Contralateral non-operated nerve to transected rat sciatic nerve shows increased expression of IL-1beta, TGF-beta1, TNF-alpha, and IL-10

The FDA-approved compound, pramipexole and the clinical-stage investigational drug, dexpramipexole, reverse chronic allodynia from sciatic nerve damage in mice, and alter IL-1β and IL-10 expression from immune cell culture

During the onset of neuropathic pain from a variety of etiologies, nociceptors become hypersensitized, releasing neurotransmitters and other factors from centrally-projecting nerve terminals within the dorsal spinal cord. Consequently, glial cells (astrocytes and microglia) in the spinal cord are activated and mediate the release of proinflammatory cytokines that act to enhance pain transmission and sensitize mechanical non-nociceptive fibers which ultimately results in light touch hypersensitivity, clinically observed as allodynia. Pramipexole, a D2/D3 preferring agonist, is FDA-approved for the treatment of Parkinson's disease and demonstrates efficacy in animal models of inflammatory pain. The clinical-stage investigational drug, R(+) enantiomer of pramipexole, dexpramipexole, is virtually devoid of D2/D3 agonist actions and is efficacious in animal models of inflammatory and neuropathic pain. The current experiments focus on the application of a mouse model of sciatic nerve neuropathy, chronic constriction injury (CCI), that leads to allodynia and is previously characterized to generate spinal glial activation with consequent release IL-1β. We hypothesized that both pramipexole and dexpramipexole reverse CCI-induced chronic neuropathy in mice, and in human monocyte cell culture studies (THP-1 cells), pramipexole prevents IL-1β production. Additionally, we hypothesized that in rat primary splenocyte culture, dexpramixole increases mRNA for the anti-inflammatory and pleiotropic cytokine, interleukin-10 (IL-10). Results show that following intravenous pramipexole or dexpramipexole, a profound decrease in allodynia was observed by 1 hr, with allodynia returning 24 hr post-injection. Pramipexole significantly blunted IL-1β protein production from stimulated human monocytes and dexpramipexole induced elevated IL-10 mRNA expression from rat splenocytes. The data support that clinically-approved compounds like pramipexole and dexpramipexole support their application as anti-inflammatory agents to mitigate chronic neuropathy, and provide a blueprint for future, multifaceted approaches for opioid-independent neuropathic pain treatment.

Contralateral Effects of Eccentric Exercise and DOMS of the Plantar Flexors: Evidence of Central Involvement

Purpose: Peripheral and central factors play important roles in the reduction of motor performance following damaging eccentric exercise and delayed onset muscle soreness (DOMS). Following this regime, contralateral limbs could also be affected; however, the factors involved remain inconclusive. The purpose of this study was to distinguish the peripheral and central factors following eccentric contraction and DOMS of the plantar flexors in treated and contralateral homologous limbs. Methods: Ten males (BMI = 25.08 ± 1.69kgm^-2; age = 28.70 ± 4.24 years) were randomly assigned to experimental (DOM) or control (CON) groups. The DOM group performed a damaging eccentric exercise, while the CON group rested. Plasma creatine kinase (CK), pain rating scale (PRS), muscle stiffness, maximal voluntary contraction (MVC), and neural voluntary activation (VA) were measured before, after 10 min, and after 24, 48, and 72 hr on treated and contralateral limbs. Results: Following exercise, CK increased until after 48 hr, while PRS increased until after 72 hr compared to the CON group. Importantly, MVC was reduced at all time points, with the greatest reduction observed after 24 hr (-16%), while VA was affected until after 48 hr, with the greatest reduction at after 10 min (-7%). Interestingly, a "cross-over effect" was observed in contralateral limbs when PRS, MVC, and VA were negatively affected following the same pattern (time line) as treated limbs (-13% peak MVC reduction; -3.5% peak VA reduction). Conclusion: These findings suggest a substantial central contribution to the reduction in force immediately following eccentric exercise and to a lesser extent during the latter part of DOMS in both treated and contralateral limbs.

rTMS induces analgesia and modulates neuroinflammation and neuroplasticity in neuropathic pain model rats

Neuropathic pain (NP) is related to the presence of hyperalgesia, allodynia, and spontaneous pain, affecting 7%-10% of the general population. Repetitive transcranial magnetic stimulation (rTMS) is applied for NP relief, especially in patients with refractory pain. As NP response to existing treatments is often insufficient, we aimed to evaluate rTMS treatment on the nociceptive response of rats submitted to an NP model and its effect on pro-and anti-neuroinflammatory cytokine and neurotrophin levels. A total of 106 adult male Wistar rats (60 days old) were divided into nine experimental groups: control, control + sham rTMS, control + rTMS, sham NP, sham neuropathic pain + sham rTMS, sham neuropathic pain + rTMS, NP, neuropathic pain + sham rTMS, and neuropathic pain + rTMS. NP establishment was achieved 14 days after the surgery to establish chronic constriction injury (CCI) of the sciatic nerve. Rats were treated with 5 min daily sessions of rTMS for eight consecutive days. Nociceptive behavior was assessed using von Frey and hot plate tests at baseline, after NP establishment, and post-treatment. Biochemical assays to assess the levels of brain-derived neurotrophic factor (BDNF), tumor necrosis factor-alpha (TNF-α), and interleukin (IL)-10, were performed in the prefrontal cortex (PFC) and spinal cord tissue homogenates. rTMS treatment promoted a partial reversal of mechanical allodynia and total reversal of thermal hyperalgesia induced by CCI. Moreover, rTMS increased the levels of BDNF, TNF-α, and IL-10 in the PFC. rTMS may be a promising tool for the treatment of NP. The alterations induced by rTMS on neurochemical parameters may have contributed to the analgesic effect presented.

Evolution of mirror-image pain in temporomandibular joint osteoarthritis mouse model

OBJECTIVE

Mirror-image pain is a kind of pain that occurs on the contralateral side, but its pathogenesis remains unclear. To develop an osteoarthritis mouse model for investigating mirror-image pain through observing nocifensive behaviors, histological changes, and nociceptive activity at days 3, 7, 14, 21, and 28 after the chemical induction of unilateral temporomandibular joint (TMJ) osteoarthritis.

METHODOLOGY

We randomly divided 6-week-old mice into sham and complete Freund adjuvant groups. To induce nocifensive behaviors, we applied 0.04 g of von Frey filament, 10 psi of air puff, and cold acetone on both sides of whisker pads at different days. The histology of TMJ on both sides was observed by hematoxylin/eosin staining and microcomputed tomography scanning. Furthermore, the nociceptive activity was evaluated using the phosphorylated cyclic AMP response element binding protein (pCREB) and a microglia marker at different days in the trigeminal subnucleus caudalis.

RESULTS

Nocifensive behaviors against mechanical and temperature stimuli on the contralateral side became stronger than the baseline on day 28, in agreement with the elevation of the pCREB and the microglia marker in the trigeminal subnucleus caudalis. Thus, hypernociception on the contralateral side occurred at day 28.

CONCLUSIONS

Clearly, the TMJ model with unilateral osteoarthritis exhibited mirror-image pain. Therefore, this model is useful in investigating the pathogenesis of pain and in developing treatments.

Interleukin-10 Reduces Neurogenic Inflammation and Pain Behavior in a Mouse Model of Type 2 Diabetes

Purpose

Neurogenic inflammation is a major component of chronic neuropathic pain. Previously, we established the db/db mouse as an animal model of painful diabetic neuropathy (PDN) of type 2 diabetes. In the current study, we investigate the roles of interleukin (IL)-10, an anti-inflammatory cytokine, in the development of neurogenic inflammation and pain behavior in db/db mouse.

Materials and Methods

We first studied IL-10 expression in lumbar dorsal root ganglion (LDRG) neurons of db/db mice using immunohistochemistry, immunoblots, and reverse transcription polymerase chain reaction during the period of pain behavior (from 8 to 16 wk of age). To determine if the reduced IL-10 expression mediates the mechanical allodynia in db/db mice, we administered recombinant mouse IL-10 or saline (control) intraperitoneally to control db/+ and db/db mice starting at 8 wk of age. IL-10 treatment was repeated every other day for 2 wk until the mice reached 10 wk of age.

Results

During the period of pain behavior, reduction of IL-10 protein and gene expression was detected in LDRG of db/db mice. Treatment with recombinant IL-10, from 8 to 10 wk of age, alleviates pain behaviors in db/db mice without affecting other diabetic parameters. In parallel, IL-10 treatment reduced the upregulation of nerve growth factor (NGF), inducible nitric oxide synthase (iNOS), tumor necrosis factor (TNF)-α, and high-affinity NGF receptor (Trk A) in LDRG, as well as the numbers of iNOS-positive Langerhans cells and CD-68-positive dermal dendritic cells in the hind-foot-pad skin in db/db mice.

Conclusion

Our findings suggest that the reduction in neuronal IL-10 increases inflammatory phenomena, ultimately contributing to PDN. These results suggest that the dysregulation of cytokine-mediated inflammation contributes to the development of PDN in db/db mice. Targeting this pathophysiologic mechanism could be an effective approach for treating PDN in type 2 diabetes.

Electroacupuncture Alleviates Mechanical Allodynia of a Rat Model of CRPS-I and Modulates Gene Expression Profiles in Dorsal Root Ganglia

Complex regional pain syndrome type-I (CRPS-I) is chronic neurological disorder accompanied with devastating pain. Most conventional medical treatments lack effectiveness, making CRPS-I a challenging clinical condition. Electroacupuncture (EA) showed effectiveness in alleviating the pain symptoms of CRPS-I patients. However, the molecular mechanisms underlying EA's therapeutic effect are still not well-understood. Here, we established the rat chronic post-ischemic pain (CPIP) model to mimic CRPS-I and performed repetitive EA on bilateral hind limbs of the CPIP model rats. We then performed RNA-sequencing (RNA-Seq) to study the differences in gene expression, gene networks, and molecular pathways in ipsilateral DRGs innervating the hind limb of the CPIP model rats with and without repetitive EA treatment. Our results found that repetitive EA treatment significantly alleviated mechanical allodynia in bilateral hind limbs of CPIP model rats. RNA-Seq analysis indicated that EA modulated the expression of multiple genes and gene networks in the DRGs of CPIP model rats. Further bioinformatics analysis identified the up-regulation of an array of genes involved in biological process such as neutrophil chemotaxis and immune response in the DRGs of CPIP model rats after EA treatment. Thus, these results suggest that EA may alleviate pain response in CPIP model rats via regulating multiple genes. Our work may help to further advance the understandings of the molecular mechanisms underlying EA's therapeutic effects on CRPS-I and help to identify novel targets for CRPS-I treatment.

Host tissue response to floating microelectrode arrays chronically implanted in the feline spinal nerve

OBJECTIVE

Neural interfacing technologies could significantly improve quality of life for people living with the loss of a limb. Both motor commands and sensory feedback must be considered; these complementary systems are segregated from one another in the spinal nerve.

APPROACH

The dorsal root ganglion-ventral root (DRG-VR) complex was targeted chronically with floating microelectrode arrays designed to record from motor neuron axons in the VR or stimulate sensory neurons in the DRG. Hematoxylin and eosin and Nissl/Luxol fast blue staining were performed. Characterization of the tissue response in regions of interest and pixel-based image analyses were used to quantify MAC387 (monocytes/macrophages), NF200 (axons), S100 (Schwann cells), vimentin (fibroblasts, endothelial cells, astrocytes), and GLUT1 (glucose transport proteins) reactivity. Implanted roots were compared to non-implanted roots and differences between the VR and DRG examined.

MAIN RESULTS

The tissue response associated with chronic array implantation in this peripheral location is similar to that observed in central nervous system locations. Markers of inflammation were increased in implanted roots relative to control roots with MAC387 positive cells distributed throughout the region corresponding to the device footprint. Significant decreases in neuronal density and myelination were observed in both the VR, which contains only neuronal axons, and the DRG, which contains both neuronal axons and cell bodies. Notably, decreases in NF200 in the VR were observed only at implant times less than ten weeks. Observations related to the blood-nerve barrier and tissue integrity suggest that tissue remodeling occurs, particularly in the VR.

SIGNIFICANCE

This study was designed to assess the viability of the DRG-VR complex as a site for neural interfacing applications and suggests that continued efforts to mitigate the tissue response will be critical to achieve the overall goal of a long-term, reliable neural interface.

LFA-1 antagonist (BIRT377) similarly reverses peripheral neuropathic pain in male and female mice with underlying sex divergent peripheral immune proinflammatory phenotypes

Aim:

The majority of preclinical studies investigating aberrant glial-neuroimmune actions underlying neuropathic pain have focused on male rodent models. Recently, studies have shown peripheral immune cells play a more prominent role than glial cells in mediating pathological pain in females. Here, we compared the onset and duration of allodynia in males and females, and the anti-allodynic action of a potentially novel therapeutic drug (BIRT377) that not only antagonizes the action of lymphocyte function-associated antigen-1 (LFA-1) to reduce cell migration in the periphery, but may also directly alter the cellular inflammatory bias.

Methods:

Male and female mice were subjected to peripheral nerve injury chronic constriction injury (CCI) applying two methods, using either 4–0 or 5–0 chromic gut suture material, to examine potential sex differences in the onset, magnitude and duration of allodynia. Hindpaw sensitivity before and after CCI and application of intravenous BIRT377 was assessed. Peripheral and spinal tissues were analyzed for protein (multiplex electrochemiluminescence technology) and mRNA expression (quantitative real-time PCR). The phenotype of peripheral T cells was determined using flow cytometry.

Results:

Sex differences in proinflammatory CCL2 and IL-1β and the anti-inflammatory IL-10 were observed from a set of cytokines analyzed. A profound proinflammatory T cell (Th17) response in the periphery and spinal cord was also observed in neuropathic females. BIRT377 reversed pain, reduced IL-1β and TNF, and increased IL-10 and transforming growth factor (TGF)-β1, also an anti-inflammatory cytokine, in both sexes. However, female-derived T cell cytokines are transcriptionally regulated by BIRT377, as demonstrated by reducing proinflammatory IL-17A production with concurrent increases in IL-10, TGF-β1 and the anti-inflammatory regulatory T cell-related factor, FOXP3.

Conclusion:

This study supports that divergent peripheral immune and neuroimmune responses during neuropathy exists between males and females. Moreover, the modulatory actions of BIRT377 on T cells during neuropathy are predominantly specific to females. These data highlight the necessity of including both sexes for studying drug efficacy and mechanisms of action in preclinical studies and clinical trials.

A Conditioning Sciatic Nerve Lesion Triggers a Pro-regenerative State in Primary Sensory Neurons Also of Dorsal Root Ganglia Non-associated With the Damaged Nerve

The primary sensory neurons of dorsal root ganglia (DRG) are a very useful model to study the neuronal regenerative program that is a prerequisite for successful axon regeneration after peripheral nerve injury. Seven days after a unilateral sciatic nerve injury by compression or transection, we detected a bilateral increase in growth-associated protein-43 (GAP-43) and superior cervical ganglion-10 (SCG-10) mRNA and protein levels not only in DRG neurons of lumbar spinal cord segments (L4-L5) associated with injured nerve, but also in remote cervical segments (C6-C8). The increase in regeneration-associated proteins in the cervical DRG neurons was associated with the greater length of regenerated axons 1 day after ulnar nerve crush following prior sciatic nerve injury as compared to controls with only ulnar nerve crush. The increased axonal regeneration capacity of cervical DRG neurons after a prior conditioning sciatic nerve lesion was confirmed by neurite outgrowth assay of in vitro cultivated DRG neurons. Intrathecal injection of IL-6 or a JAK2 inhibitor (AG490) revealed a role for the IL-6 signaling pathway in activating the pro-regenerative state in remote DRG neurons. Our results suggest that the pro-regenerative state induced in the DRG neurons non-associated with the injured nerve reflects a systemic reaction of these neurons to unilateral sciatic nerve injury.

Acute hyperalgesia and delayed dry eye after corneal abrasion injury

Introduction:

Corneal nerves mediate pain from the ocular surface, lacrimation, and blinking, all of which protect corneal surface homeostasis and help preserve vision. Because pain, lacrimation and blinking are rarely assessed at the same time, it is not known whether these responses and their underlying mechanisms have similar temporal dynamics after acute corneal injury.

Methods:

We examined changes in corneal nerve density, evoked and spontaneous pain, and ocular homeostasis in Sprague-Dawley male rats after a superficial epithelial injury with heptanol. We also measured changes in calcitonin gene-related peptide (CGRP), which has been implicated in both pain and epithelial repair.

Results:

Hyperalgesia was seen 24 hours after abrasion injury, while basal tear production was normal. One week after abrasion injury, pain responses had returned to baseline levels and dry eye symptoms emerged. There was no correlation between epithelial nerve density and pain responses. Expression of both ATF3 (a nerve injury marker) and CGRP increased in trigeminal ganglia 24 hours after injury when hyperalgesia was seen, and returned to normal one week later when pain behavior was normal. These molecular changes were absent in the contralateral ganglion, despite reductions in corneal epithelial nerve density in the uninjured eye. By contrast, CGRP was upregulated in peripheral corneal endings 1 week after injury, when dry eye symptoms emerged.

Conclusion:

Our results demonstrate dynamic trafficking of CGRP within trigeminal sensory nerves following corneal injury, with elevations in the ganglion correlated with pain behaviors and elevations in peripheral endings correlated with dry eye symptoms.

The effect of eccentric exercise and delayed onset muscle soreness on the homologous muscle of the contralateral limb

High intensity eccentric exercise induces muscle fiber damage and associated delayed-onset muscle soreness (DOMS) resulting in an impaired ability of the muscle to generate voluntary force. This study investigates the extent to which DOMS, induced by high intensity eccentric exercise, can affect the activation and performance of the non-exercised homologous muscle of the contralateral limb. Healthy volunteers performed maximal voluntary contractions of knee extension and sustained isometric knee extension at 50% of maximal force until task failure on both the ipsilateral exercised limb and the contralateral limb. Surface electromyography (EMG) was recorded from the ipsilateral and contralateral knee extensor muscles (vastus medialis, rectus femoris, and vastus lateralis). Maximal isometric knee extension force (13.7% reduction) and time to task failure (38.1% reduction) of the contralateral non-exercised leg decreased immediately after eccentric exercise, and persisted 24 h and 48 h later (p < 0.05). Moreover, the amplitude of muscle activity recorded from the contralateral knee extensor muscles was significantly lower during the post exercise maximal and submaximal contractions following high intensity eccentric exercise of the opposite limb (p < 0.05). Unilateral high intensity eccentric exercise of the quadriceps can contribute to reduced neuromuscular activity and physical work capacity of the non-exercised homologous muscle in the contralateral limb.

The foreign body response and morphometric changes associated with mesh-style peripheral nerve cuffs

Nerve cuffs have been used to anchor and protect penetrating electrodes in peripheral nerves and have been used as non-penetrating electrodes for neural recording and nerve stimulation. The material of choice for such applications is silicone, an inert synthetic biomaterial which elicits a minimal chronic foreign body response (FBR). While histological studies of solid silicone cuffs are available, to the best of our knowledge a comparison to other cuff designs is not well documented. Here, we describe the FBR and morphological changes that accompany nerve cuff implantation in the rat sciatic nerve by comparing a metallic mesh with and without a parylene coating to one made of silicone. Two months after implantation, we observed that such implants, irrespective of the cuff type, were associated with a persistent inflammatory response consisting of activated macrophages attached to the implant surfaces, which extended into the endoneurial space of the encapsulated nerve. We also observed foreign body giant cells in the epineurial space that were more prevalent in the mesh cohorts. The mesh cuff groups showed significant changes in several morphometric parameters that were not seen in the silicon group including reductions in nerve fiber packing density and a greater reduction of large diameter fibers. High magnification microscopy also showed greater evidence of foamy macrophages in the endoneurial space of the mesh implanted cohorts. Although the precise mechanisms are unknown, the results showed that mesh style nerve cuffs show a greater inflammatory response and had greater reductions in morphometric changes in the underlying nerve compared to silicone in the absence of a penetrating injury.

STATEMENT OF SIGNIFICANCE

While traditional silicone cuffs have been in use for decades, the inflammatory and morphometric effects of these cuffs on the underlying nerve have not been deeply studied. Further, manipulation of the foreign body response to nerve cuffs by using various materials and/or designs has not been well reported. Therefore, we report the inflammatory response around nerve cuffs of various materials and designs, as well as report morphometric parameters of the underlying nerve. These data provide important information regarding the potential for quantitative morphometric changes associated with the use of nerve cuffs, and, importantly, suggests that these changes are associated with the degree of inflammation associated with the cuff.

Prenatal alcohol exposure potentiates chronic neuropathic pain, spinal glial and immune cell activation and alters sciatic nerve and DRG cytokine levels

A growing body of evidence indicates that prenatal alcohol exposure (PAE) may predispose individuals to secondary medical disabilities later in life. Animal models of PAE reveal neuroimmune sequelae such as elevated brain astrocyte and microglial activation with corresponding region-specific changes in immune signaling molecules such as cytokines and chemokines. The aim of this study was to evaluate the effects of moderate PAE on the development and maintenance of allodynia induced by chronic constriction injury (CCI) of the sciatic nerve in adult male rat offspring. Because CCI allodynia requires the actions of glial cytokines, we analyzed lumbar spinal cord glial and immune cell surface markers indicative of their activation levels, as well as sciatic nerve and dorsal root ganglia (DRG) cytokines in PAE offspring in adulthood. While PAE did not alter basal sensory thresholds before or after sham manipulations, PAE significantly potentiated adult onset and maintenance of allodynia. Microscopic analysis revealed exaggerated astrocyte and microglial activation, while flow cytometry data demonstrated increased proportions of immune cells with cell surface major histocompatibility complex II (MHCII) and β-integrin adhesion molecules, which are indicative of PAE-induced immune cell activation. Sciatic nerves from CCI rats revealed that PAE potentiated the proinflammatory cytokines interleukin (IL)-1β, IL-6 and tumor necrosis factor-alpha (TNFα) protein levels with a simultaneous robust suppression of the anti-inflammatory cytokine, IL-10. A profound reduction in IL-10 expression in the DRG of PAE neuropathic rats was also observed. Taken together, our results provide novel insights into the vulnerability that PAE produces for adult-onset central nervous system (CNS) pathological conditions from peripheral nerve injury.

Effect of pioglitazone on neuropathic pain and spinal expression of TLR-4 and cytokines

The molecular mechanisms underlying neuropathic pain have yet to be elucidated. The present study aimed to examine the modulation of neuroimmune activation in the spinal cord by the synthetic peroxisome proliferator-activated receptor gamma (PPAR-γ) agonist, pioglitazone (Pio), in a rat model of neuropathic pain induced by chronic constriction injury (CCI). Rats were randomly assigned into four groups: Sham surgery with vehicle, chronic constriction injury with vehicle or Pio (10 mg/kg), and chronic constriction injury with Pio and a PPAR-γ antagonist GW9662 (2 mg/kg). Pio or vehicle was administered 1 h prior to the surgery and continued daily until day 7 post-surgery. Paw pressure threshold was measured prior to surgery and on days 0, 1, 3 and 7 post-surgery. Microglia activation markers macrophage antigen complex-1, the mRNA expression levels of tumor necrosis factor α and interleukin-1β, and the mRNA expression levels of toll like receptor (TLR-4) in the lumbar spinal cord were determined. Administration of Pio resulted in the prominent attenuation of mechanical hyperalgesia. In addition, Pio was able to significantly inhibit neuroimmune activation characterized by glial activation, the production of cytokines and expression levels of TLR-4. Concurrent administration of a PPAR-γ antagonist, GW9662, reversed the effects of Pio. The antihyperalgesic effect of administration of Pio in rats receiving CCI may, in part, be attributed to the inhibition of neuroimmune activation associated with the sustaining of neuropathic pain.

Transcriptional expression of inflammatory mediators in various somatosensory relay centers in the brain of rat models of peripheral mononeuropathy and local inflammation

Contradictory results have been reported regarding the role of inflammatory mediators in the central nervous system in mediating neuropathic pain and inflammatory hyperalgesia following peripheral nerve injury or localized inflammation. The present study aims to correlate between the mRNA expression and protein secretion of proinflammatory cytokines and nerve growth factor (NGF), in the dorsal root ganglia (DRGs), spinal cord, brainstem and thalamus, and pain-related behavior in animal models of peripheral mononeuropathy and localized inflammation. Different groups of rats (n=8, each) were subjected to either lesion of the nerves of their hindpaws to induce mononeuropathy or intraplantar injection of endotoxin (ET) and were sacrificed at various time intervals. TNF-α, IL-1β and NGF mRNA expression and protein levels in the various centers involved in processing nociceptive information were determined, by RT-PCR and ELISA. Control groups were either subjected to sham surgery or to saline injection. Mononeuropathy and ET injection produced significant and sustained increases in the mRNA expression and protein levels of TNF-α, IL-1β and NGF in the ipsilateral and contralateral DRGs, spinal cord, and brainstem. No significant and consistent changes in the mRNA expression of cytokines were noticed in the thalamus, while a downregulation of the NGF-mRNA level was observed. The temporal and spatial patterns of the observed changes in mRNA expression of cytokines and NGF are not closely in phase with the observed allodynia and hyperalgesia in the different models, suggesting that the role of these mediators may not be reduced exclusively to the production and maintenance of pain.

IL-10 and IL-1β mediate neuropathic-pain like behavior in the ventrolateral orbital cortex

Previous evidence has shown that the glial cells can be activated by peripheral nerve injury and release both pro-inflammatory and anti-inflammatory cytokines, which play crucial roles in the establishment and maintenance of neuropathic pain. The present study examined the roles of anti-inflammatory cytokine IL-10 and pro-inflammatory IL-1β on allodynia induced by spared nerve injury (SNI) in the ventrolateral orbital cortex (VLO) in the rat. The mechanical paw withdrawal threshold (PWT) was measured using von-Frey filaments. Microinjection of IL-10 (0.1, 0.5, 1 μg/0.5 μl) into the VLO, contralateral to the site of nerve injury attenuated allodynia; PWT increased in a dose-dependent manner. Similar to IL-10, administration of rabbit anti-rat IL-1β antibody (0.1, 1.0 and 10 ng/0.5 μl) into the same VLO site also alleviated allodynia with a dose-dependent fashion. Moreover, western blotting results showed expression levels of IL-10 and IL-1β significantly up-regulated in the contralateral VLO of SNI rats as compared with that of sham-operated rats. These results suggest that anti-inflammatory cytokine IL-10 and pro-inflammatory cytokine IL-1β mediate neuropathic-pain like behavior at the cerebral cortex level; IL-10 released from activated glial cells in the VLO can potentially attenuate allodynia while IL-1β released from activated glial cells in the VLO can potentially maintain or facilitate allodynia. These results provide new insights and site for therapy at the cerebral cortex level in neuropathic pain condition.

The foreign body response to the Utah Slant Electrode Array in the cat sciatic nerve

As the field of neuroprosthetic research continues to grow, studies describing the foreign body reaction surrounding chronic indwelling electrodes or microelectrode arrays will be critical for assessing biocompatibility. Of particular importance is the reaction surrounding penetrating microelectrodes that are used to stimulate and record from peripheral nerves used for prosthetic control, where such studies on axially penetrating electrodes are limited. Using the Utah Slant Electrode Array and a variety of histological methods, we investigated the foreign body response to the implanted array and its surrounding silicone cuff over long indwelling periods in the cat sciatic nerve. We observed that implanted nerves were associated with increased numbers of activated macrophages at the implant site, as well as distal to the implant, at all time points examined, with the longest observation being 350 days after implantation. We found that implanted cat sciatic nerves undergo a compensatory regenerative response after the initial injury that is accompanied by shifts in nerve fiber composition toward nerve fibers of smaller diameter and evidence of axons growing around microelectrode shafts. Nerve fibers located in fascicles that were not penetrated by the array or were located more than a few hundred microns from the implant appeared normal when examined over the course of a year-long indwelling period.

Signaling mechanisms in mirror image pain pathogenesis

It is now clear that a peripheral nerve lesion affects contralateral non-lesioned structures, and thus such a lesion can result in mirror image pain. The pathogenesis is still not exactly known, but there are some possible signaling pathways in the contralateral reaction of the nerve tissue after unilateral nerve injury. Potential signaling pathways of contralateral changes can be generally divided into humoral and neuronal mechanisms. Damage to peripheral nerves or spinal roots produces a number of breakdown products with development of an aseptic inflammatory reaction. Released immunomodulatory cytokines are believed to be transported via blood or cerebrospinal fluid into the contralateral part of the body affecting spinal roots, dorsal root ganglia or peripheral nerves. Because neurons are elements of a highly organized network, injury to the peripheral neuron results in signals that travel transneuronally into the central nervous system and affects the contralateral homonymous neurons. There is also evidence that spinal glia creates and maintain pathological pain. Additionally, there may be compensatory changes in behavior of animals with an impact on contralateral neurons, such as altered stance and motor performance or autonomic reflex changes. Although the transneuronal signaling pathway appears to be plausible, the humoral signaling pathway or other communication systems cannot be excluded at this time. Knowledge about these processes has clinical implications for the understanding of chronic neuropathic pain states, and, therefore, further studies will be necessary. Understanding signaling mechanisms in mirror image pain pathogenesis may provide novel therapeutic targets for the management of neuropathic pain.

Effects of early intraoral acesulfame-K stimulation to mice on the adult's sweet preference and the expression of α-gustducin in fungiform papilla

Exposure to artificial sweetener acesulfame-K (AK) at early development stages may influence the adult sweet preference and the periphery gustatory system. We observed that the intraoral AK stimulation to mice from postnatal day 4 (P4) to weaning decreased the preference thresholds for AK and sucrose solutions in adulthood, with the preference pattern unchanged. The preference scores were increased in the exposure group significantly when compared with the control group at a range of concentrations for AK or sucrose solution. Meanwhile, more α-Gustducin-labeled fungiform taste buds and cells in a single taste bud were induced from week 7 by the early intraoral AK stimulation. However, the growth in the number of α-Gustducin-positive taste bud or positive cell number per taste bud occurred only in the anterior region, the rostral 1-mm part, but not in the intermediate region, the caudal 4-mm part, of the anterior two-third of the tongue containing fungiform papillae. This work extends our previous observations and provides new information about the developmental and regional expression pattern of α-Gustducin in mouse fungiform taste bud under early AK-stimulated conditions.

Interleukin-10 down-regulates voltage gated sodium channels in rat dorsal root ganglion neurons

The over-expression of voltage-gated sodium channels (VGSCs) in dorsal root ganglion (DRG) neurons following peripheral nerve injury contributes to neuropathic pain by generation of the ectopic discharges of action potentials. However, mechanisms underlying the change in VGSCs' expression are poorly understood. Our previous work has demonstrated that the pro-inflammatory cytokine TNF-α up-regulates VGSCs. In the present work we tested if anti-inflammatory cytokine IL-10, which had been proven to be effective for treating neuropathic pain, had the opposite effect. Western blot and immunofluorescence results showed that IL-10 receptor was localized in DRG neurons. Recombinant rat IL-10 (200 pg/ml) not only reduced the densities of TTX-sensitive and Nav1.8 currents in control DRG neurons, but also reversed the increase of the sodium currents induced by rat recombinant TNF-α (100 pg/ml), as revealed by patch-clamp recordings. Consistent with the electrophysiological results, real-time PCR and western blot revealed that IL-10 (200 pg/ml) down-regulated VGSCs in both mRNA and protein levels and reversed the up-regulation of VGSCs by TNF-α. Moreover, repetitive intrathecal administration of rrIL-10 for 3 days (4 times per day) attenuated mechanical allodynia in L5 spinal nerve ligation model and profoundly inhibited the excitability of DRG neurons. These results suggested that the down-regulation of the sodium channels in DRG neurons might contribute to the therapeutic effect of IL-10 on neuropathic pain.

Chronic neuropathic pain-like behavior and brain-borne IL-1β

Neuropathic pain in animals results in increased IL-1β expression in the damaged nerve, the dorsal root ganglia, and the spinal cord. Here, we discuss our results showing that this cytokine is also overexpressed at supraspinal brain regions, in particular in the contralateral side of the hippocampus and prefrontal cortex and in the brainstem, in rats with neuropathic pain-like behavior. We show that neuropathic pain degree and development depend on the specific nerve injury model and rat strain studied, and that there is a correlation between hippocampal IL-1β expression and tactile sensitivity. Furthermore, the correlations between hippocampal IL-1β and IL-1ra or IL-6 observed in control animals, are disrupted in rats with increased pain sensitivity. The lateralization of increased cytokine expression indicates that this alteration may reflect nociception. The potential functional consequences of increased IL-1β expression in the brain during neuropathic pain are discussed.

Spinal interleukin-10 therapy to treat peripheral neuropathic pain

INTRODUCTION

  Current research indicates that chronic peripheral neuropathic pain includes a role for glia and the actions of proinflammatory factors. This review briefly discusses the glial and cytokine responses that occur following peripheral nerve damage in support of utilizing anti-inflammatory cytokine interleukin-10 (IL-10) therapy to suppress chronic peripheral neuropathic pain. SPINAL NONVIRAL INTERLEUKIN-10 GENE THERAPY:  IL-10 is one of the most powerful endogenous counter-regulators of proinflammatory cytokine function that acts in the nervous system. Subarachnoid (intrathecal) spinal injection of the gene encoding IL-10 delivered by nonviral vectors has several advantages over virally mediated gene transfer methods and leads to profound pain relief in several animal models. NONVIRAL GENE DELIVERY:  Lastly, data are reviewed that nonviral deoxyribonucleic acid (DNA) encapsulated by a biologically safe copolymer, poly(lactic-co-glycolic) acid (PLGA), thought to protect DNA, leads to significantly improved therapeutic gene transfer in animal models, which additionally and significantly extends pain relief.

CONCLUSIONS

  The impact of these early studies exploring anti-inflammatory genes emphasizes the exceptional therapeutic potential of new biocompatible intrathecal nonviral gene delivery approaches such as PLGA microparticles. Ultimately, ongoing expression of therapeutic genes is a viable option to treat chronic neuropathic pain in the clinic.

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

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

Functional role for interleukin-1 in the injured peripheral taste system

The peripheral taste system presents an excellent model for studying the consequences of neural injury, for the damaged nerve and sensory cells and the neighboring, intact neural cells. Sectioning a primary afferent nerve, the chorda tympani (CT), rapidly recruits neutrophils to both sides of the tongue. The bilateral neutrophil response induces transient functional deficits in the intact CT. Normal function is subsequently restored as macrophages respond to injury. We hypothesized that macrophages produce the proinflammatory cytokine interleukin (IL)-1, which contributes to the maintenance of normal taste function after nearby injury. We demonstrate that IL-1β protein levels are significantly increased on the injured side of the tongue at day 2 after injury. Dietary sodium deficiency, a manipulation that prevents macrophage recruitment, inhibits the elevation in IL-1β. IL-1β was expressed in several cell populations, including taste receptor cells and infiltrating neutrophils and macrophages. To test whether IL-1 modulates taste function after injury, we blocked signaling with an IL-1 receptor antagonist (IL-1 RA) and recorded taste responses from the intact CT. This treatment inhibited the bilateral macrophage response to injury and impaired taste responses in the intact CT. Cytokine actions in the taste system are largely unstudied. These results demonstrate that IL-1 has a beneficial effect on taste function after nearby injury, in contrast to its detrimental role in the injured central nervous system.

Effects of clonidine on bilateral pain behaviors and inflammatory response in rats under the state of neuropathic pain

This study was conducted to investigate the effects of clonidine on bilateral pain behaviors and inflammatory responses in neuropathic pain induced by partial sciatic nerve ligation (PSNL), and to better understand whether the antinociception of clonidine was related to α(2)-adrenoceptor mechanisms. Rats were divided randomly into five groups: sham-operation with saline, i.p.; PSNL with clonidine (0.2mg/kg) or saline, i.p.; PSNL with yohimbine (2mg/kg) followed by clonidine (0.2mg/kg), i.p.; and PSNL with naloxone (0.3mg/kg) followed by clonidine (0.2mg/kg), i.p. On post-operative days 1, 3, 7, 14, and 21, both ipsilateral and contralateral pain behaviors were measured. In rats receiving antagonists, bilateral behavioral changes were measured on day 14. Bilateral paw pressure threshold and paw withdrawal latencies were measured, and the extent of glial activation was dertermined by measuring macrophage antigen complex-1 (Mac-1) and glial fibrillary acidic protein (GFAP). Additionally, the levels of tumor necrosis factor α (TNF-α) and interleukin (IL)-6 were determined. PSNL induced bilateral behavioral hyperalgesia, with the ipsilateral level displaying a higher extent of behavior changes than the contralateral side. In addition, the glial activation markers and cytokine production were augmented bilaterally. Clonidine caused significant attenuation of bilateral mechanical allodynia and thermal hyperalgesia, accompanied by inhibition of glial activation and the expression of cytokines. The effects of clonidine were blocked by the α(2)-adrenoceptor antagonist yohimbine and partially reversed by the μ-opioid receptor antagonist naloxone. These data suggest that the bilateral antinoceptive effects of clonidine might mediate through immunomodulation by acting on α(2)-adrenoceptor in rats undergoing neuropathic pain.

Bilateral changes of IL-10 protein in lumbar and cervical dorsal root ganglia following proximal and distal chronic constriction injury of peripheral nerve

Interleukin-10 prevents transition of a physiological inflammatory reaction to a pathological state that may result in neuropathic pain. We studied bilateral changes of IL-10 protein levels in L4-L5 and C7-C8 dorsal root ganglia (DRG) after a chronic constriction injury (CCI) of either L4-L5 spinal nerves (pCCI) or the sciatic nerve (dCCI). Rats undergoing pCCI or dCCI were left to survive for 1, 3, 7 or 14 d, sham-operated rats for 3 or 14 d. After the survival time, C7-C8 and L4-L5 DRG were removed bilaterally from naïve, operated, and sham-operated rats and IL-10 protein was detected by immunohistochemical staining and measured using ELISA analysis. Unilateral pCCI and dCCI induced a transient bilateral elevation in IL-10 protein level not only in the homonymous lumbar DRG but also in the heteronymous cervical DRG nonassociated with the spinal segments of constricted nerve. Sham operations also induced bilateral elevation of IL-10 protein in both homonymous and heteronymous DRG. Our experiments revealed that the more proximal is a nerve injury the more rapid is the initial increase and slower the subsequent decrease of IL-10 protein level in DRG. Changes of IL-10 protein in DRG nonassociated with damaged nerve could be related to a general neuroinflammatory reaction of the nervous system to injury and thereby promote potential of the DRG neurons for regenerating their axons following a conditioning lesion.

The reinnervation and revascularization of wounds is temporarily altered after treatment with interleukin 10

Denervated wounds fail to heal normally, and hypertrophic scars are abnormally innervated. Wounds can be manipulated with cytokines to reduce subsequent scarring. Wounds treated with the antiscarring cytokine interleukin 10 (IL10) were investigated to assess if the treatment alterered patterns of reinnervation and revascularization as the wounds matured into scars. Thirty CD1 mice underwent intradermal injection of 100 μL phosphate-buffered saline (PBS) containing 125 ng IL10 or placebo at the margins of 1 cm(2) full thickness dorsal skin excisions at the time of wounding and at 24 hours after wounding. Wounds were not dressed. Six IL10-treated and six control were harvested days 7, 14, 21, 42 and 84 postoperatively. Sections underwent histological scar assessment along with immunohistochemical staining for protein gene product 9.5 (PGP9.5), a pan-neuronal marker, and the sensory neuropeptides calcitonin gene related peptide (CGRP) and substance P (SP). The endothelial marker von Willebrand factor (VWF) was used to allow co-localization and quantification of blood vessels. Quantitative analysis was performed on the periphery and center of wounds. Wounds treated with IL10 healed with dermal collagen organized into a pattern more closely resembling normal skin than control wounds. IL10 changed the pattern of CGRP reinnervation during the healing process, but at 84 days, the density levels of all nerve fiber types were similar to controls. Wounds treated with IL10 were more vascular than untreated wounds during healing, but by 84 days, VWF density was that of unwounded skin.

Inflammatory cytokine and chemokine expression is differentially modulated acutely in the dorsal root ganglion in response to different nerve root compressions

STUDY DESIGN

Inflammatory proteins were quantified in bilateral dorsal root ganglions (DRGs) at 1 hour and 1 day using a multiplexed assay after 2 different unilateral nerve root compression injuries.

OBJECTIVE

To quantify cytokines and a chemokine in the DRG after nerve root compression with and without a chemical injury to determine contributing inflammatory factors in the DRG that may mediate radicular nociception in clinically relevant nerve root pathologies.

SUMMARY OF BACKGROUND DATA

Inflammatory cytokines are known to relate to the behavioral hypersensitivity induced after injuries to the nerve root. However, the relative expression of these proteins in the DRG after cervical nerve root compression are not known.

METHODS

The right C7 nerve root underwent transient compression (10 gf) or transient compression with a chemical irritation (10 gf + chr). The chemical injury was also given alone (chr), and the nerve root was exposed (sham), providing 2 types of controls. Mechanical allodynia was measured to assess behavioral outcomes. Interleukin (IL)-1b, IL-6, tumor necrosis factor-a, and macrophage inflammatory protein 3 (MIP3) were quantified in bilateral DRGs at 1 hour and 1 day using a multiplexed assay.

RESULTS

Ipsilateral allodynia at day 1 after 10 gf + chr was significantly increased over both 10 gf and chr (P < 0.049). Cytokines and MIP3 were not statistically increased over sham at 1 hour. By day 1 after 10 gf + chr, all proteins (IL-1β, IL-6, tumor necrosis factor-a, MIP3) were significantly increased over both normal and sham in the ipsilateral DRG (P < 0.036), and the cytokines were also significantly increased over chr (P < 0.029). Despite allodynia at day 1, cytokines at that time were not increased over normal or sham after either 10 gf or chr.

CONCLUSION

Nerve root compression alone may not be sufficient to induce early increases in proinflammatory cytokines in the DRG after radiculopathy and this early protein response may not be directly responsible for nociception in this type of injury.

Bilateral changes of TNF-alpha and IL-10 protein in the lumbar and cervical dorsal root ganglia following a unilateral chronic constriction injury of the sciatic nerve

Background

There is a growing body of evidence that unilateral nerve injury induces bilateral response, the mechanism of which is not exactly known. Because cytokines act as crucial signaling molecules for response of peripheral nerves to injury, they may be induced to mediate the reaction in remote structures.

Methods

We studied levels of tumor necrosis factor α (TNF-α) and interleukin 10 (IL-10) proteins using ELISA in the ipsilateral and contralateral lumbar (L4-L5) and cervical (C7-C8) dorsal root ganglia (DRG) from naïve rats, rats operated on to create unilateral chronic constriction injury (CCI) of the sciatic nerve, and sham-operated rats. Withdrawal thresholds for mechanical allodynia and thermal hyperalgesia were measured in the ipsilateral and contralateral hind and forepaws.

Results

The ipsilateral hind paws of all rats operated upon for CCI displayed decreased withdrawal thresholds for mechanical allodynia and thermal hyperalgesia, while no significant behavioral changes were found in the contralateral hind paws and both forepaws. Significantly lower baseline levels of TNF-α and IL-10 protein were measured by ELISA in the lumbar than cervical DRG of naïve rats. Bilateral elevation of TNF-α was induced in both the lumbar and cervical DRG by unilateral CCI of the sciatic nerve for 7 and 14 days, while the level of IL-10 protein was increased bilaterally in the lumbar DRG 1 and 3 days after operation. IL-10 levels declined bilaterally even below baseline level in both cervical and lumbar DRG 7 days from CCI and normalized after 14 days. In contrast to no significant changes in TNF-α, level of IL-10 protein was significantly increased in the ipsilateral lumbar DRG after 3 days and bilaterally in the lumbar DRG after 14 days from sham operation.

Conclusions

The results of our experiments show a bilateral elevation of TNF-α and IL-10 not only in the homonymous DRG but also in the heteronymous DRG unassociated with the injured nerve. This suggests that bilaterally increased levels of TNF-α and IL-10 in DRG following unilateral CCI are linked with general neuroinflammatory reaction of the nervous system to injury rather than only to development and maintenance of neuropathic pain.

[Cytokine regulation and pain. Results of experimental and clinical research]

Cytokines are soluble peptides and proteins that are predominantly produced and secreted by immune cells. In numerous animal experiments the endogenous increase or application of exogenous pro-inflammatory cytokines is associated with pain behavior. In turn, cytokine inhibitors reduce such pain behavior in inflammatory and neuropathic pain models. Several clinical studies point out that cytokines are also important in different human pain states. Several chronic pain syndromes are associated with systemic pro-inflammatory cytokine profiles. In some pain syndromes these pro-inflammatory profiles are accompanied by a lack of analgesic anti-inflammatory cytokines. Numerous case reports and open clinical studies, but also some controlled trials show successful analgesic treatment using cytokine inhibitors. The following review article summarizes the main data of animal experiments and clinical trials concerning the role of cytokines in pain and the potential importance of cytokine modulation in pain treatment.

Cytokine mRNA expression in painful radiculopathy

Inflammatory cytokines contribute to lumbar radiculopathy. Regulation of cytokines for transient cervical injuries, with or without longer-lasting inflammation, remains to be defined. The C7 root in the rat underwent compression (10gf), chromic gut suture exposure (chr), or their combination (10gf+chr). Ipsilateral C7 spinal cord and dorsal root ganglia (DRG) were harvested at 1 hour after injury for real-time PCR analysis of IL-1beta, IL-6, and TNF-alpha. Cytokine mRNA increased after all 3 injuries. TNF-alpha mRNA in the DRG was significantly increased over sham after 10gf+chr (P = .026). Spinal IL-1beta was significantly increased over sham after 10gf and 10gf+chr (P < .024); IL-6 was significantly increased after 10gf+chr (P < .024). In separate studies, the soluble TNF-alpha receptor was administered at injury and again at 6 hours in all injury paradigms. Allodynia was assessed and tissue samples were harvested for cytokine PCR. Allodynia significantly decreased with receptor administration for 10gf and 10gf+chr (P < .005). Treatment also significantly decreased IL-1beta and TNF-alpha mRNA in the DRG for 10gf+chr (P < .028) at day 1. Results indicate an acute, robust cytokine response in cervical nerve root injury with varying patterns, dependent on injury type, and that early increases in TNF-alpha mRNA in the DRG may drive pain-related signaling for transient cervical injuries.

PERSPECTIVE

Inflammatory cytokine mRNA in the DRG and spinal cord are defined after painful cervical nerve root injury. Studies describe a role for TNF-alpha in mediating behavioral sensitivity and inflammatory cytokines in transient painful radiculopathy. Results outline an early response of inflammatory cytokine upregulation in cervical pain.

Glial elements contribute to stress-induced torsinA expression in the CNS and peripheral nervous system

DYT1 dystonia is caused by a single GAG deletion in exon 5 of TOR1A, the gene encoding torsinA, a putative chaperone protein. In this study, central and peripheral nervous system perturbations (transient forebrain ischemia and sciatic nerve transection, respectively) were used to examine the systems biology of torsinA in rats. After forebrain ischemia, quantitative real-time reverse transcriptase-polymerase chain reaction identified increased torsinA transcript levels in hippocampus, cerebral cortex, thalamus, striatum, and cerebellum at 24 h and 7 days. Expression declined toward sham values by 14 days in striatum, thalamus and cortex, and by 21 days in cerebellum and hippocampus. TorsinA transcripts were localized to dentate granule cells and pyramidal neurons in control hippocampus and were moderately elevated in these cell populations at 24 h after ischemia, after which CA1 expression was reduced, consistent with the loss of this vulnerable neuronal population. Increased in situ hybridization signal in CA1 stratum radiatum, stratum lacunosum-moleculare, and stratum oriens at 7 days after ischemia was correlated with the detection of torsinA immunoreactivity in interneurons and reactive astrocytes at 7 and 14 days. Sciatic nerve transection increased torsinA transcript levels between 24 h and 7 days in both ipsilateral and contralateral dorsal root ganglia (DRG). However, increased torsinA immunoreactivity was localized to both ganglion cells and satellite cells in ipsilateral DRG but was restricted to satellite cells contralaterally. These results suggest that torsinA participates in the response of neural tissue to central and peripheral insults and its sustained up-regulation indicates that torsinA may contribute to remodeling of neuronal circuitry. The striking induction of torsinA in astrocytes and satellite cells points to the potential involvement of glial elements in the pathobiology of DYT1 dystonia.

Early cytokine expression in mouse sciatic nerve after chronic constriction nerve injury depends on calpain

Nerve injury initiates Wallerian degeneration with subsequent alterations of cytokine expression contributing to neuropathic pain. To investigate the very early temporal pattern of cytokine regulation we studied 140 mice of C57Bl/6J background after chronic constriction injury (CCI) of the right sciatic nerve and measured the relative mRNA expression of the pro-inflammatory cytokines tumor necrosis factor-alpha (TNF) and interleukin-1beta (IL-1beta) and of the anti-inflammatory cytokines IL-4 and IL-10 with quantitative real-time polymerase chain reaction (qRT-PCR). The measurements were performed in ipsi- and contralateral sciatic nerves and dorsal root ganglia (DRG) 1, 3, 6, 9, 12, 24 h, and 3 and 7 days after CCI. We found an ipsilateral upregulation of TNF, IL-1beta and IL-10 mRNA levels as early as one hour after CCI. To investigate upstream regulatory mechanisms, we used inhibitors to the N-methyl-d-aspartate (NMDA) receptor ((+)-MK-801) and to calpain (MDL-28170). MDL-28170, but not (+)-MK-801 inhibited TNF and IL-1beta upregulation one hour after CCI. This leads us to suggest that calpain is one of the earliest mediators of cytokine upregulation in injured peripheral nerves.

Expression of IL-1beta in supraspinal brain regions in rats with neuropathic pain

We examined mRNA expression of the pro-inflammatory cytokine IL-1beta in the brainstem, thalamus, and prefrontal cortex in two rat models of neuropathic pain. Rats received a neuropathic injury: spared nerve injury (SNI) or chronic constriction injury (CCI), sham injury, or were minimally handled (control). Neuropathic pain-like behavior was monitored by tracking tactile thresholds. SNI-injured animals showed a robust decrease in tactile thresholds of the injured foot, while CCI-injured animals did not show tactile threshold changes. Ten or 24 days after nerve injury, IL-1beta gene expression in the brain was determined by RT-PCR. IL-1beta expression changes were observed mainly at 10 days after injury in the SNI animals, contralateral to the injury side, with increased expression in the brainstem and prefrontal cortex. The results indicate that neuro-immune activation in neuropathic pain conditions includes supraspinal brain regions, suggesting cytokine modulation of supraspinal circuitry of pain in neuropathic conditions.

Intra- and Extraneuronal Changes of Immunofluorescence Staining for TNF- and TNFR1 in the Dorsal Root Ganglia of Rat Peripheral Neuropathic Pain Models

1. Several lines of evidence suggest that cytokines and their receptors are initiators of changes in the activity of dorsal root ganglia (DRG) neurons, but their cellular distribution is still very limited or controversial. Therefore, the goal of present study was to investigate immunohistochemical distribution of TNF-alpha and TNF receptor-1 (TNFR1) proteins in the rat DRG following three types of nerve injury. 2. The unilateral sciatic and spinal nerve ligation as well as the sciatic nerve transection were used to induce changes in the distribution of TNF-alpha and TNFR1 proteins. The TNF-alpha and TNFR1 immunofluorescence was assessed in the L4-L5 DRG affected by nerve injury for 1 and 2 weeks, and compared with the contralateral ones and those removed from naive or sham-operated rats. A part of the sections was incubated for simultaneous immunostaining for TNF-alpha and ED-1. The immunofluorescence brightness was measured by image analysis system (LUCIA-G v4.21) to quantify immunostaining for TNF-alpha and TNFR1 in the naive, ipsi- and contralateral DRG following nerve injury. 3. The ipsilateral L4-L5 DRG and their contralateral counterparts of the rats operated for nerve injury displayed an increased immunofluorescence (IF) for TNF-alpha and TNFR1 when compared with DRG harvested from naive or sham-operated rats. The TNFalpha IF was increased bilaterally in the satellite glial cells (SGC) and contralaterally in the neuronal nuclei following sciatic and spinal nerve ligature. The neuronal bodies and their SGC exhibited bilaterally enhanced IF for TNF-alpha after sciatic nerve transection for 1 and 2 weeks. In addition, the affected DRG were invaded by ED-1 positive macrophages which displayed simultaneously TNFalpha IF. The ED-1 positive macrophages were frequently located near the neuronal bodies to occupy a position of the satellites. 4. The sciatic and spinal nerve ligature resulted in an increased TNFR1 IF in the neuronal bodies of both ipsi- and contralateral DRG. The sciatic nerve ligature for 1 week induced a rise in TNFR1 IF in the contralateral DRG neurons and their SGC to a higher level than in the ipsilateral ones. In contrast, the sciatic nerve ligature for 2 weeks caused a similar increase of TNFR1 IF in the neurons and their SGC of both ipsi- and contralateral DRG. The spinal nerve ligature or sciatic nerve transection resulted in an increased TNFR1 IF located at the surface of the ipsilateral DRG neurons, but dispersed IF in the contralateral ones. In addition, the SGC of the contralateral in contrast to ipsilateral DRG displayed a higher TNFR1 IF. 5. Our results suggest more sources of TNF-alpha protein in the ipsilateral and contralateral DRG following unilateral nerve injury including macrophages, SGC and primary sensory neurons. In addition, the SGC and macrophages, which became to be satellites, are well positioned to regulate activity of the DRG neurons by production of TNF-alpha molecules. Moreover, the different cellular distribution of TNFR1 in the ipsi- and contralateral DRG may reflect different pathways by which TNF-alpha effect on the primary sensory neurons can be mediated following nerve injury.

Cytokine responses during chronic denervation

Background

The aim of the present study was to examine inflammatory responses during Wallerian degeneration in rat peripheral nerve when the regrowth of axons was prevented by suturing.

Methods

Transected rat sciatic nerve was sutured and ligated to prevent reinnervation. The samples were collected from the left sciatic nerve distally and proximally from the point of transection. The endoneurium was separated from the surrounding epi- and perineurium to examine the expression of cytokines in both of these compartments. Macrophage invasion into endoneurium was investigated and Schwann cell proliferation was followed as well as the expression of cytokines IL-1β, IL-10, IFN-γ and TNF-α mRNA. The samples were collected from 1 day up to 5 weeks after the primary operation.

Results

At days 1 to 3 after injury in the epi-/perineurium of the proximal and distal stump, a marked expression of the pro-inflammatory cytokines TNF-α and IL-1β and of the anti-inflammatory cytokine IL-10 was observed. Concurrently, numerous macrophages started to gather into the epineurium of both proximal and distal stumps. At day 7 the number of macrophages decreased in the perineurium and increased markedly in the endoneurium of both stumps. At this time point marked expression of TNF-α and IFN-γ mRNA was observed in the endo- and epi-/perineurium of the proximal stump. At day 14 a marked increase in the expression of IL-1β could be noted in the proximal stump epi-/perineurium and in the distal stump endoneurium. At that time point many macrophages were observed in the longitudinally sectioned epineurium of the proximal 2 area as well as in the cross-section slides from the distal stump. At day 35 TNF-α, IL-1β and IL-10 mRNA appeared abundantly in the proximal epi-/perineurium together with macrophages.

Conclusion

The present studies show that even during chronic denervation there is a cyclic expression pattern for the studied cytokines. Contrary to the previous findings on reinnervating nerves the studied cytokines show increased expression up to 35 days. The high expressions of pro-inflammatory and anti-inflammatory cytokines in the proximal epi-/perineurial area at day 35 may be involved in the formation of fibrosis due to irreversible nerve injury and thus may have relevance to the formation of traumatic neuroma.

Induction of tumor necrosis factor-alpha in Schwann cells after gradual elongation of rat sciatic nerve

BACKGROUND

Although limb lengthening has become a common treatment, the biochemical responses underlying the adaptation of elongated nerves are unclear. The purpose of this study was to clarify whether expression of cytokines and neurotrophins is altered in gradually elongated peripheral nerves.

METHODS

Left sciatic nerves of adult rats were elongated by lengthening the femur up to 20 mm at a rate of 1, 2, or 20 mm/day. The ipsilateral and contralateral sciatic nerves of each group were resected 1, 4, 8, and 16 days after 20 mm of lengthening. mRNAs for interleukin-1beta, interleukin-6, tumor necrosis factor-alpha (TNFalpha), nerve growth factor, brain-derived neurotrophic factor, neurotrophin-3, and neurotrophin-4/5 were semiquantified by reverse transcription-polymerase chain reaction. Histological changes were assessed by immunoperoxidase and immunofluorescence staining.

RESULTS

Expression of TNFalpha mRNA was markedly induced in the ipsilateral sciatic nerves of the gradually elongated, 1 mm/day and 2 mm/day groups, although to a lesser extent than in the acutely elongated, 20 mm/day group. In contrast, mRNAs for other factors remained undetectable. The mRNA level for TNFalpha in each group was highest 1 day after 20 mm of lengthening. The highly up-regulated level in the acute group declined rapidly within 4 days and slowly thereafter; in contrast, the decrease in the gradual groups was always slow. Even 16 days later, the levels in all groups remained significantly elevated. Unexpectedly, TNFalpha mRNA expression was also induced in the contralateral side of all groups. Immunohistochemical staining showed that TNFalpha-immunoreactive cells in gradually elongated nerves were also positive for S-100 protein but negative for proliferating nuclear cell antigen, indicating that TNFalpha was produced by nonproliferating Schwann cells.

CONCLUSIONS

Gradual nerve elongation by limb lengthening induces production of TNFalpha in Schwann cells. Presumably, TNFalpha plays a critical role in the adaptation of peripheral nerves to elongation.

Induction of interleukin-6 in dorsal root ganglion neurons after gradual elongation of rat sciatic nerve

In the reconstruction of a segmental defect in injured peripheral nerves, gradual nerve elongation has become an important alternative to nerve grafting. To clarify biochemical responses in peripheral sensory neurons after nerve elongation, we examined the expression of cytokines and neurotrophins related to nerve regeneration. We first established rat elongation models by lengthening left femurs up to 20.0 mm at the rate of 1.0, 2.0, or 20.0 mm/day. In toluidine blue staining, the acutely elongated, 20-mm/day group showed nuclear eccentricity in the nerve cell body in L5 dorsal root ganglion (DRG) and axonal degeneration in the sciatic nerves; in contrast, the gradually elongated, 1- and 2-mm/day groups remained intact, indicating adaptation. Reverse transcription-polymerase chain reaction analysis revealed that interleukin-6 (IL-6) mRNA was induced in ipsilateral L4-6 DRG in an elongation rate-dependent manner. In contrast, none of the elongated groups exhibited a significant change in mRNA levels for interleukin-1beta, tumor necrosis factor-alpha, nerve growth factor, brain-derived neurotrophic factor, neurotropnin-3, and neurotrophin-4/5. Levels of IL-6 mRNA in all the elongated groups reached the maximum level at day 4 after 20-mm lengthening, while the axotomized group showed a decrease from the maximum level at day 1. Induction of IL-6 mRNA was also detected in the contralateral L4-6 DRG of all the elongated groups, but not detected in the axotomized group. In histochemical analysis, IL-6-immunoreactivity was predominant in neurofilament-positive, medium to large DRG neurons. Application of IL-6 to cultured Schwann cells increased mRNA for peripheral myelin protein 22 (PMP22), a major myelin component. These results suggest that IL-6 plays a key role in biochemical responses in peripheral sensory neurons after gradual nerve elongation.

Contralateral cytokine gene induction after peripheral nerve lesions: dependence on the mode of injury and NMDA receptor signaling

There is increasing evidence that unilateral nerve injury evokes contralateral responses, but the underlying mechanisms are largely unknown. In the present investigation, we analyzed cytokine and chemokine gene induction in contralateral, non-lesioned nerves after sciatic nerve crush and chronic constriction injury (CCI) by quantitative reverse transcriptase polymerase chain reaction in mice. After sciatic nerve crush, contralateral changes in cytokine gene expression were restricted to interleukin (IL)-1beta, which showed a monophasic peak at the first postoperative day. Following CCI, contralateral transcripts for IL-1beta, IL-10 and monocyte chemoattractant protein-1 (MCP-1) were significantly increased already at day 1 and upregulation persisted over the next 4 weeks. In contrast, tumor necrosis factor alpha (TNF-alpha) levels remained unchanged. Contralateral gene induction was restricted to the homonymous opposite sciatic nerve, but spared the femoral nerve. NMDA receptor blockade completely abolished contralateral cytokine expression after CCI on the mRNA level. In contralateral dorsal root ganglia, only IL-10 mRNA levels were modified after nerve injury. Sham operation significantly increased the cytokine and chemokine gene expression at the ipsilateral side, but could not mediate contralateral effects. Our study confirms that nerve injury evokes contralateral responses and identifies NMDA-mediated signaling as one underlying mechanism.

Objective evaluation of iatrogenic lingual nerve injuries using the jaw-opening reflex

The extent of reflex inhibition of masseteric electromyographic activity, after an electrical stimulus applied to lingual mucosa, was used as a test of the ability of the lingual nerve to conduct nerve impulses and this was compared with the results of standard clinical tests. Two groups of subjects were assessed: healthy subjects (n=10) and patients with lingual nerve injuries (n=17). The patients were tested 8-9 weeks after their injury and retested 6 months later when they were retrospectively allocated to either a temporary injury or a permanent injury group. The group measure of reflex inhibition after stimulation of the tongue on the opposite side to the injury was no different from the same measure in controls, whereas two-point discrimination did differ. Group measures of inhibition and of subjective function after stimulation on the side of the injury were significantly different from controls whereas light touch and two-point discrimination were not. There was good agreement between quantified masseteric inhibition and subjective function, but it was not possible at 8-9 weeks after the injury to differentiate between those that would recover and those that would be permanent.

Ca2+/calmodulin-protein kinase IIα in the trigeminal subnucleus caudalis contributes to neuropathic pain following inferior alveolar nerve transection

Calcium-calmodulin protein kinase IIalpha (CaMKIIalpha) is mainly found in brain cells, and the mRNA concentrates highly in the postsynaptic density. CaMKIIalpha is an effector of calcium and calmodulin mediated functions, and the phosphorylated CaMKIIalpha (pCaMKIIalpha) activates glutamate receptors, such as the AMPA receptor, and enhances its function. In the present study, we examined whether CaMKIIalpha in trigeminal brainstem neurons contributed to the neuropathic pain induced by inferior alveolar nerve (IAN) transection. Using immunohistochemistry and in situ hybridization, we found that the expression of CaMKIIalpha and pCaMKIIalpha increased in the trigeminal subnucleus caudalis (Vc) after IAN transection. The significant increase in the protein of CaMKIIalpha peaked at 30 min after IAN transection, and the mRNA of CaMKIIalpha increased from 2 to 14 days. Double immunofluorescent staining for CaMKIIalpha and MAP2, a marker of dendrite, revealed a significant increase in the overlapping area at 30 min after injury. This suggests that CaMKIIalpha protein is synthesized from the local mRNA pool in the dendrite 30 min after IAN transection and may quickly transmit information after nerve injury. In the behavioral test in which the escape threshold from mechanical stimulation to the lateral face was measured, intrathecal administration of KN-93, a CaMKII inhibitor, for 7 days significantly inhibited mechano-allodynia induced by IAN transection, as compared with administration of a control peptide. These data suggest that CaMKIIalpha in the trigeminal subnucleus caudalis may be involved in neuropathic pain caused by IAN transection.

Upregulation of matrix metalloproteinases following nerve injury is not mediated by mast cell activation

OBJECTIVE

Matrix metalloproteinases (MMPs) contribute to inflammatory and degenerative processes in injured nerves. Since mast cells release mediators which upregulate and activate MMPs, we tested the hypothesis that activation of mast cells is responsible for changes in the expression and activity of MMP-2 and MMP-9 in the injured peripheral nerve.

METHODS

The sciatic nerve was partially ligated in Wistar rats in which mast cells were stabilized with sodium cromoglycate. Expression and activity of MMP-2 and MMP-9 were measured in the injured and contralateral nerve using gelatin zymography, and compared between mast cell-stabilized and control groups.

RESULTS

Expression and activity of MMP-9 were increased in both the injured and contralateral nerve, but activity of MMP2 was slightly reduced by nerve injury. However, stabilization of mast cells did not alter the changes in expression or activity of MMP-2 and MMP-9 following nerve injury.

CONCLUSION

These findings suggest that the contribution of MMP-9 upregulation to the inflammatory and degenerative changes that follow nerve injury is independent of mast cell activation.

Distinct expression of TGF-beta1 mRNA in the endo- and epineurium after nerve injury

TGF-beta is a multifunctional regulatory protein with important effects on cell proliferation and differentiation, immune reactivity and extracellular matrix (ECM). During peripheral regeneration it can have growth promoting effects for axonal sprouting, but on the other hand, it may be involved in epineurial scarring and neuroma formation. We studied the expression of TGF-beta1 mRNA in the rat peripheral nerve with real time-PCR at 1, 3, 5, 7, 14, 21, 28, 35, and 42 days after transection. The sciatic nerve was sutured after transection to prevent axonal regeneration. Samples from both proximal and distal stumps were collected. To distinguish the possible different expression in the endo- and epineurium these two compartments were studied separately. The most significant finding was observed in the epineurium of the proximal stump 35 days after the operation. The expression of TGF-beta1 mRNA was over 700 times higher than that found in the non-operated controls. At the same time the expression of TGF-beta1 mRNA in the endoneurium was only twice as high as the values measured from the non-operated controls. Distally the TGF-beta1 mRNA expression in the endoneurium reached its peak after 2 weeks, and at weeks 3-6, the expression was two to four times higher than in the controls. This study supports the concept that TGF-beta1 can affect epineurial scarring.

The recovery of blood-nerve barrier in crush nerve injury--a quantitative analysis utilizing immunohistochemistry

The purpose of this study is to reveal whether the application of immunohistochemical examinations to the peripheral nervous system (PNS) can be a reliable method for the quantitative analysis of the blood-nerve barrier (BNB) and the relationship between restoration of BNB and nerve regeneration. Sciatic nerves in rats were examined after nerve crush. Immunohistochemical staining with anti-rat endothelial cell antigen-1 (anti-RECA-1) that recognizes endothelial cells and anti-endothelial barrier antigen (anti-EBA) for the detection of barrier-type endothelial cells were used. Neurofilament for staining axons was also performed. A quantitative analysis of the BNB was assessed using the ratio of EBA positive cells and RECA-1 positive cells. The ratio of EBA/RECA-1 decreased significantly 3 days postoperatively and reached its lowest level at day 7 in the segment 5 mm proximal and the entire distal stump. The ratio gradually recovered from the proximal and the regeneration of axons started a week earlier than BNB. The ratio of EBA/RECA-1 applied to the PNS can be a reliable method for the quantitative analysis of BNB. In crush injuries, the breakdown of BNB occurred simultaneously in the segment 5 mm proximal and the entire distal stump; restoration began from the proximal to distal and followed a week later to nerve regeneration.

Perioperative administration of the α2-adrenoceptor agonist clonidine at the site of nerve injury reduces the development of mechanical hypersensitivity and modulates local cytokine expression

The development of chronic pain after surgery is not rare. Nerve injury from complete or partial nerve section during surgery leads to macrophage recruitment and release of pro-inflammatory cytokines, leading in turn to sensitization. Macrophages also express alpha2-adrenoceptors, and we previously demonstrated a prolonged reduction in hypersensitivity following peri-neural injection of the alpha2-adrenoceptor agonist, clonidine, in rats with chronic nerve injury. The current study tested whether peri-neural clonidine at the time of injury could also prevent development of hypersensitivity. Rats underwent partial ligation of one sciatic nerve, and peri-neural saline, clonidine or a combination of clonidine and the alpha2A-adrenceptor-preferring antagonist, BRL44408, were administered before wound closure and, in some animals, also 24 and 48 h later. The single clonidine injection reduced hypersensitivity for only 5 h, whereas repeated injection for three days reduced hypersensitivity for 28 days. Peri-neural clonidine reduced the increase in tissue content of the proinflammatory cytokines IL-1beta and particularly TNFalpha in sciatic nerve, DRG and spinal cord while increasing concentrations of the anti-inflammatory cytokine TGF-beta1. Clonidine's effects on behavior and TNFalpha content were blocked by BRL44408. We conclude that peri-neural administration of clonidine at the site and time of injury reduces the degree of hypersensitivity in part by altering the balance of pro- and anti-inflammatory cytokines through activation of alpha2A-adrenoceptors. These results support testing of whether clonidine, as an adjuvant in continuous peripheral nerve blocks in settings of known major nerve injury, such as limb amputation, might prevent the development of chronic pain.