Regional glucose metabolism and glutamatergic neurotransmission in rat brainin vivo

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Abstract
Multivolume 1H-[13C] NMR spectroscopy in combination with i.v. [1,6-13C2]glucose infusion was used to detect regional glucose metabolism and glutamatergic neurotransmission in the halothane-anesthetized rat brain at 7 T. The regional information was decomposed into pure cerebral gray matter, white matter, and subcortical structures by means of tissue segmentation based on quantitative T1 relaxation mapping. The 13C turnover curves of [4-13C]glutamate, [4-13C]glutamine, and [3-13C]glutamate + glutamine were fitted with a two-compartment neuronal-astroglial metabolic model. The neuronal tricarboxylic acid cycle fluxes in cerebral gray matter, white matter, and subcortex were 0.79 ± 0.15, 0.20 ± 0.11, and 0.42 ± 0.09 μmol/min per g, respectively. The glutamate-glutamine neurotransmitter cycle fluxes in cerebral gray matter, white matter, and subcortex were 0.31 ± 0.07, 0.02 ± 0.04, and 0.18 ± 0.12 μmol/min per g, respectively. The exchange rate between the mitochondrial and cytosolic metabolite pools was fast relative to the neuronal tricarboxylic acid cycle flux for all cerebral tissue types.