Preproenkephalin mRNA levels are regulated by acute stress and estrogen stimulation

Enkephalins facilitate female rc productive behavior. Within the limbic sys tem and hypothalamus, estrogen induced the expression of preproenkephalin ( PPE) mRNA. Estrogen injection caused 3 biphasic increase in the PPE mRNA le vels within the ventromedial hypothalamic nucleus and posterodorsal medial amygdala. The first peak of PPE mRNA levels occurred within an hour, and th e secund 24 to 48 h after subcutaneous injection of estrogen. The present s tudies indicated that the rapid first peak of PPE mRNA expression was stres s induced, whereas the second peak was estrogen induced. In the posterodors al medial amygdala but not in the ventromedial hypothalamic nucleus, the an tiestrogen, tamoxifen, did not inhibit the first peak, but blocked the secu nd peak of PPE mRNA expression. Subcutaneous oil injection induced a 1-h pe ak of PPE mRNA levels but not a 24-h peak. Peak levels of plasma corticoste rone were coincident with peak PPE mRNA levels. Adrenalectomy plus a consta nt, low level of corticosterone eliminated the injection-induced increase o f corticosterone levels and the subsequent increase in PPE mRNA expression in the ventromedial hypothalamic nucleus and posterodorsal medial amygdala. The present results indicate that both stress steroids and estrogen positi vely regulate PPE mRNA levels in the ventromedial hypothalamic nucleus and posterodorsal medial amygdala. These results are consistent with the hypoth esis that acute, mild stress may contribute to the activation of circuits t hat facilitate reproductive behavior in the female. (C) 2000 Elsevier Scien ce Inc. All rights reserved.