The entry of [1-C-13]glucose into biochemical pathways reveals a complex compartmentation and metabolite trafficking between glia and neurons: a study by C-13-NMR spectroscopy

Glial-neuronal interactions were investigated in rats injected intraperitoneally with [1-C-13]glucose and killed after 15, 30, 45, or 60 min. Brain extracts were analyzed by C-13-NMR spectroscopy and the fractional '3C-enrichment at individual carbon positions was measured for amino acids, lactate, and N-acetyl-aspartate, [1-C-13]Glucose was shown to be metabolized by both neurons and glia, with the anaplerotic pathway through pyruvate carboxylase (PC) accounting for 10% of total cerebral glucose metabolism. The PC-mediated pathway accounted for 39% of the glutamine synthesis, and for 8, 6, 14% of glutamate, GABA and aspartate synthesis, respectively. These results reflect a compartmentation of the cerebral amino acids synthesis within glial and neuronal cells. The appearance of the C-13-label in C5 of glutamate and glutamine, C1 of GABA and C2 of lactate, is suggestive of pyruvate, formation from TCA cycle intermediates and provides evidence of metabolite trafficking between astrocytes and neurons. (C) 1997 Elsevier Science B.V.