SEXUAL STIMULATION INDUCES FOS IMMUNOREACTIVITY WITH IN GNRH NEURONS OF THE FEMALE RAT PREOPTIC AREA - INTERACTION WITH STEROID-HORMONES

We have shown previously that sexual stimulation (copulation with intr omission or vaginocervical stimulation) induces c-fos mRNA and Fos-lik e immunoreactivity (IR) within estrogen-concentrating and nonconcentra ting regions of the female rat forebrain, including regions that conta in gonadotropin-releasing hormone (GnRH) neurons in septum and anterio r preoptic area. The overall induction of Fos-like IR within these reg ions was specific to afferent sensory stimulation and did not require treatment with estrogen and progesterone. Because vaginocervical stimu lation facilitates lordosis and increases the release of luteinizing h ormone, the present study examined whether hormone treatment that prom otes sexual receptivity, with or without sexual stimulation, increases Fos-like IR specifically within GnRH-containing neurons. Sexually exp erienced ovariectomized rats were administered estradiol benzoate (10 mu g) 48 h and progesterone (500 mu g) 4 h before either Ih of paced c opulation with a sexually vigorous male, 50 vaginocervical stimulation s with a glass rod distributed over 1 h, or no stimulation. Control ra ts received injections of the oil vehicle. Fos-like IR was found withi n a significant number of GnRH-positive neurons in the anterior preopt ic area caudal to the organum vasculosum following copulation with int romission or vaginocervical stimulation as compared with no stimulatio n. Although few GnRH cells coexpressed Fos following hormone treatment alone, this treatment enhanced the number of GnRH neurons that coexpr essed Fos following vaginocervical stimulation as compared with the ef fect of vaginocervical stimulation in oil-treated rats. Together, thes e data indicate that estrogen and progesterone can augment the respons iveness of certain GnRH neurons to vaginocervical stimulation, consist ent with the effects of sexual activity on GnRH release.