Opiate antagonists and sexual behavior in female hamsters.

Mating or administration of morphine to female hamsters reliably decreases lateral displacement, a sensitive index of female sexual responsitivity. Morphine's effects are antagonized by naloxone. We asked whether endogenous opiates are significantly involved in the mating-induced inhibition of sexual responsitivity by testing whether naloxone or naltrexone attenuated the mating-induced decreases in lateral displacement. Naloxone (4 mg/kg) increased lateral displacement in only one of three tests in females before mating. Naloxone did not attenuate the mating-induced decreases in lateral displacement or lordosis behavior in either ovariectomized, hormonally supplemented or intact females. Large doses of naltrexone produced no reliable effects on sexual behavior during estrus in unmated females, nor did it attenuate the mating-induced decreases in sexual responding, regardless of the time of day of mating. Naloxone often increases the variability of sexual responding. We conclude that naloxone-sensitive mechanisms do not play a critical role in the expression of sexual behavior in female hamsters.