Sciatic and tibial neuropathies

The sciatic nerve is the body's largest peripheral nerve. Along with their two terminal divisions (tibial and fibular), their anatomic location makes them particularly vulnerable to trauma and iatrogenic injuries. A thorough understanding of the functional anatomy is required to adequately localize lesions in this lengthy neural pathway. Proximal disorders of the nerve can be challenging to precisely localize among a range of possibilities including lumbosacral pathology, radiculopathy, or piriformis syndrome. A correct diagnosis is based upon a thorough history and physical examination, which will then appropriately direct adjunctive investigations such as imaging and electrodiagnostic testing. Disorders of the sciatic nerve and its terminal branches are disabling for patients, and expert assessment by rehabilitation professionals is important in limiting their impact. Applying techniques established in the upper extremity, surgical reconstruction of lower extremity nerve dysfunction is rapidly improving and evolving. These new techniques, such as nerve transfers, require electrodiagnostic assessment of both the injured nerve(s) as well as healthy, potential donor nerves as part of a complete neurophysiological examination.

Nrf2 Activation Attenuates Chronic Constriction Injury-Induced Neuropathic Pain via Induction of PGC-1α-Mediated Mitochondrial Biogenesis in the Spinal Cord

BACKGROUND

Neuropathic pain is a debilitating disease with few effective treatments. Emerging evidence indicates the involvement of mitochondrial dysfunction and oxidative stress in neuropathic pain. Nuclear factor erythroid 2-related factor 2 (Nrf2) is a potent regulator of the antioxidant response system. In this study, we investigated whether RTA-408 (RTA, a novel synthetic triterpenoid under clinical investigation) could activate Nrf2 and promote mitochondrial biogenesis (MB) to reverse neuropathic pain and the underlying mechanisms.

METHODS

Neuropathic pain was induced by chronic constriction injury (CCI) of the sciatic nerve. Pain behaviors were measured via the von Frey test and Hargreaves plantar test. The L4-6 spinal cord was collected to examine the activation of Nrf2 and MB.

RESULTS

RTA-408 treatment significantly reversed mechanical allodynia and thermal hyperalgesia in CCI mice in a dose-dependent manner. Furthermore, RTA-408 increased the activity of Nrf2 and significantly restored MB that was impaired in CCI mice in an Nrf2-dependent manner. Peroxisome proliferator-activated receptor-gamma coactivator-1alpha (PGC-1α) is the key regulator of MB. We found that the PGC-1α activator also induced a potent analgesic effect in CCI mice. Moreover, the antinociceptive effect of RTA-408 was reversed by the preinjection of the PGC-1α inhibitor.

CONCLUSIONS

Nrf2 activation attenuates chronic constriction injury-induced neuropathic pain via induction of PGC-1α-mediated mitochondrial biogenesis in the spinal cord. Our results indicate that Nrf2 may be a potential therapeutic strategy to ameliorate neuropathic pain and many other disorders with oxidative stress and mitochondrial dysfunction.

Dynamic Change of Endocannabinoid Signaling in the Medial Prefrontal Cortex Controls the Development of Depression After Neuropathic Pain

Many patients with chronic pain conditions suffer from depression. The mechanisms underlying pain-induced depression are still unclear. There are critical links of medial prefrontal cortex (mPFC) synaptic function to depression, with signaling through the endocannabinoid (eCB) system as an important contributor. We hypothesized that afferent noxious inputs after injury compromise activity-dependent eCB signaling in the mPFC, resulting in depression. Depression-like behaviors were tested in male and female rats with traumatic neuropathy [spared nerve injury (SNI)], and neuronal activity in the mPFC was monitored using the immediate early gene c-fos and in vivo electrophysiological recordings. mPFC eCB Concentrations were determined using mass spectrometry, and behavioral and electrophysiological experiments were used to evaluate the role of alterations in eCB signaling in depression after pain. SNI-induced pain induced the development of depression phenotypes in both male and female rats. Pyramidal neurons in mPFC showed increased excitability followed by reduced excitability in the onset and prolonged phases of pain, respectively. Concentrations of the eCBs, 2-arachidonoylglycerol (2-AG) in the mPFC, were elevated initially after SNI, and our results indicate that this resulted in a loss of CB1R function on GABAergic interneurons in the mPFC. These data suggest that excessive release of 2-AG as a result of noxious stimuli triggers use-dependent loss of function of eCB signaling leading to excessive GABA release in the mPFC, with the final result being behavioral depression.SIGNIFICANCE STATEMENT Pain has both somatosensory and affective components, so the complexity of mechanisms underlying chronic pain is best represented by a biopsychosocial model that includes widespread CNS dysfunction. Many patients with chronic pain conditions develop depression. The mechanism by which pain causes depression is unclear. Although manipulation of the eCB signaling system as an avenue for providing analgesia per se has not shown much promise in previous studies. An important limitation of past research has been inadequate consideration of the dynamic nature of the connection between pain and depression as they develop. Here, we show that activity-dependent synthesis of eCBs during the initial onset of persistent pain is the critical link leading to depression when pain is persistent.

Injury-Induced HSP27 Expression in Peripheral Nervous Tissue Is Not Associated with Any Alteration in Axonal Outgrowth after Immediate or Delayed Nerve Repair

We investigated injury-induced heat shock protein 27 (HSP27) expression and its association to axonal outgrowth after injury and different nerve repair models in healthy Wistar and diabetic Goto-Kakizaki rats. By immunohistochemistry, expression of HSP27 in sciatic nerves and DRG and axonal outgrowth (neurofilaments) in sciatic nerves were analyzed after no, immediate, and delayed (7-day delay) nerve repairs (7- or 14-day follow-up). An increased HSP27 expression in nerves and in DRG at the uninjured side was associated with diabetes. HSP27 expression in nerves and in DRG increased substantially after the nerve injuries, being higher at the site where axons and Schwann cells interacted. Regression analysis indicated a positive influence of immediate nerve repair compared to an unrepaired injury, but a shortly delayed nerve repair had no impact on axonal outgrowth. Diabetes was associated with a decreased axonal outgrowth. The increased expression of HSP27 in sciatic nerve and DRG did not influence axonal outgrowth. Injured sciatic nerves should appropriately be repaired in healthy and diabetic rats, but a short delay does not influence axonal outgrowth. HSP27 expression in sciatic nerve or DRG, despite an increase after nerve injury with or without a repair, is not associated with any alteration in axonal outgrowth.

MiR-122-5p suppresses neuropathic pain development by targeting PDK4

The complex pathogenesis and limited efficacy of available treatment make neuropathic pain difficult for long periods of time. Several findings suggested the regulatory role of microRNA in the development of neuropathic pain. This study aims to investigate the functional role of miR-122-5p in the development of neuropathic pain. Down-regulation of miR-122-5p was observed in spinal cords of rats with neuropathic pain. We also found that overexpressing miR-122-5p by intrathecal injection of miR-122-5p lentivirus in a mouse model of chronic sciatic nerve injury (CCI) prevented neuropathic pain behavior. In HEK-293 T cells, luciferase activity was significantly decreased in the transfection group with mimic-miR-122-5p in wild-type PDK4 reporter, compared with mutant PDK4 reporter. Increased PDK4 expression was also observed during the progression of neuropathic pain. Intrathecal injection of both mimic-miR-122-5p and shPDK4 in CCI mice downregulated PDK4 expression to a lower level when compared with injected with shPDK4. In CCI mice, transfection of shPDK4 suppressed mechanical allodynia and thermal hyperalgesia, while co-transfection of shPDK4 and LV-miR-122-5p resulted in stronger levels of mechanical allodynia and thermal hyperalgesia inhibition. Taken together, the data suggest that miR-122-5p inhibits PDK4 expression, attenuating neuropathic pain. This result suggests the potential role of miR-122-5p acting as a target for the treatment of neuropathic pain.

Oral efficacy of Δ(9)-tetrahydrocannabinol and cannabidiol in a mouse neuropathic pain model

The psychoactive and non-psychoactive constituents of cannabis, Δ9-tetrahydrocannabinol (THC) and cannabidiol (CBD), have synergistic analgesic efficacy in animal models of neuropathic pain when injected systemically. However, the relevance of this preclinical synergy to clinical neuropathic pain studies is unclear because many of the latter use oral administration. We therefore examined the oral effectiveness of these phytocannabinoids and their interactions in a mouse chronic constriction injury (CCI) model of neuropathic pain. THC produced a dose-dependent reduction in mechanical and cold allodynia, but also induced side-effects with similar potency. CBD also reduced allodynia, albeit with lower potency than THC, but did not produce cannabinoid-like side-effects at any dose tested. Combination THC:CBD produced a dose-dependent reduction in allodynia, however, it displayed little to no synergy. Combination THC:CBD produced substantial, synergistic side-effects which increased with the proportion of CBD. These findings demonstrate that oral THC and CBD, alone and in combination, have analgesic efficacy in an animal neuropathic pain model. Unlike prior systemic injection studies, combination THC:CBD lacks analgesic synergy when delivered orally. Furthermore, both THC and combination THC:CBD display a relatively poor therapeutic window when delivered orally. This suggests that CBD provides a safer, albeit lower efficacy, oral treatment for nerve injury induced neuropathic pain than THC-containing preparations. This article is part of the special issue on 'Cannabinoids'.

Can MitoTEMPO protect rat sciatic nerve against ischemia-reperfusion injury?

Abdominal ischemia-reperfusion (I/R) is known to cause both structural and functional damage to sciatic nerve which is related to the oxidative stress. We investigated the protective effects of mitochondria-targeted antioxidant (2-(2,2,6,6-tetramethylpiperidin-1-oxyl-4-ylamino)-2-oxoethyl) triphenylphosphonium chloride (MitoTEMPO) on ischemia-reperfusion-induced nerve damage by using the conduction velocity distribution (CVD) calculations from in vitro compound nerve action potential (CNAP) recordings from rat sciatic nerve. Adult male Wistar albino rats were divided into three groups. The IR and IR + MT groups had aortic cross-clamping for 1 h followed by 2 h reperfusion, while SHAM group had the same procedure without cross-clamping. IR + MT group received 0.7 mg/kg/day MitoTEMPO injection for 28 days before I/R, while other groups received vehicle alone. Ischemia-reperfusion resulted in a significant decrease (p < .05) in maximum depolarizations (mV), areas (mV.ms), and maximum and minimum upstroke velocities (mV/ms) of CNAPs, while injection of MitoTEMPO showed a complete protective effect on these impairments. The histograms for CVD showed that I/R blocked the contribution of fast-conducting fibers (> 60 m/s). MitoTEMPO prevented that blockage and caused a shift in the CVD. Functional nerve damage caused by I/R can be prevented by MitoTEMPO, which can enter mitochondria, the main source of reactive oxygen species (ROS).

Electrospun polycaprolactone (PCL)-amnion nanofibrous membrane prevents adhesions and promotes nerve repair in a rat model of sciatic nerve compression

Adhesion and scarring after neural surgery are detrimental to nerve regeneration and functional recovery. Amniotic membranes have been used in tissue repair due to their immunogenicity and richness in cytokines. In this study, an electrospun polycaprolactone (PCL)-amnion nanofibrous membrane was prepared for the treatment of sciatic nerve compression in a rat model. The effects of the PCL-amnion nanofibrous membrane on the prevention of adhesion formation and nerve regeneration were evaluated using electrophysiology and histological analyses. Compared with the medical chitosan hydrogel dressing, the PCL-amnion nanofibrous membrane significantly reduced peripheral nerve adhesion and promoted the rapid recovery of nerve conduction. Moreover, the immunohistochemical analysis identified more Schwann cells and less pro-inflammatory M1 macrophages in the PCL-amnion group. Western blot and RT-PCR results showed that the expression levels of type-Ⅰ and Ⅲ collagen in the PCL-treated rats were half of those in the control group after 12 weeks, while the expression level of nerve growth factor was approximately 3.5 times that found in the rats treated with medical chitosan hydrogel. In summary, electrospun PCL-amnion nanofibrous membranes can effectively reduce adhesion after neural surgery and promote nerve repair and regeneration. The long-term retention in vivo and sustained release of cytokines make PCL-amnion a promising biomaterial for clinical application.

An integrated strategy for discovering effective components of Shaoyao Gancao decoction for treating neuropathic pain by the combination of partial least-squares regression and multi-index comprehensive method

ETHNOPHARMACOLOGICAL RELEVANCE

Neuropathic pain, the incidence of which ranges from 5 to 8% in the general population, remains challenge in the treatment. Shaoyao Gancao decoction (SGD) is a Chinese classical formula used to relieve pain for thousands of years and has been applied for neuropathic pain nowadays. However, the effective components of SGD for the treatment of neuropathic pain remains unclear.

AIMS OF STUDY

To investigate the effect and potential mechanism of SGD against neuropathic pain and further reveal the effective components of SGD in the treatment of neuropathic pain.

MATERIALS AND METHODS

Spared nerve injury (SNI) model rats of neuropathic pain were orally given SGD to intervene, the components in vivo after SGD administration were determined, behavior indicators, biochemical parameters, and metabolomics were applied for assessing the efficacy. Then correlation between components and biomarkers was analyzed by pearson correlation method. To further measure the contribution of components to efficacy, the combination of partial least-squares regression (PLSR) and multi-index comprehensive method was carried out, according to the corresponding contribution degree of the results, the components with large contribution degree were considered as the effective components.

RESULTS

SGD exhibited a significant regulatory effect on neuropathic pain, which could increase the pain threshold and decrease the levels of SP, β-EP, PGE2 and NO. With the high resolution of UPLC-Q-TOF/MS technology, a total of 128 compounds from SGD were identified and 44 of them were absorbed in blood. Besides, 40 serum biomarkers were identified after intervention of SGD and the metabolic pathways were constructed. The key metabolic pathways including Glycerophospholipid metabolism, Linoleic acid metabolism, Alpha-linolenic acid metabolism, Glycosylphosphatidylinositol-anchor biosynthesis and Arachidonic acid metabolism may be related to the regulation of neuropathic pain. Metabolomics combined with PLSR and multi-index comprehensive method was utilized to discover 5 components including paeonol, DL-Arabinose, benzoic acid, hispaglabridin A and paeonilactone C as effective components of SGD in the treatment of neuropathic pain. This strategy was used to explore the effective components of SGD and elucidate its possible analgesic mechanism.

CONCLUSION

This study demonstrate that SGD significantly relieved neuropathic pain and elucidated the effective components of SGD for treating neuropathic pain, the strategy as an illustrative case study can be applied to other classical formula and is beneficial to improve the quality and efficacy.

Augmented Buyang Huanwu Decoction facilitates axonal regeneration after peripheral nerve transection through the regulation of inflammatory cytokine production

ETHNOPHARMACOLOGICAL RELEVANCE

Herbal formulation Buyang Huanwu Decoction (BYHWD) has been used to treat cardiovascular disorders including cerebral ischemia. Recent studies showed its effects on promoting axonal regeneration after nerve injury. However, compositional reformulation supplemented with herbal components that regulates inflammation may increase its efficacy for nerve repair.

AIM OF THE STUDY

We prepared a new herbal decoction by adding selected herbal components to BYHWD (augmented BYHWD; ABHD) and investigated the effect of ABHD on the production of inflammatory cytokines and axonal regeneration using an animal model of nerve transection and coaptation (NTC).

MATERIALS AND METHODS

A rat model of NTC was performed on the sciatic nerve. The sciatic nerve and dorsal root ganglion (DRG) were isolated and used for immunofluorescence staining and western blot analysis. DRG tissue was also used to prepare primary neuron culture and the length of neurites was analyzed. Sensorimotor nerve activities were assessed by rotarod and von Frey tests.

RESULTS

Three herbal components that facilitated neurite outgrowth were chosen to formulate ABHD. ABHD administration into the sciatic nerve 1 week or 3 months after NTC facilitated axonal regeneration. Cell division cycle 2 (Cdc2) and brain-derived neurotrophic factor (BDNF) proteins were induced from the reconnected distal portion of the sciatic nerve and the levels were further elevated by in vivo administration of ABHD. Phospho-Erk1/2 level was increased by ABHD treatment as well, implying its role in mediating retrograde transport of BDNF signals into the neuronal cell body. Production of inflammatory cytokines IL-1β and TNF-α was induced in the reconnected nerve but attenuated by ABHD treatment. Behavioral tests revealed that ABHD treatment improved functional recovery of sensorimotor activities.

CONCLUSIONS

A newly formulated ABHD is effective at regulating the production of inflammatory cytokines and promoting axonal regeneration after nerve transection and may be considered to develop therapeutic strategies for peripheral nerve injury disorders.

Low-Level Laser Therapy in Different Wavelengths on the Tibialis Anterior Muscle of Wistar Rats After Nerve Compression Injury

OBJECTIVE

Traumatic injuries are common and may promote disruption of neuromuscular communication, triggering phenomena that lead to nerve degeneration and affect muscle function. A laser accelerates tissue recovery; however, the parameters used are varied, making it difficult to compare studies. The purpose of this study was to evaluate the effect of low-level laser therapy, at 660- and 830-nm wavelengths, on the tibialis anterior muscle of Wistar rats after sciatic nerve compression.

METHODS

Twenty animals were separated into 4 groups: control, sciatic nerve injury, lesion + 660-nm laser, and lesion + 830-nm laser. In the lesion groups, the right sciatic nerve was surgically exposed and compressed with hemostatic forceps for 30 seconds. After the third postoperative day, the groups with laser therapy were submitted to treatment for 2 weeks totaling 10 applications, performed directly on the surgical scar of the nerve injury. Grip strength was analyzed before and after the nerve injury and during the treatment period. The tibialis anterior muscle was processed for light microscopy, area measurement, smaller diameter, number of fibers, nuclei, and connective tissue.

RESULTS

The animals submitted to the injury experienced muscular atrophy and morphological changes in the number of muscle fibers and nuclei. In the connective tissue morphometry, there was a decrease in the treated groups compared with the untreated groups.

CONCLUSION

The laser treatment at different wavelengths showed no improvement in the tibialis anterior muscle of Wistar rats within the morphological and functional aspects evaluated.

Effectiveness of electrical stimulation on nerve regeneration after crush injury: Comparison between invasive and non-invasive stimulation

Several studies have investigated the use of invasive and non-invasive stimulation methods to enhance nerve regeneration, and varying degrees of effectiveness have been reported. However, due to the use of different parameters in these studies, a fair comparison between the effectiveness of invasive and non-invasive stimulation methods is not possible. The present study compared the effectiveness of invasive and non-invasive stimulation using similar parameters. Eighteen Sprague Dawley rats were classified into three groups: the iES group stimulated with fully implantable device, the tES group stimulated with transcutaneous electrical nerve stimulation (TENS), and the injury group (no stimulation). The iES and tES groups received stimulation for 6 weeks starting immediately after the injury. Motor function was evaluated using the sciatic functional index (SFI) every week. The SFI values increased over time in all groups; faster and superior functional recovery was observed in the iES group than in the tES group. Histological evaluation of the nerve sections and gastrocnemius muscle sections were performed every other week. The axon diameter and muscle fiber area in the iES group were larger, and the g-ratio in the iES group was closer to 0.6 than those in the tES group. To assess the cause of the difference in efficiency, a 3D rat anatomical model was used to simulate the induced electric fields in each group. A significantly higher concentration and intensity around the sciatic nerve was observed in the iES group than in the tES group. Vector field distribution showed that the field was orthogonal to the sciatic nerve spread in the tES group, whereas it was parallel in the iES group; this suggested that the tES group was less effective in nerve stimulation. The results indicated that even though rats in the TENS group showed better recovery than those in the injury group, it cannot replace direct stimulation yet because rats stimulated with the invasive method showed faster recovery and superior outcomes. This was likely attributable to the greater concentration and parallel distribution of electric field with respect to target nerve.

Neuroprotective Effects of Ozone Therapy After Sciatic Nerve Cut Injury

A number of antioxidants have been used to treat peripheral nerve injury. However, there are few definitive experimental studies of ozone therapy for peripheral nerve cut injury. We aimed to examine the effects of mild level ozone therapy on sciatic nerve regeneration. One hundred adult male Wistar albino rats were randomly divided into four groups: group 1 (n=20) no cut injury or therapy; group 2 (n=20) sham; group 3 (n=30) nerve cut injury, no therapy; group 4 (n=30) nerve cut injury and ozone therapy. Sciatic functional index (SFI) and withdrawal reflex (WDR) were measured for all groups before nerve cut, at postoperative day 1, and at weeks 2, 4, 6 and 8. More myelinated (M) nerve fibers were observed after nerve cut injury in the ozone-therapy group. Significant differences were seen in plasma SOD (superoxide dismutase), CAT (catalase) and GPx (glutathione peroxidase) activities (p<0.05), and significant functional improvement was observed at postoperative weeks 2 and 4 (p<0.05) after ozone treatment. This is the first study conducted for the purpose of examining the effects of ozone therapy on sciatic nerve cut injury.

Epitranscriptomic m6A Regulation of Axon Regeneration in the Adult Mammalian Nervous System

N⁶-methyladenosine (m⁶A) affects multiple aspects of mRNA metabolism and regulates developmental transitions by promoting mRNA decay. Little is known about the role of m⁶A in the adult mammalian nervous system. Here we report that sciatic nerve lesion elevates levels of m⁶A-tagged transcripts encoding many regeneration-associated genes and protein translation machinery components in the adult mouse dorsal root ganglion (DRG). Single-base resolution m⁶A-CLIP mapping further reveals a dynamic m⁶A landscape in the adult DRG upon injury. Loss of either m⁶A methyltransferase complex component Mettl14 or m⁶A-binding protein Ythdf1 globally attenuates injury-induced protein translation in adult DRGs and reduces functional axon regeneration in the peripheral nervous system in vivo. Furthermore, Pten deletion-induced axon regeneration of retinal ganglion neurons in the adult central nervous system is attenuated upon Mettl14 knockdown. Our study reveals a critical epitranscriptomic mechanism in promoting injury-induced protein synthesis and axon regeneration in the adult mammalian nervous system.

Canine Adipose-Derived Mesenchymal Stromal Cells Enhance Neuroregeneration in a Rat Model of Sciatic Nerve Crush Injury

Crush injuries in peripheral nerves are frequent and induce long-term disability with motor and sensory deficits. Due to axonal and myelin sheath disruptions, strategies for optimized axonal regeneration are needed. Multipotent mesenchymal stromal cells (MSC) are promising because of their anti-inflammatory properties and secretion of neurotrophins. The present study investigated the effect of canine adipose tissue MSC (Ad-MSC) transplantation in an experimental sciatic nerve crush injury. Wistar rats were divided into three groups: sham ( n = 8); Crush+PBS ( n = 8); Crush+MSC ( n = 8). Measurements of sciatic nerve functional index (SFI), muscle mass, and electromyography (EMG) were performed. Canine Ad-MSC showed mesodermal characteristics (CD34-, CD45-, CD44+, CD90+ and CD105+) and multipotentiality due to chondrogenic, adipogenic, and osteogenic differentiation. SFI during weeks 3 and 4 was significantly higher in the Crush+MSC group ( p < 0.001). During week 4, the EMG latency in the Crush+MSC groups had better near normality ( p < 0.05). The EMG amplitude showed results close to normality during week 4 in the Crush+MSC group ( p < 0.04). There were no statistical differences in muscle weight between the groups ( p > 0.05), but there was a tendency toward weight gain in the Crush+MSC groups. Better motor functional recovery after crush and perineural canine Ad-MSC transplantation was observed during week 2. This was maintained till week 4. In conclusion, the canine Ad-MSC transplantation showed early pro-regenerative effects between 2-4 weeks in the rat model of sciatic nerve crush injury.

Effects of Lumbar Acupuncture Stimulation on Blood Flow to the Sciatic Nerve Trunk - An Exploratory Study

Introduction

Acupuncture may have a role in the treatment of intermittent claudication of the cauda equina due to lumbar spinal canal stenosis. The aim of this study was to explore the possible physiological mechanisms.

Methods

In a laboratory experiment, manual acupuncture was performed at a point adjacent to the sixth lumbar vertebra of 13 animals and its effect on sciatic nerve blood flow was measured using a laser Doppler flowmetry. Simultaneously, changes in blood pressure and cardiac rate were observed. Each animal was stimulated four to eight times, making a total of 58 experiments.

Results

Acupuncture stimulation did not produce consistent changes in sciatic nerve blood flow, with increased and decreased blood flow as well as no change in blood flow observed. Among the 58 individual experiments, sciatic nerve blood flow was increased in 33, reduced in 12, and unchanged in 13. Approximately half of the stimulations showed a correlation between blood flow and blood pressure change.

Conclusion

Our results indicate that lumbar acupuncture stimulation can have an influence on sciatic nerve blood flow. The effect is dependent not only on blood pressure but also other factors, for example vasodilator and vasoconstrictor nerve activity. This mechanism may contribute to a clinical effect on intermittent claudication of the cauda equina.

Polycomb repression regulates Schwann cell proliferation and axon regeneration after nerve injury

The transition of differentiated Schwann cells to support of nerve repair after injury is accompanied by remodeling of the Schwann cell epigenome. The EED-containing polycomb repressive complex 2 (PRC2) catalyzes histone H3K27 methylation and represses key nerve repair genes such as Shh, Gdnf, and Bdnf, and their activation is accompanied by loss of H3K27 methylation. Analysis of nerve injury in mice with a Schwann cell-specific loss of EED showed the reversal of polycomb repression is required and a rate limiting step in the increased transcription of Neuregulin 1 (type I), which is required for efficient remyelination. However, mouse nerves with EED-deficient Schwann cells display slow axonal regeneration with significantly low expression of axon guidance genes, including Sema4f and Cntf. Finally, EED loss causes impaired Schwann cell proliferation after injury with significant induction of the Cdkn2a cell cycle inhibitor gene. Interestingly, PRC2 subunits and CDKN2A are commonly co-mutated in the transition from benign neurofibromas to malignant peripheral nerve sheath tumors (MPNST's). RNA-seq analysis of EED-deficient mice identified PRC2-regulated molecular pathways that may contribute to the transition to malignancy in neurofibromatosis.

Sciatic neuropathy and rhabdomyolysis after carbon monoxide intoxication: A case report

RATIONALE

Peripheral neuropathy is a rare complication of carbon monoxide intoxication. Peripheral neuropathy following carbon monoxide intoxication is known to completely recover within a few months.

PATIENT CONCERNS

A 40-year-old man complained of motor weakness and hypoesthesia of the right lower extremity with swelling of his right thigh after carbon monoxide intoxication resulting from a suicide attempt.

DIAGNOSES

Following nerve conduction and electromyographic studies, the patient was diagnosed with sciatic neuropathy with severe axonopathy. Clinical and laboratory findings led to a diagnosis of rhabdomyolysis.

INTERVENTIONS

The patient was treated conservatively for rhabdomyolysis and underwent comprehensive rehabilitation for sciatic neuropathy during hospitalization.

OUTCOMES

After discharge, he underwent serial follow-up tests with nerve conduction and electromyographic studies, which showed prolonged persistence of sciatic neuropathy; however, he showed significant improvement at his 26-month post-discharge follow-up.

LESSON

Patients presenting with peripheral neuropathy secondary to carbon monoxide intoxication may show variable recovery periods; however, a favorable prognosis can be expected regardless of the concomitant occurrence of rhabdomyolysis and/or compartment syndrome.

Administration of Oxygen Ultra-Fine Bubbles Improves Nerve Dysfunction in a Rat Sciatic Nerve Crush Injury Model

Ultra-fine bubbles (<200 nm in diameter) have several unique properties and have been tested in various medical fields. The purpose of this study was to investigate the effects of oxygen ultra-fine bubbles (OUBs) on a sciatic nerve crush injury (SNC) model rats. Rats were intraperitoneally injected with 1.5 mL saline, OUBs diluted in saline, or nitrogen ultra-fine bubbles (NUBs) diluted in saline three times per week for 4 weeks in four groups: (1) control, (sham operation + saline); (2) SNC, (crush + saline); (3) SNC+OUB, (crush + OUB-saline); (4) SNC+NUB, (crush + NUB-saline). The effects of the OUBs on dorsal root ganglion (DRG) neurons and Schwann cells (SCs) were examined by serial dilution of OUB medium in vitro. Sciatic functional index, paw withdrawal thresholds, nerve conduction velocity, and myelinated axons were significantly decreased in the SNC group compared to the control group; these parameters were significantly improved in the SNC+OUB group, although NUB treatment did not affect these parameters. In vitro, OUBs significantly promoted neurite outgrowth in DRG neurons by activating AKT signaling and SC proliferation by activating ERK1/2 and JNK/c-JUN signaling. OUBs may improve nerve dysfunction in SNC rats by promoting neurite outgrowth in DRG neurons and SC proliferation.

Miconazole enhances nerve regeneration and functional recovery after sciatic nerve crush injury

INTRODUCTION

Improving axonal outgrowth and remyelination is crucial for peripheral nerve regeneration. Miconazole appears to enhance remyelination in the central nervous system. In this study we assess the effect of miconazole on axonal regeneration using a sciatic nerve crush injury model in rats.

METHODS

Fifty Sprague-Dawley rats were divided into control and miconazole groups. Nerve regeneration and myelination were determined using histological and electrophysiological assessment. Evaluation of sensory and motor recovery was performed using the pinprick assay and sciatic functional index. The Cell Counting Kit-8 assay and Western blotting were used to assess the proliferation and neurotrophic expression of RSC 96 Schwann cells.

RESULTS

Miconazole promoted axonal regrowth, increased myelinated nerve fibers, improved sensory recovery and walking behavior, enhanced stimulated amplitude and nerve conduction velocity, and elevated proliferation and neurotrophic expression of RSC 96 Schwann cells.

DISCUSSION

Miconazole was beneficial for nerve regeneration and functional recovery after peripheral nerve injury. Muscle Nerve 57: 821-828, 2018.

Heparanase attenuates axon degeneration following sciatic nerve transection

Axon degeneration underlies many nervous system diseases; therefore understanding the regulatory signalling pathways is fundamental to identifying potential therapeutics. Previously, we demonstrated heparan sulphates (HS) as a potentially new target for promoting CNS repair. HS modulate cell signalling by both acting as cofactors in the formation of ligand-receptor complexes and in sequestering ligands in the extracellular matrix. The enzyme heparanase (Hpse) negatively regulates these processes by cleaving HS and releasing the attached proteins, thereby attenuating their ligand-receptor interaction. To explore a comparative role for HS in PNS axon injury/repair we data mined published microarrays from distal sciatic nerve injury. We identified Hpse as a previously unexplored candidate, being up-regulated following injury. We confirmed these results and demonstrated inhibition of Hpse led to an acceleration of axonal degeneration, accompanied by an increase in β-catenin. Inhibition of β-catenin and the addition of Heparinase I both attenuated axonal degeneration. Furthermore the inhibition of Hpse positively regulates transcription of genes associated with peripheral neuropathies and Schwann cell de-differentiation. Thus, we propose Hpse participates in the regulation of the Schwann cell injury response and axo-glia support, in part via the regulation of Schwann cell de-differentiation and is a potential therapeutic that warrants further investigation.

Crush injury to motor nerves in the G93A transgenic mouse model of amyotrophic lateral sclerosis promotes muscle reinnervation and survival of functionally intact nerve-muscle contacts

Selective survival of small motor nerve fibers and their neuromuscular contacts in the SOD1^G93A transgenic mouse model of amyotrophic lateral sclerosis (ALS) suggests that smaller regenerated nerve fibers are more able to sustain reformed nerve-muscle connections as functionally intact motor units (MUs). The sciatic nerve was crushed unilaterally in SOD1^G93A transgenic mice at 40 days of age and contractile forces of reinnervated muscles and their MUs were recorded at 90 days in order to determine the capacities of the nerves to regenerate and to form and retain functional neuromuscular connections. Reduced MU numbers in fast-twitch tibialis anterior, extensor digitorum longus and medial gastrocnemius muscles and the lesser reductions in slow-twitch soleus muscle of SOD1^G93A transgenic mice were reversed in reinnervated muscles: there were more reinnervated MUs and their contractile forces and the muscle forces and weights increased. In line with the contrasting ability of only small not large nerve fibers to sprout to form enlarged MUs in the SOD1^G93A transgenic mouse, the smaller regenerating nerve fibers formed enlarged MUs that were better able to survive. Because nerve fibers with and without muscle contacts were severed by the sciatic nerve crush injury, the conditioning lesion is untenable as the explanation for improved maintenance of reinnervated neuromuscular junctions. Elevated neurotrophic factor expression in axotomized motoneurons and/or denervated Schwann cells and the synapse withdrawal from axotomized motoneurons are other factors that, in addition to reduced size of nerve fibers reinnervating muscles, may account for increased survival and size of reinnervated MUs in ALS.

Tissue-engineered nerve graft with tetramethylpyrazine for repair of sciatic nerve defects in rats

A tissue-engineered nerve with tetramethylpyrazine (TMP) was repaired for sciatic nerve defects in rats. A total of 55 adult Sprague Dawley (SD) rats were classified into 4 groups, with 15 rats in each of groups A, B, and C as well as 10 rats in group D. About 1.5cm of a sciatic nerve of the right hind limb located 0.5cm below the inferior margin of the piriformis was resected to form the defects. Four types of nerve grafts used for bridging nerve defects in the SD rats corresponded to the 4 groups: tissue-engineered nerves with TMP in group A, tissue-engineered nerves without TMP in group B, acellular nerve grafts (ANGs) in group C, and autologous nerves in group D. Twelve weeks post-surgery, the sciatic functional index, nerve conduction velocity, and gastrocnemius wet weight of groups A and D were higher than those of groups B and C (P<0.05). Results of fluorescence microscopy and histological staining indicated that group A performed better than groups B and C (P<0.05). Similarly, the number of horseradish peroxidase-labeled positive cells was significantly larger in group A than in groups B and C. Regenerative nerve fibers were abundant in group A and consisted mainly of myelinated nerve fibers, which were better than those in groups B and C (P<0.05). The study demonstrated that tissue-engineered nerves constructed by ANGs seeded with neural stem cells and combined with TMP can effectively repair sciatic nerve defects in rats.

Neural Progenitor-Like Cells Induced from Human Gingiva-Derived Mesenchymal Stem Cells Regulate Myelination of Schwann Cells in Rat Sciatic Nerve Regeneration

Regeneration of peripheral nerve injury remains a major clinical challenge. Recently, mesenchymal stem cells (MSCs) have been considered as potential candidates for peripheral nerve regeneration; however, the underlying mechanisms remain elusive. Here, we show that human gingiva‐derived MSCs (GMSCs) could be directly induced into multipotent NPCs (iNPCs) under minimally manipulated conditions without the introduction of exogenous genes. Using a crush‐injury model of rat sciatic nerve, we demonstrate that GMSCs transplanted to the injury site could differentiate into neuronal cells, whereas iNPCs could differentiate into both neuronal and Schwann cells. After crush injury, iNPCs, compared with GMSCs, displayed superior therapeutic effects on axonal regeneration at both the injury site and the distal segment of the injured sciatic nerve. Mechanistically, transplantation of GMSCs, especially iNPCs, significantly attenuated injury‐triggered increase in the expression of c‐Jun, a transcription factor that functions as a major negative regulator of myelination and plays a central role in dedifferentiation/reprogramming of Schwann cells into a progenitor‐like state. Meanwhile, our results also demonstrate that transplantation of GMSCs and iNPCs consistently increased the expression of Krox‐20/EGR2, a transcription factor that governs the expression of myelin proteins and facilitates myelination. Altogether, our findings suggest that transplantation of GMSCs and iNPCs promotes peripheral nerve repair/regeneration, possibly by promoting remyelination of Schwann cells mediated via the regulation of the antagonistic myelination regulators, c‐Jun and Krox‐20/EGR2. Stem Cells Translational Medicine2017;6:458–470

Tetracycline-regulated expression of OLIG2 gene in human dental pulp stem cells lead to mouse sciatic nerve regeneration upon transplantation

Numerous studies have indicated dental pulp stem cells (DPSCs) potency to differentiate into several types of cell lineages. Oligodendrocyte lineage transcription factor 2 (OLIG2) plays an important role in the oligodendrogenic pathway. In this study, a tetracycline (Tet)-inducible system expressing OLIG2 gene was transfected into human DPSCs to direct their differentiation toward oligodendrocyte progenitor cells (OPCs). Following induction, the expression of stage-specific markers was studied by Reverse Transcription quantitative Polymerase Chain Reaction (RT-qPCR), immunocytochemistry and western blotting. In the following, the cells were transplanted into the mouse model of local sciatic demyelination damage by lysolecithin. Recovery of lysolecithin-induced lesions in sciatic nerve was studied by treadmill exercise, von Frey filament test and hind paw withdrawal in response to a thermal stimulus. Improvement of behavioral symptoms was efficiently observed from the second week to the sixth week post-transplantation. Our findings showed that exogenous expression of the OLIG2 gene by a Tet-regulated system could be used as an efficient way to induce the differentiation of DPSCs into functional oligodendrocytes. Meanwhile, the DPSC-derived OPCs have relevant therapeutic potential in the animal model of sciatic nerve injury and therefore might represent a valuable tool for stem cell-based therapy in inflammatory and degenerative diseases of the peripheral and central nervous systems (CNSs).

Improved neurological outcome by intramuscular injection of human amniotic fluid derived stem cells in a muscle denervation model

Purpose

The skeletal muscle develops various degrees of atrophy and metabolic dysfunction following nerve injury. Neurotrophic factors are essential for muscle regeneration. Human amniotic fluid derived stem cells (AFS) have the potential to secrete various neurotrophic factors necessary for nerve regeneration. In the present study, we assess the outcome of neurological function by intramuscular injection of AFS in a muscle denervation and nerve anastomosis model.

Materials and Methods

Seventy two Sprague-Dawley rats weighing 200–250 gm were enrolled in this study. Muscle denervation model was conducted by transverse resection of a sciatic nerve with the proximal end sutured into the gluteal muscle. The nerve anastomosis model was performed by transverse resection of the sciatic nerve followed by four stitches reconnection. These animals were allocated to three groups: control, electrical muscle stimulation, and AFS groups.

Results

NT-3 (Neurotrophin 3), BDNF (Brain derived neurotrophic factor), CNTF (Ciliary neurotrophic factor), and GDNF (Glia cell line derived neurotrophic factor) were highly expressed in AFS cells and supernatant of culture medium. Intra-muscular injection of AFS exerted significant expression of several neurotrophic factors over the distal end of nerve and denervated muscle. AFS caused high expression of Bcl-2 in denervated muscle with a reciprocal decrease of Bad and Bax. AFS preserved the muscle morphology with high expression of desmin and acetylcholine receptors. Up to two months, AFS produced significant improvement in electrophysiological study and neurological functions such as SFI (sciatic nerve function index) and Catwalk gait analysis. There was also significant preservation of the number of anterior horn cells and increased nerve myelination as well as muscle morphology.

Conclusion

Intramuscular injection of AFS can protect muscle apoptosis and likely does so through the secretion of various neurotrophic factors. This protection furthermore improves the nerve regeneration in a long term nerve anastomosis model.

Nerve guidance conduits from aligned nanofibers: improvement of nerve regeneration through longitudinal nanogrooves on a fiber surface

A novel fibrous conduit consisting of well-aligned nanofibers with longitudinal nanogrooves on the fiber surface was prepared by electrospinning and was subjected to an in vivo nerve regeneration study on rats using a sciatic nerve injury model. For comparison, a fibrous conduit having a similar fiber alignment structure without surface groove and an autograft were also conducted in the same test. The electrophysiological, walking track, gastrocnemius muscle, triple-immunofluorescence, and immunohistological analyses indicated that grooved fibers effectively improved sciatic nerve regeneration. This is mainly attributed to the highly ordered secondary structure formed by surface grooves and an increase in the specific surface area. Fibrous conduits made of longitudinally aligned nanofibers with longitudinal nanogrooves on the fiber surface may offer a new nerve guidance conduit for peripheral nerve repair and regeneration.

In vivo optical microscopy of peripheral nerve myelination with polarization sensitive-optical coherence tomography

Assessing nerve integrity and myelination after injury is necessary to provide insight for treatment strategies aimed at restoring neuromuscular function. Currently, this is largely done with electrical analysis, which lacks direct quantitative information. In vivo optical imaging with sufficient imaging depth and resolution could be used to assess the nerve microarchitecture. In this study, we examine the use of polarization sensitive-optical coherence tomography (PS-OCT) to quantitatively assess the sciatic nerve microenvironment through measurements of birefringence after applying a nerve crush injury in a rat model. Initial loss of function and subsequent recovery were demonstrated by calculating the sciatic function index (SFI). We found that the PS-OCT phase retardation slope, which is proportional to birefringence, increased monotonically with the SFI. Additionally, histomorphometric analysis of the myelin thickness and g-ratio shows that the PS-OCT slope is a good indicator of myelin health and recovery after injury. These results demonstrate that PS-OCT is capable of providing nondestructive and quantitative assessment of nerve health after injury and shows promise for continued use both clinically and experimentally in neuroscience.

Effects of extracorporeal shock wave therapy on functional recovery and neurotrophin-3 expression in the spinal cord after crushed sciatic nerve injury in rats

The study described here investigated the effects of extracorporeal shock wave therapy (ESWT) on functional recovery and neurotrophin-3 expression in the spinal cord after sciatic nerve injury in rats. Forty-five 8-wk-old rats were used and randomly divided into three groups: An experimental group, a control group and a sham group. The experimental group received ESWT after the nerve-crushing damage. The sciatic functional index and Dartfish Software were used to determine the effect of sciatic nerve damage on functional changes. A 1-cm length of spinal cord encompassing the L4-6 level was removed for Western blot analysis. The sciatic functional index significantly changed in both the ESWT and control groups after impairment. In the time course evaluation of the ankle angle in the toe off, the ESWT group had statistically significant increases from day 21 onward. There was a significant difference in neurotrophin-3 expression between the groups on days 1, 7 and 14 after impairment. Early application of ESWT increased the expression of neurotrophin-3 and neurotrophin-3 mRNA, and daily therapy facilitated the activity of macrophages and Schwann cells, which affect the survival and regeneration of neurons.

High-intensity focused ultrasound attenuates neural responses of sciatic nerves isolated from normal or neuropathic rats

Patients with diabetic neuropathy often have neuropathic pain. The purpose of our work was to investigate the effects of high-intensity focused ultrasound (HIFU) on the conduction block of normal and neuropathic nerves for soothing pain. Adult male Sprague-Dawley rats were used, and diabetes was induced by streptozotocin injection. Diabetic neuropathy was evaluated with animal behavior tests. Sciatic nerves of both control and neuropathic rats were dissected from the starting point of the sciatic nerve to the point where the sural nerve ends near the ankle. The nerves were stored in Ringer's solution. The in vitro nerve was placed on a self-developed experimental platform for HIFU exposure. Stimulation and recording of the compound action potentials (CAPs) and sensory action potentials (SAPs) were performed. Control and neuropathic nerves exposed or not exposed to HIFU were submitted to histologic analysis. For the control and neuropathic nerves, suppression of CAPs and SAPs started 2 min post-HIFU treatment. Maximum suppression of SAPs was 34.4 ± 3.2% for the control rats and 11.6 ± 2.0% and 9.8 ± 3.0% for rats 4 wk post-injection and 8 wk post-injection, respectively. Time to full recovery was 25, 70 and 80 min, respectively. Histologic analysis revealed that the nerves in which CAPs and SAPs did not fully recover were damaged thermally or mechanically by HIFU. It is feasible to reversibly block nerves with appropriate HIFU treatment. Diabetic nerves were less suppressed by HIFU and were more vulnerable to permanent damage.

Research on recovery function of two drugs combination on rat sciatic nerve injury regeneration model

This paper aims to study the recovery function of two drugs combination on rat sciatic nerve injury regeneration model. Sixty rats were divided into groups randomly and averagely. All animals after dividing left sciatic nerve were given epineurium-interrupted suture for constructing peripheral nerve injury model. Muscle on operation side in medication administration team was injected 0.5 ml drug while the contract group was given equal amount of normal saline. Sciatic nerve function evaluation and nerve electrophysiology index detection were conducted after operation at fixed period. We drew materials for morphological observation 12 weeks after operation. The results showed that group with independent administration of nerve growth factor (NGF) and nimodipine (ND) in large dose was superior than group in small dose in nerve electro physiology index (P<0.05) and group with combination administration of NGF and ND in large dose was also superior than group in small dose (P<0.05). In addition, regeneration effect of combination administration group was better than that of independent administration group when using same dose. The larger the dose was, the better the effect was. We can conclude that two-drug combination can promote recovery function on rat sciatic nerve injury regeneration model.

Low-level laser irradiation improves functional recovery and nerve regeneration in sciatic nerve crush rat injury model

The development of noninvasive approaches to facilitate the regeneration of post-traumatic nerve injury is important for clinical rehabilitation. In this study, we investigated the effective dose of noninvasive 808-nm low-level laser therapy (LLLT) on sciatic nerve crush rat injury model. Thirty-six male Sprague Dawley rats were divided into 6 experimental groups: a normal group with or without 808-nm LLLT at 8 J/cm² and a sciatic nerve crush injury group with or without 808-nm LLLT at 3, 8 or 15 J/cm². Rats were given consecutive transcutaneous LLLT at the crush site and sacrificed 20 days after the crush injury. Functional assessments of nerve regeneration were analyzed using the sciatic functional index (SFI) and hindlimb range of motion (ROM). Nerve regeneration was investigated by measuring the myelin sheath thickness of the sciatic nerve using transmission electron microscopy (TEM) and by analyzing the expression of growth-associated protein 43 (GAP43) in sciatic nerve using western blot and immunofluorescence staining. We found that sciatic-injured rats that were irradiated with LLLT at both 3 and 8 J/cm² had significantly improved SFI but that a significant improvement of ROM was only found in rats with LLLT at 8 J/cm². Furthermore, the myelin sheath thickness and GAP43 expression levels were significantly enhanced in sciatic nerve-crushed rats receiving 808-nm LLLT at 3 and 8 J/cm². Taken together, these results suggest that 808-nm LLLT at a low energy density (3 J/cm² and 8 J/cm²) is capable of enhancing sciatic nerve regeneration following a crush injury.

Orally active opioid μ/δ dual agonist MGM-16, a derivative of the indole alkaloid mitragynine, exhibits potent antiallodynic effect on neuropathic pain in mice

(E)-Methyl 2-((2S,3S,7aS,12bS)-3-ethyl-7a-hydroxy-8-methoxy-1,2,3,4,6,7,7a,12b-octahydroindolo[2,3-a]quinolizin-2-yl)-3-methoxyacrylate (7-hydroxymitragynine), a main active constituent of the traditional herbal medicine Mitragyna speciosa, is an indole alkaloid that is structurally different from morphine. 7-Hydroxymitragynine induces a potent antinociceptive effect on mouse acute pain through μ-opioid receptors. In this study, we developed dual-acting μ- and δ-opioid agonists MGM-15 and MGM-16 from 7-hydroxymitragynine for the treatment of acute and chronic pain. MGM-16 showed a higher potency than that of 7-hydroxymitragynine and MGM-15 in in vitro and in vivo assays. MGM-16 exhibited a high affinity for μ- and δ-opioid receptors, with K(i) values of 2.1 and 7.0 nM, respectively. MGM-16 showed μ- and δ-opioid full agonistic effects in a guanosine 5'-O-(3-[(35)S]thiotriphosphate) binding assay and in a functional test using electrically elicited guinea pig ileum and mouse vas deferens contractions. Systemic administration of MGM-16 produced antinociceptive effects in a mouse acute pain model and antiallodynic effects in a chronic pain model. The antinociceptive effect of MGM-16 was approximately 240 times more potent than that of morphine in a mouse tail-flick test, and its antiallodynic effect was approximately 100 times more potent than that of gabapentin in partial sciatic nerve-ligated mice, especially with oral administration. The antinociceptive effect of MGM-16 was completely and partially blocked by the μ-selective antagonist β-funaltrexamine hydrochloride (β-FNA) and by the δ-selective antagonist naltrindole, respectively, in a tail-flick test. The antiallodynic effect of MGM-16 was completely blocked by β-FNA and naltrindole in a neuropathic pain model. These findings suggest that MGM-16 could become a class of a compound with potential therapeutic utility for treating neuropathic pain.

Imaging neuroinflammation in vivo in a neuropathic pain rat model with near-infrared fluorescence and ¹⁹F magnetic resonance

Chronic neuropathic pain following surgery represents a serious worldwide health problem leading to life-long treatment and the possibility of significant disability. In this study, neuropathic pain was modeled using the chronic constriction injury (CCI). The CCI rats exhibit mechanical hypersensitivity (typical neuropathic pain symptom) to mechanical stimulation of the affected paw 11 days post surgery, at a time when sham surgery animals do not exhibit hypersensitivity. Following a similar time course, TRPV1 gene expression appears to rise with the hypersensitivity to mechanical stimulation. Recent studies have shown that immune cells play a role in the development of neuropathic pain. To further explore the relationship between neuropathic pain and immune cells, we hypothesize that the infiltration of immune cells into the affected sciatic nerve can be monitored in vivo by molecular imaging. To test this hypothesis, an intravenous injection of a novel perfluorocarbon (PFC) nanoemulsion, which is phagocytosed by inflammatory cells (e.g. monocytes and macrophages), was used in a rat CCI model. The nanoemulsion carries two distinct imaging agents, a near-infrared (NIR) lipophilic fluorescence reporter (DiR) and a ¹⁹F MRI (magnetic resonance imaging) tracer, PFC. We demonstrate that in live rats, NIR fluorescence is concentrated in the area of the affected sciatic nerve. Furthermore, the ¹⁹FF MRI signal was observed on the sciatic nerve. Histological examination of the CCI sciatic nerve reveals significant infiltration of CD68 positive macrophages. These results demonstrate that the infiltration of immune cells into the sciatic nerve can be visualized in live animals using these methods.

[The comparative pattern of neuromidin and magnetic stimulation influence on neuroplasticity in experimental traumatic neuropathy]

OBJECTIVE

Traumatic neuropathies are among the most actual problems in neurology due to the severe neurological deficit in most cases and poor prognosis of recovery. We evaluated the effect of ipidacrin (cholinesterase inhibitor) and magnetic stimulation on neuroplastic axonal changes after experimental neurotmesis of rat's sciatic nerve.

MATERIAL AND METHODS

Animals (20 rats) were stratified into 3 groups. There was no treatment in the control group; in the second -group experimental animals underwent 3-5 min daily rhythmic magnetic stimulation (0,8-1T, 3 Hz) The third group of animals received intramuscular 0,035 mg of ipidacrin daily within 1 month.

RESULTS AND CONCLUSIONS

Based on the received data on the restoration of myelin, axons, myelin nodes structure and lemmocyte ultrastructure), we have concluded that both magnetic stimulation and ipidacrin can trigger restorative and compensative processes in traumatic neuropathies.

[Involvement of peripheral NFκB in tetanic sciatic stimulation-induced neuropathic pain]

Tetanic stimulation of the sciatic nerve (TSS) induces long-term potentiation (LTP) of both C- and A-fiber-evoked field potentials in the spinal dorsal horn and long-lasting mechanical allodynia in rats. Though central mechanisms underlying those phenomena have been well studied, peripheral mechanisms still remain poorly known. Nuclear factor kappa B (NFκB) is an important transcription factor. In the spinal cord, NFκB plays a key role in regulating the expression of numerous pro-inflammation factors and contributes to glial activation in central nervous system, suggesting the involvement of spinal NFκB in central sensitization. To address whether NFκB in the dorsal root ganglion (DRG) participates in peripheral sensitization, we examined NFκB expression in the DRG and the effect of inhibiting NFκB activation on neuropathic pain using behavior test, Western blot analysis and immunohistochemical approaches. The results showed that TSS induced long-lasting mechanical allodynia in bilateral hind paws and increased phospho-NFκB expression in the bilateral DRG. The activated NFκB mainly expressed in nuclei not only of neurons, but also of Schwann cells and satellite glial cells. Moreover, NFκB inhibitor pyrrolidine dithiocarbamate (PDTC) significantly alleviated TSS-induced allodynia. Our results suggest that peripheral NFκB may be involved in TSS-induced neuropathic pain, and provide new evidence for the peripheral mechanism of 'mirror pain'.

Green tea pain modulating effect in sciatic nerve chronic constriction injury rat model

We investigated the effect of green tea (GT) in unilateral chronic constriction injury (CCI) to the rat scaitic nerve. Five groups (n = 6 rats/group) sham group: rats which underwent operation but with no ligation to the scaitic nerve, and received tap water for two weeks before and for five weeks after the surgery. Four experimental groups underwent CCI to the right sciatic nerve, divided randomly as follows: group E were given tap water throughout the study. Group B received GT before and after CCI. Group C was given GT following CCI. Group D received GT for two weeks prior to CCI. Groups which consumed GT showed significant improvement in the toe spread (P < 0.001) and foot positioning (P < 0.001) tests compared to the experimental control group. In addition, these groups showed a significant decrease in the behavioral mechanical hyperalgesia (P < 0.0001) and allodynia (P < 0.0002). Consumption of GT improves both reflexes and sensation which are often affected in the course of peripheral neuropathy.

Poly (dextrogyr-levogyr) lactide acid-triiodothyronine scaffold for peripheral nerve regeneration

OBJECTIVES

To evaluate the poly(dextrogyr-levogyr) lactide acid-triiodothyronine (PDLLA-T3) seeded with Schwann cells conduit for repairing sciatic nerve defect.

MATERIALS & METHODS

The rats were divided into three groups: autologous nerve transplantation (Group A), PDLLA-T3 + Schwann cells (Group B) and PDLLA + Schwann cells (Group C).

RESULTS

Myelin sheath thickness was significantly greater in Group A compared with Group B and Group C. The regenerated nerves had nearly normal structure in Group A, and in Groups B and C nerve tissues filled in the anastomotic site and angiogenesis was noted. The mean number of myelinated nerve fibers and neurons in Group B was greater than in Group C.

CONCLUSIONS

PDLLA-T3 is superior to PDLLA alone for repairing nerve defects.

Exogenous melatonin abolishes mechanical allodynia but not thermal hyperalgesia in neuropathic pain. The role of the opioid system and benzodiazepine-gabaergic mechanism

Melatonin (MT) is a neurohormone synthesized and secreted by the pineal gland. MT plays an important role in the regulation of physiological and neuroendocrine functions. The purpose of this study was to assess the overall effect of melatonin on neuropathic pain, the type of melatonin receptor involved, and potential role of the opioid system and GABA(A) receptors. The experiments were conducted by using the animal neuropathic pain model (CCI). The rats with CCI showed the characteristic for the mechanical allodynia and thermal hyperalgesia signs that were calculated by using the von Frey's and Hargreaves' tests. The conducted studies measured the effects of intraperitoneal administration of naloxone (opioid antagonist), prazosin (MT3 antagonist), luzindole (MT1/MT2 receptor antagonist), picrotoxin (GABA(A) antagonist) and flumazenil (benzodiazepine antagonist) on the antinociceptive effects caused by melatonin. Melatonin caused the increase in the pain threshold of the mechanical allodynia and the slight increase in the threshold of the thermal hyperalgesia. The pre-treatment with naloxone completely abolished the antinociceptive effects of melatonin in von Frey's test, but not thermal sensation in the Hargreaves's test. Prazosin did not have any effects, while administration of luzindole significantly suppressed the antinociceptive effect of melatonin. The antiallodynic effect of MT was also abolished by flumazenil and picrotoxin. Melatonin influences the mechanical allodynia but not thermal hyperalgesia via activation of opioid system and benzodiazepine-GABAergic pathway. Antinociceptive effects of melatonin are mostly related to the MT1/MT2 receptors interaction.

Synthesis and biological evaluation of the 1-arylpyrazole class of σ(1) receptor antagonists: identification of 4-{2-[5-methyl-1-(naphthalen-2-yl)-1H-pyrazol-3-yloxy]ethyl}morpholine (S1RA, E-52862)

The synthesis and pharmacological activity of a new series of 1-arylpyrazoles as potent σ(1) receptor (σ(1)R) antagonists are reported. The new compounds were evaluated in vitro in human σ(1)R and guinea pig σ(2) receptor (σ(2)R) binding assays. The nature of the pyrazole substituents was crucial for activity, and a basic amine was shown to be necessary, in accordance with known receptor pharmacophores. A wide variety of amines and spacer lengths between the amino and pyrazole groups were tolerated, but only the ethylenoxy spacer and small cyclic amines provided compounds with sufficient selectivity for σ(1)R vs σ(2)R. The most selective compounds were further profiled, and compound 28, 4-{2-[5-methyl-1-(naphthalen-2-yl)-1H-pyrazol-3-yloxy]ethyl}morpholine (S1RA, E-52862), which showed high activity in the mouse capsaicin model of neurogenic pain, emerged as the most interesting candidate. In addition, compound 28 exerted dose-dependent antinociceptive effects in several neuropathic pain models. This, together with its good physicochemical, safety, and ADME properties, led compound 28 to be selected as clinical candidate.

Bilateral sciatic nerve palsy: a new presentation of toilet bowl neuropathy

BACKGROUND

Presentations of lower extremity compression palsies are rare and exist only in case reports. The true incidence of emergency department (ED) presentations of bilateral sciatic nerve palsy, "toilet bowl neuropathy," is unknown. The following is a case of a 28-year-old active duty Navy woman who presented to our ED via ambulance with bilateral sciatic nerve palsy from prolonged immobility.

OBJECTIVES

This discussion reviews the historical precedence for the diagnosis and details the work-up and prognosis.

CASE REPORT

The patient presented complaining of bilateral lower extremity swelling, numbness, and an inability to walk after a prolonged, medication-facilitated sleep in an unusual position. She had significant weakness on examination and was admitted for further evaluation and care. Specialized neurologic studies were consistent with bilateral sciatic nerve palsy.

CONCLUSION

Bilateral sciatic nerve palsy is an uncommon cause of lower extremity weakness. In the ED, other diagnoses such as Guillain-Barré syndrome, cauda equina, disk herniation, and gluteal compartment syndrome should be considered initially. The diagnosis of toilet bowl neuropathy, however, is dependent on obtaining an accurate history. This case report adds another perspective to the literature on sciatic nerve palsy recognition, diagnosis, and prognosis.

c-Jun reprograms Schwann cells of injured nerves to generate a repair cell essential for regeneration

The radical response of peripheral nerves to injury (Wallerian degeneration) is the cornerstone of nerve repair. We show that activation of the transcription factor c-Jun in Schwann cells is a global regulator of Wallerian degeneration. c-Jun governs major aspects of the injury response, determines the expression of trophic factors, adhesion molecules, the formation of regeneration tracks and myelin clearance and controls the distinctive regenerative potential of peripheral nerves. A key function of c-Jun is the activation of a repair program in Schwann cells and the creation of a cell specialized to support regeneration. We show that absence of c-Jun results in the formation of a dysfunctional repair cell, striking failure of functional recovery, and neuronal death. We conclude that a single glial transcription factor is essential for restoration of damaged nerves, acting to control the transdifferentiation of myelin and Remak Schwann cells to dedicated repair cells in damaged tissue.

Interleukin-10 of red nucleus plays anti-allodynia effect in neuropathic pain rats with spared nerve injury

Our previous studies have shown that pro-inflammatory cytokines tumor necrosis factor-alpha (TNF-α) and interleukin-1beta (IL-1β) in red nucleus (RN) are involved in the development of neuropathic pain and play facilitated roles on the mechanical allodynia induced by peripheral nerve injury. The current study was designed to evaluate the expression and effect of IL-10, an anti-inflammatory cytokine, in the RN of rats with spared nerve injury (SNI). Immunohistochemical staining results demonstrated when 3 weeks after SNI, the expression level of IL-10 in the contralateral RN of SNI rats was apparently higher than those of sham-operated and normal rats. To further study the effect of IL-10 in the development of neuropathic pain, different doses of IL-10 (1.0, 0.5 and 0.1 μg/μl) were microinjected respectively into the RN contralateral to the nerve injury side of SNI rats. Results demonstrated that higher doses of IL-10 (1.0 and 0.5 μg/μl) significantly attenuated the mechanical allodynia of neuropathic rats, while 0.1 μg/μl of IL-10 did not show any analgesic effect. These results suggest that IL-10 of RN participates in the development of neuropathic pain and plays inhibitory roles on the mechanical allodynia induced by SNI.

Ameliorative effect of combined administration of inducible nitric oxide synthase inhibitor with cyclooxygenase-2 inhibitors in neuropathic pain in rats

OBJECTIVES

The objective of this study was to examine the effects of rofecoxib, meloxicam, both cyclooxygenase-2 (COX-2) inhibitors and aminoguanidine hydrochloride, an inducible nitric oxide synthase (iNOS) inhibitor and their combinations in neuropathic pain in rats.

METHODS

Neuropathy was induced by chronic constriction injury (CCI) of right sciatic nerve under ketamine anesthesia in rats. Effect of ED(50) of aminoguanidine hydrochloride, rofecoxib and meloxicam administered orally was investigated using behavioral tests. Effect of combinations of aminoguanidine hydrochloride with rofecoxib and meloxicam was also investigated in neuropathic pain employing behavioral tests.

RESULTS

Behavioral tests, mechanical, thermal and cold stimuli confirmed the development of neuropathic pain after CCI. Aminoguanidine hydrochloride, rofecoxib and meloxicam when administered alone, produced significant increase in paw withdrawal threshold to mechanical stimuli at 6 h in ipsilateral hind paw after CCI. Co-administration of aminoguanidine hydrochloride (30 mg/kg) with rofecoxib (1.31 mg/kg) and meloxicam (1.34 mg/kg) was also found to produce significant increase in paw withdrawal latencies to mechanical stimuli at 6 h. Combined administration of aminoguanidine hydrochloride with meloxicam and rofecoxib produced significant rise in pain threshold for mechanical hyperalgesia in ipsilateral hind paw when compared with the groups treated with aminoguanidine hydrochloride, meloxicam and rofecoxib alone.

CONCLUSION

Co-administration of meloxicam and rofecoxib with aminoguanidine hydrochloride may be an alternative approach for the treatment of neuropathic pain.

C3 peptide promotes axonal regeneration and functional motor recovery after peripheral nerve injury

Peripheral nerve injuries are frequently seen in trauma patients and due to delayed nerve repair, lifelong disabilities often follow this type of injury. Innovative therapies are needed to facilitate and expedite peripheral nerve regeneration. The purpose of this study was to determine the effects of a 1-time topical application of a 26-amino-acid fragment (C3(156-181)), derived from the Clostridium botulinum C3-exoenzyme, on peripheral nerve regeneration in 2 models of nerve injury and repair in adult rats. After sciatic nerve crush, different dosages of C3(156-181) dissolved in buffer or reference solutions (nerve growth factor or C3(bot)-wild-type protein) or vehicle-only were injected through an epineurial opening into the lesion sites. After 10-mm nerve autotransplantation, either 8.0 nmol/kg C3(156-181) or vehicle were injected into the proximal and distal suture sites. For a period of 3 to 10 postoperative weeks, C3(156-181)-treated animals showed a faster motor recovery than control animals. After crush injury, axonal outgrowth and elongation were activated and consequently resulted in faster motor recovery. The nerve autotransplantation model further elucidated that C3(156-181) treatment accounts for better axonal elongation into motor targets and reduced axonal sprouting, which are followed by enhanced axonal maturation and better axonal functionality. The effects of C3(156-181) are likely caused by a nonenzymatic down-regulation of active RhoA. Our results indicate the potential of C3(156-181) as a therapeutic agent for the topical treatment of peripheral nerve repair sites.

Role of NMDA and opioid receptors in neuropathic pain induced by chronic constriction injury of sciatic nerve in rats

BACKGROUND

The efficacy of opioids in neuropathic pain is still controversial. Earlier studies have suggested that N-methyl-D-aspartate (NMDA) receptor binding can be affected by opioids and vice versa. The present study aims to explore the interactions between NMDA and opioid receptors using various combinations of drugs acting on these receptors.

METHODS

We used an animal model of sciatic nerve ligation to induce neuropathic pain, and a hot-plate test was used to assess pain response.

RESULTS

It was observed that NMDA and naloxone increased the pain response. Ketamine reduced the pain response, which was further reduced when ketamine was administered in combination with naloxone, but not with NMDA, thus highlighting the activity of the NMDA receptor system. In addition, morphine was also found to increase latency to hind-paw lick, which was further reduced when given in combination with naloxone. Furthermore, triple drug combinations using ketamine+morphine+naloxone and ketamine+NMDA+naloxone demonstrated some significant interactions at these receptors.

CONCLUSIONS

Thus, our study establishes that neuropathic pain can probably be overcome using higher doses of opioids, and there exists some intimate relationships between NMDA and opioid systems that lead to pain modulation.

Effects of combining electrical stimulation with BDNF gene transfer on the regeneration of crushed rat sciatic nerve

BACKGROUND AND AIMS

Various techniques have been investigated to enhance peripheral nerve regeneration including the application of low-intensity electrical stimulation (ES) and the administration of growth factors, especially brain-derived neurotrophic factor (BDNF). The purpose of this study was to investigate the effects of combining short-term (ES) and recombinant adenoviral vector-mediated BDNF (BDNF-Ad) transfer, in comparison to each sole modality, on peripheral nerve regeneration in a rat model with crush-injured sciatic nerve.

METHODS

Sixty male Sprague-Dawley rats (250-300 g) were equally distributed into four groups; the control group, the ES group, the BDNF-Ad group, and the combination group (n = 15 each). A standard crush injury was introduced to the sciatic nerve. The control group received no treatment after injury, the ES group received 30 minutes of low-intensity ES, the BDNF-Ad group received an injection of recombinant BDNF-Ad (concentration = 10(11) pfu/μl, 3 μl/rat) after injury, and the combination group received both ES and BDNF-Ad. The rats were followed-up for 3 weeks.

RESULTS

At the end of the follow-up period, the sciatic function index (ES =-39, BDNF-Ad =-38) and number of the retrogradely labeled sensory neurons were significantly increased in the ES group and the BDNF-Ad group (ES = 326, BDNF-Ad = 264), but not in the combined treatment group, compared to the control group (SFI = -53, retrogradely labeled neurons = 229). Axonal counts were highest in the ES group (7,208 axons), axonal densities in the BDNF group (10,598 axons/mm(2)), and the myelin thickness was greater in both groups as compared to the control group. The combined treatment group showed no signs of superior recovery compared to the other groups.

CONCLUSIONS

Both the ES and the BDNF-Ad treatments were effective techniques enhancing the sciatic nerve regeneration following a crush injury in rats. Nevertheless, the combined treatment with ES and BDNF-Ad produces neither a synergistic effect nor an improvement in this injury model.

Effect of prior treatment with ultra-low-dose morphine on opioid- and nerve injury-induced hyperalgesia in rats

BACKGROUND

In addition to producing analgesia, opioids can increase sensitivity to pain (opioid-induced hyperalgesia [OIH]) in humans and rodents. Tolerance/OIH is likely mediated by similar mechanisms that lead to development of hyperalgesia after nerve injury (neuropathic pain). OIH may be a reason for loss of opioid efficacy and/or a worsening of pain. Ultra-low-dose (ULD) opioid evokes hyperalgesia independently of analgesia. Tolerance to ULD-OIH develops with repeated dosing in rats.

OBJECTIVE

The effects of ULD opioids were characterized in two distinct situations where hyperalgesia is expected to occur: following acute opioid treatment and after nerve injury.

DESIGN

First, ULD morphine was repeatedly administered (2x day for 5 days) by intrathecal (i.t., 0.01 microg) or intraperitoneal (i.p., 20 microg/kg) routes in rats. Second, morphine (0.01 microg i.t.; 20 microg/kg i.p.) was administered (2x day for 5 days) prior to acute morphine (30 microg i.t.; 10 mg/kg i.p). Third, ULD morphine (20 microg/kg/2x day, i.p.) was given either immediately after nerve injury (days 1-28) or when hyperalgesia was manifested (days 7-14). The tail-flick and paw-pressure tests were used in noninjured and nerve-injured rats, respectively.

RESULTS

Tolerance was developed to OIH with repeated ULD morphine by the i.p. route but not the i.t. route. Prior exposure to ULD morphine (i.p.) caused prolongation of morphine analgesia in intact rats and inhibition of the development (but not reversal) of hyperalgesia in nerve-injured rats. Abolishment of OIH (pain desensitization) may diminish activation of pain facilitatory systems due to nerve injury and opioid treatment.

CONCLUSIONS

Although the translational aspect of this preclinical study has limitations, the present data may suggest a new strategy for the pre-emptive use of ULD opioids to prevent the development of neuropathic pain with certain procedures or disease states.

Differential GABAergic disinhibition during the development of painful peripheral neuropathy

An impaired spinal GABAergic inhibitory function is known to be pivotal in neuropathic pain (NPP). At present, data concerning time-dependent alterations within the GABAergic system itself and post-synaptic GABA(A) receptor-mediated inhibitory transmission are highly controversial, likely related to the experimental NPP model used. Furthermore, it is unknown whether the severity of NPP is determined by the degree of these GABAergic disturbances. In the present study we therefore examined in one experimental animal model whether anatomical changes within the spinal GABAergic system and its GABA(A) receptor-mediated inhibitory function are gradually aggravated during the development of partial sciatic nerve injury (PSNL)-induced NPP and are related to the severity of PSNL-induced hypersensitivity. Three and 16 days after a unilateral PSNL (early and late NPP, respectively), GABA-immunoreactivity (GABA-IR) and the number of GABA-IR neuronal profiles were determined in Rexed laminae 1-3 of lumbar spinal cord cryosections. Additionally, the efficiency of dorsal horn GABA(A) receptor-induced inhibition was examined by cation chloride cotransporter 2 (KCC2) immunoblotting. NPP-induced hypersensitivity was only observed at the ipsilateral side, both at early and late time points. During early NPP, a decrease in ipsilateral dorsal horn GABA-IR was observed without alterations in the number of GABA-IR neuronal profiles or KCC2 protein levels. In contrast, bilateral increases in spinal GABA-IR accompanied by an unchanged number of GABA-IR interneurons were observed during late NPP. This was furthermore attended with decreased ipsilateral KCC2 levels. Moreover, the degree of hypersensitivity was not related to disturbances within the spinal GABAergic system at all time points examined. In conclusion, our anatomical data suggest that a dysfunctional GABA production is likely to be involved in early NPP whereas late NPP is characterized by a combined dysfunctional GABA release and decreased KCC2 levels, the latter suggesting an impaired GABA(A) receptor-mediated inhibition.