Animal models of spinal cord injury: a systematic review

Molecular Mechanism Operating in Animal Models of Neurogenic Detrusor Overactivity: A Systematic Review Focusing on Bladder Dysfunction of Neurogenic Origin

Neurogenic detrusor overactivity (NDO) is a severe lower urinary tract disorder, characterized by urinary urgency, retention, and incontinence, as a result of a neurologic lesion that results in damage in neuronal pathways controlling micturition. The purpose of this review is to provide a comprehensive framework of the currently used animal models for the investigation of this disorder, focusing on the molecular mechanisms of NDO. An electronic search was performed with PubMed and Scopus for literature describing animal models of NDO used in the last 10 years. The search retrieved 648 articles, of which reviews and non-original articles were excluded. After careful selection, 51 studies were included for analysis. Spinal cord injury (SCI) was the most frequently used model to study NDO, followed by animal models of neurodegenerative disorders, meningomyelocele, and stroke. Rats were the most commonly used animal, particularly females. Most studies evaluated bladder function through urodynamic methods, with awake cystometry being particularly preferred. Several molecular mechanisms have been identified, including changes in inflammatory processes, regulation of cell survival, and neuronal receptors. In the NDO bladder, inflammatory markers, apoptosis-related factors, and ischemia- and fibrosis-related molecules were found to be upregulated. Purinergic, cholinergic, and adrenergic receptors were downregulated, as most neuronal markers. In neuronal tissue, neurotrophic factors, apoptosis-related factors, and ischemia-associated molecules are increased, as well as markers of microglial and astrocytes at lesion sites. Animal models of NDO have been crucial for understanding the pathophysiology of lower urinary tract (LUT) dysfunction. Despite the heterogeneity of animal models for NDO onset, most studies rely on traumatic SCI models rather than other NDO-driven pathologies, which may result in some issues when translating pre-clinical observations to clinical settings other than SCI.

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

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

Rodent Models of Spinal Cord Injury: From Pathology to Application

Spinal cord injury (SCI) often has devastating consequences for the patient's physical, mental and occupational health. At present, there is no effective treatment for SCI, and appropriate animal models are very important for studying the pathological manifestations, injury mechanisms, and corresponding treatment. However, the pathological changes in each injury model are different, which creates difficulties in selecting appropriate models for different research purposes. In this article, we analyze various SCI models and introduce their pathological features, including inflammation, glial scar formation, axon regeneration, ischemia-reperfusion injury, and oxidative stress, and evaluate the advantages and disadvantages of each model, which is convenient for selecting suitable models for different injury mechanisms to study therapeutic methods.

Motor rehabilitation as a therapeutic tool for spinal cord injury: New perspectives in immunomodulation

Traumatic spinal cord injury (SCI) is a devastating condition that significantly impacts motor, sensory and autonomic function in patients. Despite advances in therapeutic approaches, there is still no curative therapy currently available. Neuroinflammation is a persisting event of the secondary injury phase of SCI that affects functional recovery, and modulation of the inflammatory response towards a beneficial anti-inflammatory state can improve recovery in preclinical SCI models. In human SCI patients, rehabilitative exercise, or motor rehabilitation as we will refer to it from here on out, remains the cornerstone of treatment to increase functional capacity and prevent secondary health implications. Motor rehabilitation is known to have anti-inflammatory effects; however, current literature is lacking in the description of the effect of motor rehabilitation on inflammation in the context of SCI. Understanding the effect on different inflammatory markers after SCI should enable the optimization of motor rehabilitation as a therapeutic regime. This review extensively describes the effect of motor rehabilitation on selected inflammatory mediators in both preclinical and human SCI studies. Additionally, we summarize how the type, duration, and intensity of motor rehabilitation can affect the inflammatory response after SCI. In doing so, we introduce a new perspective on how motor rehabilitation can be optimized as an immunomodulatory therapy to improve patient outcome after SCI.

In vivo imaging of axonal transport in peripheral nerves of rodent forelimbs

Axonal transport is the essential process by which neurons actively traffic a variety of cargoes between the cell soma and axon terminals. Accordingly, dysfunctional axonal transport is linked to many nervous system conditions. Therefore, being able to image and quantify this dynamic process in live neurons of animal disease models is beneficial for understanding neuropathology and testing new therapies at the preclinical level. As such, intravital approaches have been developed to assess cargo movement in the hindlimb sciatic nerves of live, anaesthetised mice. Here, we describe an adapted method for in vivo imaging of axonal transport in intact median and ulnar nerves of the rodent forelimb. Injection of a fluorescently labelled and non-toxic fragment of tetanus neurotoxin (H_CT) into the mouse forepaw permits the identification of signalling endosomes in intact axons of median and ulnar nerves. Through immunofluorescent analysis of forelimb lumbrical muscles and median/ulnar nerves, we confirmed that H_CT is taken up at motor nerve terminals and predominantly locates to motor axons. We then showed that the baseline trafficking of signalling endosomes is similar between the median/ulnar nerves and the sciatic nerve in adult wild-type mice. Importantly, this adapted method can be readily tailored for assessment of additional cargoes, such as mitochondria. By measuring transport in forelimb and hindlimb nerves, comparative anatomical and functional analyses can be performed in rodent disease models to aid our understanding of peripheral nerve disease pathogenesis and response to injury.

A custom-made weight-drop impactor to produce consistent spinal cord injury outcomes in a rat model

Objective

The main objective of this study is to design a custom-made weight-drop impactor device to produce a consistent spinal cord contusion model in rats in order to examine the efficacy of potential therapies for post-traumatic spinal cord injuries (SCIs).

Methods

Adult female Sprague-Dawley rats (n = 24, 11 weeks old) were randomly divided equally into two groups: sham and injured. The consistent injury pattern was produced by a 10 g stainless steel rod dropped from a height of 30 mm to cause (0.75 mm) intended displacement to the dorsal surface of spinal cord. The neurological functional outcomes were assessed at different time intervals using the following standardized neurobehavioral tests: Basso, Beattie, and Bresnahan (BBB) scores, BBB open-field locomotion test, Louisville Swim Scale (LSS), and CatWalk gait analysis system.

Results

Hind limb functional parameters between the two groups using BBB scores and LSS were significantly different (p < 0.05). There were significant differences (p < 0.05) between the SCI group and the sham group for the hind limb functional parameters using the CatWalk gait analysis.

Conclusion

We developed an inexpensive custom-made SCI device that yields a precise adjustment of the height and displacement of the impact relative to the spinal cord surface.

A Critical Comparison of Comparators Used to Demonstrate Credibility of Physics-Based Numerical Spine Models

The ability of new medical devices and technology to demonstrate safety and effectiveness, and consequently acquire regulatory approval, has been dependent on benchtop, in vitro, and in vivo evidence and experimentation. Regulatory agencies have recently begun accepting computational models and simulations as credible evidence for virtual clinical trials and medical device development. However, it is crucial that any computational model undergo rigorous verification and validation activities to attain credibility for its context of use before it can be accepted for regulatory submission. Several recently published numerical models of the human spine were considered for their implementation of various comparators as a means of model validation. The comparators used in each published model were examined and classified as either an engineering or natural comparator. Further, a method of scoring the comparators was developed based on guidelines from ASME V&V40 and the draft guidance from the US FDA, and used to evaluate the pertinence of each comparator in model validation. Thus, this review article aimed to score the various comparators used to validate numerical models of the spine in order to examine the comparator's ability to lend credibility towards computational models of the spine for specific contexts of use.

Porcine spinal cord injury model for translational research across multiple functional systems

Animal models are necessary to identify pathological changes and help assess therapeutic outcomes following spinal cord injury (SCI). Small animal models offer value in research in terms of their easily managed size, minimal maintenance requirements, lower cost, well-characterized genomes, and ability to power research studies. However, despite these benefits, small animal models have neurologic and anatomical differences that may influence translation of results to humans and thus limiting the success of their use in preclinical studies as a direct pipeline to clinical studies. Large animal models, offer an attractive intermediary translation model that may be more successful in translating to the clinic for SCI research. This is largely due to their greater neurologic and anatomical similarities to humans. The physical characteristics of pig spinal cord, gut microbiome, metabolism, proportions of white to grey matter, bowel anatomy and function, and urinary system are strikingly similar and provide great insight into human SCI conditions. In this review, we address the variety of existing porcine injury models and their translational relevance, benefits, and drawbacks in modeling human systems and functions for neurophysiology, cardiovascular, gastrointestinal and urodynamic functions.

The potential of gene therapies for spinal cord injury repair: a systematic review and meta-analysis of pre-clinical studies

Currently, there is no cure for traumatic spinal cord injury but one therapeutic approach showing promise is gene therapy. In this systematic review and meta-analysis, we aim to assess the efficacy of gene therapies in pre-clinical models of spinal cord injury and the risk of bias. In this meta-analysis, registered at PROSPERO (Registration ID: CRD42020185008), we identified relevant controlled in vivo studies published in English by searching the PubMed, Web of Science, and Embase databases. No restrictions of the year of publication were applied and the last literature search was conducted on August 3, 2020. We then conducted a random-effects meta-analysis using the restricted maximum likelihood estimator. A total of 71 studies met our inclusion criteria and were included in the systematic review. Our results showed that overall, gene therapies were associated with improvements in locomotor score (standardized mean difference [SMD]: 2.07, 95% confidence interval [CI]:1.68–2.47, Tau² = 2.13, I² = 83.6%) and axonal regrowth (SMD: 2.78, 95%CI: 1.92–3.65, Tau² = 4.13, I² = 85.5%). There was significant asymmetry in the funnel plots of both outcome measures indicating the presence of publication bias. We used a modified CAMARADES (Collaborative Approach to Meta-Analysis and Review of Animal Data in Experimental Studies) checklist to assess the risk of bias, finding that the median score was 4 (IQR:3–5). In particular, reports of allocation concealment and sample size calculations were lacking. In conclusion, gene therapies are showing promise as therapies for spinal cord injury repair, but there is no consensus on which gene or genes should be targeted.

Integration of multiple prognostic predictors in a porcine spinal cord injury model: A further step closer to reality

Introduction

Spinal cord injury (SCI) is a devastating neurological disorder with an enormous impact on individual's life and society. A reliable and reproducible animal model of SCI is crucial to have a deeper understanding of SCI. We have developed a large-animal model of spinal cord compression injury (SCI) with integration of multiple prognostic factors that would have applications in humans.

Methods

Fourteen human-like sized pigs underwent compression at T8 by implantation of an inflatable balloon catheter. In addition to basic neurophysiological recording of somatosensory and motor evoked potentials, we introduced spine-to-spine evoked spinal cord potentials (SP-EPs) by direct stimulation and measured them just above and below the affected segment. A novel intraspinal pressure monitoring technique was utilized to measure the actual pressure on the cord. The gait and spinal MRI findings were assessed in each animal postoperatively to quantify the severity of injury.

Results

We found a strong negative correlation between the intensity of pressure applied to the spinal cord and the functional outcome (P < 0.0001). SP-EPs showed high sensitivity for real time monitoring of intraoperative cord damage. On MRI, the ratio of the high-intensity area to the cross-sectional of the cord was a good predictor of recovery (P < 0.0001).

Conclusion

Our balloon compression SCI model is reliable, predictable, and easy to implement. By integrating SP-EPs, cord pressure, and findings on MRI, we can build a real-time warning and prediction system for early detection of impending or iatrogenic SCI and improve outcomes.

Protocol paper: kainic acid excitotoxicity-induced spinal cord injury paraplegia in Sprague-Dawley rats

BACKGROUND

Excitotoxicity-induced in vivo injury models are vital to reflect the pathophysiological features of acute spinal cord injury (SCI) in humans. The duration and concentration of chemical treatment controls the extent of neuronal cell damage. The extent of injury is explained in relation to locomotor and behavioural activity. Several SCI in vivo methods have been reported and studied extensively, particularly contusion, compression, and transection models. These models depict similar pathophysiology to that in humans but are extremely expensive (contusion) and require expertise (compression). Chemical excitotoxicity-induced SCI models are simple and easy while producing similar clinical manifestations. The kainic acid (KA) excitotoxicity model is a convenient, low-cost, and highly reproducible animal model of SCI in the laboratory. The basic impactor approximately cost between 10,000 and 20,000 USD, while the kainic acid only cost between 300 and 500 USD, which is quite cheap as compared to traditional SCI method.

METHODS

In this study, 0.05 mM KA was administered at dose of 10 µL/100 g body weight, at a rate of 10 µL/min, to induce spinal injury by intra-spinal injection between the T12 and T13 thoracic vertebrae. In this protocol, detailed description of a dorsal laminectomy was explained to expose the spinal cord, following intra-spinal kainic acid administration at desired location. The dose, rate and technique to administer kainic acid were explained extensively to reflect a successful paraplegia and spinal cord injury in rats. The postoperative care and complication post injury of paraplegic laboratory animals were also explained, and necessary requirements to overcome these complications were also described to help researcher.

RESULTS

This injury model produced impaired hind limb locomotor function with mild seizure. Hence this protocol will help researchers to induce spinal cord injury in laboratories at extremely low cost and also will help to determine the necessary supplies, methods for producing SCI in rats and treatments designed to mitigate post-injury impairment.

CONCLUSIONS

Kainic acid intra-spinal injection at the concentration of 0.05 mM, and rate 10 µL/min, is an effective method create spinal injury in rats, however more potent concentrations of kainic acid need to be studied in order to create severe spinal injuries.

Systematic Evaluation of Spinal Cord Injury Animal Models in the Field of Biomaterials

The large number of animal models used in spinal cord injury (SCI) research complicates the objective selection of the most appropriate model to investigate the efficacy of biomaterial-based therapies. This systematic review aims to identify a list of relevant animal models of SCI by evaluating the confirmation of SCI and animal survival in all published SCI models used in biomaterials research up until April 2021. A search in PubMed and Embase based on "spinal cord injury," "animal models," and "biomaterials" yielded 4606 papers, 393 of which were further evaluated. A total of 404 individual animal experiments were identified based on type of SCI, level of SCI, and the sex, species, and strain of the animals used. Finally, a total of 149 unique animal models were comparatively evaluated, which led to the generation of an evidence-based list of well-documented mid-thoracic rat models of SCI. These models were used most often, clearly confirmed SCI, and had relatively high survival rates, and therefore could serve as a future starting point for studying novel biomaterial-based therapies for SCI. Furthermore, the review discusses (1) the possible risk of bias in SCI animal models, (2) the difficulty in replication of such experiments due to frequent poor reporting of the methods and results, and (3) the clinical relevance of the currently utilized models. Systematic review registration: The study was prospectively registered in PROSPERO, registration number CRD42019141162. Impact statement Studies on biomaterial-based therapies within the field of spinal cord injury (SCI) research show a large inconsistency concerning the selection of animal models. This review goes beyond summarizing the existing gaps between experimental and clinical SCI by systematically evaluating all animal models used within this field. The models identified by this work were used most often, clearly confirmed SCI, and had a relatively high survival rate. This evidence-based list of well-documented animal models will serve as a practical guideline in future research on innovative biomaterial-based therapies for SCI.

Animal models of compression spinal cord injury

Compression spinal cord injuries are a common cause of morbidity in people who experience a spinal cord injury (SCI). Either as a by-product of a traumatic injury or due to nontraumatic conditions such as cervical myelitis, compression injuries are growing in prevalence clinically and many attempts of animal replication have been described within the literature. These models, however, often focus on the traumatic side of injury or mimic short-term injuries that are not representative of the majority of compression SCI. Of this, nontraumatic spinal cord injuries are severely understudied and have an increased prevalence in elderly populations, adults, and children. Therefore, there is a need to critically evaluate the current animal models of compression SCI and their suitability as a method for clinically relevant data that can help reduce morbidity and mortality of SCI. In this review, we reviewed the established and emerging methods of animal models of compression SCI. These models are the clip, balloon, solid spacer, expanding polymer, remote, weight drop, calibrated forceps, screw, and strap methods. These methods showed that there is a large reliance on the use of laminectomy to induce injury. Furthermore, the age range of many studies does not reflect the elderly and young populations that commonly suffer from compression injuries. It is therefore important to have techniques and methods that are able to minimize secondary effects of the surgeries, and are representative of the clinical cases seen so that treatments and interventions can be developed that are specific.

A functionalized collagen-I scaffold delivers microRNA 21-loaded exosomes for spinal cord injury repair

MicroRNA (miRNA)-based therapies have shown great potential in the repair of spinal cord injury (SCI). MicroRNA 21 (miR21) has been proven to have an essential protective effect on SCI. However, there are some challenges for miRNAs application due to their easy degradation and ineffective cell penetration. As natural vesicles, exosomes were considered ideal carriers for miRNAs delivery for their advantages of low immunogenicity, inherent stability and tissue/cell penetration. However, poor targeting and the low capacity of specific miRNAs impede their practical applications. This study aims to develop a type of genetically engineered miR21-loaded exosomes that can be entrapped in collagen-I (Col-I) scaffold to repair SCI. The collagen-binding domain (CBD)-fused lysosome-associated membrane glycoprotein 2b (Lamp2b) protein (CBD-LP) and miR21 were overexpressed in host HEK293T (293T) cells that were used to produce engineered miR21-loaded exosomes. The CBD peptide fused in Lamp2b on the exosome surface can stably tether exosomes to Col-I scaffold, facilitate the retention of miR21-loaded exosomes in lesion sites, promote the sustained release of miR21 to cells. Finally, a functionalized Col-I scaffold biomaterial enriched with miR21-loaded exosomes was developed and it could benefit the repair of SCI. STATEMENT OF SIGNIFICANCE: MiRNA-based therapeutics have promising potential in spinal cord injury (SCI) repair. However, easy degradation and ineffective cell penetration impede miRNAs application. Exosomes are natural vehicles for miRNAs delivery but face the challenge of diffusion in vivo. Here, the collagen-binding domain (CBD)-fused Lamp2b and miR21 were overexpressed in HEK293T cells to produce miR21-loaded and CBD-modified exosomes (CBD-LP-miR21-EXOs). The CBD modified on the exosome surface can stably tether exosomes to collagen-I scaffold to form functionalized CBD-LP-miR21-EXO-Col scaffold that can facilitate the retention of miR21-loaded exosomes, promote the sustained release of miR21 to cells and finally benefit SCI repair. Furthermore, this type of functionalized collagen-I materials can be widely applied for other tissue injury repairs by enriching the CBD-LP-EXOs loaded with appropriate miRNAs.

Long-term administration of bumetanide improve functional recovery after spinal cord injury in rats

Ion disturbances are among the most remarkable deficits in spinal cord injury (SCI). GABA is an integral part of neural interaction. Action of the GABAA receptor depends on the amount of intracellular chloride. Homeostasis of chloride is controlled by two co-transporters, NKCC1 and KCC2. Previous studies revealed that NKCC1 are disturbed in SCI. In this study, NKCC1 is highly expressed in the epicenter of the lesioned spinal cord at 3 hours after induction of the lesion and reached the peak around 6 hours after SCI. Bumetanide (2 and 4 mg/day), as a specific NKCC1 inhibitor, was used at 3 hours post SCI for 28 days. The functional recovery outcomes were measured by the Basso-Beattie-Bresnahan (BBB) locomotor rating scale, ladder walking test, and hot plate test. The rats that received bumetanide 4 mg/day exhibited improved recovery of locomotor function, reduction of NKCC1 gene expression, and upregulation of GAP protein levels 28 days post SCI. Histological tissue evaluations confirmed bumetanide's neuroprotective and regenerative effects. This study provides novel evidence for the benefits of bumetanide in early administration after SCI.

A survival model of thoracic contusion spinal cord injury in the domestic pig

Spinal cord injury (SCI) frequently results in motor, sensory and autonomic dysfunction for which there is currently no cure. Recent preclinical and clinical research has led to promising advances in treatment; however, therapeutics indicating promise in rodents have not translated successfully in human trials, likely due, in part, to gross anatomical and physiological differences between the species. Therefore, large animal models of SCI may facilitate the study of secondary injury processes that are influenced by scale, and assist the translation of potential therapeutic interventions. The aim of this study was to characterize two severities of thoracic contusion SCI in female domestic pigs, measuring motor function and spinal cord lesion characteristics, over two weeks post-SCI. A custom instrumented weight drop injury device was used to release a 50 g impactor from 10 cm (n=3) or 20 cm (n=7) onto the exposed dura, to induce a contusion at the T10 thoracic spinal level. Hind limb motor function was assessed at 8 and 13 days post-SCI using a 10-point scale. Volume and extent of lesion-associated signal hyperintensity in T2-weighted magnetic resonance (MR) images was assessed at 3, 7 and 14 days post-injury. Animals were transcardially perfused at 14 days post-SCI and spinal cord tissue was harvested for histological analysis. Bowel function was retained in all animals and transient urinary retention occurred in two animals after catheter removal. All animals displayed hind limb motor deficits. Animals in the 10 cm group demonstrated some stepping and weight bearing and scored a median 2-3 points higher on the 10-point motor function scale at 8 and 13 days post-SCI, than the 20 cm group. Histological lesion volume was 20 % greater, and 30 % less white matter was spared, in the 20 cm group than in the 10 cm group. The MR signal hyperintensity in the 20 cm injury group had a median cranial-caudal extent approximately 1.5 times greater than the 10 cm injury group at all three time points, and median volumes 1.8, 2.5 and 4.5 times greater at day 3, 7 and 14 post-injury, respectively. Regional differences in axonal injury were observed between groups, with amyloid precursor protein immunoreactivity greatest in the 20 cm group in spinal cord sections adjacent the injury epicenter. This study demonstrated graded injuries in a domestic pig strain, with outcome measures comparable to miniature pig models of contusion SCI. The model provides a vehicle for the study of SCI and potential treatments, particularly where miniature pig strains are not available and/or where small animal models are not appropriate for the research question.

The Impact of Activity-Based Interventions on Neuropathic Pain in Experimental Spinal Cord Injury

Physical activity-based rehabilitative interventions represent the main treatment concept for people suffering from spinal cord injury (SCI). The role such interventions play in the relief of neuropathic pain (NP) states is emerging, along with underlying mechanisms resulting in SCI-induced NP (SCI-NP). Animal models have been used to investigate the benefits of activity-based interventions (ABI), such as treadmill training, wheel running, walking, swimming, and bipedal standing. These activity-based paradigms have been shown to modulate inflammatory-related alterations as well as induce functional and structural changes in the spinal cord gray matter circuitry correlated with pain behaviors. Thus far, the research available provides an incomplete picture of the cellular and molecular pathways involved in this beneficial effect. Continued research is essential for understanding how such interventions benefit SCI patients suffering from NP and allow the development of individualized rehabilitative therapies. This article reviews preclinical studies on this specific topic, goes over mechanisms involved in SCI-NP in relation to ABI, and then discusses the effectiveness of different activity-based paradigms as they relate to different forms, intensity, initiation times, and duration of ABI. This article also summarizes the mechanisms of respective interventions to ameliorate NP after SCI and provides suggestions for future research directions.

Molecular Identification of Pro-Excitogenic Receptor and Channel Phenotypes of the Deafferented Lumbar Motoneurons in the Early Phase after SCT in Rats

Spasticity impacts the quality of life of patients suffering spinal cord injury and impedes the recovery of locomotion. At the cellular level, spasticity is considered to be primarily caused by the hyperexcitability of spinal α-motoneurons (MNs) within the spinal stretch reflex circuit. Here, we hypothesized that after a complete spinal cord transection in rats, fast adaptive molecular responses of lumbar MNs develop in return for the loss of inputs. We assumed that early loss of glutamatergic afferents changes the expression of glutamatergic AMPA and NMDA receptor subunits, which may be the forerunners of the developing spasticity of hindlimb muscles. To better understand its molecular underpinnings, concomitant expression of GABA and Glycinergic receptors and serotoninergic and noradrenergic receptors, which regulate the persistent inward currents crucial for sustained discharges in MNs, were examined together with voltage-gated ion channels and cation-chloride cotransporters. Using quantitative real-time PCR, we showed in the tracer-identified MNs innervating extensor and flexor muscles of the ankle joint multiple increases in transcripts coding for AMPAR and 5-HTR subunits, along with a profound decrease in GABAAR, GlyR subunits, and KCC2. Our study demonstrated that both MNs groups similarly adapt to a more excitable state, which may increase the occurrence of extensor and flexor muscle spasms.

Fighting for recovery on multiple fronts: The past, present, and future of clinical trials for spinal cord injury

Through many decades of preclinical research, great progress has been achieved in understanding the complex nature of spinal cord injury (SCI). Preclinical research efforts have guided and shaped clinical trials, which are growing in number by the year. Currently, 1,149 clinical trials focused on improving outcomes after SCI are registered in the U.S. National Library of Medicine at ClinicalTrials.gov. We conducted a systematic analysis of these SCI clinical trials, using publicly accessible data downloaded from ClinicalTrials.gov. After extracting all available data for these trials, we categorized each trial according to the types of interventions being tested and the types of outcomes assessed. We then evaluated clinical trial characteristics, both globally and by year, in order to understand the areas of growth and change over time. With regard to clinical trial attributes, we found that most trials have low enrollment, only test single interventions, and have limited numbers of primary outcomes. Some gaps in reporting are apparent; for instance, over 75% of clinical trials with "Completed" status do not have results posted, and the Phase of some trials is incorrectly classified as "Not applicable" despite testing a drug or biological compound. When analyzing trials based on types of interventions assessed, we identified the largest representation in trials testing rehab/training/exercise, neuromodulation, and behavioral modifications. Most highly represented primary outcomes include motor function of the upper and lower extremities, safety, and pain. The most highly represented secondary outcomes include quality of life and pain. Over the past 15 years, we identified increased representation of neuromodulation and rehabilitation trials, and decreased representation of drug trials. Overall, the number of new clinical trials initiated each year continues to grow, signifying a hopeful future for the clinical treatment of SCI. Together, our work provides a comprehensive glimpse into the past, present, and future of SCI clinical trials, and suggests areas for improvement in clinical trial reporting.

Genetic animal modeling for idiopathic scoliosis research: history and considerations

PURPOSE

Idiopathic scoliosis (IS) is defined as a structural lateral spinal curvature ≥ 10° in otherwise healthy children and is the most common pediatric spinal deformity. IS is known to have a strong genetic component; however, the underlying etiology is still largely unknown. Animal models have been used historically to both understand and develop treatments for human disease, including within the context of IS. This intended audience for this review is clinicians in the fields of musculoskeletal surgery and research.

METHODS

In this review article, we synthesize current literature of genetic animal models of IS and introduce considerations for researchers.

RESULTS

Due to complex genetic and unique biomechanical factors (i.e., bipedalism) hypothesized to contribute to IS in humans, scoliosis is a difficult condition to replicate in model organisms.

CONCLUSION

We advocate careful selection of animal models based on the scientific question and introduce gaps and limitations in the current literature. We advocate future research efforts to include animal models with multiple characterized genetic or environmental perturbations to reflect current understanding of the human condition.

The roles and applications of neural stem cells in spinal cord injury repair

Spinal cord injury (SCI), which has no current cure, places a severe burden on patients. Stem cell-based therapies are considered promising in attempts to repair injured spinal cords; such options include neural stem cells (NSCs). NSCs are multipotent stem cells that differentiate into neuronal and neuroglial lineages. This feature makes NSCs suitable candidates for regenerating injured spinal cords. Many studies have revealed the therapeutic potential of NSCs. In this review, we discuss from an integrated view how NSCs can help SCI repair. We will discuss the sources and therapeutic potential of NSCs, as well as representative pre-clinical studies and clinical trials of NSC-based therapies for SCI repair.

Rehabilitation combined with neural progenitor cell grafts enables functional recovery in chronic spinal cord injury

We reported previously that neural progenitor cell (NPC) grafts form neural relays across sites of subacute spinal cord injury (SCI) and support functional recovery. Here, we examine whether NPC grafts after chronic delays also support recovery and whether intensive rehabilitation further enhances recovery. One month after severe bilateral cervical contusion, rats received daily intensive rehabilitation, NPC grafts, or both rehabilitation and grafts. Notably, only the combination of rehabilitation and grafting significantly improved functional recovery. Moreover, improved functional outcomes were associated with a rehabilitation-induced increase in host corticospinal axon regeneration into grafts. These findings identify a critical and synergistic role of rehabilitation and neural stem cell therapy in driving neural plasticity to support functional recovery after chronic and severe SCI.

The immune microenvironment and tissue engineering strategies for spinal cord regeneration

Regeneration of neural tissue is limited following spinal cord injury (SCI). Successful regeneration of injured nerves requires the intrinsic regenerative capability of the neurons and a suitable microenvironment. However, the local microenvironment is damaged, including insufficient intraneural vascularization, prolonged immune responses, overactive immune responses, dysregulated bioenergetic metabolism and terminated bioelectrical conduction. Among them, the immune microenvironment formed by immune cells and cytokines plays a dual role in inflammation and regeneration. Few studies have focused on the role of the immune microenvironment in spinal cord regeneration. Here, we summarize those findings involving various immune cells (neutrophils, monocytes, microglia and T lymphocytes) after SCI. The pathological changes that occur in the local microenvironment and the function of immune cells are described. We also summarize and discuss the current strategies for treating SCI with tissue-engineered biomaterials from the perspective of the immune microenvironment.

Markerless tracking enables distinction between strategic compensation and functional recovery after spinal cord injury

Injuries to the cervical spinal cord represent around 60% of all spinal cord injuries (SCIs). A major priority for patients with cervical SCIs is the recovery of any hand or arm function. The similarities between human and rodent "reach-to-eat movements" indicate that analyzing mouse forelimb reaching behavior may be a method of identifying clinically relevant treatments for people with cervical SCIs. One popular behavioral measure of forelimb functional recovery comprises the Single Pellet Retrieval Task (SPRT). The most common outcome measure for this task, however (percentage of pellets successfully retrieved), cannot readily distinguish between recovery of pre-injury motor patterns and strategic compensation. Our objective was to establish outcome measures for the SPRT that are readily adopted by different investigators and capable of measuring recovery of limb function after SCI. We used a simple semi-automated approach to high-speed tracking of mouse forepaw movements during pellet retrieval. DeepLabCut™, a machine learning based computer vision software package, was used to track individual features of the mouse forepaw, allowing a more detailed assessment of reaching behavior after SCI. Interestingly, kinematic analysis of movements pre- and post-injury illuminated persistent deficits in specific features of the reaching motor patterns, namely pronation and paw trajectory, that were poorly correlated with recovery of the ability to successfully retrieve pellets. Thus, we have developed an inexpensive method for detailed analysis of mouse reach-to-eat behavior following SCI. Further, our results suggest that binary success/fail outcome measures primarily assess an animal's ability to compensate rather than a restoration of normal function in the injured pathways and networks.

The role of spinal cord tractography in detecting lesions following selective bladder afferent and efferent fibers: A novel method for induction of neurogenic lower urinary tract dysfunction in rabbit

OBJECTIVE

Neurogenic lower urinary tract dysfunction (NLUTD), a challenging disorder, is defined by lack of bladder control due to the abnormalities in neural pathways and can be classified based on the location of lesions within the nervous system, thus investigating the neural pathways can help us to know the site of the lesion and specify the class of the NLUTD. Diffusion Tensor Imaging (DTI) tractography, a noninvasive advanced imaging method, is capable of detecting central nervous system pathologies, even if routine magnetic resonance imaging shows no abnormality. Accordingly, tractography is an ideal technique to evaluate patients with NLUTD and visualize the pathology site within the spine. This study aimed to introduce a novel method of spinal cord injury (SCI) to establish NLUTD in the rabbit and to investigate the potential of tractography in tracing neural tracts of the spinal cord in an induced NLUTD animal model.

MATERIALS AND METHODS

An animal model of NLUTD was induced through cauterization of the spinal cord at the level T12-L1 in 12 rabbits. Then rabbits were assessed via DTI, urodynamic studies (UDS), voiding cystourethrogram (VCUG), and pathology assessments using antineurofilament 200 (NF200) antibody, anti-S100, anti-Smooth Muscle Actin, anti-Myogenin, and anti-MyoD1.

RESULTS

The tractography visualized lesions within spinal cord fibers. DTI parameters including fractional anisotropy (FA) value and tract density were significantly decreased (FA: p-value = 0.01, Tract density: p-value = 0.05) after injury. The mean diffusivity (MD) was insignificantly increased compared to before the injury. Also, the results of UDS and pathology assessments corroborated that applying SCI and the establishment of the NLUTD model was completely successful.

CONCLUSION

In the present study, we investigated the auxiliary role of tractography in detecting the spinal cord lesions in the novel established rabbit model of NLUTD. The introduced method of NLUTD induction was without the leg's neurological deficit, easily applicable, low-cost, and was accompanied by minimal surgical preparation and a satisfactory survival rate in comparison with other SCI animal models.

Effect of Valproic Acid on NLR Family Pyrin Domain Containing 1/3 (NLRP1/3) Inflammasome in Rats with Acute Spinal Cord Injury

Our study assesses valproic acid’s effect on NLRP1/3 inflammasome in rats with acute spinal cord injury (SCI). SD rats were clamped by aneurysm clips to establish SCI model followed by analysis of functional recovery by BBB score, degree of inflammatory infiltration, by H&E staining, NLRP1/NLRP3 and P2X7 level by western blot, IL-1β and IL-18 level by ELISA, blood spinal cord barrier by EVANS blue method. After SCI, the lower limb motor function of rats decreased and recovered after valproic acid treatment (P < 0.05). Inflammatory cell infiltration of SCI group increased and decreased after treatment. After SCI, NLRP1/3 level increased and P2X7 protein level elevated which were reversed after valproic acid treatment (P < 0.05). In rats with SCI, IL-1β level in spinal cord was higher than sham operation and lower after treatment (P < 0.05) without difference of IL-18 between injury group and treatment group (P > 0.05). In addition, fluorescence was higher in injury group than sham operation group and lower in valproic acid injection group than injury group. In conclusion, Valproic acid can promote motor function recovery in rats after SCI and inhibit inflammasome 1 and 3 expression, thereby inhibiting the maturation and release of IL-1β, and reducing P2X7 level after SCI.

Characterization of Ex Vivo and In Vitro Wnt Transcriptome Induced by Spinal Cord Injury in Rat Microglial Cells

It is well known that inflammation is crucial in the onset and progression of neurodegenerative diseases and traumatic central nervous system (CNS) injuries, and that microglia and monocyte-derived macrophages (MDMs) play a pivotal role in neuroinflammation. Therefore, the exploration of molecular signaling pathways that are involved in the microglia/macrophage response might help us to shed light on their eventual therapeutic modulation. Interestingly, there is growing evidence showing that the Wnt family of proteins is involved in different neuropathologies that are characterized by a dysregulated neuroinflammatory response, including spinal cord injury (SCI). Here, we aimed to validate a methodology with competence to assess the physiologically relevant Wnt expression patterns of active microglia and MDMs in a rat model of SCI. For that purpose, we have selected and adapted an in vitro system of primary microglia culture that were stimulated with a lesioned spinal cord extract (SCE), together with an ex vivo protocol of flow cytometry sorting of rat microglia/MDMs at different time-points after contusive SCI. Our study demonstrates that the expression profile of Wnt-related genes in microglia/MDM cells exhibit important differences between these particular scenarios which would be in line with previous studies where similar discrepancies have been described for other molecules. Moreover, our results provide for a first experimental report of the Wnt transcriptome in rat microglia and MDMs after SCI which, together with the research platform that was used in the study, and considering its limitations, we expect might contribute to foster the research on Wnt-driven immunomodulatory therapies.

Effectiveness of biomaterial-based combination strategies for spinal cord repair – a systematic review and meta-analysis of preclinical literature

Study design

Systematic review and meta-analysis of preclinical literature.

Objectives

To assess the effects of biomaterial-based combination (BMC) strategies for the treatment of Spinal Cord Injury (SCI), the effects of individual biomaterials in the context of BMC strategies, and the factors influencing their efficacy. To assess the effects of different preclinical testing paradigms in BMC strategies.

Methods

We performed a systematic literature search of Embase, Web of Science and PubMed. All controlled preclinical studies describing an in vivo or in vitro model of SCI that tested a biomaterial in combination with at least one other regenerative strategy (cells, drugs, or both) were included. Two review authors conducted the study selection independently, extracted study characteristics independently and assessed study quality using a modified CAMARADES checklist. Effect size measures were combined using random-effects models and heterogeneity was explored using meta-regression with tau2, I2 and R2 statistics. We tested for small-study effects using funnel plot–based methods.

Results

134 publications were included, testing over 100 different BMC strategies. Overall, treatment with BMC therapies improved locomotor recovery by 25.3% (95% CI, 20.3–30.3; n = 102) and in vivo axonal regeneration by 1.6 SD (95% CI 1.2–2 SD; n = 117) in comparison with injury only controls.

Conclusion

BMC strategies improve locomotor outcomes after experimental SCI. Our comprehensive study highlights gaps in current knowledge and provides a foundation for the design of future experiments.

Correlation Analysis Between Magnetic Resonance Imaging-Based Anatomical Assessment and Behavioral Outcome in a Rat Contusion Model of Chronic Thoracic Spinal Cord Injury

Although plenty of evidences from preclinical studies have led to potential treatments for patients with spinal cord injury (SCI), the failure to translate promising preclinical findings into clinical advances has long puzzled researchers. Thus, a more reliable combination of anatomical assessment and behavioral testing is urgently needed to improve the translational worth of preclinical studies. To address this issue, the present study was designed to relate magnetic resonance imaging (MRI)-based anatomical assessment to behavioral outcome in a rat contusion model. Rats underwent contusion with three different heights to simulate various severities of SCI, and their locomotive functions were evaluated by the grid-walking test, Louisville swim scale (LSS), especially catwalk gait analysis system and basic testing, and Basso, Beattie, Bresnahan (BBB) score. The results showed that the lesion area (LA) is a better indicator for damage assessment compared with other parameters in sagittal T2-weighted MRI (T2WI). Although two samples are marked as outliers by the box plot analysis, LA correlated closely with all of the behavioral testing without ceiling effect and floor effect. Moreover, with a moderate severity of SCI in a contusion height of 25 mm, the smaller the LA of the spinal cord measured on sagittal T2WI the better the functional performance, the smaller the cavity region and glial scar, the more spared the myelin, the higher the volatility, and the thicker the bladder wall. We found that LA significantly related with behavior outcomes, which indicated that LA could be a proxy of damage assessment. The combination of sagittal T2WI and four types of behavioral testing can be used as a reliable scheme to evaluate the prognosis for preclinical studies of SCI.

Early mobilization in spinal cord injury promotes changes in microglial dynamics and recovery of motor function

In the acute phase of spinal cord injury, the initial injury triggers secondary damage due to neuroinflammation, leading to the formation of cavities and glial scars that impair nerve regeneration. Following injuries to the central nervous system, early mobilization promotes the recovery of physical function. Therefore, in the present study, we investigated the effects of early mobilization on motor function recovery and neuroinflammation in rats. Early mobilization of rats with complete spinal cord transection resulted in good recovery of hindlimb motor function after 3 weeks. At 1 week after spinal cord injury, the early-mobilized rats expressed fewer inflammatory M1 microglia/macrophages and more anti-inflammatory M2 microglia. In addition, significantly more matrix metalloproteinase 2 (MMP2)-positive cells were observed at the lesion site 1 week after injury in the early-mobilized rats. Multiple labeling studies suggested that many MMP2-positive cells were M2 microglia. MMP9-positive cells that highly co-expressed GFAP were also observed more frequently in the early-mobilized rats. The density of growth-associated protein-positive structures in the lesion center was significantly higher in the early-mobilized rats at 3 weeks after spinal cord injury. The present results suggest that early mobilization after spinal cord injury reduced the production of M1 microglia/macrophages while increasing the production of M2 microglia at the lesion site. Early mobilization might also activate the expression of MMP2 in M2 microglia and MMP9 in astrocytes. These cellular dynamics might suppress neuroinflammation at the lesion site, thereby inhibiting the progression of tissue destruction and promoting nerve regeneration to recover motor function.

•

Early mobilization effected on motor function recovery in spinal cord injury rat.

•

Early mobilization suppressed neuroinflammation by M1 microglial reduction.

•

Early mobilization activated expression of MMP2 in microglia cells.

•

Inhibit of neuroinflammation resulted smaller spinal cord injury lesion center.

•

Inhibit of neuroinflammation resulted increase the regenerating axon.

Spinal cord bioelectronic interfaces: opportunities in neural recording and clinical challenges

Bioelectronic stimulation of the spinal cord has demonstrated significant progress in restoration of motor function in spinal cord injury (SCI). The proximal, uninjured spinal cord presents a viable target for the recording and generation of control signals to drive targeted stimulation. Signals have been directly recorded from the spinal cord in behaving animals and correlated with limb kinematics. Advances in flexible materials, electrode impedance and signal analysis will allow SCR to be used in next-generation neuroprosthetics. In this review, we summarize the technological advances enabling progress in SCR and describe systematically the clinical challenges facing spinal cord bioelectronic interfaces and potential solutions, from device manufacture, surgical implantation to chronic effects of foreign body reaction and stress-strain mismatches between electrodes and neural tissue. Finally, we establish our vision of bi-directional closed-loop spinal cord bioelectronic bypass interfaces that enable the communication of disrupted sensory signals and restoration of motor function in SCI.

Human Epidural AD–MSC Exosomes Improve Function Recovery after Spinal Cord Injury in Rats

Spinal cord injury (SCI) interferes with the normal function of the autonomic nervous system by blocking circuits between the sensory and motor nerves. Although many studies focus on functional recovery after neurological injury, effective neuroregeneration is still being explored. Recently, extracellular vesicles such as exosomes have emerged as cell-free therapeutic agents owing to their ability of cell-to-cell communication. In particular, exosomes released from mesenchymal stem cells (MSCs) have the potential for tissue regeneration and exhibit therapeutic effectiveness in neurological disorders. In this study, we isolated exosomes from human epidural adipose tissue-derived MSCs (hEpi AD–MSCs) using the tangential flow filtration method. The isolated exosomes were analyzed for size, concentration, shape, and major surface markers using nanoparticle tracking analysis, transmission electron microscopy, and flow cytometry. To evaluate their effect on SCI recovery, hEpi AD–MSC exosomes were injected intravenously in SCI-induced rats. hEpi AD–MSC exosomes improved the locomotor function of SCI-induced rats. The results of histopathological and cytokine assays showed that hEpi AD–MSC exosomes regulated inflammatory response. Genetic profiling of the rat spinal cord tissues revealed changes in the expression of inflammation-related genes after exosome administration. Collectively, hEpi AD–MSC exosomes are effective in restoring spinal functions by reducing the inflammatory response.

Therapeutic Effect of Exosomes Derived From Stem Cells in Spinal Cord Injury: A Systematic Review Based on Animal Studies

Objective

A systematic review of the role of stem cell-derived exosomes in repairing spinal cord injury (SCI) and the existing problems in animal experiments to provide a reference for better animal experiments and clinical studies in the future.

Method

Three electronic databases, namely PubMed, Web of Science, and Ovid-Embase were searched. The studies were retrieved from inception to October 2021. Two researchers independently screened the literature, extracted data, and evaluated the methodological quality based on the inclusion criteria.

Results and Discussion

Thirty-two studies were incorporated into the final analyses. Exosomes derived from stem cells could not only significantly improve the motor function of animals with SCI, but also significantly increase the expression of anti-inflammatory factors IL-4 and IL-10 and anti-apoptotic protein Bcl-2, while significantly lowering the pro-inflammatory factor IL-1β and TNF-α and the expression of the apoptotic protein BAX. However, the mechanism of exosome-mediated SCI repair, as well as the best source and dosage remain unknown. In addition, there are still some issues with the design, implementation, and reporting of animal experiments in the included studies. Therefore, future research should further standardize the implementation and reporting of animal studies and fully explore the best strategies for exosomes to repair SCI so as to promote the translation of preclinical research results to clinical research better and faster.

Stem cell treatment trials of spinal cord injuries in animals

BACKGROUND

Spinal cord injury (SCI) is a serious neurological spinal cord damage that resulted in the loss of temporary or permanent function. However, there are even now no effective therapies for it. So, a new medical promising therapeutic hotspot over the previous decades appeared which was (Stem cell (SC) cure of SCI). Otherwise, animal models are considered in preclinical research as a model for humans to trial a potential new treatment.

METHODOLOGY

Following articles were saved from different databases (PubMed, Google scholar, Egyptian knowledge bank, Elsevier, Medline, Embase, ProQuest, BMC) on the last two decades, and data were obtained then analyzed.

RESULTS

This review discusses the type and grading of SCI. As well as different types of stem cells therapy for SCI, including mesenchymal stem cells (MSCs), neural stem cells (NSCs), hematopoietic stem cells (HSCs), induced pluripotent stem cells (iPSCs), and embryonic stem cells (ESCs). The review focuses on the transplantation pathways, clinical evaluation, and clinical signs of different types of SC on different animal models which are summarized in tables to give an easy to reach.

CONCLUSION

Pharmacological and physiotherapy have limited regenerative power in comparison with stem cells medication in the treatment of SCI. Among several sources of cell therapies, mesenchymal stromal/stem cell (MSC) one is being progressively developed as a trusted important energetic way to repair and regenerate. Finally, a wide-ranged animal models have been condensed that helped in human clinical trial therapies.

A New Framework for Investigating the Biological Basis of Degenerative Cervical Myelopathy [AO Spine RECODE-DCM Research Priority Number 5]: Mechanical Stress, Vulnerability and Time

STUDY DESIGN

Literature Review (Narrative).

OBJECTIVE

To propose a new framework, to support the investigation and understanding of the pathobiology of DCM, AO Spine RECODE-DCM research priority number 5.

METHODS

Degenerative cervical myelopathy is a common and disabling spinal cord disorder. In this perspective, we review key knowledge gaps between the clinical phenotype and our biological models. We then propose a reappraisal of the key driving forces behind DCM and an individual's susceptibility, including the proposal of a new framework.

RESULTS

Present pathobiological and mechanistic knowledge does not adequately explain the disease phenotype; why only a subset of patients with visualized cord compression show clinical myelopathy, and the amount of cord compression only weakly correlates with disability. We propose that DCM is better represented as a function of several interacting mechanical forces, such as shear, tension and compression, alongside an individual's vulnerability to spinal cord injury, influenced by factors such as age, genetics, their cardiovascular, gastrointestinal and nervous system status, and time.

CONCLUSION

Understanding the disease pathobiology is a fundamental research priority. We believe a framework of mechanical stress, vulnerability, and time may better represent the disease as a whole. Whilst this remains theoretical, we hope that at the very least it will inspire new avenues of research that better encapsulate the full spectrum of disease.

Automated lever task with minimum antigravity movement for rats with cervical spinal cord injury

BACKGROUND

Although there is currently no cure for paralysis due to spinal cord injury (SCI), the highest treatment priority is restoring arm and hand function for people with cervical SCI. Preclinical animal models provide an opportunity to test innovative treatments, but severe cervical injury models require significant time and effort to assess responses to novel interventions. Moreover, there is no behavioral task that can assess forelimb movement in rats with severe cervical SCI unable to perform antigravity movements.

NEW METHOD

We developed a novel lever pressing task for rats with severe cervical SCI. We employed an automated adaptive algorithm to train animals using open-source software and commercially available hardware. We found that using the adaptive training required only 13.3 ± 2.5 training days to achieve behavioral proficiency. The lever press task could quantify immediate and long-term improvements in severely impaired forelimb function effectively. This behavior platform has potential to facilitate rehabilitative training and assess effects of therapeutic modalities following SCI.

COMPARISON WITH EXISTING METHODS

There is no existing assessment aiming to quantify forelimb extension movement in rodents without function against gravity. We found that the new lever press task in the antigravity position could assess the severity of cervical SCI as well as the compensatory movement in the proximal forelimb less affected by the injury.

CONCLUSIONS

This study demonstrates that the new behavioral task is capable of tracking the functional changes with various therapies in rats with severe forelimb impairments in a cost- and time-efficient manner.

Effects of Polyphenols on Oxidative Stress, Inflammation, and Interconnected Pathways during Spinal Cord Injury

Despite the progression in targeting the complex pathophysiological mechanisms of neurodegenerative diseases (NDDs) and spinal cord injury (SCI), there is a lack of effective treatments. Moreover, conventional therapies suffer from associated side effects and low efficacy, raising the need for finding potential alternative therapies. In this regard, a comprehensive review was done regarding revealing the main neurological dysregulated pathways and providing alternative therapeutic agents following SCI. From the mechanistic point, oxidative stress and inflammatory pathways are major upstream orchestras of cross-linked dysregulated pathways (e.g., apoptosis, autophagy, and extrinsic mechanisms) following SCI. It urges the need for developing multitarget therapies against SCI complications. Polyphenols, as plant-derived secondary metabolites, have the potential of being introduced as alternative therapeutic agents to pave the way for treating SCI. Such secondary metabolites presented modulatory effects on neuronal oxidative stress, neuroinflammatory, and extrinsic axonal dysregulated pathways in the onset and progression of SCI. In the present review, the potential role of phenolic compounds as critical phytochemicals has also been revealed in regulating upstream dysregulated oxidative stress/inflammatory signaling mediators and extrinsic mechanisms of axonal regeneration after SCI in preclinical and clinical studies. Additionally, the coadministration of polyphenols and stem cells has shown a promising strategy for improving post-SCI complications.

Frailty and pain, human studies and animal models

The hypothesis that pain can predispose to frailty development has been recently investigated in several clinical studies suggesting that frailty and pain may share some mechanisms. Both pain and frailty represent important clinical and social problems and both lack a successful treatment. This circumstance is mainly due to the absence of in-depth knowledge of their pathological mechanisms. Evidence of shared pathways between frailty and pain are preliminary. Indeed, many clinical studies are observational and the impact of pain treatment, and relative pain-relief, on frailty onset and progression has never been investigated. Furthermore, preclinical research on this topic has yet to be performed. Specific researches on the pain-frailty relation are needed. In this narrative review, we will attempt to point out the most relevant findings present in both clinical and preclinical literature on the topic, with particular attention to genetics, epigenetics and inflammation, in order to underline the existing gaps and the potential future interventional strategies. The use of pain and frailty animal models discussed in this review might contribute to research in this area.

Rehabilitative training improves skilled forelimb motor function after cervical unilateral contusion spinal cord injury in rats

Animal models of cervical spinal cord injury (SCI) have frequently utilized partial transection injuries to evaluate plasticity promoting treatments such as rehabilitation training of skilled reaching and grasping tasks. Though highly useful for studying the effects of cutting specific spinal tracts that are important for skilled forelimb motor function, cervical partial-transection SCI-models underappreciate the extensive spread of most human SCIs, thus offering poor predictability for the clinical setting. Conversely, moderate cervical contusion SCI models targeting the spinal tracts important for skilled reaching and grasping can better replicate the increased size of most human SCIs and are often considered more clinically relevant. However, it is unknown whether animals with moderate cervical contusion SCIs that damage key spinal motor tracts can train in skilled reaching and grasping tasks. In this study, we quantify the impact of injury size and distribution on recovery in a skilled motor task called the single pellet reaching, grasping and retrieval (SPRGR) task in rats with cervical unilateral contusion injuries (UCs), and compare to rats with a partial transection SCIs (i.e., dorsolateral quadrant transection; DLQ). We found that UCs damage key tracts important for performing skilled motor tasks, similar to DLQs, but UCs also produce more extensive grey matter damage and more ventral white matter damage than DLQs. We also compared forelimb functionality at 1, 3, and 5 weeks of rehabilitative motor training between trained and untrained rats and found a more severe drop in SPRGR performance than in DLQ SCIs. Nevertheless, despite more severe injuries and initially low SPRGR performance, rehabilitative training for contusion animals resulted in significant improvements in SPRGR performance and proportionally more recovery than DLQ rats. Our findings show that rehabilitative motor training can facilitate considerable amounts of motor recovery despite extensive spinal cord damage, especially grey matter damage, thus supporting the use of contusion or compression SCI models and showing that ventral grey and white matter damage are not necessarily detrimental to recovery after training.

Effects of Resistance Training on Oxidative Stress Markers and Muscle Damage in Spinal Cord Injured Rats

Simple Summary

Spinal Cord Injury is a devastating condition that compromises the individual’s health, quality of life and functional independence. Rats submitted to Spinal Cord Injury were evaluated after four weeks of resistance training. Analyses of levels of muscle damage and oxidative stress surgery were performed. Resistance training demonstrated increase antioxidative activity while decreased oxidative damage in injured rats, in addition to having presented changes in the levels of muscle damage in that same group. The results highlight that resistance training promoted a decrease in oxidative stress and a significant response in muscle damage markers.

Abstract

Background: Spinal cord injury (SCI) is a condition that affects the central nervous system, is characterized by motor and sensory impairments, and impacts individuals’ lives. The objective of this study was to evaluate the effects of resistance training on oxidative stress and muscle damage in spinal cord injured rats. Methodology: Forty Wistar rats were selected and divided equally into five groups: Healthy Control (CON), Sham (SHAM) SCI Untrained group (SCI-U), SCI Trained group (SCI- T), SCI Active Trained group (SCI- AT). Animals in the trained groups were submitted to an incomplete SCI at T9. Thereafter, they performed a protocol of resistance training for four weeks. Results: Significant differences in muscle damage markers and oxidative stress in the trained groups, mainly in SCI- AT, were found. On the other hand, SCI- U group presented higher levels of oxidative stress and biomarkers of LDH and AST. Conclusion: The results highlight that resistance training promoted a decrease in oxidative stress and a significative response in muscle damage markers.

A Simple and Cost-Effective Weight Drop Model to Induce Contusive Spinal Cord Injury: Functional and Histological Outcomes

Background: Animal spinal cord injury (SCI) models have provided a better perception of the mechanisms related to traumatic SCI and evaluation of the effectiveness of experimental therapeutic interventions. Objectives: The aim of this study is to develop a cost-effective modified Allen's device to induce contusive spinal cord injury. Methods: Adult male Wistar rats were subjected to contusive spinal cord injury using a customized weight drop model through 10-g weights delivered from a 25-mm height onto an exposed spinal cord. Locomotor and sensory function during 28 days were assessed. Moreover, histopathological changes were assessed at one week and 28 days post SCI. Results: All the SCI rats showed hind limb paralysis up to 48 h post SCI and neuropathic pain after injury. Histological changes similar to the previous reports for contusion model were observed. Conclusions: According to our findings, little variability was observed in the BBB score of individual rats at 28 days after injury. Our customized device to induce spinal cord injury is a simple and inexpensive alternative method to the highly sophisticated contusion device commonly used to induce SCI.

Systematic review of the impact of cannabinoids on neurobehavioral outcomes in preclinical models of traumatic and nontraumatic spinal cord injury

STUDY DESIGN

Systematic review.

OBJECTIVES

To evaluate the impact of cannabinoids on neurobehavioral outcomes in preclinical models of nontraumatic and traumatic spinal cord injury (SCI), with the aim of determining suitability for clinical trials involving SCI patients.

METHODS

A systematic search was performed in MEDLINE and Embase databases, following registration with PROPSERO (CRD42019149671). Studies evaluating the impact of cannabinoids (agonists or antagonists) on neurobehavioral outcomes in preclinical models of nontraumatic and traumatic SCI were included. Data extracted from relevant studies, included sample characteristics, injury model, neurobehavioural outcomes assessed and study results. PRISMA guidelines were followed and the SYRCLE checklist was used to assess risk of bias.

RESULTS

The search returned 8714 studies, 19 of which met our inclusion criteria. Sample sizes ranged from 23 to 390 animals. WIN 55,212-2 (n = 6) and AM 630 (n = 8) were the most used cannabinoid receptor agonist and antagonist respectively. Acute SCI models included traumatic injury (n = 16), ischaemia/reperfusion injury (n = 2), spinal cord cryoinjury (n = 1) and spinal cord ischaemia (n = 1). Assessment tools used assessed locomotor function, pain and anxiety. Cannabinoid receptor agonists resulted in statistically significant improvement in locomotor function in 9 out of 10 studies and pain outcomes in 6 out of 6 studies.

CONCLUSION

Modulation of the endo-cannabinoid system has demonstrated significant improvement in both pain and locomotor function in pre-clinical SCI models; however, the risk of bias is unclear in all studies. These results may help to contextualise future translational clinical trials investigating whether cannabinoids can improve pain and locomotor function in SCI patients.

Functional hydrogels as therapeutic tools for spinal cord injury: New perspectives on immunopharmacological interventions

Spinal cord injury (SCI) is a complex medical and psychological challenge for which there is no curative therapy currently available. Despite major progress in pharmacological and surgical approaches, clinical trials for SCI patients have been uniformly disappointing thus far as there are many practical and biological issues yet to be resolved. Neuroinflammation is a critical event of the secondary injury phase after SCI, and recent research strategies have focused on modulating the immune response after injury to provide a more favorable recovery environment. Biomaterials can serve this purpose by providing physical and trophic support to the injured spinal cord after SCI. Of all potential biomaterials, functional hydrogels are emerging as a key component in novel treatment strategies for SCI, including controlled and localized delivery of immunomodulatory therapies to drive polarization of immune cells towards a pro-regenerative phenotype. Here, we extensively review recent developments in the use of functional hydrogels as immunomodulatory therapies for SCI. We briefly describe physicochemical properties of hydrogels and demonstrate how advanced fabrication methods lead to the required heterogeneity and hierarchical arrangements that increasingly mimic complex spinal cord tissue. We then summarize potential SCI therapeutic modalities including: (i) hydrogels alone; (ii) hydrogels as cellular or (iii) bioactive molecule delivery vehicles, and; (iv) combinatorial approaches. By linking the structural properties of hydrogels to their functions in treatment with particular focus on immunopharmacological stimuli, this may accelerate further development of functional hydrogels for SCI, and indeed next-generation central nervous system regenerative therapies.

Selective Myostatin Inhibition Spares Sublesional Muscle Mass and Myopenia-Related Dysfunction after Severe Spinal Cord Contusion in Mice

Clinically relevant myopenia accompanies spinal cord injury (SCI), and compromises function, metabolism, body composition, and health. Myostatin, a transforming growth factor (TGF)β family member, is a key negative regulator of skeletal muscle mass. We investigated inhibition of myostatin signaling using systemic delivery of a highly selective monoclonal antibody - muSRK-015P (40 mg/kg) - that blocks release of active growth factor from the latent form of myostatin. Adult female mice (C57BL/6) were subjected to a severe SCI (65 kdyn) at T9 and were then immediately and 1 week later administered test articles: muSRK-015P (40 mg/kg) or control (vehicle or IgG). A sham control group (laminectomy only) was included. At euthanasia, (2 weeks post-SCI) muSRK-015P preserved whole body lean mass and sublesional gastrocnemius and soleus mass. muSRK-015P-treated mice with SCI also had significantly attenuated myofiber atrophy, lipid infiltration, and loss of slow-oxidative phenotype in soleus muscle. These outcomes were accompanied by significantly improved sublesional motor function and muscle force production at 1 and 2 weeks post-SCI. At 2 weeks post-SCI, lean mass was significantly decreased in SCI-IgG mice, but was not different in SCI-muSRK-015P mice than in sham controls. Total energy expenditure (kCal/day) at 2 weeks post-SCI was lower in SCI-immunoglobulin (Ig)G mice, but not different in SCI-muSRK-015P mice than in sham controls. We conclude that in a randomized, blinded, and controlled study in mice, myostatin inhibition using muSRK-015P had broad effects on physical, metabolic, and functional outcomes when compared with IgG control treated SCI animals. These findings may identify a useful, targeted therapeutic strategy for treating post-SCI myopenia and related sequelae in humans.

Cell transplantation and secretome based approaches in spinal cord injury regenerative medicine

The axonal growth-restrictive character of traumatic spinal cord injury (SCI) makes finding a therapeutic strategy a very demanding task, due to the postinjury events impeditive to spontaneous axonal outgrowth and regeneration. Considering SCI pathophysiology complexity, it has been suggested that an effective therapy should tackle all the SCI-related aspects and provide sensory and motor improvement to SCI patients. Thus, the current aim of any therapeutic approach for SCI relies in providing neuroprotection and support neuroregeneration. Acknowledging the current SCI treatment paradigm, cell transplantation is one of the most explored approaches for SCI with mesenchymal stem cells (MSCs) being in the forefront of many of these. Studies showing the beneficial effects of MSC transplantation after SCI have been proposing a paracrine action of these cells on the injured tissues, through the secretion of protective and trophic factors, rather than attributing it to the action of cells itself. This manuscript provides detailed information on the most recent data regarding the neuroregenerative effect of the secretome of MSCs as a cell-free based therapy for SCI. The main challenge of any strategy proposed for SCI treatment relies in obtaining robust preclinical evidence from in vitro and in vivo models, before moving to the clinics, so we have specifically focused on the available vertebrate and mammal models of SCI currently used in research and how can SCI field benefit from them.

Pyrrole Plasma Polymer-Coated Fibrillar Scaffold Implant: Pilot Study in Rat Spinal Cord Transection with MRI

Despite extensive research on spinal cord injury (SCI) therapies for the recovery of motor, sensory and autonomic function, currently there are no effective treatments to completely restore tissue structure and function. In this work, a polylactic acid (PLA) fibrillar scaffold coated with pyrrole plasma polymer doped with iodine (pPPy/I), was studied as therapeutic strategy in a SCI transection model. Magnetic resonance imaging (MRI) was used to evaluate tissue response to the implant. Behavioral analysis using the BBB open-field testing was conducted to evaluate functional response. MRI analysis showed the SCI model completely disrupted tissue continuity, and diffusion indices were altered at the injury site. The animals had completely paralyzed hindlimbs and bladder control loss after injury. After 8 weeks of treatment, in contrast to control and PLA-implanted animals, PLA+pPPy/I-implanted animal had regained bladder control autonomy and frequent to consistent weight supported plantar steps and occasional coordination between forelimbs and hindlimbs. These results suggest fibrillar scaffolds coated with pPPy/I constitute a promising therapy for SCI.

Histological Findings After Aortic Cross-Clamping in Preclinical Animal Models

Spinal cord ischemic injury and paralysis are devastating complications after open surgical repair of thoracoabdominal aortic aneurysms. Preclinical models have been developed to simulate the clinical paradigm to better understand the neuropathophysiology and develop therapeutic treatment. Neuropathological findings in the preclinical models have not been comprehensively examined before. This systematic review studies the past 40 years of the histological findings after open surgical repair in preclinical models. Our main finding is that damage is predominantly in the grey matter of the spinal cord, although white matter damage in the spinal cord is also reported. Future research needs to examine the neuropathological findings in preclinical models after endovascular repair, a newer type of surgical repair used to treat aortic aneurysms.

Analysis and comparison of a spinal cord injury model with a single-axle-lever clip or a parallel-moving clip compression in rats

STUDY DESIGN

Experimental animal study.

OBJECTIVES

To assess the feasibility of a custom-designed parallel-moving (PM) clip, compared with a single-axle-lever (SAL) clip, for the development of a compressional spinal cord injury (SCI) model in rats.

SETTING

Hospital laboratory in China.

METHODS

We used a PM clip and a SAL clip with same compression rate, to develop a SCI model in rats, and set a sham group as a blank control. Within 3 weeks, each group of rats was evaluated for behavioral (Basso-Beattie-Bresnahan locomotor rating score, BBB), and electrophysiological changes (somatosensory evoked potential), and historical staining to observe the differences between the three groups. In particular, the mechanical results of the PM group were calculated.

RESULTS

The BBB scores for the SAL and PM groups were significantly lower than those for the sham group (P < 0.05), no significant difference between the two methods (P > 0.05), but the values corresponding to the PM group had smaller standard deviations. The interpeak-latency (IPL) was significantly prolonged (P < 0.0001) and the peak-peak amplitude (PPA) was significantly reduced (P < 0.01) in SAL and PM groups than those in the sham group, but there was no statistical difference in both IPL and PPA between the two SCI groups (P > 0.05). Histological staining showed obvious pathological changes in two SCI groups, and the shape of the lesion zone in the PM group was more symmetrical than that in the SAL groups.

CONCLUSIONS

The use of a compressional SCI model in rats with the PM clip we designed is an appropriate method to quantify the injury. The degree of the injury caused by this clip is more stable and uniform than those with classical methods.

Spinal Cord Injury-Induced Changes in Encoding and Decoding of Bipedal Walking by Motor Cortical Ensembles

Recent studies have shown that motor recovery following spinal cord injury (SCI) is task-specific. However, most consequential conclusions about locomotor functional recovery from SCI have been derived from quadrupedal locomotion paradigms. In this study, two monkeys were trained to perform a bipedal walking task, mimicking human walking, before and after T8 spinal cord hemisection. Importantly, there is no pharmacological therapy with nerve growth factor for monkeys after SCI; thus, in this study, the changes that occurred in the brain were spontaneous. The impairment of locomotion on the ipsilateral side was more severe than that on the contralateral side. We used information theory to analyze single-cell activity from the left primary motor cortex (M1), and results show that neuronal populations in the unilateral primary motor cortex gradually conveyed more information about the bilateral hindlimb muscle activities during the training of bipedal walking after SCI. We further demonstrated that, after SCI, progressively expanded information from the neuronal population reconstructed more accurate control of muscle activity. These results suggest that, after SCI, the unilateral primary motor cortex could gradually regain control of bilateral coordination and motor recovery and in turn enhance the performance of brain–machine interfaces.