3 results
NMR of glycogen in exercise
- Thomas B. Price, Douglas L. Rothman, Robert G. Shulman
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- Journal:
- Proceedings of the Nutrition Society / Volume 58 / Issue 4 / November 1999
- Published online by Cambridge University Press:
- 12 June 2007, pp. 851-859
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Natural-abundance 13CNMR spectroscopy is a non-invasive technique that enables in vivo assessments of muscle and/or liver glycogen concentrations. Over the last several years, 13C NMR has been developed and used to obtain information about human glycogen metabolism with diet and exercise. Since NMR is non-invasive, more data points are available over a specified time course, dramatically improving the time resolution. This improved time resolution has enabled the documentation of subtleties of muscle glycogen re-synthesis following severe glycogen depletion that were not previously observed. Muscle and liver glycogen concentrations have been tracked in several different human populations under conditions that include: (1) muscle glycogen recovery from intense localized exercise with normal insulin and with insulin suppressed; (2) muscle glycogen recovery in an insulin-resistant population; (3) muscle glycogen depletion during prolonged low-intensity exercise; (4) effect of a mixed meal on postprandial muscle and liver glycogen synthesis. The present review focuses on basic 13C NMR and gives results from selected studies.
Biophysical basis of brain activity: implications for neuroimaging
- Robert G. Shulman, Fahmeed Hyder, Douglas L. Rothman
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- Journal:
- Quarterly Reviews of Biophysics / Volume 35 / Issue 3 / August 2002
- Published online by Cambridge University Press:
- 21 January 2003, pp. 287-325
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1. Summary 288
2. Introduction 288
3. Relationship between neuroenergetics and neurotransmitter flux 294
4. A model of coupling between neuroenergetics and neurotransmission 296
5. Relationship between neuroenergetics and neural spiking frequency 297
6. Comparison with previous electrophysiological and fMRI measurements 298
7. Contributions of non-oxidative energetics to a primarily oxidative brain 299
8. Possible explanation for non-oxidative energetics contributions 300
9. A model of total neuronal activity to support cerebral function 302
10. Implications for interpretation of fMRI studies 305
11. The restless brain 306
12. Acknowledgements 310
13. Appendix A. CMRO2by13C-MRS 310
14. Appendix B.Vcycand test of model 313
15. Appendix C. CMRO2by calibrated BOLD 316
16. Appendix D. Comparison of spiking activity of a neuronal ensemble with CMRO2318
17. References 320
In vivo13C magnetic resonance spectroscopy (MRS) studies of the brain have quantitatively assessed rates of glutamate–glutamine cycle (Vcyc) and glucose oxidation (CMRGlc(ox)) by detecting 13C label turnover from glucose to glutamate and glutamine. Contrary to expectations from in vitro and ex vivo studies, the in vivo13C-MRS results demonstrate that glutamate recycling is a major metabolic pathway, inseparable from its actions of neurotransmission. Furthermore, both in the awake human and in the anesthetized rat brain, Vcyc and CMRGlc(ox) are stoichiometrically related, where more than two thirds of the energy from glucose oxidation supports events associated with glutamate neurotransmission. The high energy consumption of the brain measured at rest and its quantitative relation to neurotransmission reflects a sizeable activity level for the resting brain. The high activity of the non-stimulated brain, as measured by cerebral metabolic rate of oxygen use (CMRO2), establishes a new neurophysiological basis of cerebral function that leads to reinterpreting functional imaging data because the large baseline signal is commonly discarded in cognitive neuroscience paradigms. Changes in energy consumption (ΔCMRO2%) can also be obtained from magnetic resonance imaging (MRI) experiments, using the blood oxygen level- dependent (BOLD) image contrast, provided that all the separate parameters contributing to the functional MRI (fMRI) signal are measured. The BOLD-derived ΔCMRO2% when compared with alterations in neuronal spiking rate (Δν%) during sensory stimulation in the rat reveals a stoichiometric relationship, in good agreement with 13C-MRS results. Hence fMRI when calibrated so as to provide ΔCMRO2% can provide high spatial resolution evaluation of neuronal activity. Our studies of quantitative measurements of changes in neuroenergetics and neurotransmission reveal that a stimulus does not provoke an arbitrary amount of activity in a localized region, rather a total level of activity is required where the increment is inversely related to the level of activity in the non-stimulated condition. These biophysical experiments have established relationships between energy consumption and neuronal activity that provide novel insights into the nature of brain function and the interpretation of fMRI data.
11 - Windows on the working brain: magnetic resonance spectroscopy
- from PART I - INTRODUCTION AND GENERAL PRINCIPLES
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- By James W. Prichard, Department of Neurology, Yale Medical School, New Haven, CT, USA, Jeffrey R. Alger, Department of Radiology, University of California at Los Angeles, CA, USA, Douglas Arnold, Department of Neurology, Montreal Neurological Institute, Canada, Ognen A.C. Petroff, Department of Neurology, Yale Medical School, New Haven, CT, USA, Douglas L. Rothman, Department of Diagnostic Radiology, Yale Medical School, New Haven, CT, USA
- Edited by Arthur K. Asbury, University of Pennsylvania School of Medicine, Guy M. McKhann, The Johns Hopkins University School of Medicine, W. Ian McDonald, University College London, Peter J. Goadsby, University College London, Justin C. McArthur, The Johns Hopkins University School of Medicine
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- Book:
- Diseases of the Nervous System
- Published online:
- 05 August 2016
- Print publication:
- 11 November 2002, pp 146-159
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Summary
Nuclear magnetic resonance (NMR) spectroscopy is an observational technique based on detection of signals from magnetic atomic nuclei such as 1H, 31P, 13C, 15N, and 17O. It is most familiar to physicians and the public as magnetic resonance imaging (MRI), which uses the strong signal from water protons to make the most highly detailed pictures of living tissue available from any non-invasive method. In consequence, MRI, including its special forms magnetic resonance angiography, diffusion-weighted imaging, and magnetization transfer imaging – quickly became a major tool for medical diagnosis and research on living creatures. Its applications to neurological disease are described in several other chapters of this book.
Magnetic resonance spectroscopy (MRS) is the designation used in the biomedical world for measurement of NMR signals from non-water protons and other magnetic nuclei. The usage is not accurate, MRI is the MRS of water, but it is convenient. MRS signals detectable in living brain are thousands of times weaker than the water proton signal; hence observing them requires extra time and special procedures. The reward for the effort is an abundance of chemically specific information which can be acquired as often as necessary, since the measurement process is non-invasive. In the living human brain, 1H signals can be obtained from N-acetyl aspartate, creatine, choline moieties, glutamate, glutamine, lactate, and several other small molecules. Phosphocreatine, adenosine triphosphate, and inorganic phosphate can be measured directly by their 31P signals, and intracellular pH calculated from its effect on these signals. Information from the 31P spectrum allows calculation of the rate of the creatine kinase reaction. The spectra of 13C, 15N, 17O, and other magnetic nuclei contain many more small signals from a variety of molecules which will become detectable as technology advances.
This unprecedented measurement capability provides an opportunity for characterization of human neurological diseases along several axes of chemical variation throughout their natural histories. The data are obtained without hazard to the patient, are free from artefacts of tissue preparation, and can be compared in as much detail as necessary to identically acquired information from normal subjects. As MRS matures technically over the first decades of the twenty-first century, it can be expected to take a place among the principal technologies contributing to illumination of disease processes and evaluation of new treatments.