Freeze-fracture analysis of myelin membrane changes in Wallerian degeneration
1Department of Anatomy and Cell Biology, University of Southern California, School of Medicine, Los Angeles 90033.
Abstract:
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.
Insights
Wallerian degeneration in mouse sciatic nerves causes myelin breakdown and loss of membrane particles. Schwann cells actively remove components from their membranes during this process.
Area of Science:
- Neuroscience
- Cell Biology
- Biochemistry
Background:
- Wallerian degeneration is a process that occurs after nerve injury.
- The molecular changes in myelin during degeneration are not fully understood.
Purpose of the Study:
- To investigate the macromolecular organization of myelin membranes during Wallerian degeneration.
- To correlate microscopic changes with alterations in intramembranous particles.
Main Methods:
- Transection of mouse sciatic nerves.
- Analysis of myelin using freeze-fracture electron microscopy.
Main Results:
- Myelin breakdown involved lamellar splitting and loss of intramembranous particles.
- Remaining particles showed altered distribution, and myelin ovoids lacked particles.
- Schwann cells maintained normal particle distribution on their outer membrane during early degeneration.
Conclusions:
- Wallerian degeneration involves a progressive loss of myelin intramembranous particles.
- Schwann cells selectively remove membrane components during degeneration.
