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Myelin and microsomes from rhesus monkey spinal cord: isolation and effects of trauma
Abstract:
Dispersions of rhesus monkey spinal cord and brain were separated into large particle (crude mitochondrial plus nuclear) and small particle (crude microsomal) fractions; myelin was isolated from each of these preparative fractions. In brain preparations, almost all myelin was found in the large particle fraction; in contrast, almost half the myelin from spinal cord preparations was found in the small particle fraction. In addition, much larger amounts of partially degraded myelin were found in the fraction floating on 0.32 M sucrose and in the cytosol fraction of the spinal cord preparation in comparison to those of the brain preparations. These results suggest that rhesus monkey spinal cord myelin is more fragile than brain myelin; upon dispersion of spinal cord, more small myelin vesicles (isolated from the crude microsomal fraction) and more 0.32 M sucrose floating fraction (partially degraded myelin) are formed. After trauma of the spinal cord, the proportion of small vesicle myelin was increased at the expense of large vesicle myelin, lending further support to the hypothesis that spinal cord myelin is more fragile than brain myelin. Although the lipid compositions were similar, spinal cord myelin had a lower protein content and a lower 2',3'-cyclic nucleotide phosphodiesterase specific activity than did brain myelin. The lipid composition of microsomes from brain differed somewhat from that of spinal cord microsomes.
Insights
Rhesus monkey spinal cord myelin is more fragile than brain myelin, fragmenting into smaller vesicles during preparation. This fragility is evident in increased degraded myelin and altered myelin vesicle proportions after spinal cord trauma.
Area of Science:
- Neuroscience
- Biochemistry
- Cell Biology
Background:
- Myelin, the protective sheath around nerve fibers, is crucial for neural function.
- Understanding myelin's structural integrity is vital, especially in the context of spinal cord injuries.
- Differences in myelin composition and fragility between the brain and spinal cord are not fully understood.
Purpose of the Study:
- To investigate and compare the fragility of myelin from rhesus monkey spinal cord and brain.
- To analyze the biochemical and compositional differences between spinal cord and brain myelin.
Main Methods:
- Differential centrifugation of rhesus monkey spinal cord and brain dispersions to obtain large (crude mitochondrial plus nuclear) and small (crude microsomal) particle fractions.
- Isolation of myelin from these preparative fractions.
- Analysis of myelin distribution, degradation products, lipid composition, protein content, and enzyme activity (2',3'-cyclic nucleotide phosphodiesterase).
Main Results:
- Spinal cord myelin exhibited greater fragility, with nearly half found in the small particle fraction compared to brain myelin.
- Larger amounts of partially degraded myelin were observed in spinal cord preparations.
- Spinal cord myelin had lower protein content and reduced 2',3'-cyclic nucleotide phosphodiesterase specific activity than brain myelin.
- Lipid compositions of spinal cord and brain microsomes showed some differences.
Conclusions:
- Rhesus monkey spinal cord myelin is inherently more fragile than brain myelin.
- Spinal cord myelin fragmentation leads to increased small myelin vesicles and degraded myelin upon dispersion.
- Myelin fragility differences may have implications for understanding spinal cord injury pathology.