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Volumetric Muscle Loss Injury: Temporal Impact on the Neuromuscular Junction
Author(s) -
Sorensen Jacob R.,
Johnson Trevor K.,
Hoffman Daniel B.,
Vasdev Amrit K.,
Corona Benjamin T.,
Greising Sarah M.
Publication year - 2020
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.2020.34.s1.05977
Subject(s) - axotomy , neuromuscular junction , medicine , skeletal muscle , tibialis anterior muscle , myocyte , nerve injury , peripheral nerve injury , anatomy , peripheral nerve , neuroscience , anesthesia , biology , central nervous system
Volumetric muscle loss (VML) is the traumatic loss of muscle tissue that results in reduced regenerative capacity and long‐term functional deficits. In fact, in comparison to the mass of muscle removed from the VML injury, the functional deficits observed are disproportionally greater. Clinically, it is estimated that nearly 30% of VML injured patients are further impacted by some ongoing degree of peripheral nerve damage in the injured limb. These findings suggest that VML injury has a significant impact on the neuromuscular system that extends beyond the defect area. This is further supported by our recent finding that VML injury results in chronic motor neuron axotomy of ~75% through 21 days post‐VML; however, how this impacts individual muscle fibers is not yet clear. As such, the purpose of this study was to systematically quantify the neuromuscular junctions (NMJs) surrounding the VML injury site. We hypothesized that VML injury would result in a reduced NMJ area, altered innervation and an irregular morphology that ultimately impairs skeletal muscle function. A standard VML surgery was performed by removing approximately 20% of the middle third of the tibialis anterior (TA) muscle in adult male inbred Lewis rats (n=32). Full thickness injuries were performed unilaterally so that the non‐injured leg served as an intra‐animal control. The TA muscles were harvested at 0, 3, 7, 14, 21, and 48 days post injury and ~50 individual NMJs per muscle were evaluated. Pre‐ and post‐synaptic were identified immunohistochemically and quantitative confocal microscopy was used to evaluate 2‐ and 3‐D synaptic area, fiber denervation and morphologic characteristics. As expected, the mass of the TA muscle was 20–30% of the contralateral over the 48 days post‐VML; which is supported by an ~40% loss in contractile protein content over this same period. The muscle remaining after VML indicates a significant number of denervated (reduced overlap of pre‐ and post‐synaptic structures) NMJs after injury. Additionally, substantial changes in the NMJ morphological characteristics were identified in the muscle remaining after VML. Specifically, poly‐innervation and sprouting of individual NMJs, which suggest that motor unit reorganization may be occurring after VML injury. While the most obvious consequence of VML injury is the loss of contractile protein content and muscle fibers, the disorientate changes at both the motor neuron and NMJ may exacerbate the decline in muscle function following VML injury. This work is foundational to support future work to identify interventions to support maintenance of NMJ innervation following VML injury. Support or Funding Information Supported by W81XWH‐19‐1‐0075.