Methods for functional assessment after C7 spinal cord hemisection in the rhesus monkey

Advances in spinal cord injury: insights from non-human primates

Spinal cord injury results in significant sensorimotor deficits, currently, there is no curative treatment for the symptoms induced by spinal cord injury. Basic and pre-clinical research on spinal cord injury relies on the development and characterization of appropriate animal models. These models should replicate the symptoms observed in human, allowing for the exploration of functional deficits and investigation into various aspects of physiopathology of spinal cord injury. Non-human primates, due to their close phylogenetic association with humans, share more neuroanatomical, genetic, and physiological similarities with humans than rodents. Therefore, the responses to spinal cord injury in nonhuman primates most likely resemble the responses to traumatism in humans. In this review, we will discuss nonhuman primate models of spinal cord injury, focusing on in vivo assessments, including behavioral tests, magnetic resonance imaging, and electrical activity recordings, as well as ex vivo histological analyses. Additionally, we will present therapeutic strategies developed in non-human primates and discuss the unique specificities of non-human primate models of spinal cord injury.

Emergence of functionally aberrant and subsequent reduction of neuromuscular connectivity and improved motor performance after cervical spinal cord injury in Rhesus

Introduction

The paralysis that occurs after a spinal cord injury, particularly during the early stages of post-lesion recovery (∼6 weeks), appears to be attributable to the inability to activate motor pools well beyond their motor threshold. In the later stages of recovery, however, the inability to perform a motor task effectively can be attributed to abnormal activation patterns among motor pools, resulting in poor coordination.

Method

We have tested this hypothesis on four adult male Rhesus monkeys (Macaca mulatta), ages 6-10 years, by recording the EMG activity levels and patterns of multiple proximal and distal muscles controlling the upper limb of the Rhesus when performing three tasks requiring different levels of skill before and up to 24 weeks after a lateral hemisection at C7. During the recovery period the animals were provided routine daily care, including access to a large exercise cage (5' × 7' × 10') and tested every 3-4 weeks for each of the three motor tasks.

Results

At approximately 6-8 weeks the animals were able to begin to step on a treadmill, perform a spring-loaded task with the upper limb, and reaching, grasping, and eating a grape placed on a vertical stick. The predominant changes that occurred, beginning at ∼6-8 weeks of the recovery of these tasks was an elevated level of activation of most motor pools well beyond the pre-lesion level.

Discussion

As the chronic phase progressed there was a slight reduction in the EMG burst amplitudes of some muscles and less incidence of co-contraction of agonists and antagonists, probably contributing to an improved ability to selectively activate motor pools in a more effective temporal pattern. Relative to pre-lesion, however, the EMG patterns even at the initial stages of recovery of successfully performing the different motor tasks, the level of activity of most muscle remained higher. Perhaps the most important concept that emerges from these data is the large combinations of adaptive strategies in the relative level of recruitment and the timing of the peak levels of activation of different motor pools can progressively provide different stages to regain a motor skill.

Immune response following traumatic spinal cord injury: Pathophysiology and therapies

Traumatic spinal cord injury (SCI) is a devastating condition that is often associated with significant loss of function and/or permanent disability. The pathophysiology of SCI is complex and occurs in two phases. First, the mechanical damage from the trauma causes immediate acute cell dysfunction and cell death. Then, secondary mechanisms of injury further propagate the cell dysfunction and cell death over the course of days, weeks, or even months. Among the secondary injury mechanisms, inflammation has been shown to be a key determinant of the secondary injury severity and significantly worsens cell death and functional outcomes. Thus, in addition to surgical management of SCI, selectively targeting the immune response following SCI could substantially decrease the progression of secondary injury and improve patient outcomes. In order to develop such therapies, a detailed molecular understanding of the timing of the immune response following SCI is necessary. Recently, several studies have mapped the cytokine/chemokine and cell proliferation patterns following SCI. In this review, we examine the immune response underlying the pathophysiology of SCI and assess both current and future therapies including pharmaceutical therapies, stem cell therapy, and the exciting potential of extracellular vesicle therapy.

Quantifying the kinematic features of dexterous finger movements in nonhuman primates with markerless tracking

Research using nonhuman primate models for human disease frequently requires behavioral observational techniques to quantify functional outcomes. The ability to assess reaching and grasping patterns is of particular interest in clinical conditions that affect the motor system (e.g., spinal cord injury, SCI). Here we explored the use of DeepLabCut, an open-source deep learning toolset, in combination with a standard behavioral task (Brinkman Board) to quantify nonhuman primate performance in precision grasping. We examined one male rhesus macaque (Macaca mulatta) in the task which involved retrieving rewards from variously-oriented shallow wells. Simultaneous recordings were made using GoPro Hero7 Black cameras (resolution 1920 x 1080 at 120 fps) from two different angles (from the side and top of the hand motion). The task/device design necessitates use of the right hand to complete the task. Two neural networks (corresponding to the top and side view cameras) were trained using 400 manually annotated images, tracking 19 unique landmarks each. Based on previous reports, this produced sufficient tracking (Side: trained pixel error of 2.15, test pixel error of 11.25; Top: trained pixel error of 2.06, test pixel error of 30.31) so that landmarks could be tracked on the remaining frames. Landmarks included in the tracking were the spatial location of the knuckles and the fingernails of each digit, and three different behavioral measures were quantified for assessment of hand movement (finger separation, middle digit extension and preshaping distance). Together, our preliminary results suggest that this markerless approach is a possible method to examine specific kinematic features of dexterous function.Clinical Relevance- The methodology presented below allows for the markerless tracking of kinematic features of dexterous finger movement by non-human primates. This method could allow for direct comparisons between human patients and non-human primate models of clinical conditions (e.g., spinal cord injury). This would provide objective quantitative metrics and crucial information for assessing movement impairments across populations and the potential translation of treatments, interventions and their outcomes.

How to generate graded spinal cord injuries in swine - tools and procedures

Spinal cord injury (SCI) is a medically, psychologically and socially disabling condition. A large body of our knowledge on the basic mechanisms of SCI has been gathered in rodents. For preclinical validation of promising therapies, the use of animal models that are closer to humans has several advantages. This has promoted the more-intensive development of large-animal models for SCI during the past decade. We recently developed a multimodal SCI apparatus for large animals that generated biomechanically reproducible impacts in vivo. It is composed of a spring-load impactor and support systems for the spinal cord and the vertebral column. We now present the functional outcome of farm pigs and minipigs injured with different lesion strengths. There was a correlation between the biomechanical characteristics of the impact, the functional outcome and the tissue damage observed several weeks after injury. We also provide a detailed description of the procedure to generate such a SCI in both farm pigs and minipigs, in the hope to ease the adoption of the swine model by other research groups.

Longitudinal fMRI measures of cortical reactivation and hand use with and without training after sensory loss in primates

In a series of previous studies, we demonstrated that damage to the dorsal column in the cervical spinal cord deactivates the contralateral somatosensory hand cortex and impairs hand use in a reach-to-grasp task in squirrel monkeys. Nevertheless, considerable cortical reactivation and behavioral recovery occurs over the following weeks to months after lesion. This timeframe may also be a window for targeted therapies to promote cortical reactivation and functional reorganization, aiding in the recovery process. Here we asked if and how task specific training of an impaired hand would improve behavioral recovery and cortical reorganization in predictable ways, and if recovery related cortical changes would be detectable using noninvasive functional magnetic resonance imaging (fMRI). We further asked if invasive neurophysiological mapping reflected fMRI results. A reach-to-grasp task was used to test impairment and recovery of hand use before and after dorsal column lesions (DC-lesion). The activation and organization of the affected primary somatosensory cortex (area 3b) was evaluated with two types of fMRI - either blood oxygenation level dependent (BOLD) or cerebral blood volume (CBV) with a contrast agent of monocrystalline iron oxide nanocolloid (MION) - before and after DC-lesion. At the end of the behavioral and fMRI studies, microelectrode recordings in the somatosensory areas 3a, 3b and 1 were used to characterize neuronal responses and verify the somatotopy of cortical reactivations. Our results indicate that even after nearly complete DC lesions, monkeys had both considerable post-lesion behavioral recovery, as well as cortical reactivation assessed with fMRI followed by extracellular recordings. Generalized linear regression analyses indicate that lesion extent is correlated with the behavioral outcome, as well as with the difference in the percent signal change from pre-lesion peak activation in fMRI. Monkeys showed behavioral recovery and nearly complete cortical reactivation by 9-12 weeks post-lesion (particularly when the DC-lesion was incomplete). Importantly, the specific training group revealed trends for earlier behavioral recovery and had higher magnitude of fMRI responses to digit stimulation by 5-8 weeks post-lesion. Specific kinematic measures of hand movements in the selected retrieval task predicted recovery time and related to lesion characteristics better than overall task performance success. For measures of cortical reactivation, we found that CBV scans provided stronger signals to vibrotactile digit stimulation as compared to BOLD scans, and thereby may be the preferred non-invasive way to study the cortical reactivation process after sensory deprivations from digits. When the reactivation of cortex for each of the digits was considered, the reactivation by digit 2 stimulation as measured with microelectrode maps and fMRI maps was best correlated with overall behavioral recovery.

Animal Models of Metastatic Lesions to the Spine: a Focus on Epidural Spinal Cord Compression

Epidural spinal cord compression (ESCC) secondary to spine metastases is one of the most devastating sequelae of primary cancer as it may lead to muscle weakness, paresthesia, pain, and paralysis. Spine metastases occur through a multi-step process that can result in eventual ESCC; however, the lack of a preclinical model to effectively recapitulate each step of this metastatic cascade and the symptom burden of ESCC has limited our understanding of this disease process. In this review, we discuss animal models that best recapitulate ESCC; we start with a broad discussion of commonly used models of bone metastasis and end with a focused discussion of models used to specifically study ESCC. Orthotopic models offer the most authentic recapitulation of metastasis development; however, they rarely result in symptomatic ESCC and are challenging to replicate. Conversely, models that involve injection of tumor cells directly into the bloodstream or bone better mimic the symptoms of ESCC; however, they provide limited insight into the epithelial to mesenchymal transition (EMT) and natural hematogenous spread of tumor cell. Therefore, until an ideal model is created, it is critical to select an animal model that is specifically designed to answer the scientific question of interest.

Acute spinal cord injury: Pathophysiology and pharmacological intervention (Review)

Spinal cord injury (SCI) is one of the most debilitating of all the traumatic conditions that afflict individuals. For a number of years, extensive studies have been conducted to clarify the molecular mechanisms of SCI. Experimental and clinical studies have indicated that two phases, primary damage and secondary damage, are involved in SCI. The initial mechanical damage is caused by local impairment of the spinal cord. In addition, the fundamental mechanisms are associated with hyperflexion, hyperextension, axial loading and rotation. By contrast, secondary injury mechanisms are led by systemic and cellular factors, which may also be initiated by the primary injury. Although significant advances in supportive care have improved clinical outcomes in recent years, a number of studies continue to explore specific pharmacological therapies to minimize SCI. The present review summarized some important pathophysiologic mechanisms that are involved in SCI and focused on several pharmacological and non‑pharmacological therapies, which have either been previously investigated or have a potential in the management of this debilitating injury in the near future.

A Cervical Spinal Cord Hemi-Contusion Injury Model Based on Displacement Control in Non-Human Primates (Macaca fascicularis)

Non-human primate (NHP) spinal cord injury (SCI) models can be informative in the evaluation of treatments that show promise in rodent models prior to translation to humans. In the present study, we aimed to establish a cervical spinal hemi-contusion model with controlled displacement and evaluate the abnormalities in behavior, electrophysiology, histology, and magnetic resonance imaging. Twelve adult NHPs were divided into an SCI group (n = 8, 24 and 48 weeks) and a control group (n = 4). An impactor (Φ = 4 mm) was driven to compress the left C5 cord at 800 mm/sec. The contusion displacement and peak force was 4.08 ± 0.17 mm and 19.8 ± 4.6 N. The behavioral assessment showed a consistent dysfunction below the wrist and spontaneous recovery of limb function after injury. Lesion length and lesion area at the epicenter based on T2 hyperintensity were 5.68 ± 0.47 mm and 5.99 ± 0.24 mm² at 24 weeks post-injury (wpi), and 5.29 ± 0.17 mm and 5.95 ± 0.24 mm² at 48 wpi. The spared spinal cord area immuno-positive for glial fibrillary acidic protein was significantly reduced, while the staining intensity increased at 24 wpi and 48 wpi, compared with the sham group. Ipsilateral somatosensory and motor evoked potentials were dynamic, increasing in latency and decreasing in amplitude compared with pre-operative values or the contralateral values, and correlated to varying degrees with behavioral outcomes. A shift in size-frequency distribution of sensory neurons of the dorsal root ganglia (DRG) was consistent with a loss of large-diameter cells. The present study demonstrated that the NHP SCI model resulted in consistent unilateral limb dysfunction and potential plasticity in the face of loss of spinal cord and DRG tissue.

Chondroitinase improves anatomical and functional outcomes after primate spinal cord injury

Inhibitory extracellular matrices form around mature neurons as perineuronal nets containing chondroitin sulfate proteoglycans (CSPGs) that limit axonal sprouting after CNS injury. The enzyme chondroitinase (Chase) degrades the inhibitory CSPGs and improves axonal sprouting and functional recovery after spinal cord injury (SCI) in rodents. We evaluated the effects of Chase in Rhesus monkeys that had undergone C7 spinal cord hemisection. Four weeks after hemisection, multiple intraparenchymal Chase injections targeted spinal cord circuits controlling hand function below the lesion. Hand function improved significantly in Chase-treated monkeys relative to vehicle-injected controls. Moreover, Chase significantly increased corticospinal axon growth and the number of synapses formed by corticospinal terminals in gray matter caudal to the lesion. No detrimental effects were detected. This approach appears to merit clinical translation in SCI.

The Hemisection Approach in Large Animal Models of Spinal Cord Injury: Overview of Methods and Applications

Introduction: Translating basic science research into a safe and effective therapy for spinal cord injury (SCI) requires suitable large animal models for testing both implantable devices and biologic approaches to better approximate human anatomy and function. Hemisection lesions, routinely used for investigational purposes in small animals, are less frequently described in large animals that might be appropriate for translational studies. Size constraints of small animals (mice and rats) limits the predictability of the findings when scaled up. Our goal is to review the status of hemisection SCI in large animals across species and time to prepare for the testing of a novel intradural spinal cord stimulation device for control of spasticity in an ovine model. Methods and Results: We surveyed the literature on hemisection in quadrupeds and nonhuman primates, and catalogued the species, protocols and outcomes of the experimental work in this field. Feline, lapine, canine, simian, porcine, ovine and bovine models were the primary focal points. There is a consistent body of literature reporting use of the hemisection approach in large animals, but with differences in surgical technique depending on the goals and nature of the individual studies. While the injuries are not always consistent, the experimental variability is generally lower than that of the contusion-based approach. In general, as the body size of the animal increases, animal care requirements and the associated costs follow. In most cases, this is inversely correlated with the number of animals used in hemisection models. Conclusions: The hemisection approach to modeling SCI is straightforward compared with other methods such as the contusive impact and enables the transection of isolated ascending and descending tracts and segment specific cell bodies. This has certain advantages in models investigating post-injury axonal regrowth. However, this approach is not generally in line with the patho-physiologies encountered in SCI patients. Even so, the ability to achieve more control over the level of injury makes it a useful adjunct to contusive and ischemic approaches, and suggests a useful role in future translational studies.

Restorative effects of human neural stem cell grafts on the primate spinal cord

We grafted human spinal cord-derived neural progenitor cells (NPCs) into sites of cervical spinal cord injury in rhesus monkeys (Macaca mulatta). Under three-drug immunosuppression, grafts survived at least 9 months postinjury and expressed both neuronal and glial markers. Monkey axons regenerated into grafts and formed synapses. Hundreds of thousands of human axons extended out from grafts through monkey white matter and synapsed in distal gray matter. Grafts gradually matured over 9 months and improved forelimb function beginning several months after grafting. These findings in a 'preclinical trial' support translation of NPC graft therapy to humans with the objective of reconstituting both a neuronal and glial milieu in the site of spinal cord injury.

Enhanced axonal transport: A novel form of "plasticity" after primate and rodent spinal cord injury

Deficient axonal transport after injury is believed to contribute to the failure of CNS regeneration. To better elucidate neural mechanisms associated with CNS responses to injury, we transected the dominant voluntary motor system, the corticospinal tract (CST), in the dorsolateral T10 spinal cord of rhesus monkeys. Three months later, a 4.5-fold increase in the number of CST axons located in the spared ventral corticospinal tract at both the lesion site and, surprisingly, remotely in the cervical spinal cord was observed. Additional studies of increases in corticospinal axon numbers in rat and primate models demonstrated that increases were transient and attributable to enhanced axonal transport rather than axonal sprouting. Accordingly, increases in axonal transport occur after CNS injury even in the longest projecting pathways of the non-human primate, likely representing an attempted adaptive response to injury as observed in the PNS.

Functional Test Scales for Evaluating Cell-Based Therapies in Animal Models of Spinal Cord Injury

Recently, spinal cord researchers have focused on multifaceted approaches for the treatment of spinal cord injury (SCI). However, as there is no cure for the deficits produced by SCI, various therapeutic strategies have been examined using animal models. Due to the lack of standardized functional assessment tools for use in such models, it is important to choose a suitable animal model and precise behavioral test when evaluating the efficacy of potential SCI treatments. In the present review, we discuss recent evidence regarding functional recovery in various animal models of SCI, summarize the representative models currently used, evaluate recent cell-based therapeutic approaches, and aim to identify the most precise and appropriate scales for functional assessment in such research.

Neuroprotective effect of local hypothermia in a computer-controlled compression model in minipig: Correlation of tissue sparing along the rostro-caudal axis with neurological outcome

This study investigated the neuroprotective efficacy of local hypothermia in a minipig model of spinal cord injury (SCI) induced by a computer-controlled impactor device. The tissue integrity observed at the injury epicenter, and up to 3 cm cranially and caudally from the lesion site correlated with motor function. A computer-controlled device produced contusion lesions at L3 level with two different degrees of tissue sparing, depending upon pre-set impact parameters (8N- and 15N-force impact). Hypothermia with cold (4°C) saline or Dulbecco's modified Eagle's medium (DMEM)/F12 culture medium was applied 30 min after SCI (for 5 h) via a perfusion chamber (flow 2 ml/min). After saline hypothermia, the 8N-SCI group achieved faster recovery of hind limb function and the ability to walk from one to three steps at nine weeks in comparison with non-treated animals. Such improvements were not observed in saline-treated animals subjected to more severe 15N-SCI or in the group treated with DMEM/F12 medium. It was demonstrated that the tissue preservation in the cranial and caudal segments immediately adjacent to the lesion, and neurofilament protection in the lateral columns may be essential for modulation of the key spinal microcircuits leading to a functional outcome. Tissue sparing observed only in the caudal sections, even though significant, was not sufficient for functional improvement in the 15N-SCI model.

Radiographic and Magnetic Resonance Imaging Identification of Thoracolumbar Spine Variants with Implications for the Positioning of the Conus Medullaris in Rhesus Macaques

The anatomy of the vertebral column in mammals may differ between species and between subjects of the same species, especially with regards to the composition of the thoracolumbar spine. We investigated, using several noninvasive imaging techniques, the thoracolumbar spine of a total of 44 adult rhesus macaques of both genders. Radiographic examination of the vertebral column showed a predominant spine phenotype with 12 rib-bearing thoracic vertebrae and 7 lumbar vertebrae without ribs in 82% of subjects, whereas a subset of subjects demonstrated 13 rib-bearing thoracic vertebrae and 6 lumbar vertebrae without ribs. Computer tomography studies of the thoraco-lumbar spine in two cases with a pair of supernumerary ribs showed facet joints between the most caudal pair of ribs and the associated vertebra, supporting a thoracic phenotype. Magnetic resonance imaging (MRI) studies were used to determine the relationship between the lumbosacral spinal cord and the vertebral column. The length of the conus medullaris portion of the spinal cord was 1.5 ± 0.3 vertebral units, and its rostral and caudal positions in the spinal canal were at 2.0 ± 0.3 and 3.6 ± 0.4 vertebral units below the thoracolumbar junction, respectively (n = 44). The presence of a set of supernumerary ribs did not affect the length or craniocaudal position of the conus medullaris, and subjects with13 rib-bearing vertebrae may from a functional or spine surgical perspective be considered as exhibiting12 thoracic vertebrae and an L1 vertebra with ribs. Anat Rec, 300:300-308, 2017. © 2016 Wiley Periodicals, Inc.

Evaluation of the neural function of nonhuman primates with spinal cord injury using an evoked potential-based scoring system

Nonhuman primate models of spinal cord injury (SCI) have been widely used in evaluation of the efficacy and safety of experimental restorative interventions before clinical trials. However, no objective methods are currently available for the evaluation of neural function in nonhuman primates. In our long-term clinical practice, we have used evoked potential (EP) for neural function surveillance during operation and accumulated extensive experience. In the present study, a nonhuman primate model of SCI was established in 6 adult cynomologus monkeys through spinal cord contusion injury at T8-T9. The neural function before SCI and within 6 months after SCI was evaluated based on EP recording. A scoring system including somatosensory evoked potentials (SSEPs) and transcranial electrical stimulation-motor evoked potentials (TES-MEPs) was established for the evaluation of neural function of nonhuman primates with SCI. We compared the motor function scores of nonhuman primates before and after SCI. Our results showed that the EP below the injury level significantly changed during the 6 months after SCI. In addition, a positive correlation was identified between the EP scores and motor function. The EP-based scoring system is a reliable approach for evaluating the motor function changes in nonhuman primates with SCI.

Pronounced species divergence in corticospinal tract reorganization and functional recovery after lateralized spinal cord injury favors primates

Experimental and clinical studies suggest that primate species exhibit greater recovery after lateralized compared to symmetrical spinal cord injuries. Although this observation has major implications for designing clinical trials and translational therapies, advantages in recovery of nonhuman primates over other species have not been shown statistically to date, nor have the associated repair mechanisms been identified. We monitored recovery in more than 400 quadriplegic patients and found that functional gains increased with the laterality of spinal cord damage. Electrophysiological analyses suggested that corticospinal tract reorganization contributes to the greater recovery after lateralized compared with symmetrical injuries. To investigate underlying mechanisms, we modeled lateralized injuries in rats and monkeys using a lateral hemisection, and compared anatomical and functional outcomes with patients who suffered similar lesions. Standardized assessments revealed that monkeys and humans showed greater recovery of locomotion and hand function than did rats. Recovery correlated with the formation of corticospinal detour circuits below the injury, which were extensive in monkeys but nearly absent in rats. Our results uncover pronounced interspecies differences in the nature and extent of spinal cord repair mechanisms, likely resulting from fundamental differences in the anatomical and functional characteristics of the motor systems in primates versus rodents. Although rodents remain essential for advancing regenerative therapies, the unique response of the primate corticospinal tract after injury reemphasizes the importance of primate models for designing clinically relevant treatments.

A controlled spinal cord contusion for the rhesus macaque monkey

Most in vivo spinal cord injury (SCI) experimental models use rodents. Due to the anatomical and functional differences between rodents and humans, reliable large animal models, such as non-human primates, of SCI are critically needed to facilitate translation of laboratory discoveries to clinical applications. Here we report the establishment of a controlled spinal contusion model that produces severity-dependent functional and histological deficits in non-human primates. Six adult male rhesus macaque monkeys underwent mild to moderate contusive SCI using 1.0 and 1.5mm tissue displacement injuries at T9 or sham laminectomy (n=2/group). Multiple assessments including motor-evoked potential (MEP), somatosensory-evoked potential (SSEP), MR imaging, and monkey hindlimb score (MHS) were performed. Monkeys were sacrificed at 6 months post-injury, and the lesion area was examined for cavitation, axons, myelin, and astrocytic responses. The MHS demonstrated that both the 1.0 and 1.5mm displacement injuries created discriminative neurological deficits which were severity-dependent. The MEP response rate was depressed after a 1.0mm injury and was abolished after a 1.5mm injury. The SSEP response rate was slightly decreased following both the 1.0 and 1.5mm SCI. MRI imaging demonstrated an increase in T2 signal at the lesion site at 3 and 6months, and diffusion tensor imaging (DTI) tractography showed interrupted fiber tracts at the lesion site at 4h and at 6 months post-SCI. Histologically, severity-dependent spinal cord atrophy, axonal degeneration, and myelin loss were found after both injury severities. Notably, strong astrocytic gliosis was not observed at the lesion penumbra in the monkey. In summary, we describe the development of a clinically-relevant contusive SCI model that produces severity-dependent anatomical and functional deficits in non-human primates. Such a model may advance the translation of novel SCI repair strategies to the clinic.

A Unilateral Cervical Spinal Cord Contusion Injury Model in Non-Human Primates (Macaca mulatta)

The development of a non-human primate (NHP) model of spinal cord injury (SCI) based on mechanical and computational modeling is described. We scaled up from a rodent model to a larger primate model using a highly controllable, friction-free, electronically-driven actuator to generate unilateral C6-C7 spinal cord injuries. Graded contusion lesions with varying degrees of functional recovery, depending upon pre-set impact parameters, were produced in nine NHPs. Protocols and pre-operative magnetic resonance imaging (MRI) were used to optimize the predictability of outcomes by matching impact protocols to the size of each animal's spinal canal, cord, and cerebrospinal fluid space. Post-operative MRI confirmed lesion placement and provided information on lesion volume and spread for comparison with histological measures. We evaluated the relationships between impact parameters, lesion measures, and behavioral outcomes, and confirmed that these relationships were consistent with our previous studies in the rat. In addition to providing multiple univariate outcome measures, we also developed an integrated outcome metric describing the multivariate cervical SCI syndrome. Impacts at the higher ranges of peak force produced highly lateralized and enduring deficits in multiple measures of forelimb and hand function, while lower energy impacts produced early weakness followed by substantial recovery but enduring deficits in fine digital control (e.g., pincer grasp). This model provides a clinically relevant system in which to evaluate the safety and, potentially, the efficacy of candidate translational therapies.

Leveraging biomedical informatics for assessing plasticity and repair in primate spinal cord injury

Recent preclinical advances highlight the therapeutic potential of treatments aimed at boosting regeneration and plasticity of spinal circuitry damaged by spinal cord injury (SCI). With several promising candidates being considered for translation into clinical trials, the SCI community has called for a non-human primate model as a crucial validation step to test efficacy and validity of these therapies prior to human testing. The present paper reviews the previous and ongoing efforts of the California Spinal Cord Consortium (CSCC), a multidisciplinary team of experts from 5 University of California medical and research centers, to develop this crucial translational SCI model. We focus on the growing volumes of high resolution data collected by the CSCC, and our efforts to develop a biomedical informatics framework aimed at leveraging multidimensional data to monitor plasticity and repair targeting recovery of hand and arm function. Although the main focus of many researchers is the restoration of voluntary motor control, we also describe our ongoing efforts to add assessments of sensory function, including pain, vital signs during surgery, and recovery of bladder and bowel function. By pooling our multidimensional data resources and building a unified database infrastructure for this clinically relevant translational model of SCI, we are now in a unique position to test promising therapeutic strategies' efficacy on the entire syndrome of SCI. We review analyses highlighting the intersection between motor, sensory, autonomic and pathological contributions to the overall restoration of function. This article is part of a Special Issue entitled SI: Spinal cord injury.

Three-dimensional motion analysis of arm-reaching movements in healthy and hemispinalized common marmosets

Spinal cord injury (SCI) is a devastating neurological injury. At present, pharmacological, regenerative, and rehabilitative approaches are widely studied as therapeutic interventions for motor recovery after SCI. Preclinical research has been performed on model animals with experimental SCI, and those studies often evaluate hand and arm motor function using various indices, such as the success rate of the single pellet reaching test and the grip force. However, compensatory movement strategies, involuntary muscle contraction, and the subject's motivation could affect the scores, resulting in failure to assess direct recovery from impairment. Identifying appropriate assessments of motor impairment is thus important for understanding the mechanisms of motor recovery. In this study, we developed a motion capture system capable of reconstructing three-dimensional hand positions with millimeter and millisecond accuracy and evaluated hand kinematics during food retrieval movement in both healthy and hemispinalized common marmosets. As a result, the endpoint jerk, representing the accuracy of hand motor control, was asserted to be an appropriate index of upper limb motor impairment by eliminating the influence of the subject's motivation, involuntary muscle contraction, and compensatory strategies. The result also suggested that the kinematics of the limb more consistently reflects motor restoration from deficit due to spinal cord injury than the performance in the single pellet reaching test. Because of recent attention devoted to the common marmoset as a nonhuman primate model for human diseases, the present study, which clarified arm-reaching movements in spinalized marmosets, provides fundamental knowledge for future therapeutic studies.

Development of a database for translational spinal cord injury research

Efforts to understand spinal cord injury (SCI) and other complex neurotrauma disorders at the pre-clinical level have shown progress in recent years. However, successful translation of basic research into clinical practice has been slow, partly because of the large, heterogeneous data sets involved. In this sense, translational neurological research represents a "big data" problem. In an effort to expedite translation of pre-clinical knowledge into standards of patient care for SCI, we describe the development of a novel database for translational neurotrauma research known as Visualized Syndromic Information and Outcomes for Neurotrauma-SCI (VISION-SCI). We present demographics, descriptive statistics, and translational syndromic outcomes derived from our ongoing efforts to build a multi-center, multi-species pre-clinical database for SCI models. We leveraged archived surgical records, postoperative care logs, behavioral outcome measures, and histopathology from approximately 3000 mice, rats, and monkeys from pre-clinical SCI studies published between 1993 and 2013. The majority of animals in the database have measures collected for health monitoring, such as weight loss/gain, heart rate, blood pressure, postoperative monitoring of bladder function and drug/fluid administration, behavioral outcome measures of locomotion, and tissue sparing postmortem. Attempts to align these variables with currently accepted common data elements highlighted the need for more translational outcomes to be identified as clinical endpoints for therapeutic testing. Last, we use syndromic analysis to identify conserved biological mechanisms of recovery after cervical SCI between rats and monkeys that will allow for more-efficient testing of therapeutics that will need to be translated toward future clinical trials.

The Irvine, Beatties, and Bresnahan (IBB) Forelimb Recovery Scale: An Assessment of Reliability and Validity

The IBB scale is a recently developed forelimb scale for the assessment of fine control of the forelimb and digits after cervical spinal cord injury [SCI; (1)]. The present paper describes the assessment of inter-rater reliability and face, concurrent and construct validity of this scale following SCI. It demonstrates that the IBB is a reliable and valid scale that is sensitive to severity of SCI and to recovery over time. In addition, the IBB correlates with other outcome measures and is highly predictive of biological measures of tissue pathology. Multivariate analysis using principal component analysis (PCA) demonstrates that the IBB is highly predictive of the syndromic outcome after SCI (2), and is among the best predictors of bio-behavioral function, based on strong construct validity. Altogether, the data suggest that the IBB, especially in concert with other measures, is a reliable and valid tool for assessing neurological deficits in fine motor control of the distal forelimb, and represents a powerful addition to multivariate outcome batteries aimed at documenting recovery of function after cervical SCI in rats.

The reactivation of somatosensory cortex and behavioral recovery after sensory loss in mature primates

In our experiments, we removed a major source of activation of somatosensory cortex in mature monkeys by unilaterally sectioning the sensory afferents in the dorsal columns of the spinal cord at a high cervical level. At this level, the ascending branches of tactile afferents from the hand are cut, while other branches of these afferents remain intact to terminate on neurons in the dorsal horn of the spinal cord. Immediately after such a lesion, the monkeys seem relatively unimpaired in locomotion and often use the forelimb, but further inspection reveals that they prefer to use the unaffected hand in reaching for food. In addition, systematic testing indicates that they make more errors in retrieving pieces of food, and start using visual inspection of the rotated hand to confirm the success of the grasping of the food. Such difficulties are not surprising as a complete dorsal column lesion totally deactivates the contralateral hand representation in primary somatosensory cortex (area 3b). However, hand use rapidly improves over the first post-lesion weeks, and much of the hand representational territory in contralateral area 3b is reactivated by inputs from the hand in roughly a normal somatotopic pattern. Quantitative measures of single neuron response properties reveal that reactivated neurons respond to tactile stimulation on the hand with high firing rates and only slightly longer latencies. We conclude that preserved dorsal column afferents after nearly complete lesions contribute to the reactivation of cortex and the recovery of the behavior, but second-order sensory pathways in the spinal cord may also play an important role. Our microelectrode recordings indicate that these preserved first-order, and second-order pathways are initially weak and largely ineffective in activating cortex, but they are potentiated during the recovery process. Therapies that would promote this potentiation could usefully enhance recovery after spinal cord injury.

The known-unknowns in spinal cord injury, with emphasis on cell-based therapies - a review with suggestive arenas for research

INTRODUCTION

In spite of extensive research, the progress toward a cure in spinal cord injury (SCI) is still elusive, which holds good for the cell- and stem cell-based therapies. We have critically analyzed seven known gray areas in SCI, indicating the specific arenas for research to improvise the outcome of cell-based therapies in SCI.

AREAS COVERED

The seven, specific known gray areas in SCI analyzed are: i) the gap between animal models and human victims; ii) uncertainty about the time, route and dosage of cells applied; iii) source of the most efficacious cells for therapy; iv) inability to address the vascular compromise during SCI; v) lack of non-invasive methodologies to track the transplanted cells; vi) need for scaffolds to retain the cells at the site of injury; and vii) physical and chemical stimuli that might be required for synapses formation yielding functional neurons.

EXPERT OPINION

Further research on scaffolds for retaining the transplanted cells at the lesion, chemical and physical stimuli that may help neurons become functional, a meta-analysis of timing of the cell therapy, mode of application and larger clinical studies are essential to improve the outcome.

Role of Direct vs. Indirect Pathways from the Motor Cortex to Spinal Motoneurons in the Control of Hand Dexterity

Evolutionally, development of the direct connection from the motor cortex to spinal motoneurons [corticomotoneuronal (CM) pathway] parallels the ability of hand dexterity. Damage to the corticofugal fibers in higher primates resulted in deficit of fractionated digit movements. Based on such observations, it was generally believed that the CM pathway plays a critical role in the control of hand dexterity. On the other hand, a number of "phylogenetically older" indirect pathways from the motor cortex to motoneurons still exist in primates. The indirect pathways are mediated by intercalated neurons such as segmental interneurons (sINs), propriospinal neurons (PNs) reticulospinal neurons (RSNs), or rubrospinal neurons (RuSNs). However, their contribution to hand dexterity remains elusive. Lesion of the brainstem pyramid sparing the transmission through the RuSNs and RSNs, resulted in permanent deficit of fractionated digit movements in macaque monkeys. On the other hand, in our recent study, after lesion of the dorsolateral funiculus (DLF) at the C5 segment, which removed the lateral corticospinal tract (l-CST) including the CM pathway and the transmission through sINs and RuSNs but spared the processing through the PNs and RSNs, fractionated digit movements recovered within several weeks. These results suggest that the PNs can be involved in the recovery of fractionated digit movements, but the RSNs and RuSNs have less capacity in this regard. However, on closer inspection, it was found that the activation pattern of hand and arm muscles considerably changed after the C5 lesion, suggesting limitation of PNs for the compensation of hand dexterity. Altogether, it is suggested that PNs, RSNs RuSNs, and the CM pathway (plus sINs) make a different contribution to the hand dexterity and appearance of motor deficit of the hand dexterity caused by damage to the corticofugal fibers and potential of recovery varies depending on the rostrocaudal level of the lesion.

Effects of early versus late rehabilitative training on manual dexterity after corticospinal tract lesion in macaque monkeys

Dexterous hand movements can be restored with motor rehabilitative training after a lesion of the lateral corticospinal tract (l-CST) in macaque monkeys. To maximize effectiveness, the optimal time to commence such rehabilitative training must be determined. We conducted behavioral analyses and compared the recovery of dexterous hand movements between monkeys in which hand motor training was initiated immediately after the l-CST lesion (early-trained monkeys) and those in which training was initiated 1 mo after the lesion (late-trained monkeys). The performance of dexterous hand movements was evaluated by food retrieval tasks. In early-trained monkeys, performance evaluated by the success rate in a vertical slit task (retrieval of a small piece of food through a narrow vertical slit) recovered to the level of intact monkeys during the first 1–2 mo after the lesion. In late-trained monkeys, the task success rate averaged ∼30% even after 3 mo of rehabilitative training. We also evaluated hand performance with the Klüver board task, in which monkeys retrieved small spherical food pellets from cylindrical wells. Although the success rate of the Klüver board task did not differ between early- and late-trained monkeys, kinematic movement analysis showed that there was a difference between the groups: late-trained monkeys with an improved success rate frequently used alternate movement strategies that were different from those used before the lesion. These results suggest that early rehabilitative training after a spinal cord lesion positively influences subsequent functional recovery.

A surgery protocol for adult zebrafish spinal cord injury

Adult zebrafish has a remarkable capability to recover from spinal cord injury, providing an excellent model for studying neuroregeneration. Here we list equipment and reagents, and give a detailed protocol for complete transection of the adult zebrafish spinal cord. In this protocol, potential problems and their solutions are described so that the zebrafish spinal cord injury model can be more easily and reproducibly performed. In addition, two assessments are introduced to monitor the success of the surgery and functional recovery: one test to assess free swimming capability and the other test to assess extent of neuroregeneration by in vivo anterograde axonal tracing. In the swimming behavior test, successful complete spinal cord transection is monitored by the inability of zebrafish to swim freely for 1 week after spinal cord injury, followed by the gradual reacquisition of full locomotor ability within 6 weeks after injury. As a morphometric correlate, anterograde axonal tracing allows the investigator to monitor the ability of regenerated axons to cross the lesion site and increasingly extend into the gray and white matter with time after injury, confirming functional recovery. This zebrafish model provides a paradigm for recovery from spinal cord injury, enabling the identification of pathways and components of neuroregeneration.

Animal models of neurologic disorders: a nonhuman primate model of spinal cord injury

Primates are an important and unique animal resource. We have developed a nonhuman primate model of spinal cord injury (SCI) to expand our knowledge of normal primate motor function, to assess the impact of disease and injury on sensory and motor function, and to test candidate therapies before they are applied to human patients. The lesion model consists of a lateral spinal cord hemisection at the C7 spinal level with subsequent examination of behavioral, electrophysiological, and anatomical outcomes. Results to date have revealed significant neuroanatomical and functional differences between rodents and primates that impact the development of candidate therapies. Moreover, these findings suggest the importance of testing some therapeutic approaches in nonhuman primates prior to the use of invasive approaches in human clinical trials. Our primate model is intended to: 1) lend greater positive predictive value to human translatable therapies, 2) develop appropriate methods for human translation, 3) lead to basic discoveries that might not be identified in rodent models and are relevant to human translation, and 4) identify new avenues of basic research to "reverse-translate" important questions back to rodent models.

Models of CNS injury in the nonhuman primate: A new era for treatment strategies

Central nervous system (CNS) injuries affect all levels of society indiscriminately, resulting in functional and behavioral deficits with devastating impacts on life expectancies, physical and emotional wellbeing. Considerable literature exists describing the pathophysiology of CNS injuries as well as the cellular and molecular factors that inhibit regrowth and regeneration of damaged connections. Based on these data, numerous therapeutic strategies targeting the various factors of repair inhibition have been proposed and on-going assessment has demonstrated some promising results in the laboratory environ. However, several of these treatment strategies have subsequently been taken into clinical trials but demonstrated little to no improvement in patient outcomes. As a result, options for clinical interventions following CNS injuries remain limited and effective restorative treatment strategies do not as yet exist. This review discusses some of the current animal models, with focus on nonhuman primates, which are currently being modeled in the laboratory for the study of CNS injuries. Last, we review the current understanding of the mechanisms underlying repair/regrowth inhibition and the current trends in experimental treatment strategies that are being assessed for potential translation to clinical applications.

Syndromics: a bioinformatics approach for neurotrauma research

Substantial scientific progress has been made in the past 50 years in delineating many of the biological mechanisms involved in the primary and secondary injuries following trauma to the spinal cord and brain. These advances have highlighted numerous potential therapeutic approaches that may help restore function after injury. Despite these advances, bench-to-bedside translation has remained elusive. Translational testing of novel therapies requires standardized measures of function for comparison across different laboratories, paradigms, and species. Although numerous functional assessments have been developed in animal models, it remains unclear how to best integrate this information to describe the complete translational "syndrome" produced by neurotrauma. The present paper describes a multivariate statistical framework for integrating diverse neurotrauma data and reviews the few papers to date that have taken an information-intensive approach for basic neurotrauma research. We argue that these papers can be described as the seminal works of a new field that we call "syndromics", which aim to apply informatics tools to disease models to characterize the full set of mechanistic inter-relationships from multi-scale data. In the future, centralized databases of raw neurotrauma data will enable better syndromic approaches and aid future translational research, leading to more efficient testing regimens and more clinically relevant findings.