The neuropeptide Y antagonist PYX2 decreases lordosis behavior.

Neuropeptide Y (NPY) has been localized to noradrenergic neurons and both the noradrenergic system and NPY play a facilitatory role in the control of luteinizing hormone-releasing hormone (LHRH) and luteinizing hormone (LH) release. The present experiments examined whether NPY also plays a role in the control of lordosis. Adult female guinea pigs were ovariectomized (ovx) and implanted with a cannula into the lateral ventricle. In Experiment 1, intracerebroventricular (ICV) administration of the NPY antagonist PYX2 (0, 0.5, 2.0 or 10.0 μg) caused a dose-dependent decrease in lordosis behavior in ovx, estrogen and progesterone-primed guinea pigs. In addition to an effect on the mean lordosis response, PYX2 also decreased the percent of animals showing lordosis and the maximum lordosis response. In Experiment 2, NPY administration (25 μg, ICV) 30 min after PYX2 (2 μg, ICV) to ovx estrogen and progesterone-primed females significantly reversed the effect of the PYX2. Because the NPY antagonist PYX2 reversibly decreased lordosis behavior this suggests that NPY plays a facilitatory role in the control of lordosis behavior.