ESTROGEN AND STRESS INTERACT TO REGULATE THE HYPOTHALAMIC EXPRESSION OF A HUMAN PROENKEPHALIN PROMOTER-BETA-GALACTOSIDASE FUSION GENE IN A SITE-SPECIFIC AND SEX-SPECIFIC MANNER

Gonadal steroids and physiological stressors affect the regulation of proenkephalin (PPE) gene expression in the paraventricular (PVN) and v entromedial (VMH) hypothalamic nuclei. To examine the effects of these modulators at the cellular level, the current study utilized a transg enic mouse line that expresses a human proenkephalin promoter/bacteria l beta-galactosidase fusion gene (ENK-1). Previous studies have demons trated that the regulatory sequences included in this transgene are su fficient to support appropriate transcriptional regulation of the repo rter gene in the PVN of male ENK-1 mice in response to stress. The pre sent experimental paradigm was designed to examine possible interactio ns of sex and circulating estrogen levels with the opioid responses to acute systemic stressors, an intraperitoneal injection of hypertonic (1.5 M) or isotonic (0.15 M) saline. Adult ENK-1 mice were gonadally i ntact, gonadectomized, or 21 days postpartum Forty-eight hours before perfusion, castrated males and ovariectomized females received either 10 mu g estradiol benzoate or oil vehicle and 4 animals per group rece ived no further treatment. Six h before perfusion, remaining animals r eceived a single intraperitoneal injection of either hypertonic or iso tonic saline. Tissues were sectioned through the hypothalamus and proc essed for X-gal histochemistry, In the VMH of ovariectomized females t hat received isotonic saline, estrogen significantly elevated transgen e expression. This effect was not seen in females that only received e strogen or in those that received the severe systemic stressor of an i njection of hypertonic saline. Estrogen and stress did not interact to elevate transgene expression in the VMH of males. A different pattern of expression was observed in the PVN; injection of hypertonic saline induced transgene expression only in gonadally intact males and in ca strated males given estrogen. These findings demonstrate that stress a nd estrogen have sex-specific and site-specific regulatory effects on the expression of a PPE promoter transgene in hypothalamic neurons.