Isolation of myelinoid Marchi-positive bodies from normal rabbit spinal cord.

Normal rabbit spinal cord was homogenized in sucrose and fractionated by centrifugation in a sucrose density gradient system slightly modified after the Norton-Poduslo method for the isolation of myelin. The following fractions were recovered: the fraction floating on 0.32 M sucrose, the myelin fraction at the 0.32 M/0.85 M interface and the pellet. After fixation in glutaraldehyde the fractions were subjected to Marchi staining, a histochemical method used for the demonstration of degenerating myelin. The floating fraction was enriched in Marchi-positive bodies as compared to the homogenate while the myelin fraction and the pellet contained low amounts. No esterified cholesterol was found in the floating fraction. Since histochemical and electron microscopical studies have shown that Marchi-positive myelinoid bodies in the normal CNS are associated with node-paranode regions our results indicate a possibility to isolate and biochemically characterize a presumably closely myelin-related fraction of known anatomical origin. The absence of esterified cholesterol in the floating fraction shows that biochemical or biophysical properties other than a content of esterified cholesterol may give rise to a positive Marchi reaction.