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Mol Pain. 2019 Jan-Dec;15:1744806919838191. doi: 10.1177/1744806919838191.

Characterization of neuromas in peripheral nerves and their effects on heterotopic bone formation.

Author information

1
1 Center for Cell and Gene Therapy, Baylor College of Medicine, Texas Children's Hospital and Houston Methodist Hospital, Houston, TX, USA.
2
2 Department of Orthopedic Surgery and Rehabilitation, University of Texas Medical Branch, Galveston, TX, USA.
3
3 Department of Pediatrics - Section Hematology/Oncology, Baylor College of Medicine, Houston, TX, USA.
4
4 Department of Orthopedic Surgery, Baylor College of Medicine, Houston, TX, USA.

Abstract

The formation of neuromas involves expansion of the cellular components of peripheral nerves. The onset of these disorganized tumors involves activation of sensory nerves and neuroinflammation. Particularly problematic in neuroma is arborization of axons leading to extreme, neuropathic pain. The most common sites for neuroma are the ends of transected nerves following injury; however, this rodent model does not reliably result in neuroma formation. In this study, we established a rodent model of neuroma in which the sciatic nerve was loosely ligated with two chromic gut sutures. This model formed neuromas reliably (∼95%), presumably through activation of the neural inflammatory cascade. Resulting neuromas had a disorganized structure and a significant number of replicating cells. Quantification of changes in perineurial and Schwann cells showed a significant increase in these populations. Immunohistochemical analysis showed the presence of β-tubulin 3 in the rapidly expanding nerve and a decrease in neurofilament heavy chain compared to the normal nerve, suggesting the axons forming a disorganized structure. Measurement of the permeability of the blood-nerve barrier shows that it opened almost immediately and remained open as long as 10 days. Studies using an antagonist of the β3-adrenergic receptor (L-748,337) or cromolyn showed a significant reduction in tumor size and cell expansion as determined by flow cytometry, with an improvement in the animal's gait detected using a Catwalk system. Previous studies in our laboratory have shown that heterotopic ossification is also a result of the activation of neuroinflammation. Since heterotopic ossification and neuroma often occur together in amputees, they were induced in the same limbs of the study animals. More heterotopic bone was formed in animals with neuromas as compared to those without. These data collectively suggest that perturbation of early neuroinflammation with compounds such as L-748,337 and cromolyn may reduce formation of neuromas.

KEYWORDS:

Neuroma; heterotopic ossification; nerve injury; neuroinflammation; peripheral nerve injury

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