In vivo detection of cortical GABA turnover from intravenously infused [1-13C]D-glucose.

In this study 2-(13)C] gamma-aminobutyric acid (GABA) was spectrally resolved in vivo and detected simultaneously with 4-(13)C]glutamate (Glu) and 4-(13)C]glutamine (Gln) in the proton spectra obtained from a localized 40 microL voxel in rat neocortex with the use of an adiabatic (1)H-observed, (13)C-edited (POCE) spectroscopy method and an 89-mm-bore vertical 11.7 Tesla microimager. The time-resolved kinetics of (13)C label incorporation from intravenously infused 1-(13)C]glucose into 4-(13)C]Glu, 4-(13)C]Gln, and 2-(13)C]GABA were measured after acute administration of gabaculine, a potent and specific inhibitor of GABA-transaminase. In contrast to previous observations of a rapid turnover of 2-(13)C]GABA from 1-(13)C]glucose in intact rat brain, the rate of (13)C incorporation from 1-(13)C]glucose into 2-(13)C]GABA in the gabaculine-treated rats was found to be significantly reduced as a result of the blockade of the GABA shunt.