Long-Term Regular Eccentric Exercise Decreases Neuropathic Pain-like Behavior and Improves Motor Functional Recovery in an Axonotmesis Mouse Model: the Role of Insulin-like Growth Factor-1

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.

Evaluation and management of body composition changes in cancer patients

Wasting in cancer patients has long been recognized as a condition that adversely affects cancer patients' quality of life, treatment tolerance, and oncological outcomes. Historically, this condition was mainly evaluated by changes in body weight. However, this approach is not quite accurate because body weight is the overall change of all body compartments. Conditions such as edema and ascites can mask the severity of muscle and adipose tissue depletion. Changes in body composition assessment in cancer patients have historically been underappreciated because of the limited availability of measurement tools. As more evidence highlighting the importance of body composition has emerged, it is imperative to apply a more precise evaluation of nutritional status and a more targeted approach to provide nutritional support for cancer patients. In this review, we will discuss the modalities for evaluating body composition and how to manage body composition changes in cancer patients.

Effect of Type and Dose of Exercise on Neuropathic Pain After Experimental Sciatic Nerve Injury: A Preclinical Systematic Review and Meta-Analysis

This preclinical systematic review aimed to determine the effectiveness of different types and doses of exercise on pain behavior and biomarkers in preclinical models of focal neuropathic pain. We searched MEDLINE, EMBASE, Web of Science, PubMed, SCOPUS, CINAHL, and Cochrane library from inception to November 2022 for preclinical studies evaluating the effect of exercise compared to control interventions on neuropathic pain behavior after experimental sciatic nerve injury. If possible, data were meta-analyzed using random effect models with inverse-variance weighting. Thirty-seven studies were included and 26 meta-analyzed. Risk of bias (SYRCLE tool) remained unclear in most studies and reporting quality (CAMARADES) was variable. Exercise reduced mechanical (standardized mean differences [SMD] .53 (95% CI .31, .74), P = .0001, I2 = 0%, n = 364), heat (.32 (.07, .57), P = .01, I2 = 0%, n = 266) and cold hypersensitivity (.51 (.03, 1.0), P = .04, I2 = 0%, n = 90) compared to control interventions. No relationship was apparent between exercise duration or intensity and antinociception. Exercise modulated biomarkers related to different systems (eg, immune system, neurotrophins). Whereas firm conclusions are prevented by the use of male animals only, variable reporting quality and unclear risk of bias in many studies, our results suggest that aerobic exercise is a promising tool in the management of focal neuropathic pain. PERSPECTIVE: This systematic review and meta-analysis demonstrates that aerobic exercise reduces neuropathic pain-related behavior in preclinical models of sciatic nerve injury. This effect is accompanied by changes in biomarkers associated with inflammation and neurotrophins among others. These results could help to develop exercise interventions for patients with neuropathic pain.

The effects of aerobic exercise on neuroimmune responses in animals with traumatic peripheral nerve injury: a systematic review with meta-analyses

BACKGROUND

Increasing pre-clinical evidence suggests that aerobic exercise positively modulates neuroimmune responses following traumatic nerve injury. However, meta-analyses on neuroimmune outcomes are currently still lacking. This study aimed to synthesize the pre-clinical literature on the effects of aerobic exercise on neuroimmune responses following peripheral nerve injury.

METHODS

MEDLINE (via Pubmed), EMBASE and Web of Science were searched. Controlled experimental studies on the effect of aerobic exercise on neuroimmune responses in animals with a traumatically induced peripheral neuropathy were considered. Study selection, risk of bias assessment and data extraction were performed independently by two reviewers. Results were analyzed using random effects models and reported as standardized mean differences. Outcome measures were reported per anatomical location and per class of neuro-immune substance.

RESULTS

The literature search resulted in 14,590 records. Forty studies were included, reporting 139 comparisons of neuroimmune responses at various anatomical locations. All studies had an unclear risk of bias. Compared to non-exercised animals, meta-analyses showed the following main differences in exercised animals: (1) in the affected nerve, tumor necrosis factor-α (TNF-α) levels were lower (p = 0.003), while insulin-like growth factor-1 (IGF-1) (p < 0.001) and Growth Associated Protein 43 (GAP43) (p = 0.01) levels were higher; (2) At the dorsal root ganglia, brain-derived neurotrophic factor (BDNF)/BDNF mRNA levels (p = 0.004) and nerve growth factor (NGF)/NGF mRNA (p < 0.05) levels were lower; (3) in the spinal cord, BDNF levels (p = 0.006) were lower; at the dorsal horn, microglia (p < 0.001) and astrocyte (p = 0.005) marker levels were lower; at the ventral horn, astrocyte marker levels (p < 0.001) were higher, and several outcomes related to synaptic stripping were favorably altered; (4) brainstem 5-HT2A receptor levels were higher (p = 0.001); (5) in muscles, BDNF levels (p < 0.001) were higher and TNF-α levels lower (p < 0.05); (6) no significant differences were found for systemic neuroimmune responses in blood or serum.

CONCLUSION

This review revealed widespread positive modulatory effects of aerobic exercise on neuroimmune responses following traumatic peripheral nerve injury. These changes are in line with a beneficial influence on pro-inflammatory processes and increased anti-inflammatory responses. Given the small sample sizes and the unclear risk of bias of the studies, results should be interpreted with caution.

Electrical Stimulation of the Auricular Branch Vagus Nerve Using Random and Alternating Frequencies Triggers a Rapid Onset and Pronounced Antihyperalgesia via Peripheral Annexin A1-Formyl Peptide Receptor 2/ALX Pathway in a Mouse Model of Persistent Inflammatory Pain

This study evaluated the antihyperalgesic and anti-inflammatory effects of percutaneous vagus nerve electrical stimulation (pVNS) by comparing the effects of alternating and random frequencies in an animal model of persistent inflammatory hyperalgesia. The model was induced by Freund's complete adjuvant (CFA) intraplantar (i.pl.) injection. Mice were treated with different protocols of time (10, 20, or 30 min), ear laterality (right, left or both), and frequency (alternating or random). Mechanical hyperalgesia was evaluated, and some groups received i.pl. WRW4 (FPR2/ALX antagonist) to determine the involvement. Edema, paw surface temperature, and spontaneous locomotor activity were evaluated. Interleukin-1β, IL-6, IL-10, and IL4 levels were verified by enzyme-linked immunosorbent assay. AnxA1, FPR2/ALX, neutrophil, M1 and M2 phenotype macrophage, and apoptotic cells markers were identified using western blotting. The antihyperalgesic effect pVNS with alternating and random frequency effect is depending on the type of frequency, time, and ear treated. The pVNS random frequency in the left ear for 10 min had a longer lasting antihyperalgesic effect, superior to classical stimulation using alternating frequency and the FPR2/ALX receptor was involved in this effect. There was a reduction in the levels of pro-inflammatory cytokines and an increase in the immunocontent of AnxA1 and CD86 in mice paw. pVNS with a random frequency in the left ear for 10 min showed to be optimal for inducing an antihyperalgesic effect. Thus, the random frequency was more effective than the alternating frequency. Therefore, pVNS may be an important adjunctive treatment for persistent inflammatory pain.

APP96-110 Elicits Neuroprotective Effects Following Ischemic Insult in Animal Models

Competitive amyloidogenic pathways play an important role in many neurological diseases such as the onset of various degenerative diseases and ischemic stroke. Overexpression of amyloid precursor protein (APP) and amyloid-beta is modulated via the amyloidogenic pathway, which plays a crucial role in neuroinflammation. During ischemic conditions, the activity of the anti-inflammatory non-amyloidogenic pathway decreases, thus increasing the activity of amyloidogenic pathway. The soluble alpha form of APP (sAPPα), formed via the non-amyloidogenic pathway, exhibits neuroprotective effects against neurological diseases. sAPPα is thought to have a modulatory effect on several cell survival pathways, including its ability to inhibit the phosphoinositide 3-kinases (PI3K) pathway, thereby inhibiting the inflammatory response. The APP derivative, APP96-110, could act as a functional substitute for native sAPPα. Herein, we investigated whether APP96-110 has neuroprotective effects against neuroinflammation and damage following cerebral ischemic stroke. Treatment with diluted APP96-110 (0.005 mg/kg) in mice after 30 min of transient middle cerebral artery occlusion (tMCAO) showed improved motor function and reduced expression of the inflammatory marker CD86. APP96-110 decreased the infarct size and induced an anti-inflammatory response by inhibiting the PI3K pathway. These results suggest that the treatment of APP96-110 is efficacious in reducing neuroinflammation and infarct size in ischemic stroke.

Drug repositioning: diacerein as a new therapeutic approach in a mice model of sciatic nerve injury

BACKGROUND

Peripheral nerve injuries negatively impact the quality of life of patients, with no effective treatment available that accelerates sensorimotor recovery and promotes functional improvement and pain relief. The aim of this study was to evaluate the effects of diacerein (DIA) in an experimental mice model of sciatic nerve crush.

METHOD

In this study, male Swiss mice were used, randomly separated into six groups as follows: FO (false-operated + vehicle); FO + DIA (false-operated + diacerein 30 mg/kg); SNI (sciatic nerve injury + vehicle); SNI + DIA in doses of 3, 10 and 30 mg/kg (sciatic nerve injury + treatment with diacerein in doses of 3-30 mg/kg). DIA or vehicle was administered 24 h after the surgical procedure, intragastrically, twice a day. The lesion of the right sciatic nerve was generated by crush.

RESULTS

We found that the treatment of animals with DIA accelerated sensorimotor recovery of the animal. In addition, animals in the sciatic nerve injury + vehicle (SNI) group showed hopelessness, anhedonia, and lack of well-being, which were significantly inhibited by DIA treatment. The SNI group showed a reduction in the diameters of nerve fibers, axons, and myelin sheaths, while DIA treatment recovered all these parameters. In addition, the treatment of animals with DIA prevented an increase the levels of interleukin (IL)-1β and a reduction in the levels of the brain-derived growth factor (BDNF).

CONCLUSIONS

Treatment with DIA reduces hypersensitivity and depression like behaviors in animals. Furthermore, DIA promotes functional recovery and regulates IL-1β and BDNF concentrations.

Effect of combined intervention of exercise and autologous bone marrow stromal cell transplantation on neurotrophic factors and pain-related cascades over time after sciatic nerve injury

The purpose of this study was to determine whether combined inter-vention of treadmill exercise and bone marrow stromal cell (BMSC) transplantation would affect the expression of neurotrophic factors in the sciatic nerve injury (SNI) and neuropathic pain-related cascades in ipsilateral lumbar 4-5 dorsal root ganglion (DRG) during the early or late stage of sciatic nerve regeneration. The rats were randomly divided into the normal control group (CONT, n=6), sedentary group (SS, n=24), exercise group (SE, n=24), BMSC transplantation group (SB, n=24), BMSC transplantation+exercise group (SBE, n=24) 1, 2, 3, and 5 weeks after SNI. Single dose of 5×10⁶ harvested BMSC was injected into the injury area sing by a 30 gauge needle. Treadmill exercise was performed at a speed of 8 m/min for 30 min once a day. Tropomyosin-receptor kinase B, brain-derived neurotrophic factor and ciliary neurotrophic fac-tor were significantly upregulated in the SE and SBE groups at 1- and 2-week postinjury than those in the CONT and SS groups, and SB and SBE groups continuously kept up proinflammatory cytokines until the late stage of regeneration. Nuclear factor kappa-light-chain-enhancer of activated B cells, interleukin and tumor necrosis factor alpha in ipsi-lateral DRG were progressively decreased by exercise alone application and/or BMSC transplantation at early and late stage of regeneration. Present results provide reliable information that combined intervention of treadmill exercise and BMSC transplantation might be one of the effective treatment strategies for recovering sciatic nerve injury-induced neuropathic pain over time.

Tendon pain - what are the mechanisms behind it?

OBJECTIVES

Management of chronic tendon pain is difficult and controversial. This is due to poor knowledge of the underlying pathophysiology of chronic tendon pain, priorly known as tendinitis but now termed tendinopathy. The objective of this topical review was to synthesize evolving information of mechanisms in tendon pain, using a comprehensive search of the available literature on this topic.

CONTENT

This review found no correlations between tendon degeneration, collagen separation or neovascularization and chronic tendon pain. The synthesis demonstrated that chronic tendon pain, however, is characterized by excessive nerve sprouting with ingrowth in the tendon proper, which corresponds to alterations oberserved also in other connective tissues of chronic pain conditions. Healthy, painfree tendons are devoid of nerve fibers in the tendon proper, while innervation is confined to tendon surrounding structures, such as sheaths. Chronic painful tendons exhibit elevated amounts of pain neuromediators, such as glutamate and substance p as well as up-regulated expression and excitability of pain receptors, such as the glutamate receptor NMDAR1 and the SP receptor NK1, found on ingrown nerves and immune cells. Increasing evidence indicates that mast cells serve as an important link between the peripheral nervous system and the immune systems resulting in so called neurogenic inflammation.

SUMMARY

Chronic painful tendons exhibit (1) protracted ingrowth of sensory nerves (2) elevated pain mediator levels and (3) up-regulated expression and excitability of pain receptors, participating in (4) neuro-immune pathways involved in pain regulation. Current treatments that entail the highest scientific evidence to mitigate chronic tendon pain include eccentric exercises and extracorporeal shockwave, which both target peripheral neoinnervation aiming at nerve regeneration.

OUTLOOK

Potential mechanism-based pharmacological treatment approaches could be developed by blocking promotors of nerve ingrowth, such as NGF, and promoting inhibitors of nerve ingrowth, like semaphorins, as well as blocking glutamate-NMDA-receptor pathways, which are prominent in chronic tendon pain.

The Role of Physical Exercise and Rehabilitative Implications in the Process of Nerve Repair in Peripheral Neuropathies: A Systematic Review

BACKGROUND

The various mechanisms involved in peripheral nerve regeneration, induced by exercise and electrical nerve stimulation, are still unclear.

OBJECTIVE

The aim of this review was to summarize the influence of physical exercise and/or electrical stimulation on peripheral nerve repair and regeneration and the variation of impact of intervention depending on timing, as well as kind and dosage of the intervention. A literature survey was conducted on PubMed, Scopus, and Web of Science, between February 2021 to July 2021, with an update in September 2022.

METHODOLOGY

The literature search identified 101,386 articles with the keywords: "peripheral nerve" OR "neuropathy" AND "sprouting" OR "neuroapraxia" OR "axonotmesis" OR "neurotmesis" OR "muscle denervation" OR "denervated muscle" AND "rehabilitation" OR "physical activity" OR "physical exercise" OR "activity" OR "electrical stimulation". A total of 60 publications were included. Eligible studies were focused on evaluating the process of nerve repair (biopsy, electromyographic parameters or biomarker outcomes) after electrical stimulation or physical exercise interventions on humans or animals with peripheral sensory or motor nerve injury.

SYNTHESIS

This study shows that the literature, especially regarding preclinical research, is mainly in agreement that an early physical program with active exercise and/or electrical stimulation promotes axonal regenerative responses and prevents maladaptive response. This was evaluated by means of changes in electrophysiological recordings of CMAPs for latency amplitude, and the sciatic functional index (SFI). Furthermore, this type of activity can cause an increase in weight and in muscle fiber diameter. Nevertheless, some detrimental effects of exercising and electrical stimulation too early after nerve repair were recorded.

CONCLUSION

In most preclinical studies, peripheral neuropathy function was associated with improvements after physical exercise and electrical stimulation. For humans, too little research has been conducted on this topic to reach a complete conclusion. This research supports the need for future studies to test the validity of a possible rehabilitation treatment in humans in cases of peripheral neuropathy to help nerve sprouting.

Molecular mechanisms of exercise contributing to tissue regeneration

Physical activity has been known as an essential element to promote human health for centuries. Thus, exercise intervention is encouraged to battle against sedentary lifestyle. Recent rapid advances in molecular biotechnology have demonstrated that both endurance and resistance exercise training, two traditional types of exercise, trigger a series of physiological responses, unraveling the mechanisms of exercise regulating on the human body. Therefore, exercise has been expected as a candidate approach of alleviating a wide range of diseases, such as metabolic diseases, neurodegenerative disorders, tumors, and cardiovascular diseases. In particular, the capacity of exercise to promote tissue regeneration has attracted the attention of many researchers in recent decades. Since most adult human organs have a weak regenerative capacity, it is currently a key challenge in regenerative medicine to improve the efficiency of tissue regeneration. As research progresses, exercise-induced tissue regeneration seems to provide a novel approach for fighting against injury or senescence, establishing strong theoretical basis for more and more "exercise mimetics." These drugs are acting as the pharmaceutical alternatives of those individuals who cannot experience the benefits of exercise. Here, we comprehensively provide a description of the benefits of exercise on tissue regeneration in diverse organs, mainly focusing on musculoskeletal system, cardiovascular system, and nervous system. We also discuss the underlying molecular mechanisms associated with the regenerative effects of exercise and emerging therapeutic exercise mimetics for regeneration, as well as the associated opportunities and challenges. We aim to describe an integrated perspective on the current advances of distinct physiological mechanisms associated with exercise-induced tissue regeneration on various organs and facilitate the development of drugs that mimics the benefits of exercise.

Effect of TGF-β1-Mediated Exercise Analgesia in Spared Nerve Injury Mice

Peripheral nerve injury leads to severe neuropathic pain. Previous studies have highlighted the beneficial effects of physical exercise on alleviating neuropathic pain. Exercise regulating transforming growth factor-β1 (TGF-β1) can improve several diseases and relieve neuropathic pain induced by peripheral nerve injury. Here, we investigated whether exercise could alleviate neuropathic pain by modulating TGF-β1 expression. We assessed mechanical and cold pain behavior and conducted molecular evaluation of the spinal cord. We found that spared nerve injury (SNI) led to mechanical and cold allodynia in the hind paw, elevated the expression of latency-associated peptide- (LAP-) TGF-β1, and activated astroglial in the spinal cord. Exercise decreases allodynia, astroglial activation, and LAP-TGF-β1 in SNI mice. Intrathecal injection of a TGF-type I receptor inhibitor attenuated exercise analgesia and enhanced astroglial activation. These findings demonstrate that exercise induces analgesia by promoting TGF-β1 activation and inhibiting astrogliosis. Our study reveals a new underlying mechanism for exercise-attenuated neuropathic pain in the maintenance stage of neuropathic pain after nerve injury.

Exercise medicine for cancer cachexia: targeted exercise to counteract mechanisms and treatment side effects

Purpose

Cancer-induced muscle wasting (i.e., cancer cachexia, CC) is a common and devastating syndrome that results in the death of more than 1 in 5 patients. Although primarily a result of elevated inflammation, there are multiple mechanisms that complement and amplify one another. Research on the use of exercise to manage CC is still limited, while exercise for CC management has been recently discouraged. Moreover, there is a lack of understanding that exercise is not a single medicine, but mode, type, dosage, and timing (exercise prescription) have distinct health outcomes. The purpose of this review was to examine the effects of these modes and subtypes to identify the most optimal form and dosage of exercise therapy specific to each underlying mechanism of CC.

Methods

The relevant literatures from MEDLINE and Scopus databases were examined.

Results

Exercise can counteract the most prominent mechanisms and signs of CC including muscle wasting, increased protein turnover, systemic inflammation, reduced appetite and anorexia, increased energy expenditure and fat wasting, insulin resistance, metabolic dysregulation, gut dysbiosis, hypogonadism, impaired oxidative capacity, mitochondrial dysfunction, and cancer treatments side-effects. There are different modes of exercise, and each mode has different sub-types that induce vastly diverse changes when performed over multiple sessions. Choosing suboptimal exercise modes, types, or dosages can be counterproductive and could further contribute to the mechanisms of CC without impacting muscle growth.

Conclusion

Available evidence shows that patients with CC can safely undertake higher-intensity resistance exercise programs, and benefit from increases in body mass and muscle mass.

Global Research on Neuropathic Pain Rehabilitation over the Last 20 Years

Background

Neuropathic pain has long been a very popular and productive field of clinical research. Neuropathic pain is difficult to cure radically because of its complicated etiology and uncertain pathogenesis. As pain worsens and persists, pain recovery techniques become more important, and medication alone is insufficient. No summary of bibliometric studies on neuropathic pain rehabilitation is yet available. The purpose of the present study is to analyze in a systematic manner the trends of neuropathic pain rehabilitation research over the period of 2000–2019.

Methods

Studies related to neuropathic pain rehabilitation and published between January 2000 and December 2019 were obtained from the Science Citation Index-Expanded of Web of Science. No restrictions on language, literature type, or species were established. CiteSpace V and Microsoft Excel were used to capture basic information and highlights in the field.

Results

Linear regression analysis showed that the number of publications on neuropathic pain rehabilitation significantly increased over time (P < 0.001). The United States showed absolute strength in terms of number of papers published, influence, and cooperation with other countries. Based on the subject categories of the Web of Science, “Rehabilitation” had the highest number of published papers (446), the highest number of citations (10,954), and the highest number of open-access papers (151); moreover, this category and “Clinical Neurology” had the same H-index (i.e., 52). “Randomized Controlled Trials” revealed the largest cluster in the cocitation map of references. The latest burst keywords included “Exercise” (2014–2019), “Functional Recovery” (2015–2019), and “Questionnaire” (2015–2019).

Conclusion

This study provides valuable information for neuropathic pain rehabilitation researchers seeking fresh viewpoints related to collaborators, cooperative institutions, and popular topics in this field. Some new research trends are also highlighted.

Excursion of the median nerve during a contra-lateral cervical lateral glide movement in people with and without cervical radiculopathy

BACKGROUND

A segmental, contra-lateral cervical lateral glide (CCLG) mobilization technique is effective for patients with cervical radiculopathy (CR). The CCLG technique induces median nerve sliding in healthy individuals, but this has not been assessed in patients with CR.

OBJECTIVE

This study aimed to 1) assess longitudinal excursion of the median nerve in patients with CR and asymptomatic participants during a CCLG movement, 2) reassess nerve excursions following an intervention at a 3-month follow-up in patients with CR and 3) correlate changes in nerve excursions with changes in clinical signs and symptoms.

DESIGN

Case-control study.

METHODS

During a computer-controlled mechanically induced CCLG, executed by the Occiflex™, longitudinal median nerve excursion was assessed at the wrist and elbow with ultrasound imaging (T0) in 20 patients with CR and 20 matched controls. Patients were re-assessed at a 3-month follow-up (T1), following conservative treatment including neurodynamic mobilization.

RESULTS

There was a significant difference between patients and controls in the excursion of the median nerve at both the wrist (Mdn = 0.50 mm; IQR = 0.13-1.30; 2.10 mm (IQR = 1.42-2.80, p < 0.05)) and elbow (Mdn = 1.21 mm (IQR = 0.85-1.94); 3.49 mm (IQR = 2.45-4.24, p < 0.05)) respectively at T0. There was also a significant increase in median nerve excursion at both sites between T0 and T1 in those with CR (Mdn = 1.96, 2.63 respectively). Wilcoxon Signed-Ranks Test indicated median pre-test ranks (Mdn = 0.5, 1.21; Z = - 3.82, p < 0.01; Z = -3.78, p < 0.01 respectively) and median post-test ranks. There was a strong correlation between improvement in median nerve excursion at the elbow at T1 and improvement in pain intensity (r = 0.7, p < 0.001) and functional limitations (r = 0.6, p < 0.01).

CONCLUSION

Longitudinal median nerve excursion differs significantly between patients with CR and asymptomatic volunteers at baseline, but this difference is no longer present after 3 months of conservative physiotherapy management. Improvement in nerve excursion correlates with improvement in clinical signs and symptoms.

Effect of exercise on microglial activation and transcriptome of hippocampus in fluorosis mice

Fluorosis is a widespread endemic disease. Reports have shown that high fluoride causes the dysfunction of central nervous system (CNS) in animals. The neurotoxicity of fluoride may be related to the activation of microglia. Moreover, numerous studies have found that exercise facilitates the plasticity of structure and function in CNS, partly owing to the regulation of microglia activation. The present study was conducted to explore the effect of exercise on the microglial activation of hippocampus in fluorosis mice. One hundred adult female Institute of Cancer Research (ICR) mice were randomly divided into 4 groups: control group (group C, distilled water by gavage); exercise group (group E, distilled water by gavage and treadmill exercise); fluoride group [group F, 24 mg/kg sodium fluoride (NaF) by gavage]; fluoride plus exercise group (group F + E, 24 mg/kg NaF by gavage and treadmill exercise). After 8 weeks, hippocampal morphological structure, microglial activation and RNA transcriptome of mice in each group were evaluated by hematoxylin and eosin (HE) staining, Nissl staining, immunohistochemistry (IHC), quantitative real time PCR (QRT-PCR) and transcriptome sequencing. We discovered that the number of M1-type microglia in fluorosis-mice hippocampus was significantly increased when compared to group C; group F + E showed a decrease in the number of M1-type microglia with the comparison to group F. In addition, the hippocampal transcriptome analysis showed that 576 differential expression genes (DEG) were confirmed in group F, compared to group C, and 670 DEG were differently expressed in group F + E when compared to group F. Gene Ontology (GO) analysis showed that changed genes were implicated in regulation of transcription, DNA-templated, integral component of membrane and adenosine triphosphate (ATP) binding. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis of 670 DEG was helpful to find neuroactive ligand-receptor interaction pathway. In conclusion, these results indicate that treadmill running inhibits the excessive activation of microglia in hippocampus of the fluoride-toxic mice, accompanied with the alteration of neuroactive ligand-receptor interaction pathway.

The use of zebrafish as a non-traditional model organism in translational pain research: the knowns and the unknowns

The ability of the nervous system to detect a wide range of noxious stimuli is crucial to avoid life-threatening injury and to trigger protective behavioral and physiological responses. Pain represents a complex phenomenon, including nociception associated with cognitive and emotional processing. Animal experimental models have been developed to understand the mechanisms involved in pain response, as well as to discover novel pharmacological and non-pharmacological anti-pain therapies. Due to the genetic tractability, similar physiology, low cost, and rich behavioral repertoire, the zebrafish (Danio rerio) has been considered a powerful aquatic model for modeling pain responses. Here, we summarize the molecular machinery of zebrafish to recognize painful stimuli, as well as emphasize how zebrafish-based pain models have been successfully used to understand specific molecular, physiological, and behavioral changes following different algogens and/or noxious stimuli (e.g., acetic acid, formalin, histamine, Complete Freund's Adjuvant, cinnamaldehyde, allyl isothiocyanate, and fin clipping). We also discuss recent advances in zebrafish-based studies and outline the potential advantages and limitations of the existing models to examine the mechanisms underlying pain responses from an evolutionary and translational perspective. Finally, we outline how zebrafish models can represent emergent tools to explore pain behaviors and pain-related mood disorders, as well as to facilitate analgesic therapy screening in translational pain research.

Knockdown of miR-130a-3p alleviates spinal cord injury induced neuropathic pain by activating IGF-1/IGF-1R pathway

BACKGROUND

Recent studies have elucidated the instrumental role of microRNAs (miRNAs) in neuropathic pain (NP) progression. As one member of miRNAs, miR-130a-3p has been proved as a mediator in inflammation and neuronal maturation. The present study attempted to elucidate what effect miR-130a-3p exerts on NP.

MATERIALS AND METHODS

The miR-130a-3p expression in the spinal cord tissues of rat with spinal cord compression injury (SCI) and LPS-induced BV2 microglia was determined with RT-PCR, which was further applied to analyze the clinical relevance between miR-130a-3p and neuropathic pain. Besides, the expression of IGF-1, IL-1β, IL-6, and TNF-α in the spinal cord tissues of rats was measured using RT-PCR and ELISA after intrathecal injection of miR-130a-3p inhibitors and tail vein injection of IGF-1 low-expression lentivirus (Lv-shIGF-1). Further, neuronal apoptosis (labeled by Caspase3) and microglial activation (labeled by Iba1) were examined by immunohistochemistry (IHC), and the levels of IGF-1, IGF-1R, NF-κB were determined by western blot. Additionally, bioinformatic was employed to analyze the potential target genes of miR-130a-3p. Furthermore, the dual luciferase activity assay and RNA immunoprecipitation assay were conducted to further substantiate whether miR-130a-3p targets IGF-1.

RESULTS

In comparison with the sham group, the miR-130a-3p expression was remarkably up-regulated in the spinal cord lesions of SCI rats. The ELISA results showed that inhibiting the miR-130a-3p significantly reduced NP symptoms of SCI rats, mitigated neuronal apoptosis, microglial activation, repressed NF-κB phosphorylation and the IL-1β, IL-6 and TNF-α expressions in SCI rats. Contrarily, downregulation of miR-130a-3p increased IGF-1 and IGF-1R expression. What's more, we observed the same effects in BV2 microglia. In addition, the bioinformatics analysis showed that miR-130-3p targeted at the 3'-untranslated region of IGF-1 and inhibiting its expression. However, abolishing IGF-1 not only promoted the inflammatory responses in the SCI lesions, but also aggravated NP of SCI rats, while those effects were attenuated by the downregulation of miR-130a-3p.

CONCLUSION

The inhibition of miR-130a-3p expression up-regulates the IGF-1/IGF-1R signaling pathway, thus reducing neuropathic pain caused by spinal cord injury.

Medium- and long-term functional behavior evaluations in an experimental focal ischemic stroke mouse model

Cerebrovascular accident (CVA) is one of the leading causes of death and disability worldwide, as well as a major financial burden for health care systems. CVA rodent models provide experimental support to determine possible in vivo therapies to reduce brain injury and consequent sequelae. This study analyzed nociceptive, motor, cognitive and mood functions in mice submitted to distal middle cerebral artery (DMCA) occlusion. Male C57BL mice (n = 8) were randomly allocated to control or DMCA groups. Motor function was evaluated with the tests: grip force, rotarod and open field; and nociceptive threshold with von Frey and hot plate assessments. Cognitive function was evaluated with the inhibitory avoidance test, and mood with the tail suspension test. Evaluations were conducted on the seventh- and twenty-eighth-day post DMCA occlusion to assess medium- and long-term effects of the injury, respectively. DMCA occlusion significantly decreases muscle strength and spontaneous locomotion (p < 0.05) both medium- and long term; as well as increases immobility in the tail-suspension test (p < 0.05), suggesting a depressive-type behavior. However, DMCA occlusion did not affect nociceptive threshold nor cognitive functions (p > 0.05). These results suggest that, medium- and long-term effects of DMCA occlusion include motor function impairments, but no sensory dysfunction. Additionally, the injury affected mood but did not hinder cognitive function.

The search for translational pain outcomes to refine analgesic development: Where did we come from and where are we going?

Pain measures traditionally used in rodents record mere reflexes evoked by sensory stimuli; the results thus may not fully reflect the human pain phenotype. Alterations in physical and emotional functioning, pain-depressed behaviors and facial pain expressions were recently proposed as additional pain outcomes to provide a more accurate measure of clinical pain in rodents, and hence to potentially enhance analgesic drug development. We aimed to review how preclinical pain assessment has evolved since the development of the tail flick test in 1941, with a particular focus on a critical analysis of some nonstandard pain outcomes, and a consideration of how sex differences may affect the performance of these pain surrogates. We tracked original research articles in Medline for the following periods: 1973-1977, 1983-1987, 1993-1997, 2003-2007, and 2014-2018. We identified 606 research articles about alternative surrogate pain measures, 473 of which were published between 2014 and 2018. This indicates that preclinical pain assessment is moving toward the use of these measures, which may soon become standard procedures in preclinical pain laboratories.

Voluntary exercise reduces both chemotherapy-induced neuropathic nociception and deficits in hippocampal cellular proliferation in a mouse model of paclitaxel-induced peripheral neuropathy

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Paclitaxel treatment did not alter voluntary running activity.

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Voluntary running reduced mechanical and cold allodynia induced by paclitaxel.

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Voluntary running reduced paclitaxel-induced deficits in hippocampal cellular proliferation.

Chemotherapy-induced peripheral neuropathy (CIPN) is a common dose-limiting side-effect of all major chemotherapeutic agents. Here, we explored efficacy of voluntary exercise as a nonpharmacological strategy for suppressing two distinct adverse side effects of chemotherapy treatment. We evaluated whether voluntary running would suppress both neuropathic pain and deficits in hippocampal cell proliferation in a mouse model of CIPN induced by the taxane chemotherapeutic agent paclitaxel. Mice were given free access to running wheels or were housed without running wheels during one of three different intervention phases: 1) during the onset (i.e. development phase) of paclitaxel-induced neuropathy, 2) prior to dosing with paclitaxel or its vehicle, or 3) following the establishment (i.e. maintenance phase) of paclitaxel-induced neuropathy. Paclitaxel treatment did not alter running wheel behavior relative to vehicle-treated animals in any study. Animals that engaged in voluntary running during the development phase of paclitaxel-induced neuropathy failed to display mechanical or cold hypersensitivities relative to sedentary control animals that did not have access to running wheels. A prior history of voluntary running delayed the onset of, but did not fully prevent, development of paclitaxel-induced neuropathic pain behavior. Voluntary running reduced already established mechanical and cold allodynia induced by paclitaxel. Importantly, voluntary running did not alter mechanical or cold responsivity in vehicle-treated animals, suggesting that the observed antinociceptive effect of exercise was dependent upon the presence of the pathological pain state. In the same animals evaluated for nociceptive responding, paclitaxel also reduced cellular proliferation but not cellular survival in the dentate gyrus of the hippocampus, as measured by immunohistochemistry for Ki67 and BrdU expression, respectively. Voluntary running abrogated paclitaxel-induced reductions in cellular proliferation to levels observed in vehicle-treated mice and also increased BrdU expression levels irrespective of chemotherapy treatment. Our studies support the hypothesis that voluntary exercise may be beneficial in suppressing both neuropathic pain and markers of hippocampal cellular function that are impacted by toxic challenge with chemotherapeutic agents.