Metabolic assessment of a neuron-enriched fraction of rat cerebrum using high-resolution 1H and 13C NMR spectroscopy.

This study explored the utility of 1H and 13C magnetic resonance spectroscopy to study a neuron-enriched preparation made from rat cerebrum. The preparation contained high concentrations of N-acetylaspartate and gamma-aminobutyric acid and low concentrations of glutamine, indicating that it was in fact rich in neuronal cytosol. This was confirmed by immunohistochemical studies with antibodies to neuronal and glial markers. A method of metabolite quantification based on the creatine signal yielded metabolite concentrations similar to those of rat cerebrum, whereas concentrations based on the metabolite/protein ratio were five times lower, suggesting that much protein in the preparation was not associated with functioning cytoplasm. The metabolic competence of the preparation was assessed by quantitative measurements of its ability to convert 1-13C-glucose into lactate, glutamate, aspartate, and other metabolites under well oxygenated conditions for 30 min. Calculated from the creatine standard, the mean glycolytic rate was the same as in a synaptosomal preparation studied under similar conditions and the same as rat cerebrum in vivo. Tricarboxylic acid cycle flux occurred at half the rate observed in the synaptosomal preparation and 16% of the basal cerebral metabolic rate in vivo.