A BIOCHEMICAL AND MORPHOLOGIC STUDY OF MYELINATION AND DEMYELINATION : I. LIPIDE BIOSYNTHESIS IN VITRO BY NORMAL NERVOUS TISSUE

Samples of normal grey matter, white matter, and peripheral nerves obtained from rats were incubated in Warburg vessels with glucose and a labelled lipide precursor (acetate, phosphate, choline, glycerol, glucose). The total lipides were then extracted and their radioactivity measured. The preparations were compared with respect to dry weight, lipide content, O(2) uptake, and ability to incorporate the various substrates into the lipides. Grey matter was found to be the least damaged by incubation, white matter the most. Damage to the tissue depressed lipogenesis to a greater extent than respiration. Five substrates were compared with respect to their degree of incorporation into the lipides of the various preparations. White matter, which had a greater oxygen uptake than peripheral nerves, showed the lowest degree of incorporation for most of the substrates studied. The results suggest that there are considerable quantitative differences in the metabolism of central and peripheral myelin. In the sciatic preparations, oxygen uptake and lipogenesis from acetate were found to decrease from the proximal to the distal end of the nerve. This finding may be relevant to the pathogenesis of peripheral neuropathies. The growth and metabolic activity of peripheral nerves were studied in rats aged 1 to 500 days, and the biochemical and histological findings were correlated. The results indicated that the lipogenetic activity of the Schwann cell was lowest in the newborn animal, and reached its peak at about 20 days. Comparative data were also obtained from the cerebral cortex. The growth pattern of peripheral nerves was distinctly different from that of the brain. With respect to changes in tissue weight, respiration, and lipogenesis, growing peripheral nerve correlated with body weight, while the brain matured much more rapidly.