Expression of proopiomelanocortin and proenkephalin mRNA in sexually dimorphic brain regions are altered in adult male and female rats treated prenatally with morphine.

The present study demonstrates that prenatal morphine exposure on gestation days 11-18 differentially alters proopiomelanocortin (POMC) and proenkephalin (pENK) mRNA in the hypothalamus and limbic system of adult male and female rats. In adult, prenatally morphine-exposed male rats POMC mRNA levels are decreased in the arcuate nucleus of the hypothalamus (ARC), while the pENK mRNA levels are increased in the paraventricular nucleus of the hypothalamus (PVN) and in the ventrolateral subdivision of the ventromedial nucleus of the hypothalamus (VMH), specifically in the ventrolateral subdivision of the VMH. In adult, prenatally morphine-exposed female rats, POMC mRNA levels in the ARC are increased in ovariectomized (OVX) but not in OVX, estradiol benzoate- (EB) or EB- and progesterone- (P) treated females. In contrast, pENK mRNA levels are decreased in the VMH of morphine-exposed, OVX females and increased in EB-treated females. Further, prenatal morphine exposure decreases pENK mRNA in the ARC and increases it in the medial pre-optic area independently of female gonadal hormones. Finally, POMC mRNA levels are increased in the ARC of saline-exposed, EB- or EB- and P-treated females but not in OVX females. Thus, the present study suggests that prenatal morphine exposure sex and brain region specifically alters the level of POMC and pENK mRNA.