Effects of Increased Activity on Neuromuscular Junction in Aged Rat Diaphragms

概要

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To examine the age-related functional and morphological changes in neuromuscular junction, male adult rats were divided into young (3-month; n=14), adult (1-year; n=14) and old (2-year; n=14) groups. Seven rats in each group were subjected to unilateral phrenicotomy to induce compensatory increased activity on intact hemidiaphragm. Neuromuscular transmission failure (NF) after 2min repetitive contraction was evaluated by a comparison of forces generated by the phrenic nerve and muscle stimulations. The endplate area was analyzed by immunohistochemical staining procedure and confocal imaging. The relative NF to muscle fatigue was significantly lower in the old group than the young and adult groups, indicating a functional improvement of neuromuscular transmission with aging. The compensatory activated diaphragm indicated significantly larger endplate area and lower transmission failure than those in age-matched control groups in the young and adult groups, but not in the old group. These results indicated that functional and morphological plasticity of the neuromuscular junction decreased in old diaphragm muscle.