Chronic Nerve Compression Injury Research Articles

Frankincense-Myrrh treatment alleviates neuropathic pain via the inhibition of neuroglia activation mediated by the TLR4/MyD88 pathway and TRPV1 signaling

BackgroundNeuroglia are important modulators of neuronal functionality, and thus play an integral role in the pathogenesis and treatment of neuropathic pain (NP). According to traditional Chinese medicine, Frankincense-Myrrh is capable of "activating blood and dissipating blood stasis", and as such these two biological compounds are commonly used to treat NP, however, the mechanisms underlying the efficacy of such treatment are unclear. PurposeThis study aimed to further elucidate the protective effects associated with the Frankincense-Myrrh treatment of NP. MethodsA chronic sciatic nerve compression injury (CCI) model of NP was established, after which animals were gavaged with Frankincense, Myrrh, Frankincense-Myrrh, or the positive control drug pregabalin for 14 days. Network pharmacology approaches were used to identify putative pathways and targets associated with the Frankincense-Myrrh-mediated treatment of NP, after which these targets were subjected to in-depth analyses. The impact of TLR4 blockade on NP pathogenesis was assessed by intrathecally administering a TLR4 antagonist (LRU) or the MyD88 homodimerization inhibitory peptide (MIP). ResultsSignificant alleviation of thermal and mechanical hypersensitivity in response to Frankincense and Myrrh treatment was observed in NP model mice, while network pharmacology analyses suggested that the pathogenesis of NP may be related to TLR4/MyD88-mediated neuroinflammation. Consistently, Frankincense-Myrrh treatment was found to reduce TLR4, MyD88, and p-p65 expression in spinal dorsal horn neuroglia from treated animals, in addition to inhibiting neuronal TRPV1 and inflammatory factor expression. Intrathecal LRU and MIP delivery were sufficient to alleviate thermal and mechanical hyperalgesia in these CCI model mice, with concomitant reductions in neuronal TRPV1 expression and neuroglial activation in the spinal dorsal horn. ConclusionThese data suggest that Frankincense-Myrrh treatment was sufficient to alleviate NP in part via inhibiting TLR4/MyD88 pathway and TRPV1 signaling activity. Blocking TLR4 and MyD88 activation may thus hold value as a means of treating NP.

Nerve decompression surgery suppresses TNF-ɑ expression and T cell infiltration in a rat sciatic nerve chronic constriction injury model.

Decompression surgery (DS) is a standard treatment for chronic nerve compression injuries; however, the mechanisms underlying its effects remain unclear. Here, we investigated the effects of DS on messenger RNA (mRNA) expression of tumor necrosis factor-α (TNF-α) and T cell recruitment in a rat sciatic nerve (SN) chronic constriction injury (CCI) model. Male Wistar rats were subjected to CCI to establish a model of SN injury (CCI group). DS, in which all ligatures were removed, was performed 3 days after CCI surgery (CCI + dec group). Mechanical sensitivity was assessed using the von Frey test 3, 7, and 14 days after the CCI surgery. Gene expression of Tnfa, Cd3, Cxcl10, and immunolocalization of TNF-α and the pan T cell marker, CD3, was evaluated using quantitative polymerase chain reaction (qPCR) and immunohistochemistry, respectively. In addition, the effects of TNF-α on Cxcl10 expression and CXCL10 protein production were evaluated using qPCR and enzyme-linked immunosorbent assay in SN cell culture. Rats that received DS had significantly higher withdrawal threshold levels than those in the CCI group. In addition, Tnfa, Cd3, and Cxcl10 mRNA expression increased following CCI. DS suppressed this elevated expression, with the CCI + dec group showing significantly reduced expression levels compared to the CCI group. Furthermore, TNF-α induced Cxcl10 expression and CXCL10 protein production in SN cell culture. Therefore, DS reduced TNF-α expression and T cell recruitment in the rat SN CCI model. These observations may partly explain the mechanism underlying the therapeutic effects of DS.

Systematic investigation and comparison of US FDA-approved immunosuppressive drugs FK506, cyclosporine and rapamycin for neuromuscular regeneration following chronic nerve compression injury.

Aim: To compare therapeutic benefits of different immunophilin ligands for treating nerve injuries. Materials & methods: Cyclosporine, FK506 and rapamycin, were evaluated first in vitro on a serum-free culture of embryonic dorsal root gangliafollowed by a new in vivo model of chronic nerve compression. Results: Outcomes of the in vitro study have shown a potent effect of cyclosporine and FK506, on dorsal root ganglia axonal outgrowth, comparable to the effect of nerve growth factor. Rapamycin exhibited only amoderate effect. The in vivo study revealed the beneficial effects of cyclosporine, FK506 and rapamycin for neuromuscular regeneration. Cyclosporine showed the better maintenance of the tissues and function. Conclusion: Cyclosporine, FK506 and rapamycin drugs showed potential for treating peripheral nerve chronic compression injuries.

A novel chronic nerve compression model in the rat.

Current animal models of chronic peripheral nerve compression are mainly silicone tube models. However, the cross section of the rat sciatic nerve is not a perfect circle, and there are differences in the diameter of the sciatic nerve due to individual differences. The use of a silicone tube with a uniform internal diameter may not provide a reliable and consistent model. We have established a chronic sciatic nerve compression model that can induce demyelination of the sciatic nerve and lead to atrophy of skeletal muscle. In 3-week-old pups and adult rats, the sciatic nerve of the right hind limb was exposed, and a piece of surgical latex glove was gently placed under the nerve. N-butyl-cyanoacrylate was then placed over the nerve, and after it had set, another piece of glove latex was placed on top of the target area and allowed to adhere to the first piece to form a sandwich-like complex. Thus, a chronic sciatic nerve compression model was produced. Control pups with latex or N-butyl-cyanoacrylate were also prepared. Functional changes to nerves were assessed using the hot plate test and electromyography. Immunofluorescence and electron microscopy analyses of the nerves were performed to quantify the degree of neuropathological change. Masson staining was conducted to assess the degree of fibrosis in the gastrocnemius and intrinsic paw muscles. The pup group rats subjected to nerve compression displayed thermal hypoesthesia and a gradual decrease in nerve conduction velocity at 2 weeks after surgery. Neuropathological studies demonstrated that the model caused nerve demyelination and axonal irregularities and triggered collagen deposition in the epineurium and perineurium of the affected nerve at 8 weeks after surgery. The degree of fibrosis in the gastrocnemius and intrinsic paw muscles was significantly increased at 20 weeks after surgery. In conclusion, our novel model can reproduce the functional and histological changes of chronic nerve compression injury that occurs in humans and it will be a useful new tool for investigating the mechanisms underlying chronic nerve compression.

Attenuation of Robust Glial Scar Formation Facilitates Functional Recovery in Animal Models of Chronic Nerve Compression Injury.

Late surgery for chronic nerve compression injuries usually improves sensation but rarely reverses motor atrophy. We hypothesized that a persistent glial scar after chronic nerve compression injury might account for poor motor recovery and that degradation of the glial scar as an adjunct to surgical decompression would improve functional recovery. A previously described model of chronic nerve compression injury was created in C57BL/6 mice and Sprague-Dawley rats, and the nerves were harvested early or late after electrophysiological confirmation of the injury. Western blot, polymerase chain reaction, and quantitative immunohistochemical analyses were performed to determine levels of chondroitin sulfate proteoglycans and extracellular matrix molecules. Subsets of mice were treated either with surgical decompression alone or with decompression coupled with intraepineurial injection of a low dose (0.1 μgμL) or a high dose (0.2 μg/μL) of chondroitinase ABC at 6 weeks after injury. Aggrecan showed the greatest change in mRNA and protein levels at the early and late time points following creation of the chronic nerve compression injury. Quantitative immunohistochemical analysis revealed early aggrecan upregulation localized primarily to the endoneurium and late upregulation localized to the perineurium and epineurium (p < 0.0105). Quantitative immunohistochemical analysis for collagen IV, laminin-α2, and fibronectin also showed early upregulation with perineurial scarring. Quantitative immunohistochemical analysis and Western blot analysis for aggrecan demonstrated a marked increase in the endoneurium at the early time points and upregulation of expression in the epineurium and perineurium at the late time points. Decompression along with intraepineurial injection of high-dose chondroitinase ABC at 6 weeks after creation of the compression injury resulted in marked attenuation of decorin and aggrecan expression with functional improvement in nerve conduction velocity. Significant upregulation of chondroitin sulfate proteoglycans and other extracellular matrix components contributes to the pathogenesis of compression neuropathies in murine models. The administration of chondroitinase ABC degrades these chondroitin sulfate proteoglycans and improves functional recovery after chronic nerve compression injury; thus, it can be considered as a possible therapeutic adjunct.

Sustained Local Release of NGF from a Chitosan-Sericin Composite Scaffold for Treating Chronic Nerve Compression.

Chronic nerve compression (CNC), a common form of peripheral nerve injury, always leads to chronic peripheral nerve pain and dysfunction. Current available treatments for CNC are ineffective as they usually aim to alleviate symptoms at the acute phase with limited capability toward restoring injured nerve function. New approaches for effective recovery of CNC injury are highly desired. Here we report for the first time a tissue-engineered approach for the repair of CNC. A genipin cross-linked chitosan-sericin 3D scaffold for delivering nerve growth factor (NGF) was designed and fabricated. This scaffold combines the advantages of both chitosan and sericin, such as high porosity, adjustable mechanical properties and swelling ratios, the ability of supporting Schwann cells growth, and improving nerve regeneration. The degradation products of the composite scaffold upregulate the mRNA levels of the genes important for facilitating nerve function recovery, including glial-derived neurotrophic factor (GDNF), early growth response 2 (EGR2), and neural cell adhesion molecule (NCAM) in Schwann cells, while down-regulating two inflammatory genes' mRNA levels in macrophages, tumor necrosis factor alpha (TNF-α), and interleukin-1 beta (IL-1β). Importantly, our tissue-engineered strategy achieves significant nerve functional recovery in a preclinical CNC animal model by decreasing neuralgia, improving nerve conduction velocity (NCV), accelerating microstructure restoration, and attenuating gastrocnemius muscles dystrophy. Together, this work suggests a promising clinical alternative for treating chronic peripheral nerve compression injury.

Erythropoietin is Neuroprotective During Ongoing Compression and Speeds Recovery Following Surgical Decompression in a Murine Model of Chronic Compression Neuropathy: N/A - Not a clinical study

Grant received from: American Foundation for Surgery of the Hand (Hand Surgeon Scientist Award), National Institute of Health grant (# 1 K08 AR060164-01A), Clinical and Translational Science Award (CTSA) grant (# UL1 TR000042), through the University of Rochester School of Medicine & Dentistry, University of Rochester CTSA award (# TL1 TR000096) from the National Center for Advancing Translational Sciences of the National Institutes of Health, University of Rochester Center Goldstein Grant, University of Rochester Laboratory Startup Fund, ART/CTSI Student Research Fellowship Award- salary support for Co-Investigator and medical student, Leigh Sundem There is no financial information to disclose. We previously described erythropoietin’s (EPO) effectiveness in ameliorating the effects of acute peripheral nerve crush. Pilot studies indicate that EPO therapy is an effective neuromodulatory agent for the treatment of chronic nerve compression (CNC) when used as an adjuvant to surgical decompression. This left open the question as to whether pretreatment with EPO during compression would be relevant in reducing the effect of ongoing compression. CNC injury was created in wild-type mice by placing an inert silastic sleeve around the sciatic nerve as in previous work. Decompression surgery was performed at 6 weeks with alternative mice receiving pre-decompressive treatment. Nerve conduction studies were performed weekly before decompression and every 48-hours thereafter until full recovery. Sixty mice were randomized into either a sham-surgery group, saline-treatment control (saline/saline), or 1 of 2 EPO-treatment groups with initiation of EPO at day 0 (EPO/EPO), or week 6 (saline/EPO) in conjunction with surgical decompression. Comparison of NCV was tested with one-way ANOVA followed by Student’s t-test in this dataset, which was normally distributed. During compression, there was a progressive decline in nerve conduction velocity (NCV) as compared to sham-injured animals where NCV remained normal (∼55 m/s) throughout the experiment (Figure 1A). NCV in saline-treated animals progressively decreased from normal (55.153.42 m/s) to a plateau (35.680.72 m/s) over 6 weeks of compression. This expected decline was strikingly attenuated in randomly-selected animals treated with EPO (NCV decreased from 54.091.67 to 45.771.08 m/s, P < 0.01) so that EPO-treated animals fared significantly better than saline-treated counterparts (P < 0.01). Following decompression, all animals recovered to a normal baseline NCV by day 15 (P = 0.74); however, the improvement in NCV observed was markedly accelerated within the first week post-decompression in the EPO-treated groups, and not in saline-treated counterparts (P < 0.01). Animals treated with EPO during both phases fully recovered in half the time as those treated only after decompression (day 5 versus day 9 P < 0.05). •This study supports the possibility of EPO as a neuroprotective agent during CNC injury in rodents and may support adjuvant use during active compression.•Improvement in electrophysiologic parameters is observed with EPO treatment during compression and decompression phases.•EPO may accelerate the natural recovery of decompressed nerves and protect against ongoing injury through the same mechanism, which suggests translational relevance.View Large Image Figure ViewerDownload Hi-res image Download (PPT) This research was supported by a 2013 Hand Surgeon Scientist Award from the American Foundation for Surgery of the Hand.

Chapter 22 - Occupational mononeuropathies in industry

Peripheral nerve injuries have the potential to cause significant disability and can be commonly associated with recreational and occupational activities. Acute nerve injuries are mainly related to violent trauma, while repeated mechanical trauma due to external forces or repetitive motions can produce chronic nerve compression injury. This chapter will present a narrative review of the existing evidence of the association between peripheral compressive nerve disorders and work-related risk factors. Carpal tunnel syndrome (CTS) is the most common peripheral neuropathy in the general population and in working populations employed in manual repetitive and forceful activities. The work-relatedness of CTS is essentially based on epidemiologic evidence and the results of experimental studies showing the capability of repetitive wrist extreme postures, associated with hand-wrist forceful exertions, to increase the pressure inside the carpal tunnel and to compress the median nerve. Assembly industry, food processing and packaging, hand-arm vibrating tools, and jobs involving high-repetition, high-force tasks put workers at risk for CTS. Less strong evidence exists of the association between ulnar elbow neuropathy and manual tasks or repetitive stretch on squatting and peroneal nerve neuropathy at the fibular head. Very few reports are available about the association between occupation and other compressive peripheral nerve injuries.

Early Surgical Decompression Restores Neurovascular Blood Flow and Ischemic Parameters in an in Vivo Animal Model of Nerve Compression Injury.

Chronic nerve compression neuropathies result in decreased blood flow at the site of compression. Surgical decompression of the nerve often has variable postoperative results. The current study examines whether the timing of surgical intervention is an important variable in reversing the compression-induced ischemia and associated changes in biochemical markers. An established model of chronic nerve compression injury was created in 100 C57BL/6 mice, and serial electrophysiological examinations were used to confirm the creation of a chronic nerve compression injury. Laser speckle imaging was used to measure neural blood flow. Nerves in the animals that did not undergo decompression were harvested at two, four, and six weeks after injury and analyzed for hypoxia-inducible factor 1α (HIF1α), catalase, superoxide dismutase (SOD), and matrix metalloproteinases (MMPs) 2 and 9. Surgical decompression in other animals was performed at either an early (two-week) or late (six-week) time point after injury, with specimens harvested at multiple time points after decompression. One-way analysis of variance with Bonferroni correction was performed. Chronic nerve compression injury initially induced hyperemia (1.37 ± 0.50 times that in the contralateral, uninjured nerve) followed by a decline in neural blood flow by four weeks (0.66 ± 0.14, p = 0.0313). In parallel, HIF1α, catalase, and SOD were elevated early after compression, whereas extracellular matrix-altering proteins were elevated later in the disease. Although early decompression yielded a return of blood flow to a hyperemic state (1.35 ± 0.16, p = 0.0057), late decompression did not result in reversal of the abnormal neurovascular flow. With late decompression, an MMP9-mediated structural alteration of the extracellular matrix was seen, producing irreversible changes in blood flow parameters. Although nerve conduction velocity measurements returned to normal two weeks after decompression irrespective of the timing of the surgical intervention, distal latency returned to normal only after early decompression (0.97 ± 0.06 msec compared with 1.22 ± 0.06 msec for late decompression, p = 0.009). Chronic nerve compression injuries decreased neurovascular flow and induced ischemia by upregulating HIF1α, catalase, and MMP9. Early surgical intervention offered better return to normal electrophysiological parameters compared with late intervention. These data present a clinical correlate to the variable functional outcomes seen following surgical release of chronic nerve compression injuries and provide early support for using distal latency as a predictor of outcomes following surgical release.

Expression and role of connective tissue growth factor in the peripheral nerve after chronic compression injury

Objective To investigate the effects of connective tissue growth factor (CTGF) on the chronic peripheral nerve compression injury and explore the function of CTGF in peripheral nerve compression injury and repair. Methods From July 2010 to September 2010, fifty aduh male SD rats were randomly divided into group A and B: group A (sham-operated group): only exposed the sciatic nerve; group B (compression group): undergone sciatic nerve entrapment operation on the right hind leg according to the method which Mackinnon adopted when he established the model of chronic sciatic nerve compression.Electron microscopy,immunohistochemistry,RT-PCR and Western-blot were performed to observe the morphological changes of the compressed nerve tissue and to determine the level of CTGF,collagen- Ⅰ,Ⅲ (COL- Ⅰ,Ⅲ),2,4,6,8,10 weeks after the surgery,respectively. Results After sciatic nerve compression,the collagen in nerve increased ; The expression of CTGF and COL- Ⅰ, Ⅲ in sciatic nerve of compressed group increased, which was statistically different compared with the sham-operation group (P ＜ 0.05); In the meanwhile,the contents of CTGF and COL- Ⅰ,Ⅲ were positively correlated in a certain period. Conclusion Peripheral nerve fibrosis can be caused by chronic nerve compression.The expression of COL- Ⅰ,Ⅲ in sciatic nerve increased and CTGF get involved in the pathophysiological process, which suggests that CTGF plays an important role in the process of neural injury and fibrosis. Key words: Peripheral nerve; Nerve entrapment syndrome; Chronic compression injury; Connective tissue growth factor

Biophysical stimulation induces demyelination via an integrin‐dependent mechanism

Chronic nerve compression (CNC) injuries occur when peripheral nerves are subjected to sustained mechanical forces, with increasing evidence implicating Schwann cells as key mediators. Integrins, a family of transmembrane adhesion molecules that are capable of intracellular signaling, have been implicated in a variety of biological processes such as myelination and nerve regeneration. In this study, we seek to define the physical stimuli mediating demyelination and to determine whether integrin plays a role in the demyelinating response. We used a previously described in vitro model of CNC injury where myelinating neuron-Schwann cell cocultures were subjected to independent manipulations of hydrostatic pressure, hypoxia, and glucose deprivation in a custom bioreactor. We assessed whether demyelination increased in response to applied manipulation and determined whether integrin-associated signaling cascades are upregulated. Biophysical stimulation of neural tissue induced demyelination and Schwann cell proliferation without neuronal or glial cytotoxicity or apoptosis. Although glucose deprivation and hypoxia independently had minor effects on myelin stability, together they potentiated the demyelinating effects of hydrostatic compression, and in combination, significantly destabilized myelin. Biophysical stimuli transiently increased phosphorylation of the integrin-associated tyrosine kinase Src within Schwann cells. Silencing this integrin signaling cascade blocked Src activation and prevented pressure-induced demyelination. Colocalization analysis indicated that Src is localized within Schwann cells. These results indicate that myelin is sensitive to CNC injury and support the novel concept that myelinating cocultures respond directly to mechanical loading via activating an integrin signaling cascade.

Chronic nerve compression alters schwann cell myelin architecture in a murine model

Myelinating Schwann cells compartmentalize their outermost layer to form actin-rich channels known as Cajal bands. Herein we investigate changes in Schwann cell architecture and cytoplasmic morphology in a novel mouse model of carpal tunnel syndrome. Chronic nerve compression (CNC) injury was created in wild-type and slow-Wallerian degeneration (Wld(S) ) mice. Over 12 weeks, nerves were electrodiagnostically assessed, and Schwann cell morphology was thoroughly evaluated. A decline in nerve conduction velocity and increase in g-ratio is observed without early axonal damage. Schwann cells display shortened internodal lengths and severely disrupted Cajal bands. Quite surprisingly, the latter is reconstituted without improvements to nerve conduction velocity. Chronic entrapment injuries like carpal tunnel syndrome are primarily mediated by the Schwann cell response, where decreases in internodal length and myelin thickness disrupt the efficiency of impulse propagation. Restitution of Cajal bands is not sufficient for remyelination after CNC injury.

Effects of transforming growth factor β1 and collagen type I/III on chronic peripheral nerve compression injury

Objective To investigate the effects of transforming growth factor β1(TGF-β1) and collagentype Ⅰ / Ⅲ (COL- Ⅰ / Ⅲ ) on chronic peripheral nerve compression injury and explore the relationship betweenTGF-β1 and COL- Ⅰ/Ⅲ. Methods Fifty adult male SD rats were randomly divided into group A and B. Ingroup A (sham-operated group) the sciatic nerve was exposed only. In group B ( compression group) sciaticnerve entrapment was created on the right hind leg according to Mackinnon' s procedure of chronic sciatic nervecompression. Electron microscopy, immunohistochemistry, RT-PCR and Western-Blot were performed to observethe morphological changes of the compressed nerve tissue and to determine the level of TGF-β1, collagen- Ⅰ andcollagen-Ⅲ 2, 4, 6, 8 and 10 weeks after the surgery, respectively. Results After sciatic nervecompression, collagen content in the nerve increased. The expression of TGF-β1 and COL- Ⅰ/Ⅲ in the sciaticnerve of the compressed group increased, which was significantly higher than that of the sham-operation group( P ＜0.05). In the meanwhile, the contents of TGF-β1 and COL- Ⅰ/Ⅲ were positively correlated in a certainperiod. Conclusion Peripheral nerve fibrosis can be caused by chronic nerve compression which inducesincreased expression of COL-Ⅰ/Ⅲ in the nerve. TGF-β1 is involved in the pathophysiological process, whichsuggests that TGF-β1 plays an important role in the process of neural injury and fibrosis. Key words: Peripheral nerves; Nerve compression syndromes; Transforming growth factor beta; Collagen type Ⅰ /Ⅲ

Nerve compression activates selective nociceptive pathways and upregulates peripheral sodium channel expression in Schwann cells

Chronic nerve compression (CNC) injuries, such as carpal tunnel syndrome, are common musculoskeletal conditions that affect patients with debilitating loss of sensory function and pain. Although early detection and treatment are important, our understanding of pain-related molecular mechanisms remains largely unclear. Here we investigate these mechanisms using an animal model for CNC injury. To confirm that CNC injury induces pain, we assessed expression of c-fos, a gene that is rapidly expressed in spinal sensory afferents in response to painful peripheral stimuli, and TNF-alpha and IL-6, two proinflammatory cytokines that are crucial to development of inflammatory-mediated pain. Results show c-fos upregulation 1-2 weeks postinjury in the absence of TNF-alpha or IL-6 expression, indicating increased neural sensitivity without an inflammatory response. This is consistent with previous studies that showed no morphologic evidence of inflammation in the CNC model. Surprisingly, we also found de novo expression of Na(V)1.8, a sodium channel linked to the development of neuropathic pain, in endoneurial Schwann cells following injury. Until now, Na(V)1.8 expression was thought to be restricted to sensory neurons. CNC injury appears to be a unique model of noninflammatory neuropathic pain. Further investigation of the underlying molecular basis could yield promising targets for early diagnosis and treatment.

Compressive Neuropathies of the Upper Extremity: Update on Pathophysiology, Classification, and Electrodiagnostic Findings

Clinical examination and electrodiagnostic studies remain the gold standard for diagnosis of nerve injuries. Diagnosis of chronic nerve compression (CNC) injuries can be difficult in patients with confounding factors such as diabetes. The treatment of nerve entrapment ranges from medical to surgical management, depending on the nerve involved and on the severity and duration of compression. Considerable insights have been made at the molecular level, differentiating between nerve crush injuries and CNC injuries. Although the myelin changes after CNC injury were previously thought to be a mild form of Wallerian degeneration, recent evidence points to a distinct pathophysiology involving Schwann cell mechanosensitivity. Future areas of research include Schwann cell transplantation in the treatment regimen, the correlation between demyelination and the onset of pain, and the role of Schwann cell integrins in transducing the mechanical forces involved in nerve compression injuries to Schwann cells.

AnIn-VitroTraumatic Model To Evaluate the Response of Myelinated Cultures to Sustained Hydrostatic Compression Injury

While a variety of in-vitro models have been employed to investigate the response of load-bearing tissues to hydrostatic pressure, long-term studies are limited by the need to provide for adequate gas exchange during pressurization. Applying compression in vitro may alter the equilibrium of the system and thereby disrupt the gas exchange kinetics. To address this, several sophisticated compression chamber designs have been developed. However, these systems are limited in the magnitude of pressure that can be applied and may require frequent media changes, thereby eliminating critical autocrine and paracrine signaling factors. To better isolate the cellular response to long-term compression, we created a model that features continuous gas flow through the chamber during pressurization, and a negative feedback control system to rigorously control dissolved oxygen levels. Monitoring dissolved oxygen continuously during pressurization, we find that the ensuing response exhibits characteristics of a second- or higher-order system which can be mathematically modeled using a second-order differential equation. Finally, we use the system to model chronic nerve compression injuries, such as carpal tunnel syndrome and spinal nerve root stenosis, with myelinated neuron-Schwann cell co-cultures. Cell membrane integrity assay results show that co-cultures respond differently to hydrostatic pressure, depending on the magnitude and duration of stimulation. In addition, we find that myelinated Schwann cells proliferate in response to applied hydrostatic compression.

C-Jun, krox-20, and integrin β4 expression following chronic nerve compression injury

Limited work has been done to investigate the molecular mechanisms behind the process of demyelination and remyelination that occurs in response to chronic nerve compression (CNC) injury. In the present study, we investigated the expression of the transcription factors krox-20 and c-jun, positive and negative regulators of myelination, respectively. A decrease in krox-20 expression and an increase in c-jun expression in both its phosphorylated and non-phosphorylated states were observed. In addition, we investigated the role of integrins, specifically the β4 subunit of the α6β4 dimer, as a possible upstream signal transducer in the signaling cascade leading to demyelination. We detected a decrease in β4 integrin expression at 2 and 4 weeks post-injury and a concomitant relocalization to the Schmidt–Lanterman Incisures, suggesting a role for the β4 integrin in facilitating Schwann cell–extracellular matrix interaction. The observed changes in transcription factor and integrin expression are temporally correlated with the process of demyelination, and suggest further investigation to define their definitive role in regulating the myelin response to CNC injury.

Functional assessment after sciatic nerve injury in a rat model

The aim of this study is to evaluate the effectiveness of Sciatic Function Index (SFI) and Basso, Beattie, and Bresnahan (BBB) Locomotor Rating in assessing peripheral nerve injuries. SFI is a standard method for evaluating crush and transected peripheral nerve injuries, likewise BBB for spinal cord injury. Models of chronic nerve compression (CNC), crush, and transection injury were created on Sprague-Dawley rats and functional outcomes were measured using BBB and SFI at 1-week interval for 6 weeks. All injury models showed high correlation between SFI and BBB scores. With crush injury, the SFI showed near complete recovery while BBB showed residual deficits 6 weeks after injury. Both the BBB and SFI were unable to detect motor deficits in 6-week CNC animals. The BBB score should be considered as an adjunct in evaluating peripheral nerve recovery and may be more sensitive in detecting residual deficits than SFI after crush-type injuries.

Understanding the mechanisms of entrapment neuropathies

Compression neuropathies are highly prevalent, debilitating conditions with variable functional recovery following surgical decompression. Due to the limited amount of human nerve tissue available for analysis, a number of animal models have been created to help investigators understand the molecular and cellular pathogenesis of chronic nerve compression (CNC) injury. Evidence suggests that CNC injury induces concurrent Schwann cell proliferation and apoptosis in the early stages of the disorder. These proliferating Schwann cells downregulate myelin proteins, leading to local demyelination and remyelination in the region of injury. In addition, the downregulation of myelin proteins, in particular myelin-associated glycoprotein, allows for axonal sprouting. Interestingly, these changes occur in the absence of both morphological and electrophysiological evidence of axonal damage. This is in direct contrast to acute injuries, such as transection or crush, which are characterized by axonal injury followed by Wallerian degeneration. Because the accepted trigger for Schwann cell dedifferentiation is axonal injury, an alternate mechanism for Schwann response must exist in CNC injury. In vitro studies of pure Schwann cells have shown that these cells can respond directly to mechanical stimuli by downregulating myelin proteins and proliferating. These studies suggest that although the reciprocal relationship between neurons and glial cells is maintained, chronic nerve compression injury is a Schwann cell-mediated disease.

Neuromuscular junction integrity after chronic nerve compression injury

Chronic nerve compression injuries (CNC) are progressive demyelinating disorders characterized by a gradual decline of the nerve conduction velocity (NCV) in the affected nerve region. CNC injury induces a robust Schwann cell response with axonal sprouting, but without morphologic evidence of axonal injury. We hypothesize that early CNC injury occurs without damage to neuromuscular junction of motor axons. A well-established animal model was used to assess for damage to motor axons. As sprouting is considered a hallmark of regeneration during and after axonal degeneration and sprouting was confirmed visually at 2 weeks in CNC animals, we assessed for axonal degeneration in motor nerves after CNC by evaluating the integrity of the neuromuscular junction. NCV exhibited a gradual progressive decline consistent with the human condition. Compound motor action potential amplitudes decreased slightly immediately and plateaued, indicating that there was not sustained and increasing axonal loss. Sprouting was confirmed using immunofluorescence and by an increase in number of unmyelinated axons and Remak bundles. Blind analysis of the neuromuscular junction showed no difference between control and CNC images, indicating that there was no evidence for end-unit axonal loss in the soleus muscle. Because the progressive decline in NCV was not paired with a similar progressive decline in amplitude, it is likely that axonal loss is not responsible for slowing of action potentials. Blind analysis of the neuromuscular junction provides further evidence that the axonal sprouting seen early after CNC injury is not a consequence of axonal degeneration in the motor nerves.