SciELO - Scientific Electronic Library Online

 
vol.45 issue11Dorsal periaqueductal gray stimulation facilitates anxiety-, but not panic-related, defensive responses in rats tested in the elevated T-mazeFacilitatory effects of an auditory warning stimulus in a visual location identification task and a visual shape identification task author indexsubject indexarticles search
Home Pagealphabetic serial listing  

Brazilian Journal of Medical and Biological Research

On-line version ISSN 1414-431X

Abstract

CASTELLANO, G. et al. NAA and NAAG variation in neuronal activation during visual stimulation. Braz J Med Biol Res [online]. 2012, vol.45, n.11, pp. 1031-1036.  Epub Aug 16, 2012 ISSN 1414-431X.  http://dx.doi.org/10.1590/S0100-879X2012007500128.

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.

Keywords : Proton magnetic resonance spectroscopy; Functional experiments; Brain activation; Brain energy metabolism; N-acetyl-L-aspartate; N-acetyl-aspartyl-glutamate.

        · text in English     · pdf in English