Identification of a developmental gradient of estrogen receptor expressionand cellular localization in the developing and adult female rat primary somatosensory cortex

Immunohistochemistry was used to investigate the spatiotemporal distributio n of estrogen receptor alpha and beta (ER alpha, ER beta) in the posteromed ial barrel subfield (PMBS) of the cerebral cortex in developing and adult f emale rats. Counting of immunopositive cells in predefined areas from each layer of the PMBS showed that at PN3, ER alpha immunoreactivity (IR) was pr esent in every cell, whereas ER beta -IR was not detected. At PN6, about 59 % of the cells were ER alpha immunopositive and low levels of ER beta -IR w ere observed in scattered cells. At PN18 the proportion of ER alpha -IR cel ls decreased to 49%; however, ER beta -IR became widespread and was detecte d in 39% of cells. By PN25 only faint ER alpha -IR was observed and in the adults ER alpha -IR was not detected. In contrast, at PN25 and in adults, E R beta -IR was detected in about half the cells of the PMBS. Regarding the cellular localization of ER-IR, at PN3 an outside-in gradient of cytoplasmi c to nuclear localization of ER alpha -IR was observed. At PN18 and in adul ts ER beta -IR was preferentially localized to the nucleus of principal neu rons, and to the cytoplasm of small, stellate-shaped interneurons. Together , these observations reveal a developmental transition of ER expression in the PMBS; ER alpha is expressed during early development, ER alpha and ER b eta are co-expressed at later developmental times, and only ER beta is expr essed in adults. These changes in ER expression and localization suggest th at ER alpha and ER beta may play important, but different roles in the form ation and function of the PMBS region of the primary somatosensory cortex. (C) 2001 Elsevier Science B.V. All rights reserved.