Evidence that Neural Aromatization of Androgen Regulates the Expression of Sexual Behaviour in Female Musk Shrews.

Abstract The experiments reported on here were conducted to test the hypothesis that sexual behaviour in the female musk shrew (Suncus murinus) is regulated by the neural aromatization of testosterone to oestradiol. In the first experiment ovariectomized animals received subcutaneous hormone implants containing either an aromatizable androgen (testosterone or androstenedione), a non-aromatizable androgen (dihydrotestosterone or methyltrienolone), or cholesterol. Only females that received an aromatizable androgen exhibited significant amounts of sexual behaviour as compared with controls (cholesterol). To examine the role of the oestrogen receptor, the anti-oestrogen, tamoxifen (200 or 400 mug daily) was given to ovary intact or ovariectomized females treated with testosterone. Tamoxifen treatment had significant negative effects both on female sexual behaviour and on the weights of several peripheral tissues as compared with control treatments. A similar set of experiments was conducted to examine the effect of an anti-androgen on female sexual behaviour. The androgen receptor blocker, flutamide, had no effect on sexual behaviour or weights of peripheral tissues. To determine whether flutamide can act as an anti-androgen in this species two final experiments were conducted in male musk shrews. Flutamide treatment in males did affect several measures of sexual behaviour. In summary, these data demonstrate that the oestrogen receptor is involved in the control of female copulatory behaviour. The androgen receptor plays a role in the expression of male, but not female, sexual behaviour. Female musk shrews display copulatory behaviour in advance of follicular development when oestradiol concentrations in plasma are very low. Thus, they may have evolved a strategy of aromatizing peripherally produced androgens in the brain to concentrate the oestrogen required for the expression of sexual behaviour.