Localization of estrogen receptor alpha (ER alpha) in pyramidal neurons ofthe developing rat hippocampus

During development, estrogen has a variety of effects on morphological, bio chemical and electrophysiological properties of hippocampal neurons. Corres pondingly, estrogen receptor (ER) binding and mRNA increase transiently in the developing hippocampus. In this study, we used immunocytochemistry to d etermine the localization of the ER alpha subtype in the developing rat hip pocampus. Nuclear staining was present in pyramidal cells and some interneu rons of the CAI and CA3 regions of the developing rat hippocampus. Little o r no immunoreactivity was observed in postnatal day (P)0 animals (day of bi rth = P0), however, be.-inning on P4, ER alpha -immunoreactivity (ER alpha -ir) was visible and reached maximal levels by P10. These levels subsequent ly declined to low levels so that by P15, levels approximated those of adul t females. Western blot analysis confirmed that this antibody recognized a 67 kDa protein, characteristic of the full-length ER alpha. protein, in the hippocampus and pituitary. Furthermore, most of the ER alpha -immunopositi ve cells in the hippocampus were located in the pyramidal cell layer, and d id not co-localize appreciably with gamma -aminobutyric acid (GABA) at any age examined. We conclude, based on the immunocytochemical localization of ER alpha, thatt the effects of estrogen on biochemistry and morphology of t he developing hippocampus may be direct through the ER alpha subtype in hip pocampal pyramidal cells. (C) 2001 Elsevier Science BY All rights reserved.