The turnover of glutamate, glutamine, aspartate and GABA labeled with [1-¹⁴C]acetate in caudate nucleus, thalamus and motor cortex (CAT)

Intravenously administered [1-¹⁴C]acetate was used to study the turnover of glutamic acid, glutamine, aspartic acid and γ-aminobutyric acid in sensorimotor cortex, medial thalamus and head of the caudate nucleus of the cat. Within minutes after the administration of the tracer isotope, the radioactivity in the brain tissues was predominantly in these amino acids. At all time points, the specific activity of the glutamine was greater than that of its precursor, glutamic acid. The decay curves of the 4 amino acids in the 3 areas showed 2 exponentially decreasing half-lives, a fast one of approximately 11-18 min and a slow one of approximately 2.5-5.0 h. The data are consistent with the concept of compartmentation of amino acid metabolism in these regions of the brain.