Rates of glutamatergic and GABAergic neurotransmission

Schematic depiction of glutamate (Glu) / glutamine (Gln) and GABA / Gln cycling between glutamatergic (orange) and GABAergic (green) neurons and astroglia relevant to 13C MRS experiments using 1-13C glucose or 2-13C acetate as tracer. Metabolism of 1-13C glucose through glycolysis and the tricarboxylic acid (TCA) cycle labels neuronal Glu-C4 and GABA-C2 with label transfer to Gln-C4 by neurotransmitter cycling, Vcyc(tot)= VGlu/Gln+ VGABA/Gln. 2-13C acetate metabolism in astroglia labels Gln-C4 directly with label transfer to neuronal Glu-C4 and GABA-C2 by neurotransmitter cycling, Vcyc(tot). VGAD, rate of GABA synthesis via glutamate decarboxylase; Vshunt, rate of neuronal GABA catabolism; VGln, rate of Gln synthesis; VPC, rate of pyruvate carboxylation.