Study of neurotrophism in normal/dystrophic parabiotic mice

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.

Sciatic nerve protein composition in normal and dystrophic C57BL/6J mice

Proteins were extracted from homogenized sciatic nerves of normal C57BL/6J and dystrophic C57BL/6J dy2J/dy2J mice and were separated on SDS-polyacrylamide slab gel electrophoresis. Proteins visualized on Coomassie blue-stained gels were resolved into 43 bands. These were quantitated by densitometric scanning and continuous plotting of OD 595, then heights and areas of individual peaks were measured. The relative proportions of 5 proteins of intermediate molecular weight (37-92 kDa) were greater in dystrophic than normal nerves. These augmented proteins were not related to myelin or nuclear histone proteins.