BETA-ENDORPHIN INHIBITS AND FACILITATES LORDOSIS BEHAVIOR IN RATS DEPENDING ON VENTRICULAR SITE OF ADMINISTRATION

beta-endorphin was administered intracerebroventricularly into the lat eral and third ventricles of ovariectomized, oestrogen-and progesteron e-primed rats, and its effect on lordosis and ear-wiggling was assesse d. A dose of 2 mu g beta-endorphin facilitated lordosis when infused i nto the lateral ventricle, but inhibited lordosis when infused into th e third ventricle, The effects were the same whether measured at 30, 6 0 or 90 min following infusion. beta-endorphin had no significant effe ct on ear-wiggling frequency when administered in either ventricle. Th e differential effects of beta-endorphin depending on site of administ ration may reflect the activation of distinct opioid receptor subtypes within the brain.