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Electron microscopic study of intramembranous changes in protein-extracted peripheral nervous system myelin
Abstract:
Sciatic nerves from young mice were incubated for 2-8 hours in 0.5% Triton X-100 in 0.5 M ammonium acetate, a solution which solubilizes the large and small basic proteins of the myelin sheath. As previously noted (Peterson and Gruener, 1978), myelin sheaths from treated nerves extensively split and unravelled along major dense lines. Small focal areas of compact myelin remained. In freeze-fracture replicas, areas of myelin with lamellar splitting contained few intramembranous particles, while membrane areas with greater than normal densities of particles were associated with the patches of compact myelin membrane. Fixation for as short a time as 15 minutes stabilized the myelin membrane enough to prevent the Triton X-100 effects, even when incubations were extended to 20 hours. Controls, both untreated and 0.5 M ammonium acetate-treated nerves, had predominantly compact myelin sheaths; their leaflets were covered with numerous intramembranous particles. The data suggest that Triton X-100 alters the compact structure of peripheral nervous system myelin. In areas where lamellae are split and separated, there is a loss of intramembranous particles. It appears that the loss of intramembranous particles is related to the removal of the basic proteins which are located in major dense line regions of compact myelin sheaths.
Insights
Triton X-100 disrupts the myelin sheath structure in peripheral nerves by solubilizing basic proteins, leading to a loss of intramembranous particles. Early fixation prevents this damage, preserving myelin integrity.
Area of Science:
- Neuroscience
- Cell Biology
- Biochemistry
Background:
- The myelin sheath, crucial for nerve impulse conduction, is composed of lipids and proteins.
- The structural integrity of myelin is essential for proper nervous system function.
- Understanding myelin composition and structure aids in studying neurological disorders.
Purpose of the Study:
- To investigate the effects of Triton X-100 on the structural organization of peripheral nervous system myelin.
- To determine the role of basic proteins in maintaining myelin sheath compactness.
- To explore the relationship between intramembranous particles and myelin structure.
Main Methods:
- Incubation of young mouse sciatic nerves with Triton X-100 and ammonium acetate.
- Analysis of myelin sheath structure using freeze-fracture electron microscopy.
- Assessment of myelin stability with varying fixation times.
Main Results:
- Triton X-100 treatment caused extensive splitting and unraveling of myelin sheaths along major dense lines.
- Areas with lamellar splitting showed reduced intramembranous particle density.
- Compact myelin areas were associated with higher particle densities.
- Early fixation (15 minutes) effectively stabilized myelin against Triton X-100-induced damage.
Conclusions:
- Triton X-100 alters the compact structure of peripheral nervous system myelin.
- The loss of intramembranous particles in split myelin lamellae is linked to the removal of basic proteins.
- Basic proteins are integral to maintaining the structural integrity of compact myelin.