Critical in Vivo Roles for Classical Estrogen Receptors in Rapid Estrogen Actions on Intracellular Signaling in Mouse Brain

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Abstract
Estrogen exerts classical genomic as well as rapid nongenomic actions on neurons. The mechanisms involved in rapid estrogen signaling are poorly defined, and the roles of the classical estrogen receptors (ERs α and β) are unclear. We examined here the in vivo role of classical ERs in rapid estrogen actions by evaluating the estrogen-induced effects on two major signaling pathways within the brains of αER-, βER-, and double αβER-knockout (ERKO) ovariectomized female mice. Estrogen significantly (P < 0.05) increased the numbers of phospho-cAMP response element binding protein (phospho-CREB)-immunoreactive cells in specific brain regions of wild-type mice in a time-dependent manner beginning within 15 min. In brain areas that express predominantly ERβ, this response was absent in βERKO mice, whereas brain regions that express mostly ERα displayed no change in αERKO mice. In the medial preoptic nucleus (MPN), an area that expresses both ERs, the estrogen-induced phosphorylation of CREB was normal in both αERKO and βERKO mice. However, estrogen had no effect on CREB phosphorylation in the MPN, or any other brain region, in double αβERKO animals. Estrogen was also found to increase MAPK phosphorylation levels in a rapid (<15 min) manner within the MPN. In contrast to CREB signaling, this effect was lost in either αERKO or βERKO mice. These data show that ERα and ERβ play region- and pathway-specific roles in rapid estrogen actions throughout the brain. They further indicate an indispensable role for classical ERs in rapid estrogen actions in vivo and highlight the importance of ERs in coordinating both classical and rapid actions of estrogen.

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