlorophenylalanine and copulatory behaviour in neonatally castrated male rats

Abstract

Masculine copulatory behaviour was studied in rats which had been castrated as adults or at birth to examine the hypothesis that the behavioural defects shown by neonatally castrated rats result from changes in brain systems involving the neurotransmitter 5-hydroxytryptamine (5-HT). One group of neonatally castrated rats was injected with the non-aromatizable androgen dihydrotestosterone propionate (DHTP) for the first 5 or 15 days after birth; a second group received no androgen at this stage. Animals castrated as adults or castrated at birth and treated with DHTP during infancy showed normal genital development in response to injections of testosterone propionate (TP); genital development was reduced in the neonatally castrated rats which did not receive DHTP. Copulatory behaviour was studied in adulthood in all three groups of rats during treatment with TP with or without injections of the drug parachlorophenylalanine (PCPA), a specific depletor of brain concentrations of 5-HT. PCPA increased the intromission frequency and reduced the ejaculation latency amongst the rats castrated as adults. The drug reduced the numbers of intromissions before the first ejaculation and facilitated ejaculation in most, but not all of the rats castrated at birth and treated with DHTP during infancy. However, the copulatory behaviour of rats castrated at birth and not given DHTP was almost unaffected by PCPA. These results suggest that normal penis development is necessary for PCPA to stimulate masculine copulatory behaviour in rats. Attempts to correlate the different effects of PCPA in the three groups of rats with differences in the concentrations of 5-HT in their brain during adulthood, or with differences in their sensitivities to PCPA were unsuccessful. In all three groups, both the initial concentrations of 5-HT and the specific dose-related reduction in response to PCPA were similar. These results do not support therefore the hypothesis that altered development of systems involving 5-HT is responsible for the behavioural defects of male rats castrated at birth. Part of this study has been published as an abstract [5].