Treatment of experimental autoimmune encephalomyelitis (EAE) mice with the estrogen receptor (ER) β ligand diarylpropionitrile (DPN) has been shown to have neuroprotective effects via stimulation of endogenous myelination. The direct cellular mechanisms underlying the effects of this ERβ ligand on the central nervous system are uncertain because different cell types in both the peripheral immune system and central nervous system express ERs. ERβ is the target molecule of DPN because DPN treatment fails to decrease EAE clinical symptoms in global ERβ-null mice. Here we investigated the potential role of ERβ expression in cells of oligodendrocyte (OL) lineage in ERβ ligand-mediated neuroprotection. To this end, we selectively deleted ERβ in OLs using the well-characterized Cre-loxP system for conditional gene knockout (CKO) in mice. The effects of this ERβ CKO on ERβ ligand-mediated neuroprotective effects in chronic EAE mice were investigated. ERβ CKO in OLs prevented DPN-induced decrease in EAE clinical disease. DPN treatment during EAE did not attenuate demyelination, only partially improved axon conduction, and did not activate the phosphatidylinositol 3-kinase/serine-threonine-specific protein kinase/mammalian target of rapamycin signaling pathway in ERβ CKO mice. However, DPN treatment significantly increased brainderived neurotrophic factor levels in ERβ CKO mice. These findings demonstrate that signaling through ERβ in OLs is essential for the beneficial myelination effects of the ERβ ligand DPN in chronic EAE mice. Further, these findings have important implications for neuroprotective therapies that directly target OL survival and myelination.is an inflammatory, demyelinating neurodegenerative disease characterized by physical, and often cognitive, deficits that can progress to severe debilitation. Although current MS treatments exist in the form of immunomodulatory or immunosuppressive agents, these treatments fail to halt disease progression and are not directly neuroprotective.Building on a wealth of research supporting a role for estrogens in neuroprotection, we have demonstrated that treatment of experimental autoimmune encephalomyelitis (EAE) mice with the estrogen receptor (ER) β ligand 2,3-bis(4-Hydroxyphenyl)-propionitrile (DPN) attenuates clinical disease, neurodegeneration, and axon demyelination and improves axon conduction (1-4). Notably, these effects were observed with both prophylactic and therapeutic treatment regimens, and they occurred in the presence of peripheral cytokine production and central nervous system (CNS) inflammation. Evidence of direct neuroprotection by an ERβ ligand is welcomed, because it circumvents ERα-mediated adverse effects of synthetic estrogens [i.e., increased breast and uterine endometrial growth in females and feminizing effects in males (5)].Because ERs are present in various cell types in the peripheral immune system and CNS, including cells of oligodendrocyte (OL) lineage, it is difficult to assess which cell type(s) mediate ERβ ligand-conferred neuroprote...