Estimation of aspartate synthesis in GABAergic neurons in mice by 13 C NMR spectroscopy.

Aspartate synthesis in GABAergic neurons was estimated following inhibition of glutamate decarboxylase (GAD) with 3-mercaptopropionic acid (3-MPA). Mice received 3-MPA, 50 mg/kg, and [1-13C]glucose or [2-13C]acetate. Brain extracts were analyzed by 13C NMR spectroscopy. GABA synthesis was inhibited by 50%, and the synthesis of [13C]aspartate subsequently decreased by 25%. This means that 50% of cerebral aspartate is labeled from metabolites formed through the GABA shunt. A large proportion of the remaining aspartate is labeled through the TCA cycle in GABAergic neurons.