Effects of sex steroids and estrogen receptor agonists on the expression of estrogen receptor alpha in the principal division of the bed nucleus of the stria terminalis of female rats.

ABSTRACT

Estrogen actions on neurons of the principal division of the bed nucleus of the stria terminalis (BNSTpr) are essential for the regulation of female sexual behavior. However, little is known about the effects of estradiol and progesterone (P) on estrogen receptor alpha (ERα) expression in this nucleus. To study this subject, we used stereological methods to estimate the total number of ERα-immunoreactive (ERα-ir) neurons in the BNSTpr of female rats at each stage of the estrous cycle and of ovariectomized rats after administration of estradiol benzoate (EB) and/or P. To ascertain the percentage of ERα-positive neurons in the BNSTpr, the total number of neurons in this nucleus was also estimated. In order to identify the specific role played by the selective activation of each ER in the expression of ERα, ovariectomized rats were injected with the ERα agonist, propyl-pyrazole triol (PPT), or the ERß agonist, diaryl-propionitrile (DPN). Data show that ERα is expressed in 40-60% of the BNSTpr neurons and that the number of ERα-ir neurons is lowest at proestrus. This value is paralleled by the administration of EB. The number of ERα-ir neurons was not modified by P. PPT induced no changes in the number of ERα-ir neurons. Contrariwise, DPN induced a decrease in the total number of ERα-ir neurons to values similar to those of EB-treated rats. These results show that P has no effect in the modulation of ERα expression and demonstrate that estradiol regulation of ERα in BNSTpr neurons is mediated by activation of ERß.