MRI-based assessment of function and dysfunction in myelinated axons

Repetitive electrical activity produces microstructural alteration in myelinated axons, which may afford the opportunity to non-invasively monitor function of myelinated fibers in peripheral nervous system (PNS)/CNS pathways. Microstructural changes were assessed via two different magnetic-resonance...

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Bibliographic Details
Published in:Proceedings of the National Academy of Sciences - PNAS 2018-10, Vol.115 (43), p.E10225-E10234
Main Authors: Spees, William M., Lin, Tsen-Hsuan, Sun, Peng, Song, Chunyu, George, Ajit, Gary, Sam E., Yang, Hsin-Chieh, Song, Sheng-Kwei
Format: Article
Language:English
Subjects:
Action potential
Animals
Anura
Axons
Axons - pathology
Biological Sciences
Brain Mapping - methods
Central nervous system
Correlation analysis
Diffusion
Diffusion Magnetic Resonance Imaging - methods
Diffusion Tensor Imaging - methods
Electric pulses
Electrical stimuli
Electron microscopes
Electrophysiology
Fibers
Functional magnetic resonance imaging
Image Processing, Computer-Assisted - methods
Magnetic resonance imaging
Microscopy
Microstructure
Myelin
Myelin Sheath - pathology
Nerve Fibers, Myelinated - pathology
Nerves
Peripheral nervous system
PNAS Plus
Sciatic Nerve - pathology
Spectroscopy
Stimulation
Tensors
Trauma
Vacuoles
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Summary:Repetitive electrical activity produces microstructural alteration in myelinated axons, which may afford the opportunity to non-invasively monitor function of myelinated fibers in peripheral nervous system (PNS)/CNS pathways. Microstructural changes were assessed via two different magnetic-resonance-based approaches: diffusion fMRI and dynamic T₂ spectroscopy in the ex vivo perfused bullfrog sciatic nerves. Using this robust, classical model as a platform for testing, we demonstrate that noninvasive diffusion fMRI, based on standard diffusion tensor imaging (DTI), can clearly localize the sites of axonal conduction blockage as might be encountered in neurotrauma or other lesion types. It is also shown that the diffusion fMRI response is graded in proportion to the total number of electrical impulses carried through a given locus. Dynamic T₂ spectroscopy of the perfused frog nerves point to an electrical-activity-induced redistribution of tissue water and myelin structural changes. Diffusion basis spectrum imaging (DBSI) reveals a reversible shift of tissue water into a restricted isotropic diffusion signal component. Submyelinic vacuoles are observed in electron-microscopy images of tissue fixed during electrical stimulation. A slowing of the compound action potential conduction velocity accompanies repetitive electrical activity. Correlations between electrophysiology and MRI parameters during and immediately after stimulation are presented. Potential mechanisms and interpretations of these results are discussed.
ISSN:0027-8424
1091-6490
DOI:10.1073/pnas.1801788115