Proton NMR chemical shift and J-coupling values are presented for 35 metabolites that can be detected by in vivo or in vitro NMR studies of mammalian brain. Measurements were obtained using high-field NMR spectra of metabolites in solution, under conditions typical for normal physiological temperature and pH. This information is presented with an accuracy that is suitable for computer simulation of metabolite spectra to be used as basis functions of a parametric spectral analysis procedure. This procedure is verified by the analysis of a rat brain extract spectrum, using the measured spectral parameters. In addition, the metabolite structures and example spectra are presented, and clinical applications and MR spectroscopic measurements of these metabolites are reviewed.

http://pfeifer.phas.ubc.ca/refbase/files/Govindaraju-NMRBiomed-2000-13-129.pdf

Proton NMR chemical shifts and coupling constants for brain metabolites.

N-Acetyl-L-Aspartic acid: A literature review of a compound prominent in 1H-NMR spectroscopic studies of brain

High-resolution proton NMR spectra of normal human brain in vivo have been obtained from selected 27- and 64-ml volumes-of-interest (VOI) localized in the insular area, the occipital area, the thalamus, and the cerebellum of normal volunteers. Localization was achieved by stimulated echo (STEAM) sequences using a conventional 1.5-T whole-body MRI system (Siemens Magnetom). The proton NMR spectra show resonances from lipids, lactate, acetate, N-acetylaspartate (NAA), gamma-aminobutyrate, glutamine, glutamate, aspartate, creatine and phosphocreatine, choline-containing compounds, taurine, and inositols. While T1 relaxation times of most of these metabolites were about 1100-1700 ms without significant regional differences, their T2 relaxation times varied between 100 and 500 ms. The longest T2 values of about (500 +/- 50) ms were observed for the methyl protons of NAA in the white matter of the occipital lobe compared to (320 +/- 30) ms in the other parts of the brain. No significant regional T2 differences were found for choline and creatine methyl resonances. The relative concentrations of NAA in gray and white matter were found to be 35% higher than those in the thalamus and cerebellum. Assuming a concentration of 10 mM for total creatine the resulting NAA concentrations of 13-18 mM are by a factor of 2-3 higher than previously reported using analytical techniques. Cerebral lactate reached a maximum concentration of about 1.0 mM.

/pdf/localized-proton-nmr-spectroscopy-in-different-regions-of-1aol93wlzt.pdf

Localized proton NMR spectroscopy in different regions of the human brain in vivo. Relaxation times and concentrations of cerebral metabolites.

In the progress of science, as in life, timing is important. The acidic dipeptide, N-acetylaspartylglutamate (NAAG), was discovered in the mammalian nervous system in 1965, but initially was not considered to be a neurotransmitter candidate. In the mid-1980s, a few laboratories revisited the question of NAAG's role in the nervous system and pursued hypotheses regarding its function that ranged from a precursor for the transmitter pool of glutamate to a direct role as a peptide transmitter. Since that time, NAAG has been tested against nearly all of the established criteria for identification of a neurotransmitter. It successfully meets each of these tests, including a concentrated presence in neurons and synaptic vesicles, release from axon endings in a calcium-dependent manner following initiation of action potentials, and extracellular hydrolysis by membrane-bound peptidase activity. NAAG is the most prevalent and widely distributed neuropeptide in the mammalian nervous system. NAAG activates NMDA receptors with a low potency that may vary among receptor subtypes, and it is a highly selective agonist at the type 3 metabotropic glutamate receptor (mGluR3). Acting through this receptor, NAAG reduces cyclic AMP levels, decreases voltage-dependent calcium conductance, suppresses excitotoxicity, influences long-term potentiation and depression, regulates GABA(A) receptor subunit expression, and inhibits synaptic release of GABA from cortical neurons. Cloning of peptidase activities against NAAG provides opportunities to study the cellular and molecular mechanisms by which synaptic NAAG peptidase activity is controlled. Given the codistribution of this peptide with a spectrum of traditional transmitters and its ability to activate mGluR3, we speculate that one role for NAAG following synaptic release is the activation of metabotropic autoreceptors that inhibit subsequent transmitter release. A second role is the production of extracellular glutamate following NAAG hydrolysis.

N-Acetylaspartylglutamate: the most abundant peptide neurotransmitter in the mammalian central nervous system.

Hydrolysis of the brain dipeptide N-acetyl-L-aspartyl-L-glutamate. Identification and characterization of a novel N-acetylated alpha-linked acidic dipeptidase activity from rat brain.

IN a previous investigation (CURATOLO, 1961a), a method of paper chromatography was developed for the purpose of studying the organic non-amino acids in protein-free extracts of animal tissue. The method led to the isolation and identification of N acetyl-aspartic acid (NAAA) (CURATOLO, 1961b) which had been identified a few years before by TALLAN, MOORE and STEIN (1956) using a different approach. In studying the distribution of NAAA throughout the rabbit neuraxis, we found a new acidic ninhydrin-negative spot in the chromatograms, so close to the NAAA spot as to cause some difficulty in its recognition. In paper chromatograms developed with butanol-acetic acid solvent, the R, values of the two spots were 0.70, and 0.75, respectively. To ascertain the identity of the spots, their breakdown products after elution and hydrolysis were subjected to chromatographic analysis. It was found that the spot with the R, of 0.70 was that of an amino-conjugated dipeptide, since two amino acids-glutamic and aspartic acids in an equimolecular ratio-were set free on hydrolysis. The identification of this substance as N-acetyl-aspartyl-glutamic acid (NAAGA) was the subject of a previous study (CURATOLO, 1964).

Distribution of n-acetyl-aspartic and n-acetyl-aspartyl-glutamic acids in nervous tissue.

[Distribution of N-acetyl-aspartyl-glutamic acid in the neuraxis of mammals].

[Distribution of N-acetylaspartic and N-acetylaspartylglutamic acids in the neuraxis of birds].

[Brain concentration of glutamic, aspartic, N-acetylaspartic and N-acetylaspartyl-glutamic acids in rats chronically treated with aspartic and N-acetylaspartic acids].

Concentrations of glutamic acid and aspartic acid in the brain and spinal cord of growing rats

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