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Activity‐dependent influences are greater for fibers in rat medial gastrocnemius than tibialis anterior muscle
Author(s) -
Roy Roland R.,
Zhong Hui,
Siengthai Boonclaire,
Edgerton V. Reggie
Publication year - 2005
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.20369
Subject(s) - myosin , anatomy , muscle atrophy , atrophy , gastrocnemius muscle , chemistry , tibialis anterior muscle , skeletal muscle fibers , skeletal muscle , fiber type , neuromuscular junction , muscle fibre , fiber , spinal cord , endocrinology , biology , medicine , neuroscience , biochemistry , organic chemistry
Skeletal muscles are highly adaptive to changes in loading or activation. A model of neuromuscular inactivity (spinal cord isolation, SI) was used to determine the role of activity‐independent and ‐dependent neural influences on the size and myonuclei number in type‐identified fibers of a fast extensor (medial gastrocnemius, MG) and flexor (tibialis anterior, TA) rat muscle. Fibers were categorized based on myosin heavy chain isoform composition. Four days after SI, all fiber types tended to atrophy and lose myonuclei, with the percent loss of myonuclei being disproportionately less than the decrease in fiber size. At 60 days after SI, all fiber types in MG and the fastest fibers in TA were significantly smaller and had fewer myonuclei than control. The disproportionate amount of atrophy resulted in a smaller myonuclear domain. These effects were greater in MG than TA, indicating that activity‐dependent influences were greater in the extensor than flexor. The smaller myonuclear domains after a period of chronic inactivity suggest the presence of intrinsic mechanisms operating to maintain the genetic material necessary to recover from atrophic conditions. Muscle Nerve, 2005