Quantitative study of the effects of long‐term denervation on the extensor digitorum longus muscle of the rat

Abstract

Background: In order to understand the cellular basis underlying the progressively poorer restorative capacity of long-term denervated muscle, we determined the effects of long-term denervation on the muscle fibers and satellite cell population of the rat extensor digitorum longus (EDL) muscle.Methods: In 36 male rats, the right hind legs were denervated, and EDL muscles were removed 2, 4, 7, 12, and 18 months later. Muscles were either fixed for electron microscopic analysis or were dissociated into individual muscle fibers for direct fiber counting or for confocal microscopic analysis.Results: The percentage of satellite cells rose from the 2.8% control value to 9.1% at 2 months of denervation; thereafter the percentage decreased to 1.1% at 18 months of denervation. The number of myonuclei per muscle fiber steadily declined from 410 in 4 month control muscle to 158 in 7 month denervated muscle. Up to 7 months of denervation, the total number of muscle fibers per muscle remained relatively constant at somewhat over 5,000. The calculated total satellite cell population in 4 month denervated EDL muscle was the same as that of controls at 65,000, but by 7 months of denervation it had declined to 21,000. With increasing time of denervation, the number of cross-sectional profiles of muscle fibers not containing nuclei rose from 14% in control muscle to 49% in 12 month denervated muscle. This was correlated with a pronounced regular clumping of the nuclei, with pronounced nonnucleated segments between nuclear clumps.Conclusions: Increasing times of denervation are accompanied by a pronounced decline in the number of myonuclei per muscle fiber and an initial rise and subsequent fall in satellite cell number. These changes are correlated with a decreasing restorative ability of these muscles over the same periods of denervation. Further work on the proliferative capacity of the remaining satellite cells is necessary before firm quantitative conclusions can be made. Anat. Rec. 248:346-354 1997. r 1997 Wiley-Liss, Inc.

A Regenerative Change during Muscle Adaptation to Denervation in Rats

“…A recent electromicroscopic study revealed that the number of satellite cells rose 2 months after denervation, and subsequently declined with time [24]. In the present study, activated or proliferating satellite cells were detected following denervation with immunohistochemistry for embryonic MHC, MyoD and BrdU, although the activation and proliferation of satellite cells were much less prominent than those during muscle regeneration after necrosis.…”

Testosterone mediates satellite cell activation in denervated rat levator ani muscle

“…The value obtained also exceeded that of muscles from normal (innervated and gonad-intact) as well as denervated and gonad-intact rats (Nnodim, 1999). This level of nuclear enrichment in the Venable (1966) and Viguie et al, (1997). Value given as mean Ϯ standard error of three muscles.…”

“…Table 3 also shows the derivation of whole-muscle satellite cell content from total nuclear and satellite cell frequency data, assuming a stable myofiber population (Venable, 1966;Viguie et al, 1997). The satellite cell number computed for the muscle of hormone-replaced rats (Group B) was approximately an order of magnitude greater than that of the castrated rats in Group A (408.4 ϫ 10 3 vs. 38.08 ϫ 10 3 ).…”

Effects of aging and gender on the spatial organization of nuclei in single human skeletal muscle cells

“…The exact mechanisms regulating the positioning of myonuclei in muscle fibres remain unknown; however, there are several candidates: microtubuli, the intermediate filament desmin, as well as blood vessels have all been shown to be involved in the localization and ⁄ or anchoring of nuclei in muscle fibres (Bruusgaard et al, 2006;Ralston et al, 2006). Aggregation of myonuclei has been reported in response to long-term denervation (Viguie et al, 1997) and the ongoing denervation-reinnervation process in aging skeletal muscle (Larsson & Ansved, 1995) may accordingly play an important role for the aggregation of myonuclei observed in the old men and women in this study. However, a significantly increased variability in nearest distances was only observed in muscle fibres expressing the type I MyHC isoform and the aging-related denervation process is not restricted to slow-twitch motor units according to experimental studies (Larsson & Ansved, 1995).…”