In vivo detection and automatic analysis of GABA in the mouse brain with MEGA-PRESS at 9.4 T

The goals of this study were to develop an acquisition protocol and the analysis tools for Meshcher-Garwood point-resolved spectroscopy (MEGA-PRESS) in mouse brain at 9.4 T, to allow the in vivo detection of γ-aminobutyric acid (GABA) and to examine whether isoflurane alters GABA levels in the thalamus during anesthesia. We implemented the MEGA-PRESS sequence on a Bruker 94/20 system with ParaVision 6.0.1, and magnetic resonance spectra were acquired from nine male wild-type C57BL/6 J mice at the thalamus. Four individual scans were obtained for each mouse in a 2-h time course whilst the mouse was anesthetized with isoflurane. We developed an automated analysis program with improved correction for frequency and phase drift compared with the standard creatine (Cr) fitting-based method and provided automatic quantification. During MEGA-PRESS acquisition, a single voxel with a size of 5 × 3 × 3 mm³ was placed at the thalamus to evaluate GABA to Cr (GABA/Cr) ratios during anesthesia. Detection and quantitative analysis of thalamic GABA levels were successfully achieved. We noticed a significant decrease in GABA/Cr during the 2-h anesthesia (by linear regression analysis: slope < 0, p < 0.0001). In summary, our findings demonstrate that MEGA-PRESS is a feasible technique to measure in vivo GABA levels in the mouse brain at 9.4 T.