[Ultrastructural changes after denervation of different muscles].
OBJECTIVE
To observe the ultrastructural changes and number of satellite cells in different muscles with different denervation interval and investigate the mechanism of denervation atrophy.


METHODS
Muscles of different denervation interval were harvested, which were 6 biceps brachii and 6 abductor digiti minimi. The ultrastructure of the samples were observed under transmission electron microscope. The number of nucleus and satellite cells were counted to calculate the percentage content of satellite cells.


RESULTS
In early stage of denervation, the myofilament and sarcomere of the majority were well oriented. The nucleoli of some muscle cell nucleus were enlarged and pale. Vacuolarization was also seen in some mitochondria. There was no obvious proliferation of collagen fiber around myofibers. After denervation of half a year, rupture and disorientation of myofilament was seen. The nucleus became smaller, dark stained, and some of them were condensed. There was proliferation of fibroblasts, adipose cells and collagen fibers around myofibers. Motor endplate was not recognized one year after denervation. In the early stage of denervation, satellite cell percentage of the two muscles was relatively high. It then declined with time. One year after denervation, satellite cells were scarcely detected. Comparison of the curves for satellite cell declination in two muscles revealed that the declination of the abductor digiti minimi was faster than that of biceps brachii. Decrease of the former started 3 months after denervation, while the latter started after 6 months.


CONCLUSIONS
Disappearing of motor endplate and proliferation of collagen fibers are main factors that affect the treatment outcome in late cases. Decrease of satellite cell number is another cause. The correlation of less satellite cell in abductor digiti minimi and poorer recovery of hand intrinsic muscles indicates that increment of satellite cells in long-term denervated muscles may be one of the effective measures to improve treatment outcome.
Hu
Shao-nan
SN
Department of Hand Surgery, Huashan Hospital, Fudan University, Shanghai, P. R. China 200040.
Xu
Jian-guang
JG
Gu
Yu-dong
YD
Li
Ji-feng
JF
D001917:Brachial Plexus / Q000293:injuries*; D002452:Cell Count; D006801:Humans; D066298:In Vitro Techniques; D009121:Muscle Denervation; D009133:Muscular Atrophy / Q000209:etiology / Q000473:pathology*; D032496:Satellite Cells, Skeletal Muscle / Q000648:ultrastructure*