Increased Single fiber jitter level is associated with reduction in motor function with aging

ABSTRACTObjectiveAge-associated skeletal muscle weakness is a major contributing factor to an increased late life mortality and morbidity, but its neurobiology is poorly understood. Previously, we provided histological evidence of dying-back axonal degeneration of motor neurons and denervation of neuromuscular junctions (NMJ) in age-associated muscle weakness. Given this, we aim to evaluate the relation between impaired neuromuscular transmission and various aspects of age-associated muscle weakness.DesignWe compared two electrophysiological measures, single fiber jitter and compound motor action potential (CMAP) in mice of different age groups, and correlated them with various physical performance measures, such as grip strength, standing and walking time and treadmill performance.ResultsConsistent with our previous histological data, single fiber jitter, a measure of NMJ transmission, was significantly increased in older animals, while CMAP shows no difference between young and old age groups. Neither jitter nor CMAP correlated with any of physical performance measures, except for jitter and standing activity.ConclusionImpaired neuromuscular transmission – represented as increase in SFEMG jitter level – reflects decline in motor function with aging. Objective Age-associated skeletal muscle weakness is a major contributing factor to an increased late life mortality and morbidity, but its neurobiology is poorly understood. Previously, we provided histological evidence of dying-back axonal degeneration of motor neurons and denervation of neuromuscular junctions (NMJ) in age-associated muscle weakness. Given this, we aim to evaluate the relation between impaired neuromuscular transmission and various aspects of age-associated muscle weakness. Design We compared two electrophysiological measures, single fiber jitter and compound motor action potential (CMAP) in mice of different age groups, and correlated them with various physical performance measures, such as grip strength, standing and walking time and treadmill performance. Results Consistent with our previous histological data, single fiber jitter, a measure of NMJ transmission, was significantly increased in older animals, while CMAP shows no difference between young and old age groups. Neither jitter nor CMAP correlated with any of physical performance measures, except for jitter and standing activity. Conclusion Impaired neuromuscular transmission – represented as increase in SFEMG jitter level – reflects decline in motor function with aging. Acknowledgement This work was supported by RMSTP K12 grant (5K12HD001097-19), the Dr. Miriam and Sheldon G Adelson Medical Research Foundation, the National Institutes on Aging (NIA) (R21-AG025143) and the Johns Hopkins Older Americans Independence Center (P30-AG021334). Correspondence: Tae Chung, MD, Johns Hopkins School of Medicine, Department of Physical Medicine and Rehabilitation, 4940 Eastern Avenue/Asthma Allergy bldg. 1A44, Baltimore MD 21224, Email: tchung7@jhmi.edu Copyright © 2018 Wolters Kluwer Health, Inc. All rights reserved.

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