Neuropathological and Motor Impairments after Incomplete Cervical Spinal Cord Injury in Pigs

A 72-h sedated porcine model of traumatic spinal cord injury

Introduction

There is an increasing focus on the prevention of secondary injuries following traumatic spinal cord injury (TSCI), especially through improvement of spinal cord perfusion and immunological modulation. Such therapeutic strategies require translational and controlled animal models of disease progression of the acute phases of human TSCI.

Research question

Is it possible to establish a 72-h sedated porcine model of incomplete thoracic TSCI, enabling controlled use of continuous, invasive, and non-invasive modalities during the entire sub-acute phase of TSCI?

Material and methods

A sham-controlled trial was conducted to establish the model, and 10 animals were assigned to either sham or TSCI. All animals underwent a laminectomy, and animals in the TSCI group were subjected to a weight-drop injury. Animals were then kept sedated for 72 h. The amount of injury was assessed by ex-vivo measures MRI-based fiber tractography, histology and immunohistochemistry.

Results

In all animals, we were successful in maintaining sedation for 72 h without comprising vital physiological parameters. The MRI-based fiber tractography showed that all TSCI animals revealed a break in the integrity of spinal neurons, whereas histology demonstrated no transversal sections of the spine with complete injury. Notably, some animals displayed signs of secondary ischemic tissue in the cranial and caudal sections.

Discussion and conclusions

This study succeeded in producing a porcine model of incomplete TSCI, which was physiologically stable up to 72 h. We believe that this TSCI model will constitute a potential translational model to study the pathophysiology secondary to TSCI in humans.

[Translated article] Effects of duroplasty with bovine pericardium on fibrosis and extent of spinal cord injury: An experimental study in pigs

INTRODUCTION

Traumatic spinal cord injury (SCI) leads to increased intraspinal pressure that can be prevented by durotomy and duroplasty. The aim of the study was to evaluate fibrosis and neural damage in a porcine model of SCI after duroplasty and application of hyaluronic acid (HA) in the tissue cavity.

MATERIALS AND METHODS

Experimental study. We created a porcine SCI model by durotomy and spinal cord hemisection of a cervical segment (1cm). Six pigs (Sus scrofa domestica) were used to evaluate three surgical scenarios: (1) control injury with dural reparative microsurgery, (2) duroplasty using bovine pericardium (BPD), and (3) previous method plus HA applied at the lesion. Animals were sacrificed one-month post-injury to assess fibrotic responses and neural tissue damage using conventional histological and immunohistochemical methods.

RESULTS

In the control case, dural suture prevented invasion of the lesion by extradural connective tissue, and the dura mater showed a 1-mm thickening in the perilesional area. The bovine pericardium patch blocked the entrance of extradural connective tissue, decreased dura-mater tension, and satisfactorily integrated within the receptor tissue. However, it also enhanced subdural and perilesional fibrosis, which was not inhibited by filling the lesion cavity with low- or high-molecular-weight HA.

CONCLUSIONS

Duroplasty prevents collapse of the dura-mater over the spinal cord tissue, as well as invasion of the lesion by extramedullary fibrotic tissue, without creating additional neural damage. Nevertheless, it enhances the fibrotic response in the spinal cord lesion and the perilesional area. Additional antifibrotic strategies are needed to facilitate spinal cord repair.

Effects of robotic therapy associated with noninvasive brain stimulation on motor function in individuals with incomplete spinal cord injury: A systematic review of randomized controlled trials

CONTEXT

Motor deficits are among the most common consequences of incomplete spinal cord injury (SCI). These impairments can affect patients' levels of functioning and quality of life. Combined robotic therapy and non-invasive brain stimulation (NIBS) have been used to improve motor impairments in patients with corticospinal tract lesions.

OBJECTIVES

To examine the effects of combined robotic therapy and NIBS on motor function post incomplete SCI.

METHODS

PubMed, SCOPUS, MEDLINE, PEDro, Web of Science, REHABDATA, CINAHL, and EMBASE were searched from inception until July 2023. The Physiotherapy Evidence Database (PEDro) scale was employed to evaluate the selected studies quality.

RESULTS

Of 557 studies, five randomized trials (n = 122), with 25% of participants being females, were included in this review. The PEDro scores ranged from eight to nine, with a median score of nine. There were variations in treatment protocols and outcome measures, resulting in heterogeneous findings. The findings showed revealed evidence for the impacts of combined robotic therapy and NIBS on motor function in individuals with incomplete SCI.

CONCLUSIONS

Combined robotic training and NIBS may be safe for individuals with incomplete SCI. The existing evidence concerning its effects on motor outcomes in individuals with SCI is limited. Further experimental studies are needed to understand the effects of combined robotic training and NIBS on motor impairments in SCI populations.

PEG-chitosan (Neuro-PEG) induced restoration of motor function after complete transection of the dorsal spinal cord in swine. A pilot study

Background

Spinal cord injury (SCI) remains an unmet medical need. Recently, fusogens, such as polyethylene glycol (PEG), have been proven effective in restoring sensorimotor function after complete transection of the spinal cord at different levels and in different species. Here, we report on the use of a PEG-chitosan combo in a different animal model (swine).

Methods

Five Hungarian Mangalica pigs were subjected to complete transection of the thoracic cord (T7-9). Three animals were treated with locally injected PEG-chitosan (Neuro-PEG) gel; two acted as controls. PEG-600 was also injected intra- and post-operatively intravenously. Animals were submitted to rehabilitation, including electrical myostimulation. Results were assessed after 60 days using the Individual Limb Motor Score, the Porcine Thoracic Spinal Cord Injured Behavioral Scale, and the modified motor Basso, Beattie, and Bresnahan scale; sensory and sphincter functions were also assessed. Animals underwent in vivo spinal cord tracing with DiI. Immunofluorescence histology included NF-200, DAPI, and a fluorochrome-conjugated secondary antibody.

Results

Starting on postoperative day (POD) 2, neuro-PEG-treated animals evinced the first signs of recovery, and on POD 60, they could all support their weight and were mobile. Controls never recovered any useful function. Fluorescence microscopy in the experimental group revealed axons passing through the site of injury, while degenerative post-traumatic changes were noted in controls.

Conclusion

Neuro-PEG affords sensorimotor recovery after complete spinal cord transection. This opens the door to human experimentation, including trials of spinal cord transplantation.

Effects of duroplasty with bovine pericardium on fibrosis and extent of spinal cord injury: An experimental study in pigs

INTRODUCTION

Traumatic spinal cord injury (SCI) leads to increased intraspinal pressure that can be prevented by durotomy and duroplasty. The aim of the study was to evaluate fibrosis and neural damage in a porcine model of SCI after duroplasty and application of hyaluronic acid (HA) in the tissue cavity.

MATERIALS AND METHODS

Experimental study. We created a porcine SCI model by durotomy and spinal cord hemisection of a cervical segment (1cm). Six pigs (Sus scrofa domestica) were used to evaluate three surgical scenarios: (1)control injury with dural reparative microsurgery, (2)duroplasty using bovine pericardium (BPD), and (3)previous method plus HA applied at the lesion. Animals were sacrificed one-month post-injury to assess fibrotic responses and neural tissue damage using conventional histological and immunohistochemical methods.

RESULTS

In the control case, dural suture prevented invasion of the lesion by extradural connective tissue, and the dura mater showed a 1-mm thickening in the perilesional area. The bovine pericardium patch blocked the entrance of extradural connective tissue, decreased dura-mater tension, and satisfactorily integrated within the receptor tissue. However, it also enhanced subdural and perilesional fibrosis, which was not inhibited by filling the lesion cavity with low- or high-molecular-weight HA.

CONCLUSIONS

Duroplasty prevents collapse of the dura-mater over the spinal cord tissue, as well as invasion of the lesion by extramedullary fibrotic tissue, without creating additional neural damage. Nevertheless, it enhances the fibrotic response in the spinal cord lesion and the perilesional area. Additional antifibrotic strategies are needed to facilitate spinal cord repair.

Spinal cord injury induced exacerbation of Alzheimer's disease like pathophysiology is reduced by topical application of nanowired cerebrolysin with monoclonal antibodies to amyloid beta peptide, p-tau and tumor necrosis factor alpha

Hallmark of Alzheimer's disease include amyloid beta peptide and phosphorylated tau deposition in brain that could be aggravated following traumatic of concussive head injury. However, amyloid beta peptide or p-tau in spinal cord following injury is not well known. In this investigation we measured amyloid beta peptide and p-tau together with tumor necrosis factor-alpha (TNF-α) in spinal cord and brain following 48 h after spinal cord injury in relation to the blood-spinal cord and blood-brain barrier, edema formation, blood flow changes and cell injury in perifocal regions of the spinal cord and brain areas. A focal spinal cord injury was inflicted over the right dorsal horn of the T10-11 segment (4 mm long and 2 mm deep) and amyloid beta peptide and p-tau was measured in perifocal rostral (T9) and caudal (T12) spinal cord segments as well as in the brain areas. Our observations showed a significant increase in amyloid beta peptide in the T9 and T12 segments as well as in remote areas of brain and spinal cord after 24 and 48 h injury. This is associated with breakdown of the blood-spinal cord (BSCB) and brain barriers (BBB), edema formation, reduction in blood flow and cell injury. After 48 h of spinal cord injury elevation of amyloid beta peptide, phosphorylated tau (p-tau) and tumor necrosis factor-alpha (TNF-α) was seen in T9 and T12 segments of spinal cord in cerebral cortex, hippocampus and brain stem regions associated with microglial activation as seen by upregulation of Iba1 and CD86. Repeated nanowired delivery of cerebrolysin topically over the traumatized segment repeatedly together with monoclonal antibodies (mAb) to amyloid beta peptide (AβP), p-tau and TNF-α significantly attenuated amyloid beta peptide, p-tau deposition and reduces Iba1, CD68 and TNF-α levels in the brain and spinal cord along with blockade of BBB and BSCB, reduction in blood flow, edema formation and cell injury. These observations are the first to show that spinal cord injury induces Alzheimer's disease like symptoms in the CNS, not reported earlier.

Porcine Models of Spinal Cord Injury

Large animal models of spinal cord injury may be useful tools in facilitating the development of translational therapies for spinal cord injury (SCI). Porcine models of SCI are of particular interest due to significant anatomic and physiologic similarities to humans. The similar size and functional organization of the porcine spinal cord, for instance, may facilitate more accurate evaluation of axonal regeneration across long distances that more closely resemble the realities of clinical SCI. Furthermore, the porcine cardiovascular system closely resembles that of humans, including at the level of the spinal cord vascular supply. These anatomic and physiologic similarities to humans not only enable more representative SCI models with the ability to accurately evaluate the translational potential of novel therapies, especially biologics, they also facilitate the collection of physiologic data to assess response to therapy in a setting similar to those used in the clinical management of SCI. This review summarizes the current landscape of porcine spinal cord injury research, including the available models, outcome measures, and the strengths, limitations, and alternatives to porcine models. As the number of investigational SCI therapies grow, porcine SCI models provide an attractive platform for the evaluation of promising treatments prior to clinical translation.

Composite Fibrin/Carbon Microfiber Implants for Bridging Spinal Cord Injury: A Translational Approach in Pigs

Biomaterials may enhance neural repair after spinal cord injury (SCI) and testing their functionality in large animals is essential to achieve successful clinical translation. This work developed a porcine contusion/compression SCI model to investigate the consequences of myelotomy and implantation of fibrin gel containing biofunctionalized carbon microfibers (MFs). Fourteen pigs were distributed in SCI, SCI/myelotomy, and SCI/myelotomy/implant groups. An automated device was used for SCI. A dorsal myelotomy was performed on the lesion site at 1 day post-injury for removing cloths and devitalized tissue. Bundles of MFs coated with a conducting polymer and cell adhesion molecules were embedded in fibrin gel and used to bridge the spinal cord cavity. Reproducible lesions of about 1 cm in length were obtained. Myelotomy and lesion debridement caused no further neural damage compared to SCI alone but had little positive effect on neural regrowth. The MFs/fibrin gel implant facilitated axonal sprouting, elongation, and alignment within the lesion. However, the implant also increased lesion volume and was ineffective in preventing fibrosis, thus precluding functional neural regeneration. Our results indicate that myelotomy and lesion debridement can be advantageously used for implanting MF-based scaffolds. However, the implants need refinement and pharmaceuticals will be necessary to limit scarring.

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.

Porcine Model of Spinal Cord Injury: A Systematic Review

Spinal cord injury (SCI) is a devastating disease with limited effective treatment options. Animal paradigms are vital for understanding the pathogenesis of SCI and testing potential therapeutics. The porcine model of SCI is increasingly favored because of its greater similarity to humans. However, its adoption is limited by the complexities of care and range of testing parameters. Researchers need to consider swine selection, injury method, post-operative care, rehabilitation, behavioral outcomes, and histology metrics. Therefore, we systematically reviewed full-text English-language articles to evaluate study characteristics used in developing a porcine model and summarize the interventions that have been tested using this paradigm. A total of 63 studies were included, with 33 examining SCI pathogenesis and 30 testing interventions. Studies had an average sample size of 15 pigs with an average weight of 26 kg, and most used female swine with injury to the thoracic cord. Injury was most commonly induced by weight drop with compression. The porcine model is amenable to testing various interventions, including mean arterial pressure augmentation (n = 7), electrical stimulation (n = 6), stem cell therapy (n = 5), hypothermia (n = 2), biomaterials (n = 2), gene therapy (n = 2), steroids (n = 1), and nanoparticles (n = 1). It is also notable for its clinical translatability and is emerging as a valuable pre-clinical study tool. This systematic review can serve as a guideline for researchers implementing and testing the porcine SCI model.

The Role of Microglia/Macrophages Activation and TLR4/NF-κB/MAPK Pathway in Distraction Spinal Cord Injury-Induced Inflammation

Distraction spinal cord injuries (DSCIs) often occur as the neurological complication of distraction forces following the implantation of internal fixation devices during scoliosis correction surgery. However, the underlying mechanism behind these injuries remains unclear. The present study aimed to explore the activation of microglia and macrophages, as well as changes in TLR4-mediated NF-κB and MAPK pathway activity after DSCIs in Bama miniature pigs. Prior to surgical intervention, the pigs were randomly divided into three groups: the sham group, the complete distraction spinal cord injury (CDSCI) group, and the incomplete distraction spinal cord injury (IDSCI) group. After surgery, the Tarlov scale and individual limb motor scale (ILMS) were used to evaluate changes in the pigs’ behavior. All pigs were euthanized 7 days after surgery, and histopathological examinations of the spinal cord tissues were performed. Immunohistochemistry was used to detect Caspase-3 expression in the anterior horn of spinal gray matter tissues. Immunofluorescence staining was utilized to assess the M1/M2 phenotype changes in microglia/macrophages and NF-κB P65 expression in central DSCI lesions, while western blotting was performed to determine the expression of TLR4/NF-κB/MAPK pathway-related proteins. The results of the present study showed that the Tarlov and ILMS scores decreased significantly in the two DSCI groups compared with the sham group. Hematoxylin and eosin (HE) and Nissl staining revealed that the tissue structure and nerve fiber tracts in the distracted spinal cord tissues were destroyed. Both DSCI groups showed the number of survived neurons decreased and the Caspase-3 expression increased. The results of the immunofluorescence staining indicated that the CD16 and CD206 expression in the microglia/macrophages increased. Between the two DSCI groups, the CDSCI group showed increased CD16 and decreased CD206 expression levels. The intensity of the fluorescence of NF-κB P65 was found to be significantly enhanced in pigs with DSCIs. Moreover, western blot results revealed that the expression of TLR4, p-IκBα, NF-κB P65, p-JNK, p-ERK, and p-P38 proteins increased in spinal cord tissues following DSCI. The present study was based on a porcine DSCI model that closely mimicked clinical DSCIs while clarifying DSCI-associated neuroinflammation mechanisms, in turn providing evidence for identifying potential anti-inflammatory targets.

The Cortical Motor System in the Domestic Pig: Origin and Termination of the Corticospinal Tract and Cortico-Brainstem Projections

The anatomy of the cortical motor system and its relationship to motor repertoire in artiodactyls is for the most part unknown. We studied the origin and termination of the corticospinal tract (CST) and cortico-brainstem projections in domestic pigs. Pyramidal neurons were retrogradely labeled by injecting aminostilbamidine in the spinal segment C1. After identifying the dual origin of the porcine CST in the primary motor cortex (M1) and premotor cortex (PM), the axons descending from those regions to the spinal cord and brainstem were anterogradely labeled by unilateral injections of dextran alexa-594 in M1 and dextran alexa-488 in PM. Numerous corticospinal projections from M1 and PM were detected up to T6 spinal segment and showed a similar pattern of decussation and distribution in the white matter funiculi and the gray matter laminae. They terminated mostly on dendrites of the lateral intermediate laminae and the internal basilar nucleus, and some innervated the ventromedial laminae, but were essentially absent in lateral laminae IX. Corticofugal axons terminated predominantly ipsilaterally in the midbrain and bilaterally in the medulla oblongata. Most corticorubral projections arose from M1, whereas the mesencephalic reticular formation, superior colliculus, lateral reticular nucleus, gigantocellular reticular nucleus, and raphe received abundant axonal contacts from both M1 and PM. Our data suggest that the porcine cortical motor system has some common features with that of primates and humans and may control posture and movement through parallel motor descending pathways. However, less cortical regions project to the spinal cord in pigs, and the CST neither seems to reach the lumbar enlargement nor to have a significant direct innervation of cervical, foreleg motoneurons.