Neuropathic Pain After Spinal Cord Injury: Challenges and Research Perspectives

Ion channels of cold transduction and transmission

Thermosensation requires the activation of a unique collection of ion channels and receptors that work in concert to transmit thermal information. It is widely accepted that transient receptor potential melastatin 8 (TRPM8) activation is required for normal cold sensing; however, recent studies have illuminated major roles for other ion channels in this important somatic sensation. In addition to TRPM8, other TRP channels have been reported to contribute to cold transduction mechanisms in diverse sensory neuron populations, with both leak- and voltage-gated channels being identified for their role in the transmission of cold signals. Whether the same channels that contribute to physiological cold sensing also mediate noxious cold signaling remains unclear; however, recent work has found a conserved role for the kainite receptor, GluK2, in noxious cold sensing across species. Additionally, cold-sensing neurons likely engage in functional crosstalk with nociceptors to give rise to cold pain. This Review will provide an update on our understanding of the relationship between various ion channels in the transduction and transmission of cold and highlight areas where further investigation is required.

Combined use of CLP290 and bumetanide alleviates neuropathic pain and its mechanism after spinal cord injury in rats

AIM

We aimed to explore whether the combination of CLP290 and bumetanide maximally improves neuropathic pain following spinal cord injury (SCI) and its possible molecular mechanism.

METHODS

Rats were randomly divided into five groups: Sham, SCI + vehicle, SCI + CLP290, SCI + bumetanide, and SCI + combination (CLP290 + bumetanide). Drug administration commenced on the 7th day post-injury (7 dpi) and continued for 14 days. All rats underwent behavioral assessments for 56 days to comprehensively evaluate the effects of interventions on mechanical pain, thermal pain, cold pain, motor function, and other relevant parameters. Electrophysiological assessments, immunoblotting, and immunofluorescence detection were performed at different timepoints post-injury, with a specific focus on the expression and changes of KCC2 and NKCC1 proteins in the lumbar enlargement of the spinal cord.

RESULTS

CLP290 and bumetanide alleviated SCI-associated hypersensitivity and locomotor function, with the combination providing enhanced recovery. The combined treatment group exhibited the most significant improvement in restoring Rate-Dependent Depression (RDD) levels. In the combined treatment group and the two individual drug administration groups, the upregulation of potassium chloride cotransporter 2 (K+-Cl-cotransporter 2, KCC2) expression and downregulation of sodium potassium chloride cotransporter 1 (Na+-K+-Cl-cotransporter 1, NKCC1) expression in the lumbar enlargement area resulted in a significant increase in the KCC2/NKCC1 ratio compared to the SCI + vehicle group, with the most pronounced improvement seen in the combined treatment group. Compared to the SCI + vehicle group, the SCI + bumetanide group showed no significant paw withdrawal thermal latency (PWTL) improvement at 21 and 35 dpi, but a notable enhancement at 56 dpi. In contrast, the SCI + CLP290 group significantly improved PWTL at 21 days, with non-significant changes at 35 and 56 days. At 21 dpi, KCC2 expression was marginally higher in monotherapy groups versus SCI + vehicle, but not significantly. At 56 dpi, only the SCI + bumetanide group showed a significant difference in KCC2 expression compared to the control group.

CONCLUSION

Combined application of CLP290 and bumetanide effectively increases the ratio of KCC2/NKCC1, restores RDD levels, enhances GABAA receptor-mediated inhibitory function in the spinal cord, and relieves neuropathic pain in SCI; Bumetanide significantly improves neuropathic pain in the long term, whereas CLP290 demonstrates a notable short-term effect.

Reliability and validity of simplified Chinese version of Spinal Cord Injury Pain Instrument in patients with spinal cord injury in mainland China

PURPOSE

To cross-culturally adapt the Spinal Cord Injury Pain Instrument (SCIPI) into a simplified Chinese version (SC-SCIPI) and verify reliability and validity in screening for neuropathic pain in SCI patients.

METHODS

A preliminary validation study was conducted to screen for neuropathic pain after SCI using SCIPI. A total of 130 patients with SCI treated at Shanghai Changhai Hospital were enrolled. Results for internal consistency, reliability and construct validity were compared with those of the Douleur Neuropathique (DN4), Leeds Assessment of Neuropathic Pain Questionnaire (LANSS), Neuropathic Pain Questionnaire (NPQ), ID Pain scale and VAS pain scale.

RESULTS

The SCIPI was successfully translated into Chinese and expert consensus was reached on final adapted version of SC-SCIPI. For test-retest, SC-SCIPI total score was 2.35 ± 1.75 in first round and 2.35 ± 1.76 in second round. Cronbach α coefficient of SC-SCIPI was 0.909, indicating good internal consistency. Pearson correlation coefficient (r) showed that SC-SCIPI correlated well with LANSS, DN4, NPQ and ID pain; and correlated fairly well with VAS, indicating good construct validity.

CONCLUSION

SC-SCIPI demonstrates excellent internal consistency, reliability and good construct validity in Chinese patients with neuropathic pain, suggesting that SC-SCIPI is applicable in clinical practice to screen patients for neuropathic pain. IMPLICATION FOR REHABILITATIONThe Spinal Cord Injury pain Instrument has been cross-culturally adapted into a simplified Chinese version (SC-SCIPI).The SC-SCIPI showed excellent test-retest reliability and good construct validity.The 4-item SC-SCIPI is quite convenient to complete and it might be a useful instrument for routine application in patients with SCI for rehabilitation.

Neuronal repair after spinal cord injury by in vivo astrocyte reprogramming mediated by the overexpression of NeuroD1 and Neurogenin-2

BACKGROUND

As a common disabling disease, irreversible neuronal death due to spinal cord injury (SCI) is the root cause of functional impairment; however, the capacity for neuronal regeneration in the developing spinal cord tissue is limited. Therefore, there is an urgent need to investigate how defective neurons can be replenished and functionally integrated by neural regeneration; the reprogramming of intrinsic cells into functional neurons may represent an ideal solution.

METHODS

A mouse model of transection SCI was prepared by forceps clamping, and an adeno-associated virus (AAV) carrying the transcription factors NeuroD1 and Neurogenin-2(Ngn2) was injected in situ into the spinal cord to specifically overexpress these transcription factors in astrocytes close to the injury site. 5-bromo-2´-deoxyuridine (BrdU) was subsequently injected intraperitoneally to continuously track cell regeneration, neuroblasts and immature neurons marker expression, neuronal regeneration, and glial scar regeneration. In addition, immunoprotein blotting was used to measure the levels of transforming growth factor-β (TGF-β) pathway-related protein expression. We also evaluated motor function, sensory function, and the integrity of the blood-spinal cord barrier(BSCB).

RESULTS

The in situ overexpression of NeuroD1 and Ngn2 in the spinal cord was achieved by specific AAV vectors. This intervention led to a significant increase in cell regeneration and the proportion of cells with neuroblasts and immature neurons cell properties at the injury site(p < 0.0001). Immunofluorescence staining identified astrocytes with neuroblasts and immature neurons cell properties at the site of injury while neuronal marker-specific staining revealed an increased number of mature astrocytes at the injury site. Behavioral assessments showed that the intervention did not improve The BMS (Basso mouse scale) score (p = 0.0726) and gait (p > 0.05), although the treated mice had more sensory sensitivity and greater voluntary motor ability in open field than the non-intervention mice. We observed significant repair of the BSCB at the center of the injury site (p < 0.0001) and a significant improvement in glial scar proliferation. Electrophysiological assessments revealed a significant improvement in spinal nerve conduction (p < 0.0001) while immunostaining revealed that the levels of TGF-β protein at the site of injury in the intervention group were lower than control group (p = 0.0034); in addition, P70 s6 and PP2A related to the TGF-β pathway showed ascending trend (p = 0.0036, p = 0.0152 respectively).

CONCLUSIONS

The in situ overexpression of NeuroD1 and Ngn2 in the spinal cord after spinal cord injury can reprogram astrocytes into neurons and significantly enhance cell regeneration at the injury site. The reprogramming of astrocytes can lead to tissue repair, thus improving the reduced threshold and increasing voluntary movements. This strategy can also improve the integrity of the blood-spinal cord barrier and enhance nerve conduction function. However, the simple reprogramming of astrocytes cannot lead to significant improvements in the striding function of the lower limbs.

Randomised, double-blind, placebo-controlled, parallel-group, multicentric, phase IIA clinical trial for evaluating the safety, tolerability, and therapeutic efficacy of daily oral administration of NFX88 to treat neuropathic pain in individuals with spinal cord injury

STUDY DESIGN

Double-blind, randomized, placebo-controlled, parallel-group multicentric phase IIA clinical trial.

OBJECTIVE

To assess the safety and tolerability of oral administration of NFX-88 in subjects with chronic spinal cord injury (SCI) and explore its efficacy in pain control.

SETTING

A total of 7 spinal cord injury rehabilitation units in Spain.

METHODS

A total of 61 adult with traumatic complete or incomplete spinal cord injury (C4-T12 level), were randomised 1:1:1:1 to a placebo, NFX88 1.05 g, 2.1 g, 4.2 g/day for up to 12 weeks. The placebo or NFX-88 was administered as add-on therapy to pre-existing pregabalin (150-300 mg per day). Safety and tolerability were evaluated, and the Visual Analogue Scale (VAS) was the primary measure to explore the efficacy of NFX-88 in pain control.

RESULTS

No severe treatment-related adverse effects were reported for any of the four study groups. 44 SCI individuals completed the study and were analysed. The data obtained from the VAS analysis and the PainDETECT Questionnaire (PD-Q) suggested that the combination of NFX88 with pregabalin is more effective than pregabalin with placebo at reducing neuropathic pain (NP) in individuals with SCI and that the dose 2.10 g/day causes the most dramatic pain relief.

CONCLUSIONS

NFX88 treatment was found to be highly safe and well tolerated, with the dose of 2.10 g/day being the most effective at causing pain relief. Thus, the promising efficacy of this first-in-class lipid mediator deserves further consideration in future clinical trials.

Communicating pain: emerging axonal signaling in peripheral neuropathic pain

Peripheral nerve damage often leads to the onset of neuropathic pain (NeuP). This condition afflicts millions of people, significantly burdening healthcare systems and putting strain on families' financial well-being. Here, we will focus on the role of peripheral sensory neurons, specifically the Dorsal Root Ganglia neurons (DRG neurons) in the development of NeuP. After axotomy, DRG neurons activate regenerative signals of axons-soma communication to promote a gene program that activates an axonal branching and elongation processes. The results of a neuronal morphological cytoskeleton change are not always associated with functional recovery. Moreover, any axonal miss-targeting may contribute to NeuP development. In this review, we will explore the epidemiology of NeuP and its molecular causes at the level of the peripheral nervous system and the target organs, with major focus on the neuronal cross-talk between intrinsic and extrinsic factors. Specifically, we will describe how failures in the neuronal regenerative program can exacerbate NeuP.

The effect of neuropathic pain treatments on pain interference following spinal cord injury: A systematic review

CONTEXT

Neuropathic pain is a common and debilitating condition following SCI. While treatments for neuropathic pain intensity have been reviewed, the impact on pain interference has not been summarized.

OBJECTIVE

To systematically review the effect of neuropathic pain interventions on pain interference in individuals with spinal cord injury.

METHODS

This systematic review included randomized controlled trials and quasi-experimental (non-randomized) studies which assessed the impact of an intervention on pain interference in individuals with spinal cord injury and neuropathic pain. Articles were identified by searching MEDLINE (1996 to April 11, 2022), EMBASE (1996 to April 11, 2022), PsycInfo (1987 to April, week 2, 2022). Studies were assessed for methodologic quality using a modified GRADE approach and were given quality of evidence (QOE) scores on a 4-point scale ranging from very low to high.

RESULTS

Twenty studies met the inclusion criteria. These studies fell into the following categories: anticonvulsants (n = 2), antidepressants (n = 1), analgesics (n = 1), antispasmodics (n = 1), acupuncture (n = 2), transcranial direct current stimulation (n = 1), active cranial electrotherapy stimulation (n = 2), transcutaneous electrical nerve stimulation (n = 2), repetitive transcranial magnetic stimulation (n = 1), functional electrical stimulation (n = 1), meditation and imagery (n = 1), self-hypnosis and biofeedback (n = 1), and interdisciplinary pain programs (n = 4).

CONCLUSION

When considering studies of moderate to high quality, pregabalin, gabapentin, intrathecal baclofen, transcranial direct current stimulation, and transcutaneous electrical nerve stimulation (in 1 of 2 studies) were shown to have beneficial effects on pain interference. However, due to the low number of high-quality studies further research is required to confirm the efficacy of these interventions prior to recommending their use to reduce pain interference.

Spinal Cord Stimulation for Central Neuropathic Pain After Spinal Cord Injury: A Single-Center Case Series

Purpose

Central neuropathic pain (CNP) following spinal cord injury (SCI) presents a formidable therapeutic challenge, affecting over 50% of the patients post-SCI. For those who experience CNP, conventional treatments often prove insufficient. Spinal cord stimulation (SCS) emerges as a potential intervention for chronic pain after SCI that is unresponsive to pharmacotherapy and supportive measures. However, the efficacy of SCS in alleviating CNP is notably limited. The objective of our study was to evaluate novel stimulation paradigms in SCS for patients with severe CNP after SCI, based on our extensive experience.

Patients and Methods

From a pool of 112 patients treated with SCS for chronic neuropathic pain in the Department of Neurosurgery and Neurology, we selected eight individuals (4 males and 4 females) with CNP for our case series. Burst and high frequency SCS was applied. The assessment involved utilizing the Numeric Rating Scale (NRS), the Neuropathic Pain Symptom Inventory (NPSI), and the EQ-5D quality of life scale before surgery and during a 12-month follow-up period.

Results

Over the course of the one-year follow-up, only two patients experienced satisfactory relief from pain, demonstrating the effectiveness of the stimulation. Moreover, high-frequency and burst SCS failed to show improvement in the remaining six patients.

Conclusion

Our findings suggest that, despite the incorporation of new stimulation paradigms such as burst stimulation and high-frequency stimulation, SCS does not exhibit significant effectiveness in treating neuropathic pain in patients after SCI. These findings highlight the ongoing challenge of treating CNP and emphasize the importance of investigating alternative therapeutic strategies for this group.

Positive Correlation Between Motor Function and Neuropathic Pain-Like Behaviors After Spinal Cord Injury: A Longitudinal Study of Mice

Abstract With the recovery of motor function, some spinal cord injury (SCI) patients still suffer from severe pain-like behaviors symptoms. Whether motor function correlates with neuropathic pain-like behaviors remain unclear. In this study, a longitudinal cohort study of mice with moderate thoracic 10 contusion was performed to explore the characteristics of neuropathic pain-like behaviors and its correlation with motor function in different sexes. Pain-like behaviors data up to 42 days post-injury (dpi) were collected and compared. Mice of both sexes were divided into three groups based on their Basso Mouse Scale at 42 dpi. There was no significant difference in motor function recovery between the sexes. Female mice showed more significant mechanical allodynia than males at 14 dpi, which was sustained until 42 dpi without significant dynamic changes. However, males showed a gradually worsening state and more severe mechanical allodynia than females at 28 dpi, and then the differences disappeared. Interestingly, male mice obtained more severe cold hyperalgesia symptoms than females. Additionally, we found that there was a correlation between the occurrence of mechanical allodynia and cold and thermal hyperalgesia. Importantly, motor function recovery was positively associated with the outcomes of neuropathic pain-like behaviors after SCI, which was more obvious in female mice. Our data not only revealed the characteristics of neuropathic pain-like behaviors but also clarified the correlations between motor function recovery and neuropathic pain-like behaviors after SCI. These findings may provide new opinions and suggestions for promoting the clinical diagnosis and treatment of neuropathic pain-like behaviors after SCI.

Chemogenetic Attenuation of Acute Nociceptive Signaling Enhances Functional Outcomes Following Spinal Cord Injury

Identifying novel therapeutic approaches to promote recovery of neurological functions following spinal cord injury (SCI) remains a great unmet need. Nociceptive signaling in the acute phase of SCI has been shown to inhibit recovery of locomotor function and promote the development of chronic neuropathic pain. We therefore hypothesized that inhibition of nociceptive signaling in the acute phase of SCI might improve long-term functional outcomes in the chronic phase of injury. To test this hypothesis, we took advantage of a selective strategy utilizing AAV6 to deliver inhibitory (hM4Di) Designer Receptors Exclusively Activated by Designer Drugs (DREADDs) to nociceptors of the L4-L6 dorsal root ganglia to evaluate the effects of transient nociceptor silencing on long-term sensory and motor functional outcomes in a rat thoracic contusion SCI model. Following hM4Di-mediated nociceptor inhibition from 0-14 days post-SCI, we conducted behavioral assessments until 70 days post-SCI, then performed histological assessments of lesion severity and axon plasticity. Our results show highly selective expression of hM4Di within small diameter nociceptors including calcitonin gene-related peptide (CGRP)+ and IB4-binding neurons. Expression of hM4Di in less than 25% of nociceptors was sufficient to increase hindlimb thermal withdrawal latency in naïve rats. Compared with subjects who received AAV-yellow fluorescent protein (YFP; control), subjects who received AAV-hM4Di exhibited attenuated thermal hyperalgesia, greater coordination, and improved hindlimb locomotor function. However, treatment did not impact the development of cold allodynia or mechanical hyperalgesia. Histological assessments of spinal cord tissue suggested trends toward reduced lesion volume, increased neuronal sparing and increased CGRP+ axon sprouting in hM4Di-treated animals. Together, these findings suggest that nociceptor silencing early after SCI may promote beneficial plasticity in the acute phase of injury that can impact long-term functional outcomes, and support previous work highlighting primary nociceptors as possible therapeutic targets for pain management after SCI.

Anxiety and Depression in Pediatric-Onset Traumatic Spinal Cord Injury: A Systematic Review

BACKGROUND

Traumatic spinal cord injury (TSCI) is a debilitating neurological condition with significant long-term consequences on the mental health and well-being of affected individuals. We aimed to investigate anxiety and depression in individuals with pediatric-onset TSCI.

METHODS

PubMed, Scopus, and Web of Science databases were searched from inception to December 20th, 2022 following the Preferred Reporting Items for Systematic Reviews and Meta-Analysis guidelines, and studies were included according to the eligibility criteria.

RESULTS

A total of 1013 articles were screened, and 18 studies with 4234 individuals were included in the final review. Of these, 1613 individuals (38.1%) had paraplegia, whereas 1658 (39.2%) had tetraplegia. A total of 1831 participants (43.2%) had complete TSCI, whereas 1024 (24.2%) had incomplete TSCI. The most common etiology of TSCI with 1545 people (36.5%) was motor vehicle accidents. The youngest mean age at the time of injury was 5.92 ± 4.92 years, whereas the oldest was 14.6 ± 2.8 years. Patient Health Questionnaire-9 was the most common psychological assessment used in 9 studies (50.0%). Various risk factors, including pain in 4 studies (22.2%), reduced sleep quality, reduced functional independence, illicit drug use, incomplete injury, hospitalization, reduced quality of life, and duration of injury in 2 (11.1%) studies, each, were associated with elevated anxiety and depression.

CONCLUSIONS

Different biopsychosocial risk factors contribute to elevated rates of anxiety and depression among individuals with pediatric-onset TSCI. Individuals at risk of developing anxiety and depression should be identified, and targeted support should be provided. Future large-scale studies with long-term follow-up are required to validate and extend these findings.

Higher Regional Gray Matter Volume and White Matter Integrity in Individuals With Central Neuropathic Pain After Spinal Cord Injury

Spinal cord injury (SCI) is a debilitating neurological condition that often leads to central neuropathic pain (CNP). As the fundamental mechanism of CNP is not fully established, its management is one of the most challenging problems among people with SCI. To shed more light on CNP mechanisms, the aim of this cross-sectional study was to compare the brain structure between individuals with SCI and CNP and those without CNP by examining the gray matter (GM) volume and the white matter (WM) integrity. Fifty-two individuals with SCI-28 with CNP and 24 without CNP-underwent a magnetic resonance imaging (MRI) session, including a T1-weighted scan for voxel-based morphometry, and a diffusion-weighted imaging (DWI) scan for WM integrity analysis, as measured by fractional anisotropy (FA) and mean diffusivity (MD). We found significantly higher GM volume in individuals with CNP compared with pain-free individuals in the right superior (p < 0.0014) and middle temporal gyri (p < 0.0001). Moreover, individuals with CNP exhibited higher WM integrity in the splenium of the corpus callosum (p < 0.0001) and in the posterior cingulum (p < 0.0001), compared with pain-free individuals. The results suggest that the existence of CNP following SCI is associated with GM and WM structural abnormalities in regions involved in pain intensification and spread, and which may reflect maladaptive neural plasticity in CNP.

Transient Receptor Potential Channels: Multiple Modulators of Peripheral Neuropathic Pain in Several Rodent Models

Neuropathic pain, a prevalent chronic condition in clinical settings, has attracted widespread societal attention. This condition is characterized by a persistent pain state accompanied by affective and cognitive disruptions, significantly impacting patients' quality of life. However, current clinical therapies fall short of addressing its complexity. Thus, exploring the underlying molecular mechanism of neuropathic pain and identifying potential targets for intervention is highly warranted. The transient receptor potential (TRP) receptors, a class of widely distributed channel proteins, in the nervous system, play a crucial role in sensory signaling, cellular calcium regulation, and developmental influences. TRP ion channels are also responsible for various sensory responses including heat, cold, pain, and stress. This review highlights recent advances in understanding TRPs in various rodent models of neuropathic pain, aiming to uncover potential therapeutic targets for clinical management.

Cypin Inhibition as a Therapeutic Approach to Treat Spinal Cord Injury-Induced Mechanical Pain

Cypin (cytosolic postsynaptic density protein 95 interactor) is the primary guanine deaminase in the central nervous system (CNS), promoting the metabolism of guanine to xanthine, an important reaction in the purine salvage pathway. Activation of the purine salvage pathway leads to the production of uric acid (UA). UA has paradoxical effects, specifically in the context of CNS injury as it confers neuroprotection, but it also promotes pain. Since neuropathic pain is a comorbidity associated with spinal cord injury (SCI), we postulated that small molecule cypin inhibitor B9 treatment could attenuate SCI-induced neuropathic pain, potentially by interfering with UA production. However, we also considered that this treatment could hinder the neuroprotective effects of UA and, in doing so, exacerbate SCI outcomes. To address our hypothesis, we induced a moderate midthoracic contusion SCI in female mice and assessed whether transient intrathecal administration of B9, starting at 1 d postinjury (dpi) until 7 dpi, attenuates mechanical pain in hindlimbs at 3 weeks pi. We also evaluated the effects of B9 on the spontaneous recovery of locomotor function. We found that B9 alleviates mechanical pain but does not affect locomotor function. Importantly, B9 does not exacerbate lesion volume at the epicenter. In accordance with these findings, B9 does not aggravate glutamate-induced excitotoxic death of SC neurons in vitro. Moreover, SCI-induced increased astrocyte reactivity at the glial scar is not altered by B9 treatment. Our data suggest that B9 treatment reduces mechanical pain without exerting major detrimental effects following SCI.

Comprehensive and Visualized Analysis of Interventional Clinical Trials of Spinal Cord Injury in the Past Two Decades: A Bibliometric Study

OBJECTIVE

The aim of this study was to provide a bibliometric analysis of reported clinical trials of interventional spinal cord injury (SCI) and present the current status, global trends, and scholars' knowledge in this field.

METHODS

Data were obtained from PubMed and Web of Science (WOS) Core Collection. A literature screening process was conducted to select reports of interventional SCI clinical trials. Qualitative and quantitative analysis was performed based on information from the WOS database. Co-occurrence analysis of keywords, collaboration analysis, and co-citation analysis were performed using VOSviewer.

RESULTS

A total of 849 articles were selected for analysis. Therapeutic strategies in the articles were classified into 10 subgroups. Locomotor training, local complication-related treatments, and neuromodulation are the top 3 subgroups. Spinal Cord was the most productive and most frequently cited journal in SCI clinical trials. The most productive country, institution, and author are the United States, the University of Miami, and Harvey LA, respectively. The collaboration network analysis shows that researchers and institutions from the United States, Canada, the United Kingdom, and Australia were the pivotal driving forces in this field. Spinal cord injury, rehabilitation, individuals, electrical stimulation, and exercise are the top 5 most frequent keywords. The co-citation analysis shows that the most frequently cited references are all international standards and guidelines of SCI clinical trials.

CONCLUSIONS

There is a broad research collaboration network, although it is distributed unevenly worldwide. International standards and guidelines are needed to conduct high-quality clinical trials in the future.

The oral administration of Lotus corniculatus L. attenuates acute and chronic pain models in male rats

ETHNOPHARMACOLOGICAL RELEVANCE

Lotus corniculatus L. (Fabaceae) traditionally used in Persian folk medicine to heal peritoneal inflammation and back pain.

AIM OF THE STUDY

To explore the antinociceptive (acute pain) and anti-neuropathic (chronic pain) activities of Lotus corniculatus leaves essential oil (LCEO) in addition to uncovering the possible mechanisms of antinociception.

MATERIALS AND METHODS

LCEO as well as the pure oleanolic acid (OA) compound, were assayed for their effects on acute (formalin induced paw licking test or FIPT) and chronic (cervical contusion injury models on the fifth cervical vertebra or CCS; 14-day intervals) pain. The possible involvements of NO-cGMP-K+ channel, TRPV, dopamine, cannabinoid, PPAR, adrenergic, and opioid mechanisms in the antinociceptive activity of LCEO have studied by formalin test. The levels of p53 and inflammatory markers were measured using a streptavidin biotin immune peroxidase complex and ELISA methods, respectively.

RESULTS

The LCEO and OA exerted antinociceptive activity in the first-phase of FIPT. Pretreatment with antagonists of TRPV1, dopamine D2, cannabinoid type1 and 2, and NO-cGMP-K+ channel blockers (glibenclamide, L-NAME and methylene blue) attenuated the antinociceptive effect of LCEO in FIPT. In addition, LCEO and OA meaningfully reduced hyperalgesia (days 6-14) and mechanical allodynia (days 2-14) in the CCS model. LCEO suppressed the apoptotic marker (p53) in CCS model and also ameliorated IL-2, TNF-α, and IL-1 in the spinal cord.

CONCLUSION

Finally, LCEO inhibited acute (possibly via the modulation of opioid, TRPV, dopamine, cannabinoid mechanisms as well as NO-cGMP-K+ channel) and chronic pain (via suppressing apoptotic and inflammatory markers) in male rats. The results also suggest that OA has analgesic activity against acute and chronic pain conditions.

Impact of inflammation and Treg cell regulation on neuropathic pain in spinal cord injury: mechanisms and therapeutic prospects

Spinal cord injury is a severe neurological trauma that can frequently lead to neuropathic pain. During the initial stages following spinal cord injury, inflammation plays a critical role; however, excessive inflammation can exacerbate pain. Regulatory T cells (Treg cells) have a crucial function in regulating inflammation and alleviating neuropathic pain. Treg cells release suppressor cytokines and modulate the function of other immune cells to suppress the inflammatory response. Simultaneously, inflammation impedes Treg cell activity, further intensifying neuropathic pain. Therefore, suppressing the inflammatory response while enhancing Treg cell regulatory function may provide novel therapeutic avenues for treating neuropathic pain resulting from spinal cord injury. This review comprehensively describes the mechanisms underlying the inflammatory response and Treg cell regulation subsequent to spinal cord injury, with a specific focus on exploring the potential mechanisms through which Treg cells regulate neuropathic pain following spinal cord injury. The insights gained from this review aim to provide new concepts and a rationale for the therapeutic prospects and direction of cell therapy in spinal cord injury-related conditions.

The Role of Interleukin-10 in the Pathogenesis and Treatment of a Spinal Cord Injury

Spinal cord injury (SCI) is a devastating condition that often leads to severe and permanent neurological deficits. The complex pathophysiology of an SCI involves a cascade of events, including inflammation, oxidative stress, and secondary injury processes. Among the myriad of molecular players involved, interleukin-10 (IL-10) emerges as a key regulator with the potential to modulate both the inflammatory response and promote neuroprotection. This comprehensive review delves into the intricate interplay of IL-10 in the pathogenesis of an SCI and explores its therapeutic implications in the quest for effective treatments. IL-10 has been found to regulate inflammation, oxidative stress, neuronal apoptosis, and glial scars after an SCI. Its neuroprotective properties have been evaluated in a plethora of animal studies. IL-10 administration, either isolated or in combination with other molecules or biomaterials, has shown neuroprotective effects through a reduction in inflammation, the promotion of tissue repair and regeneration, the modulation of glial scar formation, and improved functional outcomes. In conclusion, IL-10 emerges as a pivotal player in the pathogenesis and treatment of SCIs. Its multifaceted role in modulating inflammation, oxidative stress, neuronal apoptosis, glial scars, and neuroprotection positions IL-10 as a promising therapeutic target. The ongoing research exploring various strategies for harnessing the potential of IL-10 offers hope for the development of effective treatments that could significantly improve outcomes for individuals suffering from spinal cord injuries. As our understanding of IL-10's intricacies deepens, it opens new avenues for innovative and targeted therapeutic interventions, bringing us closer to the goal of alleviating the profound impact of SCIs on patients' lives.

Biodegradable nanoparticles targeting circulating immune cells reduce central and peripheral sensitization to alleviate neuropathic pain following spinal cord injury

ABSTRACT

Neuropathic pain is a critical source of comorbidity following spinal cord injury (SCI) that can be exacerbated by immune-mediated pathologies in the central and peripheral nervous systems. In this article, we investigate whether drug-free, biodegradable, poly(lactide- co -glycolide) (PLG) nanoparticle treatment mitigates the development of post-SCI neuropathic pain in female mice. Our results show that acute treatment with PLG nanoparticles following thoracic SCI significantly reduces tactile and cold hypersensitivity scores in a durable fashion. Nanoparticles primarily reduce peripheral immune-mediated mechanisms of neuropathic pain, including neuropathic pain-associated gene transcript frequency, transient receptor potential ankyrin 1 nociceptor expression, and MCP-1 (CCL2) chemokine production in the subacute period after injury. Altered central neuropathic pain mechanisms during this period are limited to reduced innate immune cell cytokine expression. However, in the chronic phase of SCI, nanoparticle treatment induces changes in both central and peripheral neuropathic pain signaling, driving reductions in cytokine production and other immune-relevant markers. This research suggests that drug-free PLG nanoparticles reprogram peripheral proalgesic pathways subacutely after SCI to reduce neuropathic pain outcomes and improve chronic central pain signaling.

Gabapentin improves neuropathic pain in Minamata disease model rats

BACKGROUND

Methylmercury (MeHg), the causative agent of Minamata disease, damages the cranial nervous system and causes specific sensory disturbances, especially hypoesthesia, in the extremities. However, recent reports demonstrate that patients with chronic Minamata disease conversely develop neuropathic pain in the lower extremities. Studies on our established Minamata disease model rats showed that MeHg-mediated neurodegeneration might induce neuropathic pain by over time through inducing rewiring with neuronal activation in the somatosensory cortex via microglial activation in the spinal dorsal horn.

METHODS

In this study, the effects of gabapentin, a potentially effective treatment for neuropathic pain, was evaluated using this Minamata disease model rats. To further elucidate the mechanism of its medicinal effects, histochemical and biochemical analyses of the nervous system of Minamata disease model rats were conducted.

RESULTS

Gabapentin treatment restored the reduction in the pain threshold caused by MeHg exposure in rats. Histochemical and biochemical analyses revealed that gabapentin showed no effect on MeHg-induced neurodegeneration in entire nervous system and microglial activation in the spinal dorsal horn. However, it was shown that gabapentin may reduce excessive synaptogenesis through its antagonist action on the alpha2-delta-1 subunit of calcium channels in the somatosensory cortex.

CONCLUSIONS

These results indicate that gabapentin may alleviated neuropathic pain in MeHg poisoning, as typified by Minamata disease, by reversibly modulation synaptic rewiring in the somatosensory cortex.

Combination Gene Delivery Reduces Spinal Cord Pathology in Rats With Peripheral Neuropathic Pain

Although peripheral neuropathic pain is caused by peripheral nerve injury, it is not simply a peripheral nervous system disease. It causes abnormalities in both the central and peripheral nervous systems. Pathological phenomena, such as hyperactivation of sensory neurons and inflammation, are observed in both the dorsal root ganglion and spinal cord. Pain signals originating from the periphery are transmitted to the brain via the SC, and the signals are modulated by pathologically changing SC conditions. Therefore, the modulation of SC pathology is important for peripheral NP treatment. We investigated the effects of KLS-2031 (recombinant adeno-associated viruses expressing glutamate decarboxylase 65, glial cell-derived neurotrophic factor, and interleukin-10) delivered to the dorsal root ganglion on aberrant neuronal excitability and neuroinflammation in the SC of rats with peripheral NP. Results showed that KLS-2031 administration restored excessive excitatory transmission and inhibitory signals in substantia gelatinosa neurons. Moreover, KLS-2031 restored the in vivo hypersensitivity of wide dynamic range neurons and mitigated neuroinflammation in the SC by regulating microglia and astrocytes. Collectively, these findings demonstrated that KLS-2031 efficiently suppressed pathological pain signals and inflammation in the SC of peripheral NP model, and is a potential novel therapeutic approach for NP in clinical settings. PERSPECTIVE: Our study demonstrated that KLS-2031, a combination gene therapy delivered by transforaminal epidural injection, not only mitigates neuroinflammation but also improves SC neurophysiological function, including excitatory-inhibitory balance. These findings support the potential of KLS-2031 as a novel modality that targets multiple aspects of the complex pathophysiology of neuropathic pain.

IL-6/JAK2/STAT3 axis mediates neuropathic pain by regulating astrocyte and microglia activation after spinal cord injury

After spinal cord injury (SCI), the control of activated glial cells such as microglia and astrocytes has emerged as a promising strategy for neuropathic pain management. However, signaling mechanism involved in glial activation in the process of neuropathic pain development and maintenance after SCI is not well elucidated. In this study, we investigated the potential role and mechanism of the JAK2/STAT3 pathway associated with glial cell activation in chronic neuropathic pain development and maintenance after SCI. One month after contusive SCI, the activation of JAK2/STAT3 pathway was markedly upregulated in both microglia and astrocyte in nociceptive processing regions of the lumbar spinal cord. In addition, both mechanical allodynia and thermal hyperalgesia was significantly inhibited by a JAK2 inhibitor, AG490. In particular, AG490 treatment inhibited both microglial and astrocyte activation in the lumbar (L) 4-5 dorsal horn and significantly decreased levels of p-p38MAPK, p-ERK and p-JNK, which are known to be activated in microglia (p-p38MAPK and p-ERK) and astrocyte (p-JNK). Experiments using primary cell cultures also revealed that the JAK2/STAT3 pathway promoted microglia and astrocyte activation after lipopolysaccharide stimulation. Furthermore, JAK2/STAT3 signaling and pain behaviors were significantly attenuated when the rats were treated with anti-IL-6 antibody. Finally, minocycline, a tetracycline antibiotic, inhibited IL-6/JAK2/STAT3 signaling pathway in activated glial cells and restored nociceptive thresholds and the hyperresponsiveness of dorsal neurons. These results suggest an important role of the IL-6/JAK2/STAT3 pathway in the activation of microglia and astrocytes and in the maintenance of chronic below-level pain after SCI.

Development of a pain self-management intervention framework for people with spinal cord injury

BACKGROUND

 Pain is the most common reason for medical visits to primary health care practitioners. Pain self-management interventions are encouraged and there is no known self-management intervention framework available that clinicians and people with spinal cord injury (PWSCI) can use to guide treatment selection.

AIM

 This study aimed to develop a pain self-management intervention framework for PWSCI.

SETTING

 Online and facilitated in Gauteng, South Africa.

METHODS

 A three-round modified e-Delphi method was used to reach an 80% consensus among a 21-expert panel. Fifty-nine interventions were distributed via REDCap and a final online audio meeting was held to either include or exclude interventions in the final framework. SPSS v27 was used to analyse descriptive data and content analysis was used for qualitative responses.

RESULTS

 The final developed pain self-management framework consists of 56 interventions and includes interventions from multiple health professions to encompass medical, psychological, therapeutic and social interventions. Interventions are also specified for nociceptive and/or neuropathic pain and grouped according to the biopsychosocial model.

CONCLUSION

 The interprofessional framework may be used as a guideline for PWSCI to alleviate pain, as well as assist health professionals in clinical decision-making, by providing them with the freedom to choose acceptable and adequate interventions that may be appropriate to treat the affected individual's pain.Contribution: Pain management is a basic need at the primary healthcare level and PWSCI need access to the broad range of interventions available to manage their pain. The framework highlights the variety of appropriate interventions to guide both health professionals and PWSCI with pain relief options.

Role of DNA methylation during recovery from spinal cord injury with and without β2-adrenergic receptor agonism

Daily treatment with the FDA-approved β2-adrenergic receptor agonist formoterol beginning 8 h after severe spinal cord injury (SCI) induces mitochondrial biogenesis and improves recovery in mice. We observed decreased DNA methyltransferase (DNMT) expression, global DNA methylation and methylation of the mitochondrial genes PGC-1α and NDUFS1 in the injury site of formoterol-treated mice 1 DPI, but this effect was lost by 7 DPI. To investigate the role of DNA methylation on recovery post-SCI, injured mice were treated daily with formoterol or vehicle, plus the DNMT inhibitor decitabine (DAC) on days 7-9. While DAC had no apparent effect on formoterol-induced recovery, mice treated with vehicle plus DAC exhibited increased BMS scores compared to vehicle alone beginning 15 DPI, reaching a degree of functional recovery similar to that of formoterol-treated mice by 21 DPI. Furthermore, DAC treatment increased injury site mitochondrial protein expression in vehicle-treated mice to levels comparable to that of formoterol-treated mice. The effect of DNMT inhibition on pain response with and without formoterol was assessed following moderate SCI. While all injured mice not treated with DAC displayed thermal hyperalgesia by 21 DPI, mice treated with formoterol exhibited decreased thermal hyperalgesia compared to vehicle-treated mice by 35 DPI. Injured mice treated with DAC, regardless of formoterol treatment, did not demonstrate thermal hyperalgesia at any time point assessed. Although these data do not suggest enhanced formoterol-induced recovery with DNMT inhibition, our findings indicate the importance of DNA methylation post-SCI and support both DNMT inhibition and formoterol as potential therapeutic avenues.

Muscimol as a treatment for nerve injury-related neuropathic pain: a systematic review and meta-analysis of preclinical studies

Background

: Muscimol's quick onset and GABAergic properties make it a promising candidate for the treatment of pain. This systematic review and meta-analysis of preclinical studies aimed at summarizing the evidence regarding the efficacy of muscimol administration in the amelioration of nerve injury-related neuropathic pain.

Methods

: Two independent researchers performed the screening process in Medline, Embase, Scopus and Web of Science extracting data were extracted into a checklist designed according to the PRISMA guideline. A standardized mean difference (SMD [95% confidence interval]) was calculated for each. To assess the heterogeneity between studies, I2 and chi-square tests were utilized. In the case of heterogeneity, meta-regression and subgroup analyses were performed to identify the potential source.

Results

: Twenty-two articles met the inclusion criteria. Pooled data analysis showed that the administration of muscimol during the peak effect causes a significant reduction in mechanical allodynia (SMD = 1.78 [1.45-2.11]; P < 0.0001; I2 = 72.70%), mechanical hyperalgesia (SMD = 1.62 [1.28-1.96]; P < 0.0001; I2 = 40.66%), and thermal hyperalgesia (SMD = 2.59 [1.79-3.39]; P < 0.0001; I2 = 80.33%). This significant amendment of pain was observed at a declining rate from 15 minutes to at least 180 minutes post-treatment in mechanical allodynia and mechanical hyperalgesia, and up to 30 minutes in thermal hyperalgesia (P < 0 .0001).

Conclusions

: Muscimol is effective in the amelioration of mechanical allodynia, mechanical hyperalgesia, and thermal hyperalgesia, exerting its analgesic effects 15 minutes after administration for up to at least 3 hours.

Misuse of gabapentinoids (pregabalin and gabapentin) in patients with neuropathic pain related to spinal cord injury

OBJECTIVE

To investigate the misuse of gabapentinoids (pregabalin and gabapentin) in patients with neuropathic pain related to spinal cord injury.

STUDY DESIGN

Cross-sectional study.

SETTING

Outpatient clinic in a physical therapy and rehabilitation hospital.

PARTICIPANTS

127 patients, aged 18-70 years, who had neuropathic pain related to spinal cord injury (SCI) and disease duration of at least 12 months.

OUTCOME MEASURES

Gabapentinoid use disorder of the patients was determined based on the DSM-5 diagnostic criteria for substance-related disorders. Patients were divided into 2 groups as those with drug misuse and those without drug misuse. Demographic and clinical information of the patients were compared between the groups. Factors associated with drug misuse were analyzed.

RESULTS

The misuse rate was 81.9% in patients using pregabalin and 69.69% in patients using gabapentin. Duration of disease and the Leeds assessment of neuropathic symptoms and signs (LANSS) score were statistically significantly higher in the drug misuse group. A statistically significant difference was found between the groups in terms of marital status, education and income level, and smoking and alcohol use. A statistically significant relationship was observed between drug misuse and duration of disease and LANSS score.

CONCLUSION

Misuse of gabapentinoids is prevalent in patients with neuropathic pain related to spinal cord injury. The duration of disease and the severity of NP are associated with misuse. Clinicians should exercise caution when prescribing gabapentinoids to patients with SCI.

The role of the insula in chronic pain following spinal cord injury: A resting-state fMRI study

BACKGROUND AND PURPOSE

Spinal cord injury (SCI) results in the loss of motor and sensory function from disconnections between efferent and afferent pathways. Most SCI patients are affected with chronic neuropathic pain, but there is a paucity of data concerning neuroplastic changes following SCI. Chronic pain disrupts default networks and is associated with abnormal insular connectivity. The posterior insula (PI) is associated with the degree of pain and intensity of pain. The anterior insula (AI) is related to signal changes. Comprehension of SCI pain mechanisms is essential to elucidate effective treatment options.

METHODS

This study examines the insular gyri functional connectivity (FC) of seven (five male, two female) SCI participants with moderate-severe chronic pain compared to 10 (five male, five female) healthy controls (HC). All subjects had 3-Tesla MRI performed and resting-state functional MRI (fMRI) was acquired. FC metrics were obtained from the comparisons of resting-state fMRI among our various groups. A seed-to-voxel analysis was pursued, encompassing six gyri of the insula. For multiple comparisons, a correction was applied with a significance level of p < .05.

RESULTS

There were significant differences in FC of the insula between SCI participants with chronic pain compared with HC. In the SCI participants, there was hyperconnectivity of the AI and PI to the frontal pole. In addition, there was increased FC noted between the PI and the anterior cingulate cortex. Hyperconnectivity was also observed between the AI and the occipital cortex.

CONCLUSIONS

These findings illustrate that there is a complex hyperconnectivity and modulation of pain pathways after traumatic SCI.

Differential target multiplexed spinal cord stimulation using a paddle-type lead placed at the appropriate site for neuropathic pain after spinal cord injury in patients with past spinal surgical histories: study protocol for an exploratory clinical trial

BACKGROUND

Neuropathic pain after spinal cord injury (SCI), both traumatic and non-traumatic, is refractory to various treatments. Spinal cord stimulation (SCS) is one of the neuromodulation therapies for neuropathic pain, although SCS has insufficient efficacy for neuropathic pain after SCI. The reasons are presumed to be inappropriate locations of SCS leads and conventional tonic stimulation itself does not have a sufficient analgesic effect for the pain. In patients with past spinal surgical histories, the cylinder-type leads are likely to be placed on the caudal side of the SCI because of surgical adhesions. Differential target multiplexed (DTM) stimulation is one of the latest new stimulation patterns that is superior to conventional stimulation.

METHODS

A single-center, open-label, randomized, two-way crossover trial is planned to investigate the efficacy of SCS using DTM stimulation placing a paddle lead at the appropriate site for neuropathic pain after SCI in patients with spinal surgical histories. The paddle-type lead delivers energy more efficiently than a cylinder-type lead. This study consists of two steps: SCS trial (first step) and SCS system implantation (second step). The primary outcome is rates of achieving pain improvement with more than 33% reduction 3 months after SCS system implantation. The secondary outcomes are to be evaluated as follows: (1) effectiveness of DTM and tonic stimulations during the SCS trial; (2) changes of assessment items from 1 to 24 months; (3) relationships between the result of the SCS trial and the effects 3 months after SCS system implantation; (4) preoperative factors associated with a long-term effect, defined as continuing for more than 12 months; and (5) whether gait function improves from 1 to 24 months.

DISCUSSION

A paddle-type lead placed on the rostral side of SCI and using DTM stimulation may provide significant pain relief for patients with intractable neuropathic pain after SCI in patients with past spinal surgical histories.

TRIAL REGISTRATION

Japan Registry of Clinical Trials (jRCT) jRCT 1042220093. Registered on 21 November 2022, and last modified on 6 January 2023. jRCT is approved as a member of the Primary Registry Network of WHO ICTRP.

Transcranial direct current stimulation regulates phenotypic transformation of microglia to relieve neuropathic pain induced by spinal cord injury

Objective

Neuropathic pain is a common complication after spinal cord injury (SCI). Transcranial direct current stimulation (tDCS) has been confirmed to be effective in relieving neuropathic pain in patients with SCI. The aim of this study is to investigate the effect of tDCS on neuropathic pain induced by SCI and its underlying mechanism.

Materials and methods

The SCI model was induced by a clip-compression injury and tDCS stimulation was performed for two courses (5 days/each). The motor function was evaluated by Basso-Beattie-Bresnahan (BBB) score, and the thermal withdrawal threshold was evaluated by the thermal radiation method. The effects of tDCS on the cerebral cortex, thalamus, midbrain, and medulla were detected by the enzyme-linked immunosorbent assay (ELISA) and immunofluorescence.

Results

The results showed that SCI reduced the thermal withdrawal threshold and increased the concentration of inflammatory cytokines in the cortex, thalamus, midbrain, and medulla, including the tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), and interleukin-6 (IL-6). In addition, the activation of microglia and the proportion of M1 phenotypic polarization increased significantly in the ventral posterolateral (VPL), ventral tegmental (VTA), and periaqueductal gray (PAG) regions after SCI. After tDCS treatment, the thermal withdrawal threshold and motor function of SCI rats were significantly improved compared to the vehicle group. Meanwhile, tDCS effectively reduced the concentration of pro-inflammatory cytokines in the cortex, thalamus, midbrain, and medulla and increased the concentration of anti-inflammatory cytokines interleukin-10 (IL-10) in the thalamus. In addition, tDCS reduced the proportion of the M1 phenotype of microglia in VPL, VTA, and PAG regions and increase the proportion of the M2 phenotype.

Conclusion

The results suggest that tDCS can effectively relieve SCI-induced neuropathic pain. Its mechanism may be related to regulating the inflammatory and anti-inflammatory cytokines in corresponding brain regions via promoting the phenotypic transformation of microglia.

The potential effects of polyunsaturated ω-3 fatty acids on spinal cord injury: A systematic review & meta-analysis of preclinical evidence

Polyunsaturated fatty acids (PUFAs) have received attention for their anti-inflammatory and antioxidant properties. Preclinical studies have investigated the efficacy of PUFAs in animal models of spinal cord injury (SCI) to determine if these properties can translate to neuroprotection and locomotor recovery. Findings from such studies have been promising, suggesting PUFAs as potential treatments against the neurological dysfunction induced by SCI. This systematic review and meta-analysis sought to investigate the efficacy of PUFAs for promoting locomotor recovery in animal models of SCI. PubMed, Web of Science and Embase (Ovid) were searched for relevant papers and those that examined the restorative effects of PUFAs on locomotor recovery in preclinical SCI models were included in our analysis. A random effects meta-analysis (restricted maximum likelihood estimator) was employed. A total of 28 studies were included and the results showed the claim that PUFAs have a beneficial therapeutic effect for promoting locomotor recovery (SMD = 1.037, 95% CI = 0.809-1.2644, p = <0.001) and cell survival (SMD = 1.101, 95% CI = 0.889-1.313, p = <0.001) in animal models of SCI. No significant differences for the secondary outcomes of neuropathic pain and lesion volume. Moderate asymmetry was observed in the funnel plots for locomotor recovery, cell survival and neuropathic pain measures, suggesting publication bias. Trim-and-fill analysis estimated 13, 3, 0 and 4 missing studies for locomotor recovery, cell survival, neuropathic pain, and lesion volume, respectively. A modified CAMARADES checklist was also used to assess risk of bias, showing that the median score for all included papers was 4 out of a possible 7.

Evaluating Pain Behaviours: Widely Used Mechanical and Thermal Methods in Rodents

Globally, over 300 million surgical procedures are performed annually, with pain being one of the most common post-operative side effects. During the onset of injury, acute pain plays a protective role in alerting the individual to remove noxious stimuli, while long-lasting chronic pain without any physiological reason is detrimental to the recovery process. Hence, it created an urgent need to better understand the pain mechanism and explore therapeutic targets. Despite the hardship in performing human pain studies due to ethical considerations, clinically relevant rodent pain models provide an excellent opportunity to perform pain studies. Several neurobehavioural tests are used to assess the drug efficacy in rodents to determine avoidance behaviour latency and threshold. This review article provides a methodological overview of mechanical (i.e. von Frey, Mechanical Conflict System) and thermal (i.e. Hargreaves Assay, Hot and Cold Plate, Temperature Place Preference) tests to assess pain in clinically relevant pain rodent models. We further discussed the current modifications of those tests along with their use in literature, the impact of confounding variables, advantages and disadvantages.

Sex Differences in Pain: Spinal Cord Injury in Female and Male Mice Elicits Behaviors Related to Neuropathic Pain

Spinal cord injury (SCI) in humans frequently causes intractable chronic pain. Females are susceptible to worse pain than males, and females may show higher pain prevalence after SCI. Despite this difference in the clinical prevalence of SCI pain, few pre-clinical studies have systematically studied sex differences in SCI-elicited pain-related behaviors in rodents. Here, we leverage data from a large cohort of mice to test whether contusion SCI consistently causes pain symptoms in mice, and to establish whether female (vs. male) mice display heightened hypersensitivity after SCI. Mechanical and heat sensory thresholds were assessed using the von Frey and Hargreaves tests, respectively. In an initial experiment, female mice receiving moderate 60 kDyn SCI or moderate-to-severe 75 kDyn SCI at T9 both exhibited mechanical and heat pain symptoms compared with sham controls. A 75 kDyn SCI caused excess motor deficits that confounded defining pain sensitivity at acute times; therefore, the moderate SCI force was used for subsequent experiments. Next, adult female and male C57BL6/J mice received sham surgery or T9 moderate contusion SCI. Comparing female to male mice after SCI, we reveal that mice of both sexes displayed mechanical and heat hypersensitivity compared with sham controls, from acute-to-chronic post-injury times. Females had amplified SCI-elicited hypersensitivity compared with males. Our data suggest that thoracic contusion SCI elicits consistent and persistent pain-associated symptoms, which are more intense in female than in male mice. These results have important implications for uncovering sex-specific mechanisms and therapeutic targets to ameliorate neuropathic pain after SCI.

Hydralazine plays an immunomodulation role of pro-regeneration in a mouse model of spinal cord injury

Spinal cord injury (SCI) results in severe motor and sensory dysfunction with no effective therapy. Spinal cord debris (sp) from injured spinal cord evokes secondary SCI continuously. We and other researchers have previously clarified that it is mainly bone marrow derived macrophages (BMDMs) infiltrating in the lesion epicenter to clear sp, rather than local microglia. Unfortunately, the pro-inflammatory phenotype of these infiltrating BMDMs is predominant which impairs wound healing. Hydralazine, as a potent vasodilator and scavenger of acrolein, has protective effects in many diseases. Hydralazine is also confirmed to promote motor function and hypersensitivity in SCI rats through scavenging acrolein. However, few studies have explored the effects of hydralazine on immunomodulation, as well as spontaneous pain and emotional response, the important syndromes in clinical patients. It remains unclear whether hydralazine affects infiltrating BMDMs after SCI. In this study, we targeted BMDMs to explore the influence of hydralazine on immune cells in a mouse model of SCI, and also investigated the contribution of polarized BMDMs to hydralazine-induced neurological function recovery after SCI in male mice. The adult male mice underwent T10 spinal cord compression. The results showed that in addition to improving motor function and hypersensitivity, hydralazine relieved SCI-induced spontaneous pain and emotional response, which is a newly discovered function of hydralazine. Hydralazine inhibited the recruitments of pro-inflammatory BMDMs and educated infiltrated BMDMs to a more reparative phenotype involving in multiple biological processes associated with SCI pathology, including immune/inflammation response, neurogenesis, lipid metabolism, oxidative stress, fibrosis formation, and angiogenesis, etc. As an overall effect, hydralazine-treated BMDMs loaden with sp partially rescued neurological function after SCI. It is concluded that hydralazine plays an immunomodulation role of educating pro-inflammatory BMDMs to a more reparative phenotype; and hydralazine-educated BMDMs contribute to hydralazine-induced improvement of neurological function in SCI mice, which provides support for drug and cell treatment options for SCI therapy.

Primary Care in the Spinal Cord Injury Population: Things to Consider in the Ongoing Discussion

Purpose of Review

Spinal cord injury (SCI) creates unique needs that if not recognized and addressed timely can have detrimental effects on the health and quality of life (QOL) of people living with a SCI. Primary preventive health care is shown to decrease morbidity and mortality, yet the SCI population reportedly faces challenges getting access to this care. This area in SCI health care is still largely understudied with no consensus on the ideal way or which health care provider is best to provide primary care for this population.

Findings

Preventive care is generally provided by general primary care providers, but not all primary care providers are trained in recognizing and addressing spinal cord injury-specific needs. SCI providers generally are not trained in addressing all aspects of preventive care. Knowing the recommended preventive care screenings, recognizing and managing specific conditions seen after a SCI, and seamless coordination of care between general practitioners and SCI specialists are some of the interventions to help prevent health complications, decrease morbidity and mortality, improve health outcomes, and promote QOL in this patient population.

Summary

Prioritized focus on preventive care is necessary for a positive impact on the overall health and QOL in this population. Addressing the knowledge gap reported by primary care providers and SCI providers may help increase the probability of SCI patients getting their preventive and specialty care needs addressed. We present a "cheat sheet" of recommendations for the preventive care evaluation of a person living with a SCI.

Electrical stimulation for the treatment of spinal cord injuries: A review of the cellular and molecular mechanisms that drive functional improvements

Spinal cord injury (SCI) is a devastating condition that causes severe loss of motor, sensory and autonomic functions. Additionally, many individuals experience chronic neuropathic pain that is often refractory to interventions. While treatment options to improve outcomes for individuals with SCI remain limited, significant research efforts in the field of electrical stimulation have made promising advancements. Epidural electrical stimulation, peripheral nerve stimulation, and functional electrical stimulation have shown promising improvements for individuals with SCI, ranging from complete weight-bearing locomotion to the recovery of sexual function. Despite this, there is a paucity of mechanistic understanding, limiting our ability to optimize stimulation devices and parameters, or utilize combinatorial treatments to maximize efficacy. This review provides a background into SCI pathophysiology and electrical stimulation methods, before exploring cellular and molecular mechanisms suggested in the literature. We highlight several key mechanisms that contribute to functional improvements from electrical stimulation, identify gaps in current knowledge and highlight potential research avenues for future studies.

Ectopic expression of Nav1.7 in spinal dorsal horn neurons induced by NGF contributes to neuropathic pain in a mouse spinal cord injury model

Neuropathic pain (NP) induced by spinal cord injury (SCI) often causes long-term disturbance for patients, but the mechanisms behind remains unclear. Here, our study showed SCI-induced ectopic expression of Nav1.7 in abundant neurons located in deep and superficial laminae layers of the spinal dorsal horn (SDH) and upregulation of Nav1.7 expression in dorsal root ganglion (DRG) neurons in mice. Pharmacologic studies demonstrated that the efficacy of the blood-brain-barrier (BBB) permeable Nav1.7 inhibitor GNE-0439 for attenuation of NP in SCI mice was significantly better than that of the BBB non-permeable Nav1.7 inhibitor PF-05089771. Moreover, more than 20% of Nav1.7-expressing SDH neurons in SCI mice were activated to express FOS when there were no external stimuli, suggesting that the ectopic expression of Nav1.7 made SDH neurons hypersensitive and Nav1.7-expressing SDH neurons participated in central sensitization and in spontaneous pain and/or walking-evoked mechanical pain. Further investigation showed that NGF, a strong activator of Nav1.7 expression, and its downstream JUN were upregulated after SCI in SDH neurons with similar distribution patterns and in DRG neurons too. In conclusion, our findings showed that the upregulation of Nav1.7 was induced by SCI in both SDH and DRG neurons through increased expression of NGF/JUN, and the inhibition of Nav1.7 in both peripheral and spinal neurons alleviated mechanical pain in SCI mice. These data suggest that BBB permeable Nav1.7 blockers might relieve NP in patients with SCI and that blocking the upregulation of Nav1.7 in the early stage of SCI via selective inhibition of the downstream signaling pathways of NGF or Nav1.7-targeted RNA drugs could be a strategy for therapy of SCI-induced NP.

Research Progress of Long Non-coding RNAs in Spinal Cord Injury

Spinal cord injury (SCI) can result in a partial or complete loss of motor and sensory function below the injured segment, which has a significant impact on patients' quality of life and places a significant social burden on them. Long non-coding RNA (LncRNA) is a 200-1000 bp non-coding RNA that has been shown to have a key regulatory role in the progression of a variety of neurological illnesses. Many studies have demonstrated that differentially expressed LncRNAs following spinal cord injury can participate in inflammatory damage, apoptosis, and nerve healing by functioning as competitive endogenous RNA (ceRNA); at the same time, it has a significant regulatory effect on sequelae such neuropathic pain. As a result, we believe that LncRNAs could be useful as a molecular regulatory target in the diagnosis, treatment, and prognosis of spinal cord injury.

Intraperitoneal Administration of Etizolam Improves Locomotor Function in Mice After Spinal Cord Injury

Neuroinflammation occurs in the acute phase of spinal cord injury (SCI) and inhibits neural regeneration. In mouse models, etizolam (ETZ) is a strong anxiolytic with unclear effects on SCI. This study investigated the effects of short-term administration of ETZ on neuroinflammation and behavior in mice after SCI. We administrated an ETZ (0.5 mg/kg) daily intraperitoneal injection from the day after SCI for 7 days. Mice were randomly divided into three groups (sham group: only laminectomy, saline group, and ETZ group). Inflammatory cytokine concentrations in the injured spinal cord epicenter were measured using an enzyme-linked immunosorbent assay on day 7 after SCI to evaluate spinal cord inflammation in the acute phase. Behavior analysis was performed the day before surgery and on days 7, 14, 28, and 42 after surgery. The behavioral analysis included anxiety-like behavior using the open field test, locomotor function using the Basso Mouse Scale, and sensory function using the mechanical and heat test. Inflammatory cytokine concentrations were significantly lower in the ETZ group than in the saline group in the acute phase after spinal surgery. After SCI, anxiety-like behaviors and sensory functions were comparable between the ETZ and saline groups. ETZ administration reduced neuroinflammation in the spinal cord and improved locomotor function. Gamma-amino butyric acid type A receptor stimulants may be effective therapeutic agents for patients with SCI.

Domino reaction of neurovascular unit in neuropathic pain after spinal cord injury

The mechanism of neuropathic pain after spinal cord injury is complex, and the communication between neurons, glia, and blood vessels in neurovascular units significantly affects the occurrence and development of neuropathic pain. After spinal cord injury, a domino chain reaction occurs in the neuron-glia-vessel, which affects the permeability of the blood-spinal cord barrier and jointly promotes the development of neuroinflammation. This article discusses the signal transduction between neuro-glial-endothelial networks from a multidimensional point of view and reviews its role in neuropathic pain after spinal cord injury.

The role of KCC2 and NKCC1 in spinal cord injury: From physiology to pathology

The balance of ion concentrations inside and outside the cell is an essential homeostatic mechanism in neurons and serves as the basis for a variety of physiological activities. In the central nervous system, NKCC1 and KCC2, members of the SLC12 cation-chloride co-transporter (CCC) family, participate in physiological and pathophysiological processes by regulating intracellular and extracellular chloride ion concentrations, which can further regulate the GABAergic system. Over recent years, studies have shown that NKCC1 and KCC2 are essential for the maintenance of Cl^- homeostasis in neural cells. NKCC1 transports Cl^- into cells while KCC2 transports Cl^- out of cells, thereby regulating chloride balance and neuronal excitability. An imbalance of NKCC1 and KCC2 after spinal cord injury will disrupt CI^- homeostasis, resulting in the transformation of GABA neurons from an inhibitory state into an excitatory state, which subsequently alters the spinal cord neural network and leads to conditions such as spasticity and neuropathic pain, among others. Meanwhile, studies have shown that KCC2 is also an essential target for motor function reconstruction after spinal cord injury. This review mainly introduces the physiological structure and function of NKCC1 and KCC2 and discusses their pathophysiological roles after spinal cord injury.

Feasibility, Acceptability, and Efficacy of Mindfulness Training in People With Upper Motor Neuron Disorders: A Systematic Review

OBJECTIVES

This systematic review aims to gain a comprehensive understanding of the feasibility, acceptability, and efficacy of mindfulness-based interventions (MBIs) on depression, anxiety, fatigue, and health-related quality of life among individuals with upper motor neuron disorders (UMNDs).

DATA SOURCES

PubMed, PsycINFO, Excerpta Medica Database, and Cumulative Index to Nursing and Allied Health Literature were searched for relevant studies published between January 2001 and June 2021.

STUDY SELECTION

Clinical trials published in English evaluating MBIs in adults with the 4 most common UMNDs (multiple sclerosis, brain injury including stroke, spinal cord injury, amyotrophic lateral sclerosis) were included.

DATA EXTRACTION

Two reviewers independently performed the risk of bias assessment using standardized tools and extracted desired data electronically.

DATA SYNTHESIS

A total of 44 studies were included: 26 randomized controlled trials, 10 nonrandomized controlled trials, and 8 pre-post intervention studies. The average ± SD duration of MBIs was 8±2 weeks. On average, 85%±14% of participants completed the MBI, and the retention rate at follow-up was 80%±16%. Only 14% of the studies delivered MBIs virtually, and feasibility metrics were similar to in-person studies. Among studies reporting acceptability data, most participants reported satisfaction with the MBI. Randomized controlled trials that evaluated the effects of MBI on depression, anxiety, fatigue, and quality of life revealed greater relative improvement in these outcomes among MBI participants compared with controls, with differences greater when compared with passive control than active control participants. None of the studies included in this review studied dose response.

CONCLUSIONS

Based on current data, MBIs are feasible and offer a promising approach to address the biopsychosocial needs of individuals with UMNDs. MBIs are associated with a high acceptance rate among participants, with notable improvements in depression, anxiety, fatigue, and quality of life post intervention. Future studies are needed to evaluate alternate models of delivery of MBIs and the dose-response relationship.

Coexistence of chronic hyperalgesia and multilevel neuroinflammatory responses after experimental SCI: a systematic approach to profiling neuropathic pain

Background

People with spinal cord injury (SCI) frequently develop neuropathic pain (NP) that worsens disability and diminishes rehabilitation efficacy. Chronic NP is presently incurable due to poor understanding of underlying mechanisms. We hypothesized that multilocus neuroinflammation (NIF) might be a driver of SCI NP, and tested it by investigating whether NP coexisted with central NIF, neurotransmission (NTM), neuromodulation (NML) and neuroplasticity (NPL) changes post-SCI.

Methods

Female Sprague–Dawley rats (230–250 g) with T10 compression or laminectomy were evaluated for physical conditions, coordinated hindlimb functions, neurological reflexes, and mechanical/thermal sensitivity thresholds at 1 day post-injury (p.i.) and weekly thereafter. Eight weeks p.i., central nervous system tissues were histochemically and immunohistochemically characterized for parameters/markers of histopathology and NIF/NTM/NML/NPL. Also analyzed was the correlative relationship between levels of selected biomarkers and thermosensitivity thresholds via statistical linear regression.

Results

SCI impaired sensorimotor functions, altered reflexes, and produced spontaneous pain signs and hypersensitivity to evoked nociceptive, mechanical, and thermal inputs. Only injured spinal cords exhibited neural lesion, microglia/astrocyte activation, and abnormal expression of proinflammatory cytokines, as well as NIF/NTM/NML/NPL markers. Brains of SCI animals displayed similar pathophysiological signs in the gracile and parabrachial nuclei (GrN and PBN: sensory relay), raphe magnus nucleus and periaqueduct gray (RMN and PAG: pain modulation), basolateral amygdala (BLA: emotional-affective dimension of pain), and hippocampus (HPC: memory/mood/neurogenesis). SCI augmented sensory NTM/NPL (GrN and PBN); increased GAD67 (PAG) level; reduced serotonin (RMN) and fear-off neuronal NTR2 (BLA) expressions; and perturbed neurogenesis (HPC).

Conclusion

T10 compression caused chronic hyperalgesia that coexisted with NIF/NTM/NML/NPL responses at multilevel neuroaxis centers. The data have provided multidimensional biomarkers as new mechanistic leads to profile SCI NP for therapeutic/therapy development.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-022-02628-2.

Cerium Oxide Nanoparticles Alleviate Neuropathic Pain by Modulating Macrophage Polarization in a Rat SCI Model

Context

Chronic neuropathic pain (NP) frequently occurs after spinal cord injury (SCI) but lacks effective therapeutic options in the clinic. Numerous evidence indicates the involvement of macrophages activation in the NP, and the modulation of macrophages is promising for NP treatment. In this study, we introduce Cerium oxide nanoparticles (CONPs) and aim to investigate whether it can relieve the NP by modulating macrophage polarization.

Methods

CONPs were prepared using the hydrothermal method. In vitro, different concentrations of CONPs were used to cultivate macrophages (RAW 264.7). In vivo, the analgesic effect of CONPs was investigated in a contusive rat SCI model. Mechanical paw withdrawal threshold (PWT) and thermal paw withdrawal latency (PWL) were tested to evaluate pain behaviors. Immunofluorescence staining and real-time quantitative polymerase chain reaction were applied to assess macrophage phenotypes.

Results

The synthesized CONPs were 6.8 ± 0.5 nm in size, presenting a cubic morphology. Live/dead staining showed that the relatively low concentrations of CONPs (less than 800 μg/mL) displayed good biocompatibility with macrophages. Intrathecal injection of CONPs could significantly increase the mechanical PWT and thermal PWL of SCI rats. Molecular experiments results showed the expression of M2 macrophage-related markers (CD206, Arg-1, IL-10) were significantly increased, while that of M1 macrophage-related markers (CD86, TNF-α, iNOS) were downregulated after CONPs treatment.

Conclusion

Our study suggests that CONPs can relive the NP following SCI by promoting M2 macrophages polarization, which provides a novel insight for the treatment of SCI induced NP.

Posterior Cord Syndrome After Spinal Cord Stimulation Electrode Lead Insertion: A Case Report

Chronic neuropathic pain after spinal cord injury is often refractory to conventional treatments. Spinal cord stimulation (SCS) is used to manage intractable chronic neuropathic pain. A 42-year-old man presented with chronic neuropathic pain in his right lower extremity for 5 years. He had undergone posterior fusion from T11 to L3 for a burst fracture of L1 vertebra and conus medullaris syndrome. Conservative treatment with medications, pain blocks, and physical therapy did not relieve the neuropathic pain in the right lower limb. A paddle-type SCS electrode lead was inserted at the level of T9-11 vertebrae for test stimulation. Postoperatively, the patient immediately complained of decreased proprioception, while the motor and sensory neurologic states did not change. Since his neurological deficit did not recover spontaneously, we had to remove the epidural SCS electrode to resolve the neurological symptoms.

Lateralized Supraspinal Functional Connectivity Correlate with Pain and Motor Dysfunction in Rat Hemicontusion Cervical Spinal Cord Injury

Afferent nociceptive activity in the reorganizing spinal cord after SCI influences supraspinal regions to establish pain. Clinical evidence of poor motor functional recovery in SCI patients with pain, led us to hypothesize that sensory-motor integration transforms into sensory-motor interference to manifest pain. This was tested by investigating supraspinal changes in a rat model of hemicontusion cervical SCI. Animals displayed ipsilateral forelimb motor dysfunction and pain, which persisted at 6 weeks after SCI. Using resting state fMRI at 8 weeks after SCI, RSFC across 14 ROIs involved in nociception, indicated lateral differences with a relatively weaker right-right connectivity (deafferented-contralateral) compared to left-left (unaffected-ipsilateral). However, the sensory (S1) and motor (M1/M2) networks showed greater RSFC using right hemisphere ROI seeds when compared to left. Voxel seeds from the somatosensory forelimb (S1FL) and M1/M2 representations reproduced the SCI-induced sensory and motor RSFC enhancements observed using the ROI seeds. Larger local connectivity occurred in the right sensory and motor networks amidst a decreasing overall local connectivity. This maladaptive reorganization of the right (deafferented) hemisphere localized the sensory component of pain emerging from the ipsilateral forepaw. A significant expansion of the sensory and motor network s overlap occurred globally after SCI when compared to sham, supporting the hypothesis that sensory and motor interference manifests pain. Voxel-seed based analysis revealed greater sensory and motor network overlap in the left hemisphere when compared to the right. This left predominance of the overlap suggested relatively larger pain processing in the unaffected hemisphere, when compared to the deafferented side.

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.

Interleukin-17 as a potential therapeutic target for chronic pain

Chronic pain remains to be a clinical challenge and is recognized as a major health problem with varying impacts on quality of life. Currently, the first-line therapy for chronic pain is opioids, which are often accompanied by unwanted psychoactive side effects. Thus, new and effective treatments for chronic pain are urgently needed and eagerly pursued. Inflammatory cytokines, especially interleukin-17 (IL-17), are reportedly potential therapeutic targets owing to their pivotal role in chronic pain from the neuroinflammation perspective. Recently, substantial evidence confirmed that IL-17 and IL-17 receptors (IL-17Rs) were increased in neuropathic, inflammatory, and cancer pain models. Notably, IL-17/IL-17R antibodies also reportedly relieve or cure inflammatory- and pain-related diseases. However, existing studies have reported controversial results regarding IL-17/IL-17Rs as potential therapeutic targets in diverse animal models of chronic pain. In this review, we present a summary of published studies and discuss the evidence, from basic to clinical to research, regarding the role and mechanism of action between IL-17 and diverse kinds of chronic pain in animal models and clinical patients. Furthermore, we evaluated IL-17-based therapy as a potential therapeutic strategy for inflammatory- and pain-related disease. Importantly, we also discussed clinical trials of IL-17/IL-17R targeting monoclonal antibodies. Overall, we found that IL-17 is a potential therapeutic target for chronic pain from the perspective of neuroinflammation.

Moving Beyond the Neck and Arm: The Pain Experience of People With Degenerative Cervical Myelopathy Who Have Pain

STUDY DESIGN

Cross-sectional internet survey of people living with degenerative cervical myelopathy.

OBJECTIVE

The purpose of this study was to quantify pain distribution, severity, and interference in persons with degenerative cervical myelopathy.

METHODS

Eighty-two participants with degenerative cervical myelopathy were recruited for this internet survey. This survey utilized the Michigan Body Map and brief pain inventory (BPI) to assess anatomical distribution and severity of pain as well as the patient derived modified Japanese Orthopedic Association scale (p-mJOA) for myelopathic severity and SF-36 for measures of health-related quality of life. Internal consistency was evaluated with Cronbach's alpha. Pearson's correlations were assessed with p-mJOA and SF-36. Multivariate analysis of variance was used to determine if history of prior surgery or concomitant pain diagnosis impacted experience of pain.

RESULTS

Michigan body map distribution and brief pain inventory severity and interference were correlated with p-mJOA and SF-36 scores (p < 0.05). Pain was moderate to severe in 78% of participants. Pain was commonly widespread. Pain scales were sufficiently internally consistent (α > 0.9). History of surgery or other pain diagnosis did not impact experience of pain in myelopathy.

CONCLUSIONS

Pain is commonly identifiable in large areas of the body, is frequently moderate to severe in intensity and impacts quality of life and severity of myelopathy in a cohort of individuals with myelopathy who have pain.

Spinal Cord Injury Provoked Neuropathic Pain and Spasticity, and Their GABAergic Connection

Traumatic spinal cord injury (SCI) is the devastating neurological damage to the spinal cord that becomes more complicated in the secondary phase. The secondary injury comes with inevitable long-lasting complications, such as chronic neuropathic pain (CNP) and spasticity which interfere with day to day activities of SCI patients. Mechanisms underlying CNP post-SCI are complex and remain refractory to current medical treatment. Due to the damage, extensive inhibitory, excitatory tone dysregulation causes maladaptive synaptic transmissions, further altering the nociceptive and nonnociceptive pathways. Excitotoxicity mediated GABAergic cell loss, downregulation of glutamate acid decarboxylase enzyme, upregulation of gamma-aminobutyric acid (GABA) transporters, overactivation of glutamate receptors are some of the key evidence for hypoactive inhibitory tone contributing to CNP and spasticity post-SCI. Restoring the inhibitory GABAergic tone and preventing damage-induced excitotoxicity by employing various strategies provide neuroprotective and analgesic effects. The present article will discuss CNP and spasticity post-SCI, understanding their pathophysiological mechanisms, especially GABA-glutamate-related mechanisms, therapeutic interventions targeting them, and progress regarding how regulating the excitatory-inhibitory tone may lead to more targeted treatments for these distressing complications. Taking background knowledge of GABAergic analgesia and recent advancements, we aim to highlight how far we have reached in promoting inhibitory GABAergic tone for SCI-CNP and spasticity.

Translocator Protein 18 kDa (TSPO) as a Novel Therapeutic Target for Chronic Pain

Chronic pain is an enormous modern public health problem, with significant numbers of people debilitated by chronic pain from a variety of etiologies. Translocator protein 18 kDa (TSPO) was discovered in 1977 as a peripheral benzodiazepine receptor. It is a five transmembrane domain protein, mainly localized in the outer mitochondrial membrane. Recent and increasing studies have found changes in TSPO and its ligands in various chronic pain models. Reversing their expressions has been shown to alleviate chronic pain in these models, illustrating the effects of TSPO and its ligands. Herein, we review recent evidence and the mechanisms of TSPO in the development of chronic pain associated with peripheral nerve injury, spinal cord injury, cancer, and inflammatory responses. The cumulative evidence indicates that TSPO-based therapy may become an alternative strategy for treating chronic pain.