FGF2 expression is increased during acute cuprizone demyelination and can inhibit OP differentiation and oligodendrocyte regeneration during subsequent remyelination (11, 12) . Using in situ hybridization for FGF2 mRNA transcripts, we have shown that elevated FGF2 expression persists within chronic cuprizone lesions, as compared with nonlesioned corpus callosum (Fig. 4) . FGF2 mRNA transcript abundance related to changes in FGF2 protein detection in developing white matter and after acute demyelination (10, 19) . We predicted that in chronic lesions, FGF2 inhibition of differentiation could contribute to the limited capacity to generate remyelinating oligodendrocytes (Figs. 1, 2) , especially in the context of a reduce OP pool (Fig. 3A) .