Exercise training modulates glutamic acid decarboxylase-65/67 expression through TrkB signaling to ameliorate neuropathic pain in rats with spinal cord injury

Contribution of mechanoreceptors to spinal cord injury-induced mechanical allodynia

ABSTRACT

Evidence from previous studies supports the concept that spinal cord injury (SCI)-induced neuropathic pain (NP) has its neural roots in the peripheral nervous system. There is uncertainty about how and to which degree mechanoreceptors contribute. Sensorimotor activation-based interventions (eg, treadmill training) have been shown to reduce NP after experimental SCI, suggesting transmission of pain-alleviating signals through mechanoreceptors. The aim of the present study was to understand the contribution of mechanoreceptors with respect to mechanical allodynia in a moderate mouse contusion SCI model. After genetic ablation of tropomyosin receptor kinase B expressing mechanoreceptors before SCI, mechanical allodynia was reduced. The identical genetic ablation after SCI did not yield any change in pain behavior. Peptidergic nociceptor sprouting into lamina III/IV below injury level as a consequence of SCI was not altered by either mechanoreceptor ablation. However, skin-nerve preparations of contusion SCI mice 7 days after injury yielded hyperexcitability in nociceptors, not in mechanoreceptors, which makes a substantial direct contribution of mechanoreceptors to NP maintenance unlikely. Complementing animal data, quantitative sensory testing in human SCI subjects indicated reduced mechanical pain thresholds, whereas the mechanical detection threshold was not altered. Taken together, early mechanoreceptor ablation modulates pain behavior, most likely through indirect mechanisms. Hyperexcitable nociceptors seem to be the main drivers of SCI-induced NP. Future studies need to focus on injury-derived factors triggering early-onset nociceptor hyperexcitability, which could serve as targets for more effective therapeutic interventions.

Role of Exercise on Inflammation Cytokines of Neuropathic Pain in Animal Models

Neuropathic pain (NP) resulting from a lesion or disease of the somatosensory system can lead to loss of function and reduced life quality. Neuroinflammation plays a vital role in the development and maintenance of NP. Exercise as an economical, effective, and nonpharmacological treatment, recommended by clinical practice guidelines, has been proven to alleviate chronic NP. Previous studies have shown that exercise decreases NP by modifying inflammation; however, the exact mechanisms of exercise-mediated NP are unclear. Therefore, from the perspective of neuroinflammation, this review mainly discussed the effects of exercise on inflammatory cytokines in different parts of NP conduction pathways, such as the brain, spinal cord, dorsal root ganglion, sciatic nerve, and blood in rat/mice models. Results suggested that exercise training could modulate neuroinflammation, inhibit astrocyte glial cell proliferation and microglial activation, alter the macrophage phenotype, reduce the expression of proinflammatory cytokines, increase anti-inflammatory cytokine levels, and positively modulate the state of the immune system, thereby relieving NP.

Exoskeleton-Assisted Rehabilitation and Neuroplasticity in Spinal Cord Injury

Spinal cord injury (SCI) results in neurological deficits below the level of injury, causing motor dysfunction and various severe multisystem complications. Rehabilitative training plays a crucial role in the recovery of individuals with SCI, and exoskeleton serves as an emerging and promising tool for rehabilitation, especially in promoting neuroplasticity and alleviating SCI-related complications. This article reviews the classifications and research progresses of medical exoskeletons designed for SCI patients and describes their performances in practical application separately. Meanwhile, we discuss their mechanisms for enhancing neuroplasticity and functional remodeling, as well as their palliative impacts on secondary complications. The potential trends in exoskeleton design are raised according to current progress and requirements on SCI rehabilitation.

Effects of swimming exercise on neuropathic pain in a rat model: role of glutamate

OBJECTIVE

The pain-reducing effects of the exercise were exerted through different mechanisms. Knowing more clear mechanisms helps to find more approach that is therapeutic. The objective of the present study is the evaluation of cerebrospinal fluid (CSF) glutamate level alteration in neuropathic pain rats and whether physical activity could modulate it.

METHODS

In the present study 104 male Wistar rats weighing 180-220 g were randomly divided into 4 groups (Sham, Sham + Exe, Neuropathy, and Neuropathy + Exe) which in turn each group subdivided into 4 groups according to time points for behavioral testing and CSF sampling (Baseline, 2 weeks, 3 weeks, and 4 weeks). To induction of neuropathy (by chronic constriction injury,), after anesthetizing with a mixture of ketamine (80 mg/kg) and xylazine (10 mg/kg), the animal's right sciatic nerve was exposed and was ligated using four movable catgut chromic suture 4/0. The exercise protocol included 25 min of daily swimming, 5 days a week for 4 weeks. Thermal hyperalgesia and mechanical tactile threshold were detected using the plantar test and Von Frey filaments, respectively. CSF glutamate level was determined using high-performance liquid chromatography.

RESULTS

Findings indicated that mechanical and thermal thresholds significantly (p < 0.01, p < 0.05 respectively) decreased in the neuropathy group against that in sham groups. On the other hand, exercise significantly increased mechanical tactile threshold (p < 0.0012) and thermal threshold (p < 0.05) compared to the neuropathy group. Moreover, CSF glutamate level prominently (p < 0.01) was increased in the neuropathy group compared to the sham group, and swimming exercise significantly (p < 0.001) reduced it.

IN CONCLUSION

The present findings provide new evidence showing that medium-intensity swimming exercise attenuates pain-like behaviors in neuropathic pain animals, which is possibly due to decreasing CSF glutamate level and its neurotransmission.

Exercise, Spinal Microglia and Neuropathic Pain: Potential Molecular Mechanisms

As one of the most common neuropathic disorders, neuropathic pain often has a negative impact on patients with persistent pain, mood disorders and sleep disturbances. Currently, neuropathic pain is not treated with any specific drug, instead, drugs for other diseases are used as replacements in clinics, but most have adverse effects. In recent years, the role of spinal cord microglia in the pathogenesis of neuropathic pain has been widely recognized, and they are being explored as potential therapeutic targets. Spinal microglia are known to be involved in the pathogenic mechanisms of neuropathic pain through purine signaling, fractalkine signaling, and p38 MAPK signaling. Exercise is a safe and effective treatment, and numerous studies have demonstrated its effectiveness in improving neurological symptoms. Nevertheless, it remains unclear what the exact molecular mechanism is. This review summarized the specific molecular mechanisms of exercise in alleviating neuropathic pain by mediating the activity of spinal microglia and maintaining the phenotypic homeostasis of spinal microglia through purine signaling, fractalkine signaling and p38 MAPK signaling. In addition, it has been proposed that different intensities and types of exercise affect the regulation of the above-mentioned signaling pathways differently, providing a theoretical basis for the improvement of neuropathic pain through exercise.

The Role of Exercise in the Alleviation of Neuropathic Pain Following Traumatic Spinal Cord Injuries: A Systematic Review and Meta-analysis

OBJECTIVE

The objective of this systematic review and meta-analysis was to assess the efficacy of exercise in neuropathic pain following traumatic spinal cord injuries.

METHODS

The search was conducted in MEDLINE, Embase, Scopus, and Web of Science by the end of 2022. Two independent researchers included the articles based on the inclusion and exclusion criteria. A standardized mean difference was calculated for each data and they were pooled to calculate an overall effect size. To assess the heterogeneity between studies, I2 and chi-square tests were utilized. In the case of heterogeneity, meta-regression was performed to identify the potential source.

RESULTS

Fifteen preclinical studies were included. Meta-analysis demonstrated that exercise significantly improves mechanical allodynia (standardized mean difference [SMD], -1.59; 95% confidence interval [CI], -2.16 to -1.02; p < 0.001; I2 = 90.37%), thermal hyperalgesia (SMD, 1.95; 95% CI, 0.96-2.94; p < 0.001), and cold allodynia (SMD, -2.92; 95% CI, -4.4 to -1.43; p < 0.001). The improvement in mechanical allodynia is significantly more in animals with a compression model of SCI (meta-regression coefficient, -1.33; 95% CI, -1.84 to -0.57; p < 0.001) and in mild SCI (p < 0.001). Additionally, the improvement was more prominent if the training was started 7 to 8 days postinjury (coefficient, -2.54; 95% CI, -3.85 to -1.23; p < 0.001) and was continued every day (coefficient, -1.99; 95% CI, -3.07 to -0.9; p < 0.001). Likewise, voluntary exercise demonstrated a significantly more effect size (coefficient, -1.45; 95% CI, -2.67 to -0.23; p = 0.02).

CONCLUSION

Exercise is effective in the amelioration of neuropathic pain. This effect in mechanical allodynia is more prominent if voluntary, continuous training is initiated in the subacute phase of mild SCI.

Effects of exercise training on neurological recovery, TGF-β1, HIF-1α, and Nogo-NgR signaling pathways after spinal cord injury in rats

OBJECTIVE

To evaluate the effects of exercise training on neurological recovery, Growth Transforming Factor-β1 (TGF-β1), Hypoxia Inducible Factor-1α (HIF-1α), and Nogo-NgR signaling pathways after spinal cord injury in rats.

METHODS

Forty-eight male Sprague-Dawley rats were randomly divided into four groups: normal group, sham-operated group, model group, and training group. The rat spinal cord injury model was established using Allen's method, and the training group received exercise training on the 8th day postoperatively. The Basso, Beattie and Bresnahan (BBB) score, modified Tarlow score, and inclined plane test scores were compared in each group before injury and 1, 7, 14, 21 and 28 days after injury.

RESULTS

The BBB score and modified Tarlow score of the model group and the training group were 0 at the first day after the injury, and gradually increased on the seventh day onwards (p < 0.05). The BBB score and modified Tarlow score of the training group were higher than those of the model group at the 14th, 21st and 28th day (p < 0.05). The angles of the inclined plate at multiple time points after injury were lower in the model group and the training group than in the normal group and the sham-operated group (p < 0.05); The angles of the inclined plate at the 14th, 21st and 28th day after injury were higher in the training group than in the model group (p < 0.05).

CONCLUSION

The mechanism of exercise training may be connected to the inhibition of the Nogo-NgR signaling pathway to promote neuronal growth.

Changes in synaptic inputs to dI3 INs and MNs after complete transection in adult mice

Introduction

Spinal cord injury (SCI) is a debilitating condition that disrupts the communication between the brain and the spinal cord. Several studies have sought to determine how to revive dormant spinal circuits caudal to the lesion to restore movements in paralyzed patients. So far, recovery levels in human patients have been modest at best. In contrast, animal models of SCI exhibit more recovery of lost function. Previous work from our lab has identified dI3 interneurons as a spinal neuron population central to the recovery of locomotor function in spinalized mice. We seek to determine the changes in the circuitry of dI3 interneurons and motoneurons following SCI in adult mice.

Methods

After a complete transection of the spinal cord at T9-T11 level in transgenic Isl1:YFP mice and subsequent treadmill training at various time points of recovery following surgery, we examined changes in three key circuits involving dI3 interneurons and motoneurons: (1) Sensory inputs from proprioceptive and cutaneous afferents, (2) Presynaptic inhibition of sensory inputs, and (3) Central excitatory glutamatergic synapses from spinal neurons onto dI3 INs and motoneurons. Furthermore, we examined the possible role of treadmill training on changes in synaptic connectivity to dI3 interneurons and motoneurons.

Results

Our data suggests that VGLUT1⁺ inputs to dI3 interneurons decrease transiently or only at later stages after injury, whereas levels of VGLUT1⁺ remain the same for motoneurons after injury. Levels of VGLUT2⁺ inputs to dI3 INs and MNs may show transient increases but fall below levels seen in sham-operated mice after a period of time. Levels of presynaptic inhibition to VGLUT1⁺ inputs to dI3 INs and MNs can rise shortly after SCI, but those increases do not persist. However, levels of presynaptic inhibition to VGLUT1⁺ inputs never fell below levels observed in sham-operated mice. For some synaptic inputs studied, levels were higher in spinal cord-injured animals that received treadmill training, but these increases were observed only at some time points.

Discussion

These results suggest remodeling of spinal circuits involving spinal interneurons that have previously been implicated in the recovery of locomotor function after spinal cord injury in mice.

High intensity interval training attenuates osteoarthritis-associated hyperalgesia in rats

High-intensity interval training (HIIT) is a physical therapy that may benefit patients with osteoarthritis (OA). Cacna2d1 is a calcium channel subunit protein that plays an important role in the activity of nerve cells. However, there is currently no evidence on HIIT relieving OA-associate hyperalgesia by decreased Cacna2d1. Our study established the OA rat models with intra-articular injection of monosodium iodoacetate (MIA). This experiment was divided into two stages. The first stage comprised three groups: the control, OA, and OA-HIIT groups. The second stage comprised two groups, including the AAV-C and AAV-shRNA-Cacna2d1 groups. OA rats were positioned at the L5-L6 segments, and 20 µl of AAV virus was injected intrathecally. The pain threshold, cartilage analysis, Cacna2d1, and pain neurotransmitters were measured and compared. The pain threshold was significantly lower in OA rats than in control rats from the first to the tenth week. Starting from the sixth week, OA-HIIT rats exhibited significantly increased pain thresholds. The expression of Cacna2d1 increased in OA rats. Moreover, the knockdown of Cacna2d1 significantly down-regulated the expression of c-Fos, SP, and Vglut2 in the posterior horn of the spinal cord. In conclusion, HIIT attenuates OA-associated hyperalgesia, which may be related to the down-regulation of Cacna2d1.

The Rehabilitation-Related Effects on the Fear, Pain, and Disability of Patients With Lumbar Fusion Surgery: A Systematic Review and Meta-Analysis

Objective: The lumbar fusion is an important surgery for the orthopedic diseases. The rehabilitation might improve the outcome of patients with lumbar fusion surgery. The rehabilitation-related effects can be revealed by a systemic review and meta-analysis of randomized clinical trials (RCTs). The purpose of this study is to clarify the rehabilitation effects in the patients with lumbar fusion surgery.Methods: We performed a systematic search and a meta-analysis for the RCT of rehabilitation treatment on the patients with lumbar fusion surgery. The comparison between rehabilitation treatment (including psychological rehabilitation, exercise, and multimodal rehabilitation) and typical treatment was performed to find if the rehabilitation treatment can improve the outcome after the lumbar fusion surgery. Fifteen studies of lumbar fusion patients under rehabilitation treatment and typical treatment were enrolled in a variety of rehabilitation modalities. The focused outcome was the rehabilitation-related effects on the fear, disability, and pain of patients after the lumbar fusion surgery.Results: Five hundred twenty-eight rehabilitation subjects and 498 controls were enrolled. The psychological-related rehabilitation showed a significant decrease in pain-related fear when compared to usual treatment. The multimodal rehabilitation can improve the disability outcome to a greater extent when compared to usual treatment. The multimodal rehabilitation seemed to have a more significantly positive effect to decrease disability after lumbar fusion surgery. In addition, the exercise and multimodal rehabilitation can relieve the pain after lumbar fusion surgery. The exercise rehabilitation seemed to have a more significantly positive effect to relieve pain after lumbar fusion surgery.Conclusion: The rehabilitation might relieve the pain-related fear, disability, and pain after lumbar fusion surgery.

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.

Effect of Acute Physical Interventions on Pathophysiology and Recovery After Spinal Cord Injury: A Comprehensive Review of the Literature

Physical rehabilitation is essential for enhancing recovery in individuals with spinal cord injury (SCI); however, aside from early surgical intervention and hemodynamic management, there are no proven interventions for promoting recovery in the acute phase. In general, early rehabilitation is considered beneficial, but optimal parameters and potential contraindications for implementing rehabilitation at very early time points are unclear. Moreover, clinical trials to date are limited to studies initiating rehabilitation 2 weeks after injury and later. To address these gaps, this article reviews the preclinical literature on physical interventions initiated within the first 8 days postinjury. Effects of early rehabilitation on molecular and structural nervous system changes, behavioral function, and body systems are considered. Most studies utilized treadmill or cycle training as the primary intervention. Treadmill training initiated within the first 3 days and terminated by 1 week after injury worsened autonomic function, inflammation, and locomotor outcomes, while swim training during this period increased microvascular dysfunction. In contrast, lower-intensity rehabilitation such as reach training, ladder training, or voluntary wheel or ball training showed benefits when implemented during the first 3 days. Rehabilitation initiated at 4 days postinjury was also associated with enhanced motor recovery. Cycling appears to have the greatest risk-benefit ratio; however, the effects of cycle training in the first 3 days were not investigated. Overall, research suggests that lower intensity or voluntary rehabilitation during the hyperacute phase is more appropriate until at least 4 days postinjury, at which point higher-intensity activity becomes safer and more beneficial for recovery.

Pharmacological and non-pharmacological therapeutic interventions for the treatment of spinal cord injury-induced pain

Spinal cord injury (SCI) is a complex neurophysiological disorder, which can result in many long-term complications including changes in mobility, bowel and bladder function, cardiovascular function, and metabolism. In addition, most individuals with SCI experience some form of chronic pain, with one-third of these individuals rating their pain as severe and unrelenting. SCI-induced chronic pain is considered to be "high impact" and broadly affects a number of outcome measures, including daily activity, physical and cognitive function, mood, sleep, and overall quality of life. The majority of SCI pain patients suffer from pain that emanates from regions located below the level of injury. This pain is often rated as the most severe and the underlying mechanisms involve injury-induced plasticity along the entire neuraxis and within the peripheral nervous system. Unfortunately, current therapies for SCI-induced chronic pain lack universal efficacy. Pharmacological treatments, such as opioids, anticonvulsants, and antidepressants, have been shown to have limited success in promoting pain relief. In addition, these treatments are accompanied by many adverse events and safety issues that compound existing functional deficits in the spinally injured, such as gastrointestinal motility and respiration. Non-pharmacological treatments are safer alternatives that can be specifically tailored to the individual and used in tandem with pharmacological therapies if needed. This review describes existing non-pharmacological therapies that have been used to treat SCI-induced pain in both preclinical models and clinical populations. These include physical (i.e., exercise, acupuncture, and hyper- or hypothermia treatments), psychological (i.e., meditation and cognitive behavioral therapy), and dietary interventions (i.e., ketogenic and anti-inflammatory diet). Findings on the effectiveness of these interventions in reducing SCI-induced pain and improving quality of life are discussed. Overall, although studies suggest non-pharmacological treatments could be beneficial in reducing SCI-induced chronic pain, further research is needed. Additionally, because chronic pain, including SCI pain, is complex and has both emotional and physiological components, treatment should be multidisciplinary in nature and ideally tailored specifically to the patient.

LncRNA/miRNA/mRNA ceRNA network analysis in spinal cord injury rat with physical exercise therapy

Noncoding RNAs have been implicated in the pathophysiology of spinal cord injury (SCI), including cell death, glial scar formation, axonal collapse and demyelination, and inflammation. The evidence suggests that exercise therapy is just as effective as medical treatment in SCI. However, studies of competing endogenous RNA (ceRNA)-mediated regulation mechanisms in the therapy of SCI with exercise are rare. The focus of this research was to investigate the effect of exercise therapy on the expression levels of long noncoding RNA (lncRNA), microRNA (miRNA), and mRNA in rats with SCI. The RNA-seq technology has been used to examine the differentially expressed circRNAs (DECs), lncRNAs (DELs), miRNAs (DEMs), and genes (DEGs) between SCI and exercise therapy rats. The ceRNA network was established using interactions between miRNAs and mRNAs, as well as between miRNAs and lncRNAs/circRNAs. The Database for Annotation, Visualization, and Integrated Discovery was used to anticipate the underlying functions of mRNAs. Our current study identified 76 DELs, 33 DEMs, and 30 DEGs between groups of SCI rats and exercise therapy rats. Subsequently, these newly discovered ceRNA interaction axes could be important targets for the exercise treatment of SCI.

Treadmill workouts alleviate neuropathic allodynia and scratching behavior in rats following thoracotomy

BACKGROUND

The aim of the experiment was to investigate the effects of treadmill exercise on postthoracotomy pain and the expression of spinal pro-inflammatory and anti-inflammatory cytokines.

METHODS

Animals were randomly distributed into four groups: (a) sham surgery, (b) rats following 60 min thoracotomy and rib retraction (thoracotomy), (c) thoracotomy rats received treadmill training (thoracotomy+treadmill), and (d) sham surgery rats received treadmill training (sham surgery+treadmill). Treadmill workouts were started on postoperative day 10 (POD10) and lasted for 6 weeks (5 days per week). Rats were examined for cold allodynia using acetone and mechanical allodynia using von Frey hairs (in grams) at the surgical site. Spinal pro-inflammatory and anti-inflammatory cytokines were analyzed on PODs 28 and 49.

RESULTS

Both thoracotomy and thoracotomy+treadmill groups exhibited a decrease in mechanical force thresholds (g) and an increase in scratches per min on POD10. Mechanical hypersensitivity and incremental scratches lasted from POD14 and POD49 in the thoracotomy group. Although force thresholds and scratches remained not return to baseline, incremental force thresholds (p < 0.001) and diminutive scratches (p < 0.001) occurred after 6-week treadmill workouts. The rise in spinal interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α) concentrations or the decline in spinal IL-10 concentration in thoracotomy+treadmill rats was less (p < 0.05) than thoracotomy rats without exercise.

CONCLUSIONS

Mechanical allodynia using von Frey filament testing and cold allodynia by acetone testing were improved in thoracotomy rats after treadmill workouts.. Treadmill exercise restrained excess pro-inflammatory cytokine expression but increased anti-inflammatory cytokine level in a rib retraction model.

Systematic analysis of critical genes and pathways identified a signature of neuropathic pain after spinal cord injury

Spinal cord injury (SCI) damages sensory systems, producing chronic neuropathic pain that is resistant to medical treatment. The specific mechanisms underlying SCI-induced neuropathic pain (SCI-NP) remain unclear, and protein biomarkers have not yet been integrated into diagnostic screening. To better understand the host molecular pathways involved in SCI-NP, we used the bioinformatics method, the PubMed database, and bioinformatics methods to identify target genes and their associated pathways. We reviewed 2504 articles on the regulation of SCI-NP and used the text mining of PubMed database abstracts to determine associations among 12 pathways and networks. Based on this method, we identified two central genes in SCI-NP: interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α). Adult male Sprague-Dawley rats were used to build the SCI-NP models. The threshold for paw withdrawal was significantly reduced in the SCI group and TLR4 was activated in microglia after SCI. ELISA analysis of TNF-α and IL-6 levels was significantly higher in the SCI group than in the sham group. Western blot showed that expressions of the TLR4/MyD88/NF-κB inflammatory pathway protein increased dramatically in the SCI group. Using the TLR4 inhibitor TAK-242, the pain threshold and expressions of inflammatory factors and proteins of the proteins of the inflammatory signal pathway were reversed, TLR4 in microglia was suppressed, suggesting that SCI-NP was related to neuroinflammation mediated by the TLR4 signaling pathway. In conclusion, we found TNF-α and IL-6 were the neuroinflammation-related genes involved in SCI-NP that can be alleviated by inhibiting the inflammatory pathway upstream of the TLR4/MyD88/NF-κB inflammatory pathway.

Voluntary exercise ameliorates neuropathic pain by suppressing calcitonin gene-related peptide and ionized calcium-binding adapter molecule 1 overexpression in the lumbar dorsal horns in response to injury to the cervical spinal cord

BACKGROUND

Neuropathic pain (NP) is a frequent finding in patients diagnosed with spinal cord injuries (SCIs). To improve our understanding of the maladaptive changes taking place in the lumbar spinal cord that can lead to the development of NP and to find alternative options to treat this condition, we aimed to investigate the effects of voluntary exercise on NP after SCI and to elucidate its potential mechanisms.

METHODS

A rat model of post-SCI NP induced by compression of the posterior or lateral cervical spinal cord was used to evaluate the effects of voluntary exercise by measuring the bilateral withdrawal of the hind paws using the Von Frey filament and Hargreaves tests. The place escape/avoid paradigm was used to evaluate supraspinal pain processing and somatosensory evoked potentials (SEPs) were used to examine disturbances in proprioception. Locomotor function was evaluated using Basso, Beattie, and Bresnahan (BBB) scoring. Pathologic findings in hematoxylin and eosin-stained tissue and magnetic resonance imaging were used to evaluate the morphological changes after SCI. The lesion size within the cervical spinal cord was evaluated by staining with Eriochrome cyanine R. Quantitative polymerase chain reaction and immunohistochemistry were used to assess the expression of calcitonin gene-related peptide (CGRP) and ionized calcium-binding adapter molecule 1 (Iba-1) in the lumbar dorsal horns.

RESULTS

All injured rats developed mechanical hypersensitivity, hyposensitivity, and thermal hyperalgesia in the contralateral hind paws at 1 week post-injury. Rats that underwent lateral compression injury developed NP in the ipsilateral hind paws 1 week later than rats with a posterior compression injury. Our findings revealed that voluntary exercise ameliorated mechanical allodynia and thermal hyperalgesia, and significantly improved proprioception as measured by SEP, but had no impact on mechanical hypoalgesia or motor recovery and provided no significant neuroprotection after recovery from an acute SCI. SCI-induced NP was accompanied by increased expression of CGRP and Iba-1 in the lumbar dorsal horn. These responses were reduced in rats that underwent voluntary exercise.

CONCLUSIONS

Voluntary exercise ameliorates NP that develops in rats after compression injury. Increased expression of CGRP and Iba-1 in the lumbar dorsal horns of rats exhibiting symptoms of NP suggests that microglial activation might play a crucial role in its development. Collectively, voluntary exercise may be a promising therapeutic modality to treat NP that develops clinically in response to SCI.

Physiological Changes and Pathological Pain Associated with Sedentary Lifestyle-Induced Body Systems Fat Accumulation and Their Modulation by Physical Exercise

A sedentary lifestyle is associated with overweight/obesity, which involves excessive fat body accumulation, triggering structural and functional changes in tissues, organs, and body systems. Research shows that this fat accumulation is responsible for several comorbidities, including cardiovascular, gastrointestinal, and metabolic dysfunctions, as well as pathological pain behaviors. These health concerns are related to the crosstalk between adipose tissue and body systems, leading to pathophysiological changes to the latter. To deal with these health issues, it has been suggested that physical exercise may reverse part of these obesity-related pathologies by modulating the cross talk between the adipose tissue and body systems. In this context, this review was carried out to provide knowledge about (i) the structural and functional changes in tissues, organs, and body systems from accumulation of fat in obesity, emphasizing the crosstalk between fat and body tissues; (ii) the crosstalk between fat and body tissues triggering pain; and (iii) the effects of physical exercise on body tissues and organs in obese and non-obese subjects, and their impact on pathological pain. This information may help one to better understand this crosstalk and the factors involved, and it could be useful in designing more specific training interventions (according to the nature of the comorbidity).

Exercise Improved the Anti-Epileptic Effect of Carbamazepine through GABA Enhancement in Epileptic Rats

Carbamazepine (CBZ) is an anticonvulsant drug that usually is used for the treatment of seizures. The anti-epileptic and the anti-epileptogenic effect of exercise has been reported, as well. This study was aimed to evaluate the synergic effect of combined therapy of exercise and CBZ in epileptic rats, as well as the alternation of the GABA pathway as a possible involved mechanism. The seizure was induced by pentylenetetrazol (PTZ) injection. Animals were divided into sham, seizure, exercise (EX), CBZ (25, 50 and 75), EX + CBZ (25, 50 and 75). Treadmill forced running for 30 min has been considered as the exercise 5 days per week for four weeks. CBZ was injected in doses of 25, 50 and 75 mg/kg, half an hour before seizure induction and 5 h after doing exercise in the animals forced to exercise. Seizure severity reduced and latency increased in the EX + CBZ (25) and EX + CBZ (50) groups compared to the seizure group. The distribution of GAD65 in both hippocampal CA1 and CA3 areas increased in the EX + CBZ (75) group. GABAA receptor α1 was up-regulated in the CA3 area of the EX + CBZ (75) group. The distribution of GAD65 in the cortical area increased in EX, EX + CBZ (50), CBZ (75) and EX + CBZ (75) groups. GABAA receptor α1 was up-regulated in the neocortex of EX + CBZ (50), CBZ (75) and EX + CBZ (75) groups. Our findings suggested that exercise has improved the efficacy of CBZ and reduced the anti-epileptic dose. The enhancement of GABA signaling might be involved in the synergistic effect of exercise and CBZ.

Exercise-Induced Plasticity in Signaling Pathways Involved in Motor Recovery after Spinal Cord Injury

Spinal cord injury (SCI) leads to numerous chronic and debilitating functional deficits that greatly affect quality of life. While many pharmacological interventions have been explored, the current unsurpassed therapy for most SCI sequalae is exercise. Exercise has an expansive influence on peripheral health and function, and by activating the relevant neural pathways, exercise also ameliorates numerous disorders of the central nervous system (CNS). While the exact mechanisms by which this occurs are still being delineated, major strides have been made in the past decade to understand the molecular underpinnings of this essential treatment. Exercise rapidly and prominently affects dendritic sprouting, synaptic connections, neurotransmitter production and regulation, and ionic homeostasis, with recent literature implicating an exercise-induced increase in neurotrophins as the cornerstone that binds many of these effects together. The field encompasses vast complexity, and as the data accumulate, disentangling these molecular pathways and how they interact will facilitate the optimization of intervention strategies and improve quality of life for individuals affected by SCI. This review describes the known molecular effects of exercise and how they alter the CNS to pacify the injury environment, increase neuronal survival and regeneration, restore normal neural excitability, create new functional circuits, and ultimately improve motor function following SCI.

Exercise Ameliorates Spinal Cord Injury by Changing DNA Methylation

Exercise training is a traditional method to maximize remaining function in patients with spinal cord injury (SCI), but the exact mechanism by which exercise promotes recovery after SCI has not been identified; whether exercise truly has a beneficial effect on SCI also remains unclear. Previously, we showed that epigenetic changes in the brain motor cortex occur after SCI and that a treatment leading to epigenetic modulation effectively promotes functional recovery after SCI. We aimed to determine how exercise induces functional improvement in rats subjected to SCI and whether epigenetic changes are engaged in the effects of exercise. A spinal cord contusion model was established in rats, which were then subjected to treadmill exercise for 12 weeks. We found that the size of the lesion cavity and the number of macrophages were decreased more in the exercise group than in the control group after 12 weeks of injury. Immunofluorescence and DNA dot blot analysis revealed that levels of 5-methylcytosine (5mC) and 5-hydroxymethylcytosine (5hmC) in the brain motor cortex were increased after exercise. Accordingly, the expression of ten-eleven translocation (Tet) family members (Tet1, Tet2, and Tet3) in the brain motor cortex also elevated. However, no macrophage polarization was induced by exercise. Locomotor function, including Basso, Beattie, and Bresnahan (BBB) and ladder scores, also improved in the exercise group compared to the control group. We concluded that treadmill exercise facilitates functional recovery in rats with SCI, and mechanistically epigenetic changes in the brain motor cortex may contribute to exercise-induced improvements.