Measurement of Human Tricarboxylic Acid Cycle Rates During Visual Activation by super(13)C Magnetic Resonance Spectroscopy

• Published in: Journal of neuroscience research 2001-12, Vol.66 (5), p.737-746
• Main Authors: Chhina, N, Kuestermann, E, Halliday, J, Simpson, L J, Macdonald, IA, Bachelard, H S, Morris, P G
• Format: Article
• Language: English
• Subjects: magnetic resonance spectroscopy
• ISSN: 0360-4012

Measurement by super(13)C magnetic resonance spectroscopy (MRS) of the incorporation of label from [1- super(13)C] glucose, initially into C4 of glutamate, allows the regional tricarboxylic acid (TCA) cycle flux (F sub(TCA)) to be determined in the human brain. In this study, a direct super(13)C MRS approach was used at 3T, with NOE enhancement and super(1)H decoupling with WALTZ16, to determine basal F sub(TCA) in six volunteers. The values found in the visual cortex are similar to those reported in previous super(13)C MRS studies, and consistent with PET measurements of the cerebral metabolic rate for glucose, CMRglc. In two preliminary activation studies using light emitting diode (LED) goggles flashing at 8 Hz, compared to darkness as control, increases in F sub(TCA) were found from 0.60 plus or minus 0.10 to 0.94 plus or minus 0.03 mu mol/min/g (56%) and from 0.34 plus or minus 0.14 to 0.56 plus or minus 0.07 mu mol/min/g (65%). These are upper estimates, but they are similar to the increases in CMRglc reported in PET studies, and strongly suggest, in contrast to these PET studies, that cerebral glucose is metabolized oxidatively, even during intense visual stimulation. This is supported by the observation that very little super(13)C label is incorporated into C3 lactate, as would be expected if glucose were metabolized anaerobically. There is evidence for incorporation of glucose into cerebral glycogen, but this is a relatively minor component of cerebral glucose metabolism.