The up-regulation of IL-6 in DRG and spinal dorsal horn contributes to neuropathic pain following L5 ventral root transection

Exploring Localized Provoked Vulvodynia: Insights from Animal Model Research

Provoked vulvodynia represents a challenging chronic pain condition, characterized by its multifactorial origins. The inherent complexities of human-based studies have necessitated the use of animal models to enrich our understanding of vulvodynia's pathophysiology. This review aims to provide an exhaustive examination of the various animal models employed in this research domain. A comprehensive search was conducted on PubMed, utilizing keywords such as "vulvodynia", "chronic vulvar pain", "vulvodynia induction", and "animal models of vulvodynia" to identify pertinent studies. The search yielded three primary animal models for vulvodynia: inflammation-induced, allergy-induced, and hormone-induced. Additionally, six agents capable of triggering the condition through diverse pathways were identified, including factors contributing to hyperinnervation, mast cell proliferation, involvement of other immune cells, inflammatory cytokines, and neurotransmitters. This review systematically outlines the various animal models developed to study the pathogenesis of provoked vulvodynia. Understanding these models is crucial for the exploration of preventative measures, the development of novel treatments, and the overall advancement of research within the field.

Changes of inflammatory cytokines in vertebral compression fractures patients with percutaneous balloon kyphoplasty

Objective: To explore the changes of a series of cytokines before and after percutaneous balloon kyphoplasty (PKP) and prognostic markers for response to PKP.Methods: From 1 January 2019 to 31 May 2019, all single-level lumbar osteoporotic vertebral compression fracture (OVCF) patients diagnosed by MRI who matched the inclusion and exclusion criteria were enrolled in this study. They were classified into the effective group and the ineffective group based on the outcome after PKP. The levels of a series of inflammatory factors and indices of spinal functions were obtained before and after PKP.Results: A total of 72 patients were included in this study, 59 in the effective group and 13 in the ineffective group. The anterior height (AH) and posterior height (PH) were 77.3 ± 11.2% and 91.2 ± 9.3%, respectively, in the effective group after PKP, which were higher than that in the ineffective group (p<.001). While, the Kyphotic angle, visual analog scale (VAS), and Oswestry Disability Index (ODI) score were 9.1 ± 4.3°, 3.1 ± 1.9, and 19.2 ± 4.1 in the effective group, which was lower than that in ineffective group (p<.001). The serum levels of IL-1β, IL-6, and TNF-α were found significantly decreased after treatment in the effective group (p<.05). The logistic regression showed that the levels of IL-6 TNF-α and AH were significant predictor of outcome.Conclusions: Our results demonstrated that PKP can reduce the serum levels of IL-6, IL-1β, and TNF-α, moreover, the IL-6, TNF-α, and AH were significant predictors of outcome.

Sexually Dimorphic Pattern of Pain Mitigation Following Prophylactic Regenerative Peripheral Nerve Interface (RPNI) in a Rat Neuroma Model

BACKGROUND

Treating neuroma pain is a clinical challenge. Identification of sex-specific nociceptive pathways allows a more individualized pain management. The Regenerative Peripheral Nerve Interface (RPNI) consists of a neurotized autologous free muscle using a severed peripheral nerve to provide physiological targets for the regenerating axons.

OBJECTIVE

To evaluate prophylactic RPNI to prevent neuroma pain in male and female rats.

METHODS

F344 rats of each sex were assigned to neuroma, prophylactic RPNI, or sham groups. Neuromas and RPNIs were created in both male and female rats. Weekly pain assessments including neuroma site pain and mechanical, cold, and thermal allodynia were performed for 8 weeks. Immunohistochemistry was used to evaluate macrophage infiltration and microglial expansion in the corresponding dorsal root ganglia and spinal cord segments.

RESULTS

Prophylactic RPNI prevented neuroma pain in both sexes; however, female rats displayed delayed pain attenuation when compared with males. Cold allodynia and thermal allodynia were attenuated exclusively in males. Macrophage infiltration was mitigated in males, whereas females showed a reduced number of spinal cord microglia.

CONCLUSION

Prophylactic RPNI can prevent neuroma site pain in both sexes. However, attenuation of both cold allodynia and thermal allodynia occurred in males exclusively, potentially because of their sexually dimorphic effect on pathological changes of the central nervous system.

Upregulated TNF-α and lactate following ERK-SGK1 activation in the spinal dorsal horn underlies chronic postsurgical pain

Skin/muscle incision and retraction (SMIR) during surgeries can lead to chronic postsurgical pain (CPSP). The underlying mechanisms are still unclear. In the present study, we showed that SMIR of the thigh induced phosphorylation of extracellular signal-regulated kinase (ERK), followed by serum- and glucocorticoid-inducible kinase-1 (SGK1) activation in the spinal dorsal horn. Intrathecal injection of PD98059, an ERK inhibitor, or GSK650394, a SGK1 inhibitor, significantly attenuated mechanical pain hypersensitivity in SMIR rats. The level of tumor necrosis factor α and lactate in spinal cord was significantly decreased by PD98059 or GSK650394 injection. Furthermore, PD98059 decreased the activation of SGK1 in the spinal dorsal horn. These results indicate that ERK-SGK1 activation followed by proinflammatory mediator release in the spinal dorsal horn underlies CPSP.

In situ delivery of a curcumin-loaded dynamic hydrogel for the treatment of chronic peripheral neuropathy

Patients with peripheral nerve injuries would highly likely suffer from chronic neuropathic pain even after surgical intervention. The primary reasons for this involve sustained neuroinflammatory and dysfunctional changes in the nervous system after the nerve injury. We previously reported an injectable boronic ester-based hydrogel with inherent antioxidative and nerve protective properties. Herein, we first explored the anti-neuroinflammatory effects of Curcumin on primary sensory neurons and activated macrophages in vitro. Next, we incorporated thiolated Curcumin-Pluronic F-127 micelles (Cur-M) into our boronic ester-based hydrogel to develop an injectable hydrogel that serves as sustained curcumin release system (Gel-Cur-M). By orthotopically injecting the Gel-Cur-M to sciatic nerves of mice with chronic constriction injuries, we found that the bioactive components could remain on the nerves for at least 21 days. In addition, the Gel-Cur-M exhibited superior functions compared to Gel and Cur-M alone, which includes ameliorating hyperalgesia while simultaneously improving locomotor and muscular functions after the nerve injury. This could stem from in situ anti-inflammation, antioxidation, and nerve protection. Furthermore, the Gel-Cur-M also showed extended beneficial effects for preventing the overexpression of TRPV1 as well as microglial activation in the lumbar dorsal root ganglion and spinal cord, respectively, which also contributed to its analgesic effects. The underlying mechanism may involve the suppression of CC chemokine ligand-2 and colony-stimulating factor-1 in the injured sensory neurons. Overall, this study suggests that orthotopic injection of the Gel-Cur-M is a promising therapeutic strategy that especially benefits patients with peripheral neuropathy who require surgical interventions.

Evolving techniques for reducing phantom limb pain

At least two million people in the United States of America live with lost limbs, and the number is expected to double by 2050, although the incidence of amputations is significantly greater in other parts of the world. Within days to weeks of the amputation, up to 90% of these individuals develop neuropathic pain, presenting as phantom limb pain (PLP). The pain level increases significantly within one year and remains chronic and severe for about 10%. Amputation-induced changes are considered to underlie the causation of PLP. Techniques applied to the central nervous system (CNS) and peripheral nervous system (PNS) are designed to reverse amputation-induced changes, thereby reducing/eliminating PLP. The primary treatment for PLP is the administration of pharmacological agents, some of which are considered but provide no more than short-term pain relief. Alternative techniques are also discussed, which provide only short-term pain relief. Changes induced by various cells and the factors they release are required to change neurons and their environment to reduce/eliminate PLP. It is concluded that novel techniques that utilize autologous platelet-rich plasma (PRP) may provide long-term PLP reduction/elimination.

Anti-inflammatory and analgesic effect of Forsythiaside B on complete Freund's adjuvant-induced inflammatory pain in mice

Chronic pain is frequently reported in clinical practice. Therefore, it is important to identify effective therapy to relieve pain. In this work, we selected Forsythoside B (FB), a phenylethanoid glycoside isolated from Forsythia suspensa (Thunb.) Vahl, to evaluate its effect in modulating inflammatory pain induced by complete Freund's adjuvant (CFA) and the involved mechanisms. We discovered that FB could attenuate inflammatory pain triggered by CFA injection and exert anti-anxiety effects. In detail, proinflammatory cytokines, consisting of IL-6 and TNF-α, were decreased after FB administration in the CFA-injected mice. Furthermore, the FB application ameliorated the activation of ionized calcium-binding adaptor molecule 1 (Iba-1) and glial fibrillary acidic protein (GFAP), the microglia and astrocytes markers respectively. Therefore, our findings indicate that FB could be a promising treatment for chronic inflammatory pain.

Perturbations in Neuroinflammatory Pathways Are Associated With a Worst Pain Profile in Oncology Patients Receiving Chemotherapy

Unrelieved pain occurs in 55% of cancer patients. Identification of molecular mechanisms for pain may provide insights into therapeutic targets. Purpose was to evaluate for perturbations in neuroinflammatory pathways between oncology patients with and without severe pain. Worst pain severity was rated using a 0 to 10 numeric rating scale six times over two cycles of chemotherapy. Latent profile analysis was used to identify subgroups of patients with distinct pain profiles. Pathway impact analyses were performed in two independent samples using gene expression data obtained from RNA sequencing (n = 192) and microarray (n = 197) technologies. Fisher's combined probability test was used to identify significantly perturbed pathways between None versus the Severe pain classes. In the RNA sequencing and microarray samples, 62.5% and 56.3% of patients were in the Severe pain class, respectively. Nine perturbed pathways were related to neuroinflammatory mechanisms (i.e., retrograde endocannabinoid signaling, gamma-aminobutyric acid synapse, glutamatergic synapse, Janus kinase-signal transducer and activator of transcription signaling, phagosome, complement and coagulation cascades, cytokine-cytokine receptor interaction, chemokine signaling, calcium signaling). First study to identify perturbations in neuroinflammatory pathways associated with severe pain in oncology outpatients. Findings suggest that complex neuroimmune interactions are involved in the maintenance of chronic pain conditions. Perspective: In this study that compared oncology patients with none versus severe pain, nine perturbed neuroinflammatory pathways were identified. Findings suggest that complex neuroimmune interactions are involved in the maintenance of persistent pain conditions.

Roles of Phosphorylation of N-Methyl-D-Aspartate Receptor in Chronic Pain

Phosphorylation of N-methyl-D-aspartate receptor (NMDAR) is widely regarded as a vital modification of synaptic function. Various protein kinases are responsible for direct phosphorylation of NMDAR, such as cyclic adenosine monophosphate-dependent protein kinase A, protein kinase C, Ca²⁺/calmodulin-dependent protein kinase II, Src family protein tyrosine kinases, cyclin-dependent kinase 5, and casein kinase II. The detailed function of these kinases on distinct subunits of NMDAR has been reported previously and contributes to phosphorylation at sites predominately within the C-terminal of NMDAR. Phosphorylation underlies both structural and functional changes observed in chronic pain, and studies have demonstrated that inhibitors of kinases are significantly effective in alleviating pain behavior in different chronic pain models. In addition, the exploration of drugs that aim to disrupt the interaction between kinases and NMDAR is promising in clinical research. Based on research regarding the modulation of NMDAR in chronic pain models, this review provides an overview of the phosphorylation of NMDAR-related mechanisms underlying chronic pain to elucidate molecular and pharmacologic references for chronic pain management.

Neuroinflammation in the anterior cingulate cortex: the potential supraspinal mechanism underlying the mirror-image pain following motor fiber injury

Background

Peripheral nerve inflammation or lesion can affect contralateral healthy structures, and thus result in mirror-image pain. Supraspinal structures play important roles in the occurrence of mirror pain. The anterior cingulate cortex (ACC) is a first-order cortical region that responds to painful stimuli. In the present study, we systematically investigate and compare the neuroimmune changes in the bilateral ACC region using unilateral- (spared nerve injury, SNI) and mirror-(L5 ventral root transection, L5-VRT) pain models, aiming to explore the potential supraspinal neuroimmune mechanism underlying the mirror-image pain.

Methods

The up-and-down method with von Frey hairs was used to measure the mechanical allodynia. Viral injections for the designer receptors exclusively activated by designer drugs (DREADD) were used to modulate ACC glutamatergic neurons. Immunohistochemistry, immunofluorescence, western blotting, protein microarray were used to detect the regulation of inflammatory signaling.

Results

Increased expressions of tumor necrosis factor alpha (TNF-α), interleukin-6 (IL-6) and chemokine CX3CL1 in ACC induced by unilateral nerve injury were observed on the contralateral side in the SNI group but on the bilateral side in the L5-VRT group, representing a stronger immune response to L5-VRT surgery. In remote ACC, both SNI and L5-VRT induced robust bilateral increase in the protein level of Nav1.6 (SCN8A), a major voltage-gated sodium channel (VGSC) that regulates neuronal activity in the mammalian nervous system. However, the L5-VRT-induced Nav1.6 response occurred at PO 3d, earlier than the SNI-induced one, 7 days after surgery. Modulating ACC glutamatergic neurons via DREADD-Gq or DREADD-Gi greatly changed the ACC CX3CL1 levels and the mechanical paw withdrawal threshold. Neutralization of endogenous ACC CX3CL1 by contralateral anti-CX3CL1 antibody attenuated the induction and the maintenance of mechanical allodynia and eliminated the upregulation of CX3CL1, TNF-α and Nav1.6 protein levels in ACC induced by SNI. Furthermore, contralateral ACC anti-CX3CL1 also inhibited the expression of ipsilateral spinal c-Fos, Iba1, CD11b, TNF-α and IL-6.

Conclusions

The descending facilitation function mediated by CX3CL1 and its downstream cascade may play a pivotal role, leading to enhanced pain sensitization and even mirror-image pain. Strategies that target chemokine-mediated ACC hyperexcitability may lead to novel therapies for the treatment of neuropathic pain.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-022-02525-8.

Mu and Delta Opioid Receptor Targeting Reduces Connexin 43-Based Heterocellular Coupling during Neuropathic Pain

Chronic neuropathic pain emerges from either central or peripheral lesions inducing spontaneous or amplified responses to non-noxious stimuli. Despite different pharmacological approaches to treat such a chronic disease, neuropathic pain still represents an unmet clinical need, due to long-term therapeutic regimens and severe side effects that limit application of currently available drugs. A critical phenomenon involved in central sensitization is the exchange of signalling molecules and cytokines, between glia and neurons, driving the chronicization process. Herein, using a chronic constriction injury (CCI) model of neuropathic pain, we evaluated the efficacy of the mu (M-) and delta (D-) opioid receptor (-OR) targeting agent LP2 in modulating connexin-based heterocellular coupling and cytokine levels. We found that long-term efficacy of LP2 is consequent to MOR-DOR targeting resulting in the reduction of CCI-induced astrocyte-to-microglia heterocellular coupling mediated by connexin 43. We also found that single targeting of DOR reduces TNF and IL-6 levels in the chronic phase of the disease, but the peripheral and central discharge as the primary source of excitotoxic stimulation in the spinal cord requires a simultaneous MOR-DOR targeting to reduce CCI-induced neuropathic pain.

Red Nucleus Interleukin-6 Evokes Tactile Allodynia in Male Rats Through Modulating Spinal Pro-inflammatory and Anti-inflammatory Cytokines

Our previous studies have clarified that red nucleus (RN) interleukin (IL)-6 is involved in the maintenance of neuropathic pain and produces a facilitatory effect by activating JAK2/STAT3 and ERK pathways. In this study, we further explored the immune molecular mechanisms of rubral IL-6-mediated descending facilitation at the spinal cord level. IL-6-evoked tactile allodynia was established by injecting recombinant IL-6 into the unilateral RN of naive male rats. Following intrarubral administration of IL-6, obvious tactile allodynia was evoked in the contralateral hindpaw of rats. Meanwhile, the expressions of pro-inflammatory cytokines tumor necrosis factor-α (TNF-α), IL-1β, and IL-6 were elevated in the contralateral spinal dorsal horn (L4–L6), blocking spinal TNF-α, IL-1β, or IL-6 with neutralizing antibodies relieved IL-6-evoked tactile allodynia. Conversely, the levels of anti-inflammatory cytokines transforming growth factor-β (TGF-β) and IL-10 were reduced in the contralateral spinal dorsal horn (L4–L6), an intrathecal supplement of exogenous TGF-β, or IL-10 attenuated IL-6-evoked tactile allodynia. Further studies demonstrated that intrarubral pretreatment with JAK2/STAT3 inhibitor AG490 suppressed the elevations of spinal TNF-α, IL-1β, and IL-6 and promoted the expressions of TGF-β and IL-10 in IL-6-evoked tactile allodynia rats. However, intrarubral pretreatment with ERK inhibitor PD98059 only restrained the increase in spinal TNF-α and enhanced the expression of spinal IL-10. These findings imply that rubral IL-6 plays descending facilitation and produces algesic effect through upregulating the expressions of spinal pro-inflammatory cytokines TNF-α, IL-1β, and IL-6 and downregulating the expressions of spinal anti-inflammatory cytokines TGF-β and IL-10 by activating JAK2/STAT3 and/or ERK pathways, which provides potential therapeutic targets for the treatment of pathological pain.

TNFα in MS and Its Animal Models: Implications for Chronic Pain in the Disease

Multiple Sclerosis (MS) is a debilitating autoimmune disease often accompanied by severe chronic pain. The most common type of pain in MS, called neuropathic pain, arises from disease processes affecting the peripheral and central nervous systems. It is incredibly difficult to study these processes in patients, so animal models such as experimental autoimmune encephalomyelitis (EAE) mice are used to dissect the complex mechanisms of neuropathic pain in MS. The pleiotropic cytokine tumor necrosis factor α (TNFα) is a critical factor mediating neuropathic pain identified by these animal studies. The TNF signaling pathway is complex, and can lead to cell death, inflammation, or survival. In complex diseases such as MS, signaling through the TNFR1 receptor tends to be pro-inflammation and death, whereas signaling through the TNFR2 receptor is pro-homeostatic. However, most TNFα-targeted therapies indiscriminately block both arms of the pathway, and thus are not therapeutic in MS. This review explores pain in MS, inflammatory TNF signaling, the link between the two, and how it could be exploited to develop more effective TNFα-targeting pain therapies.

Probucol attenuates NF-κB/NLRP3 signalling and augments Nrf-2 mediated antioxidant defence in nerve injury induced neuropathic pain

Neuroinflammation is one of the most significant pathological drivers following nerve injury which along with immune cell activation, oxidative stress and other associated molecular mechanisms contribute to development of neuropathic pain characterized by hyperalgesia and allodynia. In the current study we have investigated the pharmacological effect of probucol (prb) using chronic constriction injury (CCI) of sciatic nerve induced neuropathic pain (NP) model in rats. CCI of sciatic nerve resulted in marked decrease in pain threshold along with perturbations in anti-oxidant defence, enhanced inflammatory mediators and abnormal foot posture. Administration of prb at the doses of 8 and 16 mg/kg, p.o. for 14 days significantly attenuated the behavioural, biochemical and functional deficits following CCI of sciatic nerve. To further explore the molecular mechanisms of prb, we assessed the post treatment levels of inflammatory and oxidative stress markers like NLRP3 inflammasome, NF-κB and associated proinflammatory molecules such as IL-1 β, TNF-α & IL-6 along with Nrf-2 and HO-1. Our findings demonstrated that CCI induced changes in levels of these markers were dose dependently reversed by administration of prb. Of note, at molecular level the elevated expression of transcription factors such as NF-κB which is crucial for Nlrp3 activation and diminished levels of Nrf-2 were manifested following CCI induction, these changes were markedly reversed with 14 days treatment of prb at both the doses. Our findings highlighted the dual pharmacological effect of prb, anti-inflammatory and anti-oxidant via modulation of NF-κB/NLRP3 signalling and Nrf-2 pathway in attenuation of CCI of sciatic nerve induced NP.

CNTF-STAT3-IL-6 Axis Mediates Neuroinflammatory Cascade across Schwann Cell-Neuron-Microglia

Neuroinflammation is a crucial mechanism in many neurological disorders. Injury to the peripheral sensory nerves leads to a neuroinflammatory response in the somatosensory pathway, from dorsal root ganglia (DRG) to the spinal cord, contributing to neuropathic pain. How the immune reaction is initiated peripherally and propagated to the spinal cord remains less clear. Here, we find that ciliary neurotrophic factor (CNTF), highly expressed in Schwann cells, mediates neuroinflammatory response through the activating signal transducer and activator of transcription 3 (STAT3) and inducing interleukin 6 (IL-6) in sensory neurons. Cntf deficiency attenuates neuroinflammation in DRG and the spinal cord with alleviated pain post-injury. Recombinant CNTF applied to the sensory nerves recapitulates neuroinflammation in the DRG and spinal cord, with consequent pain development. We delineate the CNTF-STAT3-IL-6 axis in mediating the onset and progression of the inflammatory cascade from the periphery to the spinal cord with therapeutic implications for neuropathic pain.

ATF3-Expressing Large-Diameter Sensory Afferents at Acute Stage as Bio-Signatures of Persistent Pain Associated with Lumbar Radiculopathy

The mechanism of pain chronicity is largely unknown in lumbar radiculopathy (LR). The anatomical location of nerve injury is one of the important factors associated with pain chronicity of LR. Accumulating evidence has shown constriction distal to the dorsal root ganglion (DRG) caused more severe radiculopathy than constriction proximal to the DRG; thereby, the mechanism of pain chronicity in LR could be revealed by comparing the differences in pathological changes of DRGs between nerve constriction distal and proximal to the DRG. Here, we used 2 rat models of LR with nerve constriction distal or proximal to the DRG to probe how the different nerve injury sites could differentially affect pain chronicity and the pathological changes of DRG neuron subpopulations. As expected, rats with nerve constriction distal to the DRG showed more persistent pain behaviors than those with nerve constriction proximal to the DRG in 50% paw withdraw threshold, weight-bearing test, and acetone test. One day after the operation, distal and proximal nerve constriction showed differential pathological changes of DRG. The ratios of activating transcription factor3 (ATF3)-positive DRG neurons were significantly higher in rats with nerve constriction distal to DRG than those with nerve constriction proximal to DRG. In subpopulation analysis, the ratios of ATF3-immunoreactivity (IR) in neurofilament heavy chain (NFH)-positive DRG neurons significantly increased in distal nerve constriction compared to proximal nerve constriction; although, both distal and proximal nerve constriction presented increased ratios of ATF3-IR in calcitonin gene-related peptide (CGRP)-positive DRG neurons. Moreover, the nerve constriction proximal to DRG caused more hypoxia than did that distal to DRG. Together, ATF3 expression in NHF-positive DRG neurons at the acute stage is a potential bio-signature of persistent pain in rat models of LR.

The effect of IL-6/Piezo2 on the trigeminal neuropathic pain

The nature of trigeminal neuropathic pain (TN) attacks is regarded as the ignition of ectopic action potentials from the trigeminal root following vascular compression, which seemed to be related to transmembrane proteins and inflammation factors. This study focused on the mechanosensitive channel Piezo2 and cytokine IL-6. The chronic constriction injury of infraorbital nerve in SD rats was used to establish the TN model. The trigeminal ganglion was then achieved to perform immunocytochemistry studies. A significant upregulation of Piezo2 and IL-6 was showed in the TN model rats. The Piezo2 positive accounted for 72.3±9.5% in those IL-6 positive neurons. The Piezo2 co-localized with CGRP, IB4 and NF-200 but not with GFAP, which implied that it was expressed in both the C-type and the A-type neurons. After administration of GsMTx4 or anti-rat IL-6 antibody in the TN model, the dynamic allodynia and pinprick hyperalgesia scores as well as the mechanical threshold changed significantly. In the sham-operation rates, with local administration of IL-6, an upregulation of Piezo2 was also exhibited. Our study demonstrated that the up-regulation of Piezo2 in the pain afferent neurons following trigeminal nerve injury may play a role in the development of the neuralgia. Meanwhile, the expression of Piezo2 may be modulated by inflammatory cytokines, such as IL-6.

SUR1, newly expressed in astrocytes, mediates neuropathic pain in a mouse model of peripheral nerve injury

BACKGROUND

Neuropathic pain following peripheral nerve injury (PNI) is linked to neuroinflammation in the spinal cord marked by astrocyte activation and upregulation of interleukin 6 (IL-6), chemokine (C-C motif) ligand 2 (CCL2) and chemokine (C-X-C motif) ligand 1 (CXCL1), with inhibition of each individually being beneficial in pain models.

METHODS

Wild type (WT) mice and mice with global or pGfap-cre- or pGFAP-cre/ERT2-driven Abcc8/SUR1 deletion or global Trpm4 deletion underwent unilateral sciatic nerve cuffing. WT mice received prophylactic (starting on post-operative day [pod]-0) or therapeutic (starting on pod-21) administration of the SUR1 antagonist, glibenclamide (10 µg IP) daily. We measured mechanical and thermal sensitivity using von Frey filaments and an automated Hargreaves method. Spinal cord tissues were evaluated for SUR1-TRPM4, IL-6, CCL2 and CXCL1.

RESULTS

Sciatic nerve cuffing in WT mice resulted in pain behaviors (mechanical allodynia, thermal hyperalgesia) and newly upregulated SUR1-TRPM4 in dorsal horn astrocytes. Global and pGfap-cre-driven Abcc8 deletion and global Trpm4 deletion prevented development of pain behaviors. In mice with Abcc8 deletion regulated by pGFAP-cre/ERT2, after pain behaviors were established, delayed silencing of Abcc8 by tamoxifen resulted in gradual improvement over the next 14 days. After PNI, leakage of the blood-spinal barrier allowed entry of glibenclamide into the affected dorsal horn. Daily repeated administration of glibenclamide, both prophylactically and after allodynia was established, prevented or reduced allodynia. The salutary effects of glibenclamide on pain behaviors correlated with reduced expression of IL-6, CCL2 and CXCL1 by dorsal horn astrocytes.

CONCLUSION

SUR1-TRPM4 may represent a novel non-addicting target for neuropathic pain.

Inflammation in the intervertebral disc herniation

Up until fairly recently, it was thought that sciatic pain in the lumbar herniated disc was caused by compression on the nerve root. However, the lumbar herniated disc shows mixed pictures which are difficult to explain by simple mechanical compromise. In recent years various immunology, immunohistochemistry and molecular biology studies have shown that the herniated tissue is not an inert material, but rather it Is biologically very active with the capability of expressing a series of inflammatory mediators: cytokines such as interleukin-1, interleukin-6, interleuquin-8 and tumor necrosis factor being the ones which stand out. The inflammation is not only induced by the chemical irritation of the bioactive substances released by the nucleus pulposus but also by an autoimmune response against itself. Thus, in addition to the mechanical factor, the biomechanical mediation plays an important role in the pathophysiology of sciatic pain and of radiculopathy. Through a review of a wide range of literature, we researched the cellular molecular mediators involved in this inflammatory process around the lumbar herniated disc and its involvement in sciatic pain.

Intravenous Administration of Triptonide Attenuates CFA-Induced Pain Hypersensitivity by Inhibiting DRG AKT Signaling Pathway in Mice

Background

Currently, medical treatment of inflammatory pain is limited by a lack of safe and effective therapies. Triptonide (TPN), a major component of Tripterygium wilfordii Hook.f. with low toxicity, has been shown to have good anti-inflammatory and neuroprotective effects. The present study aims to investigate the effects of TPN on chronic inflammatory pain.

Materials and Methods

Inflammatory pain was induced by intraplantar injection of complete Freund’s adjuvant (CFA). TPN’s three different doses were intravenously administered to compare the analgesic efficacy: 0.1 mg/kg, 0.5 mg/kg, and 2.0 mg/kg. The foot swelling was quantitated by measuring paw volume. Mechanical allodynia and thermal hyperalgesia were assessed with von Frey filament testing and Hargreaves’ test, respectively. Western blots, qRT–PCR and immunofluorescence tests were used to analyze the expression of pAKT, tumor necrosis factor-α (TNF-α), interleukin 1 beta (IL-1β), and interleukin 6 (IL-6). Two AKT inhibitors, AKT inhibitor Ⅳ and MK-2206, were used to examine AKT’s effects on pain behavior and cytokines expression.

Results

Intravenous treatment with TPN attenuated CFA-induced paw edema, mechanical allodynia, and thermal hyperalgesia. Western blotting and immunofluorescence results showed that CFA induced AKT activation in the dorsal root ganglion (DRG) neurons. However, these effects were suppressed by treatment with TPN. Furthermore, TPN treatment inhibited CFA-induced increase of pro-inflammatory cytokines, including TNF-α, IL-1β, and IL-6. Consistent with the in vivo data, TPN inhibited LPS-induced Akt phosphorylation and inflammatory mediator production in ND7/23 cells. Finally, intrathecal treatment with AKT inhibitor Ⅳ or MK-2206, attenuated CFA-induced mechanical allodynia and thermal hyperalgesia, and simultaneously decreased the mRNA expression of TNF-α, IL-1β, and IL-6 in DRG.

Conclusion

These data indicate that TPN attenuates CFA-induced pain potentially via inhibiting AKT-mediated pro-inflammatory cytokines production in DRG. TPN may be used for the treatment of chronic inflammatory pain.

Pulsed Ultrasound Remedies Post-thoracotomy Hypersensitivity and Increases Spinal Anti-inflammatory Cytokine in Rats

The purpose of the experiment was to study the effect of pulsed ultrasound (PUS) on post-thoracotomy pain and local tissue temperature and to correlate the findings with the alteration in spinal anti-inflammatory and pro-inflammatory cytokines. Mechanical sensitivity, subcutaneous temperature and spinal interleukin-10 (IL-10), IL-6 or tumor necrosis factor-alpha (TNF-α) expression were examined in a rat model of experimental post-thoracotomy pain. Group 1 received a sham surgery where thoracotomy was performed except for rib retraction. Group 2 underwent thoracotomy with rib retraction (TRR). Group 3 received the TRR procedure followed by PUS. Group 4 underwent the TRR procedure followed by only the massage with the ultrasound turned off. Compared with group 1 (sham), groups 2-4 showed a decrease in mechanical withdrawal thresholds on postoperative days (PODs) 10 and 11. On PODs 16, 23 and 30, group 3 (TRR+PUS-1) displayed an increase in mechanical withdrawal thresholds compared with groups 2 and 4. Subcutaneous and body temperatures in group 3 were not prominently different from group 1, group 2 (TRR only) or group 4 (TRR+PUS-0). Compared with group 2, group 3 had an increase in spinal IL-10 level on POD 30 and a decrease in spinal IL-6 or TNF-α expression on PODs 16 and 30. We concluded that mechanical hypersensitivity after TRR is postponed by PUS, and its effect continues for 3 wk. A PUS dose not increase local tissue temperature. The beneficial effect of PUS appears related to upregulation of spinal anti-inflammatory cytokine and downregulation of spinal pro-inflammatory cytokines.

Peripheral-to-central immune communication at the area postrema glial-barrier following bleomycin-induced sterile lung injury in adult rats

The pathways for peripheral-to-central immune communication (P → C I-comm) following sterile lung injury (SLI) are unknown. SLI evokes systemic and central inflammation, which alters central respiratory control and viscerosensory transmission in the nucleus tractus solitarii (nTS). These functional changes coincide with increased interleukin-1 beta (IL-1β) in the area postrema, a sensory circumventricular organ that connects P → C I-comm to brainstem circuits that control homeostasis. We hypothesize that IL-1β and its downstream transcriptional target, cyclooxygenase-2 (COX-2), mediate P → C I-comm in the nTS. In a rodent model of SLI induced by intratracheal bleomycin (Bleo), the sigh frequency and duration of post-sigh apnea increased in Bleo- compared to saline- treated rats one week after injury. This SLI-dependent change in respiratory control occurred concurrently with augmented IL-1β and COX-2 immunoreactivity (IR) in the funiculus separans (FS), a barrier between the AP and the brainstem. At this barrier, increases in IL-1β and COX-2 IR were confined to processes that stained for glial fibrillary acidic protein (GFAP) and that projected basolaterally to the nTS. Further, FS radial-glia did not express TNF-α or IL-6 following SLI. To test our hypothesis, we blocked central COX-1/2 activity by intracerebroventricular (ICV) infusion of Indomethacin (Ind). Continuous ICV Ind treatment prevented Bleo-dependent increases in GFAP + and IL-1β + IR, and restored characteristics of sighs that reset the rhythm. These data indicate that changes in sighs following SLI depend partially on activation of a central COX-dependent P → C I-comm via radial-glia of the FS.

Red nucleus IL-6 mediates the maintenance of neuropathic pain by inducing the productions of TNF-α and IL-1β through the JAK2/STAT3 and ERK signaling pathways

We previously reported that interleukin (IL)-6 in the red nucleus (RN) is involved in the maintenance of neuropathic pain induced by spared nerve injury (SNI), and exerts a facilitatory effect via Janus-activated kinase 2/signal transducer and activator of transcription 3 (JAK2/STAT3) and extracellular signal-regulated kinase (ERK) signal transduction pathways. The present study aimed at investigating the roles of tumor necrosis factor-α (TNF-α) and IL-1β in RN IL-6-mediated maintenance of neuropathic pain and related signal transduction pathways. Being similar to the elevation of RN IL-6 three weeks after SNI, increased protein levels of both TNF-α and IL-1β were also observed in the contralateral RN three weeks after the nerve injury. The upregulations of TNF-α and IL-1β were closely correlative with IL-6 and suppressed by intrarubral injection of a neutralizing antibody against IL-6. Administration of either the JAK2 antagonist AG490 or the ERK antagonist PD98059 to the RN of rats with SNI remarkably increased the paw withdrawal threshold (PWT) and inhibited the up-regulations of local TNF-α and IL-1β. Further experiments indicated that intrarubral injection of exogenous IL-6 in naive rats apparently lowered the PWT of the contralateral hindpaw and boosted the local expressions of TNF-α and IL-1β. Pretreatment with AG490 could block IL-6-induced tactile hypersensitivity and suppress the up-regulations of both TNF-α and IL-1β. However, injection of PD98059 in advance only inhibited the upregulation of IL-1β, but not TNF-α. These findings indicate that RN IL-6 mediates the maintenance of neuropathic pain by inducing the productions of TNF-α and IL-1β. IL-6 induces the expression of TNF-α through the JAK2/STAT3 pathway, and the production of IL-1β through the JAK2/STAT3 and ERK pathways.

Mechanism underlying cranial nerve rhizopathy

The cranial nerve rhizophathy, commonly presented with trigeminal neuralgia (TN) or hemifacial spasm (HFS), is a sort of hyperexcitability disorders with higher incidence in senior Asian. In this paper, a novel hypothesis on the pathogenesis is proposed and with which some clinical phenomena are explained. In those with crowded cerebellopontine angle in anatomy, the cranial nerve root and surrounding vessel are getting closer and closer to each other with aging and finally the neurovascular conflict happens. As the interfacial friction associated with pulse, the nerve incurs demyelination. Since this pathological change develops to a certain degree, some transmembrane proteins emerge from the nerve due to a series of signaling pathway mediated by inflammatory cytokines. Among them, voltage-gated (Na_v1.3) and mechanosensitive (Piezo2) ion channels may play the important role. With pulsatile compressions, the Piezo2 drives the resting potential toward depolarization forming a state of subthreshold membrane potential oscillation. Under this condition, just an appropriate pressure can make the membrane potential easy to reach threshold and activate the sodium channel, eventually generating conductible action potentials from the axon. When these ectopic action potentials propagate to the central nerve system, an illusion of sharp pain is perceived; while to the nerve-muscle junctions, an attack of irregular muscle constriction occurs. This hypothesis can well explain the symptomatic manifestation of paroxysmal attacks aroused by emotions. When we get nervous or excited, our heart rate and blood pressure alter correspondingly, which may give rise to "a just right pressure" - with specific frequency, amplitude and angle - impacting the suffered nerve to reach the threshold of impulse ignition. After a successful microvascular decompression surgery, the trigger is gone (there is no compression anymore) and the symptom is alleviated. While the postoperative recurrence could be attributable to Teflon granuloma development if had been placed improperly - for this nerve root has been susceptible no matter to arteries or to neoplasms. Besides, it may illustrate the clinical phenomenon that secondary TN or HFS cases are seldom caused by schwannoma: with a proliferative sheath, the nerve root is actually insulated. By contrast, not all neurovascular contacts can lead to the onset: it demands an exclusive extent of demyelination firstly.

Satellite glia activation in dorsal root ganglion contributes to mechanical allodynia after selective motor fiber injury in adult rats

Increasing evidence suggests that activation of satellite glia cells (SGCs) in sensory ganglia play important roles in the development of neuropathic pain. The present study aimed to investigate the involvement of SGC activation in a novel model of motor nerve injury induced pain hypersensitivity. The neuropathic pain model was established by cervical 8 ventral root avulsion (C8VA). Glial fibrillary acidic protein (GFAP) was used as a marker of SGC activation. Unilateral C8VA resulted in mechanical allodynia, but not thermal hyperalgesia in bilateral paws. Expectedly, SGCs were robustly activated on as early as 1 day and persisted for at least 7 days in the ipsilateral and contralateral dorsal root ganglia (DRG) of C6, C7 and C8 after C8VA. Double immunofluorescence showed that almost all the activated SGCs enveloped neurofilament 200 (NF200) positive myelinated neurons in DRG. Local application of fluorocitrate (FC), a glial metabolism inhibitor, significantly decreased the number of activated SGCs and alleviated bilateral mechanical allodynia. These results suggest that SGC activation contributed to ipsilateral and mirror-image pain hypersensitivity after C8VA. Inhibition of SGC activation represented a promising therapeutic strategy for the management of neuropathic pain following brachial plexus root avulsion.

IL-6 contributes to Nav1.3 up-regulation in trigeminal nerve following chronic constriction injury

Background: To verify the hypothesis that the nature of trigeminal neuralgia (TN) is an ectopic impulse induced by sodium channel modulated by cytokines, we conducted an animal study using the infraorbital nerve chronic constriction injury (CCI) model in rats.Method: The expression of Nav1.3 or IL-6 in the infraorbital nerve (ION) and trigeminal ganglion (TG) were detected by western blot and immunocytochemistry after administration of antisense oligodeoxynucleotide sequence (AS), IL-6 or Anti-IL-6.Results: With intrathecal administration of AS or mismatch oligodeoxynucleotide sequence (MM) in the CCI rats, the Nav1.3-IR in ION and TG accounted for 2.2 ± 0.51% and 8.5 ± 3.1% in AS+CCI group vs. 6.9 ± 1.3% and 38.7 ± 4.8% in MM+CCI group (p < 0.05), respectively. While with local administration of IL-6 in those with sham operation, it accounted for 7.4 ± 2.1% and 45.5 ± 3.4% in IL-6+ sham group vs. 1.9 ± 0.67% and 8.1 ± 1.3% in vehicle+sham group (p < 0.05); with local administration of anti-IL-6 in CCI rats, 4.5 ± 0.78% and 32.1 ± 9.6% in Anti-IL-6+ CCI group vs 8.9 ± 2.1% and 61.4 ± 11.2% in vehicle+CCI group (p < 0.05).Discussion: We believe that the emergence of Na_v1.3 from the compressed trigeminal nerve might be an important structural basis for the development of the ectopic excitability on the axon and IL-6 may play a role of necessary precondition.

Blockade of IL-6 signaling prevents paclitaxel-induced neuropathy in C57Bl/6 mice

The microtubule-stabilizing agent paclitaxel frequently leads to chemotherapy-induced peripheral neuropathy (CIN), which further increases the burden of disease and often necessitates treatment limitations. The pathophysiology of CIN appears to involve both “upstream” effects including altered intracellular calcium signaling and activation of calcium dependent proteases such as calpain as well as subsequent “downstream” neuro-inflammatory reactions with cytokine release and macrophage infiltration of dorsal root ganglia. In this study, we aimed to investigate whether these processes are linked by the pro-inflammatory cytokine interleukin-6 (IL-6). We observed that paclitaxel exposure induced IL-6 synthesis in cultured sensory neurons from postnatal Wistar rats, which could be prevented by co-treatment with a calpain inhibitor. This suggests a calcium dependent process. We demonstrate that adult C57BL/6 mice deficient in IL-6 are protected from developing functional and histological changes of paclitaxel-induced neuropathy. Furthermore, pretreatment with an IL-6-neutralizing antibody resulted in the prevention of paclitaxel-induced neuropathy in C57BL/6 mice. Electrophysiological data from our preclinical model was adequately reflected by measurements of patients undergoing paclitaxel therapy for ovarian cancer. In this cohort, measured Il-6 levels correlated with the severity of neuropathy. Our findings demonstrate that IL-6 plays a pivotal role in the pathophysiology of paclitaxel-induced neuropathy per se and that pharmacological or genetic interference with this signaling pathway prevents the development of this potentially debilitating adverse effect. These findings provide a rationale for a clinical trial with IL-6 neutralizing antibodies to prevent dose-limiting neurotoxic adverse effects of paclitaxel chemotherapy.

Epigenetic reduction of miR-214-3p upregulates astrocytic colony-stimulating factor-1 and contributes to neuropathic pain induced by nerve injury

Emerging evidence has indicated that colony-stimulating factor-1 (CSF1) modulates neuroinflammation in the central nervous system and the development of neuropathic pain, while the underlying mechanism remains unknown. Here, we identified the increased expression of CSF1 derived from activated astrocytes in the ipsilateral dorsal horn in rats with spinal nerve ligation (SNL). Suppression of CSF1 expression alleviated neuroinflammation, neuronal hyperexcitability, and glutamatergic receptor subunit upregulation in the dorsal horn and improved SNL-induced pain behavior. We also found reduced miR-214-3p expression in the ipsilateral dorsal horn following an SNL procedure; miR-214-3p directly bound to the 3'-UTR of CSF1 mRNA and negatively regulated CSF1 expression. Intrathecal delivery of miR-214-3p mimic reversed the enhanced expression of CSF1 and astrocyte overactivity and alleviated the IL-6 upregulation and pain behavior induced by SNL. Moreover, suppression of spinal miR-214-3p increased astrocyte reactivity, promoted CSF1 and IL-6 production, and induced pain hypersensitivity in naive animals. Furthermore, SNL induced the expression of DNA methyltransferase 3a (DNMT3a) that was associated with the hypermethylation of the miR-214-3p promoter, leading to reduced miR-214-3p expression in the model rodents. Treatment with the DNMT inhibitor zebularine significantly reduced cytosine methylation in the miR-214-3p promoter; this reduced methylation consequently increased the expression of miR-214-3p and decreased the content of CSF1 in the ipsilateral dorsal horn and, further, attenuated IL-6 production and pain behavior in rats with SNL. Together, our data indicate that the DNMT3a-mediated epigenetic suppression of miR-214-3p enhanced CSF1 production in astrocytes, which subsequently induced neuroinflammation and pain behavior in SNL model rats.

The Secretomes of Painful Versus Nonpainful Human Schwannomatosis Tumor Cells Differentially Influence Sensory Neuron Gene Expression and Sensitivity

Schwannomatosis is a multiple tumor syndrome in which patients develop benign tumors along peripheral nerves throughout the body. The first symptom with which schwannomatosis patients often present, prior to discovery of tumors, is pain. This pain can be debilitating and is often inadequately alleviated by pharmacological approaches. Schwannomatosis-associated pain can be localized to the area of a tumor, or widespread. Moreover, not all tumors are painful, and the occurrence of pain is often unrelated to tumor size or location. We speculate that some individual tumors, but not others, secrete factors that act on nearby nerves to augment nociception by producing neuronal sensitization or spontaneous neuronal firing. We created cell lines from human SWN tumors with varying degrees of pain. We have found that conditioned medium (CM) collected from painful SWN tumors, but not that from nonpainful SWN tumors, sensitized DRG neurons, causing increased sensitivity to depolarization by KCl, increased response to noxious TRPV1 and TRPA1 agonists and also upregulated the expression of pain-associated genes in DRG cultures. Multiple cytokines were also detected at higher levels in CM from painful tumors. Taken together our data demonstrate a differential ability of painful versus non-painful human schwannomatosis tumor cells to secrete factors that augment sensory neuron responsiveness, and thus identify a potential determinant of pain heterogeneity in schwannomatosis.

Electrophysiological and transcriptomic correlates of neuropathic pain in human dorsal root ganglion neurons

Neuropathic pain encompasses a diverse array of clinical entities affecting 7-10% of the population, which is challenging to adequately treat. Several promising therapeutics derived from molecular discoveries in animal models of neuropathic pain have failed to translate following unsuccessful clinical trials suggesting the possibility of important cellular-level and molecular differences between animals and humans. Establishing the extent of potential differences between laboratory animals and humans, through direct study of human tissues and/or cells, is likely important in facilitating translation of preclinical discoveries to meaningful treatments. Patch-clamp electrophysiology and RNA-sequencing was performed on dorsal root ganglia taken from patients with variable presence of radicular/neuropathic pain. Findings establish that spontaneous action potential generation in dorsal root ganglion neurons is associated with radicular/neuropathic pain and radiographic nerve root compression. Transcriptome analysis suggests presence of sex-specific differences and reveals gene modules and signalling pathways in immune response and neuronal plasticity related to radicular/neuropathic pain that may suggest therapeutic avenues and that has the potential to predict neuropathic pain in future cohorts.

Upregulation of tumor necrosis factor-alpha in the anterior cingulate cortex contributes to neuropathic pain and pain-associated aversion

Injury associated pain involves subjective perception and emotional experience. The anterior cingulate cortex (ACC) is a key area involved in the affective component of pain processing. However, the neuroimmune mechanisms underlying enhanced ACC excitability following peripheral nerve injury are still not fully understood. Our previous work has shown that tumor necrosis factor-alpha (TNF-α) overexpression leads to peripheral afferent hyperexcitability and synaptic transmission potentiation in spinal cord. Here, we aimed to reveal the potential role of ACC TNF-α in ACC hyperexcitability and neuropathic pain. c-Fos, a widely used neuronal activity marker, was induced especially in contralateral ACC early [postoperative (PO) 1 h] and later (PO day 7 and 10) during the development of neuropathic pain. Spared nerve injury (SNI) elevated TNF-α level in contralateral ACC from PO day 5 to 14, delayed relative to decreased ipsilateral paw withdrawal threshold apparent from PO day 1 to 14. Microinjection of anti-TNF-α antibody into the ACC completely eliminated c-Fos overexpression and greatly attenuated pain aversion and mechanical allodynia induced by SNI, suggesting an important role of ACC TNF-α in the pain aversiveness and pain maintenance. Furthermore, modulating ACC pyramidal neurons via a Gi-coupled human M4 muscarinic receptor (hM4Di) or a Gq-coupled human M3 muscarinic receptor (hM3Dq), a type of designer receptors exclusively activated by designer drugs (DREADD), greatly changed the ACC TNF-α level and the mechanical paw withdrawal threshold. The positive interactions between TNF-α and ACC neurons might modulate the cytokine microenvironment thus contribute to the neuropathic pain.

The expression of voltage-gated sodium channels in trigeminal nerve following chronic constriction injury in rats

Objectives: Despite the etiology of trigeminal neuralgia has been verified by microvascular decompression as vascular compression of the trigeminal root, very few researches concerning its underlying pathogenesis has been reported in the literature. The present study focused on those voltage-gated sodium channels, which are the structural basis for generation of ectopic action potentials. Methods: The trigeminal neuralgia modeling was obtained with infraorbital nerve chronic constriction injury (ION-CCI) in rats. Two weeks postoperatively, the infraorbital nerve (TN), the trigeminal ganglion (TG), and the brain stem (BS) were removed and analyzed with a series of molecular biological techniques. Results: Western blot depicted a significant up-regulation of Nav1.3 in TN and TG but not in BS, while none of the other isoforms (Nav1.6, Nav1.7, Nav1.8, or Nav1.9) presented a statistical change. The Nav1.3 from ION-CCI group was quantified as 2.5-fold and 1.7-fold than that from sham group in TN and TG, respectively (p < .05). Immunocytochemistry showed the Nav1.3-IR from ION-CCI group accounted for 21.2 ± 2.3% versus 6.1 ± 1.2% from sham group in TN, while the Nav1.3-positive neurons from ION-CCI group accounted for 34.1 ± 3.5% versus 11.2 ± 1.8% from sham group in TG. Immunohistochemical labeling showed the Nav1.3 was co-localized with CGRP and IB4 but not with GFAP or NF-200 in TG. Conclusion: ION-CCI may give rise to an up-regulation of Nav1.3 in trigeminal nerve as well as in C-type neurons at the trigeminal ganglion. It implied that the ectopic action potential may generate from both the compressed site of the trigeminal nerve and the ganglion rather than from the trigeminal nuclei.

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.

Interleukin-6 Serum Levels Are Elevated in Individuals with Degenerative Cervical Myelopathy and Are Correlated with Symptom Severity

Background

Few studies have investigated systemic inflammation levels in degenerative cervical myelopathy (DCM). This study evaluated the concentration of inflammatory cytokines in DCM patients and assessed whether they can predict symptom severity.

Material/Methods

A total of 40 consecutive DCM patients and 10 healthy volunteers were included in this study. Concentrations of interleukin (IL)-1β, IL-6, interferon-γ, and tumor necrosis factor-α were compared between DCM patients and normal controls. Spearman’s correlation coefficient was used to examine relationships of cytokines with age, body mass index (BMI), symptom duration, and symptom severity. A DCM compression rat model was established to examine the levels of inflammatory cytokines in serum and cerebrospinal fluid (CSF).

Results

Serum level of IL-6 is significantly higher in DCM patients compared with normal people (0.8±0.5 pg/ml vs. 0.5±0.3 pg/ml, P=0.036). Positive correlations were found between IL-6 levels with BMI (ρ=0.519; P=0.001) and symptom severity (ρ=−0.556, P<0.001). In DCM compression model rats, IL-6 was elevated in CSF (40.5±3.3 vs. 13.2±2.4 pg/ml, P<0.001) and serum (7.1±1.7 vs. 2.9±1.6 pg/ml, P<0.001) samples from rats in the compression operation group compared with the sham operation group. Infusion of IL-6 in rats receiving the sham operation also led to motor function damage and mechanical allodynia threshold decline.

Conclusions

Serum IL-6 level was elevated in DCM patients and its concentration can predict symptom severity. Local infusion of IL-6 led to myelopathy symptoms in model rats, which suggests that anti-inflammation can effectively treat DCM.

Upregulation of N-type calcium channels in the soma of uninjured dorsal root ganglion neurons contributes to neuropathic pain by increasing neuronal excitability following peripheral nerve injury

N-type voltage-gated calcium (Cav2.2) channels are expressed in the central terminals of dorsal root ganglion (DRG) neurons, and are critical for neurotransmitter release. Cav2.2 channels are also expressed in the soma of DRG neurons, where their function remains largely unknown. Here, we showed that Cav2.2 was upregulated in the soma of uninjured L4 DRG neurons, but downregulated in those of injured L5 DRG neurons following L5 spinal nerve ligation (L5-SNL). Local application of specific Cav2.2 blockers (ω-conotoxin GVIA, 1-100 μM or ZC88, 10-1000 μM) onto L4 and 6 DRGs on the operated side, but not the contralateral side, dose-dependently reversed mechanical allodynia induced by L5-SNL. Patch clamp recordings revealed that both ω-conotoxin GVIA (1 μM) and ZC88 (10 μM) depressed hyperexcitability in L4 but not in L5 DRG neurons of L5-SNL rats. Consistent with this, knockdown of Cav2.2 in L4 DRG neurons with AAV-Cav2.2 shRNA substantially prevented L5-SNL-induced mechanical allodynia and hyperexcitability of L4 DRG neurons. Furthermore, in L5-SNL rats, interleukin-1 beta (IL-1β) and IL-10 were upregulated in L4 DRGs and L5 DRGs, respectively. Intrathecal injection of IL-1β induced mechanical allodynia and Cav2.2 upregulation in bilateral L4-6 DRGs of naïve rats, whereas injection of IL-10 substantially prevented mechanical allodynia and Cav2.2 upregulation in L4 DRGs in L5-SNL rats. Finally, in cultured DRG neurons, Cav2.2 was dose-dependently upregulated by IL-1β and downregulated by IL-10. These data indicate that the upregulation of Cav2.2 in uninjured DRG neurons via IL-1β over-production contributes to neuropathic pain by increasing neuronal excitability following peripheral nerve injury.

IKK/NF-κB-dependent satellite glia activation induces spinal cord microglia activation and neuropathic pain after nerve injury

Increasing evidence indicates that both microglia and satellite glial cell (SGC) activation play causal roles in neuropathic pain development after peripheral nerve injury; however, the activation mechanisms and their contribution to neuropathic pain remain elusive. To address this issue, we generated Ikkβ conditional knockout mice (Cnp-Cre/Ikkβ; cIkkβ) in which IKK/NF-κB-dependent proinflammatory SGC activation was abrogated. In these mice, nerve injury-induced spinal cord microglia activation and pain hypersensitivity were significantly attenuated compared to those in control mice. In addition, nerve injury-induced proinflammatory gene expression and macrophage infiltration into the dorsal root ganglion (DRG) were severely compromised. However, macrophages recruited into the DRG had minimal effects on spinal cord microglia activation, suggesting a causal effect for SGC activation on spinal cord microglia activation. In an effort to elucidate the molecular mechanisms, we measured Csf1 expression in the DRG, which is implicated in spinal cord microglia activation after nerve injury. In cIkkβ mice, nerve injury-induced Csf1 upregulation was ameliorated indicating that IKK/NF-κΒ-dependent SGC activation induced Csf1 expression in sensory neurons. Taken together, our data suggest that nerve injury-induced SGC activation triggers Csf1 induction in sensory neurons, spinal cord microglia activation, and subsequent central pain sensitization.

Activation of spinal dorsal horn P2Y13 receptors can promote the expression of IL-1β and IL-6 in rats with diabetic neuropathic pain

Objective

The dorsal horn P2Y₁₃ receptor is involved in the development of pain behavior induced by peripheral nerve injury. It is unclear whether the expression of proinflammatory cytokines interleukin (IL)-1β and IL-6 at the spinal dorsal horn are influenced after the activation of P2Y₁₃ receptor in rats with diabetic neuropathic pain (DNP).

Methods

A rat model of type 1 DNP was induced by intraperitoneal injection of streptozotocin (STZ). We examined the expression of P2Y₁₃ receptor, Iba-1, IL-1β, IL-6, JAK2, STAT3, pTyr₁₃₃₆, and pTyr₁₄₇₂ NR2B in rat spinal dorsal horn.

Results

Compared with normal rats, STZ-diabetic rats displayed obvious mechanical allodynia and the increased expression of P2Y₁₃ receptor, Iba-1, IL-1β, and IL-6 in the dorsal spinal cord that was continued for 6 weeks in DNP rats. The data obtained indicated that, in DNP rats, administration of MRS2211 significantly attenuated mechanical allodynia. Compared with DNP rats, after MRS2211 treatment, expression of the P2Y₁₃ receptor, Iba-1, IL-1β, and IL-6 were reduced 4 weeks after the STZ injection. However, MRS2211 treatment did not attenuate the expression of the P2Y₁₃ receptor, Iba-1, IL-1β, and IL-6 at 6 weeks after the STZ injection. MRS2211 suppressed JAK2 and STAT3 expression in the early stage, but not in the later stage. Moreover, pTyr₁₃₃₆ NR2B was significantly decreased, whereas pTyr₁₄₇₂ NR2B was unaffected in the dorsal spinal cord of MRS2211-treated DNP rats.

Conclusion

Intrathecal MRS2211 produces an anti-nociceptive effect in early-stage DNP. A possible mechanism involved in MRS2211-induced analgesia is that blocking the P2Y₁₃ receptor downregulates levels of IL-1β and IL-6, which subsequently inhibit the activation of the JAK2/STAT3 signaling pathway. Furthermore, blocking the activation of the P2Y₁₃ receptor can decrease NR2B-containing NMDAR phosphorylation in dorsal spinal cord neurons, thereby attenuating central sensitization in STZ-induced DNP rats.

Red nucleus interleukin-6 participates in the maintenance of neuropathic pain through JAK/STAT3 and ERK signaling pathways

We previously reported that interleukin-6 (IL-6) in the red nucleus (RN) is up-regulated at 3weeks after spared nerve injury (SNI), and plays facilitated role in the later maintenance of neuropathic pain. The current study aimed to reveal the roles of different signaling pathways, including Janus kinase/signal transducer and activator of transcription 3 (JAK/STAT3), extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), p38 mitogen-activated protein kinase (MAPK) and phosphatidylinositide 3-kinase/protein kinase B (PI3K/AKT), in RN IL-6-mediated pain modulation. In accord with the increase of IL-6 in the RN following SNI, the protein levels of phospho-STAT3 (p-STAT3), p-ERK and p-JNK were also up-regulated in the RN contralateral to the nerve injury side at 3weeks after SNI. The increases of p-STAT3 and p-ERK (but not p-JNK) were associated with IL-6 and could be blocked by anti-IL-6 antibody. Microinjection of JAK2 inhibitor AG490, ERK inhibitor PD98059 and also JNK inhibitor SP600125 into the RN significantly increased the paw withdrawal threshold (PWT) and alleviated SNI-induced mechanical allodynia. Further studies showed that microinjection of recombinant rat IL-6 (rrIL-6, 20ng) into the RN of normal rats significantly decreased the PWT of rats and increased the local protein levels of p-STAT3 and p-ERK, but not p-JNK. Pre-treatment with AG490 and PD98059 could prevent IL-6-induced mechanical allodynia. Whereas, p-p38 MAPK and p-AKT did not show any expression changes in the RN of rats with SNI or rats treated with rrIL-6. These results suggest that RN IL-6 participates in the later maintenance of SNI-induced neuropathic pain and plays facilitated role through activating JAK/STAT3 and ERK signaling pathways.

Differential expression of systemic inflammatory mediators in amputees with chronic residual limb pain

Chronic postsurgical pain impacts most amputees, with more than half experiencing neuralgic residual limb pain. The transition from normal acute postamputation pain to chronic residual limb pain likely involves both peripheral and central inflammatory mechanisms. As part of the Veterans Integrated Pain Evaluation Research study, we investigated links between systemic inflammatory mediator levels and chronic residual limb pain. Subjects included 36 recent active duty military traumatic amputees with chronic residual limb pain and 40 without clinically significant pain. Blood samples were obtained and plasma concentrations of an array of inflammatory mediators were analyzed. Residual limb pain intensity and pain catastrophizing were assessed to examine associations with inflammatory mediators. Pro-inflammatory mediators including tumor necrosis factor (TNF)-α, TNF-β, interleukin (IL)-8, ICAM-1, Tie2, CRP, and SAA were elevated in patients with chronic residual limb pain. Across all patients, residual limb pain intensity was associated positively with levels of several proinflammatory mediators (IL-8, TNF-α, IL-12, TNF-β, PIGF, Tie2, SAA, and ICAM-1), and inversely with concentrations of the anti-inflammatory mediator IL-13, as well as IL-2 and Eotaxin-3. Pain catastrophizing correlated positively with IL-8, IL-12, TNF-β, PIGF, and ICAM-1, and inversely with IL-13. Significant associations between catastrophizing and residual limb pain intensity were partially mediated by TNF-α, TNF- β, SAA, and ICAM-1 levels. Results suggest that chronic postamputation residual limb pain is associated with excessive inflammatory response to injury or to inadequate resolution of the postinjury inflammatory state. Impact of pain catastrophizing on residual limb pain may be because of part to common underlying inflammatory mechanisms.

Fascin-1 Contributes to Neuropathic Pain by Promoting Inflammation in Rat Spinal Cord

Neuropathic pain is a complicated clinical syndrome caused by heterogeneous etiology. Despite the fact that the underlying mechanisms remain elusive, it is well accepted that neuroinflammation plays a critical role in the development of neuropathic pain. Fascin-1, an actin-bundling protein, has been proved to be involved in the processing of diverse biological events including cellular development, immunity, and tumor invasion etc. Recent studies have shown that Fascin-1 participates in antigen presentation and the regulation of pro-inflammatory agents. However, whether Fascin-1 is involved in neuropathic pain has not been reported. In the present study we examined the potential role of Fascin-1 by using a rodent model of chronic constriction injury (CCI). Our results showed that Fascin-1 increased rapidly in dorsal root ganglions (DRG) and spinal cord (SC) after CCI. The increased Fascin-1 widely expressed in DRG, however, it localized predominantly in microglia, seldom in neuron, and hardly in astrocyte in the SC. Intrathecal injection of Fascin-1 siRNA not only suppressed the activation of microglia and the release of pro-inflammatory mediators, but also attenuated the mechanical allodynia and thermal hyperalgesia induced by CCI.

Liver X Receptor α Is Involved in Counteracting Mechanical Allodynia by Inhibiting Neuroinflammation in the Spinal Dorsal Horn

BACKGROUND

Liver X receptors, including α and β isoforms, are ligand-activated transcription factors. Whether liver X receptor α plays a role in neuropathic pain is unknown.

METHODS

A spared nerve injury model was established in adult male rats and mice. Von Frey tests were performed to evaluate the neuropathic pain behavior; Western blot and immunohistochemistry were performed to understand the underlying mechanisms.

RESULTS

Intrathecal injection of a specific liver X receptor agonist T0901317 or GW3965 could either prevent the development of mechanical allodynia or alleviate the established mechanical allodynia, both in rats and wild-type mice. GW3965 could inhibit the activation of glial cells and the expression of tumor necrosis factor-α (mean ± SD: 196 ± 48 vs. 119 ± 57; n = 6; P < 0.01) and interleukin 1β (mean ± SD: 215 ± 69 vs. 158 ± 74; n = 6; P < 0.01) and increase the expression of interleukin 10 in the spinal dorsal horn. All of the above effects of GW3965 could be abolished by liver X receptor α mutation. Moreover, more glial cells were activated, and more interleukin 1β was released in the spinal dorsal horn in liver X receptor α knockout mice than in wild-type mice after spared nerve injury. Aminoglutethimide, a neurosteroid synthesis inhibitor, blocked the inhibitory effect of T0901317 on mechanical allodynia, on the activation of glial cells, and on the expression of cytokines.

CONCLUSIONS

Activation of liver X receptor α inhibits mechanical allodynia by inhibiting the activation of glial cells and rebalancing cytokines in the spinal dorsal horn via neurosteroids.

P2Y12 and P2Y13 receptors involved in ADPβs induced the release of IL-1β, IL-6 and TNF-α from cultured dorsal horn microglia

Objective

P2 receptors have been implicated in the release of neurotransmitter and pro-inflammatory cytokines due to their response to neuroexcitatory substances in the microglia. Dorsal horn P2Y₁₂ and P2Y₁₃ receptors are involved in the development of pain behavior induced by peripheral nerve injury. However, it is not known whether P2Y₁₂ and P2Y₁₃ receptors activation is associated with the expression and the release of interleukin-1B (IL-1β), interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α) in cultured dorsal spinal cord microglia. For this reason, we examined the effects of ADPβs (ADP analog) on the expression and the release of IL-1β, IL-6, and TNF-α.

Methods and results

In this study, we observed the effect of P2Y receptor agonist ADPβs on the expression and release of IL-1β, IL-6 and TNF-α by using real-time fluorescence quantitative polymerase chain reaction (PCR) and enzyme-linked immunosorbent assay (ELISA). ADPβs induced the increased expression of Iba-1, IL-1β, IL-6 and TNF-α at the level of messenger RNA (mRNA). ADPβs-evoked increase in Iba-1, IL-1β, IL-6 and TNF-α mRNA expression was inhibited only partially by P2Y₁₂ receptor antagonist MRS2395 or P2Y₁₃ receptor antagonist MRS2211, respectively. Similarly, ADPβs-evoked release of IL-1β, IL-6 and TNF-α was inhibited only partially by MRS2395 or MRS2211. Furthermore, ADPβs-evoked increased expression of Iba-1, IL-1β, IL-6 and TNF-α mRNA, and release of IL-1β, IL-6 and TNF-α were nearly all blocked after co-administration of MRS2395 plus MRS2179. Further evidence indicated that P2Y₁₂ and P2Y₁₃ receptor-evoked increased gene expression of IL-1β, IL-6 and TNF-α were inhibited by Y-27632 (ROCK inhibitor), SB203580 (P38MAPK inhibitor) and PDTC (NF-κb inhibitor), respectively. Subsequently, P2Y₁₂ and P2Y₁₃ receptor-evoked release of IL-1β, IL-6 and TNF-α, were also inhibited by Y-27632, SB203580 and PDTC, respectively.

Conclusion

These observations suggest that P2Y₁₂ and P2Y₁₃ receptor-evoked gene expression and release of IL-1β, IL-6 and TNF-α are associated with ROCK/P38MAPK/NF-κb signaling pathway.

Down-Regulation of miRNA-128 Contributes to Neuropathic Pain Following Spinal Cord Injury via Activation of P38

Background

Neuropathic pain (NPP) arises from a lesion or dysfunction of the somatosensory nervous system. Recent studies have demonstrated multiple microRNAs (miRNAs) play key roles in NPP development. This study aimed to investigate the effects of miR-128 on microglial cells.

Material/Methods

We established a compressive spinal cord injury (SCI) model and collected the spinal cord segment-derived conditioned medium (CM). We then measured the expression of miR-128 in the murine microglial cell line BV2 treated with CM-SCI or CM obtained from control (CM-NC). Furthermore, lentivirus production of miR-128 and scrambled control were transfected into BV2 cells, which were first treated with CM-SCI or CM-NC. Moreover, the effects of miR-128 on cell viability, M1/M2 microglial gene expression, inflammatory cytokines concentration, and the protein expression of P38 and phosphorylated P38 (P-P38) were investigated.

Results

The expression of miR-128 was downregulated in murine microglial BV2 cells treated with CM-SCI. Overexpression of miR-128 markedly promoted the viability of murine microglial cells. In addition, miR-128 overexpression significantly decreased the expression levels of microglial M1 phenotypic markers CD86 and CD32, and increased the expression levels of M2 phenotypic markers Arg1 and CD206. Furthermore, miR-128 overexpression obviously decreased the concentration of TNF-α, IL-1β, and IL-6. We found that miR-128 overexpression significantly downregulated the expression levels of P38 andP-P38.

Conclusions

Our findings indicate that down-regulation of miR-128 in murine microglial cells may contribute to the development of NPP following SCI via activation of P38. MiR-128 may be a potential intervention target for NPP.

Estrogen-Induced Monocytic Response Correlates with TMD Pain: A Case Control Study

Temporomandibular disorders (TMD) are a set of conditions characterized by pain and dysfunction in the temporomandibular joint and muscles of mastication. These pain conditions are associated with considerable morbidity, societal costs, and reduced quality of life. The prevalence varies between 4% and 10%, with females at higher risk, and a higher prevalence occurs during reproductive years. The increased prevalence of TMD in females and low prevalence in childhood reinforce that sex hormones, like estrogen, play an important, complex role in the pathophysiology of these disorders. The goal of this study was to determine whether women with TMD exhibit a monocytic hyperinflammatory response compared with control women, and to examine associations of monocytic inflammatory responses with clinical pain. Eighteen women, aged 18 to 35 y, were seen during their follicular menstrual phase. A blood sample was collected, a clinical questionnaire about pain history was administered, and a Research Diagnostic Criteria (RDC) exam was performed. Extracted monocytes were stimulated with the toll-like receptor (TLR)-4 ligand, lipopolysaccharide (LPS), in the presence and absence of estrogen, and the levels of IL6 expression evaluated. Women with TMD showed a systemic hyperinflammatory phenotype, manifested by an increased monocytic release of cytokines after an inflammatory insult, and this was further increased by estrogen. In addition, monocytes from participants who self-reported more pain on the VAS scale produced higher levels of IL6 compared with those from participants who self-reported lower pain sensitivity. These data suggest that an estrogen-induced hyperinflammatory phenotype in women with TMD may at least in part contribute to heightened clinical pain, perhaps via central sensitization.

Therapeutic Ultrasound and Treadmill Training Suppress Peripheral Nerve Injury-Induced Pain in Rats

BACKGROUND

Although evidence suggests that therapeutic ultrasound (TU) in combination with treadmill training (TT) suppresses nerve injury-associated pain, the molecular mechanisms for this action are not clear.

OBJECTIVE

The purpose of this research was to study the possible beneficial effects of TU and TT, alone and in combination, on 2 clinical indicators of neuropathic pain and correlate these findings with changes in inflammatory mediators within the spinal cord. Our experimental model used the well-known chronic constriction injury (CCI) of the rat sciatic nerve.

DESIGN

This was an experimental study.

METHODS

Each group contained 10 rats. Group 1 underwent only the CCI procedure. Group 2 underwent a sham operation where the sciatic nerve was exposed but not ligated. Group 3 had the sham operation followed by both TT and TU. Groups 4, 5, and 6 underwent the CCI procedure followed by TT alone, TU alone, and both the TT and TU interventions, respectively. Heat and mechanical sensitivity, interleukin-6 (IL-6), interleukin-10 (IL-10), and ionized calcium binding adaptor molecule 1 (Iba1) were evaluated.

RESULTS

Compared with group 1 animals, TT or TU, or both, produced smaller decreases in mechanical withdrawal threshold and heat withdrawal latencies. The combination of TT and TU was more effective than either treatment alone. In addition, rats that received these treatments did not express the upregulation of IL-6 and Iba1 in their spinal cords on postoperative days 14 and 28, as was found in the group 1 animals.

LIMITATIONS

These experimental findings may not be generalizable to humans.

CONCLUSIONS

The combination of TU and TT reduces neuropathic pain more than either modality alone. This beneficial effect appears related to downregulation of proinflammatory IL-6 and Iba1, while upregulating the anti-inflammatory IL-10.

Emerging Relationships between Exercise, Sensory Nerves, and Neuropathic Pain

The utilization of physical activity as a therapeutic tool is rapidly growing in the medical community and the role exercise may offer in the alleviation of painful disease states is an emerging research area. The development of neuropathic pain is a complex mechanism, which clinicians and researchers are continually working to better understand. The limited therapies available for alleviation of these pain states are still focused on pain abatement and as opposed to treating underlying mechanisms. The continued research into exercise and pain may address these underlying mechanisms, but the mechanisms which exercise acts through are still poorly understood. The objective of this review is to provide an overview of how the peripheral nervous system responds to exercise, the relationship of inflammation and exercise, and experimental and clinical use of exercise to treat pain. Although pain is associated with many conditions, this review highlights pain associated with diabetes as well as experimental studies on nerve damages-associated pain. Because of the global effects of exercise across multiple organ systems, exercise intervention can address multiple problems across the entire nervous system through a single intervention. This is a double-edged sword however, as the global interactions of exercise also require in depth investigations to include and identify the many changes that can occur after physical activity. A continued investment into research is necessary to advance the adoption of physical activity as a beneficial remedy for neuropathic pain. The following highlights our current understanding of how exercise alters pain, the varied pain models used to explore exercise intervention, and the molecular pathways leading to the physiological and pathological changes following exercise intervention.