Prenatal exposure to morphine alters brain mu opioid receptor characteristics in rats.

Prenatal morphine exposure alters neither the binding capacity nor the affinity of ligand binding to mu opioid receptors of adult male brains. However, males have significantly higher Bmax in the hypothalamus than ovariectomized females. In females, prenatal exposure to morphine reduces the Bmax of mu opioid receptors 25% in the hypothalamus and preoptic area. Estrogen treatment increases the Bmax of mu opioid receptors in the striatum of all ovariectomized females but in the hypothalamus only of morphine-exposed females, thereby eliminating the sex difference observed in control animals.