Fig. 1. Neuronal and glial signals in the regulation of myelin biogenesis. (A) An electron micrograph of myelinated nerve fibers within the optic nerve. (B) (1) Astrocytes and/or neurons release several growth/trophic factors factors, such as PDGF, FGF-2, IGF-1, NT-3 and CNTF that regulate oligodendrocyte proliferation and/or survival. (2) Membrane-associated or soluble neuregulin binds the ErbB receptor on oligodendrocytes to promote survival and maturation of oligodendrocytes. (3) Interaction of the Notch 1 receptor with Jagged 1 inhibits the differentiation of oligodendrocytes. (4) An increase in electrical activity causes the release of promyelinating factors such as LIF from astrocytes (4a), adenosine from neurons (4b) and changes the expression level of axonal cell adhesion molecules (4c).