| Abstract: | The sites of stimulatory feedback of ovarian steroids on gonadotropin release were examined. In estrogen-primed ovariectomized rats, estradiol or progesterone was implanted stereotaxically into various hypothalamic and extrahypothalamic areas. Both steroids elevated plasma LH and FSH levels at 6 h when implanted unilaterally into the preoptic-anterior hypothalamic area. Bilateral implants at this site were ineffective; presumably, this was due to the destructive lesion produced by the cannulae since in sham-implanted or anteriorly deafferented rats systemic estrogen was also ineffective. Unilateral estradiol implants in the medial basal hypothalamus elevated LH and FSH at 30 but not at 6 h. Maximum increases of plasma gonadotropins occurred 30 h after implantation of estradiol in the medial amygdaloid nuclei; progesterone implants at this site elevated only FSH at 6 h. Dissociation in the release of LH and FSH was also observed following implantation of estradiol into the hippocampus. Plasma FSH levels were dramatically reduced at 30 h while LH was slightly elevated. Progesterone implants in the hippocampus or medial basal hypothalamus did not alter plasma gonadotropin levels. |
