CHEMICAL COMPOSITION OF MYELIN IN ORGAN-CULTURES OF RAT CEREBELLUM

Myelinating organ cultures of rat cerebellum were maintained in vitro for up to 130 days. Extensive myelination took place between 7 DIV (days in vitro) and 28 DIV. Centrifugation of a crude culture myelin fraction on a discontinuous gradient yielded 3 layers termed light myelin, heavy myelin and membrane fraction, which exhibited an ultrastructure virtually identical to that of comparable layers prepared from surviving littermates. However, culture myelin layers showed a gross deficiency of galactolipids with a relative increase in phospholipids. The 2,3''-cyclic nucleoside-monophosphate phosphodiesterase (CNP) activity was decreased in the culture myelin layers, but not to an extent comparable to the cerebroside deficiency. A form of slow myelin maturation took place in vitro with both myelin cerebrosides and sulfatides increasing in cultures older than 60 DIV. CNS myelination evidently comprises at least 2 phases, and that the 2nd phase involving galactolipid enrichment of myelin can, under experimental conditions, be partly uncoupled from the 1st phase without affecting the morphology or ultrastructure of the sheaths.