Grupo de Neurofísica, Departamento de Raios Cósmicos e Cronologia, Instituto de Física Gleb Wataghin, Universidade Estadual de Campinas, Campinas, SP, Brasil.
Braz J Med Biol Res. 2012 Nov;45(11):1031-6. doi: 10.1590/s0100-879x2012007500128. Epub 2012 Aug 16.
N-acetyl-aspartyl-glutamate (NAAG) and its hydrolysis product N-acetyl-L-aspartate (NAA) are among the most important brain metabolites. NAA is a marker of neuron integrity and viability, while NAAG modulates glutamate release and may have a role in neuroprotection and synaptic plasticity. Investigating on a quantitative basis the role of these metabolites in brain metabolism in vivo by magnetic resonance spectroscopy (MRS) is a major challenge since the main signals of NAA and NAAG largely overlap. This is a preliminary study in which we evaluated NAA and NAAG changes during a visual stimulation experiment using functional MRS. The paradigm used consisted of a rest period (5 min and 20 s), followed by a stimulation period (10 min and 40 s) and another rest period (10 min and 40 s). MRS from 17 healthy subjects were acquired at 3T with TR/TE = 2000/288 ms. Spectra were averaged over subjects and quantified with LCModel. The main outcomes were that NAA concentration decreased by about 20% with the stimulus, while the concentration of NAAG concomitantly increased by about 200%. Such variations fall into models for the energy metabolism underlying neuronal activation that point to NAAG as being responsible for the hyperemic vascular response that causes the BOLD signal. They also agree with the fact that NAAG and NAA are present in the brain at a ratio of about 1:10, and with the fact that the only known metabolic pathway for NAAG synthesis is from NAA and glutamate.
N-乙酰天冬氨酸谷氨酸（NAAG）及其水解产物 N-乙酰-L-天冬氨酸（NAA）是最重要的脑代谢物之一。NAA 是神经元完整性和活力的标志物，而 NAAG 调节谷氨酸释放，可能在神经保护和突触可塑性中发挥作用。通过磁共振波谱（MRS）在体内对这些代谢物在脑代谢中的作用进行定量研究是一项重大挑战，因为 NAA 和 NAAG 的主要信号在很大程度上重叠。这是一项初步研究，我们使用功能 MRS 评估了在视觉刺激实验过程中 NAA 和 NAAG 的变化。使用的范式包括休息期（5 分钟 20 秒），随后是刺激期（10 分钟 40 秒）和另一个休息期（10 分钟 40 秒）。在 3T 上使用 TR/TE = 2000/288 ms 从 17 名健康受试者中采集 MRS。对受试者进行平均光谱，并使用 LCModel 进行定量。主要结果是，随着刺激，NAA 浓度降低了约 20%，而 NAAG 浓度同时增加了约 200%。这些变化符合神经元激活下能量代谢的模型，这些模型表明 NAAG 负责引起 BOLD 信号的充血性血管反应。它们还与 NAAG 和 NAA 在大脑中的比例约为 1:10 的事实以及 NAAG 合成的唯一已知代谢途径是来自 NAA 和谷氨酸的事实一致。
