Estrogen receptor beta immunoreactivity in differentiating cells of the developing rat cerebellum

Estrogen receptors (ER) play a significant role in the development of some regions of the mammalian brain. Recently, ER-beta (ER beta) mRNA and protei n were shown to be expressed in the rat cerebellum. In the present study, t he ontogeny of ER beta protein expression was examined in the rat cerebellu m during postnatal development. Western blot analysis indicated that a sing le ER beta -like immunoreactive species of similar to 55 kDa was present in protein lysates prepared from the cerebella of female and male Sprague-Daw ley rat pups. Immunocytochemical analysis of cerebellar sections from the m idline vermis revealed that during development, the expression of ER beta v aried with age and cell-type, but not sex. In the developing cerebellum, hi ghest levels of ER beta -immunoreactivity (IR) were detected in neurons dur ing neurite growth, and in some glia during migration. Throughout the first postnatal week, ER beta -IR was localized to differentiating granule cells in the external germinal layer and to migrating glia. Differentiating gran ule cells expressed detectable levels of ER beta throughout development. In Purkinje cells, ER beta -IR was first detected on postnatal day 6 (P6), wi th peak intensities of immunostaining coinciding with the initiation of axo nal and dendritic growth that occurs between P7 and P8. Expression of ER be ta -IR remained high during maturation of Purkinje cell dendrites, and then decreased to a lower level maintained in the adult. From the third postnat al week, ERP-LR was also detected in the later developing Golgi, stellate, and basket neurons. These results suggest that ER beta may play a role in g rowth-related mechanisms during differentiation of cerebellar neurons and g lia. J. Comp. Neurol. 430.396-409, 2001. (C) 2001 Wiley-Liss, Inc.