Quantitative ultrastructural differences in the development of normal and dystrophic muscle

Opioid receptors in skeletal muscle of normal and dystrophic mice

Autoradiography was used to investigate the presence of opioid receptors in soleus, extensor digitorum longus (EDL) and diaphragm muscles in two strains (C57BL/6J and C57BL/10) of mice which can inherit muscular dystrophy. Binding sites for two radiolabelled opioid ligands [125I]beta-endorphin and [3H]naloxone, were seen in a few muscle fibres in the normal mice. However, a significantly greater number of fibres exhibited the binding sites in the dystrophic individuals of both strains. The binding sites were not restricted to the endplate regions but were present over the entire surface in these fibres.

Altered contents of tocopherols in chickens with inherited muscular dystrophy

Oxidative damage has been hypothesized as the basis for some of the changes in enzymatic functions and physical properties of membranes in inherited muscular dystrophy. The contents of alpha- and gamma-tocopherol (vitamin E) and their oxidation products, the tocopheryl quinones, were measured at 1 to 4 weeks after hatching in the muscle and other tissues of chickens with inherited muscular dystrophy. Analyses at these early ages minimized the potential influence of pathological changes on the measured parameters. The affected muscle (pectoralis major) of dystrophic birds contained significantly higher levels of alpha-tocopheryl quinone and a decreased ratio of alpha- to gamma-tocopherol. Consistent changes in these parameters were not observed in other tissues. Although their basis remains unclear, these changes in the tocopherols are suggestive of oxidative stress in dystrophic muscle membranes. Lipid extracts of tissues of normal and dystrophic birds exhibited no significant differences in the content of conjugated dienes or lipofuscins, two other indices of oxidative stress. These data do not consistently support the hypothesis that oxidative stress plays a causal role in damage to dystrophic muscle, although it remains possible that free-radical damage is involved in the secondary alterations associated with muscular dystrophy.

Effect of nerve section on beta-endorphin and alpha-melanotropin immunoreactivity in motor nerves of normal and dystrophic mice

beta-Endorphin and alpha-melanotropin immunoreactivity was demonstrated in some motor nerves in histological sections of soleus and extensor digitorum longus muscles of the mouse. In two strains (C57BL/6J and 129/ReJ) which can inherit muscular dystrophy, the proportion of immunoreactive nerves was greater in the dystrophic individuals than in their healthy littermates. At 24 h after section of the sciatic nerve in the normal mice the proportion of immunoreactive nerve profiles had increased significantly in the denervated muscles even though most of the nerve axons had degenerated. Similar increases were also seen in nerves in the unoperated contralateral muscles.

Electron microscopic and autoradiographic characterization of hindlimb muscle regeneration in the mdx mouse

The pattern of postnatal growth and development of skeletal muscle in mdx mice was studied by light and transmission electron microscopy and by autoradiography and was compared with that in their normal age-matched controls at 4 and 32 weeks of age. The muscle weights of both the extensor digitorum longus (EDL) and soleus muscles of mdx mice were significantly greater than those in control mice at both ages. Body weights of male and female mdx mice were also increased over controls up to 12 weeks of age. At 4 weeks, both the EDL and soleus muscles exhibited focal areas of degeneration, necrosis, and regeneration of centrally nucleated extrafusal fibers resulting in a wide range of fiber sizes. By 32 weeks, the majority of fibers in both muscles were centrally nucleated, and focal areas of recent regeneration were observed. By electron microscopy, the course of macrophage infiltration into areas of degenerating fibers and the ongoing regeneration of myofibers within redundant cylinders of external lamina were noted. This pattern was frequent in 4-week-old mdx muscles and was present to a lesser degree at 32 weeks. A notable lack of both adipose tissue infiltration and fibrotic change in the endomysium were observed in muscles at both ages. Autoradiograms of muscles from 4-week-old mdx mice injected with tritiated thymidine showed an increased proportion of labeled sublaminal nuclei at 24 and 48 hours after injection compared to controls. At 32 weeks of age, labeling of nuclei in muscles of mdx mice was also greater than in controls, but was reduced compared to muscle labeling in 4-week-old mdx mice. The observed features of mdx muscle tissue suggest that this animal model is more applicable to the study of regeneration dynamics than to Duchenne-type human muscular dystrophy.

Impaired muscle-nerve interaction (motility) characterizes the brachial region of dystrophic embryos

During development ex ovo, the avian mutant with an hereditary form of muscular dystrophy demonstrates biochemical, histochemical, and physiological (functional) abnormalities which may result from impaired muscle-nerve interaction. To investigate if impaired functional activity also characterizes the dystrophic process during development in ovo, limb motility, an index of embryonic functional muscle-nerve interaction, was compared between normal and dystrophic embryos from day 6E through day 16E. A highly significant reduction in this parameter was exhibited by dystrophic wings from day 11E to day 14E inclusive. In contrast, genotypically dystrophic hind limbs demonstrated values equivalent to normal legs. Thus, in the dystrophic embryo, impaired muscle-nerve interaction characterized the brachial region exclusively during a specific period of embryogenesis.

Presence of immunoreactive alpha-melanotropin and beta-endorphin in spinal motoneurones of the dystrophic mouse

Two derivatives of the stem hormone opiomelanocortin, alpha-melanotropin (alpha-MSH) and beta-endorphin, were detected immunocytochemically in the cell bodies and in the peripheral axon terminals of spinal motoneurones in immature but not in adult healthy mice. Immunoreactivity was demonstrated in motoneurones in both immature and adult mice with inherited muscular dystrophy. These results provide evidence for a motoneurone abnormality in murine dystrophy. The observations are discussed in the light of trophic influences over neuromuscular transmission which have been attributed to this family of neuropeptides.