Sex influences diaphragm muscle response in exercised mdx mice.

Physical exercise promotes increased muscle damage in the mdx mice, the experimental model of Duchenne muscular dystrophy. Studies suggest that the estrogen level in females makes them less susceptible to muscle injuries. The aim of this study was to characterize the diaphragm (DIA) muscle response to physical exercise in male and female mdx mice. The animals were divided into four groups: female sedentary mdx; male sedentary mdx; female mdx submitted to exercise; and male mdx mice submitted to exercise. Blood samples were used to determine creatine kinase (CK). Regenerated muscle fibers were indicated by the presence of central nucleus and also inflammation areas were determined in DIA muscle sections. The alpha and beta estrogen receptors (ER) were determined by means of immunohistochemistry evaluation in the dystrophic DIA muscle. Male mdx animals submitted to exercise showed increased CK levels and inflammatory area. The quantification of regenerated fibers was higher in male animals, submitted or not to physical exercise. Greater alpha and beta ER expression was verified in the females submitted to exercise in the DIA muscle than in the other experimental groups. Therefore, estrogen may have contributed to the prevention of increased inflammatory process and DIA injury in females submitted to exercise.

Muscle and nerve responses after different intervals of electrical stimulation sessions on denervated rat muscle.

OBJECTIVE: Electrical stimulation is a procedure used to treat denervated muscles. The number of electrical stimulation sessions varies across muscle rehabilitation protocols, from daily to certain days throughout the week. The purpose of this study was to evaluate how muscle and nerve respond to different intervals of electrical stimulation applied to denervated muscle. DESIGN: Denervation of rat gastrocnemius muscle was imposed via nerve crush, and electrical stimulation was applied to the muscle either daily (Monday through Friday) or on alternate days (Monday, Wednesday, and Friday). Four experimental groups were studied: denervated, denervated plus daily electrical stimulation, denervated plus alternate-day electrical stimulation, and control. RESULTS: On the 12th day after nerve crush, levels of MyoD, myostatin, and atrogin-1 gene expression, as well as muscle fiber and nerve morphometry, were evaluated. Expression levels of all three genes were higher in the denervated group when compared with control. Also, expression levels of MyoD and myostatin were higher in denervated plus alternate-day electrical stimulation and denervated plus daily electrical stimulation groups when compared with denervated. The denervated plus daily electrical stimulation group had lower atrogin-1 expression, lower density of intramuscular connective tissue, and better morphometric nerve characteristics when compared with the denervated and denervated plus alternate-day electrical stimulation. CONCLUSIONS: These results indicate that the responses of both muscle and nerve to electrical stimulation after muscle denervation depend on the intervals of electrical stimulation application.

Primary nerve repair by muscle autografts prepared with local anesthetic.

We evaluated the usefulness of muscle autografts obtained immediately after graft preparation with lidocaine injections for primary nerve repair. The right sciatic nerve of adult Wistar rats was sectioned, and muscle grafts obtained 15 min or 24 h after lidocaine injection were used to repair a gap 1.5 cm long. Axon and fiber diameters, as well as myelin thickness, decreased to similar extents for grafts of both time intervals. The G-ratios in the distal stumps of both groups were not different from controls, indicating that regenerated axons had a proper level of myelination. The ultrastructural appearance of the neuromuscular junctions was similar to that of normal samples. These results indicate that there are no restrictions to the use of a muscle graft for primary nerve repair, immediately after lidocaine injection, since the nerve regeneration was comparable to that observed with this type of graft used 24 h after being prepared.