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Use of fMRS for the study of N-acetyl-aspartate and N-acetyl-aspartyl-glutamate variation during brain activation

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Author(s):
Ricardo Cesar Giorgetti Landim
Total Authors: 1
Document type: Master's Dissertation
Press: Campinas, SP.
Institution: Universidade Estadual de Campinas (UNICAMP). Instituto de Física Gleb Wataghin
Defense date:
Examining board members:
Gabriela Castellano; Roberto José Maria Covolan; Fernando Fernandes Paiva
Advisor: Gabriela Castellano
Abstract

Metabolic changes that occur in the brain underlying neuronal activation are still far form being understood and, therefore, are a subject matter of great interest for the scientific community of this research field. One way to study these variations is through the technique of functional Magnetic Resonance Spectroscopy (fMRS), in which spectra from a given brain region are collected dynamically, while the volunteer is subject to some sensory stimulus or cognitive task. In particular, N-acetyl-aspartate (NAA) is the metabolite that generates the main peak found the MR spectra of the brain using the hydrogen nucleus. Indeed, this peak originates from NAA itself (90 %) and also from a derivative thereof, N-acetylaspartyl-glutamate (NAAG). In fMRS experiments performed by our group, NAA and NAAG changes were found in the visual cortex of normal individuals when they are subject to a visual stimulus. However, the MRS signal variations of NAA in fMRS experiments are a controversial subject in the literature, since there are studies that point to its variation with the stimulus and others that show that there is no variation. In addition, the existing works measured the joint NAA and NAAG variation. Thus, to elucidate what happens to these metabolites during brain activation it would be interesting to measure them separately. The main objective of this study was, therefore, to perform fMRS experiments in which these metabolites could be measured independently by implementing the MEGA-PRESS pulse sequence, which separates the NAA and NAAG contributions at the time of measurement. The experiments were performed in healthy subjects during visual stimulation. Several tests were performed to standardize the preprocessing and two methods were used. Several quantifications were made and as result NAA and NAAG variations (decrease and increase, respectively) were found during the stimulus. The results agree with those presented in two out of three similar studies found in the literature, and also with the previous results from our group. The NAA decrease may be explained through the hypothesis that it works as a molecular water pump, whereas the NAAG production agrees with the fact that this metabolite is a neuropeptide that is released at the synapses and acts as a modulator for the release of certain neurotransmitters, and also agrees with models for energy metabolism that point to this metabolite as related to the vascular hyperemic response that originates the BOLD signal (AU)

FAPESP's process: 11/01106-1 - Use of fMRS for the study of N-acetyl-aspartate and N- acetyl-aspartyl-glutamate variation during brain activation
Grantee:Ricardo Cesar Giorgetti Landim
Support Opportunities: Scholarships in Brazil - Master