Dyke Katherine, Pépés Sophia E, Chen Chen, Kim Soyoung, Sigurdsson Hilmar P, Draper Amelia, Husain Masud, Nachev Parashkev, Gowland Penelope A, Morris Peter G, Jackson Stephen R
School of Psychology, University of Nottingham, UK.
Sir Peter Mansfield Imaging Centre, University of Nottingham, UK.
Neuroimage. 2017 May 15;152:360-370. doi: 10.1016/j.neuroimage.2017.03.011. Epub 2017 Mar 9.
Imbalances in glutamatergic (excitatory) and GABA (inhibitory) signalling within key brain networks are thought to underlie many brain and mental health disorders, and for this reason there is considerable interest in investigating how individual variability in localised concentrations of these molecules relate to brain disorders. Magnetic resonance spectroscopy (MRS) provides a reliable means of measuring, in vivo, concentrations of neurometabolites such as GABA, glutamate and glutamine that can be correlated with brain function and dysfunction. However, an issue of much debate is whether the GABA observed and measured using MRS represents the entire pool of GABA available for measurement (i.e., metabolic, intracellular, and extracellular) or is instead limited to only some portion of it. GABA function can also be investigated indirectly in humans through the use of non-invasive transcranial magnetic stimulation (TMS) techniques that can be used to measure cortical excitability and GABA-mediated physiological inhibition. To investigate this issue further we collected in a single session both types of measurement, i.e., TMS measures of cortical excitability and physiological inhibition and ultra-high-field (7 T) MRS measures of GABA, glutamate and glutamine, from the left sensorimotor cortex of the same group of right-handed individuals. We found that TMS and MRS measures were largely uncorrelated with one another, save for the plateau of the TMS IO curve that was negatively correlated with MRS-Glutamate (Glu) and intra-cortical facilitation (10ms ISI) that was positively associated with MRS-Glutamate concentration. These findings are consistent with the view that the GABA concentrations measured using the MRS largely represent pools of GABA that are linked to tonic rather than phasic inhibition and thus contribute to the inhibitory tone of a brain area rather than GABAergic synaptic transmission.
关键脑网络中谷氨酸能（兴奋性）和GABA（抑制性）信号失衡被认为是许多脑和精神健康障碍的基础，因此，人们对研究这些分子局部浓度的个体差异与脑疾病之间的关系兴趣浓厚。磁共振波谱（MRS）提供了一种在体内测量神经代谢物（如GABA、谷氨酸和谷氨酰胺）浓度的可靠方法，这些神经代谢物浓度可与脑功能和功能障碍相关联。然而，一个备受争议的问题是，使用MRS观察和测量到的GABA是代表可用于测量的全部GABA池（即代谢型、细胞内型和细胞外型），还是仅代表其中的一部分。GABA功能也可以在人类中通过使用非侵入性经颅磁刺激（TMS）技术进行间接研究，该技术可用于测量皮层兴奋性和GABA介导的生理抑制。为了进一步研究这个问题，我们在同一组右利手个体的左感觉运动皮层单次采集了两种测量数据，即TMS对皮层兴奋性和生理抑制的测量，以及超高场（7T）MRS对GABA、谷氨酸和谷氨酰胺的测量。我们发现，TMS和MRS测量结果在很大程度上彼此不相关，除了TMS IO曲线的平台期与MRS-谷氨酸（Glu）呈负相关，以及皮层内易化（10ms间隔刺激）与MRS-谷氨酸浓度呈正相关。这些发现与以下观点一致，即使用MRS测量的GABA浓度在很大程度上代表与紧张性而非相位性抑制相关的GABA池，因此有助于脑区的抑制性张力而非GABA能突触传递。
