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.

Abstract

Gonadal steroids and physiological stressors affect the regulation of proenkephalin (PPE) gene expression in the paraventricular (PVN) and ventromedial (VMH) hypothalamic nuclei. To examine the effects of these modulators at the cellular level, the current study utilized a transgenic mouse line that expresses a human proenkephalin promoter/bacterial beta-galactosidase fusion gene (ENK-1). Previous studies have demonstrated that the regulatory sequences included in this transgene are sufficient to support appropriate transcriptional regulation of the reported gene in the PVN of male ENK-1 mice in response to stress. The present experimental paradigm was designed to examine possible interactions 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 intact, gonadectomized, or 21 days postpartum. Forty-eight hours before perfusion, castrated males and ovariectomized females received either 10 micrograms estradiol benzoate or oil vehicle and 4 animals per group received no further treatment. Six h before perfusion, remaining animals received a single intraperitoneal injection of either hypertonic or isotonic saline. Tissues were sectioned through the hypothalamus and processed for X-gal histochemistry. In the VMH of ovariectomized females that received isotonic saline, estrogen significantly elevated transgene expression. This effect was not seen in females that only received estrogen or in those that received the severe systemic stressor of a injection 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 castrated males given estrogen. These findings demonstrate that stress and estrogen have sex-specific and site-specific regulatory effects on the expression of a PPE promoter transgene in hypothalamic neurons.