Glial cells are thought to supply energy for neurotransmission by increasing nonoxidative glycolysis; however, oxidative metabolism in glia may also contribute to increased brain activity. To study glial contribution to cerebral energy metabolism in the unanesthetized state, we measured neuronal and glial metabolic fluxes in the awake rat brain by using a double isotopic-labeling technique and a twocompartment mathematical model of neurotransmitter metabolism. Rats (n ϭ 23) were infused simultaneously with ). The glial TCA cycle rate was ϳ30% of total TCA cycle activity. A high pyruvate carboxylase rate (V PC , ϳ0.14 -0.18 mol ⅐ gm Ϫ1 ⅐ min Ϫ1) contributed to the glial TCA cycle flux. This anaplerotic rate in the awake rat brain was severalfold higher than under deep pentobarbital anesthesia, measured previously in our laboratory using the same 13 C-labeling technique. We postulate that the high rate of anaplerosis in awake brain is linked to brain activity by maintaining glial glutamine concentrations during increased neurotransmission.

A new scheme is proposed to edit the 3.0 ppm GABA resonance without macromolecule (MM) contamination. Like previous difference spectroscopy approaches, the new scheme manipulates J‐modulation of this signal using a selective editing pulse. The elimination of undesirable MM contribution at 3.0 ppm is obtained by applying this pulse symmetrically about the J‐coupled MM resonance, at 1.7 ppm, in the two steps of the editing scheme. The effectiveness of the method is demonstrated in vitro, using lysine to mimic MM, and in vivo. As compared to the most commonly used editing scheme, which necessitates the acquisition and processing of two distinct difference spectroscopy experiments, the new scheme offers a reduction in experimental time (–33%) and an increase in accuracy. Magn Reson Med 45:517–520, 2001. © 2001 Wiley‐Liss, Inc.

Purpose To determine if neurochemical concentrations obtained at two MRI sites using clinical 3 T scanners can be pooled when a highly optimized, non-vendor short-echo, single voxel proton MRS pulse sequence is utilized in conjunction with identical calibration and quantification procedures. Methods A modified semi-LASER sequence (TE = 28 ms) was used to acquire spectra from two brain regions (cerebellar vermis and pons) on two Siemens 3 T scanners using the same B0 and B1 calibration protocols from two different cohorts of healthy volunteers (N=24–33 per site) matched for age and BMI. Spectra were quantified with LCModel using water scaling. Results The spectral quality was very consistent between the two sites and allowed reliable quantification of at least 13 metabolites in the vermis and pons compared to 3 – 5 metabolites in prior multi-site MRS trials using vendor-provided sequences. The neurochemical profiles were nearly identical at the two sites and showed the feasibility to detect inter-individual differences in the healthy brain. Conclusion Highly reproducible neurochemical profiles can be obtained on different clinical 3 T scanners at different sites, provided that the same, optimized acquisition and analysis techniques are utilized. This will allow pooling of multi-site data in clinical studies, which is particularly critical for rare neurological diseases.