A model of neuropathic pain in brachial plexus avulsion injury and associated spinal glial cell activation

Methylcobalamin in Combination with Early Intervention of Low-Intensity Pulsed Ultrasound Potentiates Nerve Regeneration and Functional Recovery in a Rat Brachial Plexus Injury Model

This study evaluated and compared the functional recovery and histopathological outcomes of treatment involving low-intensity pulsed ultrasound (LIPUS) and methylcobalamin (B12) on brachial plexus injury (BPI) in an experimental rat model. Three days after BPI, the rats were assigned to receive either LIPUS or methylcobalamin alone or in combination consecutively for 12 days. Serial changes in sensory and motor behavioral responses, as well as morphological and immunohistochemical changes for substance P (SP), ionized calcium-binding adapter molecule 1 (iba1), brain-derived neurotrophic factor (BDNF), and S100 were examined 28 days after BPI as the outcome measurements. Early intervention of LIPUS and methylcobalamin, whether alone or in combination, augmented the sensory and motor behavioral recovery as well as modulated SP and iba1 expression in spinal dorsal horns, BDNF, and S100 in the injured nerve. Moreover, the combined therapy with its synergistic effect gave the most beneficial effect in accelerating functional recovery. In view of the effective initiation of early recovery of sensory and motor functions, treatment with LIPUS and methylcobalamin in combination has a potential role in the clinical management of early-phase BPI.

Acetylglutamine facilitates motor recovery and alleviates neuropathic pain after brachial plexus root avulsion in rats

BACKGROUND

Brachial plexus root avulsion (BPRA), a disabling peripheral nerve injury, induces substantial motoneuron death, motor axon degeneration and denervation of biceps muscles, leading to the loss of upper limb motor function. Acetylglutamine (N-acetyl-L-glutamine, NAG) has been proven to exert neuroprotective and anti-inflammatory effects on various disorders of the nervous system. Thus, the present study mainly focused on the influence of NAG on motor and sensory recovery after BPRA in rats and the underlying mechanisms.

METHODS

Male adult Sprague Dawley (SD) rats were subjected to BPRA and reimplantation surgery and subsequently treated with NAG or saline. Behavioral tests were conducted to evaluate motor function recovery and the mechanical pain threshold of the affected forelimb. The morphological appearance of the spinal cord, musculocutaneous nerve, and biceps brachii was assessed by histological staining. Quantitative real-time PCR (qRT‒PCR) was used to measure the mRNA levels of remyelination and regeneration indicators in myocutaneous nerves. The protein levels of inflammatory and pyroptotic indicators in the spinal cord anterior horn were measured using Western blotting.

RESULTS

NAG significantly accelerated the recovery of motor function in the injured forelimbs, enhanced motoneuronal survival in the anterior horn of the spinal cord, inhibited the expression of proinflammatory cytokines and pyroptosis pathway factors, facilitated axonal remyelination in the myocutaneous nerve and alleviated atrophy of the biceps brachii. Additionally, NAG attenuated neuropathic pain following BPRA.

CONCLUSION

NAG promotes functional motor recovery and alleviates neuropathic pain by enhancing motoneuronal survival and axonal remyelination and inhibiting the pyroptosis pathway after BPRA in rats, laying the foundation for the use of NAG as a novel treatment for BPRA.

Comparison of two methods for extracting exosomes from the nucleus accumbens in mice

BACKGROUND

Exosomes bind to and are endocytosed by neurons of various brain regions. Methods for isolating and extracting exosomes from specific brain samples are critical. At present, the most important extractive methods for exosomes are Ultracentrifugation and exosome isolation kit extraction. Both of these extraction methods have applications in neuroscience. We compare these methods to reveal the differences.

METHODS

We sectioned the nucleus accumbens of mice, and isolated exosomes. A culture medium containing exosomes was extracted using ultracentrifugation (UC) and a total exosome isolation kit (TEI). The exosomes were examined using transmission electron microscopy (TEM), measurement regarding the diameter of the exosomes was done, and the thermal allodynia and western blotting analysis were also conducted, respectively.

RESULTS

Transmission electron microscopy observations showed that the ultracentrifugation samples had higher purity and fewer impurities than the kit samples. The results from the two methods were then compared with a number ratio regarding the percentage was not statistically significant. Marker protein tests showed that proteins were expressed under both methods. The thermal allodynia testing observed that the two extraction methods did not affect pain behavior regarding the detection. After the kit extraction method, there were substantial white subjects suspended by PBS.

CONCLUSION

Our study compared the different protocols regarding exosome extraction from the nucleus accumbens and compared the quality of two principal methods for exosome extraction from a culture medium containing exosomes. It was found that the extraction quality of exosomes by ultracentrifugation was better, but the technical difficulty was greater.

Quercetin Ameliorates Neuropathic Pain after Brachial Plexus Avulsion via Suppressing Oxidative Damage through Inhibition of PKC/MAPK/ NOX Pathway

BACKGROUND

Brachial plexus avulsion (BPA) animally involves the separation of spinal nerve roots themselves and the correlative spinal cord segment, leading to formidable neuropathic pain of the upper limb.

METHODS

The right seventh cervical (C7) ventral and dorsal roots were avulsed to establish a neuropathic pain model in rats. After operation, rats were treated with quercetin (QCN) by intragastric administration for 1 week. The effects of QCN were evaluated using mechanical allodynia tests and biochemical assay kits.

RESULTS

QCN treatment significantly attenuated the avulsion-provoked mechanical allodynia, elevated the levels of catalase (CAT), superoxide dismutase (SOD) and glutathione peroxidase (GPx) and total antioxidant capacity (TAC) in the C7 spinal dorsal horn. In addition, QCN administration inhibited the activations of macrophages, microglia and astrocytes in the C6 dorsal root ganglion (DRG) and C6-8 spinal dorsal horn, as well as attenuated the release of purinergic 2X (P2X) receptors in C6 DRG. The molecular mechanism underlying the above alterations was found to be related to the suppression of the PKC/MAPK/NOX signal pathway. To further study the anti-oxidative effects of QCN, we applied QCN on the H2O2-induced BV-2 cells in vitro, and the results attested that QCN significantly ameliorated the H2O2-induced ROS production in BV-2 cells, inhibited the H2O2-induced activation of PKC/MAPK/NOX pathway.

CONCLUSION

Our study for the first time provided evidence that QCN was able to attenuate pain hypersensitivity following the C7 spinal root avulsion in rats, and the molecular mechanisms involve the reduction of both neuro-inflammatory infiltration and oxidative stress via suppression of P2X receptors and inhibition of the activation of PKC/MAPK/NOX pathway. The results indicate that QCN is a natural compound with great promise worthy of further development into a novel therapeutic method for the treatment of BPA-induced neuropathic pain.

Site of Nerve Division Affects Pain-Related Behavior and Spinal Cord Glial Proliferation after C7 Neurotomy in a Rat Stroke Model

Objective

This study aimed to evaluate whether the site of C7 neurotomy affects spinal cord glial cell activation and pain-related behavior on the paralyzed side in a rat stroke model.

Methods

After middle cerebral artery occlusion (MCAO) was induced in male Sprague-Dawley rats, they underwent C7 neurotomy 0, 2, and 4 mm distal to the intervertebral foramen on the paralyzed side. Pain-related behavior and immunofluorescence examination of spinal cord glial cell activation in the ipsilateral C7 dorsal horn were evaluated.

Results

Mechanical paw withdrawal threshold (MPWT) was lower, and the number of microglia and astrocytes (/mm²) was higher as the distance between the site of C7 neurotomy and the intervertebral foramen decreased from 4 mm to 0.

Conclusion

The site of C7 neurotomy affects MPWT and spinal cord glial proliferation in rats with MCAO. Nerve division closer to intervertebral foramen resulted in lower MPWT and higher degree of glial proliferation in the spinal cord.

Involvement of the BDNF-TrkB-KCC2 pathway in neuropathic pain after brachial plexus avulsion

INTRODUCTION

Brachial plexus avulsion significantly increased brain-derived neurotrophic factor (BDNF) release in the spinal cord. Here we investigated the involvement of the BDNF-TrkB-KCC2 pathway in neuropathic pain caused by BPA injury. We hypothesized that activation of BDNF-TrkB may inhibit neuronal excitability by downregulating KCC2 to maintain a high intracellular Cl-concentration. We established a neuropathic pain rat model by avulsion of the lower trunk brachial plexus, and investigated the effects of the TrkB-specific antibody K-252a on the expression of BDNF, TrkB, and KCC2.

METHODS

We randomly divided 40 male SD rats into four groups. In the brachial plexus avulsion group, C8-T1 roots were avulsed from the spinal cord at the lower trunk level. In the K252a group, 5uL K252a was applied intrathecally daily for three days after avulsion. In the sham surgery group, expose only and without damage. The control group did not undergo any treatment. Mechanical hyperalgesia and cold allodynia were analyzed by electronic pain measuring instrument and acetone spray method at different time points on days 1, 3, 7, 10, 14, and 21 after surgery. At 21 days after surgery, the expression of BDNF and TrkB in dorsal horn neurons and GFAP in astrocytes were detected by immunohistochemistry at the C5-T1 segment of the spinal cord. The expression levels of BDNF, TrkB, and KCC2 in the C5-T1 spinal cord were measured by Western Blot at 7 and 21 days.

RESULTS

Mechanical hyperalgesia and cold allodynia were significantly reduced in the K252a group compared with the brachial plexus avulsion group. Compared with the BPA group, BDNF, TrkB and GFAP were significantly decreased in the K252a group at 21 days after treatment by immunohistochemical test. In the WB test, the expressions of BDNF and TrkB in the K252a group were quantitatively detected to be decreased, while the expression of KCC2 was increased, which was obvious at 7 and 21 days.

CONCLUSION

BDNF-TrkB-KCC2 pathway can significantly relieve neuropathic pain after BPA, and is a potential target for the treatment of neuropathic pain.

A Novel Progress: Glial Cells and Inflammatory Pain

Inflammatory pain is the perception of noxious stimuli that occurs during inflammation or an immune response. Glial cells are widespread in the central and peripheral nervous systems, supporting and guiding the migration of neurons, participating in the immune response, forming the myelin sheath and blood-brain barrier, and maintaining the concentration of potassium ions outside nerve cells. Recent studies have shown that glial cells have a significant connection with the production and development of inflammatory pain. This article reviews the relationship, mechanisms, therapeutic targets between five types of glial cells and inflammatory pain, and the medicine composition that can effectively inhibit inflammatory pain. It expands the study on the mechanism of glial cells regulating pain and provides new ideas for the therapy of inflammatory pain.

Early Intervention of Cold-Water Swimming on Functional Recovery and Spinal Pain Modulation Following Brachial Plexus Avulsion in Rats

Brachial plexus avulsion (BPA) causes peripheral nerve injury complications with motor and sensory dysfunction of the upper limb. Growing evidence has shown an active role played by cold-water swimming (CWS) in alleviating peripheral neuropathic pain and functional recovery. This study examined whether CWS could promote functional recovery and pain modulation through the reduction of neuroinflammation and microglial overactivation in dorsal horn neurons at the early-stage of BPA. After BPA surgery was performed on rats, they were assigned to CWS or sham training for 5 min twice a day for two weeks. Functional behavioral responses were tested before and after BPA surgery, and each week during training. Results after the two-week training program showed significant improvements in BPA-induced motor and sensory loss (p < 0.05), lower inflammatory cell infiltration, and vacuole formation in injured nerves among the BPA-CWS group. Moreover, BPA significantly increased the expression of SP and IBA1 in dorsal horn neurons (p < 0.05), whereas CWS prevented their overexpression in the BPA-CWS group. The present findings evidenced beneficial rehabilitative effects of CWS on functional recovery and pain modulation at early-stage BPA. The beneficial effects are partially related to inflammatory suppression and spinal modulation. The synergistic role of CWS combined with other management approaches merits further investigation.

The influence of shoulder arthrodesis on the function of the upper limb in adult patients after a brachial plexus injury: a systematic literature review with elements of meta-analysis

Based on the literature, 294 shoulder arthrodeses after brachial plexus injury in adults were assessed, mostly male; the mean age of the patients was 33 years, and the mean follow-up time was 5.5 years. The most common cause of injury was a traffic accident, especially on a motorcycle.

Arthrodesis position ranged from 15 to 40 degrees of flexion, 15 to 60 degrees of abduction, and 0 to 50 degrees of internal rotation with the predominance of position by the 30-30-30 rule. Plates, screws, and external fixation were used for stabilization. The complication rate was at the level of 28%, the most common complication being delayed union or nonunion.

Active movements of flexion and abduction averaged 61 and 56 degrees, respectively, while reaching the hand to the mouth, front pocket, and buttock was feasible for 69%, 71%, and 38%, respectively, after surgery. Shoulder pain was present in 77% of patients, and 28% experienced no relevant pain reduction after surgery. The subjective satisfaction rate was 82% based on significant improvement and satisfaction reported by patients after arthrodesis.

Arthrodesis of the shoulder, in adult patients after brachial plexus palsy, can reduce shoulder pain, increase stability, and result in a range of motion that increases the possibility of carrying out everyday activities. This affects the high level of subjective patient satisfaction after surgery.

Cite this article: EFORT Open Rev 2021;6:797-807. DOI: 10.1302/2058-5241.6.200114

Transferrin receptor 1 plays an important role in muscle development and denervation-induced muscular atrophy

Previous studies demonstrate an accumulation of transferrin and transferrin receptor 1 (TfR1) in regenerating peripheral nerves. However, the expression and function of transferrin and TfR1 in the denervated skeletal muscle remain poorly understood. In this study, a mouse model of denervation was produced by complete tear of the left brachial plexus nerve. RNA-sequencing revealed that transferrin expression in the denervated skeletal muscle was upregulated, while TfR1 expression was downregulated. We also investigated the function of TfR1 during development and in adult skeletal muscles in mice with inducible deletion or loss of TfR1. The ablation of TfR1 in skeletal muscle in early development caused severe muscular atrophy and early death. In comparison, deletion of TfR1 in adult skeletal muscles did not affect survival or glucose metabolism, but caused skeletal muscle atrophy and motor functional impairment, similar to the muscular atrophy phenotype observed after denervation. These findings suggest that TfR1 plays an important role in muscle development and denervation-induced muscular atrophy. This study was approved by the Institutional Animal Care and Use Committee of Beijing Institute of Basic Medical Sciences, China (approval No. SYXK 2017-C023) on June 1, 2018.

Comparison of Different In Vivo Animal Models of Brachial Plexus Avulsion and Its Application in Pain Study

Brachial plexus injuries (BPIs) are high-energy trauma that can result in serious functional problems in the affected upper extremities, and brachial plexus avulsion (BPA) could be considered the most severe type of them. The booming occurrence rate of BPA brings up devastating impact on patients' life. Complications of muscle atrophy, neuropathic pain, and denervation-associated psychological disorders are major challenges in the treatment of BPA. Animal models of BPA are good vehicles for this kind of research. Full understanding of the current in vivo BPA models, which could be classified into anterior approach avulsion, posterior approach avulsion, and closed approach avulsion groups, could help researchers select the appropriate type of models for their studies. Each group of the BPA model has its distinct merits and demerits. An ideal BPA model that can inherit the advantages and make up for the disadvantages is still required for further exploration.

Satellite glia activation in dorsal root ganglion contributes to mechanical allodynia after selective motor fiber injury in adult rats

Increasing evidence suggests that activation of satellite glia cells (SGCs) in sensory ganglia play important roles in the development of neuropathic pain. The present study aimed to investigate the involvement of SGC activation in a novel model of motor nerve injury induced pain hypersensitivity. The neuropathic pain model was established by cervical 8 ventral root avulsion (C8VA). Glial fibrillary acidic protein (GFAP) was used as a marker of SGC activation. Unilateral C8VA resulted in mechanical allodynia, but not thermal hyperalgesia in bilateral paws. Expectedly, SGCs were robustly activated on as early as 1 day and persisted for at least 7 days in the ipsilateral and contralateral dorsal root ganglia (DRG) of C6, C7 and C8 after C8VA. Double immunofluorescence showed that almost all the activated SGCs enveloped neurofilament 200 (NF200) positive myelinated neurons in DRG. Local application of fluorocitrate (FC), a glial metabolism inhibitor, significantly decreased the number of activated SGCs and alleviated bilateral mechanical allodynia. These results suggest that SGC activation contributed to ipsilateral and mirror-image pain hypersensitivity after C8VA. Inhibition of SGC activation represented a promising therapeutic strategy for the management of neuropathic pain following brachial plexus root avulsion.

The release of exosomes in the medial prefrontal cortex and nucleus accumbens brain regions of chronic constriction injury (CCI) model mice could elevate the pain sensation

BACKGROUND

Brain function relies on the capacity of neurons to locally modulate each other at the level of synapses. Therefore, the exosomal pathway may constitute a well-designed mechanism for local and systemic interneuronal transfer of information within functional brain networks. Exosomes bind to and are endocytosed by neurons of different brain regions to play a definite role. The medial prefrontal cortex (mPFC) and nucleus accumbens (NAc) brain regions are known to involve in pain modulation. Our study observes the roles of exosomal activity in these two dominant regions of the pain-related pathway, and there influence on the analgesic effects in CCI mice.

METHODS

We induced pain exosomes in the mPFC and NAc in the mice of chronic constriction injury of the sciatic nerve model to produce neuropathic pain, and assessed changes that might affect analgesic behaviors. These changes were measured through a combination of behavioral, surgical, and other cellular testings.

RESULTS

Our study found that pain expression was elevated in mice given exogenous exosomes isolated from CCI mice, especially at the 2 h and 4 h time interval, in mice given exosomes at the mPFC and NAc, respectively. We also found that inhibiting formation of pain exosomes through GW4869 within the mPFC and NAc can elevate the pain threshold.

CONCLUSION

Results from our study supported the idea that the release of mPFC and NAc exosomes of CCI model has elevated the pain sensations in the subjected mice. This study will further help in designing new clinical trials, and will revolutionize the drug-induced anesthetic responses.

CCL2-CCR2 Axis Potentiates NMDA Receptor Signaling to Aggravate Neuropathic Pain Induced by Brachial Plexus Avulsion

Brachial plexus avulsion (BPA) represents the most devastating nerve injury in the upper extremity and is always considered as a sophisticated problem due to its resistance to most standard pain relief medications or neurosurgical interventions. There is also a lack of understanding on the underlying mechanisms. Our study aimed to investigate whether spinal CCL2-CCR2 signaling contributed to the development of neuropathic pain following BPA via modulating glutamate N-methyl-d-aspartate receptor (NMDAR). A rat model of BPA on lower trunk (C8-T1) was established, and the sham- and BPA-operated animals were intrathecally injected with saline, C-C chemokine receptor type 2 (CCR2) inhibitor INCB3344 and NMDAR antagonist DL-AP5 one week postoperatively, the behavioral performance of the treated animals and expressions of C-C motif ligand 2 (CCL2), CCR2, and N-methyl-D-aspartic acid receptor 2B (NR2B) in spinal cord sections of each group were examined. It was shown that BPA injury significantly reduced mechanic withdrawal thresholds the next day after surgery until the end of the observation. Both CCL2 and CCR2 expressions increased in BPA rats compared to those in sham rats. CCL2 was mainly localized in astrocytes, and CCR2 was preferably expressed on astrocytes and neurons. Besides, NMDAR subunit NR2B increased in BPA-operated rats, which was reversed in response to CCR2 and NR2B inhibition. However, these inhibitors didn't change the spinal NMDAR level in sham rats. CCR2 and NMDAR inhibition efficiently alleviated mechanical allodynia caused by BPA either at early or late phase of neuropathic pain. Collectively, CCL2-CCR2 axis is associated with mechanical pain after BPA by elevating NMDAR signaling.

Peripheral Nerve Microscopic Changes Related to Study Procedures: Two Nonclinical Case Studies

Peripheral nerves are routinely examined microscopically during the nonclinical safety assessment of therapeutics. In addition to test article-related on- or off-target changes, microscopic changes in peripheral nerves may also be caused by study procedures, such as parenteral test article administration and blood or tissue sampling. We present 2 nonclinical case studies in which nonstandard peripheral nerves had study procedure-related histologic changes. The first case study describes mouse trigeminal nerve changes as a result of blood sampling via retro-orbital sinus puncture. These changes included minimal-to-mild nerve fiber (axonal) degeneration associated with macrophage infiltration. The second case study presents rat brachial plexus changes associated with animal handling and blood sampling. Brachial plexus changes included minimal-to-moderate inflammation, focal hemorrhage, and nerve fiber degeneration. In both cases, the histological changes were morphologically indistinguishable from those that might be due to test article. Therefore, careful consideration of the incidence and severity across groups and a review of study procedures to rule out handling-related nerve damage are essential before identifying a test article-related effect on peripheral nerves. Study design considerations to avoid such procedure-related changes will be discussed, as well as sampling strategies to help distinguish these from test article-related effects.