Abstract
activity accumulated was determined by scintillation spectrometry. To localize the cellular sites of uptake of y-[3H]aminobutyric acid individual organs were incubated with 5p~-y-[~H]aminobutyric acid, fixed in 5 % glutaraldehyde solution in the original incubation medium and prepared for light and electron-microscopic radioautography. In all four tissues accumulations of silver grains were observed exclusively over glial cell bodies and their processes, in contrast with the neuronal components which were completely devoid of label. The accumulation of y-[3H]-aminobutyric acid observed in biochemical experiments was greatly enhanced by the addition of amino-oxyacetic acid (10~~) to the incubation medium. Since at this concentration amino-oxyacetic acid potently blocks y-aminobutyrate-2-oxoglutarate aminotransferase without affecting y-aminobutyric acid uptake in brain slices (Snodgrass & Iversen, 1973), glial-rich tissues probably metabolize exogenously accumulated y-aminobutyric acid more rapidly than neuronal uptake sites in brain. The endogenous y-aminobutyric acid contents of the tissues were determined by using a radiochemical microassay similar to that described by Snodgrass & Iversen (1972) in which y-aminobutyric acid was measured as it radioactively labelled dansyl derivative. The activities of the enzymes E-glutamate 1-carboxy-lyase and y-aminobutyrate-2oxoglutarate aminotransferase were determined by sensitive radiochemical procedures, measuring the 14C02 evolved (Roberts & Simonsen, 1963) and the formation of labelled succinate from y-[14C]aminobutyric acid (Beart et al., 1972) respectively. All of the tissues examined contained significant amounts of endogenous y-aminobutyric acid, and L-glutamate 1-carboxy-lyase and y-aminobutyrate-2-oxoglutarate aminotransferase activities (Table 1). Further, the concentrations of endogenous y-aminobutyric acid were surprisingly high when compared with those in brain and spinal cord. In general the relative proportions of y-aminobutyric acid, L-glutamate 1-carboxy-lyase and
Published Version
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