Regulation of sexual behaviour in male macaques by sex steroid modulation of the serotonergic system.

The view that androgen action is the primary impetus underlying male-typical behaviour has been irrevocably altered by the profound perturbations in social and sexual behaviour observed in recent models of oestrogen insufficiency in male mice. Evidence is also accumulating for an involvement of oestrogens in the modulation of neural systems that are thought to play important roles in male reproductive functioning. Specifically, the serotonergic system is implicated in diverse autonomic functions, most or all of which are sensitive to oestradiol as well. Although their interaction domains have yet to be examined in male primates, roles have been established for both oestrogen and serotonin in the regulation of male sexual behaviour. We used a blinded, sham-treated and self-controlled, randomized, multitreatment cross-over design to test the hypothesis that male sexual behaviour is regulated by oestrogen modulation of the serotonergic system in intact male Japanese macaques. Regression analysis revealed that oestradiol and whole blood tryptophan, but not testosterone or 5alpha-dihydrotestosterone, had additive, independent effects on male potentia over a range of hormone concentrations, whereas androgens were confirmed to be the primary determinants of sexual motivation. We suggest that modulation of the serotonergic system by 'female hormones' may be fundamental to the regulation of male mating success in higher primates. This might also explain, at least in part, why significant correlations between steroid hormones and male copulatory behaviour have traditionally proven so elusive in this order, thereby warranting a re-evaluation of the current notion that male sexual behaviour has been emancipated from activational hormonal control in higher primates.

Transcriptional repression mechanisms of nucleolus organizer regions (NORs) in humans and chimpanzees.

Polymorphisms related to transcriptional inactivation of nucleolus organizer regions (NORs) have long been described in many animals, particularly humans. However, the precise aetiology of such variations is not always clear. We conducted analyses to investigate the repression mechanisms in humans and chimpanzees using FISH (fluorescence in situ hybridisation) with 18S rDNA, Ag-NOR (silver nitrate) staining, C-banding, and the in situ nick translation technique with the HpaII restriction enzyme. Examination of 48 humans and 46 chimpanzees suggested that there are at least three different mechanisms that produce inactivation of NORs. These include: (1) elimination of rDNA; (2) DNA methylation: (3) gene silencing due to position effects induced by heterochromatin (C-bands) and/or telomeres.