Reproductively-relevant stimuli induce Fos-immunoreactivity within progestin receptor-containing neurons in localized regions of female rat forebrain.

An experiment was conducted to determine if neurons that respond to stimuli associated with mating in female brain also contain progestin receptors. We found that a portion of the neurons that respond to stimuli associated with mating also contains progestin receptors. While the appropriate hormonal conditions are important for sexual receptivity, somatosensory information provided by the male also influences sexual behavior. One important stimulus provided by the male during copulation is vaginal-cervical stimulation (VCS). VCS has been shown to elicit many different behavioral and endocrine changes in female rats, such as increases in lordosis, pseudopregnancy, and termination of sexual receptivity. VCS also increases the expression of the immediate early gene product, Fos, in areas associated with reproduction. A portion of the neurons responding to VCS with increased Fos-immunoreactivity (Fos-IR) in female rat forebrain also contains estrogen receptors, illustrating that hormonal and mating-stimuli converge in a population of cells. As progesterone also plays an important role in female sex behavior, it is important to determine if some of the neurons also integrate information concerning serum progesterone levels and social interactions. Thus, we used a dual immunofluorescent technique to label both Fos-IR and progestin receptor-immunoreactivity (PR-IR) in the brains of estradiol-primed, ovariectomized female rats following VCS manually applied by the experimenter. Many of the neurons that respond to VCS with increased Fos-IR within the medial preoptic area, the arcuate nucleus, and the progestin receptor-rich areas of the rostral and caudal ventromedial nucleus of the hypothalamus also contain PR-IR.