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

Dual ipsilateral, contralateral and bilateral 28-gauge estradiol (E2) 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 E2 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 E2, 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 E2 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 E2-induced progestin receptors in the MPO and VMH.