Diencephalic organization of estradiol sensitive sites regulating sociosexual behavior in female golden hamsters: contralateral versus ipsilateral activation

Abstract

Dual ipsilateral, contralateral and bilateral 28-gauge estradiol (E 2) filled cannulae were implanted in the medial preoptic area (MPO) and ventromedial hypothalamus (VMH) of ovariectomized female golden hamsters housed in large arenas with male partners. Twenty-four hours after implantation, vaginal scent-marking patterns were significantly and equally elevated in all groups. Forty-four hours after implantation, progesterone was administered and females were tested for sexual receptivity 4–5 h later. Bilateral E 2 implants in the VMH as well as dual ipsilateral and contralateral MPO-VMH implants were significantly more likely to facilitate sexual responsiveness than bilateral MPO implants. More importantly, ipsilateral MPO-VMH implants produced significantly longer lordosis duration scores than bilateral VMH and contralateral MPO-VMH implants. After mating, females with bilateral MPO implants attacked their mates more frequently than females with bilateral VMH and dual MPO-VMH implants. Taken together, results suggest that: (1) although MPO and VMH regions are equally sensitive to the vaginal marking promoting effects of E 2, these same regions require synergistic ipsilateral activation for the effective priming of sexual responsiveness; (2) the heightened duration of lordosis behavior after ipsilateral MPO-VMH E 2 implantation may reflect an anterior diencephalic estrogenic removal of an inhibitory process occurring primarily in the ipsilateral VMH region; and (3) the difference in postcopulatory attacks may reflect variable actions of progesterone on E 2-induced progestin receptors in the MPO and VMH.