Low concentrations of oxytocin suppress lordosis when infused into the lateral ventricle of female rats.

The first experiment was undertaken to compare the effects on lordosis of the infusion of oxytocin into the lateral versus the third ventricle. Female rats fitted with bilateral cannulae aimed at these ventricles were primed with 5 micrograms estradiol benzoate and 150 micrograms progesterone and received an infusion of 0.34 ng oxytocin into either the left lateral or the third ventricle. The infusion of 0.34 ng oxytocin into the left lateral ventricle inhibited lordosis behavior, while the same dose infused into the third ventricles of the same animals did not. Since a facilitation of lordosis in response to the infusion of oxytocin into the lateral ventricle has been reported in other studies, it seemed possible that the inhibition and facilitation could be produced by different doses of oxytocin. In the second experiment this hypothesis was tested in another set of female rats fitted with unilateral cannulae aimed at the left lateral ventricle, primed with 5 micrograms estradiol benzoate and 150 micrograms progesterone and infused with different doses of oxytocin. In these animals the inhibition occurred with 0.34 ng but not with 3.4 ng or 34 ng of oxytocin. No facilitation was observed at any of these doses.