ESTRADIOL UP-REGULATES BCL-2 EXPRESSION IN ADULT BRAIN NEURONS

BCL-2, a protein which negatively modulates apoptosis, is up-regulated by estrogen in several tissues. To determine the effect of estradiol on Bcl-2 in the adult brain, its immunoreactive distribution was exami ned in the hypothalamic arcuate nucleus of female rats under different endocrine conditions. The number of Bcl-2-immunoreactive neurons was significantly increased (p < 0.001) on the day of estrus compared with proestrus, diestrus and metestrus, was decreased by ovariectomy and s howed a dose-response increase after estradiol administration to ovari ectomized rats. Progesterone, when injected simultaneously with estrad iol, reduced the effect of estradiol. These findings indicate that ova rian hormones regulate Bcl-2 in hypothalamic neurons and suggest that this protein may be involved in the neuroprotective effects of estroge n.