The fatty acid composition of rat brain glucocerebrosides changes during development from 16.4% fatty acids with more than 20 carbons (VLC) at 6 days to absence in the adult. The most significant decrease occurs between 15-20 days, at the onset of myelination, which raises 2 questions: 1. Is the glucosyltransferase of adult rat brain specific for ceramides with less than 20 carbons (less than C20) and what is the difference to the enzyme from immature brain? and 2. Is the removal of the VLC-glucocerebrosides at that particular point in development essential for proper myelination and is the responsible glucocerebrosidase specific for the VLC-glucocerebrosides? A preliminary experiment to 1. using chemically synthesized C18 minus, C24 minus and HFA-ceramides indicated the expected specificity in adult brain and the presence of 2 enzymes in immature brain. We would like to ascertain the existence of 2 specific ceramide:glucosyltransferases by studying differences in their developmental pattern and their cellular and subcellular distribution as well as in their temperature and detergent stability and in their kinetic parameters. Bulk isolated neurons and glia and primary rat brain astrocyte cultures will be used as cell fractions. Association of the enzymes with particular membranes can serve as evidence for the function of glucocerebrosides in brain maturation. This role will be also assessed by experiments regarding question 2. An inhibitor of beta-glucosidase, Conduritol-B-epoxide, will be injected into rats at the specific ages of VLC-glucocerebroside decrease and the effect on their concentration and on galactocerebrosides as index for myelination will be determined. Accumulation of VLC-glucocerebrosides could account for the neurological symptoms in neuropathic infantile Gaucher's disease without necessarily resulting in a general increase in glucocerebrosides. The specificity of rat brain glucocerebrosidase for C18 minus and C24 minus glucocerebrosides and the interaction with an activating factor found in considerable amounts in preliminary experiments will then be tested. The experiments proposed will provide new insights into the mechanism of Gaucher's disease and into the process of brain maturation, its dysfunction and degeneration.