Diencephalic Sites of Progesterone Action for Inhibiting Aggression and Facilitating Sexual Receptivity in Estrogen-Primed Golden Hamsters*

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Abstract
Diencephalic sites of action of progesterone (P) responsible for inhibiting aggression and facilitating sexual receptivity were examined in ovariectomized golden hamsters primed with Silastic capsules of estradiol. P was applied centrally by inserting a hormone-filled, 27-gauge cannula into a 22-gauge guide cannula that was implanted unilaterally in the medial preoptic area (MPO), the anterior hypothalamus (AH) or the ventromedial hypothalamus (VMH). Control implants consisted of cholesterol-filled cannulae placed within the same regions of the brain. Tests for sexual and aggressive behavior occurred 1, 2, 4 and 6 h after hormone implantation by introducing a sexually experienced male into the home cage of the female. Nine of 20 females with P in the VMH exhibited lordosis, in comparison to 1 of 12 females in the MPO group and 5 of 16 animals in the AH group. The induction of sexual responsiveness after P implantation in the VMH was further demonstrated in 6 of 11 ovariectomized-adrenalectomized females, indicating that the observed receptivity was not contingent upon activation of the hypothalamic-pituitary-adrenal axis. In addition to the receptive promoting action of P in the VMH, P implantation in the MPO and VMH but not in AH regions, was highly effective in inhibiting female biting attacks upon males. Apparently, P can both facilitate sexual receptivity and inhibit aggressive behavior, and P induces these changes in behavior at different locations in the diencephalon.