Comparison of in vivo and in vitro subcellular localization of estrogen receptors α and β in oligodendrocytes

The existence of estrogen receptors (ERs) in oligodendrocytes (OLGs) in vivo and in vitro is unresolved, as their presence has been reported in some studies and their absence in others. Using molecular and immunocytochemical techniques, we describe the subcellular localization of ERα and ERβ in OLGs in vivo and in vitro. Both ERα and ERβ are detected in an immortalized OLG cell line and in enriched OLG cultures by RT‐PCR and western blot. Immunocytochemistry of OLGs from enriched cultures shows ERα receptors are nuclear, whereas ERβ receptors are cytoplasmic. Confocal and deconvolution microscopy of enriched OLG cultures reveals ERβ immunoreactivity is concentrated in perikarya and veins of OLG membrane sheets; lesser reactivity is present in their plasma membranes and nuclei. In vivo, we readily detect ERα in neurons but not in OLGs, even though we used different fixation procedures and different ERα antibodies. The presence of ERα in cultured OLGs may be due to culture media that contains factors stimulating ERα expression but are reduced in normal brain. In vivo, ERβ immunoreactivity is readily detectable in OLG cytoplasm and in myelin sheaths. Incubation of glial cultures without or with increasing concentrations of 17β–estradiol (E2) shows that E2 significantly accelerates OLG process formation.