Indeed, castrated male rats preferred to approach the pheromones in soiled estrous bedding only if they had received TP, and TP treatment was required in order for castrated male rats to show a significant increase in neuronal Fos-IR in the VNO-AOB olfactory pathway after exposure to these pheromones. In experiment 3, we found that scent gathering (sniffing) was significantly increased in gonadectomized ferrets exposed to pheromones, regardless of whether they received TP or oil vehicle. In agreement with a previous study using rats, locomotor activity in male ferrets was actually reduced by TP treatment. It seems unlikely that the facili-tatory effect of TP on ferrets’ neuronal Fos-IR responses to pheromones can be explained by a hormone-induced increase in scent-gathering behavior. ampicillin antibiotic
A second alternative is that TP acted directly via ARs to augment pheromone-induced Fos-IR in the ferret’s MOB. Our observation that AR-IR was present in the ferret’s MOB and AOB corroborates a previous study in which AR mRNA was found in the rat’s MOB and AOB. Simerly et al. also found low levels of ER mRNA in the MOB; however, we were unable to detect any ER-IR in either the MOB or AOB of gonadectomized ferrets. Our results suggest that if testosterone acts directly at the level of the MOB, it does so via AR and not after aromatization to estradiol and a subsequent activation of ER. Testosterone may facilitate pheromone-stimulated neuronal Fos-IR in the MOB by acting on a steroid response element in the c-fos gene promoter. Sex steroids have previously been shown to influence c-fos gene transcription (reviewed in ). The c-fos gene contains both estrogen and glucocorticoid response elements on its promoter, and these may also bind androgen and progesterone receptors. While estrogens have been reported to increase c-fos gene expression, androgens have, if anything, been reported to inhibit c-fos gene transcription. Interactions between steroid hormone receptors and their response elements on immediate early genes such as c-fos are sufficiently complex so as not to rule out a direct modulation of c-fos gene transcription by testosterone.