Incorporation of N‐Acetylmannosamine into Rat Brain Subcellular Gangliosides: Effect of Pentylenetetrazol‐Induced Convulsions on Brain Gangliosides

Abstract: The labeling pattern of the major individual gangliosides from the microsomal and synaptosomal fractions of rat brain was determined following intracerebral injection of the radioactive sialic acid precursor, N‐acetylmannosamine. Microsomal gangliosides initially had a higher specific radioactivity than synaptosomal gangliosides, with both fractions reaching similar specific radioactivities 18 h after precursor injection. In both subcellular fractions, the polysialogangliosides G_T1b and G_Q1b were initially more highly labeled than all other gangliosides. With the establishment of the labeling pattern, the effect of the convulsant pentylenetetrazol on brain gangliosides was examined in detail. Significant decreases in radioactive label were noted in the polysialogangliosides, G_T1b and G_Q1b, from the synaptosomal and microsomal fractions of the convulsed animals. The decreases may be due to activation of the membrane‐bound neuraminidase present with the gangliosides in neuronal tissue. Prior to experimentation, a methodology was developed to insure quantitative isolation of small amounts of ganglioside free of other lipids and water‐soluble contaminants. Combination of this isolation procedure with quantitative densitometry of thin‐layer chromatograms permits accurate distributional analyses for individual gangliosides. In applications involving radioactive gangliosides, the method allows the determination of both radioactivity and sialic acid distributions from the same thin‐layer chromatogram.