Investigation Of Naa And Naag Dynamics Underlying Visual Stimulation Using Mega-press In A Functional Mrs Experiment

Abstract

N-acetyl-aspartate (NAA) is responsible for the majority of the most prominent peak in H-1-MR spectra, and has been used as diagnostic marker for several pathologies. However, similar to 10% of this peak can be attributed to N-acetyl-aspartyl-glutamate (NAAG), a neuropeptide whose release may be triggered by intense neuronal activation. Separate measurement of NAA and NAAG using MRS is difficult due to large superposition of their spectra. Specifically, in functional MRS (fMRS) experiments, most work has evaluated the sum NM + NAAG, which does not appear to change during experiments. The aim of this work was to design and perform an fMRS experiment using visual stimulation and a spectral editing sequence, MEGA-PRESS, to further evaluate the individual dynamics of NM and NAAG during brain activation. The functional paradigm used consisted of three blocks, starting with a rest (baseline) block of 320 s, followed by a stimulus block (640 s) and a rest block (640 s). Twenty healthy subjects participated in this study. On average, subjects followed a pattern of NAA decrease and NAAG increase during stimulation, with a tendency to return to basal levels at the end of the paradigm, with a peak NM decrease of-(21 +/- 19)% and a peak NAAG increase of (64 62)% (Wilcoxon test p < 0.05). These results may relate to: 1) the only known NAAG synthesis pathway is from NM and glutamate; 2) a relationship between NAAG and the BOLD response. (C) 2015 Elsevier Inc. All rights reserved.