A metabolomic approach to ionotropic glutamate receptor subtype function: a nuclear magnetic resonance in vitro investigation.

A range of behaviours are elucidated via ionotropic glutamate receptors (iGluR). In this work, we examined the acute activation of iGluRs by a range of receptor ligands and effectors to see whether distinguishable metabolic sequelae were elucidated by the activity. We used a guinea-pig brain cortical tissue slice model using targeted receptor ligands ((RS)-(tetrazol-5-yl)glycine (TZG), (5S,10R)-(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine maleate (MK-801, dizocilpine), cis-4-[phosphomethyl]-piperidine-2-carboxylic acid (CGS 19755), (RS)-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid, (2S, 3S, 4S)-2-carboxy-4-(1-methylethenyl)-3-pyrrolidineacetic acid (kainate) and D-serine (D-Ser), as well as compounds (quinolinic acid and kynurenic acid (KynA)) involved in some neuroinflammatory responses. The data were derived using 13C and 1H NMR spectroscopy, and analysed by metabolomic approaches and multivariate statistics. The metabolic effects of agonists at the three major classes of iGluR were easily separated from each other using this method. The classical N-methyl-D-aspartate receptor agonist TZG and the antagonist CGS 19755 produced excitatory and inhibitory metabolic responses, respectively, while the blocker MK-801 resulted in a significant decrease in net metabolism and produced the largest decrease in all metabolite pool sizes seen by any glutamatergic ligand we have studied. Quinolinic acid and KynA produced similar acute metabolic responses, which were unlike those to TZG or CGS 19755, but similar to that of D-Ser. D-Ser was highly stimulatory of net flux into the Krebs cycle. These data show that the metabolic response to iGluR perturbation in vitro is a sensitive discriminator of function.