Treadmill training based on the overload principle promotes locomotor recovery in a mouse model of chronic spinal cord injury

Electrical stimulation of the sciatic nerve restores inspiratory diaphragm function in mice after spinal cord injury

Introduction

Spinal cord injury in the high cervical cord can impair breathing due to disruption of pathways between brainstem respiratory centers and respiratory motor neurons in the spinal cord. Electrical stimulation of limb afferents can increase ventilation in healthy humans and animals, but it is not known if limb afferent stimulation can improve breathing following a cervical injury.

Methods

We stimulated the sciatic nerve while using electromyography to measure diaphragm function in anesthetized mice following a cervical (C2) hemisection spinal cord injury, as well as in uninjured controls. The amplitude and frequency of inspiratory bursts was analyzed over a range of stimulation thresholds.

Results

We show that electrical stimulation (at sufficient current thresholds) of either the left or right sciatic nerve could restore inspiratory activity to the previously paralyzed diaphragm ipsilateral to a C2 hemisection injury at either acute (1 day) or chronic (2 months) stages after injury. We also show that sciatic nerve stimulation can increase the frequency and amplitude of diaphragm inspiratory bursts in uninjured mice.

Discussion

Our findings indicate that therapies targeting limb afferents could potentially be used to improve breathing in patients with cervical spinal cord injury and provide an experimental model to further investigate the neural pathways by which limb afferents can increase respiratory muscle activity.

The effects of weight- and non-weight-bearing exercise on corticospinal axon sprouting, regeneration-related proteins and functional recovery after spinal cord contusion

The purpose of this study was to investigate the effects of weight- and non-weight-bearing exercises on the Basso-Beattie-Bresnahan (BBB) locomotor rating scale, corticospinal axon regrowth and regeneration-related proteins following spinal cord injury (SCI). Twenty-four male Sprague-Dawley rats were randomly divided into four groups: control group (n=6), SCI+sedentary group (SED, n=6), SCI+treadmill exercise group (TREAD, n=6), and SCI+swimming exercise group (SWIM, n=6). All rats in the SCI group were given the rest for 2 weeks after SCI, and then they were allowed to engage in low-intensity exercise for 6 weeks on treadmill device. Motor function (BBB score) was improved more in the SWIM group compared to the SED group at 3 and 6 weeks after SCI. The SWIM group also showed higher levels of axonal outgrowth in corticospinal tract and increased expression of phosphorylated extracellular signal-regulated kinase, a marker of axonal regeneration in the dorsal horn of the caudal region, compared to the TREAD group. Additionally, the SWIM group significantly upregulated the expression of regeneration-related proteins. Our findings suggest that non-weight-bearing exercise may be one of several rehabilitation methods for improving locomotor function and corticospinal axon regeneration after SCI.

Multiple lines of evidence for disruption of nuclear lamina and nucleoporins in FUS amyotrophic lateral sclerosis

Advanced pathological and genetic approaches have revealed that mutations in fused in sarcoma/translated in liposarcoma (FUS/TLS), which is pivotal for DNA repair, alternative splicing, translation and RNA transport, cause familial amyotrophic lateral sclerosis (ALS). The generation of suitable animal models for ALS is essential for understanding its pathogenesis and developing therapies. Therefore, we used CRISPR-Cas9 to generate FUS-ALS mutation in the non-classical nuclear localization signal (NLS), H517D (mouse position: H509D) and genome-edited mice. Fus WT/H509D mice showed progressive motor impairment (accelerating rotarod and DigiGait system) with age, which was associated with the loss of motor neurons and disruption of the nuclear lamina and nucleoporins and DNA damage in spinal cord motor neurons. We confirmed the validity of our model by showing that nuclear lamina and nucleoporin disruption were observed in lower motor neurons differentiated from patient-derived human induced pluripotent stem cells (hiPSC-LMNs) with FUS-H517D and in the post-mortem spinal cord of patients with ALS. RNA sequence analysis revealed that most nuclear lamina and nucleoporin-linking genes were significantly decreased in FUS-H517D hiPSC-LMNs. This evidence suggests that disruption of the nuclear lamina and nucleoporins is crucial for ALS pathomechanisms. Combined with patient-derived hiPSC-LMNs and autopsy samples, this mouse model might provide a more reliable understanding of ALS pathogenesis and might aid in the development of therapeutic strategies.

Regenerative medicine for spinal cord injury using induced pluripotent stem cells: from animals to humans

ABSTRACT

Spinal cord injury (SCI) results in permanent neurological dysfunction and neuropathic pain. To address this pathology, we recently conducted a clinical study in which we transplanted neural precursor cells (NPCs) derived from human induced pluripotent stem cells into patients during the subacute phase of SCI. One of the therapeutic mechanisms of cell transplantation is the formation of synaptic connections with the host's neural tissues, which we demonstrated using a chemogenetic tool. In addition, we have developed innovative strategies to enhance the effectiveness of cell transplantation through gene therapy. Moreover, our current study is focused on developing cell therapy for chronic SCI, a more challenging pathology characterized by the formation of cavities and scar tissue. In such situations, transplanting NPCs with neurogenic properties could effectively penetrate scar tissue and form functional synapses with the host neurons. To improve the outcomes of cell transplantation alone, we have found that incorporating rehabilitation is beneficial. In animal models of SCI, we have established an effective rehabilitative training program in which NPCs were transplanted during the chronic phase. Robotic rehabilitation has demonstrated improvements in gait ability and trunk function in clinical situations. Therefore, regenerative medicine shows promise for chronic SCI, particularly when rehabilitation strategies are incorporated.

Research Progress on the Effects of Different Exercise Modes on the Secretion of Exerkines After Spinal Cord Injury

Exercise training is a conventional treatment strategy throughout the entire treatment process for patients with spinal cord injury (SCI). Currently, exercise modalities for SCI patients primarily include aerobic exercise, endurance training, strength training, high-intensity interval training, and mind-body exercises. These exercises play a positive role in enhancing skeletal muscle function, inducing neuroprotection and regeneration, thereby influencing neural plasticity, reducing limb spasticity, and improving motor function and daily living abilities in SCI patients. However, the mechanism by which exercise training promotes functional recovery after SCI is still unclear, and there is no consensus on a unified and standardized exercise treatment plan. Different exercise methods may bring different benefits. After SCI, patients' physical activity levels decrease significantly due to factors such as motor dysfunction, which may be a key factor affecting changes in exerkines. The changes in exerkines of SCI patients caused by exercise training are an important and highly relevant and visual evaluation index, which may provide a new research direction for revealing the intrinsic mechanism by which exercise promotes functional recovery after SCI. Therefore, this article summarizes the changes in the expression of common exerkines (neurotrophic factors, inflammatory factors, myokines, bioactive peptides) after SCI, and intends to analyze the impact and role of different exercise methods on functional recovery after SCI from the perspective of exerkines mechanism. We hope to provide theoretical basis and data support for scientific exercise treatment programs after SCI.

The Impact of Treadmill Training on Tissue Integrity, Axon Growth, and Astrocyte Modulation

Spinal cord injury (SCI) presents a complex challenge in neurorehabilitation, demanding innovative therapeutic strategies to facilitate functional recovery. This study investigates the effects of treadmill training on SCI recovery, emphasizing motor function enhancement, neural tissue preservation, and axonal growth. Our research, conducted on a rat model, demonstrates that controlled treadmill exercises significantly improve motor functions post-SCI, as evidenced by improved scores on the Basso, Beattie, and Bresnahan (BBB) locomotor rating scale and enhanced electromyography readings. Notably, the training facilitates the preservation of spinal cord tissue, effectively reducing secondary damage and promoting the maintenance of neural fibers in the injured area. A key finding is the significant stimulation of axonal growth around the injury epicenter in trained rats, marked by increased growth-associated protein 43 (GAP43) expression. Despite these advancements, the study notes a limited impact of treadmill training on motoneuron adaptation and highlights minimal changes in the astrocyte and neuron-glial antigen 2 (NG2) response. This suggests that, while treadmill training is instrumental in functional improvements post-SCI, its influence on certain neural cell types and glial populations is constrained.

Rehabilitation training enhanced the therapeutic effect of calycosin on neurological function recovery of rats following spinal cord injury

BACKGROUND

Calycosin (CA), a flavonoids component, has demonstrated potential neuroprotection effects by inhibiting oxidative stress in spinal cord injury (SCI) models. This study aims to investigate the impact of combined rehabilitation training (RT) and calycosin therapy on neurological function following SCI, primarily by assessing changes in motor function recovery, neuronal survival, neuronal oxidative stress levels, and neural proliferation, in order to provide novel insights for the treatment of SCI.

MATERIALS AND METHODS

The SCI model was constructed by compressing the spinal cord using vascular clamps. Calycosin was injected intraperitoneally into the SCI model rats, and a group of 5 rats underwent RT. The motor function of rats after SCI was evaluated using the Basso Beattle Bresnaha (BBB) score and the inclined plate test. Histopathological changes were evaluated by NeuN immunohistochemistry, HE and Nissl staining. Apoptosis was detected by TUNEL staining. The antioxidant effect of combined treatment was assessed by measuring changes in oxidative stress markers after SCI. Western blot analysis was conducted to examine changes in Hsp90-Akt/ASK1-p38 pathway-related proteins. Finally, cell proliferation was detected by BrdU and Ki67 assays.

RESULTS

RT significantly improved the BBB score and angle of incline promoted by calycosin, resulting in enhanced motor function recovery in rats with SCI. Combining rehabilitation training with calycosin has a positive effect on morphological recovery. Similarly, combined RT enhanced the Nissl and NeuN staining signals of spinal cord neurons increased by calycosin, thereby increasing the number of neurons. TUNEL staining results indicated that calycosin treatment reduced the apoptosis signal in SCI, and the addition of RT further reduced the apoptosis. Moreover, RT combined with calycosin reduced oxidative stress by increasing SOD and GSH levels, while decreasing MDA, NO, ROS, and LDH expressions compared to the calycosin alone. RT slightly enhanced the effect of calycosin in activating Hsp90 and Akt and inhibiting the activation of ASK1 and p38, leading to enhanced inhibition of oxidative stress by calycosin. Additionally, the proliferation indexes (Ki67 and BrdU) assays showed that calycosin treatment alone increased both, whereas the combination treatment further promoted cell proliferation.

CONCLUSION

Our research findings demonstrate that rehabilitation training enhances the ability of calycosin to reduce oxidative stress, resulting in a decrease in neuronal apoptosis and an increase in proliferation, ultimately promoting neuronal survival.

Do Pharmacological Treatments Act in Collaboration with Rehabilitation in Spinal Cord Injury Treatment? A Review of Preclinical Studies

There is no choice other than rehabilitation as a practical medical treatment to restore impairments or improve activities after acute treatment in people with spinal cord injury (SCI); however, the effect is unremarkable. Therefore, researchers have been seeking effective pharmacological treatments. These will, hopefully, exert a greater effect when combined with rehabilitation. However, no review has specifically summarized the combinatorial effects of rehabilitation with various medical agents. In the current review, which included 43 articles, we summarized the combinatorial effects according to the properties of the medical agents, namely neuromodulation, neurotrophic factors, counteraction to inhibitory factors, and others. The recovery processes promoted by rehabilitation include the regeneration of tracts, neuroprotection, scar tissue reorganization, plasticity of spinal circuits, microenvironmental change in the spinal cord, and enforcement of the musculoskeletal system, which are additive, complementary, or even synergistic with medication in many cases. However, there are some cases that lack interaction or even demonstrate competition between medication and rehabilitation. A large fraction of the combinatorial mechanisms remains to be elucidated, and very few studies have investigated complex combinations of these agents or targeted chronically injured spinal cords.

Chronic Spinal Cord Injury Regeneration with Combined Therapy Comprising Neural Stem/Progenitor Cell Transplantation, Rehabilitation, and Semaphorin 3A Inhibitor

Spinal cord injury (SCI) often results in various long-term sequelae, and chronically injured spinal cords exhibit a refractory feature, showing a limited response to cell transplantation therapies. To our knowledge, no preclinical studies have reported a treatment approach with results surpassing those of treatment comprising rehabilitation alone. In this study of rats with SCI, we propose a novel combined therapy involving a semaphorin 3A inhibitor (Sema3Ai), which enhances axonal regeneration, as the third treatment element in combination with neural stem/progenitor cell transplantation and rehabilitation. This comprehensive therapeutic strategy achieved significant improvements in host-derived neuronal and oligodendrocyte differentiation at the SCI epicenter and promoted axonal regeneration even in the chronically injured spinal cord. The elongated axons established functional electrical connections, contributing to significant enhancements in locomotor mobility when compared with animals treated with transplantation and rehabilitation. As a result, our combined transplantation, Sema3Ai, and rehabilitation treatment have the potential to serve as a critical step forward for chronic SCI patients, improving their ability to regain motor function.

Synergistic effect of chemogenetic activation of corticospinal motoneurons and physical exercise in promoting functional recovery after spinal cord injury

Single therapeutic interventions have not yet been successful in restoring function after spinal cord injury. Accordingly, combinatorial interventions targeting multiple factors may hold greater promise for achieving maximal functional recovery. In this study, we applied a combinatorial approach of chronic chemogenetic neuronal activation and physical exercise including treadmill running and forelimb training tasks to promote functional recovery. In a mouse model of cervical (C5) dorsal hemisection of the spinal cord, which transects almost all descending corticospinal tract axons, combining selective activation of corticospinal motoneurons (CMNs) by intersectional chemogenetics with physical exercise significantly promoted functional recovery evaluated by the grid walking test, grid hanging test, rotarod test, and single pellet-reaching tasks. Electromyography and histological analysis showed increased activation of forelimb muscles via chemogenetic stimuli, and a greater density of vGlut1+ innervation in spinal cord grey matter rostral to the injury, suggesting enhanced neuroplasticity and connectivity. Combined therapy also enhanced activation of mTOR signaling and reduced apoptosis in spinal motoneurons, Counts revealed increased numbers of detectable choline acetyltransferase-positive motoneurons in the ventral horn. Taken together, the findings from this study validate a novel combinatorial approach to enhance motor function after spinal cord injury.

Osteopontin enhances the effect of treadmill training and promotes functional recovery after spinal cord injury

In this study, we examined the combined impact of osteopontin (OPN) and treadmill training on mice with spinal cord injury (SCI). OPN was overexpressed by injecting AAV9-SPP1-GFP into the sensorimotor cortex, followed by a left incomplete C5 crush injury two weeks later. Mice (Ex or Ex + OPN group) were trained at 50% maximum running speed for 8 weeks. To analyze the effects, we used biotinylated dextran amine (BDA) for tracing the corticospinal tract (CST) and performed Western blotting and immunohistochemical methods to assess the activation of the mammalian target of rapamycin (mTOR). We also examined axonal regeneration and conducted behavioral tests to measure functional recovery. The results demonstrated that treadmill training promoted the expression of neurotrophic factors such as brain-derived neurotrophic factor (BNDF) and insulin-like growth factor I (IGF-1) and activated mTOR signaling. OPN amplified the effect of treadmill training on activating mTOR signaling indicated by upregulated phosphorylation of ribosomal protein S6 kinase (S6). The combination of OPN and exercise further promoted functional recovery and facilitated limited CST axonal regeneration which did not occur with treadmill training and OPN treatment alone. These findings indicate that OPN enhances the effects of treadmill training in the treatment of SCI and offer new therapeutic insights for spinal cord injury.

A shift of brain network hub after spinal cord injury

Background

Spinal cord injury (SCI) causes severe sequelae and significant social loss, depending on the extent of the damage. Most previous studies have focused on the pathology of the spinal cord to develop treatments for SCI. However, it is now known that the brain, which is not directly damaged, also undergoes morphological changes after spinal cord injury, which could affect natural recovery and treatment. In recent years, magnetic resonance imaging (MRI) has been developed to analyze functional changes in the brain. Resting-state functional MRI (rsfMRI), which captures brain activity at rest, can calculate functional connections between brain areas and identify central hubs by network analysis.

Purpose

We aim to investigate functional connectivity in the brain using rsfMRI after SCI and to determine how brain-network main hubs change over time.

Methods

We evaluated rsfMRI in 10 mice of the contusional SCI model and calculated connectivity using graph theory. We evaluated "centrality," a representative parameter of network analysis. The subtype of centrality was degree centrality, which indicates the hub function of a single area. The five times of rsfMRI were performed in each individual mouse: before injury and at 1, 3, 7, and 14 weeks post-injury.

Results

Before the injury, the degree centralities of the primary and secondary motor cortex were high, suggesting that these motor cortices served as main hubs for motor function. After SCI, the hub function of the motor cortices decreased by 14 weeks. In contrast, hub function in the external capsule and the putamen comparatively increased with time after injury, suggesting that the extrapyramidal/subcortical system, which runs the ventral side of the spinal cord and remains after injury in this model, becomes dominant.

Conclusion

We demonstrated the shift of the brain network hub after SCI. The results of this study provide basic information for understanding brain network changes after SCI and would be useful for treatment selection and evaluation of its efficacy in SCI patients.

Effect of mechanical stimulation on tissue heterotopic ossification: an in vivo experimental study

Background: Heterotopic ossification of tendons and ligaments (HOTL) is a common clinical condition characterized by the absence of discernible features and a lack of effective treatment. In vitro experiments have demonstrated that mechanical stimulation can induce cell differentiation toward osteogenesis, thereby promoting heterotopic ossification. Currently, there are few experimental designs aimed at inducing ligament stretching in mice, and the mechanism of heterotopic ossification may not entirely mirror that observed in clinical cases. Therefore, there is an urgent imperative to develop a novel and feasible animal model. Methods: In this study, all the Enpp1 gene deficiency mice (a mouse model with heterotopic ossification of multiple ligaments) were divided into three groups: the control group, the spinal brake group, and the hyperactive group (treadmill training group). An external spinal fixation device was designed to restrict mice's spinal flexion and extension at 6 weeks of age. The brace was adjusted weekly according to the changes in the size of the mice. Additionally, treadmill training was used to increase activity in the spinal ligaments and Achilles tendons of the mice. Micro-CT scanning and HE staining were performed at 12, 20, and 28 W to evaluate the degree of ossification in the spinal ligament and Achilles tendon. What's more, As one of the mechanical stimulation transduction signals, YAP plays a crucial role in promoting osteogenic differentiation of cells. Immunofluorescence was utilized to assess YAP expression levels for the purpose of determining the extent of mechanical stimulation in tissues. Results: Our findings showed that a few ossification lesions were detected behind the vertebral space of mice at 8 weeks of age. Spinal immobilization effectively restricts the flexion and extension of cervical and thoracic vertebrae in mice, delaying spinal ligament ossification and reducing chronic secondary spinal cord injury. Running exercises not only enhance the ossification area of the posterior longitudinal ligament (PLL) and Achilles tendons but also exacerbate secondary spinal cord injury. Further immunofluorescence results revealed a notable increase in YAP expression levels in tissues with severe ossification, suggesting that these tissues may be subjected to higher mechanical stimulation. Conclusion: Mechanical stimulation plays a pivotal role in the process of heterotopic ossification in tissues. Our study provided valid animal models to further explore the pathological mechanism of mechanical stimulation in HOTL development.

Body Weight Support Treadmill Training Combined With Sciatic Nerve Electrical Stimulation Ameliorating Motor Function by Enhancing PI3K/Akt Proteins Expression via BDNF/TrkB Signaling Pathway in Rats with Spinal Cord Injury

OBJECTIVE

To investigate the effects of body weight support treadmill training (BWSTT) and sciatic nerve electrical stimulation (SNES) on motor function recovery in spinal cord injury (SCI) rats and its possible mechanism.

METHODS

Modified Allen's method was utilized for T10 incomplete SCI. The Basso-Beattie-Bresnahan (BBB) score and modified Tarlov score were applied to assess motor function. Pathologic alterations of the spinal cord and muscles were observed by hematoxylin and eosin (HE) staining. The positive staining region of collagen fibers was assessed with Masson staining. Immunofluorescence was applied to count the positive cells of brain-derived neurotrophic factor (BDNF) and tropomyosin-related kinase B (TrkB). BDNF, TrkB, phosphatidylinositol-3-kinase (PI3K), and protein kinase B (Akt) relative mRNA and protein expressions were evaluated by reverse transcription polymerase chain reaction (RT-PCR) and Western blotting.

RESULTS

On the 21st day of the intervention, the motor scores in SNES and BWSTT + SNES groups were higher than that in SCI group (P < 0.05). Compared with SCI group, mRNA and protein expressions of BDNF/TrkB and PI3K/Akt were more significant on the 21st day of the intervention in SNES and BWSTT + SNES groups (P < 0.05), but there was no difference in BWSTT group (P > 0.05).

CONCLUSIONS

This experiment demonstrated that BWSTT combined with SNES contributed to alleviating spinal cord tissue injury, delaying muscle atrophy and improving locomotion. One of the possible mechanisms may be related to the regulation of the BDNF/TrkB signaling pathway, which changes the expression of PI3K/Akt protein. Furthermore, it was discovered that the ultra-early BWSTT may not be conducive to recovery.

A Review of Treatment Methods Focusing on Human Induced Pluripotent Stem Cell-Derived Neural Stem/Progenitor Cell Transplantation for Chronic Spinal Cord Injury

Cell transplantation therapy using human induced pluripotent stem cell-derived neural stem/progenitor cells (hiPSC-NS/PCs) has attracted attention as a regenerative therapy for spinal cord injury (SCI), and its efficacy in treating the subacute phase of SCI has been reported in numerous studies. However, few studies have focused on treatment in the chronic phase, which accounts for many patients, suggesting that there are factors that are difficult to overcome in the treatment of chronic SCI. The search for therapeutic strategies that focus on chronic SCI is fraught with challenges, and the combination of different therapies is thought to be the key to a solution. In addition, many issues remain to be addressed, including the investigation of therapeutic approaches for more severe injury models of chronic SCI and the acquisition of practical motor function. This review summarizes the current progress in regenerative therapy for SCI and discusses the prospects for regenerative medicine, particularly in animal models of chronic SCI.

Microenvironmental modulation in tandem with human stem cell transplantation enhances functional recovery after chronic complete spinal cord injury

While rapid advancements in regenerative medicine strategies for spinal cord injury (SCI) have been made, most research in this field has focused on the early stages of incomplete injury. However, the majority of patients experience chronic severe injury; therefore, treatments for these situations are fundamentally important. Here, we hypothesized that environmental modulation via a clinically relevant hepatocyte growth factor (HGF)-releasing scaffold and human iPS cell-derived neural stem/progenitor cells (hNS/PCs) transplantation contributes to functional recovery after chronic complete transection SCI. Effective release of HGF from a collagen scaffold induced progressive axonal elongation and increased grafted cell viability by activating microglia/macrophages and meningeal cells, inhibiting inflammation, reducing scar formation, and enhancing vascularization. Furthermore, hNS/PCs transplantation enhanced endogenous neuronal regrowth, the extension of graft axons, and the formation of circuits around the lesion and lumbar enlargement between host and graft neurons, resulting in the restoration of locomotor and urinary function. This study presents an effective therapeutic strategy for severe chronic SCI and provides evidence for the feasibility of regenerative medicine strategies using clinically relevant materials.

Rehabilitative Training Enhances Therapeutic Effect of Human-iPSC-Derived Neural Stem/Progenitor Cells Transplantation in Chronic Spinal Cord Injury

Cell transplantation therapy using human-induced pluripotent stem cell-derived neural stem/progenitor cells (hiPSC-NS/PCs) is a new therapeutic strategy for spinal cord injury (SCI). Preclinical studies have demonstrated the efficacy of hiPSC-NS/PCs transplantation in the subacute phase of SCI. However, locomotor recovery secondary to hiPSC-NS/PCs transplantation is limited in the chronic phase, suggesting that additional treatment, including rehabilitative training, is required to ensure recovery. The therapeutic potential of hiPSC-NS/PCs that qualify for clinical application is yet to be fully delineated. Therefore, in this study, we investigated the therapeutic effect of the combined therapy of clinical-grade hiPSC-NS/PCs transplantation and rehabilitative training that could produce synergistic effects in a rodent model of chronic SCI. Our findings indicated that rehabilitative training promoted the survival rate and neuronal differentiation of transplanted hiPSC-NS/PCs. The combination therapy was able to enhance the expressions of the BDNF and NT-3 proteins in the spinal cord tissue. Moreover, rehabilitation promoted neuronal activity and increased 5-HT-positive fibers at the lumbar enlargement. Consequently, the combination therapy significantly improved motor functions. The findings of this study suggest that the combined therapy of hiPSC-NS/PCs transplantation and rehabilitative training has the potential to promote functional recovery even when initiated during chronic SCI.

Moderate-Intensity Treadmill Exercise Promotes mTOR-Dependent Motor Cortical Neurotrophic Factor Expression and Functional Recovery in a Murine Model of Crush Spinal Cord Injury (SCI)

Treadmill exercise is widely considered an effective strategy for restoration of skilled motor function after spinal cord injury (SCI). However, the specific exercise intensity that optimizes recovery and the underlying mechanistic basis of this recovery remain unclear. To that end, we sought to investigate the effect of different treadmill exercise intensities on cortical mTOR activity, a key regulator of functional recovery following CNS trauma, in an animal model of C5 crush spinal cord injury (SCI). Following injury, animals were subjected to treadmill exercise for 4 consecutive weeks at three different intensities (low intensity [LEI]; moderate intensity [MEI]; and high intensity [HEI]). Motor function recovery was assessed by horizontal ladder test, cylinder rearing test, and electrophysiology, while neurotrophic factors and cortical mechanistic target of rapamycin (mTOR) pathway-related proteins were assessed by Western blotting. The activation of the cortical mTOR pathway and axonal sprouting was evaluated by immunofluorescence and the changes of plasticity in motor cortex neurons were assessed by Golgi staining. In keeping with previous studies, we found that 4 weeks of treadmill training resulted in improved skilled motor function, enhanced nerve conduction capability, increased neuroplasticity, and axonal sprouting. Importantly, we also demonstrated that when compared with the LEI group, MEI and HEI groups demonstrated elevated expression of brain-derived neurotrophic factor (BDNF), insulin-like growth factor 1 (IGF-1), phosphorylated ribosomal S6 protein (p-S6), and protein kinase B (p-Akt), consistent with an intensity-dependent activation of the mTOR pathway and neurotrophic factor expression in the motor cortex. We also observed impaired exercise endurance and higher mortality during training in the HEI group than in the LEI and MEI groups. Collectively, our findings suggest that treadmill exercise following SCI is an effective means of promoting recovery and highlight the importance of the cortical mTOR pathway and neurotrophic factors as mediators of this effect. Importantly, our findings also demonstrate that excessive exercise can be detrimental, suggesting that moderation may be the optimal strategy. These findings provide an important foundation for further investigation of treadmill training as a modality for recovery following spinal cord injury and of the underlying mechanisms.

Multimodal rehabilitation promotes axonal sprouting and functional recovery in a murine model of spinal cord injury (SCI)

Spinal cord injury (SCI) is a devastating neurological disorder affecting millions of people worldwide, resulting in severe and permanent disabilities that significantly impact the individual's life. Rehabilitation is a commonly accepted and effective clinical treatment modality for neurological disabilities. A single form of rehabilitation training is, however, limited. Indeed, recent studies have reported that a combination of various training strategies may be more promising in promoting functional recovery. However, few studies have focused on combining different forms of rehabilitative training. Here, we investigated the effect of combining treadmill training and single pellet grasping in a well-established model of murine SCI to assess whether combining rehabilitation approaches improve outcomes. In brief, one week following crush SCI, mice were subjected to the treadmill and single pellet grasping training (SPG) for a period of six weeks. Biotinylated dextran amine (BDA) was used to anterogradely trace corticospinal tract axons to assess functionally relevant axonal sprouting. Our results revealed that the combined training upregulated p-S6 expression, facilitated axonal sprouting, increased the formation of functional synaptic connections, and promoted functional recovery of the upper limb. Our study provides experimental evidence for the benefit of combining multiple modalities of rehabilitative strategies.

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.

A Narrative Review of Advances in Neural Precursor Cell Transplantation Therapies for Spinal Cord Injury

A spinal cord injury (SCI) is a destructive event that causes a permanent deficit in neurological function because of poor regenerative potential. Transplantation therapies have attracted attention for restoration of the injured spinal cord, and transplantation of neural precursor cells (NPCs) has been studied worldwide. Several groups have demonstrated functional recovery via this therapeutic intervention due to the multiple beneficial effects of NPC transplantation, such as reconstruction of neuronal circuits, remyelination of axons, and neuroprotection by trophic factors. Our group developed a method to induce NPCs from human induced pluripotent stem cells (hiPSCs) and established a transplantation strategy for SCI. Functional improvement in SCI animals treated with hiPSC-NPCs was observed, and the safety of transplanting these cells was evaluated from multiple perspectives. With selection of a safe cell line and pretreatment of the cells to encourage maturation and differentiation, hiPSC-NPC transplantation therapy is now in the clinical phase of testing for subacute SCI. In addition, a research challenge will be to expand the efficacy of transplantation therapy for chronic SCI. More comprehensive strategies involving combination treatments are required to treat this problematic situation.

biPACT: A method for three-dimensional visualization of mouse spinal cord circuits of long segments with high resolution

BACKGROUND

The spatial complexity of neuronal circuits in the central nervous system is a hurdle in understanding and treating brain and spinal cord injury (SCI). Although several methods have recently been developed to render the spinal cord transparent and label specific neural circuits, three-dimensional visualization of long segments of spinal cord with high resolution remains challenging for SCI researchers.

NEW METHOD

We present a method that combines tissue staining of neuronal tracts traced with biotinylated dextran amine (BDA) and a modified passive clarity clearing protocol to describe individual fibers in long segments of mouse spinal cord.

RESULTS

Corticospinal tract was traced with BDA with a mouse model of thoracic spinal cord injury. The spinal cord was stained and cleared in two weeks with four solutions: staining solution, hydrogel solution, clearing solution, and observation solution. The samples were observed with a light-sheet microscope, and three-dimensional reconstruction was performed with ImageJ software. High resolution-images comparable with tissue sections were obtained continuously and circumferentially. By tiling, it was possible to obtain high-resolution images of long segments of the spinal cord. The tissue could be easily re-stained in case of fading.

COMPARISON WITH EXISTING METHODS

The present method does not require special equipment such as vacuum devices, can label specific circuits without genetic technology, and re-staining rounds can be easily implemented.

CONCLUSIONS

By using simple neural staining and clearing methods, it was possible to acquire a wide range of high-resolution three-dimensional images of the spinal cord.

Current progress of rehabilitative strategies in stem cell therapy for spinal cord injury: a review

Stem cell-based regenerative therapy has opened an avenue for functional recovery of patients with spinal cord injury (SCI). Regenerative rehabilitation is attracting wide attention owing to its synergistic effects, feasibility, non-invasiveness, and diverse and systemic properties. In this review article, we summarize the features of rehabilitation, describe the mechanism of combinatorial treatment, and discuss regenerative rehabilitation in the context of SCI. Although conventional rehabilitative methods have commonly been implemented alone, especially in studies of acute-to-subacute SCI, the combinatorial effects of intensive and advanced methods, including various neurorehabilitative approaches, have also been reported. Separating the concept of combined rehabilitation from regenerative rehabilitation, we suggest that the main roles of regenerative rehabilitation can be categorized as conditioning/reconditioning, functional training, and physical exercise, all of which are indispensable for enhancing functional recovery achieved using stem cell therapies.