Objective: Volumetric muscle loss results in intramuscular axotomy, denervating muscle distal to the injury and leading to paralysis, denervation, and loss of muscle function. Once the nerve is damaged, paralyzed skeletal muscle will atrophy and accumulate noncontractile connective tissue. The objective of this study was to determine differences in connective tissue, atrophy, and inflammatory signaling between two paralysis models, botulinum toxin (Botox), which blocks acetylcholine transmission while keeping nerves intact, and neurectomy, which eliminates all nerve-to-muscle signaling. Approach: Twenty male Sprague Dawley rats were randomized and received a sciatic-femoral neurectomy (SFN), Botox-induced muscle paralysis of the proximal femur muscles, quadriceps femoris, hamstrings, and calf muscles (BTX), or sham. Muscle force was measured 52 days postsurgery, and samples were collected for histology, protein, and mRNA assays. Results: SFN and BTX decreased twitch and tetanic force, decreased fiber size by twofold, and increased myogenic expression compared with controls. SFN increased the levels of all major extracellular matrix proteins correlating with fibrosis [e.g., laminin, fibronectin, and collagen type(s) I, III, VI]. SFN also increased profibrotic and proinflammatory mRNA compared with BTX and controls. Innovation: SFN and BTX were similar in gross morphology and functional deficiencies. However, SFN exhibited a higher amount of fibrosis in histological sections and immunoblotting. The present study shows evidence that nerve signaling changes NF-κB and TGF-β signaling, warranting future studies to determine the mechanisms involved. Conclusion: These data indicate that nerve signaling may influence fibrogenesis following denervation, but the mechanisms involved may differ as a function of the method of paralysis.
Keywords: Botox; atrophy; fibrosis; muscle paralysis; neuromuscular junction.