Estrogen receptor ? 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 (ERβ) mRNA and protein were shown to be expressed in the rat cerebellum. In the present study, the ontogeny of ERβ protein expression was examined in the rat cerebellum during postnatal development. Western blot analysis indicated that a single ERβ-like immunoreactive species of ∼55 kDa was present in protein lysates prepared from the cerebella of female and male Sprague-Dawley rat pups. Immunocytochemical analysis of cerebellar sections from the midline vermis revealed that during development, the expression of ERβ varied with age and cell-type, but not sex. In the developing cerebellum, highest levels of ERβ-immunoreactivity (IR) were detected in neurons during neurite growth, and in some glia during migration. Throughout the first postnatal week, ERβ-IR was localized to differentiating granule cells in the external germinal layer and to migrating glia. Differentiating granule cells expressed detectable levels of ERβ throughout development. In Purkinje cells, ERβ-IR was first detected on postnatal day 6 (P6), with peak intensities of immunostaining coinciding with the initiation of axonal and dendritic growth that occurs between P7 and P8. Expression of ERβ-IR remained high during maturation of Purkinje cell dendrites, and then decreased to a lower level maintained in the adult. From the third postnatal week, ERβ-IR was also detected in the later developing Golgi, stellate, and basket neurons. These results suggest that ERβ may play a role in growth-related mechanisms during differentiation of cerebellar neurons and glia. J. Comp. Neurol. 430:396–409, 2001. © 2001 Wiley-Liss, Inc.