The biosynthesis and concentration of galactosyl diglyceride in glial and neuronal enriched fractions of actively myelinating rat brain.

Abstract

Abstract—In continuation of our studies on the association of the galactosyl diglycerides of brain with myelination, we have measured the biosynthesis and concentration of these glyceride glycolipids, in oligodendroglial, astroglial, neuronal, and myelin enriched fractions from brains of rats of postnatal age 16, 19 and 29 days. The relative purity of cell fractions and myelin derived from 50 to 60 brains of each age‐group was checked by phase contrast microscopy and 2′,3′‐cyclic nucleotide‐3′‐phosphohydrolase activity. The relative purity was comparable to that reported by other investigators for cell fractions from bovine brain. Of the three cell types, the oligodendroglia had the highest and the neurons had the lowest capacity to enzymatically synthesize and to accumulate monogalactosyl diglyceride. The amount of monogalactosyl diglyceride found in myelin compared to that found in oligodendroglial fraction greatly increased during development between 16 and 29 days of age. The biosynthesis of galactosyl ceramide but not glucosyl ceramide was highest in oligodendroglial enriched cell fraction. However, ceramide glucosyl‐transferase activity, which was greatly affected by the method used for cellular separation, was highest in a microsomal fraction derived from grey matter. Our results support the contention that the oligodendroglial cells are the site of synthesis of myelin constituents of the central nervous system, and that there is a temporal relationship between this site of synthesis and the site of deposition (myelin).