The role of sodium channels in chronic pain

2-Aminopyridines as Potent and Selective Nav1.8 Inhibitors Exhibiting Efficacy in a Nonhuman Primate Pain Model

Herein we describe the discovery of a 2-aminopyridine scaffold as a potent and isoform selective inhibitor of the Nav1.8 sodium channel. Parallel library synthesis, guided by in silico predictions, rapidly transformed initial hits into a novel 2-aminopyridine lead class possessing good ADME and pharmacokinetic profiles that were able to display activity in a clinically translatable nonhuman primate capsaicin-sensitized thermode pharmacodynamic assay. Progress toward the lead identification, optimization, and in vivo efficacy of these compounds will be discussed.

Sodium and water dynamics in the progression of chronic kidney disease: mechanisms and clinical significance

AIM

Lifestyle modifications can postpone the progression of chronic kidney disease toward its terminal stage. This mini-review aims to explore the impact of salt and water intake on the progression of chronic kidney disease (CKD) and provide insights into the optimal consumption levels to preserve the glomerular filtration rate.

METHODS

We reviewed relevant literature to examine the association between salt and water consumption and CKD progression. Our analysis includes discussions on the pathophysiology, findings from clinical trials, and recommended intake guidelines.

RESULTS

Sodium intake, often linked to cardiovascular risk and CKD progression, has shown a complex J-shaped association in some studies, leading to uncertainty about the ideal salt intake level. Sodium and fluid retention are key factors contributing to hypertension, a well-established risk factor for CKD progression. Low-sodium diets have demonstrated promise in reducing blood pressure and enhancing the effects of renin-angiotensin-aldosterone system inhibitors in non-dialysis CKD patients. However, a debate persists regarding the independent effect of salt restriction on CKD progression. Despite medical recommendations, salt consumption remains high among CKD patients. Additionally, the role of water consumption in CKD remains controversial despite its established benefits for CKD prevention in the general population.

CONCLUSION

Lifestyle modifications involving salt and water intake can influence the progression of CKD. While low-sodium diets have shown potential for mitigating hypertension and proteinuria in non-dialysis CKD patients, their independent impact on CKD progression warrants further investigation. The role of water consumption in CKD remains uncertain, and there is a need for additional research in this area. Clinicians should consider individualized dietary recommendations for CKD patients to help preserve the glomerular filtration rate and improve overall outcomes.

Effects of Nutraceutical Compositions Containing Rhizoma Gastrodiae or Lipoic Acid in an In Vitro Induced Neuropathic Pain Model

BACKGROUND

Peripheral neuropathy is caused by a malfunction in the axons and myelin sheaths of peripheral nerves and motor and sensory neurons. In this context, nonpharmacological treatments with antioxidant potential have attracted much attention due to the issues that some conventional pharmaceutical therapy can generate. Most of these treatments contain lipoic acid, but issues have emerged regarding its use. Considering this, the present study evaluated the beneficial effects of nutraceuticals based on Gastrodiae elata dry extract 10:1 or lipoic acid in combination with other substances (such as citicholine, B vitamins, and acetyl L-carnitine).

METHOD

To assess the combination's absorption and biodistribution and exclude cytotoxicity, its bioavailability was first examined in a 3D intestinal barrier model that replicated oral ingestion. Subsequently, a 3D model of nerve tissue was constructed to investigate the impacts of the new combination on the significant pathways dysregulated in peripheral neuropathy.

RESULTS

Our findings show that the novel combination outperformed in initial pain relief response and in recovering the mechanism of nerve healing following Schwann cell injury by successfully crossing the gut barrier and reaching the target site.

CONCLUSION

This article describes a potential alternative nutraceutical approach supporting the effectiveness of combinations with Gastrodiae elata extract in decreasing neuropathy and regulating pain pathways.

Prolonged exposure to lactate causes TREK1 channel clustering in rat hippocampal astrocytes

Increased concentrations of lactate (15-30 mM) are associated with and found to be neuroprotective in various brain pathophysiology. In our earlier studies we showed that high levels of lactate can increase TREK1 channel activity and expression within 1 h. TREK1 channels are two pore domain leak potassium ion channels that are upregulated during cerebral ischemia, epilepsy and other brain pathologies. They play a prominent neuroprotective role against excitotoxicity. Although it has been previously shown that chronic application of lactate (6 h) causes increased gene transcription and protein expression, we observe clustering of TREK1 channels that is dependent on time of exposure (3-6 h) and concentration of lactate (15-30 mM). Using immunofluorescence techniques and image analysis, we show that the clustering of TREK1 channels is dependent on the actin cytoskeletal network of the astrocytes. Clustering of TREK1 channels can augment astrocytic functions during pathophysiological conditions and have significant implications in lactate mediated neuroprotection.

Role of autophagy in the pathogenesis and regulation of pain

Pain is a ubiquitous and highly concerned clinical symptom, usually caused by peripheral or central nervous injury, tissue damage, or other diseases. The long-term existence of pain can seriously affect daily physical function and quality of life and produce great torture on the physiological and psychological levels. However, the complex pathogenesis of pain involving molecular mechanisms and signaling pathways has not been fully elucidated, and managing pain remains highly challenging. As a result, finding new targets to pursue effective and long-term pain treatment strategies is required and urgent. Autophagy is an intracellular degradation and recycling process that maintains tissue homeostasis and energy supply, which can be cytoprotective and is vital in maintaining neural plasticity and proper nervous system function. Much evidence has shown that autophagy dysregulation is linked to the emergence of neuropathic pain, such as postherpetic neuralgia and cancer-related pain. Autophagy has also been connected to pain caused by osteoarthritis and lumbar disc degeneration. It is worth noting that in recent years, studies on traditional Chinese medicine have also proved that several traditional Chinese medicine monomers involve autophagy in the mechanism of pain relief. Therefore, autophagy can serve as a potential regulatory target to provide new ideas and inspiration for pain management.

Peripheral nerve blocks for the management of lumbo-sacral radiculopathy: A prospective study

Background

The epidural injections used to treat lumbar radiculopathy are potentially associated with serious complications like neurological injuries and epidural abscess. The nociceptors have the unique property of being pseudo-unipolar, as its both ends are expected to be functionally same. We have hypothesized that peripheral nerve blocks given at the distal site should be able to provide pain relief. This prospective study was planned to assess the efficacy of peripheral nerve blocks in lumbar radiculopathy.

Methods

Thirty-four patients who fit the eligibility criteria were included in this open labeled prospective preliminary study. They were administered peripheral nerve blocks at ankle level with 4 ml of 0.25% bupivacaine and 40 mg of triamcinolone.

Outcomes measured

The outcomes measured at 15 days, 1 month, 2 months, and 3 months after the intervention were the pain intensity (Numerical Rating Scale), the Global Perceived Effect, functional status (Roland Morris Disability Questionnaire), Beck's Depression Inventory score, employment status, and analgesic intake.

Results

At 15 days, 1 month, and 2 months, 88% of the patients reported a ≥50% decrease in their pain scores and a GPE ≥6, while at 3 months 85% of the patients reported a significant decrease in their pain scores and a GPE ≥6.

Conclusion

Peripheral nerve blocks are effective in the management of pain in patients with chronic lumbosacral radiculopathy. The ability to administer it in an outpatient setting, without image guidance and the absence of debilitating side effects, makes it an attractive treatment option.

Stress-induced headache in the general working population is moderated by the NRCAM rs2300043 genotype

OBJECTIVES

Earlier findings suggest that social stress such as abusive supervision may promote pain. In the present study we examine the possible moderating role of genetic variability in the NRCAM gene in this process.

METHODS

The data were collected through a national survey drawn from the National Central Employee Register by Statistics Norway. A total of 1,205 individuals returned both the questionnaire and the saliva kit. Abusive supervision was scored by a 5-item version of the Tepper's 2,000 scale. Headache was measured on a four-category scale; 'not bothered,' 'a little bothered,' 'considerably bothered', 'seriously bothered'. Genotyping with regards to NRCAM rs2300043 was carried out using Taqman assay. Ordinal logistic regression was used to analyse the data.

RESULTS

For males exposed to abusive supervision, those carrying the rs2300043 CC genotype reported the highest levels of headache. Women showed a trend towards the opposite pattern. Women with the rs2300043 CC genotype seem to have a weaker effect of abusive supervision regarding reported headache than their male counterparts with the CC genotype when exposed to abusive supervision.

CONCLUSIONS

The present results indicated that the association between abusive supervision and headache in men with the NRCAM rs2300043 C allele was stronger than in other men. This suggests that the NRCAM genotype in men is important for the tolerance of social stress e.g., repeated negative acts from a superior. In contrast, a trend, though non-significant, towards the opposite pattern was observed in women. Our result suggests that the NRCAM genotype in men manifestly affects stress-induced pain such as headache.

Pathophysiological and Neuroplastic Changes in Postamputation and Neuropathic Pain: Review of the Literature

Despite advancements in surgical and rehabilitation strategies, extremity amputations are frequently associated with disability, phantom limb sensations, and chronic pain. Investigation into potential treatment modalities has focused on the pathophysiological changes in both the peripheral and central nervous systems to better understand the underlying mechanism in the development of chronic pain in persons with amputations.

Methods

Presented in this article is a discussion outlining the physiological changes that occur in the peripheral and central nervous systems following amputation. In this review, the authors examine the molecular and neuroplastic changes occurring in the nervous system, as well as the state-of-the-art treatment to help reduce the development of postamputation pain.

Results

This review summarizes the current literature regarding neurological changes following amputation. Development of both central sensitization and neuronal remodeling in the spinal cord and cerebral cortex allows for the development of neuropathic and phantom limb pain postamputation. Recently developed treatments targeting these pathophysiological changes have enabled a reduction in the severity of pain; however, complete resolution remains elusive.

Conclusions

Changes in the peripheral and central nervous systems following amputation should not be viewed as separate pathologies, but rather two interdependent mechanisms that underlie the development of pathological pain. A better understanding of the physiological changes following amputation will allow for improvements in therapeutic treatments to minimize pathological pain caused by amputation.

Etv4 regulates nociception by controlling peptidergic sensory neuron development and peripheral tissue innervation

The perception of noxious environmental stimuli by nociceptive sensory neurons is an essential mechanism for the prevention of tissue damage. Etv4 is a transcriptional factor expressed in most nociceptors in dorsal root ganglia (DRG) during the embryonic development. However, its physiological role remains unclear. Here, we show that Etv4 ablation results in defects in the development of the peripheral peptidergic projections in vivo, and in deficits in axonal elongation and growth cone morphology in cultured sensory neurons in response to NGF. From a mechanistic point of view, our findings reveal that NGF regulates Etv4-dependent gene expression of molecules involved in extracellular matrix (ECM) remodeling. Etv4-null mice were less sensitive to noxious heat stimuli and chemical pain, and this behavioral phenotype correlates with a significant reduction in the expression of the pain-transducing ion channel TRPV1 in mutant mice. Together, our data demonstrate that Etv4 is required for the correct innervation and function of peptidergic sensory neurons, regulating a transcriptional program that involves molecules associated with axonal growth and pain transduction.

Preclinical nerve conduction: Nerve battery options for primate studies

Electrophysiological neurodiagnostic tests of nerve conduction (NC) are key assays included in preclinical safety and toxicology programs to assess the peripheral neuropathy (PN) liability of a new drug. Despite their increased use, standardization of nerve conduction studies (NCS) is lacking in the preclinical space, with limited regulatory guidelines stipulating type and number of nerves or minimum combinations appropriate for each stage of drug development or indication. Detection of subtle peripheral toxicities depends on choosing appropriate nerve targets for testing, especially when functional changes remain above the lower limit of normal values. To support robust preclinical toxicology study designs, the current short communication provides options and recommendations for selecting peripheral nerves for clinically translatable nerve conduction batteries applicable to toxicology and gene therapy, with a focus on clinically translatable primate models. A comprehensive compilation of accessible nerve locations is offered including lower and upper extremity motor nerves, and sensory nerves with origin at multiple DRG levels. Rankings of technique difficulty and repeatability across serial collections are presented for each assay informed by serial nerve conduction from 500 adult primates. The goal of this communication is to support the standardization and preclinical implementation of this important assay.

Potential Role of Yoga Intervention in the Management of Chronic Non-malignant Pain

Pain is an unpleasant and upsetting experience. Persistent pain has an impact on an individual's quality of life which causes stress and mood disorders. There are currently no pain-relieving techniques available that can eliminate pain and offer relief without causing any adverse effects. These factors draw attention to traditional treatments like yoga and meditation, which can reduce biological stress and hence increase immunity, as well as alleviate the psychological and emotional suffering produced by pain. Yoga reduces the stress response and the pain cascade via the downregulation of the hypothalamus-pituitary-adrenal (HPA) axis and vagal stimulation. Yoga is a cost-effective growing health practice that, unlike pharmaceuticals, has no side effects and can help patients stay in remission for longer periods of time with fewer relapses. Yoga not only reduces stress and depression severity but also improves functional status and reduces pain perception. This article highlights the impact of yoga on pain management and on a malfunctioning immune system, which leads to improved health, pain reduction, disease management, and improvement in overall quality of life.

Lidocaine reduces pain behaviors by inhibiting the expression of Nav1.7 and Nav1.8 and diminishing sympathetic sprouting in SNI rats

Chronic neuropathic pain is a significant clinical challenge, and the mechanisms of neuropathic pain remain elusive. Previous studies have shown that spontaneous potential, which is triggered by Nav1.7 and Nav1.8 in the dorsal root ganglion (DRG), is crucial for the development of inflammatory and neuropathic pain. Functional coupling between the sympathetic nervous system and somatosensory nerves after a nerve injury has also been noted as an important factor in neuropathic pain. However, the relationship of sympathetic sprouting with Nav1.7 and Nav1.8 remains unclear. Therefore, we dynamically examined the mechanical withdrawal threshold (MWT), changes in Nav1.7 and Nav1.8, and sympathetic sprouting after lidocaine treatment in the spared nerve injury (SNI) model of rats. After lidocaine treatment, the MWT obviously increased, showing that hypersensitivity was significantly relieved and the abnormal expression of Nav1.7 and Nav1.8 caused by SNI was also significantly reduced. In addition, lidocaine distinctly inhibited sympathetic nerve sprouting and basket formation around the Nav1.7 and Nav1.8 neurons in the DRG. These results indicate that lidocaine may alleviate neuropathic pain by inhibiting the expression of Nav1.7 and Nav1.8, and diminishing sympathetic sprouting in DRG.

Mechanisms and Physiological Implications of Cooperative Gating of Ion Channels Clusters

Ion channels play a central role in the regulation of nearly every cellular process. Dating back to the classic 1952 Hodgkin-Huxley model of the generation of the action potential, ion channels have always been thought of as independent agents. A myriad of recent experimental findings exploiting advances in electrophysiology, structural biology, and imaging techniques, however, have posed a serious challenge to this long-held axiom as several classes of ion channels appear to open and close in a coordinated, cooperative manner. Ion channel cooperativity ranges from variable-sized oligomeric cooperative gating in voltage-gated, dihydropyridine-sensitive Ca_v1.2 and Ca_v1.3 channels to obligatory dimeric assembly and gating of voltage-gated Na_v1.5 channels. Potassium channels, transient receptor potential channels, hyperpolarization cyclic nucleotide-activated channels, ryanodine receptors (RyRs), and inositol trisphosphate receptors (IP₃Rs) have also been shown to gate cooperatively. The implications of cooperative gating of these ion channels range from fine tuning excitation-contraction coupling in muscle cells to regulating cardiac function and vascular tone, to modulation of action potential and conduction velocity in neurons and cardiac cells, and to control of pace-making activity in the heart. In this review, we discuss the mechanisms leading to cooperative gating of ion channels, their physiological consequences and how alterations in cooperative gating of ion channels may induce a range of clinically significant pathologies.

Nerve Interface Strategies for Neuroma Management and Prevention: A Conceptual Approach Guided by Institutional Experience

In this article, the authors propose a strategy to manage and prevent symptomatic neuromas using a combination of nerve interface approaches. By using a reconstructive paradigm, these procedures provide the components integral to organized nerve regeneration, conferring both improvements in pain and potential for myoelectric control of prostheses in the future. Given the lack of evidence at this point indicating the advantage of any single nerve interface procedure, the authors propose a management approach that maximizes physiologic restoration while limiting morbidity where possible.

The Changes in Expression of NaV1.7 and NaV1.8 and the Effects of the Inhalation of Their Blockers in Healthy and Ovalbumin-Sensitized Guinea Pig Airways

Background: The presented study evaluated the suppositional changes in the airway expression of Nav1.8 and Nav1.7 and their role in the airway defense mechanisms in healthy animals and in an experimental asthma model. Methods: The effects of the blockers inhalation on the reactivity of guinea pig airways, number of citric-acid-induced coughs and ciliary beating frequency (CBF) were tested in vivo. Chronic inflammation simulating asthma was induced by repetitive exposure to ovalbumin. The expression of Nav1.7 and Nav1.8 was examined by ELISA. Results: The Nav 1.8 blocker showed complex antitussive and bronchodilatory effects and significantly regulated the CBF in healthy and sensitized animals. The Nav1.7 blockers significantly inhibited coughing and participated in CBF control in the ovalbumin-sensitized animals. The increased expression of the respective ion channels in the sensitized animals corresponded to changes in CBF regulation. The therapeutic potency of the Nav1.8 blocker was evidenced in combinations with classic bronchodilators. Conclusion: The allergic-inflammation-upregulated expression of Nav1.7 and Nav1.8 and corresponding effects of blocker inhalation on airway defense mechanisms, along with the Nav1.8 blocker’s compatibility with classic antiasthmatic drugs, bring novel possibilities for the treatment of various respiratory diseases. However, the influence of the Nav1.8 blocker on CBF requires further investigation.

Determinants of conductance of a bacterial voltage-gated sodium channel

Through molecular dynamics (MD) and free energy simulations in electric fields, we examine the factors influencing conductance of bacterial voltage-gated sodium channel Na_vMs. The channel utilizes four glutamic acid residues in the selectivity filter (SF). Previously, we have shown, through constant pH and free energy calculations of pKa values, that fully deprotonated, singly protonated, and doubly protonated states are all feasible at physiological pH, depending on how many ions are bound in the SF. With 173 MD simulations of 450 or 500 ns and additional free energy simulations, we determine that the conductance is highest for the deprotonated state and decreases with each additional proton bound. We also determine that the pKa value of the four glutamic residues for the transition between deprotonated and singly protonated states is close to the physiological pH and that there is a small voltage dependence. The pKa value and conductance trends are in agreement with experimental work on bacterial Na_v channels, which show a decrease in maximal conductance with lowering of pH, with pKa in the physiological range. We examine binding sites for Na⁺ in the SF, compare with previous work, and note a dependence on starting structures. We find that narrowing of the gate backbone to values lower than the crystal structure's backbone radius reduces the conductance, whereas increasing the gate radius further does not affect the conductance. Simulations with some amount of negatively charged lipids as opposed to purely neutral lipids increases the conductance, as do simulations at higher voltages.

Neuroscience and Neuroimmunology Solutions for Osteoarthritis Pain: Biological Drugs, Growth Factors, Peptides and Monoclonal Antibodies Targeting Peripheral Nerves

Neuroscience is a vast discipline that deals with the anatomy, biochemistry, molecular biology, physiology and pathophysiology of central and peripheral nerves. Advances made through basic, translational, and clinical research in the field of neuroscience have great potential for long-lasting and beneficial impacts on human and animal health. The emerging field of biological therapy is intersecting with the disciplines of neuroscience, orthopaedics and rheumatology, creating new horizons for interdisciplinary and applied research. Biological drugs, growth factors, therapeutic peptides and monoclonal antibodies are being developed and tested for the treatment of painful arthritic and rheumatic diseases. This concise communication focuses on the solutions provided by the fields of neuroscience and neuroimmunology for real-world clinical problems in the field of orthopaedics and rheumatology, focusing on synovial joint pain and the emerging biological treatments that specifically target pathways implicated in osteoarthritis pain in peripheral nerves.

Pharmacological Management of Adults with Chronic Non-Cancer Pain in General Practice

Chronic pain is a public health priority that affects about 20% of the general population, causing disability and impacting productivity and quality of life. It is often managed in the primary care setting. Chronic pain management is most effective when the pain mechanism has been identified and addressed by appropriate therapy. This document provides an overview of pharmacological therapy for chronic non-cancer pain in the primary care setting, with the aim of improving treatment decisions based on the underlying pain mechanisms and pain neuroscience.

Assessment of the impact of PTGS1, PTGS2 and CYP2C9 polymorphisms on pain, effectiveness and safety of NSAID therapies

Cyclooxygenase 1 and 2 (COX-1, COX-2) are enzymes that catalyze the first reaction in the arachidonic acid pathway. COXs are the therapeutic target for non-steroidal anti-inflammatory drugs. Inhibition of COX enzymatic activity has an analgesic, anti-inflammatory and sometimes antiplatelet effect. Single-nucleotide polymorphisms (SNPs) within genes encoding COX-1 and COX-2 (PTGS1, PTGS2) influence the risk of pain and their intensity in some diseases. They also affect the effectiveness of NSAID therapy in rheumatoid diseases. Moreover, the relationship between certain polymorphisms of PTGS2 and a higher risk of migraine and the development of aspirin resistance in the prophylaxis of cardiovascular diseases was demonstrated. The isoform of cytochrome P450, CYP2C9 has a significant influence on the efficacy and safety of NSAID use. It is responsible for the metabolism and speed of removal of these drugs. The occurrence of some of its polymorphic forms is associated with a decrease in CYP2C9 enzymatic activity, leading to changes in the pharmacokinetics and pharmacodynamics of NSAIDs. The prolonged half-life and decrease in clearance of these drugs lead to serious side effects such as hepatotoxicity, nephrotoxicity, anaphylactic reactions, cardiovascular or gastrointestinal incidents. Studies on polymorphisms of cyclooxygenases and CYP2C9 may improve the safety and efficacy of NSAIDs therapy by adjusting the dose to individual polymorphic variants, as well as expanding knowledge about the pathomechanism of inflammatory diseases.

Neuro-biochemical changes induced by zinc oxide nanoparticles

Nanoparticles are now widely used in various aspects of life, especially zinc oxide nanoparticles (ZnNPs) that used in mouth washing, cosmetics, sunscreens, toothpaste and root canal flings. This research aims to determine the impact of ZnNPs on healthy mice's brain tissue. ZnNPs have caused major changes in the brain monoamines (dopamine, norepinephrine and serotonin) and ions such as Ca²⁺, Na⁺, K⁺ and Zn²⁺. Concerning the histological picture, administration of ZnNPs caused some histopathological impairment in brain tissue. In addition, ZnNPs reduced the level of glutathione and catalase in brain tissue, although an increase in the level of nitrite / nitrate and ROS was observed, while the level of malondialdhyde was not significantly altered. Moreover, ZnNPs induced DNA fragmentation in brain of mice. Collectively, the obtained results revealed that ZnNPs affected the brain levels of investigated monamines, ions, enzymatic and non-enzymatic antioxidants thus they may have potential influence on central nervous system.

Supraorbital Nerve Radiofrequency for Severe Neuralgia Caused by Herpes Zoster Ophthalmicus

Background

Radiofrequency of the Gasserian ganglion can be used for ophthalmic herpetic neuralgia (OHN), but it is associated with complications. This study aimed to use the supraorbital nerve for computed tomography- (CT-) guided radiofrequency thermocoagulation to treat refractory OHN.

Methods

This was a retrospective case series study of patients with simple or combined OHN treated at our hospital between 06/2012 and 06/2018. The numerical rating score (NRS), spontaneous pain, allodynia, gabapentin dosage, paracetamol/oxycodone dosage, patient global impression of change (PGIC) score, Barrow numbness score, postoperative 360-day recurrence rate, and complications were recorded before the operation and at 1, 30, 90, 180, and 360 days after the operation.

Results

Compared with baseline, the NRS was decreased, and PGIC was increased at postoperative 1, 30, 90, 180, and 360 days, and the gabapentin and paracetamol oxycodone doses at postoperative 30, 90, 180, and 360 days were decreased (all P < 0.001). Compared with 1 day after the operation, numbness was decreased at 30, 90, 180, and 360 days after the operation (P < 0.001). Compared with baseline, the number of patients with allodynia at each time point after the operation was decreased (P < 0.001), but without a difference for spontaneous pain (P=0.407). No subjects showed drooping eyelid, corneal ulcers, eyeball damage, decreased vision, and other severe complications.

Conclusion

CT-guided supraorbital nerve radiofrequency thermocoagulation for the treatment of OHN can effectively relieve pain and reduce the dose of analgesics, without any serious complication. This study suggests that this technique is feasible and applicable to clinical practice.

Conserved Expression of Nav1.7 and Nav1.8 Contribute to the Spontaneous and Thermally Evoked Excitability in IL-6 and NGF-Sensitized Adult Dorsal Root Ganglion Neurons In Vitro

Sensory neurons respond to noxious stimuli by relaying information from the periphery to the central nervous system via action potentials driven by voltage-gated sodium channels, specifically Nav1.7 and Nav1.8. These channels play a key role in the manifestation of inflammatory pain. The ability to screen compounds that modulate voltage-gated sodium channels using cell-based assays assumes that key channels present in vivo is maintained in vitro. Prior electrophysiological work in vitro utilized acutely dissociated tissues, however, maintaining this preparation for long periods is difficult. A potential alternative involves multi-electrode arrays which permit long-term measurements of neural spike activity and are well suited for assessing persistent sensitization consistent with chronic pain. Here, we demonstrate that the addition of two inflammatory mediators associated with chronic inflammatory pain, nerve growth factor (NGF) and interleukin-6 (IL-6), to adult DRG neurons increases their firing rates on multi-electrode arrays in vitro. Nav1.7 and Nav1.8 proteins are readily detected in cultured neurons and contribute to evoked activity. The blockade of both Nav1.7 and Nav1.8, has a profound impact on thermally evoked firing after treatment with IL-6 and NGF. This work underscores the utility of multi-electrode arrays for pharmacological studies of sensory neurons and may facilitate the discovery and mechanistic analyses of anti-nociceptive compounds.

Scope and Applications of Nanomedicines for the Management of Neuropathic Pain

Neuropathic pain, resulting from the dysfunction of the peripheral and central nervous system, occurs in a variety of pathological conditions including trauma, diabetes, cancer, HIV, surgery, multiple sclerosis, ischemic attack, alcoholism, spinal cord damage, and many others. Despite the availability of various treatment strategies, the percentage of patients achieving adequate pain relief remains low. The clinical failure of most effective drugs is often not due to a lack of drug efficacy but due to the dose-limiting central nervous system (CNS) toxicity of the drugs that preclude dose escalation. There is a need for cross-disciplinary collaborations to meet these challenges. In this regard, the integration of nanotechnology with neuroscience is one of the most important fields. In recent years, promising preclinical research has been reported in this field. This review highlights the current challenges associated with conventional neuropathic pain treatments, the scope for nanomaterials in delivering drugs across the blood-brain barrier, and the state and prospects of nanomaterials for the management of neuropathic pain.

Postoperative pain pathophysiology and treatment strategies after CRS + HIPEC for peritoneal cancer

Background

Cytoreductive surgery (CRS) combined with hyperthermic intraperitoneal chemotherapy (HIPEC) is a treatment choice for peritoneal cancer. However, patients commonly suffer from severe postoperative pain. The pathophysiology of postoperative pain is considered to be from both nociceptive and neuropathic origins.

Main body

The recent advances on the etiology of postoperative pain after CRS + HIPEC treatment were described, and the treatment strategy and outcomes were summarized.

Conclusion

Conventional analgesics could provide short-term symptomatic relief. Thoracic epidural analgesia combined with opioids administration could be an effective treatment choice. In addition, a transversus abdominis plane block could also be an alternative option, although further studies should be performed.

The clustering of voltage-gated sodium channels in various excitable membranes

In excitable membranes, the clustering of voltage-gated sodium channels (VGSC) serves to enhance excitability at critical sites. The two most profoundly studied sites of channel clustering are the axon initial segment, where action potentials are generated and the node of Ranvier, where action potentials propagate along myelinated axons. The clustering of VGSC is found, however, in other highly excitable sites such as axonal terminals, postsynaptic membranes of dendrites and muscle fibers, and pre-myelinated axons. In this review, different examples of axonal as well as non-axonal clustering of VGSC are discussed and the underlying mechanisms are compared. Whether the clustering of channels is intrinsically or extrinsically induced, it depends on the submembranous actin-based cytoskeleton that organizes these highly specialized membrane microdomains through specific adaptor proteins.

Coccydynia relieved by a tarsal tunnel block: a case series

BACKGROUND

This case series describes, for the first time, to the author's knowledge, a novel treatment for coccydynia. Tarsal tunnel block with lignocaine only brought relief of chronic coccydynia lasting more than 6 months in three patients. The author adopts the theory that the myelin sheath of the posterior tibial nerve will convey the lipid-soluble lignocaine upward toward the dorsal root ganglia and the nerve roots of the lumbar spine through the uninterrupted myelin sheath, which is itself mainly formed of lipids. The author thinks that most coccyx pain is actually a radiating pain from the lumbar spine, which is not always apparent on magnetic resonance imaging of the lumbar spine. Certainly, the author acknowledges that large-scale studies need to be done to prove the efficacy of this new technique and to prove that the myelin sheath can convey the lignocaine chemical upward.

CASE PRESENTATION

Three Arab patients presented with chronic coccydynia of more than 6 months' duration in whom conservative management had failed to control their symptoms. They had no past medical history of significance and no history of trauma. The results of physical examination of all of the patients were normal apart from tenderness on palpation of the coccyx. They all received local coccyx injection with steroids on two occasions, which failed to relieve their pain. One patient underwent manipulation under anesthesia, and one underwent coccygectomy with no pain relief. Magnetic resonance imaging results were reported to be normal in two of them, whereas the other one had a prolapsed disc at the L4/L5 level. The three patients described pain relief 30 minutes after tarsal tunnel block with lignocaine only lasting more than 6 months. All patients had heel anesthesia 15 minutes after the tarsal tunnel injection, which lasted only 1 hour.

CONCLUSIONS

Tarsal tunnel block with lignocaine can relieve coccyx pain for a long time. Tarsal tunnel block can be done to achieve heel anesthesia before injection of lignocaine into the plantar fascia in patients with plantar fasciitis.

Pathological Mechanisms and Therapeutic Targets for Trigeminal Neuropathic Pain

Trigeminal neuropathic pain is a chronic pain condition caused by damage or inflammation of the trigeminal nerve or its branches, with both peripheral and central nervous system dysfunction contributing to the disorder. Trigeminal pain conditions present with diagnostic and therapeutic challenges to healthcare providers and often require multiple therapeutic approaches for pain reduction. This review will provide the overview of pathophysiology in peripheral and central nociceptive circuits that are involved in neuropathic pain conditions involving the trigeminal nerve and the current therapeutics that are used to treat these disorders. Recent advances in treatment of trigeminal pain, including novel therapeutics that target ion channels and receptors, gene therapy and monoclonal antibodies that have shown great promise in preclinical studies and clinical trials will also be described.

Relationship Between Impulsivity and Clinical and Sociodemographic Variables Among Lebanese Patients With Bipolar Disorder: Results of a Cross-Sectional Study

Impulsivity is a psychiatric symptom that seems to be more prevalent in some mental disorders such as bipolar disorders (BDs). It is a trait that seems to be influenced by many clinical and sociodemographic variables across BD. To examine the relationship between impulsivity and these variables, we performed a cross-sectional study on 50 patients diagnosed with BD and 50 healthy subjects. Both groups were administered the Barratt Impulsiveness Scale; the Structural Clinical Interview for Diagnostic and Statistical Manual of Mental Disorders, 5th Edition, for borderline personality disorder; the Beirut District Scale; and the Athens Insomnia Scale to assess impulsivity, borderline personality disorder, psychological distress, and sleep disturbances, respectively. A significantly higher nonplanning impulsivity (p = 0.001), motor impulsivity (p < 0.0001), total impulsivity (p < 0.0001), body mass index (p < 0.0001), and insomnia (p = 0.002) were found in subjects with BDs compared with healthy ones. Exposure to violence (odds ratio [OR] = 7.63), the loss of a parent (OR = 3.83), being a current smoker (OR = 14.56), and a higher motor impulsivity score (OR = 1.27) were all significantly associated with the presence of BD. Impulsivity was shown to be strongly associated with the presence of a diagnosis of BD, and further studies are warranted to fully characterize it through the course of the illness.

Human Dorsal Root Ganglia

Sensory neurons with cell bodies situated in dorsal root ganglia convey information from external or internal sites of the body such as actual or potential harm, temperature or muscle length to the central nervous system. In recent years, large investigative efforts have worked toward an understanding of different types of DRG neurons at transcriptional, translational, and functional levels. These studies most commonly rely on data obtained from laboratory animals. Human DRG, however, have received far less investigative focus over the last 30 years. Nevertheless, knowledge about human sensory neurons is critical for a translational research approach and future therapeutic development. This review aims to summarize both historical and emerging information about the size and location of human DRG, and highlight advances in the understanding of the neurochemical characteristics of human DRG neurons, in particular nociceptive neurons.

Reversible Conduction Failure in Chronic Immune-Mediated Sensorimotor and Autonomic Polyneuropathy

Reversible conduction failure (RCF) has been described in several subtypes of Guillain-Barre syndrome and is typically observed within the first 10 weeks. We describe the presence of RCF lasting for at least 9 months or longer without secondary axonal degeneration in a case of chronic sensorimotor and autonomic polyneuropathy. A 63-year-old woman presented with lower back pain, limb pain, paresthesia, and weakness after a sinus infection. She was diagnosed with mild Guillain-Barre syndrome and treated symptomatically. Four months later, she developed symptoms of dysautonomia and worsening neuropathic pain, and treatment with intravenous immunoglobulin led to significant clinical improvement. Electrodiagnostic study revealed significant improvement, manifesting as increased response amplitudes, improved conduction velocities, shortening of distal latencies, and reduction of sensory and motor response durations without temporal dispersion, thus fitting to the RCF definition. Detection of RCF may have further important implications in the evaluation and management of chronic immune-mediated polyneuropathy.

A correlative analysis between inflammatory cytokines and trigeminal neuralgia or hemifacial spasm

BACKGROUND

It is necessary to understand the mechanism of trigeminal neuralgia (TN) and hemifacial spasm (HFS) in order to seek for an effective noninvasive remedy. As previous studies implied that inflammatory cytokines induced by demyelination following the nerve injury may be the initiated factor causing neuropathic pain, we attempt to analyze the correlation between cytokines and these hyperactive cranial nerve disorders.

METHOD

The consecutive patients whose diagnosis were confirmed by microvascular decompression surgery as primary TN or HFS caused by vascular compression and healthy volunteers between March and May 2018 in XinHua Hospital Shanghai JiaoTong University School of Medicine were recruited. Preoperatively, venous blood was collected and the protein concentrations of IL-1β, IL-2, IL-6, IL-8, IL-10, TNF-α and IFN-γ were determined with ELISA. Each cytokine was compared between the patients and healthy volunteers.

RESULTS

Ultimately, 28 healthy volunteers as well as 44 TN and 47 HFS patients were enrolled in this investigation. The serum levels of IL-1β, IL-6, IL-8 and TNF-α in either HFS or TN patients were significantly higher than that in healthy volunteers (p < 0.05), yet which were similar between TN and HFS patients (p > 0.05). Besides, there was a significantly correlation between IL-6 concentration and severity of HFS (r = 0.933, p < 0.05) or TN (r = 0.943, p < 0.05).

DISCUSSION

Vascular compression of trigeminal or facial nerve roots may induce a rise in variety of cytokines, and IL-6 may play an important role in the signaling pathways to generate ectopic impulses from these cranial nerves.

Schwann Cell Responses and Plasticity in Different Dental Pulp Scenarios

Mammalian teeth have evolved as dentin units that enclose a complex system of sensory innervation to protect and preserve their structure and function. In human dental pulp (DP), mechanosensory and nociceptive fibers form a dense meshwork of nerve endings at the coronal dentin-pulp interface, which arise from myelinated and non-myelinated axons of the Raschkow plexus (RP). Schwann cells (SCs) play a crucial role in the support, maintenance and regeneration after injury of these fibers. We have recently characterized two SC phenotypes hierarchically organized within the coronal and radicular DP in human teeth. Myelinating and non-myelinating SCs (nmSCs) display a high degree of plasticity associated with nociceptive C-fiber sprouting and axonal degeneration in response to DP injuries from dentin caries or physiological root resorption (PRR). By comparative immunolabeling, confocal and electron microscopy, we have characterized short-term adaptive responses of SC phenotypes to nerve injuries, and long-term changes related to aging. An increase of SCs characterizes the early responses to caries progression in association with axonal sprouting in affected DP domains. Moreover, during PRR, the formation of bands of Büngner is observed as part of SC repair tracks functions. On the other hand, myelinated axon density is significantly reduced with tooth age, as part of a gradual decrease in DP defense and repair capacities. The remarkable plasticity and capacity of SCs to preserve DP innervation in different dental scenarios constitutes a fundamental aspect to improve clinical treatments. This review article discusses the central role of myelinating and non-mSCs in long-term tooth preservation and homeostasis.

The intriguing nature of dorsal root ganglion neurons: Linking structure with polarity and function

Dorsal root ganglion (DRG) neurons are the first neurons of the sensory pathway. They are activated by a variety of sensory stimuli that are then transmitted to the central nervous system. An important feature of DRG neurons is their unique morphology where a single process -the stem axon- bifurcates into a peripheral and a central axonal branch, with different functions and cellular properties. Distinctive structural aspects of the two DRG neuron branches may have important implications for their function in health and disease. However, the link between DRG axonal branch structure, polarity and function has been largely neglected in the field, and relevant information is rather scattered across the literature. In particular, ultrastructural differences between the two axonal branches are likely to account for the higher transport and regenerative ability of the peripheral DRG neuron axon when compared to the central one. Nevertheless, the cell intrinsic factors contributing to this central-peripheral asymmetry are still unknown. Here we critically review the factors that may underlie the functional asymmetry between the peripheral and central DRG axonal branches. Also, we discuss the hypothesis that DRG neurons may assemble a structure resembling the axon initial segment that may be responsible, at least in part, for their polarity and electrophysiological features. Ultimately, we suggest that the clarification of the axonal ultrastructure of DRG neurons using state-of-the-art techniques will be crucial to understand the physiology of this peculiar cell type.

Arthropod toxins and their antinociceptive properties: From venoms to painkillers

The complex process of pain control commonly involves the use of systemic analgesics; however, in many cases, a more potent and effective polypharmacological approach is needed to promote clinically significant improvement. Additionally, considering side effects caused by current painkillers, drug discovery is once more turning to nature as a source of more efficient therapeutic alternatives. In this context, arthropod venoms contain a vast array of bioactive substances that have evolved to selectively bind to specific pharmacological targets involved in the pain signaling pathway, playing an important role as pain activators or modulators, the latter serving as promising analgesic agents. The current review explores how the pain pathway works and surveys neuroactive compounds obtained from arthropods' toxins, which function as pain modulators through their interaction with specific ion channels and membrane receptors, emerging as promising candidates for drug design and development.

Transcutaneous electrical nerve stimulation (TENS) for neuropathic pain in adults

BACKGROUND

Neuropathic pain, which is due to nerve disease or damage, represents a significant burden on people and society. It can be particularly unpleasant and achieving adequate symptom control can be difficult. Non-pharmacological methods of treatment are often employed by people with neuropathic pain and may include transcutaneous electrical nerve stimulation (TENS). This review supersedes one Cochrane Review 'Transcutaneous electrical nerve stimulation (TENS) for chronic pain' (Nnoaham 2014) and one withdrawn protocol 'Transcutaneous electrical nerve stimulation (TENS) for neuropathic pain in adults' (Claydon 2014). This review replaces the original protocol for neuropathic pain that was withdrawn.

OBJECTIVES

To determine the analgesic effectiveness of TENS versus placebo (sham) TENS, TENS versus usual care, TENS versus no treatment and TENS in addition to usual care versus usual care alone in the management of neuropathic pain in adults.

SEARCH METHODS

We searched CENTRAL, MEDLINE, Embase, PsycINFO, AMED, CINAHL, Web of Science, PEDro, LILACS (up to September 2016) and various clinical trials registries. We also searched bibliographies of included studies for further relevant studies.

SELECTION CRITERIA

We included randomised controlled trials where TENS was evaluated in the treatment of central or peripheral neuropathic pain. We included studies if they investigated the following: TENS versus placebo (sham) TENS, TENS versus usual care, TENS versus no treatment and TENS in addition to usual care versus usual care alone in the management of neuropathic pain in adults.

DATA COLLECTION AND ANALYSIS

Two review authors independently screened all database search results and identified papers requiring full-text assessment. Subsequently, two review authors independently applied inclusion/exclusion criteria to these studies. The same review authors then independently extracted data, assessed for risk of bias using the Cochrane standard tool and rated the quality of evidence using GRADE.

MAIN RESULTS

We included 15 studies with 724 participants. We found a range of treatment protocols in terms of duration of care, TENS application times and intensity of application. Briefly, duration of care ranged from four days through to three months. Similarly, we found variation of TENS application times; from 15 minutes up to hourly sessions applied four times daily. We typically found intensity of TENS set to comfortable perceptible tingling with very few studies titrating the dose to maintain this perception. Of the comparisons, we had planned to explore, we were only able to undertake a quantitative synthesis for TENS versus sham TENS. Insufficient data and large diversity in the control conditions prevented us from undertaking a quantitative synthesis for the remaining comparisons.For TENS compared to sham TENS, five studies were suitable for pooled analysis. We described the remainder of the studies in narrative form. Overall, we judged 11 studies at high risk of bias, and four at unclear risk. Due to the small number of eligible studies, the high levels of risk of bias across the studies and small sample sizes, we rated the quality of the evidence as very low for the pooled analysis and very low individual GRADE rating of outcomes from single studies. For the individual studies discussed in narrative form, the methodological limitations, quality of reporting and heterogeneous nature of interventions compared did not allow for reliable overall estimates of the effect of TENS.Five studies (across various neuropathic conditions) were suitable for pooled analysis of TENS versus sham TENS investigating change in pain intensity using a visual analogue scale. We found a mean postintervention difference in effect size favouring TENS of -1.58 (95% confidence interval (CI) -2.08 to -1.09, P < 0.00001, n = 207, six comparisons from five studies) (very low quality evidence). There was no significant heterogeneity in this analysis. While this exceeded our prespecified minimally important difference for pain outcomes, we assessed the quality of evidence as very low meaning we have very little confidence in this effect estimate and the true effect is likely to be substantially different from that reported in this review. Only one study of these five investigated health related quality of life as an outcome meaning we were unable to report on this outcome in this comparison. Similarly, we were unable to report on global impression of change or changes in analgesic use in this pooled analysis.Ten small studies compared TENS to some form of usual care. However, there was great diversity in what constituted usual care, precluding pooling of data. Most of these studies found either no difference in pain outcomes between TENS versus other active treatments or favoured the comparator intervention (very low quality evidence). We were unable to report on other primary and secondary outcomes in these single trials (health-related quality of life, global impression of change and changes in analgesic use).Of the 15 included studies, three reported adverse events which were minor and limited to 'skin irritation' at or around the site of electrode placement (very low quality evidence). Three studies reported no adverse events while the remainder did not report any detail with regard adverse events.

AUTHORS' CONCLUSIONS

In this review, we reported on the comparison between TENS and sham TENS. The quality of the evidence was very low meaning we were unable to confidently state whether TENS is effective for pain control in people with neuropathic pain. The very low quality of evidence means we have very limited confidence in the effect estimate reported; the true effect is likely to be substantially different. We make recommendations with respect to future TENS study designs which may meaningfully reduce the uncertainty relating to the effectiveness of this treatment modality.

A novel substituted aminoquinoline selectively targets voltage-sensitive sodium channel isoforms and NMDA receptor subtypes and alleviates chronic inflammatory and neuropathic pain

Recent understanding of the systems that mediate complex disease states, has generated a search for molecules that simultaneously modulate more than one component of a pathologic pathway. Chronic pain syndromes are etiologically connected to functional changes (sensitization) in both peripheral sensory neurons and in the central nervous system (CNS). These functional changes involve modifications of a significant number of components of signal generating, signal transducing and signal propagating pathways. Our analysis of disease-related changes which take place in sensory neurons during sensitization led to the design of a molecule that would simultaneously inhibit peripheral NMDA receptors and voltage sensitive sodium channels. In the current report, we detail the selectivity of N,N-(diphenyl)-4-ureido-5,7-dichloro-2-carboxy-quinoline (DCUKA) for action at NMDA receptors composed of different subunit combinations and voltage sensitive sodium channels having different α subunits. We show that DCUKA is restricted to the periphery after oral administration, and that circulating blood levels are compatible with its necessary concentrations for effects at the peripheral cognate receptors/channels that were assayed in vitro. Our results demonstrate that DCUKA, at concentrations circulating in the blood after oral administration, can modulate systems which are upregulated during peripheral sensitization, and are important for generating and conducting pain information to the CNS. Furthermore, we demonstrate that DCUKA ameliorates the hyperalgesia of chronic pain without affecting normal pain responses in neuropathic and inflammation-induced chronic pain models.

Altered potassium channel distribution and composition in myelinated axons suppresses hyperexcitability following injury

Neuropathic pain following peripheral nerve injury is associated with hyperexcitability in damaged myelinated sensory axons, which begins to normalise over time. We investigated the composition and distribution of shaker-type-potassium channels (Kv1 channels) within the nodal complex of myelinated axons following injury. At the neuroma that forms after damage, expression of Kv1.1 and 1.2 (normally localised to the juxtaparanode) was markedly decreased. In contrast Kv1.4 and 1.6, which were hardly detectable in the naïve state, showed increased expression within juxtaparanodes and paranodes following injury, both in rats and humans. Within the dorsal root (a site remote from injury) we noted a redistribution of Kv1-channels towards the paranode. Blockade of Kv1 channels with α-DTX after injury reinstated hyperexcitability of A-fibre axons and enhanced mechanosensitivity. Changes in the molecular composition and distribution of axonal Kv1 channels, therefore represents a protective mechanism to suppress the hyperexcitability of myelinated sensory axons that follows nerve injury.

Congenital insensitivity to pain: Fracturing without apparent skeletal pathobiology caused by an autosomal dominant, second mutation in SCN11A encoding voltage-gated sodium channel 1.9

Congenital insensitivity to pain (CIP) comprises the rare heritable disorders without peripheral neuropathy that feature inability to feel pain. Fracturing and joint destruction are common complications, but lack detailed studies of mineral and skeletal homeostasis and bone histology. In 2013, discovery of a heterozygous gain-of-function mutation in SCN11A encoding voltage-gated sodium channel 1.9 (Nav1.9) established a distinctive CIP in three unrelated patients who suffered multiple painless fractures, self-inflicted mutilation, chronic diarrhea, and hyperhidrosis. Here, we studied a mother and two children with CIP by physical examination, biochemical testing, radiological imaging including DXA, iliac crest histology, and mutation analysis. She suffered fractures primarily of her lower extremities beginning at age two years, and had Charcot deformity of both ankles and joint hypermobility. Nerve conduction velocity together with electromyography were normal. Her children had recurrent major fractures beginning in early childhood, joint hypermobility, and chronic diarrhea. She had an excoriated external nare, and both children had hypertrophic scars from scratching. Skin collagen studies were normal. Radiographs revealed fractures and deformities. However, lumbar spine and total hip BMD Z-scores, biochemical parameters of mineral and skeletal homeostasis, and iliac crest histology of the mother (after in vivo tetracycline labeling) were normal. Genomic DNA from the children revealed a unique heterozygous missense mutation in exon 23 (c.3904C>T, p.Leu1302Phe) of SCN11A that is absent in SNP databases and alters an evolutionarily conserved amino acid. This autosomal dominant CIP reflects the second gain-of-function mutation of SCN11A. Perhaps joint hypermobility is an unreported feature. How mutation of Nav1.9 causes fracturing remains unexplained. Lack of injury awareness is typically offered as the reason, and was supported by our unremarkable biochemical, radiological, and histological findings indicating no skeletal pathobiology. However, low-trauma fracturing in these patients suggests an uncharacterized defect in bone quality.

The in vitro mechanisms and in vivo efficacy of intravenous lidocaine on the neuroinflammatory response in acute and chronic pain

INTRODUCTION

The neuroinflammatory response plays a key role in several pain syndromes. Intravenous (iv) lidocaine is beneficial in acute and chronic pain. This review delineates the current literature concerning in vitro mechanisms and in vivo efficacy of iv lidocaine on the neuroinflammatory response in acute and chronic pain.

DATABASES AND DATA TREATMENT

We searched PUBMED and the Cochrane Library for in vitro and in vivo studies from July 1975 to August 2014. In vitro articles providing an explanation for the mechanisms of action of lidocaine on the neuroinflammatory response in pain were included. Animal or clinical studies were included concerning iv lidocaine for acute or chronic pain or during inflammation.

RESULTS

Eighty-eight articles regarding iv lidocaine were included: 36 in vitro studies evaluating the effect on ion channels and receptors; 31 animal studies concerning acute and chronic pain and inflammatory models; 21 clinical studies concerning acute and chronic pain. Low-dose lidocaine inhibits in vitro voltage-gated sodium channels, the glycinergic system, some potassium channels and Gαq-coupled protein receptors. Higher lidocaine concentrations block potassium and calcium channels, and NMDA receptors. Animal studies demonstrate lidocaine to have analgesic effects in acute and neuropathic pain syndromes and anti-inflammatory effects early in the inflammatory response. Clinical studies demonstrate lidocaine to have advantage in abdominal surgery and in some neuropathic pain syndromes.

CONCLUSIONS

Intravenous lidocaine has analgesic, anti-inflammatory and antihyperalgesic properties mediated by an inhibitory effect on ion channels and receptors. It attenuates the neuroinflammatory response in perioperative pain and chronic neuropathic pain.

Redistribution of voltage-gated sodium channels after nerve decompression contributes to relieve neuropathic pain in chronic constriction injury

Nerve decompression is an important therapeutic strategy to relieve neuropathic pain and promote the peripheral nerve regeneration. To address these issues, we investigated the effects of nerve decompression on relief of neuropathic pain behaviors, redistribution of voltage-gated sodium channels (VGSCs), and skin reinnervation with chronic constriction injury (CCI). At post-operative week (POW) 4, animals were divided into a decompression group, in which the ligatures were removed, and a CCI group, in which the ligatures remained. Thermal hyperalgesia and mechanical allodynia at POW 8 had distinct reductions in decompression group compared to CCI group. At that time in CCI group, morphological evidence of pan VGSCs (Pan Nav) and isoforms of VGSCs (Nav1.6, Nav1.9, except for Nav1.8) were shown the widely distribution along the injured sciatic nerve. All of the VGSCs in decompression group became clustering around the node of Ranvier, similar to the pattern of control sciatic nerve at POW 8. Skin reinnervation was demonstrated by epidermal nerve density (END) for protein gene product 9.5 (PGP 9.5)-immunoreactive (IR) nerve fibers and a significant difference between groups only at POW 24 (p=0.01). Growth-associated protein 43 (GAP-43) is participated in the nerve fiber growth and sprouting, a difference in END for GAP-43-IR nerve fibers at POW 24 between groups were also significant (p=0.02). These observations demonstrated that nerve decompression was accompanied with the disappearance of neuropathic pain behaviors after CCI. Morphological studies provided the evidence that redistribution of VGSCs along the injured sciatic nerve but still with an incomplete skin reinnervation. These significant findings demonstrated a role of VGSCs in the pathogenesis of neuropathic pain, and gave an approaching in pharmacological basis of therapeutics.

Correlation of Nav1.8 and Nav1.9 sodium channel expression with neuropathic pain in human subjects with lingual nerve neuromas

Background

Voltage-gated sodium channels Nav1.8 and Nav1.9 are expressed preferentially in small diameter sensory neurons, and are thought to play a role in the generation of ectopic activity in neuronal cell bodies and/or their axons following peripheral nerve injury. The expression of Nav1.8 and Nav1.9 has been quantified in human lingual nerves that have been previously injured inadvertently during lower third molar removal, and any correlation between the expression of these ion channels and the presence or absence of dysaesthesia investigated.

Results

Immunohistochemical processing and quantitative image analysis revealed that Nav1.8 and Nav1.9 were expressed in human lingual nerve neuromas from patients with or without symptoms of dysaesthesia. The level of Nav1.8 expression was significantly higher in patients reporting pain compared with no pain, and a significant positive correlation was observed between levels of Nav1.8 expression and VAS scores for the symptom of tingling. No significant differences were recorded in the level of expression of Nav1.9 between patients with or without pain.

Conclusions

These results demonstrate that Nav1.8 and Nav1.9 are present in human lingual nerve neuromas, with significant correlations between the level of expression of Nav1.8 and symptoms of pain. These data provide further evidence that changes in expression of Nav1.8 are important in the development and/or maintenance of nerve injury-induced pain, and suggest that Nav1.8 may be a potential therapeutic target.

Node of Ranvier disruption as a cause of neurological diseases

Dysfunction and/or disruption of nodes of Ranvier are now recognized as key contributors to the pathophysiology of various neurological diseases. One reason is that the excitable nodal axolemma contains a high density of Nav (voltage-gated Na⁺ channels) that are required for the rapid and efficient saltatory conduction of action potentials. Nodal physiology is disturbed by altered function, localization, and expression of voltage-gated ion channels clustered at nodes and juxtaparanodes, and by disrupted axon–glial interactions at paranodes. This paper reviews recent discoveries in molecular/cellular neuroscience, genetics, immunology, and neurology that highlight the critical roles of nodes of Ranvier in health and disease.

Skin matters: identifying pain mechanisms and predicting treatment outcomes

The skin acts as a complex sensory organ. The emerging new data on peripheral pain mechanisms from within the skin is presented. This data has led to new insights into the potential pain mechanisms for various pain conditions including neuropathic pain (from small fiber neuropathies) and Complex Regional Pain Syndrome. The somatosensory neurons that innervate our skin constantly update our brains on the objects and environmental factors that surround us. Cutaneous sensory neurons expressing nociceptive receptors such as transient receptor potential vanilloid 1 channels and voltage-gated sodium channels are critical for pain transmission. Epidermal cells (such as keratinocytes, Langerhans cells, and Merkel cells) express sensor proteins and neuropeptides; these regulate the neuroimmunocutaneous system and participate in nociception and neurogenic inflammation. In the past two decades, there has been widespread use of modalities such as punch skin biopsies, quantitative sensory testing, and laser-evoked potentials to evaluate small caliber nerve fibers. This paper explores these laboratory techniques as well as the phenomenon of small fiber neuropathy. Treatment using transdermal drug delivery is discussed. There is potential for these findings to predict treatment outcomes in clinical practice and to develop new therapies for different pain conditions. These findings should enhance the physician's ability to evaluate and treat diverse types of pain.