Non-nuclear estrogen receptor beta and alpha in the hippocampus of male and female rats

Estrogens play important roles in the brain, acting through two receptor types, ER alpha and ER beta, both recognized as transcription factors. In this study, we investigated the ER beta mRNA and protein expression in the male and female rat brain, focusing on the hippocampus, an comparing with well-known ER alpha expression patterns. Extranuclear ER localization, as shown by light microscopic immunocytochemistry and tissue fractionation experiments, was noted in the hippocampus, whereas nuclear ER beta was present in the amygdala. Despite these marked differences in subcellular localizations, similar expression levels of ER beta proteins as well as the profile of ER beta mRNA isoforms were observed in the two brain structures. ER alpha was localized to the nucleus more so than ER beta, yet not without an extranuclear component. Our results suggest that cytoplasmic estrogen receptors may play an important role in hippocampal physiology. (c) 2005 Wiley-Liss, Inc.