Regenerating Outgrowth of the Proximal Axon Stump itself of Transected Myelinated Fibers in the Mouse Sciatic Nerve

Regenerating outgrowth of the proximal axon stump itself of myelinated fibers was examined in the transected mouse sciatic nerve by electron microscopy and with silver impregnation method. Attention was paid to the importance of the myelin sheath removal for survival and outgrowth of the proximal axon stump itself. Within one to two days after transection, myelin sheath degradation due to the injury extensively cccurred near the cut end. It appeared that Schwann cells and macrophages were involved in the progressive demyelination in the proximal stump. Proximal axon stumps which became free from tight myelin sheath covering exhibited no morphological features indicative of an extensive degeneration such as cytoautolysis or increase of autophagosomes in the axoplasm. This reveals that demyelinated axon stumps can retain their viability. Owing to demyelination, axon stumps can make direct contact with the cytoplasm and basal laminae of Schwann cells. We found that these naked parent axons grew out, emanated some sprouts and formed mini-neuromas in the connective tissue compartment. These findings suggest that demyelination might be an indispensable requisite for the survival and outgrowing of the parent axon stump itself.