SEXUAL STIMULATION ACTIVATES C-FOS WITHIN ESTROGEN-CONCENTRATING REGIONS OF THE FEMALE RAT FOREBRAIN

Regions of the brain that concentrate estrogen and progesterone are th ought to regulate female sexual behavior by altering gene expression a nd neural sensitivity to afferent stimulation. We used immunocytochemi stry and in situ hybridization to examine c-fos gene expression within estrogen-concentrating regions of the forebrain following various typ es of sexual stimulation with or without hormone treatment. Ovariectom ized rats received injections of estradiol benzoate 48 h and progester one 4 h before testing. Control rats that had been ovariectomized at l east 5 months before testing did not receive hormone treatment. Rats w ere then either placed into bilevel testing chambers with sexually vig orous males, received manual stimulation of the flanks, received vagin ocervical stimulation with a glass rod, or were left in their home cag es. Copulation with intromission and ejaculation in hormone-treated ra ts, or stimulation of the vaginal cervix in both hormone-treated and c ontrol rats, produced a dramatic induction of c-fos mRNA and Fos-like immunoreactivity in estrogen-concentrating regions, such as the latera l septum, medial preoptic area, bed nucleus of the stria terminalis, p araventricular nucleus of the hypothalamus, ventromedial hypothalamus, lateral habenula, and medial amygdala, in addition to regions that do not readily concentrate estrogen, such as the neocortex, thalamus, an d striatum. Mechanical stimulation of the flanks produced a smaller in duction of Fos in these rats, whereas hormone treatment alone had no e ffect. These data demonstrate that afferent sensory stimulation, but n ot estrogen or progesterone, regulates c-fos gene expression within di fferent estrogen-concentrating and non-concentrating regions of the fe male rat forebrain.