Myelin and microsomes from rhesus monkey spinal cord: isolation and effects of trauma.

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.