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Level of independence of motor unit properties from neuromuscular activity
Author(s) -
Pierotti David J.,
Roy Roland R.,
Hodgson John A.,
Edgerton V. Reggie
Publication year - 1994
Publication title -
muscle and nerve
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.025
H-Index - 145
eISSN - 1097-4598
pISSN - 0148-639X
DOI - 10.1002/mus.880171112
Subject(s) - motor unit , physical medicine and rehabilitation , independence (probability theory) , neuromuscular disease , medicine , electromyography , psychology , physical therapy , neuroscience , mathematics , disease , statistics
Neuromuscular activity was eliminated in the tibialis anterior muscle of adult cats for 6 months by spinal isolation (Sl), i.e., complete spinal cord transections at T‐12–13 and at L‐7–S‐1, plus bilateral dorsal rhizotomy between the two transection sites. One motor unit from each muscle was isolated using ventral root teasing procedures and physiologically tested. The fibers belonging to each motor unit were visualized in PAS‐staired sections by the loss of glycogen following prolonged repetitive stimulation. Qualitatively, the normal enzymatic interrelationships among fibers identified by myosin heavy chain composition were unchanged by SI. Generally, each motor unit from SI cats were of a single myosin immunohistochemical type. The same physiological motor unit types that typify control muscles were found in SI cats. In Sl compared to control cats, there was approximately a 10% increase in the number of muscle fibers expressing fast myosin. Mean fiber activity levels of ATPase and SDH for a given fiber type (based on MHC antibody reactions) decreased by approximately 10% and 25%, whereas GPD activity increased approximately 35%. It is concluded that differential levels or patterns of activity are not essential to maintain the range of histochemical and physiological motor unit types found in the tibialis anterior of normal adult cats. © 1994 John Wiley & Sons, Inc.