title: 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 (1)H-MR spectra, and has been used as diagnostic marker for several pathologies. However, ~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 NAA+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 NAA 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 NAA 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 NAA and glutamate; 2) a relationship between NAAG and the BOLD response.
authors.affiliation: Neurophysics Group, Cosmic Rays and Chronology Department, Institute of Physics Gleb Wataghin, University of Campinas - UNICAMP, Brazil; CInAPCe Program (Cooperação Interinstitucional de Apoio a Pesquisas sobre o Cérebro), São Paulo State, Brazil.
authors.forename: Ricardo C G
authors.initials: RC
authors.lastname: Landim
authors.affiliation: Russell H. Morgan Department of Radiology and Radiological Science, The Johns Hopkins University School of Medicine, United States; F. M. Kirby Center for Functional MRI, Kennedy Krieger Institute, Baltimore, MD, UK.
authors.forename: Richard A E
authors.initials: RA
authors.lastname: Edden
authors.affiliation: Philips Medical Systems, São Paulo, Brazil; CInAPCe Program (Cooperação Interinstitucional de Apoio a Pesquisas sobre o Cérebro), São Paulo State, Brazil.
authors.forename: Bernd
authors.initials: B
authors.lastname: Foerster
authors.affiliation: Neurology Department, Faculty of Medical Sciences, UNICAMP, Brazil; CInAPCe Program (Cooperação Interinstitucional de Apoio a Pesquisas sobre o Cérebro), São Paulo State, Brazil; Brazilian Institute of Neuroscience and Neurotechnology (BRAINN-CEPID-FAPESP), Campinas, SP, Brazil.
authors.forename: Li Min
authors.initials: LM
authors.lastname: Li
authors.affiliation: Neurophysics Group, Cosmic Rays and Chronology Department, Institute of Physics Gleb Wataghin, University of Campinas - UNICAMP, Brazil; CInAPCe Program (Cooperação Interinstitucional de Apoio a Pesquisas sobre o Cérebro), São Paulo State, Brazil; Brazilian Institute of Neuroscience and Neurotechnology (BRAINN-CEPID-FAPESP), Campinas, SP, Brazil.
authors.forename: Roberto J M
authors.initials: RJ
authors.lastname: Covolan
authors.affiliation: Neurophysics Group, Cosmic Rays and Chronology Department, Institute of Physics Gleb Wataghin, University of Campinas - UNICAMP, Brazil; CInAPCe Program (Cooperação Interinstitucional de Apoio a Pesquisas sobre o Cérebro), São Paulo State, Brazil; Brazilian Institute of Neuroscience and Neurotechnology (BRAINN-CEPID-FAPESP), Campinas, SP, Brazil. Electronic address: gabriela@ifi.unicamp.br.
authors.forename: Gabriela
authors.initials: G
authors.lastname: Castellano
mesh_terms: D000328:Adult; D001224:Aspartic Acid / Q000031:analogs & derivatives* / Q000737:chemistry; D001921:Brain / Q000378:metabolism; D004151:Dipeptides / Q000737:chemistry*; D005260:Female; D018698:Glutamic Acid / Q000737:chemistry; D064368:Healthy Volunteers; D006801:Humans; D008279:Magnetic Resonance Imaging; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D009474:Neurons / Q000473:pathology; D009479:Neuropeptides / Q000737:chemistry; D014785:Vision, Ocular; D055815:Young Adult
chemical_list: D004151:Dipeptides; D009479:Neuropeptides; C027172:isospaglumic acid; D001224:Aspartic Acid; D018698:Glutamic Acid; C000179:N-acetylaspartate
keywords: Functional experiments; MEGA-PRESS; N-acetyl-aspartate; N-acetyl-aspartyl-glutamate; Proton magnetic resonance spectroscopy; Visual stimulation