NAA and NAAG variation in neuronal activation during visual stimulation

Author(s)

Castellano, G. ^[1] ; Dias, C. S. B. ^[1] ; Foerster, B. ^[2] ; Li, L. M. ^[3] ; Covolan, R. J. M. ^[1]

Affiliation

^[1] Univ Estadual Campinas, Inst Fis Gleb Wataghin, Dept Raios Cosmicos & Cronol, Grp Neurofis, Campinas, SP - Brazil

^[2] Philips Med Syst, Sao Paulo, SP - Brazil

^[3] Univ Estadual Campinas, Fac Ciencias Med, Dept Neurol, Campinas, SP - Brazil

• Document type: Journal article
• Source: Brazilian Journal of Medical and Biological Research; v. 45, n. 11, p. 1031-1036, NOV 2012.
• Web of Science Citations: 11

Abstract

N-acetyl-aspartyl-glutamate (NAAG) and its hydrolysis product N-acetyl-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. (AU)

• FAPESP's process: 08/02246-9 - Combined application of dynamic MR spectroscopy and EEG techniques for studying the brain metabolism underlying spike activity in epileptic patients
• Grantee: Carlos Sato Baraldi Dias
• Support Opportunities: Scholarships in Brazil - Master
• FAPESP's process: 05/56578-4 - Multimodal neuroimaging center for studies in epilepsy
• Grantee: Fernando Cendes
• Support Opportunities: Inter-institutional Cooperation in Support of Brain Research (CINAPCE) - Thematic Grants
• FAPESP's process: 09/10046-2 - Functional Magnetic Resonance Spectroscopy (fMRS)
• Grantee: Gabriela Castellano
• Support Opportunities: Regular Research Grants