Fig 4. Absence of axon ensheathment, myelin and basal lamina in cAMP-treated SC-neuron cultures.

Cells that were subjected to the same experimental treatments as in Fig. 2 were fixed and analyzed by TEM (Methods). Higher magnification images of selected areas (boxes) are shown to better resolve the interaction between SC processes (SC) and axons (ax). As opposed to ascorbate, CPT-cAMP treatment did not support the ensheathment of axons, the formation of a basal lamina, the deposition of extracellular collagen fibers (arrowheads) or the production of myelin membranes (bracket). Similar to the control condition (left panels), CPT-cAMP-treated SCs (cAMP) associated with multiple low diameter axons leaving many neurites deprived of direct contact with SC processes. The asynchronous responses in myelination induced by ascorbate are illustrated by the multiple ensheathment profiles shown in the upper right panel, as follows: (1) – No ensheathment; (2) Partial ensheathment; (3) Complete ensheathment, no myelin; (4) Complete ensheathment, myelin.