LOCALIZED IN-VIVO C-13-NMR OF GLUTAMATE METABOLISM IN THE HUMAN BRAIN- INITIAL RESULTS AT 4 TESLA

Using optimized administration of C-13-labeled glucose, the time cours e of the specific activity of glucose was measured directly by in vivo C-13-NMR in the human brain at 4 Tesla. Subsequent label incorporatio n was measured at the C2, C3 and C4 positions of both glutamate and th e well-resolved C2, C3 and C4 resonances of glutamine and at the C2 an d C3 positions of aspartate. GABA was clearly observed for the first t ime in vivo, suggesting a substantial GABA turnover in the normal huma n visual cortex. Likewise, lactate C3 labeled with an estimated active pool size on the order of 0.5 mM. A model of cerebral glutamate metab olism is proposed which predicts that glutamatergic action ('neurotran smission'), pyruvate carboxylase flux, TCA cycle activity, glucose con sumption and exchange across the mitochondrial membrane can be assesse d simultaneously in the human brain.