Kinematic analysis of limb position during quadrupedal locomotion in rats

Automatic detection of foot-strike onsets in a rhythmic forelimb movement

Rhythmic movement is the fundamental motion dynamics characterized by repetitive patterns. Precisely defining onsets in rhythmic movement is essential for a comprehensive analysis of motor functions. Our study introduces an automated method for detecting rat's forelimb foot-strike onsets using deep learning tools. This method demonstrates high accuracy of onset detection by combining two techniques using joint coordinates and behavioral confidence scale. The analysis extends to neural oscillatory responses in the rat's somatosensory cortex, validating the effectiveness of our combined approach. Our technique streamlines experimentation, demanding only a camera and GPU-accelerated computer. This approach is applicable across various contexts and promotes our understanding of brain functions during rhythmic movements.

Rehabilitative Training in Animal Models of Spinal Cord Injury

Rehabilitative motor training is currently one of the most widely used approaches to promote moderate recovery following injuries of the central nervous system. Such training is generally applied in the clinical setting, whereas it is not standard in preclinical research. This is a concern as it is becoming increasingly apparent that neuroplasticity enhancing treatments require training or some form of activity as a co-therapy to promote functional recovery. Despite the importance of training and the many open questions regarding its mechanistic consequences, its use in preclinical animal models is rather limited. Here we review approaches, findings and challenges when training is applied in animal models of spinal cord injury, and we suggest recommendations to facilitate the integration of training using an appropriate study design, into pre-clinical studies.

Neurochemical excitation of thoracic propriospinal neurons improves hindlimb stepping in adult rats with spinal cord lesions

Using an in vitro neonatal rat brainstem-spinal cord preparation, we previously showed that cervicothoracic propriospinal neurons contribute to descending transmission of the bulbospinal locomotor command signal, and neurochemical excitation of these neurons facilitates signal propagation. The present study examined the relevance of these observations to adult rats in vivo. The first aim was to determine the extent to which rats are able to spontaneously recover hindlimb locomotor function in the presence of staggered contralateral hemisections (left T2-4 and right T9-11) designed to abolish all long direct bulbospinal projections. The second aim was to determine whether neurochemical excitation of thoracic propriospinal neurons in such animals facilitates hindlimb stepping. In the absence of intrathecal drug injection, all animals (n=24) displayed some degree of hindlimb recovery ranging from weak ankle movements to brief periods of unsupported hindlimb stepping on the treadmill. The effect of boluses of neurochemicals delivered via an intrathecal catheter (tip placed midway between the rostral and caudal thoracic hemisections) was examined at post-lesion weeks 3, 6 and 9. Quipazine was particularly effective facilitating hindlimb stepping. Subsequent complete transection above the rostral (n=3) or caudal (n=2) hemisections at week 9 had no consistent effect on drug-free locomotor performance, but the facilitatory effect of drug injection decreased in 4/5 animals. Two animals underwent complete transection at T3 as the first and only surgery and implantation of two intrathecal catheters targeted to the mid-thoracic and lumbar regions, respectively. A similar facilitatory effect on stepping was observed in response to drugs administered via either catheter. The results indicate that partial spontaneous recovery of stepping occurs in adult rats after abolishing all long direct bulbospinal connections, in contrast to previous studies suggesting that hindlimb stepping after dual hemisections either does not occur or is observed only if the second hemisection surgery is delayed relative to the first. The results support the hypothesis that artificial modulation of propriospinal neuron excitability may facilitate recovery of motor function after spinal cord injury. However, whether this facilitation is due to enhanced transmission of a descending locomotor signal or is the result of excitation of thoracolumbar circuits independent of supraspinal influence, requires further study.

From basics to clinical: a comprehensive review on spinal cord injury

Spinal cord injury (SCI) is a devastating neurological disorder that affects thousands of individuals each year. Over the past decades an enormous progress has been made in our understanding of the molecular and cellular events generated by SCI, providing insights into crucial mechanisms that contribute to tissue damage and regenerative failure of injured neurons. Current treatment options for SCI include the use of high dose methylprednisolone, surgical interventions to stabilize and decompress the spinal cord, and rehabilitative care. Nonetheless, SCI is still a harmful condition for which there is yet no cure. Cellular, molecular, rehabilitative training and combinatorial therapies have shown promising results in animal models. Nevertheless, work remains to be done to ascertain whether any of these therapies can safely improve patient's condition after human SCI. This review provides an extensive overview of SCI research, as well as its clinical component. It starts covering areas from physiology and anatomy of the spinal cord, neuropathology of the SCI, current clinical options, neuronal plasticity after SCI, animal models and techniques to assess recovery, focusing the subsequent discussion on a variety of promising neuroprotective, cell-based and combinatorial therapeutic approaches that have recently moved, or are close, to clinical testing.

Genome-wide gene expression profiling of stress response in a spinal cord clip compression injury model

Background

The aneurysm clip impact-compression model of spinal cord injury (SCI) is a standard injury model in animals that closely mimics the primary mechanism of most human injuries: acute impact and persisting compression. Its histo-pathological and behavioural outcomes are extensively similar to human SCI. To understand the distinct molecular events underlying this injury model we analyzed global mRNA abundance changes during the acute, subacute and chronic stages of a moderate to severe injury to the rat spinal cord.

Results

Time-series expression analyses resulted in clustering of the majority of deregulated transcripts into eight statistically significant expression profiles. Systematic application of Gene Ontology (GO) enrichment pathway analysis allowed inference of biological processes participating in SCI pathology. Temporal analysis identified events specific to and common between acute, subacute and chronic time-points. Processes common to all phases of injury include blood coagulation, cellular extravasation, leukocyte cell-cell adhesion, the integrin-mediated signaling pathway, cytokine production and secretion, neutrophil chemotaxis, phagocytosis, response to hypoxia and reactive oxygen species, angiogenesis, apoptosis, inflammatory processes and ossification. Importantly, various elements of adaptive and induced innate immune responses span, not only the acute and subacute phases, but also persist throughout the chronic phase of SCI. Induced innate responses, such as Toll-like receptor signaling, are more active during the acute phase but persist throughout the chronic phase. However, adaptive immune response processes such as B and T cell activation, proliferation, and migration, T cell differentiation, B and T cell receptor-mediated signaling, and B cell- and immunoglobulin-mediated immune response become more significant during the chronic phase.

Conclusions

This analysis showed that, surprisingly, the diverse series of molecular events that occur in the acute and subacute stages persist into the chronic stage of SCI. The strong agreement between our results and previous findings suggest that our analytical approach will be useful in revealing other biological processes and genes contributing to SCI pathology.

A semi-automated software tool to study treadmill locomotion in the rat: from experiment videos to statistical gait analysis

A computer-aided method for the tracking of morphological markers in fluoroscopic images of a rat walking on a treadmill is presented and validated. The markers correspond to bone articulations in a hind leg and are used to define the hip, knee, ankle and metatarsophalangeal joints. The method allows a user to identify, using a computer mouse, about 20% of the marker positions in a video and interpolate their trajectories from frame-to-frame. This results in a seven-fold speed improvement in detecting markers. This also eliminates confusion problems due to legs crossing and blurred images. The video images are corrected for geometric distortions from the X-ray camera, wavelet denoised, to preserve the sharpness of minute bone structures, and contrast enhanced. From those images, the marker positions across video frames are extracted, corrected for rat "solid body" motions on the treadmill, and used to compute the positional and angular gait patterns. Robust Bootstrap estimates of those gait patterns and their prediction and confidence bands are finally generated. The gait patterns are invaluable tools to study the locomotion of healthy animals or the complex process of locomotion recovery in animals with injuries. The method could, in principle, be adapted to analyze the locomotion of other animals as long as a fluoroscopic imager and a treadmill are available.

Rat Models of Traumatic Spinal Cord Injury to Assess Motor Recovery

Devastating motor, sensory, and autonomic dysfunctions render long-term personal hardships to the survivors of traumatic spinal cord injury (SCI). The suffering also extends to the survivors' families and friends, who endure emotional, physical, and financial burdens in providing for necessary surgeries, care, and rehabilitation. After the primary mechanical SCI, there is a complex secondary injury cascade that leads to the progressive death of otherwise potentially viable axons and cells and that impairs endogenous recovery processes. Investigations of possible cures and of ways to alleviate the hardships of traumatic SCI include those of interventions that attenuate or overcome the secondary injury cascade, enhance the endogenous repair mechanisms, regenerate axons, replace lost cells, and rehabilitate. These investigations have led to the creation of laboratory animal models of the different types of traumatic human SCI and components of the secondary injury cascade. However, no particular model completely addresses all aspects of traumatic SCI. In this article, we describe adult rat SCI models and the motor, and in some cases sensory and autonomic, deficits that each produces. Importantly, as researchers in this area move toward clinical trials to alleviate the hardships of traumatic SCI, there is a need for standardized small and large animal SCI models as well as quantitative behavioral and electrophysiological assessments of their outcomes so that investigators testing various interventions can directly compare their results and correlate them with the molecular, biochemical, and histological alterations.

Quantification of Locomotor Recovery following Spinal Cord Contusion in Adult Rats

Injury to the spinal cord not only disrupts the functioning of spinal circuits at the site of the impact, but also limits sensorimotor function caudal to the level of the lesion. Ratings of gross locomotor skill are generally used to quantify locomotor recovery following spinal cord injury (SCI). The purpose of this study was to assess behavioral recovery following SCI with three tasks: (1) BBB ratings, (2) walking on a horizontal ladder, and (3) footprint analyses. Behavioral testing was conducted for 6 postoperative weeks, and then the spinal cords were processed for the amount of white matter spared. As expected, BBB ratings dramatically decreased and then improved during recovery. The number of hindlimb foot-faults on the horizontal ladder increased after injury and remained elevated during the recovery period. Footprint analyses revealed that sham-control rats used several different gaits to cross the runway. In contrast, the locomotor function of rats with a SCI was impaired throughout the postoperative period. Some locomotor parameters of the injured rats improved slightly (velocity, stride length, stride duration, stance duration), some did not change (interlimb coordination, swing duration, forelimb base of support, hindpaw angle), and others declined (hindlimb base of support) during the recovery period. Together, these results show that gross locomotor skill improved after SCI, while recovery of fine locomotor function was more limited. Multiple tests should be included in future experiments in order to assess gross and fine changes in sensorimotor function following SCI.

A comparison analysis of hindlimb kinematics during overground and treadmill locomotion in rats

The convenience of the motor-driven treadmill makes it an attractive instrument for investigating rat locomotion. However, no data are available to indicate whether hindlimb treadmill kinematic findings may be compared or generalized to overground locomotion. In this investigation, we compared overground and treadmill locomotion for differences in the two-dimensional angular kinematics and temporal and spatial measurements for the hindlimb. Ten female rats were evaluated at the same speed for natural overground and treadmill walking. The walking velocity, swing duration and stride length were statistically indistinguishable between the two testing conditions. Significant differences were found between overground and treadmill locomotion for step cycle duration and stance phase duration parameters. During the stance phase of walking, the angular movement of the hip, knee and ankle joints were significantly different in the two conditions, with greater flexion occurring on the overground. Despite this, the sagittal joint movements of the hindlimb were similar between the two walking conditions, with only three parameters being significantly different in the swing. Hip height and angle-angle cyclograms were also only found to display subtle differences. This study suggests that reliable kinematic measurements can be obtained from the treadmill gait analysis in rats.

Effect of skin movement on the analysis of hindlimb kinematics during treadmill locomotion in rats

In rat gait kinematics, the method most frequently used for measuring hindlimb movement involves placing markers on the skin surface overlying the joints being analyzed. Soft tissue movement around the knee joint has been considered the principle source of error when estimating hindlimb joint kinematics in rodents. However, the motion of knee marker was never quantified, nor the different variations in joint angle associated with this gait analysis system. The purpose of this study was two-fold. The first purpose was to expand upon the limited pool of information describing the effect of soft tissue movement over the knee upon the angular positions of the hip, knee and ankle of rats during treadmill locomotion. Secondly, it was a goal of this study to document the magnitude of the skin displacement when using markers that were attached superficially to the knee joint. This was examined by comparing the hindlimb kinematics in sagittal plane during treadmill locomotion determined from the marker attached to the knee and when the knee position was determined indirectly by computer analysis. Results showed that there is a considerable skin movement artefact which propagates to knee joint position and hindlimb kinematics estimates. It was concluded that these large errors can decrease data reliability in the research of rat gait analysis.

Neuromechanical control of locomotion in the rat

Rodent models are being extensively used to investigate the effects of traumatic injury and develop and assess the mechanisms of repair and regeneration. We present quantitative assessment of two-dimensional (2D) kinematics of overground walking and for the first time three-dimensional (3D) joint angle kinematics of all four limbs during treadmill walking in intact adult female Long-Evans rats. Gait cycle with subphases and intralimb and interlimb cyclograms are presented. Phase relationships between joint angles on a cycle-by-cycle basis and interlimb footfalls are assessed using a simple technique. Electromyogram (EMG) data from major flexor and extensor muscles for each of the hindlimb joints and elbow extensor muscles of the forelimbs synchronized to the 3D kinematics are also obtained. Overground walking kinematics, provides information on base of support, stride length, and hindfoot rotation. Treadmill walking kinematics indicate primarily monophasic angle trajectories for the hip and shoulder joints, weak double peak patterns for the knee and elbow joints, and a prominent double peak pattern for the ankle joints. Maximum flexion of the knee during swing precedes that of the ankle, which precedes that of the hip. A mild exercise regimen over 8 weeks does not alter the kinematics. EMG activity indicates specific relationships of the neural activity to joint angle kinematics. We find that the ankle flexors as well as the hip and elbow extensors maintain constant burst duration with changing cycle duration. Data and techniques described here are likely to be useful for quantitative assessment of altered gait and neural control mechanisms after neurotrauma.

Treadmill locomotion in the intact and spinal mouse

Because the genetic characteristics of several inbred strains of mice are well identified, their use is becoming increasingly popular in spinal cord injury research. In this context, it appears particularly important to document adequately motor patterns, such as locomotion in normal mice, to establish some baseline values of locomotor characteristics. It also seems crucial to determine the extent to which mice can express a locomotor pattern after a complete spinal transection to establish a baseline on which one can evaluate the effects of treatments after spinal injury. Therefore, we have used conventional techniques to document the kinematics of treadmill locomotion in intact mice (n = 11) and in mice with a complete section of the spinal cord at T8 (n = 12). The results show that the kinematics and EMG of adult normal mice can be adequately monitored with such conventional equipment and that mice can re-express hindlimb locomotion within 14 d after spinalization, without any pharmacological treatments. The angular excursions of the hip, knee, and ankle are similar to those of the intact mice, although the joints are sometimes more flexed. After spinal cord transection, out-of-phase alternation between the homologous limbs recovered, whereas the timing between homolateral limbs was completely lost. This remarkable ability of mice to express hindlimb locomotion after a complete spinalization should be taken into account in the evaluation of various procedures aimed at promoting the functional recovery of locomotion after spinal lesions.

Bridging areas of injury in the spinal cord

There is a devastating loss of function when substantial numbers of axons are interrupted by injury to the spinal cord. This loss may be eventually reversed by providing bridging prostheses that will enable axons to regrow across the injury site and enter the spinal cord beyond. This review addresses the bridging strategies that are being developed in a number of spinal cord lesion models: complete and partial transection and cavities arising from contusion. Bridges containing peripheral nerve, Schwann cells, olfactory ensheathing glia, fetal tissue, stem cells/neuronal precursor cells, and macrophages are being evaluated as is the administration of neurotrophic factors, administered by infusion or secreted by genetically engineered cells. Biomaterials may be an important factor in developing successful strategies. Due to the complexity of the sequelae following spinal cord injury, no one strategy will be effective. The compelling question today is: What combinations of the strategies discussed, or new ones, along with an initial neuroprotective treatment, will substantially improve outcome after spinal cord injury?

Efficient testing of motor function in spinal cord injured rats

In experimental spinal cord injury studies, animal models are widely used to examine anatomical and functional changes after different treatments and lesion types. A variety of behavioral paradigms exists in the literature, but definitions and criteria for motor performance vary considerably. In this study, we examined the outcome and relation of tests such as the BBB open field locomotion score, footprint analysis, kinematic analysis, placing response, grid walk and narrow beam crossing following two different lesion types. The information obtained was used to design an efficient and reliable testing strategy, which includes a broad spectrum of parameters to enhance sensitivity. This approach should help to standardize modular testing procedures across different laboratories working on spinal cord injury.

Treadmill training in incomplete spinal cord injured rats

Treadmill training has been shown to accelerate locomotor recovery and to improve weight bearing during treadmill walking in spinal cats. In human patients treadmill training is increasingly used in rehabilitation after incomplete spinal cord injury. In this study we examined training effects in spinal cord injured rats with an incomplete dorsal lesion. Recovery was examined with an open field locomotor score, kinematic analysis on the treadmill, and several functional tests (i.e. foot print evaluation, narrow beam crossing, grid walking, open field exploratory activity). During the course of 5 weeks after the injury, a substantial amount of recovery occurred in the treadmill trained as well as in the untrained rats. If compared to the control lesioned rats, which showed a high level of spontaneous hindlimb movements at 7-14 days post lesion, no additional beneficial effect of a 5-week daily treadmill training on the locomotor outcome could be detected in the trained group. The only change observed was a slightly larger exploratory activity of the trained rats. It is probable that the spared ventral and ventro-lateral fibers allowed spontaneous recovery and 'self-training' to occur to such an extend that systematic treadmill training did not provide additional improvement.

Activation of locomotion in adult chronic spinal rats is achieved by transplantation of embryonic raphe cells reinnervating a precise lumbar level

Traumatic lesions of the spinal cord yield a loss of supraspinal control of voluntary locomotor activity, although the spinal cord contains the necessary circuitry to generate the basic locomotor pattern. In spinal rats, this network, known as central pattern generator (CPG), was shown to be sensitive to serotonergic pharmacological stimulation. In previous works we have shown that embryonic raphe cells transplanted into the sublesional cord of adult rats can reinnervate specific targets, restore the lesion-induced increase in receptor densities of neurotransmitters, promote hindlimb weight support, and trigger a locomotor activity on a treadmill without any other pharmacological treatment or training. With the aim of discriminating whether the action of serotonin on CPG is associated to a specific level of the cord, we have transplanted embryonic raphe cells at two different levels of the sublesional cord (T9 and T11) and then performed analysis of the kinematic and EMG activity synchronously recorded during locomotion. Locomotor performances were correlated to the reinnervated level of the cord and compared to that of intact and transected nontransplanted animals. The movements expressed by T11 transplanted animals correspond to a well defined locomotor pattern comparable to that of the intact animals. On the contrary, T9 transplanted animals developed limited and disorganized movements as those of nontransplanted animals. The correlation of the locomotor performances with the level of reinnervation of the spinal cord suggests that serotonergic reinnervation of the L1-L2 level constitutes a key element in the genesis of this locomotor rhythmic activity. This is the first in vivo demonstration that transplanted embryonic raphe cells reinnervating a specific level of the cord activate a locomotor behavior.

The effects of unilateral pyramidal tract section on hindlimb motor performance in the rat

Most investigations on selective lesions of the pyramidal tract in rodents have focused on the functional impairment of the forelimbs. This study describes the effects of a unilateral transection of the pyramidal tract rostral to the decussation on hindlimb function. Using kinematic locomotion analysis, the narrow beam test, open field locomotion ranking, analysis of footprints and air righting, we found severe impairments including hypermetria, trunk instability, lateral shifts in weight support, toe dragging, and hindlimb exo-rotation. Most impairments recovered rapidly within the first week after operation. Slight hypermetria persisted after 4 weeks. The rather mild long term deficits after unilateral pyramidotomy may stress the need for extremely sensitive behavioural tasks to enable the detection. We conclude that the possibility to correlate regenerative changes following selective pyramidal tract lesions with hindlimb function is thus limited.

The ability of human Schwann cell grafts to promote regeneration in the transected nude rat spinal cord

Advances in the purification and expansion of Schwann cells (SCs) from adult human peripheral nerve, together with biomaterials development, have made the construction of unique grafts with defined properties possible. We have utilized PAN/PVC guidance channels to form solid human SC grafts which can be transplanted either with or without the channel. We studied the ability of grafts placed with and without channels to support regeneration and to influence functional recovery; characteristics of the graft and host/graft interface were also compared. The T9-T10 spinal cord of nude rats was resected and a graft was placed across the gap; methylprednisolone was delivered acutely to decrease secondary injury. Channels minimized the immigration of connective tissue into grafts but contributed to some necrotic tissue loss, especially in the distal spinal cord. Grafts without channels contained more myelinated axons (x = 2129 +/- 785) vs (x = 1442 +/- 514) and were larger in cross-sectional area ( x = 1.53 +/- 0.24 mm2) vs (x = 0.95 +/- 0.86 mm2). The interfaces formed between the host spinal cord and the grafts placed without channels were highly interdigitated and resembled CNS-PNS transition zones; chondroitin sulfate proteoglycans was deposited there. Whereas several neuronal populations including propriospinal, sensory, motoneuronal, and brainstem neurons regenerated into human SC grafts, only propriospinal and sensory neurons were observed to reenter the host spinal cord. Using combinations of anterograde and retrograde tracers, we observed regeneration of propriospinal neurons up to 2.6 mm beyond grafts. We estimate that 1% of the fibers that enter grafts reenter the host spinal cord by 45 days after grafting. Following retrograde tracing from the distal spinal cord, more labeled neurons were unexpectedly found in the region of the dextran amine anterograde tracer injection site where a marked inflammatory reaction had occurred. Animals with bridging grafts obtained modestly higher scores during open field [(x = 8.2 +/- 0.35) vs (x = 6.8 +/- 0.42), P = 0.02] and inclined plane testing (x = 38.6 +/- 0. 542) vs (x = 36.3 +/- 0.53), P = 0.006] than animals with similar grafts in distally capped channels. In summary, this study showed that in the nude rat given methylprednisolone in combination with human SC grafts, some regenerative growth occurred beyond the graft and a modest improvement in function was observed.

Gait analysis of adult paraplegic rats after spinal cord repair

This study presents a novel detailed method of analysis of rat gait and uses this method to demonstrate recovery of forward locomotion patterns in adult rats made paraplegic by surgical spinal cord transection and subjected to a novel strategy for spinal cord repair. Six normal rats were compared to five animals in which the cord was transected at T8-T9, and a 5-mm segment of the spinal cord removed, and to seven animals in which, following spinal cord transection and removal of a spinal cord segment, multiple intercostal peripheral nerve bridges were implanted, rerouting pathways from white to gray matter in both directions. The implanted area was filled with fibrin glue containing acidic fibroblast growth factor. Details of the repair strategy have been published (H. Cheng, Y. Cao, and L. Olson, 1996, Science 273: 510-513). Gait analysis was carried out 3 and 4 months after surgery and once in the normal animals. Animals were allowed to walk across a runway with a transparent floor. Each test consisted of five trials, and each trial was videorecorded from underneath. Using frame-by-frame playback, individual footprints were then recorded regarding location and order of limb use, as well as step quality (degree of weight bearing, etc.). These data allowed measuring runway transit time, five different measures of step numbers, all possible temporal patterns of limb use, stride length, and base of support. Transected controls remained paralyzed in the hindlimbs with only occasional reflex hindlimb movements without weight bearing. Animals subjected to the full repair procedure were significantly faster than the controls, used their hindlimbs for 25-30% of the movements, and regained several of the specific limb recruitment patterns used by normal rats. Taken together, the gait analysis data demonstrate remarkable recovery of coordinated gait in the repaired animals, which was significantly better than controls for all relevant parameters, while at the same time clearly inferior to normal rats for most of the examined parameters. We conclude that normal rats use a multitude of interchangeable step sequence patterns, and that our spinal cord repair strategy leads to recovery of some of these patterns following complete spinal cord transection. These data suggest functionally relevant neuronal communication across the lesion.