Parameters related to lipid metabolism as markers of myelination in mouse brain

Myelination, during both normal development and with respect to disorders o f myelination, is commonly studied by morphological and/or biochemical tech niques that assay as their endpoints the extent of myelination. The rate of myelination is potentially a more useful parameter, but it is difficult an d time-consuming to establish, requiring a complete developmental study wit h labor-intensive methodology. We report herein development of methodology to assay the absolute rate of myelination at any desired time during develo pment. This involves intraperitoneal injection of (H2O)-H-3 to label body w ater pools, followed by determination of label in the myelin-specific lipid , cerebroside. The absolute amount of cerebroside synthesized can then be c alculated from the specific radioactivity of body water and knowledge of th e number of hydrogens from water incorporated into cerebroside. During deve lopment, the rate of cerebroside synthesis correlated well with the rate of accumulation of the myelin-specific components, myelin basic protein and c erebroside. For purposes of control, we also tested other putative, albeit less quantitative, indices of the rate of myelination. Levels of mRNA for c eramide galactosyltransferase (rate-limiting enzyme in cerebroside synthesi s) and for myelin basic protein did not closely correlate with myelination at all times. Cholesterol synthesis closely matched the rate of cholesterol accumulation but did not track well with myelination. Synthesis of fatty a cids did not correlate well with accumulation of either fatty acids (phosph olipids) or myelin markers. We conclude that measurement of cerebroside syn thesis rates provides a good measure of the rate of myelination. This appro ach may be useful as an additional parameter for examining the effects of e nvironmental or genetic alterations on the rate of myelination.