AGE-RELATED-CHANGES IN THE CERAMIDE COMPOSITION OF THE MAJOR GANGLIOSIDES PRESENT IN RAT-BRAIN SUBCELLULAR-FRACTIONS ENRICHED IN PLASMA-MEMBRANES OF NEURONAL AND MYELIN ORIGIN

Age-related changes of the ceramide composition of gangliosides were s tudied in the synaptosomal and myelin fractions from rat brain, carryi ng plasma membranes of neuronal and glial origin, respectively. The fi ve major gangliosides (GM1, GD1a, GD1b, GT1b, and GQ1b) present in the se fractions were separated and quantitated by normal-phase HPLC. Each ganglioside was then fractionated by reverse-phase HPLC into the mole cular species carrying a single long-chain base (LCB). The largely pre ponderant LCBs in the synaptosomal and myelin fractions were the C18:1 and C20:1. The content of C20:1 LCB, generally low at 1 month, increa sed with age in all analyzed gangliosides and in all subcellular fract ions and was greater in the ''b series'' than in the ''a series'' gang liosides. Remarkably, GM1 was the only ganglioside where the proportio n of LCB 20:1 was higher in the synaptosomal fraction than in the myel in fraction. The fatty acid composition of the C18:1 or C20:1 LCB spec ies of the different gangliosides in the synaptosomal and myelin fract ions did not undergo appreciable changes with age. Stearic acid was la rgely predominant in all the gangliosides of the synaptosomal fraction , more in the C18:1 than in the C20:1 LCB species (80-90% vs. 60-70%). The gangliosides of the myelin fraction were characterized by a lower content of 18:0 and a much higher content of 16:0 and 18:1 fatty acid s than those of the synaptosomal fraction. Thus, the ceramide composit ion is different in the gangliosides of neuronal and myelin origin and appears to be subjected to an age-related control.