Estrogen regulates bcl-x expression in rat hippocampus.

In this study, we examined whether experimental alterations of circulating estrogen levels are associated with changes in the expression of bcl-x, an inhibitor of apoptosis. We report that bcl-x mRNA expression in rat hippocampus significantly decreases after reduction of estrogen levels resulting from ovariectomy. Exposure of ovariectomized rats to 17beta-estradiol for either 5 or 28 days restored bcl-x mRNA expression to levels at or above those observed in sham-ovariectomized control animals. These data demonstrate that physiological levels of estrogen regulate hippocampal expression of bcl-x, an important modulator of neuronal apoptosis. Estrogen-mediated regulation of bcl-x may be relevant to the maintenance of neuronal viability and may contribute to the mechanism of estrogen neuroprotection.