Freeze-fracture analysis of myelin membrane changes in Wallerian degeneration.
Transection of mouse sciatic nerves produced microscopic changes in the myelin sheaths distal to the transection. Studied with freeze-fracture, these microscopic changes were correlated with alterations in the macromolecular organization of nerve membranes. In control mice, sciatic nerve myelin contained randomly distributed intramembranous particles. In the early stages of myelin breakdown the lamellae split and large areas of myelin membrane lacked intramembranous particles. The remaining particles clustered with a greater than normal density. Degenerating myelin was found within Schwann cells which still had an outer mesaxon and a normal distribution of intramembranous particles on the cell outer membrane. As the degeneration proceeded, myelin ovoids formed which completely lacked intramembranous particles. The findings suggest that during Wallerian degeneration there is a progression of myelin changes leading to the eventual loss of myelin intramembranous particles. These observations are morphological evidence that Schwann cells remove components from selective portions of their membrane during Wallerian degeneration.
Department of Anatomy and Cell Biology, University of Southern California, School of Medicine, Los Angeles 90033.
M J
MJ
Cullen
D000818:Animals; D005614:Freeze Fracturing; D051379:Mice; D008810:Mice, Inbred C57BL; D008854:Microscopy, Electron; D009186:Myelin Sheath / Q000378:metabolism / Q000648:ultrastructure*; D009410:Nerve Degeneration; D012583:Schwann Cells / Q000648:ultrastructure; D012584:Sciatic Nerve / Q000648:ultrastructure; D014855:Wallerian Degeneration