Investigations on myelination in vitro: biochemical and morphological changes in cultures of dissociated brain cells from embryonic mice.

The incorporation of 35SO4(2-) and [3H]galactose into myelin-associated lipids, the activity of enzymes catalyzing the synthesis of these lipids, and the activity of 2',3'-cyclic nucleotide phosphohydrolase were determined in primary cultures of dissociated cells from brains of 15-day embryonic mice. These biochemical parameters of myelination were barely detectable before about 10 days in culture, but their activity increased in parallel after this time and reached a maximum at about 40 days in culture. The activities of the selected enzymes in homogenates of the cultured cells at their optimum age were of the same order of magnitude as the same enzymes derived from fresh brain. Scanning electron microscopic studies showed that the cells after adhering to the surface by the 4th day form aggregates and extensive membranes; the aggregates increase in size and coalesce to form nests of cells by the 15th day; the surface of the aggregates becomes smoother until by the 43rd day the entire surface is covered by and cells are buried in a membrane-like substance. These biochemical measurements and morphological data suggest that the cultures of dissociated cells from brain of 15 day embryonic mice provide a useful system for studying myelination and its regulation in vitro.