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. 2001 Feb;76(4):975-89.
doi: 10.1046/j.1471-4159.2001.00074.x.

In vivo (13)C NMR measurement of neurotransmitter glutamate cycling, anaplerosis and TCA cycle flux in rat brain during

N R Sibson  1 , G F Mason, J Shen, G W Cline, A Z Herskovits, J E Wall, K L Behar, D L Rothman, R G Shulman
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Free article

In vivo (13)C NMR measurement of neurotransmitter glutamate cycling, anaplerosis and TCA cycle flux in rat brain during

N R Sibson et al. J Neurochem. 2001 Feb.
Free article

Abstract

The aims of this study were twofold: (i) to determine quantitatively the contribution of glutamate/glutamine cycling to total astrocyte/neuron substrate trafficking for the replenishment of neurotransmitter glutamate; and (ii) to determine the relative contributions of anaplerotic flux and glutamate/glutamine cycling to total glutamine synthesis. In this work in vivo and in vitro (13)C NMR spectroscopy were used, with a [2-(13)C]glucose or [5-(13)C]glucose infusion, to determine the rates of glutamate/glutamine cycling, de novo glutamine synthesis via anaplerosis, and the neuronal and astrocytic tricarboxylic acid cycles in the rat cerebral cortex. The rate of glutamate/glutamine cycling measured in this study is compared with that determined from re-analysis of (13)C NMR data acquired during a [1-(13)C]glucose infusion. The excellent agreement between these rates supports the hypothesis that glutamate/glutamine cycling is a major metabolic flux ( approximately 0.20 micromol/min/g) in the cerebral cortex of anesthetized rats and the predominant pathway of astrocyte/neuron trafficking of neurotransmitter glutamate precursors. Under normoammonemic conditions anaplerosis was found to comprise 19-26% of the total glutamine synthesis, whilst this fraction increased significantly during hyperammonemia ( approximately 32%). These findings indicate that anaplerotic glutamine synthesis is coupled to nitrogen removal from the brain (ammonia detoxification) under hyperammonemic conditions.

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