The autotomy relief effect of a silicone tube covering the proximal nerve stump

Abstract

A technique of covering the proximal nerve stump (PNS) has been reported as a preventative method or treatment for neuroma. However, its detailed pain relief mechanism remains unknown. We created a silicone tube model in which the PNS of the rat sciatic nerve was introduced into the tube, whereas the controls had no tube. The score of autotomy observed in the tube group was lower than that in the control group at 3 days to 2 weeks after surgery, which suggested that the silicone tube had pain-like behavior inhibitory action. To elucidate the mechanism of autotomy inhibition, immunohistochemistry and Toluidine blue staining were performed in the PNS. The increase in S-100-immunoreactivity (IR) including Schwann cells was inhibited at 1 week after surgery in the tube group, and the increase in the number of macrophages shown by ED-1-IR at 1, 2, and 4 weeks after surgery was similarly inhibited. Toluidine blue staining showed that the increase in the number of mast cells was inhibited at 1, 2, and 4 weeks after surgery and in the number of lymphocytes at 1 and 2 weeks after surgery in the tube group. Therefore, blocking of the infiltration of inflammatory cells into the PNS by the silicone tube was thought to be the mechanism of autotomy inhibition. To further explore details of this mechanism, the expression of nerve growth factor (NGF), production of which is induced by inflammatory cells and of the NGF receptor TrkA was examined in the PNS and the dorsal root ganglion using immunohistochemistry and a ribonuclease protection assay. In the PNS, the increase in NGF-IR was inhibited at 1, 2, and 4 weeks after surgery in the tube group, suggesting that this could be one of the pain-like behavior inhibitory effects. ß

Reduction of post‐traumatic neuroma and epineural scar formation in rat sciatic nerve by application of microcrystallic chitosan

“…However, the exact role of mast cells in nerve regeneration is still controversial. Okuda et al34 attributed the decrease of neuropathic pain to reduction in mast cells accumulation in regenerating nerves. This is in opposition to other researches who found that mast cells accumulation during neural elongation not only does not elicit any pain symptoms but even stimulates the nerve regeneration 26, 35, 36…”

“…However, the onset of autotomy as well as average autotomy index in both groups did not differ significantly. We believe that inflammatory cells derived cytokines, such as tumor necrosis factor‐b (TNF‐β) or transforming growth factor‐b1 (TGF‐β1), may play a role in the generation of neuropathic pain in the chitosan group, despite absence of neuromas 3, 34…”

A systematic review of animal models for experimental neuroma

“…Morphological analysis is the most commonly used method, usually performed in light, 18,22,24,26,27,29,45,46,32,34,50,36,38,43,44,49,19,20,47,39,49 electron, 10,30,32,50,36,40 fluorescence 19,37,38,40 or confocal laser microscopy. 20,43,44 Data on the level where biopsies of the nerve and the neuroma are taken and analysed are heterogeneous and often missing, preventing appropriate comparison of results: Chim et al 16 Haematoxylin and eosin 16,18e20,36,50,37,40,49 and toluidine blue 10,18,22,32,45,46,24,19,25,27,30,38,43,…”

“…20,43,44 Data on the level where biopsies of the nerve and the neuroma are taken and analysed are heterogeneous and often missing, preventing appropriate comparison of results: Chim et al 16 Haematoxylin and eosin 16,18e20,36,50,37,40,49 and toluidine blue 10,18,22,32,45,46,24,19,25,27,30,38,43,44 are the most commonly used stains; some studies also use Masson's thricome, 10,20,37 which also allows the labelling of the connective tissue. 70 This is sometimes combined with immunolabelling, the most common targets being S100 protein, 16,25e27,43 neurofilament 200 (NF200), 10,25,30,37,38 neuronal growthassociated protein (GAP)-43, 20,24,43,44 macrophages (ED-1), 20,27,28,43 nerve growth factor (NGF) 27 and calcitonin gene-related peptide (CGRP). 24,28,30 Double staining has also been reported to identify axons of different origin.…”

“…To date, the most popular model for terminal neuroma continues to be sciatic nerve neurotmesis in the rat, 10,19,20,24,25,27,29,30,32,34,35,38 but recently, a number of alternative models have been developed, which focus on the investigation of specific aspects of peripheral neuromas.…”