Response to male odours in progestin receptor- and oestrogen receptor-containing cells in female rat brain

Sensory cues from male rats, such as odours and vaginal-cervical stimulation (VCS), play a modulatory role in female rat sexual behaviour. For example, exposure to male odours and VCS appears to be at least partially responsible for increases in sexual behaviour following repeated mating of oestradiol-primed female rats. Although there is evidence that VCS influences sexual behaviour via a ligand-independent progestin receptor (PR)-dependent mechanism, the mechanism by which odours influence sexual behaviour is not known. We tested the hypothesis that, similar to VCS, the effects of male odours on sexual behaviour are mediated by progestin receptors. Female rats were injected with the progestin antagonist, RU486, or oil vehicle and were then exposed to male-soiled bedding or clean bedding. Although exposure to male-soiled bedding resulted in higher levels of Fos immunoreactivity in brain areas associated with female sexual behaviour, the progestin antagonist did not reduce this effect. Furthermore, there was minimal coexpression of odour-induced Fos and progestin receptors in brain areas associated with female sexual behaviour. Together, these results suggest that the effects of male odours are not mediated by a PR-dependent mechanism. Therefore, we tested the hypothesis that oestrogen receptor (ER)-containing cells are involved in the effects of olfactory cues. Although there was virtually no coexpression of ERbeta and odour-induced Fos in brain areas associated with female sexual behaviour, exposure to male odours slightly increased the number of cells coexpressing ERalpha and odour-induced Fos in the posterodorsal medial amygdala. Although, these results do not support the hypothesis that the effects of odours are mediated by a PR-dependent mechanism, they suggest that integration of male odours and hormonal cues may occur in ERalpha-containing cells in the posterodorsal medial amygdala.