Differential induction of Fos in the female rat brain following different amounts of vaginocervical stimulation: modulation by steroid hormones.

Vaginocervical stimulation (VCS), produced either by copulation with intromission or by manual stimulation of vagina and cervix with a glass rod, induces neuroendocrine and behavioral responses that are critical for female reproduction in many species. We and others have shown that Fos mRNA and protein are induced within different estrogen-concentrating and -non-concentrating regions of the female rat brain following copulation with intromission and manual VCS. In the present study, we investigated the amount of distributed VCS required to induce Fos immunoreactivity within estrogen-concentrating regions of the medial preoptic area, lateral septum, bed nucleus of the stria terminalis, ventromedial hypothalamus, medial amygdala, and mesencephalic central gray, and whether estrogen and progesterone could alter the threshold or pattern of induction. Ovariectomized rats were administered estradiol benzoate (10 micrograms) 48 h and progesterone (500 micrograms) 4 h before receiving either 0, 1, 5, 10, 20, 30, 40, or 50 manual VCSs with a lubricated glass rod. Ovariectomized hormone control rats received injections of the sesame oil vehicle 48 and 4 h before VCS. All rats were sacrificed 75 min after the first VCS. Fos immunoreactivity was induced differentially by VCS within the different regions, and the hormones either augmented, inhibited, or had no effect on the induction. These data demonstrate that cells within different estrogen-concentrating regions of the female rat brain are differentially sensitive to VCS, and that steroid hormones can either increase or decrease the amount of Fos induced by different amounts of VCS. Different brain regions may participate in gating the sensory information of VCS into different behavioral and neuroendocrine events.