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Abstract

In vivo (13)C magnetic resonance spectroscopy (MRS) enables the investigation of cerebral metabolic compartmentation while, e.g. infusing (13)C-labeled glucose. Metabolic flux analysis of (13)C turnover previously yielded quantitative information of glutamate and glutamine metabolism in humans and rats, while the application to in vivo mouse brain remains exceedingly challenging. In the present study, (13)C direct detection at 14.1 T provided highly resolved in vivo spectra of the mouse brain while infusing [1,6-(13)C2]glucose for up to 5 h. (13)C incorporation to glutamate and glutamine C4, C3, and C2 and aspartate C3 were detected dynamically and fitted to a two-compartment model: flux estimation of neuron-glial metabolism included tricarboxylic acid cycle (TCA) flux in astrocytes (Vg = 0.16 ± 0.03 µmol/g/min) and neurons (VTCA(n )= 0.56 ± 0.03 µmol/g/min), pyruvate carboxylase activity (VPC = 0.041 ± 0.003 µmol/g/min) and neurotransmission rate (VNT = 0.084 ± 0.008 µmol/g/min), resulting in a cerebral metabolic rate of glucose (CMRglc) of 0.38 ± 0.02 µmol/g/min, in excellent agreement with that determined with concomitant (18)F-fluorodeoxyglucose positron emission tomography ((18)FDG PET).We conclude that modeling of neuron-glial metabolism in vivo is accessible in the mouse brain from (13)C direct detection with an unprecedented spatial resolution under [1,6-(13)C2]glucose infusion.

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