Oxytocin-induced facilitation of lordosis behaviour in rats is progesterone-dependent.

Oxytocin was administered intracerebroventricularly to ovariectomized female rats and its effect on lordosis was examined. In Experiment 1a, oxytocin (0.17 mU in 4 microliters saline) failed to facilitate lordosis behaviour in animals primed acutely with 10 micrograms estradiol benzoate (EB) and 300 micrograms progesterone (P). In Experiment 1b, however, oxytocin significantly facilitated lordosis in animals primed acutely with 10 micrograms EB and 250 or 200 micrograms P. In Experiments 2a and 2b, oxytocin failed to facilitate lordosis in animals treated acutely with 10 micrograms EB, or chronically with 0.8 micrograms EB daily for eight days prior to testing. These results support the hypothesis that the facilitation of lordosis in ovariectomized rats by centrally-administered oxytocin is progesterone-dependent.

beta-endorphin inhibits and facilitates lordosis behaviour in rats depending on ventricular site of administration.

beta-endorphin was administered intracerebroventricularly into the lateral and third ventricles of ovariectomized, oestrogen- and progesterone-primed rats, and its effect on lordosis and ear-wiggling was assessed. A dose of 2 micrograms beta-endorphin facilitated lordosis when infused into the lateral ventricle, but inhibited lordosis when infused into the third ventricle. The effects were the same whether measured at 30, 60 or 90 min following infusion. beta-endorphin had no significant effect on ear-wiggling frequency when administered in either ventricle. The differential effects of beta-endorphin depending on site of administration may reflect the activation of distinct opioid receptor subtypes within the brain.

Effect of novel and familiar mating partners on the duration of sexual receptivity in the female hamster.

The lordosis duration of the female golden hamster (Mesocricetus auratus) in response to novel and familiar mating partners was examined. In Experiment 1, females mated to the point of sexual satiation with one male hamster, and following its removal, showed renewed receptivity in response to the introduction of a second male. Upon sexual satiation with the second male, females either received a novel third male or were reexposed to the original male. Total lordosis duration in the third bout in the group receiving a novel male was significantly greater than in the group reexposed to the original male. In Experiment 2, the insertion of a 1-h delay between the second and the third mating partner had no effect on the female's responsiveness, regardless of whether the third male was the original male or a novel male. In Experiment 3, removal of the ovaries followed by hormone replacement treatment (40 micrograms estradiol benzoate, 72 h prior to testing, and 500 micrograms progesterone, 4 h prior to testing) failed to alter the females' ability to discriminate between novel and familiar mating partners. These results demonstrate that females make clear discriminations among individual mating partners, that this can affect sexual receptivity and will continue to do so following a delay of at least 1 h, and that the effect is not mediated by the release of ovarian steroids.