Gliopathy ensures persistent inflammation and chronic pain after spinal cord injury. Exp Neurol. 2008;214:6-9. [PMID: 18708053 DOI: 10.1016/j.expneurol.2008.07.016]

Peripheral and central neurobiological effects of botulinum toxin A (BoNT/A) in neuropathic pain: a systematic review

ABSTRACT

Botulinum toxin (BoNT), a presynaptic inhibitor of acetylcholine (Ach) release at the neuromuscular junction (NMJ), is a successful and safe drug for the treatment of several neurological disorders. However, a wide and recent literature review has demonstrated that BoNT exerts its effects not only at the "periphery" but also within the central nervous system (CNS). Studies from animal models, in fact, have shown a retrograde transport to the CNS, thus modulating synaptic function. The increasing number of articles reporting efficacy of BoNT on chronic neuropathic pain (CNP), a complex disease of the CNS, demonstrates that the central mechanisms of BoNT are far from being completely elucidated. In this new light, BoNT might interfere with the activity of spinal, brain stem, and cortical circuitry, modulating excitability and the functional organization of CNS in healthy conditions. Botulinum toxins efficacy on CNP is the result of a wide and complex action on many and diverse mechanisms at the basis of the maladaptive plasticity, the core of the pathogenesis of CNP. This systematic review aims to discuss in detail the BoNT's mechanisms and effects on peripheral and central neuroplasticity, at the basis for the clinical efficacy in CNP syndromes.

Alterations in the spinal cord, trigeminal nerve ganglion, and infraorbital nerve through inducing compression of the dorsal horn region at the upper cervical cord in trigeminal neuralgia

BACKGROUND

Idiopathic trigeminal neuralgia (TN) cases encountered frequently in daily practice indicate significant gaps that still need to be illuminated in the etiopathogenesis. In this study, a novel TN animal model was developed by compressing the dorsal horn (DH) of the upper cervical spinal cord.

METHODS

Eighteen rabbits were equally divided into three groups, namely control (CG), sham (SG), and spinal cord compression (SCC) groups. External pressure was applied to the left side at the C3 level in the SCC group. Dorsal hemilaminectomy was performed in the SG, and the operative side was closed without compression. No procedure was implemented in the control group. Samples from the SC, TG, and ION were taken after seven days. For the histochemical staining, damage and axons with myelin were scored using Hematoxylin and Eosin and Toluidine Blue, respectively. Immunohistochemistry, nuclei, apoptotic index, astrocyte activity, microglial labeling, and CD11b were evaluated.

RESULTS

Mechanical allodynia was observed on the ipsilateral side in the SCC group. In addition, both the TG and ION were partially damaged from SC compression, which resulted in significant histopathological changes and increased the expression of all markers in both the SG and SCC groups compared to that in the CG. There was a notable increase in tissue damage, an increase in the number of apoptotic nuclei, an increase in the apoptotic index, an indication of astrocytic gliosis, and an upsurge in microglial cells. Significant increases were noted in the SG group, whereas more pronounced significant increases were observed in the SCC group. Transmission electron microscopy revealed myelin damage, mitochondrial disruption, and increased anchoring particles. Similar changes were observed to a lesser extent in the contralateral spinal cord.

CONCLUSION

Ipsilateral trigeminal neuropathic pain was developed due to upper cervical SCC. The clinical finding is supported by immunohistochemical and ultrastructural changes. Thus, alterations in the DH due to compression of the upper cervical region should be considered as a potential cause of idiopathic TN.

Inhibition of aquaporin-4 and its subcellular localization attenuates below-level central neuropathic pain by regulating astrocyte activation in a rat spinal cord injury model

The mechanisms of central neuropathic pain (CNP) caused by spinal cord injury have not been sufficiently studied. We have found that the upregulation of astrocytic aquaporin-4 (AQP4) aggravated peripheral neuropathic pain after spinal nerve ligation in rats. Using a T13 spinal cord hemisection model, we showed that spinal AQP4 was markedly upregulated after SCI and mainly expressed in astrocytes in the spinal dorsal horn (SDH). Inhibition of AQP4 with TGN020 suppressed astrocyte activation, attenuated the development and maintenance of below-level CNP and promoted motor function recovery in vivo. In primary astrocyte cultures, TGN020 also changed cell morphology, diminished cell proliferation and suppressed astrocyte activation. Moreover, T13 spinal cord hemisection induced cell-surface abundance of the AQP4 channel and perivascular localization in the SDH. Targeted inhibition of AQP4 subcellular localization with trifluoperazine effectively diminished astrocyte activation in vitro and further ablated astrocyte activation, attenuated the development and maintenance of below-level CNP, and accelerated functional recovery in vivo. Together, these results provide mechanistic insights into the roles of AQP4 in the development and maintenance of below-level CNP. Intervening with AQP4, including targeting AQP4 subcellular localization, might emerge as a promising agent to prevent chronic CNP after SCI.

Testosterone signaling pathways for reducing neuropathic pain in a rat model of spinothalamic tract lesion

Objectives

Most individuals who suffer from spinal cord injury (SCI) experience neuropathic pain, which currently has no effective treatment. In this study, we examined how testosterone affects neuropathic pain resulting from SCI.

Materials and Methods

We administered three different doses of testosterone (4, 8, 16 mg/kg, intraperitoneal) to male rats after an electrolytic lesion of the spinothalamic tract. We then conducted behavioral tests, including open field and von Frey tests, within 28 days post-SCI. On day 28 after SCI, we analyzed spinal tissue using western blot to measure the levels of ionized calcium binding adaptor molecule 1 (Iba1), glial fibrillary acidic protein (GFAP), phospho-extracellular signal-regulated kinase (p-ERK1/2), and p-P38 at the injury site.

Results

The results showed that testosterone significantly improved both motor activity and mechanical allodynia compared to the SCI-only group. Testosterone also inhibited microglia and astrocyte activation. Furthermore, testosterone significantly decreased p-P38 and p-ERK levels.

Conclusion

The findings indicate that testosterone may alleviate SCI-induced neuropathic pain by inhibiting the activation of astrocytes and microglia, as well as suppressing MAPK signaling pathways.

The impact of time from injury to surgery on the risk of neuropathic pain after traumatic spinal cord injury

Traumatic spinal cord injury (SCI) is a devastating neurological disorder often accompanied by neuropathic pain (NeP), significantly affecting patients' quality of life. This retrospective study aimed to investigate the impact of the time from injury to surgery on the development of NeP following traumatic SCI. Medical records of patients with traumatic SCI who underwent surgical intervention between January 2017 and January 2021 at two specialized centers were reviewed. Variables associated with NeP including demographics, injury profiles, medical history, surgical details, and pain assessments were investigated. Independent risk factors related to NeP were identified using multivariate logistic regression analysis. A total of 320 patients met the inclusion criteria, with 245 (76.6%) being male and a mean age of 56.5 ± 13.2 years. NeP was identified in 48.4% of patients (155 of 320). The multivariate analysis identifies age at injury, Injury Severity Score, and the neurological level of injury as independent risk factors for the development of NeP in both AIS A and AIS B, C, and D subgroups. Additionally, a significant association between the time from injury to surgery and NeP was observed in AIS B, C, and D patients, while no such association was found in AIS A patients. This study highlights the benefits of early and ultra-early surgical intervention in preventing NeP in patients with incomplete traumatic SCI (AIS B, C, and D), underscoring the importance of optimizing surgical timing to improve patient outcomes. Prospective studies are warranted to establish evidence-based surgical guidelines for managing traumatic SCI and preventing NeP effectively.

Attenuation of SCI-Induced Hypersensitivity by Intensive Locomotor Training and Recombinant GABAergic Cells

The underlying mechanisms of spinal cord injury (SCI)-induced chronic pain involve dysfunctional GABAergic signaling and enhanced NMDA signaling. Our previous studies showed that SCI hypersensitivity in rats can be attenuated by recombinant rat GABAergic cells releasing NMDA blocker serine-histogranin (SHG) and by intensive locomotor training (ILT). The current study combines these approaches and evaluates their analgesic effects on a model of SCI pain in rats. Cells were grafted into the spinal cord at 4 weeks post-SCI to target the chronic pain, and ILT was initiated 5 weeks post-SCI. The hypersensitivity was evaluated weekly, which was followed by histological and biochemical assays. Prolonged effects of the treatment were evaluated in subgroups of animals after we discontinued ILT. The results show attenuation of tactile, heat and cold hypersensitivity in all of the treated animals and reduced levels of proinflammatory cytokines IL1β and TNFα in the spinal tissue and CSF. Animals with recombinant grafts and ILT showed the preservation of analgesic effects even during sedentary periods when the ILT was discontinued. Retraining helped to re-establish the effect of long-term training in all of the groups, with the greatest impact being in animals with recombinant grafts. These findings suggest that intermittent training in combination with cell therapy might be an efficient approach to manage chronic pain in SCI patients.

Research progress on the mechanism of chronic neuropathic pain

Chronic neuropathic pain (CNP) refers to pain that lasts for more than three months due to a disease or an injury to the somatosensory nervous system. The incidence of CNP has been increasing in the world, causing it to become a global concern and patients often experience spontaneous pain, hyperalgesia, abnormal pain or even abnormal sensation as some of its main symptoms. In addition to serious pain and poor physical health, CNP also negatively affects patients' mental health, thus impacting the overall quality of their lives. The pathogenesis of CNP is not clear, but some studies have proved that central sensitization, peripheral sensitization, neuroinflammation, dysfunction in descending nociceptive modulatory systems, oxidative stress reaction, activation of glial cells and psychological factors play an important role in the occurrence and development of CNP. In this context, this article summarizes the current research progress on the mechanism of CNP to provide a basis for further research in preventing and treating the disease.

The Impact of Activity-Based Interventions on Neuropathic Pain in Experimental Spinal Cord Injury

Physical activity-based rehabilitative interventions represent the main treatment concept for people suffering from spinal cord injury (SCI). The role such interventions play in the relief of neuropathic pain (NP) states is emerging, along with underlying mechanisms resulting in SCI-induced NP (SCI-NP). Animal models have been used to investigate the benefits of activity-based interventions (ABI), such as treadmill training, wheel running, walking, swimming, and bipedal standing. These activity-based paradigms have been shown to modulate inflammatory-related alterations as well as induce functional and structural changes in the spinal cord gray matter circuitry correlated with pain behaviors. Thus far, the research available provides an incomplete picture of the cellular and molecular pathways involved in this beneficial effect. Continued research is essential for understanding how such interventions benefit SCI patients suffering from NP and allow the development of individualized rehabilitative therapies. This article reviews preclinical studies on this specific topic, goes over mechanisms involved in SCI-NP in relation to ABI, and then discusses the effectiveness of different activity-based paradigms as they relate to different forms, intensity, initiation times, and duration of ABI. This article also summarizes the mechanisms of respective interventions to ameliorate NP after SCI and provides suggestions for future research directions.

Emerging Evidence for Intrathecal Management of Neuropathic Pain Following Spinal Cord Injury

A high prevalence of patients with spinal cord injury (SCI) suffer from chronic neuropathic pain. Unfortunately, the precise pathophysiological mechanisms underlying this phenomenon have yet to be clearly elucidated and targeted treatments are largely lacking. As an unfortunate consequence, neuropathic pain in the population with SCI is refractory to standard of care treatments and represents a significant contributor to morbidity and suffering. In recent years, advances from SCI-specific animal studies and translational models have furthered our understanding of the neuronal excitability, glial dysregulation, and chronic inflammation processes that facilitate neuropathic pain. These developments have served advantageously to facilitate exploration into the use of neuromodulation as a treatment modality. The use of intrathecal drug delivery (IDD), with novel pharmacotherapies, to treat chronic neuropathic pain has gained particular attention in both pre-clinical and clinical contexts. In this evidence-based narrative review, we provide a comprehensive exploration into the emerging evidence for the pathogenesis of neuropathic pain following SCI, the evidence basis for IDD as a therapeutic strategy, and novel pharmacologics across impactful animal and clinical studies.

Reactive astrocytes in pain neural circuit pathogenesis

Reactive astrocytes are commonly activated in the spinal dorsal horn (SDH) of various animal models of pathological pain. Previous investigations suggest an association between astrogliosis and pain pathogenesis. However, our understanding of the mechanisms underlying astrogliosis activation and the contributions of reactive astrocytes to pain neural circuit malfunction is rudimentary. This short review highlights recent advances in these areas.

Bioactive compounds for neuropathic pain: An update on preclinical studies and future perspectives

Among different types of chronic pain, neuropathic pain (NP), arising from damage to the nervous system, including peripheral fibers and central neurons, is notoriously difficult to treat and affects 7-10% of the general population. Currently available treatment options for NP are limited and opioid analgesics have severe side effects and can result in opioid use disorder. Recent studies have exhibited the role of dietary bioactive compounds in the mitigation of NP. Here, we assessed the effects of commonly consumed bioactive compounds (ginger, curcumin, omega-3 polyunsaturated fatty acids, epigallocatechin gallate, resveratrol, soy isoflavones, lycopene, and naringin) on NP and NP-related neuroinflammation. Cellular studies demonstrated that these bioactive compounds reduce inflammation via suppression of NF-κB and MAPK signaling pathways that regulate apoptosis/cell survival, antioxidant, and anti-inflammatory responses. Animal studies strongly suggest that these regularly consumed bioactive compounds have a pronounced anti-NP effect as shown by decreased mechanical allodynia, mechanical hyperalgesia, thermal hyperalgesia, and cold hyperalgesia. The proposed molecular mechanisms include (1) the enhancement of neuron survival, (2) the reduction of neuronal hyperexcitability by activation of antinociceptive cannabinoid 1 receptors and opioid receptors, (3) the suppression of sodium channel current, and (4) enhancing a potassium outward current in NP-affected animals, triggering a cascade of chemical changes within, and between neurons for pain relief. Human studies administered in this area have been limited. Future randomized controlled trials are warranted to confirm the findings of preclinical efficacies using bioactive compounds in patients with NP.

miR-338-5p Levels and Cigarette Smoking are Associated With Neuropathic Pain Severity in Individuals With Spinal Cord Injury: Preliminary Findings From a Genome-Wide microRNA Expression Profiling Screen

OBJECTIVE

To identify microRNA biomarkers and clinical factors associated with neuropathic pain after spinal cord injury.

DESIGN

Cross-sectional, secondary analysis of baseline data collected from ongoing clinical studies. Using a genome-wide microRNA screening approach, we studied differential microRNA expression in serum from 43 adults with spinal cord injury enrolled in ongoing clinical studies. Least squares regression was used to identify associations between microRNA expression, clinical factors, and neuropathic pain severity.

SETTING

Community-dwelling individuals with spinal cord injury.

PARTICIPANTS

Participants (N=43) were at least 18 years old with spinal cord injury, with 28 reporting neuropathic pain and 15 reporting no neuropathic pain.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Pain presence, type, and intensity were assessed with the International Spinal Cord Injury Pain Basic Data Set. Serum microRNA normalized deep sequencing counts were quantified from blood samples. Participant demographic factors, injury characteristics, medication use, and health habits were collected via questionnaire.

RESULTS

miR-338-5p expression and history of cigarette smoking were associated with and explained 37% of the variance in neuropathic pain severity (R2=0.37, F2,18=5.31, P=.02) independent of other clinical factors. No association was identified between miR-338-5p levels and nociceptive pain severity.

CONCLUSIONS

Our findings suggest that miR-338-5p and cigarette smoking may both play a role in the development or maintenance of neuropathic pain after spinal cord injury. While additional work is needed to confirm these findings, validated target analysis suggests a neuroprotective role of miR-338-5p in modulating neuroinflammation and neuronal apoptosis and that its downregulation may result in maladaptive neuroplastic mechanisms contributing to neuropathic pain after spinal cord injury.

Dorsal horn neuronal sparing predicts the development of at-level mechanical allodynia following cervical spinal cord injury in mice

Spinal cord injury (SCI) frequently results in immediate and sustained neurological dysfunction, including intractable neuropathic pain in approximately 60-80% of individuals. SCI induces immediate mechanical damage to spinal cord tissue followed by a period of secondary injury in which tissue damage is further propagated, contributing to the development of anatomically unique lesions. Variability in lesion size and location influences the degree of motor and sensory dysfunction incurred by an individual. We predicted that variability in lesion parameters may also explain why some, but not all, experimental animals develop mechanical sensitivity after SCI. To characterize the relationship of lesion anatomy to mechanical allodynia, we utilized a mouse cervical hemicontusion model of SCI that has been shown to lead to the development and persistence of mechanical allodynia in the ipsilateral forelimb after injury. At four weeks post-SCI, the numbers and locations of surviving neurons were quantified along with total lesion volume and nociceptive fiber sprouting. We found that the subset of animals exhibiting mechanical allodynia had significantly increased neuronal sparing in the ipsilateral dorsal horn around the lesion epicenter compared to animals that did not exhibit mechanical allodynia. Additionally, we failed to observe significant differences between groups in nociceptive fiber density in the dorsal horn around the lesion epicenter. Notably, we found that impactor probe displacement upon administration of the SCI surgery was significantly lower in sensitive animals compared with not-sensitive animals. Together, our data indicate that lesion severity negatively correlates with the manifestation of at-level mechanical hypersensitivity and suggests that sparing of dorsal horn neurons may be required for the development of neuropathic pain.

Microglial deactivation by adeno-associated virus expressing small-hairpin GCH1 has protective effects against neuropathic pain development in a spinothalamic tract-lesion model

AIMS

Neuropathic pain after spinal cord injury is one of the most difficult clinical problems after the loss of mobility, and pharmacological or neuromodulation therapy showed limited efficacy. In this study, we examine the possibility of pain modulation by a recombinant adeno-associated virus (rAAV) encoding small-hairpin RNA against GCH1 (rAAV-shGCH1) in a spinal cord injury model in which neuropathic pain was induced by a spinothalamic tract (STT) lesion.

METHODS

Micro-electric lesioning was used to damage the left STT in rats (n = 32), and either rAAV-shGCH1 (n = 19) or rAAV control (n = 6) was injected into the dorsal horn of the rats at the same time. On postoperative days 3, 7, and 14, we evaluated neuropathic pain using a behavioral test and microglial activation by immunohistochemical staining.

RESULTS

A pain modulation effect of shGCH1 was observed from postoperative days 3 to 14. The mechanical withdrawal threshold was 13.0 ± 0.95 in the shGCH1 group, 4.3 ± 1.37 in the control group, and 3.49 ± 0.85 in sham on postoperative day 3 (p < 0.0001) and continued to postoperative day 14 (shGCH1 vs. control: 11.4 ± 1.1 vs. 2.05 ± 0.60, p < 0.001 and shGCH1 vs. sham: 11.4 ± 1.1 vs. 1.43 ± 0.54, p < 0.001). Immunohistochemical staining of the spinal cord dorsal horn showed deactivation of microglia in the shGCH1 group without any change of delayed pattern of astrocyte activation as in STT model.

CONCLUSIONS

Neuropathic pain after spinal cord injury can be modulated bilaterally by deactivating microglial activation after a unilateral injection of rAAV-shGCH1 into the dorsal horn of a STT lesion spinal cord pain model. This new attempt would be another therapeutic approach for NP after SCI, which once happens; there is no clear curative options still now.

Cystine-glutamate antiporter deletion accelerates motor recovery and improves histological outcomes following spinal cord injury in mice

xCT is the specific subunit of System xc-, an antiporter importing cystine while releasing glutamate. Although xCT expression has been found in the spinal cord, its expression and role after spinal cord injury (SCI) remain unknown. The aim of this study was to characterize the role of xCT on functional and histological outcomes following SCI induced in wild-type (xCT+/+) and in xCT-deficient mice (xCT−/−). In the normal mouse spinal cord, slc7a11/xCT mRNA was detected in meningeal fibroblasts, vascular mural cells, astrocytes, motor neurons and to a lesser extent in microglia. slc7a11/xCT gene and protein were upregulated within two weeks post-SCI. xCT−/− mice recovered muscular grip strength as well as pre-SCI weight faster than xCT+/+ mice. Histology of xCT−/− spinal cords revealed significantly more spared motor neurons and a higher number of quiescent microglia. In xCT−/− mice, inflammatory polarization shifted towards higher mRNA expression of ym1 and igf1 (anti-inflammatory) while lower levels of nox2 and tnf-a (pro-inflammatory). Although astrocyte polarization did not differ, we quantified an increased expression of lcn2 mRNA. Our results show that slc7a11/xCT is overexpressed early following SCI and is detrimental to motor neuron survival. xCT deletion modulates intraspinal glial activation by shifting towards an anti-inflammatory profile.

Blocking the Spinal Fbxo3/CARM1/K+ Channel Epigenetic Silencing Pathway as a Strategy for Neuropathic Pain Relief

Many epigenetic regulators are involved in pain-associated spinal plasticity. Coactivator-associated arginine methyltransferase 1 (CARM1), an epigenetic regulator of histone arginine methylation, is a highly interesting target in neuroplasticity. However, its potential contribution to spinal plasticity-associated neuropathic pain development remains poorly explored. Here, we report that nerve injury decreased the expression of spinal CARM1 and induced allodynia. Moreover, decreasing spinal CARM1 expression by Fbxo3-mediated CARM1 ubiquitination promoted H3R17me2 decrement at the K+ channel promoter, thereby causing K+ channel epigenetic silencing and the development of neuropathic pain. Remarkably, in naïve rats, decreasing spinal CARM1 using CARM1 siRNA or a CARM1 inhibitor resulted in similar epigenetic signaling and allodynia. Furthermore, intrathecal administration of BC-1215 (a novel Fbxo3 inhibitor) prevented CARM1 ubiquitination to block K+ channel gene silencing and ameliorate allodynia after nerve injury. Collectively, the results reveal that this newly identified spinal Fbxo3-CARM1-K+ channel gene functional axis promotes neuropathic pain. These findings provide essential insights that will aid in the development of more efficient and specific therapies against neuropathic pain.

Intensive Locomotor Training Provides Sustained Alleviation of Chronic Spinal Cord Injury-Associated Neuropathic Pain: A Two-Year Pre-Clinical Study

Neuropathic pain often accompanies the functional deficits associated with spinal cord injury (SCI) and further reduces a patient's quality of life. Clinical and pre-clinical research is beginning to highlight the beneficial role that rehabilitative therapies such as locomotor training can have not only on functional recovery but also on chronic pain management. Our group has previously developed an intensive locomotor training (ILT) treadmill protocol on rats that reduced SCI neuropathic pain symptoms for at least 3 months. We have extended these findings in the current study to evaluate the ability of regular ILT regimen over a 2 year period post-SCI to maintain neuropathic pain reduction. To assess this, the rat clip compression SCI model (T7/8) was used and treadmill training was initiated starting 4 weeks after SCI and continuing through the duration of the study. Results showed continued suppression of SCI neuropathic pain responses (reduced mechanical, heat, and cold hypersensitivity throughout the entire time course of the study). In contrast, non-exercised rats showed consistent and sustained neuropathic pain responses during this period. In addition, prolonged survival and improved locomotor outcomes were observed in rats undergoing ILT as the study longevity progressed. Potential contributory mechanisms underlying beneficial effects of ILT include reduced inflammation and restoration of anti-nociceptive inhibitory processes as indicated by neurochemical assays in spinal tissue of remaining rats at 2 years post-SCI. The benefits of chronic ILT suggest that long-term physical exercise therapy can produce powerful and prolonged management of neuropathic pain, partly through sustained reduction of spinal pathological processes.

Intercellular communication and ion channels in neuropathic pain chronicization

BACKGROUND

Neuropathic pain is caused by primary lesion or dysfunction of either peripheral or central nervous system. Due to its complex pathogenesis, often related to a number of comorbidities, such as cancer, neurodegenerative and neurovascular diseases, neuropathic pain still represents an unmet clinical need, lacking long-term effective treatment and complex case-by-case approach.

AIM AND METHODS

We analyzed the recent literature on the role of selective voltage-sensitive sodium, calcium and potassium permeable channels and non-selective gap junctions (GJs) and hemichannels (HCs) in establishing and maintaining chronic neuropathic conditions. We finally focussed our review on the role of extracellular microenvironment modifications induced by resident glial cells and on the recent advances in cell-to-cell and cell-to-extracellular environment communication in chronic neuropathies.

CONCLUSION

In this review, we provide an update on the current knowledge of neuropathy chronicization processes with a focus on both neuronal and glial ion channels, as well as on channel-mediated intercellular communication.

Mutually beneficial effects of intensive exercise and GABAergic neural progenitor cell transplants in reducing neuropathic pain and spinal pathology in rats with spinal cord injury

Spinal cord injury (SCI) produces both locomotor deficits and sensory dysfunction that greatly reduce the overall quality of life. Mechanisms underlying chronic pain include increased neuro-inflammation and changes in spinal processing of sensory signals, with reduced inhibitory GABAergic signaling a likely key player. Our previous research demonstrated that spinal transplantation of GABAergic neural progenitor cells (NPCs) reduced neuropathic pain while intensive locomotor training (ILT) could reduce development of pain and partially reverse already established pain behaviors. Therefore, we evaluate the potential mutually beneficial anti-hypersensitivity effects of NPC transplants cells in combination with early or delayed ILT. NPC transplants were done at 4 weeks post-SCI. ILT, using a progressive ramping treadmill protocol, was initiated either 5 days post-SCI (early: pain prevention group) or at 5 weeks post-SCI (delayed: to reverse established pain) in male Sprague Dawley rats. Results showed that either ILT alone or NPCs alone could partially attenuate SCI neuropathic pain behaviors in both prevention and reversal paradigms. However, the combination of ILT with NPC transplants significantly enhanced neuropathic pain reduction on most of the outcome measures including tests for allodynia, hyperalgesia, and ongoing pain. Immunocytochemical and neurochemical analyses showed decreased pro-inflammatory markers and spinal pathology with individual treatments; these measures were further improved by the combination of either early or delayed ILT and GABAergic cellular transplantation. Lumbar dorsal horn GABAergic neuronal and process density were nearly restored to normal levels by the combination treatment. Together, these interventions may provide a less hostile and more supportive environment for promoting functional restoration in the spinal dorsal horn and attenuation of neuropathic pain following SCI. These findings suggest mutually beneficial effects of ILT and NPC transplants for reducing SCI neuropathic pain.

Myalgic Encephalomyelitis/Chronic Fatigue Syndrome: A Comprehensive Review

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a debilitating chronic disease of unknown aetiology that is recognized by the World Health Organization (WHO) and the United States Center for Disease Control and Prevention (US CDC) as a disorder of the brain. The disease predominantly affects adults, with a peak age of onset of between 20 and 45 years with a female to male ratio of 3:1. Although the clinical features of the disease have been well established within diagnostic criteria, the diagnosis of ME/CFS is still of exclusion, meaning that other medical conditions must be ruled out. The pathophysiological mechanisms are unclear but the neuro-immuno-endocrinological pattern of CFS patients gleaned from various studies indicates that these three pillars may be the key point to understand the complexity of the disease. At the moment, there are no specific pharmacological therapies to treat the disease, but several studies' aims and therapeutic approaches have been described in order to benefit patients' prognosis, symptomatology relief, and the recovery of pre-existing function. This review presents a pathophysiological approach to understanding the essential concepts of ME/CFS, with an emphasis on the population, clinical, and genetic concepts associated with ME/CFS.

Inhibition of NOX2 signaling limits pain-related behavior and improves motor function in male mice after spinal cord injury: Participation of IL-10/miR-155 pathways

NADPH oxidase (NOX2) is an enzyme that induces reactive oxygen species (ROS) and serves as a switch between the pro-inflammatory and neurorestorative microglial/macrophage phenotypes; such changes play an important role in neuropathic pain and motor dysfunction. Increased NOX2 expression after spinal cord injury (SCI) has been reported, and inhibition of NOX2 improves motor function. However, the underlying mechanisms of NOX2 in post-traumatic pain and motor deficit remain unexplored. In the present study, we report that depletion of NOX2 (NOX2^-/-) or inhibition of NOX2 using NOX2ds-tat significantly reduced mechanical/thermal cutaneous hypersensitivity and motor dysfunction after moderate contusion SCI at T10 in male mice. Western blot (WB, 3 mm lesion area) and immunohistochemistry (IHC) showed that SCI elevates NOX2 expression predominantly in microglia/macrophages up to 8 weeks post-injury. Deletion of NOX2 significantly reduced CD11b⁺/CD45^hiF4/80⁺ macrophage infiltration at 24 h post-injury detected by flow cytometry and 8-OHG⁺ ROS production at 8 weeks post-injury by IHC in both lesion area and lumbar enlargement. NOX2 deficiency also altered microglial/macrophage pro-inflammatory and anti-inflammatory balance towards the neurorestorative response. WB analysis showed robust increase of Arginase-1 and YM1 proteins in NOX2^-/- mice. Furthermore, qPCR analysis showed significant up-regulation of anti-inflammatory cytokine IL-10 levels in NOX2^-/- mice, associated with reduced microRNA-155 expression. These findings were confirmed in CD11b⁺ microglia/macrophages isolated from spinal cord at 3 days post-injury. Taken together, our data suggest an important role for IL-10/miR-155 pathway in regulating NOX2-mediated SCI-dysfunction. Thus, specific targeting of NOX2 may provide an effective strategy for treating neurological dysfunction in SCI patients.

Administration of ONO-2506 suppresses neuropathic pain after spinal cord injury by inhibition of astrocytic activation

BACKGROUND CONTEXT

Spinal cord injury (SCI) results in not only motor dysfunction but also chronic neuropathic pain. Allodynia, an abnormal sensation that evokes pain against non-noxious stimuli, is a major symptom of post-SCI neuropathic pain. Astrocytic activation is a cause of post-SCI neuropathic pain and is considered a key treatment target. However, no effective treatment for these problems is available to date. ONO-2506 is a novel agent that suppresses astrocytic activation by inhibition of S100B production from astrocytes. Recently, it has been demonstrated that ONO-2506 inhibits secondary injury and improves motor function after SCI.

PURPOSE

This study aimed to investigate the effect of ONO-2506 on post-SCI neuropathic pain.

STUDY DESIGN

Animal study of a rat model of spinal cord contusion.

METHODS

A total of 22 male Sprague-Dawley rats aged 6 weeks were used. Incomplete SCI was created at T10 level. Animals were divided into two groups: Saline group and ONO-2506 group. Nine animals in each group were finally included for this study. Intraperitoneal administration of ONO-2506 (20 mg/kg) or saline was continued daily for 1 week following SCI. Recovery of hind limb motor function was assessed using the Basso, Beattie, and Bresnahan (BBB) score. Mechanical and thermal allodynia of hind paws were evaluated by the withdrawal threshold using a von Frey filament and the withdrawal latency using the plantar test device. At 6 weeks after SCI, sagittal sections at the injured site and axial sections at L 4/5 were evaluated by fluorescent immunohistochemistry staining using S100B and glial fibrillary acidic protein (GFAP) antibodies.

RESULTS

The improvement course of BBB scores was similar between the two groups. However, the withdrawal thresholds for mechanical stimuli and the withdrawal latency for thermal stimuli were significantly higher in the ONO-2506 group than in the Saline group over 6 weeks after SCI. The histologic assessments at the injured site demonstrated a significant reduction in the cross-sectional area of the cysts and a high fluorescence intensity area of S100B and GFAP in the ONO-2506 group. By correlation analysis, a high absolute value of the correlation coefficient was confirmed between the intensity of S100B expression at the injured site and the allodynia severity.

CONCLUSION

Administration of ONO-2506 attenuated post-SCI neuropathic pain in a rat model of incomplete SCI. Histologic results support that the inhibition of S100B production and subsequent suppression of astrocytic activation contributed to the reduction in neuropathic pain.

Bone Marrow-Derived Monocytes Drive the Inflammatory Microenvironment in Local and Remote Regions after Thoracic Spinal Cord Injury

Spinal cord injury (SCI) produces a toxic inflammatory microenvironment that negatively affects plasticity and recovery. Recently, we showed glial activation and peripheral myeloid cell infiltration extending beyond the epicenter through the remote lumbar cord after thoracic SCI. The presence and role of infiltrating monocytes is important, especially in the lumbar cord where locomotor central pattern generators are housed. Therefore, we compared the inflammatory profile of resident microglia and peripheral myeloid cells after SCI. Bone marrow chimeras received midthoracic contusive SCI, and trafficking was determined 1-7 days later. Fluorescence-activated cell (FAC) sorting showed similar infiltration timing of both neutrophils and macrophages in epicenter and lumbar regions. While neutrophil numbers were attenuated by day 3, macrophages remained unchanged at day 7, suggesting that macrophages have important long-term influence on the microenvironment. Nanostring gene array identified a strong proinflammatory profile of infiltrating macrophages relative to microglia at both epicenter and lumbar sites. Macrophages had elevated expression of inflammatory cytokines (IL-1β, IFNγ), chemokines (CCL2, CXCL2), mediators (COX-1, MMP-9), and receptors (CCR2, Ly6C), and decreased expression of growth promoting genes (GDNF, BDNF). Importantly, lumbar macrophages had elevated expression of active trafficking genes (CCR2, l-selectin, MMP-9) compared with epicenter macrophages. Further, acute rehabilitation exacerbated the inflammatory profile of infiltrated macrophages in the lumbar cord. Such high inflammatory potential and negative response to rehabilitation of infiltrating macrophages within lumbar locomotor central pattern generators likely impedes activity-dependent recovery. Therefore, limiting active trafficking of macrophages into the lumbar cord identifies a novel target for SCI therapies to improve locomotion.

Sustained reversal of central neuropathic pain induced by a single intrathecal injection of adenosine A2A receptor agonists

Central neuropathic pain is a debilitating outcome of spinal cord injury (SCI) and current treatments to alleviate this pain condition are ineffective. A growing body of literature suggests that activating adenosine A_2A receptors (A_2ARs) decreases the production of proinflammatory cytokines and increases the production of anti-inflammatory cytokines. Here, the effect of administering intrathecal A_2AR agonists on central neuropathic pain was measured using hindpaw mechanical allodynia in a rat model of SCI termed spinal neuropathic avulsion pain (SNAP). Other models of SCI cause extensive damage to the spinal cord, resulting in paralysis and health problems. SNAP rats with unilateral low thoracic (T13)/high lumbar (L1) dorsal root avulsion develop below-level bilateral allodynia, without concomitant motor or health problems. A single intrathecal injection of the A_2AR agonist 2-p-(2-carboxyethyl)phenethylamino-5'-N-ethylcarboxamido adenosine HCl (CGS21680) reversed SCI-induced allodynia for at least 6 weeks. The reversal is likely in part mediated by interleukin (IL)-10, as intrathecally administering neutralizing IL-10 antibodies 1 week after CGS21680 abolished the anti-allodynic effect of CGS21680. Dorsal spinal cord tissue from the ipsilateral site of SCI (T13/L1) was assayed 1 and 6 weeks after CGS21680 for IL-10, CD11b, and tumor necrosis factor (TNF) gene expression. CGS21680 treatment did not change IL-10 gene expression but did significantly decrease CD11b and TNF gene expression at both timepoints. A second A_2AR agonist, 4-(3-(6-amino-9-(5-cyclopropylcarbamoyl-3,4-dihydroxytetrahydrofuran-2-yl)-9H-purin-2-yl)prop-2-ynyl)piperidine-1-carboxylic acid methyl ester (ATL313), was also able to significantly prevent and reverse SCI-induced allodynia for several weeks after a single intrathecal injection, providing converging lines of evidence of A_2AR involvement. The enduring pain reversal after a single intrathecal injection of A_2AR agonists suggests that A_2AR agonists could be exciting new candidates for treating SCI-induced central neuropathic pain.

Rapid recovery and altered neurochemical dependence of locomotor central pattern generation following lumbar neonatal spinal cord injury

KEY POINTS

Spinal compression injury targeted to the neonatal upper lumbar spinal cord, the region of highest hindlimb locomotor rhythmogenicity, leads to an initial paralysis of the hindlimbs. Behavioural recovery is evident within a few days and approaches normal function within about 3 weeks. Fictive locomotion in the isolated injured spinal cord cannot be elicited by a neurochemical cocktail containing NMDA, dopamine and serotonin 1 day post-injury, but can 3 days post-injury as readily as in the uninjured spinal cord. Low frequency coordinated rhythmic activity can be elicited in the isolated uninjured spinal cord by NMDA + dopamine (without serotonin), but not in the isolated injured spinal cord. In both the injured and uninjured spinal cord, eliciting bona fide fictive locomotion requires the additional presence of serotonin.

ABSTRACT

Following incomplete compression injury in the thoracic spinal cord of neonatal mice 1 day after birth (P1), we previously reported that virtually normal hindlimb locomotor function is recovered within about 3 weeks despite substantial permanent thoracic tissue loss. Here, we asked whether similar recovery occurs following lumbar injury that impacts more directly on the locomotor central pattern generator (CPG). As in thoracic injuries, lumbar injuries caused about 90% neuronal loss at the injury site and increased serotonergic innervation below the injury. Motor recovery was slower after lumbar than thoracic injury, but virtually normal function was attained by P25 in both cases. Locomotor CPG status was tested by eliciting fictive locomotion in isolated spinal cords using a widely used neurochemical cocktail (NMDA, dopamine, serotonin). No fictive locomotion could be elicited 1 day post-injury, but could within 3 days post-injury as readily as in age-matched uninjured control spinal cords. Burst patterning and coordination were largely similar in injured and control spinal cords but there were differences. Notably, in both groups there were two main locomotor frequencies, but injured spinal cords exhibited a shift towards the higher frequency. Injury also altered the neurochemical dependence of locomotor CPG output, such that injured spinal cords, unlike control spinal cords, were incapable of generating low frequency rhythmic coordinated activity in the presence of NMDA and dopamine alone. Thus, the neonatal spinal cord also exhibits remarkable functional recovery after lumbar injuries, but the neurochemical sensitivity of locomotor circuitry is modified in the process.

Neuronal-Glial Interactions Maintain Chronic Neuropathic Pain after Spinal Cord Injury

The hyperactive state of sensory neurons in the spinal cord enhances pain transmission. Spinal glial cells have also been implicated in enhanced excitability of spinal dorsal horn neurons, resulting in pain amplification and distortions. Traumatic injuries of the neural system such as spinal cord injury (SCI) induce neuronal hyperactivity and glial activation, causing maladaptive synaptic plasticity in the spinal cord. Recent studies demonstrate that SCI causes persistent glial activation with concomitant neuronal hyperactivity, thus providing the substrate for central neuropathic pain. Hyperactive sensory neurons and activated glial cells increase intracellular and extracellular glutamate, neuropeptides, adenosine triphosphates, proinflammatory cytokines, and reactive oxygen species concentrations, all of which enhance pain transmission. In addition, hyperactive sensory neurons and glial cells overexpress receptors and ion channels that maintain this enhanced pain transmission. Therefore, post-SCI neuronal-glial interactions create maladaptive synaptic circuits and activate intracellular signaling events that permanently contribute to enhanced neuropathic pain. In this review, we describe how hyperactivity of sensory neurons contributes to the maintenance of chronic neuropathic pain via neuronal-glial interactions following SCI.

Neuropathic Pain and Spinal Cord Injury: Phenotypes and Pharmacological Management

Chronic neuropathic pain is a complicated condition after a spinal cord injury (SCI) that often has a lifelong and significant negative impact on life after the injury; therefore, improved pain management is considered a significant and unmet need. Neuropathic pain mechanisms are heterogeneous and the difficulty in determining their individual contribution to specific pain types may contribute to poor treatment outcomes in this population. Thus, identifying human neuropathic pain phenotypes based on pain symptoms, somatosensory changes, or cognitive and psychosocial factors that reflect specific spinal cord or brain mechanisms of neuropathic pain is an important goal. Once a pain phenotype can be reliably replicated, its relationship with biomarkers and clinical treatment outcomes can be analyzed, and thereby facilitate translational research and further the mechanistic understanding of individual differences in the pain experience and in clinical trial outcomes. The present article will discuss clinical aspects of SCI-related neuropathic pain, neuropathic pain phenotypes, pain mechanisms, potential biomarkers and pharmacological interventions, and progress regarding how defining neuropathic pain phenotypes may lead to more targeted treatments for these difficult pain conditions.

The Neuroinflammatory Etiopathology of Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS)

Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) is a debilitating multi-systemic chronic illness of unknown etiology, classified as a neurological disorder by the World Health Organization (WHO). The symptomatology of the condition appears to emanate from a variety of sources of chronic neurological disturbance and associated distortions, and chronicity, in noxious sensory signaling and neuroimmune activation. This article incorporates a summary review and discussion of biomedical research considered relevant to this essential conception perspective. It is intended to provide stakeholders with a concise, integrated outline disease model in order to help demystify this major public health problem. The primary etiopathological factors presented are: (A) Postural/biomechanical pain signaling, affecting adverse neuroexcitation, in the context of compression, constriction, strain, or damage of vertebral-regional bone and neuromuscular tissues; (B) Immune mediated inflammatory sequelae, in the context of prolonged immunotropic neurotrophic infection—with lymphotropic/gliotropic/glio-toxic varieties implicated in particular; (C) A combination of factors A and B. Sustained glial activation under such conditions is associated with oxidative and nitrosative stress, neuroinflammation, and neural sensitivity. These processes collectively enhance the potential for multi-systemic disarray involving endocrine pathway aberration, immune and mitochondrial dysfunction, and neurodegeneration, and tend toward still more intractable synergistic neuro-glial dysfunction (gliopathy), autoimmunity, and central neuronal sensitization.

Nor-Binaltorphimine Blocks the Adverse Effects of Morphine after Spinal Cord Injury

Opioids are frequently used for the treatment of pain following spinal cord injury (SCI). Unfortunately, we have shown that morphine administered in the acute phase of SCI results in significant, adverse secondary consequences including compromised locomotor and sensory recovery. Similarly, we showed that selective activation of the κ-opioid receptor (KOR), even at a dose 32-fold lower than morphine, is sufficient to attenuate recovery of locomotor function. In the current study, we tested whether activation of the KOR is necessary to produce morphine's adverse effects using nor-Binaltorphimine (norBNI), a selective KOR antagonist. Rats received a moderate spinal contusion (T12) and 24 h later, baseline locomotor function and nociceptive reactivity were assessed. Rats were then administered norBNI (0, 0.02, 0.08, or 0.32 μmol) followed by morphine (0 or 0.32 μmol). Nociception was reassessed 30 min after drug treatment, and recovery was evaluated for 21 days. The effects of norBNI on morphine-induced attenuation of recovery were dose dependent. At higher doses, norBNI blocked the adverse effects of morphine on locomotor recovery, but analgesia was also significantly decreased. Conversely, at low doses, analgesia was maintained, but the adverse effects on recovery persisted. A moderate dose of norBNI, however, adequately protected against morphine's adverse effects without eliminating its analgesic efficacy. This suggests that activation of the KOR system plays a significant role in the morphine-induced attenuation of recovery. Our research suggests that morphine, and other opioid analgesics, may be contraindicated for the SCI population. Blocking KOR activity may be a viable strategy for improving the safety of clinical opioid use.

Progressive inflammation-mediated neurodegeneration after traumatic brain or spinal cord injury

Traumatic brain injury (TBI) has been linked to dementia and chronic neurodegeneration. Described initially in boxers and currently recognized across high contact sports, the association between repeated concussion (mild TBI) and progressive neuropsychiatric abnormalities has recently received widespread attention, and has been termed chronic traumatic encephalopathy. Less well appreciated are cognitive changes associated with neurodegeneration in the brain after isolated spinal cord injury. Also under-recognized is the role of sustained neuroinflammation after brain or spinal cord trauma, even though this relationship has been known since the 1950s and is supported by more recent preclinical and clinical studies. These pathological mechanisms, manifested by extensive microglial and astroglial activation and appropriately termed chronic traumatic brain inflammation or chronic traumatic inflammatory encephalopathy, may be among the most important causes of post-traumatic neurodegeneration in terms of prevalence. Importantly, emerging experimental work demonstrates that persistent neuroinflammation can cause progressive neurodegeneration that may be treatable even weeks after traumatic injury.

GLT1 overexpression reverses established neuropathic pain-related behavior and attenuates chronic dorsal horn neuron activation following cervical spinal cord injury

Development of neuropathic pain occurs in a major portion of traumatic spinal cord injury (SCI) patients, resulting in debilitating and often long-term physical and psychological burdens. Following SCI, chronic dysregulation of extracellular glutamate homeostasis has been shown to play a key role in persistent central hyperexcitability of superficial dorsal horn neurons that mediate pain neurotransmission, leading to various forms of neuropathic pain. Astrocytes express the major CNS glutamate transporter, GLT1, which is responsible for the vast majority of functional glutamate uptake, particularly in the spinal cord. In our unilateral cervical contusion model of mouse SCI that is associated with ipsilateral forepaw heat hypersensitivity (a form of chronic at-level neuropathic pain-related behavior), we previously reported significant and long-lasting reductions in GLT1 expression and functional GLT1-mediated glutamate uptake in cervical spinal cord dorsal horn. To therapeutically address GLT1 dysfunction following cervical contusion SCI, we injected an adeno-associated virus type 8 (AAV8)-Gfa2 vector into the superficial dorsal horn to increase GLT1 expression selectively in astrocytes. Compared to both contusion-only animals and injured mice that received AAV8-eGFP control injection, AAV8-GLT1 delivery increased GLT1 protein expression in astrocytes of the injured cervical spinal cord dorsal horn, resulting in a significant and persistent reversal of already-established heat hypersensitivity. Furthermore, AAV8-GLT1 injection significantly reduced expression of the transcription factor and marker of persistently increased neuronal activation, ΔFosB, in superficial dorsal horn neurons. These results demonstrate that focal restoration of GLT1 expression in the superficial dorsal horn is a promising target for treating chronic neuropathic pain following SCI.

Somatosensory phenotype is associated with thalamic metabolites and pain intensity after spinal cord injury

Neuropathic pain is one of the most difficult consequences of spinal cord injury (SCI). The clinical correlates of the underlying mechanisms responsible for neuropathic pain are not well understood, although methods such as quantitative somatosensory testing (QST) or brain imaging have been used to further a mechanism-based understanding of pain. Our previous SCI study demonstrated a significantly lower glutamate-glutamine/myo-inositol ratio (Glx/Ins) in the anterior cingulate cortex in persons with severe neuropathic pain compared with those with less severe neuropathic pain or pain-free, able-bodied controls, suggesting that a combination of decreased glutamatergic metabolism and glial activation may contribute to the development of severe neuropathic pain after SCI. The present study aimed to determine the relationships between somatosensory function below the level of injury and low thalamic Glx/Ins in persons with intense neuropathic pain after SCI. Participants underwent QST and a 3 Tesla proton magnetic resonance spectroscopy. A cluster analysis including SCI participants resulted in 1 group (n = 19) with significantly (P < 0.001) greater pain intensity (6.43 ± 1.63; high neuropathic pain [HNP], and lower Glx/Ins [1.22 ± 0.16]) and another group (n = 35) with lower pain intensity ratings (1.59 ± 1.52, low neuropathic pain [LNP], and higher Glx/Ins [1.47 ± 0.26]). After correcting for age, QST indicated significantly greater somatosensory function in the HNP group compared with the LNP group. Our results are consistent with research suggesting that damage to, but not abolition of, the spinothalamic tract contributes to development of neuropathic pain after SCI and that secondary inflammatory processes may amplify residual spinothalamic tract signals by facilitation, disinhibition, or sensitization.

Human iPS cell-derived astrocyte transplants preserve respiratory function after spinal cord injury

Transplantation-based replacement of lost and/or dysfunctional astrocytes is a promising therapy for spinal cord injury (SCI) that has not been extensively explored, despite the integral roles played by astrocytes in the central nervous system (CNS). Induced pluripotent stem (iPS) cells are a clinically-relevant source of pluripotent cells that both avoid ethical issues of embryonic stem cells and allow for homogeneous derivation of mature cell types in large quantities, potentially in an autologous fashion. Despite their promise, the iPS cell field is in its infancy with respect to evaluating in vivo graft integration and therapeutic efficacy in SCI models. Astrocytes express the major glutamate transporter, GLT1, which is responsible for the vast majority of glutamate uptake in spinal cord. Following SCI, compromised GLT1 expression/function can increase susceptibility to excitotoxicity. We therefore evaluated intraspinal transplantation of human iPS cell-derived astrocytes (hIPSAs) following cervical contusion SCI as a novel strategy for reconstituting GLT1 expression and for protecting diaphragmatic respiratory neural circuitry. Transplant-derived cells showed robust long-term survival post-injection and efficiently differentiated into astrocytes in injured spinal cord of both immunesuppressed mice and rats. However, the majority of transplant-derived astrocytes did not express high levels of GLT1, particularly at early times post-injection. To enhance their ability to modulate extracellular glutamate levels, we engineered hIPSAs with lentivirus to constitutively express GLT1. Overexpression significantly increased GLT1 protein and functional GLT1-mediated glutamate uptake levels in hIPSAs both in vitro and in vivo post-transplantation. Compared to human fibroblast control and unmodified hIPSA transplantation, GLT1-overexpressing hIPSAs reduced (1) lesion size within the injured cervical spinal cord, (2) morphological denervation by respiratory phrenic motor neurons at the diaphragm neuromuscular junction, and (3) functional diaphragm denervation as measured by recording of spontaneous EMGs and evoked compound muscle action potentials. Our findings demonstrate that hiPSA transplantation is a therapeutically-powerful approach for SCI.

Repetitive Treatment with Diluted Bee Venom Attenuates the Induction of Below-Level Neuropathic Pain Behaviors in a Rat Spinal Cord Injury Model

The administration of diluted bee venom (DBV) into an acupuncture point has been utilized traditionally in Eastern medicine to treat chronic pain. We demonstrated previously that DBV has a potent anti-nociceptive efficacy in several rodent pain models. The present study was designed to examine the potential anti-nociceptive effect of repetitive DBV treatment in the development of below-level neuropathic pain in spinal cord injury (SCI) rats. DBV was applied into the Joksamli acupoint during the induction and maintenance phase following thoracic 13 (T13) spinal hemisection. We examined the effect of repetitive DBV stimulation on SCI-induced bilateral pain behaviors, glia expression and motor function recovery. Repetitive DBV stimulation during the induction period, but not the maintenance, suppressed pain behavior in the ipsilateral hind paw. Moreover, SCI-induced increase in spinal glia expression was also suppressed by repetitive DBV treatment in the ipsilateral dorsal spinal cord. Finally, DBV injection facilitated motor function recovery as indicated by the Basso–Beattie–Bresnahan rating score. These results indicate that the repetitive application of DBV during the induction phase not only decreased neuropathic pain behavior and glia expression, but also enhanced locomotor functional recovery after SCI. This study suggests that DBV acupuncture can be a potential clinical therapy for SCI management.

Activation of PI3Kγ/Akt pathway mediates bone cancer pain in rats

Bone cancer pain (BCP) is one of the most common and severe complications in patients suffering from primary bone cancer or metastatic bone cancer such as breast, prostate, or lung, which profoundly compromises their quality of life. Emerging lines of evidence indicate that central sensitization is required for the development and maintenance of BCP. However, the underlying mechanisms are largely unknown. In this study, we investigated the role of PI3Kγ/Akt in the central sensitization in rats with tumor cell implantation in the tibia, a widely used model of BCP. Our results showed that PI3Kγ and its downstream target pAkt were up-regulated in a time-dependent manner and distributed predominately in the superficial layers of the spinal dorsal horn neurons, astrocytes and a minority of microglia, and were colocalized with non-peptidergic, calcitonin gene-related peptide-peptidergic, and A-type neurons in dorsal root ganglion ipsilateral to tumor cell inoculation in rats. Inhibition of spinal PI3Kγ suppressed BCP-associated behaviors and the up-regulation of pAkt in the spinal cord and dorsal root ganglion. This study suggests that PI3Kγ/Akt signal pathway mediates BCP in rats. Central sensitization is required for the development and maintenance of bone cancer pain (BCP). In this study, we reported that PI3Kγ/Akt mediated the function of ephrinBs/EphBs in the central sensitization under BCP condition, and inhibition of spinal PI3Kγ suppressed BCP-associated behaviors. Our results suggest that inhibition of PI3Kγ/Akt may be a new target for the treatment of BCP.

New advances on glial activation in health and disease

In addition to being the support cells of the central nervous system (CNS), astrocytes are now recognized as active players in the regulation of synaptic function, neural repair, and CNS immunity. Astrocytes are among the most structurally complex cells in the brain, and activation of these cells has been shown in a wide spectrum of CNS injuries and diseases. Over the past decade, research has begun to elucidate the role of astrocyte activation and changes in astrocyte morphology in the progression of neural pathologies, which has led to glial-specific interventions for drug development. Future therapies for CNS infection, injury, and neurodegenerative disease are now aimed at targeting astrocyte responses to such insults including astrocyte activation, astrogliosis and other morphological changes, and innate and adaptive immune responses.

Pathogenesis of spinal cord injury induced edema and neuropathic pain: expression of multiple isoforms of wnk1

Background

Neuropathic pain (NP) is a common occurrence following spinal cord injury (SCI). Identification of specific molecular pathways that are involved in pain syndromes has become a major priority in current SCI research. We have investigated the role of a cation-dependent chloride transporter, Cl-regulatory protein Na⁺-K⁺-Cl^- 1 (NKCC1), phosphorylation profile of NKCC1 and its specific involvement in neuropathic pain following contusion SCI (cSCI) using a rat model. Administration of the NKCC1 inhibitor bumetanide (BU) increases the mean hindpaw withdrawal latency time (WLT), thermal hyperalgesia (TH) following cSCI. These results demonstrate implication of NKCC1 co-transporter and BUin SCI-induced neuropathic pain. The with-no-lysine (K)–1 (WNK1) kinase has been shown to be an important regulator of NKCC1 phosphorylation in many systems, including nocioception. Mutations in a neuronal-specific exon of WNK1 (HSN2) was identified in patients that have hereditary sensory neuropathy type II (HSANII) also implicates WNK1 in nocioception, such that these patients have loss of perception to pain, touch and heat. In our ongoing research we proposed two studies utilizing our contusion SCI (cSCI) NP model of rat.

Purpose

Study 1 aimed at NKCC1 expression and activity is up-regulated following cSCI in the early edema and chronic neuropathic pain phases. Study 2 aimed at identifying the expression profile of alternatively spliced WNK1 isoforms in animals exhibiting thermal hyperalgesia (TH) following cSCI.

Methods

Adult male Sprague Dawley rats (275–300 g) following laminectomy received cSCI at T9 with the NYU impactor-device II by dropping 10 g weight from the height of 12.5 mm. Control rats obtained laminectomy but no impaction. Following injury, functional recovery was assessed by BBB locomotor scores on day 1, 7, 14, 21, 35, and 42 and development of thermal hyperalgesia on day 21, 28, 35, and 42 day of injury by monitoring hind paw withdraw latency time (WLT) in seconds compared with the baseline data before injury.

Results

Increased NKCC1 may explain observed increase in magnetic resonance imaging (MRI) T2, exhibiting NKCC1 localization in neurons. This data supports NKCC1’s role in the pathogenesis of acute and chronic phases of injury, namely spinal cord edema and chronic phase neuropathic pain. NKCC1 dependent chloride influx requires the phosphorylation at specific residues. Probing for the HSN2 exon of WNK1 reveals two key findings: i) the HSN2 exon is found in alternatively spliced neuronal isoforms found at 250 kDa and 230 kDa; ii) the 250 kDa isoform is found only in tissue that is injured.

Conclusions

This data implicates the NKCC1/WNK1/WNK1HSN2 involvement in post-injury response that contributes to the development of neuropathic pain. Targeting this system may have therapeutic benefit.

Transplantation of glial progenitors that overexpress glutamate transporter GLT1 preserves diaphragm function following cervical SCI

Approximately half of traumatic spinal cord injury (SCI) cases affect cervical regions, resulting in chronic respiratory compromise. The majority of these injuries affect midcervical levels, the location of phrenic motor neurons (PMNs) that innervate the diaphragm. A valuable opportunity exists following SCI for preventing PMN loss that occurs during secondary degeneration. One of the primary causes of secondary injury is excitotoxicity due to dysregulation of extracellular glutamate homeostasis. Astrocytes express glutamate transporter 1 (GLT1), which is responsible for the majority of CNS glutamate clearance. Given our observations of GLT1 dysfunction post-SCI, we evaluated intraspinal transplantation of Glial-Restricted Precursors (GRPs)--a class of lineage-restricted astrocyte progenitors--into ventral horn following cervical hemicontusion as a novel strategy for reconstituting GLT1 function, preventing excitotoxicity and protecting PMNs in the acutely injured spinal cord. We find that unmodified transplants express low levels of GLT1 in the injured spinal cord. To enhance their therapeutic properties, we engineered GRPs with AAV8 to overexpress GLT1 only in astrocytes using the GFA2 promoter, resulting in significantly increased GLT1 protein expression and functional glutamate uptake following astrocyte differentiation in vitro and after transplantation into C4 hemicontusion. Compared to medium-only control and unmodified GRPs, GLT1-overexpressing transplants reduced lesion size, diaphragm denervation and diaphragm dysfunction. Our findings demonstrate transplantation-based replacement of astrocyte GLT1 is a promising approach for SCI.

Purinergic Modulation of Spinal Neuroglial Maladaptive Plasticity Following Peripheral Nerve Injury

Modulation of spinal reactive gliosis following peripheral nerve injury (PNI) is a promising strategy to restore synaptic homeostasis. Oxidized ATP (OxATP), a nonselective antagonist of purinergic P2X receptors, was found to recover a neuropathic behavior following PNI. We investigated the role of intraperitoneal (i.p.) OxATP treatment in restoring the expression of neuronal and glial markers in the mouse spinal cord after sciatic spared nerve injury (SNI). Using in vivo two-photon microscopy, we imaged Ca(2+) transients in neurons and astrocytes of the dorsal horn of spinal cord at rest and upon right hind paw electrical stimulation in sham, SNI, and OxATP-treated mice. Neuropathic behavior was investigated by von Frey and thermal plantar test. Glial [glial fibrillary acidic protein (GFAP), ionized calcium-binding adaptor molecule 1 (Iba1)] and GABAergic [vesicular GABA transporter (vGAT) and glutamic acid decarboxylase 65/76 (GAD65/67)] markers and glial [glutamate transporter (GLT1) and GLAST] and neuronal amino acid [EAAC1, vesicular glutamate transporter 1 (vGLUT1)] transporters have been evaluated. In SNI mice, we found (i) increased glial response, (ii) decreased glial amino acid transporters, and (iii) increased levels of neuronal amino acid transporters, and (iv) in vivo analysis of spinal neurons and astrocytes showed a persistent increase of Ca(2+) levels. OxATP administration reduced glial activation, modulated the expression of glial and neuronal glutamate/GABA transporters, restored neuronal and astrocytic Ca(2+) levels, and prevented neuropathic behavior. In vitro studies validated that OxATP (i) reduced levels of reactive oxygen species (ROS), (ii) reduced astrocytic proliferation, (iii) increase vGLUT expression. All together, these data support the correlation between reactive gliosis and perturbation of the spinal synaptic homeostasis and the role played by the purinergic system in modulating spinal plasticity following PNI.

Neuroinflammatory contributions to pain after SCI: roles for central glial mechanisms and nociceptor-mediated host defense

Neuropathic pain after spinal cord injury (SCI) is common, often intractable, and can be severely debilitating. A number of mechanisms have been proposed for this pain, which are discussed briefly, along with methods for revealing SCI pain in animal models, such as the recently applied conditioned place preference test. During the last decade, studies of animal models have shown that both central neuroinflammation and behavioral hypersensitivity (indirect reflex measures of pain) persist chronically after SCI. Interventions that reduce neuroinflammation have been found to ameliorate pain-related behavior, such as treatment with agents that inhibit the activation states of microglia and/or astroglia (including IL-10, minocycline, etanercept, propentofylline, ibudilast, licofelone, SP600125, carbenoxolone). Reversal of pain-related behavior has also been shown with disruption by an inhibitor (CR8) and/or genetic deletion of cell cycle-related proteins, deletion of a truncated receptor (trkB.T1) for brain-derived neurotrophic factor (BDNF), or reduction by antisense knockdown or an inhibitor (AMG9810) of the activity of channels (TRPV1 or Nav1.8) important for electrical activity in primary nociceptors. Nociceptor activity is known to drive central neuroinflammation in peripheral injury models, and nociceptors appear to be an integral component of host defense. Thus, emerging results suggest that spinal and systemic effects of SCI can activate nociceptor-mediated host defense responses that interact via neuroinflammatory signaling with complex central consequences of SCI to drive chronic pain. This broader view of SCI-induced neuroinflammation suggests new targets, and additional complications, for efforts to develop effective treatments for neuropathic SCI pain.

[Diagnostic biomarkers in traumatic brain injury]

BACKGROUND

Despite advances in medicine in head trauma management, traumatic brain injury (TBI) still remains a serious health concern, affecting people regardless of age. It is a leading cause of morbidity and mortality particularly in children and young adults. Therefore, studies are being carried out to try to establish reliable biomarkers to improve the accuracy of TBI diagnosis and associated secondary pathologies.

METHODS

Implementation of valid TBI biomarkers could possibly reduce the necessity to use computed cranial tomography (CCT), especially in patients suffering from mild TBI to rule out intracranial bleeding.

AIM

This review provides a critical assessment of biomarkers currently under investigation and their clinical value for the diagnosis, treatment and outcome prediction of TBI.

Gp120 in the pathogenesis of human immunodeficiency virus-associated pain

OBJECTIVE

Chronic pain is a common neurological comorbidity of human immunodeficiency virus (HIV)-1 infection, but the etiological cause remains elusive. The objective of this study was to identify the HIV-1 causal factor that critically contributes to the pathogenesis of HIV-associated pain.

METHODS

We first compared the levels of HIV-1 proteins in postmortem tissues of the spinal cord dorsal horn (SDH) from HIV-1/acquired immunodeficiency syndrome patients who developed chronic pain (pain-positive HIV-1 patients) and HIV-1 patients who did not develop chronic pain (pain-negative HIV-1 patients). Then we used the HIV-1 protein that was specifically increased in the pain-positive patients to generate mouse models. Finally, we performed comparative analyses on the pathological changes in the models and the HIV-1 patients.

RESULTS

We found that HIV-1 gp120 was significantly higher in pain-positive HIV-1 patients (vs pain-negative HIV-1 patients). This finding suggested that gp120 was a potential causal factor of the HIV-associated pain. To test this hypothesis, we used a mouse model generated by intrathecal injection of gp120 and compared the pathologies of the model and the pain-positive human HIV-1 patients. The results showed that the mouse model and pain-positive human HIV-1 patients developed extensive similarities in their pathological phenotypes, including pain behaviors, peripheral neuropathy, glial reactivation, synapse degeneration, and aberrant activation of pain-related signaling pathways in the SDH.

INTERPRETATION

Our findings suggest that gp120 may critically contribute to the pathogenesis of HIV-associated pain.

Identification of potential therapeutic targets in a model of neuropathic pain

Neuropathic pain (NP) is caused by damage to the nervous system, resulting in dysfunction and aberrant pain. The cellular functions (e.g., peripheral neuron spinal cord innervation, neuronal excitability) associated with NP often develop over time and are likely associated with gene expression changes. Gene expression studies on the cells involved in NP (e.g., sensory dorsal root ganglion neurons) are publically available; the mining of these studies may enable the identification of novel targets and the subsequent development of therapies that are essential for improving quality of life for the millions of individuals suffering with NP. Here we analyzed a publically available microarray dataset (GSE30165) in order to identify new RNAs (e.g., messenger RNA (mRNA) isoforms and non-coding RNAs) underlying NP. GSE30165 profiled gene expression in dorsal root ganglion neurons (DRG) and in sciatic nerve (SN) after resection, a NP model. Gene ontological analysis shows enrichment for sensory and neuronal processes. Protein network analysis demonstrates DRG upregulated genes typical to an injury and NP response. Of the top changing genes, 34 and 36% are associated with more than one protein coding isoform in the DRG and SN, respectively. The majority of genes are receptor and enzymes. We identified 15 long non-coding RNAs (lncRNAs) targeting these genes in LNCipedia.org, an online comprehensive lncRNA database. These RNAs represent new therapeutic targets for preventing NP development and this approach demonstrates the feasibility of data reanalysis for their identification.

Chronic at-level thermal hyperalgesia following rat cervical contusion spinal cord injury is accompanied by neuronal and astrocyte activation and loss of the astrocyte glutamate transporter, GLT1, in superficial dorsal horn

Neuropathic pain is a form of pathological nociception that occurs in a significant portion of traumatic spinal cord injury (SCI) patients, resulting in debilitating and often long-term physical and psychological burdens. While many peripheral and central mechanisms have been implicated in neuropathic pain, central sensitization of dorsal horn spinothalamic tract (STT) neurons is a major underlying substrate. Furthermore, dysregulation of extracellular glutamate homeostasis and chronic astrocyte activation play important underlying roles in persistent hyperexcitability of these superficial dorsal horn neurons. To date, central sensitization and astrocyte changes have not been characterized in cervical SCI-induced neuropathic pain models, despite the fact that a major portion of SCI patients suffer contusion trauma to cervical spinal cord. In this study, we have characterized 2 rat models of unilateral cervical contusion SCI that behaviorally result in chronic persistence of thermal hyperalgesia in the ipsilateral forepaw. In addition, we find that STT neurons are chronically activated in both models when compared to laminectomy-only uninjured rats. Finally, persistent astrocyte activation and significantly reduced expression of the major CNS glutamate transporter, GLT1, in superficial dorsal horn astrocytes are associated with both excitability changes in STT neurons and the neuropathic pain behavioral phenotype. In conclusion, we have characterized clinically-relevant rodent models of cervical contusion-induced neuropathic pain that result in chronic activation of both STT neurons and astrocytes, as well as compromise in astrocyte glutamate transporter expression. These models can be used as important tools to further study mechanisms underlying neuropathic pain post-SCI and to test potential therapeutic interventions.

Multidimensional clinical pain phenotypes after spinal cord injury

SUMMARY Persistent neuropathic pain after spinal cord injury (SCI) is a serious problem that significantly affects general health and wellbeing over and above what is caused by other medical consequences after SCI. The ideal approach to the management of the neuropathic pain conditions after SCI would be to identify the primary contributing mechanisms of pain in each person and tailor the treatment to these. However, despite significant basic and clinical research progress, this approach remains elusive. One strategy to further this effort is to define neuropathic pain phenotypes based on pain symptoms, sensory function/dysfunction and psychosocial factors, and determine the relationship between these and treatment outcomes and biomarkers including brain imaging. This approach will facilitate the interaction between basic and clinical science and translational research, further the understanding of the mechanisms that contribute to the development and maintenance of neuropathic pain after SCI, and thus the development of effective mechanisms-based pain treatment strategies.

Activation of spinal phosphatidylinositol 3-kinase/protein kinase B mediates pain behavior induced by plantar incision in mice

The etiology of postoperative pain may be different from antigen-induced inflammatory pain and neuropathic pain. However, central neural plasticity plays a key role in incision pain. It is also known that phosphatidylinositol 3-kinase (PI3K) and protein kinase B/Akt (PKB/Akt) are widely expressed in laminae I-IV of the spinal horn and play a critical role in spinal central sensitization. In the present study, we explored the role of PI3K and Akt in incision pain behaviors. Plantar incision induced a time-dependent activation of spinal PI3K-p110γ and Akt, while activated Akt and PI3K-p110γ were localized in spinal neurons or microglias, but not in astrocytes. Pre-treatment with PI3K inhibitors, wortmannin or LY294002 prevented the activation of Akt brought on by plantar incision in a dose-dependent manner. In addition, inhibition of spinal PI3K signaling pathway prevented pain behaviors (dose-dependent) and spinal Fos protein expression caused by plantar incision. These data demonstrated that PI3K signaling mediated pain behaviors caused by plantar incision in mice.