Abstract
The purpose of this study was to investigate changes after denervation in rats diaphragm. Old (2-year, n = 16) and young (10-week, n = 16) male Wistar rats were used. The unilateral diaphragms of eight rats in each age group was denervated by cutting the phrenic nerve at the cervical level, and sham operation was performed on the other eight in each. The undenervated side diaphragms of old and young sham rats were studied to investigate the age-related changes. Four weeks after the denervation, isometric contraction properties, fiber type composition, and expression of myosin heavy chain (MHC) isoforms in all groups were observed. The changes caused by denervation were observed in each age group. The difference of the changes was compared between old and young groups. After the denervation, in the young rats, the area of slow oxidative (SO) fibers were not significantly different from those of the same age sham group. Further fast-twitch oxidative glycolytic (FOG) fibers were significantly larger than those of the same age sham group. On the contrary, in the old rats, the area of SO fibers and FOG fibers were significantly smaller than those of the sham group. The changes caused by denervation were different depending upon the case of the young rats and that of the old rats. The characteristics of slower muscles in the diaphragm of young rats after the denervation were considered to be due to the effect of the stretch stimuli caused by the respiratory contraction of the contralateral diaphragm.
