Compensatory locomotor adjustments of rats with cervical or thoracic spinal cord hemisections

Spinal control of locomotion before and after spinal cord injury

Thoracic spinal cord injury affects long propriospinal neurons that interconnect the cervical and lumbar enlargements. These neurons are crucial for coordinating forelimb and hindlimb locomotor movements in a speed-dependent manner. However, recovery from spinal cord injury is usually studied over a very limited range of speeds that may not fully expose circuitry dysfunction. To overcome this limitation, we investigated overground locomotion in rats trained to move over an extended distance with a wide range of speeds both pre-injury and after recovery from thoracic hemisection or contusion injuries. In this experimental context, intact rats expressed a speed-dependent continuum of alternating (walk and trot) and non-alternating (canter, gallop, half-bound gallop, and bound) gaits. After a lateral hemisection injury, rats recovered the ability to locomote over a wide range of speeds but lost the ability to use the highest-speed gaits (half-bound gallop and bound) and predominantly used the limb contralateral to the injury as lead during canter and gallop. A moderate contusion injury caused a greater reduction in maximal speed, loss of all non-alternating gaits, and emergence of novel alternating gaits. These changes resulted from weak fore-hind coupling together with appropriate control of left-right alternation. After hemisection, animals expressed a subset of intact gaits with appropriate interlimb coordination even on the side of the injury, where the long propriospinal connections were severed. These observations highlight how investigating locomotion over the full range of speeds can reveal otherwise hidden aspects of spinal locomotor control and post-injury recovery.

Spinal control of locomotion before and after spinal cord injury

Thoracic spinal cord injury affects long propriospinal neurons that interconnect the cervical and lumbar enlargements. These neurons are crucial for coordinating forelimb and hindlimb movements in a speed-dependent manner. At the same time, recovery from spinal cord injury is usually studied over a very limited range of speeds. To overcome this limitation, we investigated overground locomotion in rats over the full range of speeds pre-injury and after recovery from thoracic hemisection or contusion injuries. Intact rats expressed a speed-dependent continuum of alternating (walk and trot) and non-alternating (canter, gallop, half-bound gallop, and bound) gaits. After a lateral hemisection injury, rats recovered the ability to locomote over a wide range of speeds but lost the ability to move using the highest-speed gaits (half-bound gallop and bound) and predominantly used the limb contralateral to injury as lead during canter and gallop. A moderate contusion injury resulted in a greater reduction in maximal speed, loss of non-alternating gaits, and emergence of novel alternating gaits. Analysis of the gait structure in phase space and the variability of limb coupling suggests substantial reorganization of intraspinal pathways mediating interlimb coordination following recovery of locomotion after lateral hemisection or midline contusion injuries. This reorganization appears as an increased reliance on local enlargement circuitry and suggests that speed-dependent gait changes in the forelimbs rely on ascending information from the lumbar circuitry that is impaired post-injury. These observations highlight how investigating the full repertoire of locomotor speeds can reveal otherwise hidden aspects of spinal circuitry and post-injury reorganization.

Ultrasonographic assessment of skeletal muscles after experimentally induced neurogenic inflammation (facet injury) in rats

This study set out to examine ultrasonographic attributes of non-neurosegmentally (pectoral-forelimb) and neurosegmentally linked (hindlimb) myotomes in an experimental model that leads to neurogenic inflammation in segmentally linked myotomes, and to evaluate quantitative correlations among ultrasonographic attributes of the muscles, relative content of various inflammatory mediators, and nociceptive thresholds (hot and mechanical) in rats. Twelve male Wistar Kyoto rats were randomly divided into two equinumerous groups: surgery group, in which the left lumbar (L4-L6) facet joints were compressed for 3 min with modified Kelly forceps under general anesthesia, and sham-operated rats. All ultrasonograms were obtained with the Vevo 2100 Visual Sonic scanner connected to a 24-MHz transducer at four different time points: pre-surgery and 7, 14, and 21 days after surgical procedures. Digital ultrasonographic images of quadriceps femoris, hamstring, and pectoral-brachial muscle groups were analyzed using a polygonal meter region of interest placed on the largest cross-sectional area of the muscles displayed in Image ProPlus^® analytical software to compute numerical pixel values and pixel heterogeneity (standard deviation of mean pixel values). On day 21, pain behavior tests (hot plate and von Frey) were performed and then all animals were euthanized. Protein expression of inflammatory mediators in biceps brachii and rectus femoris muscles was measured by Western blot. The most prominent differences in muscle echotextural attributes between the two subsets of rats occurred 14 days post-surgery in pectoral-brachial and quadriceps femoris muscles. The expression of calcitonin-gene-related peptide was directly related to both echotextural variables only in biceps brachii (pixel intensity: r = 0.65, P = 0.02; and heterogeneity: r = 0.66, P = 0.02, respectively). Our findings have revealed the occurrence of echotextural changes in skeletal muscles of rats during myositis; however, the accumulation of inflammatory mediators and the outcomes of sensory tests did not relate to the changes in first-order echotextural characteristics of affected hindlimb muscles.

Phenotypes of Motor Deficit and Pain after Experimental Spinal Cord Injury

Motor disability is a common outcome of spinal cord injury (SCI). The recovery of motor function after injury depends on the severity of neurotrauma; motor deficit can be reversible, at least partially, due to the innate tissue capability to recover, which, however, deteriorates with age. Pain is often a comorbidity of injury, although its prediction remains poor. It is largely unknown whether pain can attend motor dysfunction. Here, we implemented SCI for modelling severe and moderate neurotrauma and monitored SCI rats for up to 5 months post-injury to determine the profiles of both motor deficit and nociceptive sensitivity. Our data showed that motor dysfunction remained persistent after a moderate SCI in older animals (5-month-old); however, there were two populations among young SCI rats (1 month-old) whose motor deficit either declined or exacerbated even more over 4–5 weeks after identical injury. All young SCI rats displayed changed nociceptive sensitivity in thermal and mechanical modalities. The regression analysis of the changes revealed a population trend with respect to hyper- or hyposensitivity/motor deficit. Together, our data describe the phenotypes of motor deficit and pain, the two severe complications of neurotrauma. Our findings also suggest the predictability of motor dysfunction and pain syndromes following SCI that can be a hallmark for long-term rehabilitation and recovery after injury.

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

Humans, primates, and rodents with cervical spinal cord injury (SCI) show permanent sensorimotor dysfunction of the upper/forelimb as consequence of axonal damage and local neuronal death. This work aimed at characterizing a model of cervical SCI in domestic pigs in which hemisection with excision of 1 cm of spinal cord was performed to reproduce the loss of neural tissue observed in human neuropathology. Posture and motor control were assessed over 3 months by scales and kinematics of treadmill locomotion. Histological measurements included lesion length, atrophy of the adjacent spinal cord segments, and neuronal death. In some animals, the retrograde neural tracer aminostilbamidine was injected in segments caudal to the lesion to visualize propriospinal projection neurons. Neuronal loss extended for 4-6 mm from the lesion borders and was more severe in the ipsilateral, caudal spinal cord stump. Axonal Wallerian degeneration was observed caudally and rostrally, associated with marked atrophy of the white matter in the spinal cord segments adjacent to the lesion. The pigs showed chronic monoplegia or severe monoparesis of the foreleg ipsilateral to the lesion, whereas the trunk and the other legs had postural and motor impairments that substantially improved during the first month post-lesion. Adaptations of the walking cycle such as those reported for rats and humans ameliorated the negative impact of focal neurological deficits on locomotor performance. These results provide a baseline of behavior and histology in a porcine model of cervical spinal cord hemisection that can be used for translational research in SCI therapeutics.

The Gigantocellular Reticular Nucleus Plays a Significant Role in Locomotor Recovery after Incomplete Spinal Cord Injury

Traditionally, the brainstem has been seen as hardwired and poorly capable of plastic adaptations following spinal cord injury (SCI). Data acquired over the past decades, however, suggest differently: following SCI in various animal models (lamprey, chick, rodents, nonhuman primates), different forms of spontaneous anatomic plasticity of reticulospinal projections, many of them originating from the gigantocellular reticular nucleus (NRG), have been observed. In line with these anatomic observations, animals and humans with incomplete SCI often show various degrees of spontaneous motor recovery of hindlimb/leg function. Here, we investigated the functional relevance of two different modes of reticulospinal fiber growth after cervical hemisection, local rewiring of axotomized projections at the lesion site versus compensatory outgrowth of spared axons, using projection-specific, adeno-associated virus-mediated chemogenetic neuronal silencing. Detailed assessment of joint movements and limb kinetics during overground locomotion in female adult rats showed that locally rewired as well as compensatory NRG fibers were responsible for different aspects of recovered forelimb and hindlimb functions (i.e., stability, strength, coordination, speed, or timing). During walking and swimming, both locally rewired as well as compensatory NRG plasticity were crucial for recovered function, while the contribution of locally rewired NRG plasticity to wading performance was limited. Our data demonstrate comprehensively that locally rewired as well as compensatory plasticity of reticulospinal axons functionally contribute to the observed spontaneous improvement of stepping performance after incomplete SCI and are at least partially causative to the observed recovery of function, which can also be observed in human patients with spinal hemisection lesions.SIGNIFICANCE STATEMENT Following unilateral hemisection of the spinal cord, reticulospinal projections are destroyed on the injured side, resulting in impaired locomotion. Over time, a high degree of recovery can be observed in lesioned animals, like in human hemicord patients. In the rat, recovery is accompanied by pronounced spontaneous plasticity of axotomized and spared reticulospinal axons. We demonstrate the causative relevance of locally rewired as well as compensatory reticulospinal plasticity for the recovery of locomotor functions following spinal hemisection, using chemogenetic tools to selectively silence newly formed connections in behaviorally recovered animals. Moving from a correlative to a causative understanding of the role of neuroanatomical plasticity for functional recovery is fundamental for successful translation of treatment approaches from experimental studies to the clinics.

Repression of the Glucocorticoid Receptor Increases Hypoxic-Ischemic Brain Injury in the Male Neonatal Rat

Hypoxic-ischemic encephalopathy (HIE) resulting from asphyxia is the most common cause of neonatal brain damage and results in significant neurological sequelae, including cerebral palsy. The current therapeutic interventions are extremely limited in improving neonatal outcomes. The present study tests the hypothesis that the suppression of endogenous glucocorticoid receptors (GRs) in the brain increases hypoxic-ischemic (HI) induced neonatal brain injury and worsens neurobehavioral outcomes through the promotion of increased inflammation. A mild HI treatment of P9 rat pups with ligation of the right common carotid artery followed by the treatment of 8% O₂ for 60 min produced more significant brain injury with larger infarct size in female than male pups. Intracerebroventricular injection of GR siRNAs significantly reduced GR protein and mRNA abundance in the neonatal brain. Knockdown of endogenous brain GRs significantly increased brain infarct size after HI injury in male, but not female, rat pups. Moreover, GR repression resulted in a significant increase in inflammatory cytokines TNF-α and IL-10 at 6 h after HI injury in male pups. Male pups treated with GR siRNAs showed a significantly worsened reflex response and exhibited significant gait disturbances. The present study demonstrates that endogenous brain GRs play an important role in protecting the neonatal brain from HI induced injury in male pups, and suggests a potential role of glucocorticoids in sex differential treatment of HIE in the neonate.

Development of a Novel Gait Analysis Tool Measuring Center of Pressure for Evaluation of Canine Chronic Thoracolumbar Spinal Cord Injury

Gait evaluation after spinal cord injury (SCI) is an important component of determining functional status. Analysis of center of pressure (COP) provides a dynamic reflection of global locomotion and postural control and has been used to quantify various gait abnormalities. We hypothesized that COP variability would be greater for SCI versus normal dogs and that COP would be able to differentiate varying injury severity. Our objective was to investigate COP, COP variability, and body weight support percentage in dogs with chronic SCI. Eleven chronically non-ambulatory dogs after acute severe thoracolumbar SCI were enrolled. COP measurements in x (right-to-left, COPx) and y (craniocaudal, COPy) directions were captured while dogs walked on a pressure-sensitive treadmill with pelvic limb sling support. Root mean square values (RMS_COPx and RMS_COPy) were calculated to assess variability in COP. Body weight support percentage was measured using a load cell. Gait also was quantified using an open field scale (OFS) and treadmill-based stepping and coordination scores (SS, RI). Mean COPx, COPy, RMS_COPx, and RMS_COPy were compared between dogs with SCI and previously evaluated healthy controls. RMS measurements and support percentage were compared with standard gait scales (OFS, SS, RI). Mean COPy was more cranial and RMS_COPx and RMS_COPy were greater in SCI versus normal dogs (p < 0.001). Support percentage moderately correlated with SS (p = 0.019; R² = 0.47). COP analysis and body weight support measurements offer information about post-injury locomotion. Further development is needed before consideration as an outcome measure to complement validated gait analysis methods in dogs with SCI.

Riluzole promotes neurological function recovery and inhibits damage extension in rats following spinal cord injury: a meta-analysis and systematic review

Spinal cord injury (SCI) is a devastating condition that has few treatment options. Riluzole, a sodium channel blocker used to treat amyotrophic lateral sclerosis, has been initially trialed in human SCI. We performed a systematic review to critically assess the efficacy of riluzole in locomotor recovery and damage extension in SCI rat models, and the potential for clinical translation. PubMed, Embase, Cochrane Library, and Chinese databases were searched from their inception date to March 2018. Two reviewers independently selected animal studies that evaluated neurological recovery and lesion area following riluzole treatment in SCI rat models, extracted data and assessed methodological quality. Pairwise meta-analysis, subgroup analysis, and network meta-analysis were performed to assess the effects of riluzole on SCI. Ten eligible studies were included. Two studies had high methodological quality. Overall, the Basso, Beattie, and Bresnahan scores were increased in riluzole-treated animals versus controls, and effect sizes showed a gradual increase from the 1st (five studies, n = 104, mean difference = 1.24, 95% CI = 0.11 to 2.37, p = 0.03) to 6th week after treatment (five studies, n = 120, mean difference = 2.34, 95% CI = 1.26 to 3.42, p < 0.0001). Riluzole was associated with improved outcomes in the inclined plane test and the tissue preservation area. Subgroup analyses suggested an association of locomotor recovery with riluzole dose. Network meta-analysis showed that 5 mg/kg riluzole exhibited greater protection than 2.5 and 8 mg/kg riluzole. Collectively, this review suggests that riluzole has a protective effect on SCI, with good safety and a clear mechanism of action and may be suitable for future clinical trials or applications. However, animal results should be interpreted with caution given the known limitations in animal experimental design and methodological quality.

Kinematic and kinetic gait analysis to evaluate functional recovery in thoracic spinal cord injured rats

The recovery of walking function following spinal cord injury (SCI) is of major importance to patients and clinicians. In experimental SCI studies, a rat model is widely used to assess walking function, following thoracic spinal cord lesion. In an effort to provide a resource which investigators can refer to when seeking the most appropriate functional assay, the authors have compiled and categorized the behavioral assessments used to measure the deficits and recovery of the gait in thoracic SCI rats. These categories include kinematic and kinetic measurements. Within this categorization, we discuss the advantages and disadvantages of each type of measurement. The present review includes the type of outcome data that they produce, the technical difficulty and the time required to potentially train the animals to perform them, and the need for expensive or highly specialized equipment. The use of multiple kinematic and kinetic parameters is recommended to identify subtle deficits and processes involved in the compensatory mechanisms of walking function after experimental thoracic SCI in rats.

Fitting unanchored puzzle pieces in the skeleton: appropriate 3D scapular positions for the quadrupedal support in tetrapods

Deducing the scapular positions of extinct tetrapod skeletons remains difficult, because the scapulae and rib cage are connected with each other not directly by skeletal joint, but by thoracic muscles. In extant non-testudine quadrupedal tetrapods, the top positions of the scapulae/suprascapulae occur at the anterior portion of the rib cage, above the vertebral column and near the median plane. The adequacy of this position was tested using three-dimensional mechanical models of Felis, Rattus and Chamaeleo that assumed stances on a forelimb on a single side and the hindlimbs. The net moment about the acetabulum generated by the gravity force and the contractive forces of the anti-gravity thoracic muscles, and the resistance of the rib to vertical compression between the downward gravity and upward lifting force from the anti-gravity thoracic muscle depend on the scapular position. The scapular position common among quadrupeds corresponds to the place at which the roll and yaw moments of the uplifted portion of the body are negligible, where the pitch moment is large enough to lift the body, and above the ribs having high strength against vertical compression. These relationships between scapular position and rib cage morphology should allow reliable reconstruction of limb postures of extinct taxa.

Reversible silencing of lumbar spinal interneurons unmasks a task-specific network for securing hindlimb alternation

Neural circuitry in the lumbar spinal cord governs two principal features of locomotion, rhythm and pattern, which reflect intra- and interlimb movement. These features are functionally organized into a hierarchy that precisely controls stepping in a stereotypic, speed-dependent fashion. Here, we show that a specific component of the locomotor pattern can be independently manipulated. Silencing spinal L2 interneurons that project to L5 selectively disrupts hindlimb alternation allowing a continuum of walking to hopping to emerge from the otherwise intact network. This perturbation, which is independent of speed and occurs spontaneously with each step, does not disrupt multi-joint movements or forelimb alternation, nor does it translate to a non-weight-bearing locomotor activity. Both the underlying rhythm and the usual relationship between speed and spatiotemporal characteristics of stepping persist. These data illustrate that hindlimb alternation can be manipulated independently from other core features of stepping, revealing a striking freedom in an otherwise precisely controlled system.

Intra- and interlimb coordination during locomotion is governed by hierarchically organized lumbar spinal networks. Here, the authors show that reversible silencing of spinal L2–L5 interneurons specifically disrupts hindlimb alternation leading to a continuum of walking to hopping.

Constraints on Stance-Phase Force Production during Overground Walking in Persons with Chronic Incomplete Spinal Cord Injury

Persons with incomplete spinal cord injury (iSCI) face ongoing struggles with walking, including reduced speed and increased reliance on assistive devices (ADs). The forces underlying body weight support and gait, as measured by ground reaction forces (GRFs), are likely altered after iSCI because of weakness and AD dependence but have not been studied. The purpose of this study was to examine GRF production during overground walking after iSCI, because greater insight into GRF constraints is important for refining therapeutic interventions. Because of reduced and discoordinated motor output after iSCI, we hypothesized that persons with iSCI would exert smaller GRFs and altered GRF modifications to increased cadence compared with able-bodied (AB) persons, especially when using an AD. Fifteen persons with chronic iSCI, stratified into no AD (n = 7) and AD (n = 8) groups, walked across an instrumented walkway at self-selected and fast (115% self-selected) cadences. Fifteen age-matched AB controls walked at their own cadences and iSCI-matched conditions (cadence and AD). Results showed fore-aft GRFs are reduced in persons with iSCI compared with AB controls, with reductions greatest in persons dependent on an AD. When controlling for cadence and AD, propulsive forces were still lower in persons with iSCI. Compared with AB controls, persons with iSCI demonstrated altered GRF modifications to increased cadence. Persons with iSCI exhibit different stance-phase forces compared with AB controls, which are impacted further by AD use and slower walking speed. Minimizing AD use and/or providing propulsive biofeedback during walking could enhance GRF production after iSCI.

Opposite, bidirectional shifts in excitation and inhibition in specific types of dorsal horn interneurons are associated with spasticity and pain post-SCI

Spasticity, a common complication after spinal cord injury (SCI), is frequently accompanied by chronic pain. The physiological origin of this pain (critical to its treatment) remains unknown, although spastic motor dysfunction has been related to the hyperexcitability of motoneurons and to changes in spinal sensory processing. Here we show that the pain mechanism involves changes in sensory circuits of the dorsal horn (DH) where nociceptive inputs integrate for pain processing. Spasticity is associated with the DH hyperexcitability resulting from an increase in excitation and disinhibition occurring in two respective types of sensory interneurons. In the tonic-firing inhibitory lamina II interneurons, glutamatergic drive was reduced while glycinergic inhibition was potentiated. In contrast, excitatory drive was boosted to the adapting-firing excitatory lamina II interneurons while GABAergic and glycinergic inhibition were reduced. Thus, increased activity of excitatory DH interneurons coupled with the reduced excitability of inhibitory DH interneurons post-SCI could provide a neurophysiological mechanism of central sensitization and chronic pain associated with spasticity.

Rodent, large animal and non-human primate models of spinal cord injury

In this narrative review we aimed to assess the usefulness of the different animal models in identifying injury mechanisms and developing therapies for humans suffering from spinal cord injury (SCI). Results obtained from rodent studies are useful but, due to the anatomical, molecular and functional differences, confirmation of these findings in large animals or non-human primates may lead to basic discoveries that cannot be made in rodent models and that are more useful for developing treatment strategies in humans. SCI in dogs can be considered as intermediate between rodent models and human clinical trials, but the primate models could help to develop appropriate methods that might be more relevant to humans. Ideally, an animal model should meet the requirements of availability and repeatability as well as reproduce the anatomical features and the clinical pathological changing process of SCI. An animal model that completely simulates SCI in humans does not exist. The different experimental models of SCI have advantages and disadvantages for investigating the different aspects of lesion development, recovery mechanisms and potential therapeutic interventions. The potential advantages of non-human primate models include genetic similarities, similar caliber/length of the spinal cord as well as biological and physiological responses to injury which are more similar to humans. Among the potential disadvantages, high operating costs, infrastructural requirements and ethical concerns should be considered. The translation from experimental repair strategies to clinical applications needs to be investigated in future carefully designed studies.

Comparative outcome measures in peripheral regeneration studies

Traumatic peripheral nerve injuries are common and often result in partial or permanent paralysis, numbness of the affected limb, and debilitating neuropathic pain. Experimental animal models of nerve injury have utilized a diversity of outcome measures to examine functional recovery following injury. Four primary categories of outcome measures of regenerative success including retrograde labeling with counts of regenerating neurons, immunohistochemistry and histomorphometry, reinnervation of target muscles, and behavioral analysis of recovery will be reviewed. Validity of different outcome measures are discussed in context of hindlimb, forelimb, and facial nerve injury models. Severity of nerve injury will be highlighted, and comparisons between nerve crush injury and more severe transection and neuroma-in-continuity nerve injury paradigms will be evaluated. The case is made that specific outcome measures may be more sensitive to assessing functional recovery following nerve injury than others. This will be discussed in the context of the lack of association between certain outcome measures of nerve regeneration. Examples of inaccurate conclusions from specific outcome measures will also be considered. Overall, researchers must therefore take care to select appropriate outcome measures for animal nerve injury studies dependant on the specific experimental interventions and scientific questions addressed.

A simplified method of walking track analysis to assess short-term locomotor recovery after acute spinal cord injury caused by thoracolumbar intervertebral disc extrusion in dogs

The purpose of this study was to evaluate a simplified method of walking track analysis to assess treatment outcome in canine spinal cord injury. Measurements of stride length (SL) and base of support (BS) were made using a 'finger painting' technique for footprint analysis in all limbs of 20 normal dogs and 27 dogs with 28 episodes of acute thoracolumbar spinal cord injury (SCI) caused by spontaneous intervertebral disc extrusion. Measurements were determined at three separate time points in normal dogs and on days 3, 10 and 30 following decompressive surgery in dogs with SCI. Values for SL, BS and coefficient of variance (COV) for each parameter were compared between groups at each time point. Mean SL was significantly shorter in all four limbs of SCI-affected dogs at days 3, 10, and 30 compared to normal dogs. SL gradually increased toward normal in the 30 days following surgery. As measured by this technique, the COV-SL was significantly higher in SCI-affected dogs than normal dogs in both thoracic limbs (TL) and pelvic limbs (PL) only at day 3 after surgery. BS-TL was significantly wider in SCI-affected dogs at days 3, 10 and 30 following surgery compared to normal dogs. These findings support the use of footprint parameters to compare locomotor differences between normal and SCI-affected dogs, and to assess recovery from SCI. Additionally, our results underscore important changes in TL locomotion in thoracolumbar SCI-affected dogs.

Thoracic Hemisection in Rats Results in Initial Recovery Followed by a Late Decrement in Locomotor Movements, with Changes in Coordination Correlated with Serotonergic Innervation of the Ventral Horn

Lateral thoracic hemisection of the rodent spinal cord is a popular model of spinal cord injury, in which the effects of various treatments, designed to encourage locomotor recovery, are tested. Nevertheless, there are still inconsistencies in the literature concerning the details of spontaneous locomotor recovery after such lesions, and there is a lack of data concerning the quality of locomotion over a long time span after the lesion. In this study, we aimed to address some of these issues. In our experiments, locomotor recovery was assessed using EMG and CatWalk recordings and analysis. Our results showed that after hemisection there was paralysis in both hindlimbs, followed by a substantial recovery of locomotor movements, but even at the peak of recovery, which occurred about 4 weeks after the lesion, some deficits of locomotion remained present. The parameters that were abnormal included abduction, interlimb coordination and speed of locomotion. Locomotor performance was stable for several weeks, but about 3-4 months after hemisection secondary locomotor impairment was observed with changes in parameters, such as speed of locomotion, interlimb coordination, base of hindlimb support, hindlimb abduction and relative foot print distance. Histological analysis of serotonergic innervation at the lumbar ventral horn below hemisection revealed a limited restoration of serotonergic fibers on the ipsilateral side of the spinal cord, while on the contralateral side of the spinal cord it returned to normal. In addition, the length of these fibers on both sides of the spinal cord correlated with inter- and intralimb coordination. In contrast to data reported in the literature, our results show there is not full locomotor recovery after spinal cord hemisection. Secondary deterioration of certain locomotor functions occurs with time in hemisected rats, and locomotor recovery appears partly associated with reinnervation of spinal circuitry by serotonergic fibers.

Protein-Energy Malnutrition Causes Deficits in Motor Function in Adult Male Rats

BACKGROUND

Adult protein-energy malnutrition (PEM) often occurs in combination with neurological disorders affecting hand use and walking ability. The independent effects of PEM on motor function are not well characterized and may be obscured by these comorbidities.

OBJECTIVE

Our goal was to undertake a comprehensive evaluation of sensorimotor function with the onset and progression of PEM in an adult male rat model.

METHODS

In Expt. 1 and Expt. 2, male Sprague-Dawley rats (14-15 wk old) were assigned ad libitum access for 4 wk to normal-protein (NP) or low-protein (LP) diets containing 12.5% and 0.5% protein, respectively. Expt. 1 assessed muscle strength, balance, and skilled walking ability on days 2, 8, and 27 by bar-holding, cylinder, and horizontal ladder walking tasks, respectively. In addition to food intake and body weight, nutritional status was determined on days 3, 9, and 28 by serum acute-phase reactant and corticosterone concentrations and liver lipids. Expt. 2 addressed the effect of an LP diet on hindlimb muscle size.

RESULTS

PEM evolved over time in rats consuming the LP diet. Total food intake decreased by 24% compared with the NP group. On day 28, body weight and serum albumin decreased by 31% and 26%, respectively, and serum α2-macroglobulin increased by 445% (P < 0.05) in the LP group compared with the NP group. Forelimb dysfunction (173% increase in adaptive flexed-arm-hang score) developed on day 2 in rats fed the LP diet (P < 0.001), whereas abnormal walking (34% decreased incidence of correct hindlimb placement) developed by day 27 (P < 0.05). Relative to the NP diet, the LP diet reduced the cross-sectional area of gastrocnemius medialis (P < 0.05).

CONCLUSIONS

PEM in adult male rats causes a variety of sensorimotor abnormalities that develop at different stages of malnutrition. This model can be used in combination with disease models of sensorimotor deficits to examine the interactions between nutritional status, other treatments, and disease progression.

Stress exacerbates neuron loss and microglia proliferation in a rat model of excitotoxic lower motor neuron injury

All individuals experience stress and hormones (e.g., glucocorticoids/GCs) released during stressful events can affect the structure and function of neurons. These effects of stress are best characterized for brain neurons; however, the mechanisms controlling the expression and binding affinity of glucocorticoid receptors in the spinal cord are different than those in the brain. Accordingly, whether stress exerts unique effects on spinal cord neurons, especially in the context of pathology, is unknown. Using a controlled model of focal excitotoxic lower motor neuron injury in rats, we examined the effects of acute or chronic variable stress on spinal cord motor neuron survival and glial activation. New data indicate that stress exacerbates excitotoxic spinal cord motor neuron loss and associated activation of microglia. In contrast, hypertrophy and hyperplasia of astrocytes and NG2+ glia were unaffected or were modestly suppressed by stress. Although excitotoxic lesions cause significant motor neuron loss and stress exacerbates this pathology, overt functional impairment did not develop in the relevant forelimb up to one week post-lesion. These data indicate that stress is a disease-modifying factor capable of altering neuron and glial responses to pathological challenges in the spinal cord.

Bridging the gap: a reticulo-propriospinal detour bypassing an incomplete spinal cord injury

Anatomically incomplete spinal cord injuries are often followed by considerable functional recovery in patients and animal models, largely because of processes of neuronal plasticity. In contrast to the corticospinal system, where sprouting of fibers and rearrangements of circuits in response to lesions have been well studied, structural adaptations within descending brainstem pathways and intraspinal networks are poorly investigated, despite the recognized physiological significance of these systems across species. In the present study, spontaneous neuroanatomical plasticity of severed bulbospinal systems and propriospinal neurons was investigated following unilateral C4 spinal hemisection in adult rats. Injection of retrograde tracer into the ipsilesional segments C3-C4 revealed a specific increase in the projection from the ipsilesional gigantocellular reticular nucleus in response to the injury. Substantial regenerative fiber sprouting of reticulospinal axons above the injury site was demonstrated by anterograde tracing. Regrowing reticulospinal fibers exhibited excitatory, vGLUT2-positive varicosities, indicating their synaptic integration into spinal networks. Reticulospinal fibers formed close appositions onto descending, double-midline crossing C3-C4 propriospinal neurons, which crossed the lesion site in the intact half of the spinal cord and recrossed to the denervated cervical hemicord below the injury. These propriospinal projections around the lesion were significantly enhanced after injury. Our results suggest that severed reticulospinal fibers, which are part of the phylogenetically oldest motor command system, spontaneously arborize and form contacts onto a plastic propriospinal relay, thereby bypassing the lesion. These rearrangements were accompanied by substantial locomotor recovery, implying a potential physiological relevance of the detour in restoration of motor function after spinal injury.

Gait impairment in a rat model of focal cerebral ischemia

The availability of proper tests for gait evaluation following cerebral ischemia in rats has been limited. The automated, quantitative CatWalk system, which was initially designed to measure gait in models of spinal cord injury, neuropathic pain, and peripheral nerve injury, is said to be a useful tool for the study of motor impairment in stroke animals. Here we report our experiences of using CatWalk XT with rats subjected to transient middle cerebral artery occlusion (MCAO), during their six-week followup. Large corticostriatal infarct was confirmed by MRI in all MCAO rats, which was associated with severe sensorimotor impairment. In contrast, the gait impairment was at most mild, which is consistent with seemingly normal locomotion of MCAO rats. Many of the gait parameters were affected by body weight, walking speed, and motivation despite the use of a goal box. In addition, MCAO rats showed bilateral compensation, which was developed to stabilize proper locomotion. All of these interferences may confound the data interpretation. Taken together, the translational applicability of CatWalk XT in evaluating motor impairment and treatment efficacy remains to be limited at least in rats with severe corticostriatal infarct and loss of body weight.

Dynamic motor compensations with permanent, focal loss of forelimb force after cervical spinal cord injury

Incomplete cervical lesion is the most common type of human spinal cord injury (SCI) and causes permanent paresis of arm muscles, a phenomenon still incompletely understood in physiopathological and neuroanatomical terms. We performed spinal cord hemisection in adult rats at the caudal part of the segment C6, just rostral to the bulk of triceps brachii motoneurons, and analyzed the forces and kinematics of locomotion up to 4 months postlesion to determine the nature of motor function loss and recovery. A dramatic (50%), immediate and permanent loss of extensor force occurred in the forelimb but not in the hind limb of the injured side, accompanied by elbow and wrist kinematic impairments and early adaptations of whole-body movements that initially compensated the balance but changed continuously over the follow-up period to allow effective locomotion. Overuse of both contralateral legs and ipsilateral hind leg was evidenced since 5 days postlesion. Ipsilateral foreleg deficits resulted mainly from interruption of axons that innervate the spinal cord segments caudal to the lesion, because chronic loss (about 35%) of synapses was detected at C7 while only 14% of triceps braquii motoneurons died, as assessed by synaptophysin immunohistochemistry and retrograde neural tracing, respectively. We also found a large pool of propriospinal neurons projecting from C2-C5 to C7 in normal rats, with topographical features similar to the propriospinal premotoneuronal system of cats and primates. Thus, concurrent axotomy at C6 of brain descending axons and cervical propriospinal axons likely hampered spontaneous recovery of the focal neurological impairments.

Changes in forelimb-hindlimb coordination after partial spinal lesions of different extent in the rat

Forelimb-hindlimb coordination in adult rats moving freely along 2m long runway was investigated using the method of footprint recording. Rats were divided into 3 groups with different extent of spinal lesions (T(9)). Before surgery rats moved with a mean locomotor speed of 73±20 to 96±18cms(-1), stride lengths of 17.5±2.0 to 21.2±2.0cm, and trot like coordination. Early after surgery the locomotor speed and the stride lengths were decreased. The forelimb steps were shorter than hindlimb steps, which led to the occurrence of unpaired forelimb steps. Unpaired steps occurred when the hind paw print lay more than half the hindlimb stride length in front of the ipsilateral paw. The number of unpaired steps was negatively correlated with the difference between the fore- and hindlimb step lengths. The recovery of locomotor speed, stride length, and step sequence patterns took up to 3.5 months depending on the extent of lesion. In the last testings the coordination was characterized by increased distances between ipsilateral footprints leading to a change from an almost synchronized trot to a lesion-dependent walk. This change was accompanied by a switch from the use of both patterns A and C to the most frequent use of the Aa pattern that is better adapted to maintain the body balance. All locomotor changes depended on the extent of the injury of lateral and ventral funiculi. These results demonstrate that footprint analysis can be used for the evaluation of forelimb-hindlimb coordination after spinal lesion in rats.

Phrenic motor neuron degeneration compromises phrenic axonal circuitry and diaphragm activity in a unilateral cervical contusion model of spinal cord injury

Respiratory dysfunction is the leading cause of morbidity and mortality following traumatic spinal cord injury (SCI). Injuries targeting mid-cervical spinal cord regions affect the phrenic motor neuron pool that innervates the diaphragm, the primary respiratory muscle of inspiration. Contusion-type injury in the cervical spinal cord is one of the most common forms of human SCI; however, few studies have evaluated mid-cervical contusion in animal models or characterized consequent histopathological and functional effects of degeneration of phrenic motor neuron-diaphragm circuitry. In an attempt to target the phrenic motor neuron pool, two unilateral contusion injury paradigms were tested, a single injury at level C4 and a double injury both at levels C3 and C4, and animals were followed for up to 6 weeks post-injury. Both unilateral cervical injury paradigms are reproducible with no mortality or need for breathing assistance, and are accompanied by phrenic motor neuron loss, phrenic nerve axon degeneration, diaphragm atrophy, denervation and subsequent partial reinnervation at the diaphragm neuromuscular junction, changes in spontaneous diaphragm EMG recordings, and reduction in phrenic nerve compound muscle action potential amplitude. These findings demonstrate significant and chronically persistent respiratory compromise following mid-cervical SCI due to phrenic motor neuron degeneration. These injury paradigms and accompanying analyses provide important tools both for understanding mechanisms of phrenic motor neuron and diaphragm pathology following SCI and for evaluating therapeutic strategies in clinically relevant cervical SCI models.

Locomotor behavior of bonnet monkeys after spinal contusion injury: footprint study

Analysis of gait functions following spinal cord injury has been widely studied in rats, mice but limited in primates. This investigation was performed to quantitatively analyze the degree of functional recovery in bipedal locomotion in bonnet monkeys after induced spinal cord contusion. The degree of locomotor recovery was examined by measuring four gait variables, viz., tip of opposite foot (TOF), print-length (PL), toe-spread (TS), and intermediary toe-spread (IT) from the recorded hindlimb prints of monkeys using ink and paper technique. Contusion was induced in spinal cord at T12-L1 level in anaesthetized monkeys by using the Allen's weight drop technique. Postoperatively, all spinal contused animals initially showed a significant decrease in TOF, which then gradually increased for longer duration and attained the near normal values by the sixth month. On the other hand, PL, TS, and IT variables in hindlimb prints of contused animals were found to dramatically increase initially and then slowly decrease subsequently. Later there was a recovery to insignificant levels which differed from the corresponding preoperative values by the fifth month. The observations of this study suggest that the functional contributions of the spared fibers, especially in ventral and ventrolateral funiculi, through collateral sprouts or synaptic plasticity that were formed in the contused spinal cord may be responsible for substantial recovery of hindlimb movements. Moreover, based on analysis of footprint variables observed in locomotion in these subjected monkeys, we understand that spinal automatism and development of responses by afferent stimuli from outside the cord could possibly contribute to recovery of the paralyzed hindlimbs.

The biomechanics of locomotor compensation after peripheral nerve lesion in the rat

Functional recovery in animal models of nervous system disorders commonly involves behavioural compensation, in which animals alter the use of their limbs after injury, making it difficult to distinguish 'true' recovery from substitution of novel movements. The purpose of this study is to investigate how abnormal movements are produced by using biomechanical assessment of limb joint motion, an approach commonly used to diagnose human pathological gait. Rats were trained to cross a runway whilst kinetic (ground reaction forces) and kinematic (limb segment positions) data were synchronously recorded. Inverse dynamic analysis was used to calculate limb joint moments, or torques, and joint mechanical power throughout the stride for major joints of the forelimbs and hindlimbs, both before and after denervation of a major ankle extensor muscle. Before surgery, rats moved with joint moment and power profiles comparable to other quadrupeds, with differences attributable to species variation in limb posture. After surgery, rats trotted asymmetrically, with a near plantigrade stance of the left hindlimb. Surprisingly, ankle joint moments and power were largely preserved, with dramatic reductions in range of motion and joint moments at the proximal joints of the affected limb. Stiffening of the proximal limb compensated for increased compliance at the ankle but decreased the total mechanical work done by the injured limb. In turn, more work was done by the opposite, i.e. uninjured, hindlimb. This is the first study to quantify the biomechanical adjustments made within and between limbs in laboratory rodents after nervous system injury.

Motor deficits and recovery in rats with unilateral spinal cord hemisection mimic the Brown-Sequard syndrome

Cervical incomplete spinal cord injuries often lead to severe and persistent impairments of sensorimotor functions and are clinically the most frequent type of spinal cord injury. Understanding the motor impairments and the possible functional recovery of upper and lower extremities is of great importance. Animal models investigating motor dysfunction following cervical spinal cord injury are rare. We analysed the differential spontaneous recovery of fore- and hindlimb locomotion by detailed kinematic analysis in adult rats with unilateral C4/C5 hemisection, a lesion that leads to the Brown-Séquard syndrome in humans. The results showed disproportionately better performance of hindlimb compared with forelimb locomotion; hindlimb locomotion showed substantial recovery, whereas the ipsilesional forelimb remained in a very poor functional state. Such a differential motor recovery pattern is also known to occur in monkeys and in humans after similar spinal cord lesions. On the lesioned side, cortico-, rubro-, vestibulo- and reticulospinal tracts and the important modulatory serotonergic, dopaminergic and noradrenergic fibre systems were interrupted by the lesion. In an attempt to facilitate locomotion, different monoaminergic agonists were injected intrathecally. Injections of specific serotonergic and noradrenergic agonists in the chronic phase after the spinal cord lesion revealed remarkable, although mostly functionally negative, modulations of particular parameters of hindlimb locomotion. In contrast, forelimb locomotion was mostly unresponsive to these agonists. These results, therefore, show fundamental differences between fore- and hindlimb spinal motor circuitries and their functional dependence on remaining descending inputs and exogenous spinal excitation. Understanding these differences may help to develop future therapeutic strategies to improve upper and lower limb function in patients with incomplete cervical spinal cord injuries.

Characterization of a graded cervical hemicontusion spinal cord injury model in adult male rats

Most experimental models of spinal cord injury (SCI) in rodents induce damage in the thoracic cord and subsequently examine hindlimb function as an indicator of recovery. In these models, functional recovery is most attributable to white-matter preservation and is less influenced by grey-matter sparing. In contrast, most clinical cases of SCI occur at the lower cervical levels, a region in which both grey-matter and white-matter sparing contribute to functional motor recovery. Thus experimental cervical SCI models are beginning to be developed and used to assess protective and pharmacological interventions following SCI. The objective of this study was to characterize a model of graded cervical hemicontusion SCI with regard to several histological and behavioral outcome measures, including novel forelimb behavioral tasks. Using a commercially available rodent spinal cord impactor, adult male rats received hemicontusion SCI at vertebral level C5 at 100, 200, or 300 kdyn force, to produce mild, moderate, or severe injury severities. Tests of skilled and unskilled forelimb and locomotor function were employed to assess functional recovery, and spinal cord tissue was collected to assess lesion severity. Deficits in skilled and unskilled forelimb function and locomotion relating to injury severity were observed, as well as decreases in neuronal numbers, white-matter area, and white-matter gliosis. Significant correlations were observed between behavioral and histological data. Taken together, these data suggest that the forelimb functional and locomotor assessments employed here are sensitive enough to measure functional changes, and that this hemicontusion model can be used to evaluate potential protective and regenerative therapeutic strategies.

Kinematics and ground reaction force determination: a demonstration quantifying locomotor abilities of young adult, middle-aged, and geriatric rats

Behavior, in its broadest definition, can be defined as the motor manifestation of physiologic processes. As such, all behaviors manifest through the motor system. In the fields of neuroscience and orthopedics, locomotion is a commonly evaluated behavior for a variety of disease models. For example, locomotor recovery after traumatic injury to the nervous system is one of the most commonly evaluated behaviors ^1-3. Though locomotion can be evaluated using a variety of endpoint measurements (e.g. time taken to complete a locomotor task, etc), semiquantitative kinematic measures (e.g. ordinal rating scales (e.g. Basso Beattie and Bresnahan locomotor (BBB) rating scale, etc)) and surrogate measures of behaviour (e.g. muscle force, nerve conduction velocity, etc), only kinetics (force measurements) and kinematics (measurements of body segments in space) provide a detailed description of the strategy by which an animal is able to locomote ¹. Though not new, kinematic and kinetic measurements of locomoting rodents is now more readily accessible due to the availability of commercially available equipment designed for this purpose. Importantly, however, experimenters need to be very familiar with theory of biomechanical analyses and understand the benefits and limitations of these forms of analyses prior to embarking on what will become a relatively labor-intensive study. The present paper aims to describe a method for collecting kinematic and ground reaction force data using commercially available equipment. Details of equipment and apparatus set-up, pre-training of animals, inclusion and exclusion criteria of acceptable runs, and methods for collecting the data are described. We illustrate the utility of this behavioral analysis technique by describing the kinematics and kinetics of strain-matched young adult, middle-aged, and geriatric rats.

Cortical hyperexcitability in response to preserved spinothalamic inputs immediately after spinal cord hemisection

Chronic injury of the main somatosensory pathways ascending along the spinal cord - the dorsal columns and the spinothalamic tract - can produce both changes in the organization of cortical somatotopic maps and neuropathic pain. Little is known, however, about the early neurophysiological changes occurring immediately after injury. We bilaterally recorded the neural activity of the hindpaw representation of the primary somatosensory cortex evoked by stimuli delivered to the hindpaws before and immediately after a thoracic spinal cord hemisection in anesthetized rats. This unilateral spinal cord injury allowed us to separately investigate the cortical effects of deafferenting the dorsal column (stimuli ipsilateral to the hemisection) or the spinothalamic tract (stimuli contralateral to the hemisection). The hemisection produced immediate bilateral changes in the cortical responses evoked by stimuli delivered to the hindpaw ipsilateral to the hemisection (deafferented dorsal column): an expected loss of classical short-latency cortical responses, accompanied by an unexpected appearance of long-latency activations. At the population level, these activations reflected a progressive stimulus-induced transition of the hindpaw somatosensory cortex from up-and-down states to a sustained activated state. At the single-cell level, these cortical activations resembled the "wind-up" typically observed - with the same type of stimuli - in the dorsal horn cells originating the spinothalamic tract. Virtually no changes were observed in the responses evoked by stimuli delivered to the hindpaw contralateral to the hemisection (deafferented spinothalamic tract). These results suggest that spinal cord hemisection immediately produces an abnormal hyperexcitability of the primary somatosensory cortex in response to preserved spinothalamic inputs from the hindpaw. This immediate cortical hyperexcitability could be important to understand the long-term development of cortical reorganization and neuropathic pain after incomplete spinal cord lesions.

A new rating scale for open-field evaluation of behavioral recovery after cervical spinal cord injury in rats

The Basso, Beattie, Bresnahan (BBB) locomotor rating scale has proven a reliable tool to evaluate impairments of hindlimb locomotor skills after thoracic spinal cord injury (SCI). With the increasing use of cervical SCI rat models, there is a critical need to develop scoring scales designed to more precisely examine alteration and recovery of forelimb functions. The main goal of the present study was to elaborate and evaluate a new rating scale for open-field testing of the fore- and hindlimb locomotor functions after cervical SCI. We also assessed the effectiveness of this rating scale for discriminating the functional consequences of dorsolateral (Hdl group), lateral (Hl group), or complete C4 unilateral hemisections (Hc group). Our findings show that the new rating scale can be considered as a sensitive and reliable descriptor of the postoperative time course of deficits affecting differentially the fore- and hindlimb sensorimotor functions following injuries of various severities. This new method provides reproducible data and can be used reliably by non-expert examiners. The proposed rating scale appears to be a useful tool for the assessment of various treatments designed to promote functional recovery after SCI. See online Supplementary Material (scoring spreadsheet and videotape recordings) at www.liebertonline.com.

Sensorimotor training promotes functional recovery and somatosensory cortical map reactivation following cervical spinal cord injury

Sensorimotor activity has been shown to play a key role in functional recovery after partial spinal cord injury (SCI). Most studies in rodents have focused on the rehabilitation of hindlimb locomotor functions after thoracic or lumbar SCI, whereas forelimb motor and somatosensory abilities after cervical SCI remain largely uninvestigated, despite the high incidence of such injuries in humans. Moreover, little is known about the neurophysiological substrates of training-induced recovery in supraspinal structures. This study was aimed at evaluating the effects of a training procedure combining both motor and sensory stimulation on behavioral performance and somatosensory cortical map remodeling after cervical (C4-C5) spinal hemisection in rats. This SCI severely impaired both sensory and motor capacities in the ipsilateral limbs. Without training, post-lesion motor capacities gradually improved, whereas forepaw tactile abilities remained impaired. Consistently, no stimulus-evoked responses were recorded within the forepaw representational zone in the primary somatosensory (S1) cortex at 2 months after the SCI. However, our data reveal that with training started from the 7th day post-lesion, a nearly complete recovery (characterized by an early and rapid improvement of motor functions) was associated with a gradual compensation of tactile deficits. Furthermore, the recovery of tactile abilities was correlated with the areal extent of reactivation of S1 cortex forepaw representations. Rehabilitative training promoted post-lesion adaptive plasticity, probably by enhancing endogenous activity within spared spinal and supraspinal circuits and pathways sustaining sensory and motor functions. This study highlights the beneficial effect of sensorimotor training in motor improvement and its critical influence on tactile recovery after SCI.

Differential tactile and motor recovery and cortical map alteration after C4-C5 spinal hemisection

After incomplete spinal cord injury (SCI), the adult central nervous system is spontaneously capable of substantial reorganizations that can underlie functional recovery. Most studies have focused on intraspinal reorganizations after SCI and not on the correlative cortical remodeling. Yet, differential studies of neural correlates of the recovery of sensory and motor abilities may be conducted by segregating motor and somatosensory representations in distinct and topologically organized primary cortical areas. This study was aimed at evaluating the effects of a cervical (C4-C5) spinal cord hemisection on sensorimotor performances and electrophysiological maps in primary somatosensory (S1) and motor (M1) cortices in adult rats. After SCI, an enduring loss of the affected forepaw tactile sensitivity was paralleled by the abolishment of somatosensory evoked responses in the deprived forepaw area within the S1 cortex. In contrast, severe motor deficits in unilateral forelimb were partially restored over the first postoperative month, despite remnant deficits in distal movement. The overall M1 map size was drastically reduced in SCI rats relative to intact rats. In the remaining M1 map, the shoulder and elbow movements were over-represented, consistent with the behavioral recovery of proximal joint movements in almost all rats. By contrast, residual wrist representations were observed in M1 maps of half of the rats that did not systematically correlate with a behavioral recovery of these joint movements. This study highlights the differential potential of ascending and descending pathways to reorganize after SCI.

Forelimb locomotor assessment scale (FLAS): novel assessment of forelimb dysfunction after cervical spinal cord injury

We describe here a novel forelimb locomotor assessment scale (FLAS) that assesses forelimb use during locomotion in rats injured at the cervical level. A quantitative scale was developed that measures movements of shoulder, elbow, and wrist joints, forepaw position and digit placement, forelimb-hindlimb coordination, compensatory behaviors adopted while walking, and balance. Female Sprague-Dawley rats received graded cervical contusions ranging from 200 to 230 ("mild," n=11) and 250-290 kdyn ("moderate," n=13) between C5 and C8. Rats were videotaped post-injury as they walked along an alley to determine deficits and recovery of forelimb function. Recovery of shoulder and elbow joint movement occurred rapidly (within 1-7 days post-injury), whereas recovery of wrist joint movement was slower and more variable. Most rats in all groups displayed persistent deficits in forepaw and digit movement, but developed compensatory behaviors to allow functional forward locomotion within 1-2 weeks post-injury. Recovery of forelimb function as measured by the FLAS reached a plateau by 3 weeks post-injury in all groups. Rats with mild contusions displayed greater locomotor recovery than rats with moderate contusions, but exhibited persistent deficits compared to sham controls. Reliability was tested by having seven raters (three internal, four external) from different laboratories, independently and blindly score videos of all rats. The multivariate correlation between all raters, all animals, and all time points ranged from r(2)=0.88-0.96 (p<0.0001), indicating a high inter-rater reliability. Thus, the FLAS is a simple, inexpensive, sensitive, and reliable measure of forelimb function during locomotion following cervical SCI.

A straight alley version of the BBB locomotor scale

We describe here an alternative procedure for assessing hindlimb locomotor function after spinal cord injury that uses the BBB scale, but tests animals in a reward-baited straight alley rather than an open field. Rats were trained to ambulate in a straight alley and habituated to the open field typically used for BBB open field testing. Three groups of rats were tested. Sprague-Dawley rats received either 200 kD (n=19) or 300 kD contusions (n=9) at T9 with the Infinite Horizon device. Fisher rats (n=8) received moderate contusions (12.5 mm) at T8 with the NYU impactor. BBB scores were assessed at different post-injury intervals in the open field and the straight alley, and scores were compared by correlation analyses. BBB scores in the open field vs. the straight alley were highly correlated (r=0.90), validating the use of the straight alley for locomotor assessment. Rats exhibited a larger number of bouts of continuous steps in the straight alley vs. the open field (termed passes), providing more opportunities to score hindlimb use and coordination over the 4 min testing interval. Comparisons of scores across days revealed higher day-to-day correlations in the straight alley vs. the open field (r(2) values of 0.90 and 0.74 for the straight alley and open field respectively), revealing that the straight alley yielded more reliable scores.

[Morphological study of CNS lesions and the consequences on rat neuromuscular junction and peripheral nerve using confocal laser scanning microscopy and Koelle's technique]

STATE OF THE ART

In humans, it is currently believed that peripheral nerves remain intact after central nervous system (CNS) injuries. This should lead us to observe a lack of amyotrophy in the peripheral projection areas of CNS damage. Nevertheless, the appearance of amyotrophy, described as underuse amyotrophy, is common in victims of CNS injury. Its pathophysiology remains poorly understood and is currently being debated. Amyotrophy could result directly from the structural deterioration of a nervous fiber in the muscular area corresponding to the CNS injury caused by neuromuscular junction (NMJ) changes.

AIMS OF THIS STUDY

The aims of this study were to assess the repercussions of a CNS injury on the NMJ and peripheral nerve complex and to evaluate the involvement of peripheral nerves and NMJs in plasticity.

METHODOLOGY

Peripheral nerve and muscle biopsies were collected from a group of 35 female Wistar rats that had previously undergone a thoracic spinal cord hemisection (15 rats at the T2 level (group 1), 15 rats at the T6 level (group 2), and 5 matched rats used as controls). We studied the localization and expression of the NMJ molecular components in muscle specimens by immunohistochemistry using confocal microscopy. We also searched for signs of nerve and muscle degeneration using light and electron microscopy.

RESULTS

We observed nonpathologic NMJs coexisting with completely denervated and partially reinnervated NMJs. We also found characteristics of embryonic behavior in rat axons secondary to axonal caliber distortions. Some authors associate this decrease in axonal activity with physiological denervation.

CONCLUSION

This project was designed to improve the understanding of the mechanisms involved in the interactions between the first and second motoneurons after different types of CNS injuries, with variable functional repercussions. Our results strongly suggest that CNS injuries lead to both morphological and functional repercussions at the NMJ and the peripheral nerve.

Task-dependent compensation after pyramidal tract and dorsolateral spinal lesions in rats

The purpose of this research was to investigate whether pathways in the dorsal part of the lateral spinal funiculus (DLF) can compensate for loss of corticospinal input (CST) to the spinal cord. The CST is known to control skilled limb movements in rats. The DLF contains several different pathways, including the rubrospinal tract (RST) which is also thought to influence limb movements. After lesions of either the corticospinal or the rubrospinal system, it is unclear how much of the remaining forelimb function is due to the presence of the alternate pathway. To begin to address this issue, the present study investigates the compensatory role of pathways in the DLF, including the rubrospinal tract, after bilateral lesions of the pyramidal tract (PT). We initially performed bilateral PT lesions in rats, which effectively removed the CST input to the spinal cord. We tested these rats during overground locomotion, skilled locomotion and skilled forelimb usage. After a 6 week recovery period, we then performed bilateral DLF lesions and compared the behavioural abilities of these rats to those of animals which underwent simultaneous PT and DLF lesions. If DLF pathways do compensate for PT lesions, then animals with PT lesions would rely more on DLF pathways than animals without PT lesions. Thus we hypothesized that animals with DLF lesions which were performed 6 weeks after PT lesions would exhibit more deficits on several behavioural tasks compared to animals which received PT and DLF lesions simultaneously. Our hypothesis was supported only for skilled pellet retrieval. Hence some DLF pathways, including the RST, were able to compensate for loss of CST input during skilled reaching but not during overground or skilled locomotion in PT-lesioned rats. These differential responses suggest that behavioural tasks vary in their reliance on specific pathways after injury, and, furthermore, that compensation for loss of specific connections can arise from numerous sources.

Effects of combined dorsolateral and dorsal funicular lesions on sensorimotor behaviour in rats

The purpose of this research was to investigate the compensatory role of undamaged spinal pathways after partial spinal injury in rats. We have previously shown that bilateral lesions of the dorsal funiculus (DF) at the cervical level caused changes in overground and skilled locomotion that affected the forelimbs more than the hindlimbs. The same lesions also caused fore-paw deficits during a skilled pellet retrieval task (Kanagal and Muir, 2007). In contrast, bilateral cervical lesions of the dorsolateral funiculus (DLF) caused alterations in overground and skilled locomotion that were most marked in the hindlimbs rather than the forelimbs, but also caused fore-paw deficits during skilled pellet retrieval (Muir et al., 2007). We hypothesized that the relative lack of forelimb deficits during locomotion after DLF lesions was due to compensatory input arising from intact pathways in the DF. We tested this hypothesis in the present study by performing bilateral DF lesions in animals in which both DLFs had been transected 6 weeks previously. These secondary DF lesions involved either only ascending sensory pathways (DLF+ASP group) in the DF, i.e. sparing the corticospinal tract (CST), or involved both the ASP and the CST (DLF+DF group). All animals were assessed during overground locomotion, while crossing a horizontal ladder and during a pellet retrieval task. During overground locomotion, both groups moved with slightly altered forces and timing in both forelimbs and hindlimbs. During both ladder crossing and reaching, secondary lesions to DF (with or without CST) exacerbated the deficits seen after initial DLF lesions and additionally caused changes in the manner in which the rats used their forelimbs during reaching. Nevertheless, the relative magnitude of the deficits indicates that DF pathways in rats likely do not compensate for loss of DLF pathways during the execution of locomotor tasks, though there is indirect evidence that DLF-lesioned rats might rely more on ascending sensory pathways in the DF during skilled forelimb movements. The plastic changes mediating recovery are therefore necessarily occurring in other regions of the CNS, and, importantly, need time to develop, because animals with DLF+DF lesions performed simultaneously displayed marked functional deficits and were unable to use their forelimbs for skilled locomotion or reaching.

Glial precursor cell transplantation therapy for neurotrauma and multiple sclerosis

Traumatic injury to the brain or spinal cord and multiple sclerosis (MS) share a common pathophysiology with regard to axonal demyelination. Despite advances in central nervous system (CNS) repair in experimental animal models, adequate functional recovery has yet to be achieved in patients in response to any of the current strategies. Functional recovery is dependent, in large part, upon remyelination of spared or regenerating axons. The mammalian CNS maintains an endogenous reservoir of glial precursor cells (GPCs), capable of generating new oligodendrocytes and astrocytes. These GPCs are upregulated following traumatic or demyelinating lesions, followed by their differentiation into oligodendrocytes. However, this innate response does not adequately promote remyelination. As a result, researchers have been focusing their efforts on harvesting, culturing, characterizing, and transplanting GPCs into injured regions of the adult mammalian CNS in a variety of animal models of CNS trauma or demyelinating disease. The technical and logistic considerations for transplanting GPCs are extensive and crucial for optimizing and maintaining cell survival before and after transplantation, promoting myelination, and tracking the fate of transplanted cells. This is especially true in trials of GPC transplantation in combination with other strategies such as neutralization of inhibitors to axonal regeneration or remyelination. Overall, such studies improve our understanding and approach to developing clinically relevant therapies for axonal remyelination following traumatic brain injury (TBI) or spinal cord injury (SCI) and demyelinating diseases such as MS.

Overground Locomotion after Incomplete Spinal Lesions in the Rat: Quantitative Gait Analysis

In rats with incomplete low thoracic spinal cord lesions of different extents, the basic indices of gait such as locomotor velocity, step and stance phase duration and the duty factor (i.e., the relative duration of the stance phase) during overground runway locomotion were analyzed using contact electrodes on each paw for data recording. In animals with lesions confined to the dorsal columns (DC), tested 3 weeks postsurgery, these gait indices were essentially unchanged compared to the preoperative period. After the same recovery period, rats with larger lesions, comprising the dorsal columns plus a major part of the dorsolateral funiculi (DL), showed a transient increase in the hindlimb stance phase duration and the duty factor. More extensive injuries, with additional damage to parts of the ventrolateral and ventral funiculi (VL), produced increments in the stance phase duration and duty factor much above that which would be expected from changes in step cycle duration due to slowing down of locomotion. These changes, which lasted for at least 3 months, were more conspicuous in animals with extensive spinal cord injuries and were due to an altered relationship between the stance phase and step cycle duration. It is suggested that the excessive increment in the hindlimb stance phase and the duty factor constitute a reliable indicator of impairment in locomotor movements, which is correlated with the extent of spinal cord injury.