Ovariectomized female hamsters received small unilateral implants of estradiol at a variety of anterior-posterior levels of the medial preoptic area and hypothalamus. The results of an initial experiment using 27-ga. implants showed that females with estradiol implants in the ventromedial hypothalamus (VMN) or nearby anterior hypothalamus consistently showed higher levels of sexual receptivity than did females with implants farther rostral, in the preoptic area, or farther caudal, in the posterior hypothalamus. A second experiment used smaller, 28-ga. implants to compare directly the two areas at which implants were effective in the first experiment. The results confirm the findings of other recent studies of hamsters and rats by identifying the VMN as the most effective hypothalamic site for the estrogen priming of sexual receptivity.

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