Blocking Autophagy in Oligodendrocytes Limits Functional Recovery after Spinal Cord Injury.

Autophagy mechanisms are well documented in neurons after spinal cord injury (SCI), but the direct functional role of autophagy in oligodendrocyte (OL) survival in SCI pathogenesis remains unknown. Autophagy is an evolutionary conserved lysosomal-mediated catabolic pathway that ensures degradation of dysfunctional cellular components to maintain homeostasis in response to various forms of stress, including nutrient deprivation, hypoxia, reactive oxygen species, DNA damage, and endoplasmic reticulum (ER) stress. Using pharmacological gain and loss of function and genetic approaches, we investigated the contribution of autophagy in OL survival and its role in the pathogenesis of thoracic contusive SCI in female mice. Although upregulation of Atg5 (an essential autophagy gene) occurs after SCI, autophagy flux is impaired. Purified myelin fractions of contused 8 d post-SCI samples show enriched protein levels of LC3B, ATG5, and BECLIN 1. Data show that, while the nonspecific drugs rapamycin (activates autophagy) and spautin 1 (blocks autophagy) were pharmacologically active on autophagy in vivo, their administration did not alter locomotor recovery after SCI. To directly analyze the role of autophagy, transgenic mice with conditional deletion of Atg5 in OLs were generated. Analysis of hindlimb locomotion demonstrated a significant reduction in locomotor recovery after SCI that correlated with a greater loss in spared white matter. Immunohistochemical analysis demonstrated that deletion of Atg5 from OLs resulted in decreased autophagic flux and was detrimental to OL function after SCI. Thus, our study provides evidence that autophagy is an essential cytoprotective pathway operating in OLs and is required for hindlimb locomotor recovery after thoracic SCI.SIGNIFICANCE STATEMENT This study describes the role of autophagy in oligodendrocyte (OL) survival and pathogenesis after thoracic spinal cord injury (SCI). Modulation of autophagy with available nonselective drugs after thoracic SCI does not affect locomotor recovery despite being pharmacologically active in vivo, indicating significant off-target effects. Using transgenic mice with conditional deletion of Atg5 in OLs, this study definitively identifies autophagy as an essential homeostatic pathway that operates in OLs and exhibits a direct functional role in SCI pathogenesis and recovery. Therefore, this study emphasizes the need to discover novel autophagy-specific drugs that specifically modulate autophagy for further investigation for clinical translation to treat SCI and other CNS pathologies related to OL survival.

Impact of Activity-Based Training on Bowel Function in a Rat Model of Spinal Cord Injury.

Significant bowel-related issues after spinal cord injury (SCI) that affect morbidity and quality of life (QOL) include diminished bowel motility, loss of sphincter control, gastric ulcers, autonomic dysreflexia, pain, diarrhea, constipation, and fecal incontinence. Clinical diagnoses and research in humans have largely relied on anorectal manometry (ARM) procedures to increase understanding of the functional effects of SCI on colorectal motility and defecation physiology. Recent pre-clinical rodent studies have also used ARM to further our understanding of bowel-related dysfunctions post-SCI. In the present study, the benefits of different activity-based training (ABT) durations on bowel function were examined. Six groups of male rats including two non-training (NT; uninjured and SCI) and four ABT (quadrupedal [Quad or Q] stepping on a treadmill) groups. All ABT animals received 4 weeks of 1-h daily stepping beginning 2 weeks post-SCI followed by variable amounts for 4 additional weeks (none; daily; once a week; daily for final 4th week only). Outcome measures included fecal output (home cage; metabolic cage) throughout the study and terminal measurements (post 8-week ABT) of external anal sphincter (EAS) electromyography, resting anorectal pressure, and giant contraction (GC) activation under urethane anesthesia. The results indicate that treadmill training normalized defecation amount based on feces weight and food intake, as well as GC frequency, EAS latency and amplitude during fecal expulsion, and resting pressure in specific areas within the colorectum. The two intermittent training groups consistently showed recorded metrics comparable to the non-injured group. The results demonstrate bowel dysfunction in the rodent SCI contusion model with improvements in functional outcomes following ABT. Importantly, the benefits to bowel-related functions with versus without intermittent ABT illustrate the need for periodic therapy to maintain the functional gains of ABT.

Unintentional Effects from Housing Enhancement Resulting in Functional Improvement in Spinal Cord-Injured Mice.

It is well established that both positive and negative housing conditions of laboratory animals can affect behavioral, biochemical, and physiological responses. Housing enhancements have been shown to have beneficial effects on locomotor outcomes in rodents with spinal cord injury (SCI). Subsequent to an unplanned housing enhancement of the addition of a balcony to home cages by animal care personnel at a research facility, a retrospective analysis of multiple SCI studies was performed to determine whether outcomes differed before (four studies, N = 28) and after (four studies, N = 23) the addition of the balcony. Locomotor and morphological differences were compared after a mild-moderate T9 spinal cord contusion injury in wild-type mice. Post-injury assessments of locomotor function for 6 weeks included Basso Mouse Scale (BMS) and treadmill kinematic assessments (week 6). Balcony-housed mice showed greater improvements not only in basic locomotor functions (weight-supported stepping, balance) compared to those in standard housing, but also surpassed mice in standard housing without the balcony in higher-order locomotor recovery outcomes, including BMS late-stage recovery measures (paw, tail, and trunk indices). Additionally, balcony-housed mice had overall higher BMS scores, consistently attained more BMS subscores, and had better treadmill track width and stride length compared to those with no balcony. The housing enhancement of a balcony led to unforeseen consequences and unexpected higher recovery outcomes compared to mice in standard housing. This retrospective study highlights the importance of housing conditions in the key outcomes of locomotor recovery after incomplete contusive SCIs in mice.

Mutant and curli-producing E. coli enhance the disease phenotype in a hSOD1-G93A mouse model of ALS.

The gut microbiome is a potential non-genetic contributing factor for Amyotrophic Lateral Sclerosis. Differences in gut microbial communities have been detected between ALS subjects and healthy controls, including an increase in Escherichia coli in ALS subjects. E. coli and other gram-negative bacteria produce curli proteins, which are functional bacterial amyloids. We examined whether long-term curli overexposure in the gut can exacerbate the development and progression of ALS. We utilized the slow-developing hSOD1-G93A mouse model of ALS with their C57BL/6J WT littermate controls, including males and females, with a total of 91 animals. These mice were on a normal chow diet and fed curli-producing or curli-nonproducing (mutant) E. coli in applesauce (vehicle) 3 times/week, from 1 through 7 months of age. Male hSOD1 mice demonstrated gradual slowing in running speed month 4 onwards, while females exhibited no signs of locomotive impairment even at 7 months of age. Around the same time, male hSOD1 mice showed a gradual increase in frequency of peripheral CD19+ B cells. Among the male hSOD1 group, chronic gut exposure to curli-producing E. coli led to significant shifts in α- and ß-diversities. Curli-exposed males showed suppression of immune responses in circulation, but an increase in markers of inflammation, autophagy and protein turnover in skeletal muscle. Some of these markers were also changed in mutant E. coli-exposed mice, including astrogliosis in the brainstem and demyelination in the lumbar spinal cord. Overall, chronic overexposure to a commensal bacteria like E. coli led to distant organ pathology in our model, without the presence of a leaky gut at 6 months. Mechanisms underlying gut-distant organ communication are of tremendous interest to all disciplines.

Silencing long-descending inter-enlargement propriospinal neurons improves hindlimb stepping after contusive spinal cord injuries.

Spinal locomotor circuitry is comprised of rhythm generating centers, one for each limb, that are interconnected by local and long-distance propriospinal neurons thought to carry temporal information necessary for interlimb coordination and gait control. We showed previously that conditional silencing of the long ascending propriospinal neurons (LAPNs) that project from the lumbar to the cervical rhythmogenic centers (L1/L2 to C6), disrupts right-left alternation of both the forelimbs and hindlimbs without significantly disrupting other fundamental aspects of interlimb and speed-dependent coordination (Pocratsky et al., 2020). Subsequently, we showed that silencing the LAPNs after a moderate thoracic contusive spinal cord injury (SCI) resulted in better recovered locomotor function (Shepard et al., 2021). In this research advance, we focus on the descending equivalent to the LAPNs, the long descending propriospinal neurons (LDPNs) that have cell bodies at C6 and terminals at L2. We found that conditional silencing of the LDPNs in the intact adult rat resulted in a disrupted alternation of each limb pair (forelimbs and hindlimbs) and after a thoracic contusion SCI significantly improved locomotor function. These observations lead us to speculate that the LAPNs and LDPNs have similar roles in the exchange of temporal information between the cervical and lumbar rhythm generating centers, but that the partial disruption of the pathway after SCI limits the independent function of the lumbar circuitry. Silencing the LAPNs or LDPNs effectively permits or frees-up the lumbar circuitry to function independently.

Direct Ryanodine Receptor-2 Knockout in Primary Afferent Fibers Modestly Affects Neurological Recovery after Contusive Spinal Cord Injury.

Neuronal ryanodine receptors (RyR) release calcium from internal stores and play a key role in synaptic plasticity, learning, and memory. Dysregulation of RyR function contributes to neurodegeneration and negatively impacts neurological recovery after spinal cord injury (SCI). However, the individual role of RyR isoforms and the underlying mechanisms remain poorly understood. To determine whether RyR2 plays a direct role in axonal fate and functional recovery after SCI, we bred Advillin-Cre: tdTomato (Ai9) reporter mice with "floxed" RyR2 mice to directly knock out (KO) RyR2 function in dorsal root ganglion neurons and their spinal projections. Adult 6- to 8-week-old RyR2KO and littermate controls were subjected to a contusive SCI and their dorsal column axons were imaged in vivo using two-photon excitation microscopy. We found that direct RyR2KO in dorsal column primary afferents did not significantly alter secondary axonal degeneration after SCI. We next assessed behavioral recovery after SCI and found that direct RyR2KO in primary afferents worsened open-field locomotor scores (Basso Mouse Scale subscore) compared to littermate controls. However, both TreadScan™ gait analysis and overground kinematic gait analysis tests revealed subtle, but no fundamental, differences in gait patterns between the two groups after SCI. Subsequent removal of spared afferent fibers using a dorsal column crush revealed similar outcomes in both groups. Analysis of primary afferents at the lumbar (L3-L5) level similarly revealed no noticeable differences between groups. Together, our results support a modest contribution of dorsal column primary afferent RyR2 in neurological recovery after SCI.

Acute Neural and Proteostasis Messenger Ribonucleic Acid Levels Predict Chronic Locomotor Recovery after Contusive Spinal Cord Injury.

One of the difficulties in identifying novel therapeutic strategies to manage central nervous system (CNS) trauma is the need for behavioral assays to assess chronic functional recovery. In vitro assays and/or acute behavioral assessments cannot accurately predict long-term functional outcome. Using data from 13 independent T9 moderate contusive spinal cord injury (SCI) studies, we asked whether the ratio of acute (24-72 h post-injury) changes in the levels of neuron-, oligodendrocyte-, astrocyte-specific and/or endoplasmic reticulum stress response (ERSR) messenger ribonucleic acids (mRNAs) could predict the extent of chronic functional recovery. Increased levels of neuron, oligodendrocyte, and astrocyte mRNAs all correlated with enhanced Basso Mouse Scale (BMS) scores. Reduced levels of the ERSR mRNAs Atf4 and Chop correlate with improved chronic locomotor function. Neither neural or ERSR mRNAs were predictive for chronic recovery across all behavioral changes. The ratio of oligodendrocyte/ERSR mRNAs, however, did predict "improved," "no change," or "worse" functional recovery. Neuronal/ERSR mRNA ratios predicted functional improvement, but could not distinguish between worse or no change outcomes. Astrocyte/ERSR mRNA ratios were not predictive. This approach can be used to confirm biological action of injected drugs in vivo and to optimize dose and therapeutic window. It may prove useful in cervical and lumbar SCI and in other traumatic CNS injuries such as traumatic brain injury and stroke, where prevention of neuronal loss is paramount to functional recovery. Although the current analysis was directed toward ERSR whose activity was targeted in all but one study, acute mRNA markers for other pathophysiological cascades may be as predictive of chronic recovery when those cascades are targeted for neuroprotection.

Silencing long ascending propriospinal neurons after spinal cord injury improves hindlimb stepping in the adult rat.

Long ascending propriospinal neurons (LAPNs) are a subpopulation of spinal cord interneurons that directly connect the lumbar and cervical enlargements. Previously we showed, in uninjured animals, that conditionally silencing LAPNs disrupted left-right coordination of the hindlimbs and forelimbs in a context-dependent manner, demonstrating that LAPNs secure alternation of the fore- and hindlimb pairs during overground stepping. Given the ventrolateral location of LAPN axons in the spinal cord white matter, many likely remain intact following incomplete, contusive, thoracic spinal cord injury (SCI), suggesting a potential role in the recovery of stepping. Thus, we hypothesized that silencing LAPNs after SCI would disrupt recovered locomotion. Instead, we found that silencing spared LAPNs post-SCI improved locomotor function, including paw placement order and timing, and a decrease in the number of dorsal steps. Silencing also restored left-right hindlimb coordination and normalized spatiotemporal features of gait such as stance and swing time. However, hindlimb-forelimb coordination was not restored. These data indicate that the temporal information carried between the spinal enlargements by the spared LAPNs post-SCI is detrimental to recovered hindlimb locomotor function. These findings are an illustration of a post-SCI neuroanatomical-functional paradox and have implications for the development of neuronal- and axonal-protective therapeutic strategies and the clinical study/implementation of neuromodulation strategies.

Limited changes in locomotor recovery and unaffected white matter sparing after spinal cord contusion at different times of day.

The circadian gene expression rhythmicity drives diurnal oscillations of physiological processes that may determine the injury response. While outcomes of various acute injuries are affected by the time of day at which the original insult occurred, such influences on recovery after spinal cord injury (SCI) are unknown. We report that mice receiving moderate, T9 contusive SCI at ZT0 (zeitgeber time 0, time of lights on) and ZT12 (time of lights off) showed similar hindlimb function recovery in the Basso mouse scale (BMS) over a 6 week post-injury period. In an independent study, no significant differences in BMS were observed after SCI at ZT18 vs. ZT6. However, the ladder walking test revealed modestly improved performance for ZT18 vs. ZT6 mice at week 6 after injury. Consistent with those minor effects on functional recovery, terminal histological analysis revealed no significant differences in white matter sparing at the injury epicenter. Likewise, blood-spinal cord barrier disruption and neuroinflammation appeared similar when analyzed at 1 week post injury at ZT6 or ZT18. Therefore, locomotor recovery after thoracic contusive SCI is not substantively modulated by the time of day at which the neurotrauma occurred.

Enhanced adenoviral gene delivery to motor and dorsal root ganglion neurons following injection into demyelinated peripheral nerves.

Injection of viral vectors into peripheral nerves may transfer specific genes into their dorsal root ganglion (DRG) neurons and motoneurons. However, myelin sheaths of peripheral axons block the entry of viral particles into nerves. We studied whether mild, transient peripheral nerve demyelination prior to intraneural viral vector injection would enhance gene transfer to target DRG neurons and motoneurons. The right sciatic nerve of C57BL/6 mice was focally demyelinated with 1% lysolecithin, and the left sciatic nerve was similarly injected with saline (control). Five days after demyelination, 0.5 microl of Ad5-GFP was injected into both sciatic nerves at the site of previous injection. The effectiveness of gene transfer was evaluated by counting GFP(+) neurons in the DRGs and ventral horns. After peripheral nerve demyelination, there was a fivefold increase in the number of infected DRG neurons and almost a 15-fold increase in the number of infected motoneurons compared with the control, nondemyelinated side. Focal demyelination reduced the myelin sheath barrier, allowing greater virus-axon contact. Increased CXADR expression on the demyelinated axons facilitated axoplasmic viral entry. No animals sustained any prolonged neurological deficits. Increased gene delivery into DRG neurons and motoneurons may provide effective treatment for amyotrophic lateral sclerosis, pain, and spinal cord injury.

Treadmill-Based Gait Kinematics in the Yucatan Mini Pig.

Yucatan miniature pigs (YMPs) are similar to humans in spinal cord size as well as physiological and neuroanatomical features, making them a useful model for human spinal cord injury. However, little is known regarding pig gait kinematics, especially on a treadmill. In this study, 12 healthy YMPs were assessed during bipedal and/or quadrupedal stepping on a treadmill at six speeds (1.0, 1.5, 2.0, 2.5, 3.0, and 3.5 km/h). Kinematic parameters, including limb coordination and proximal and distal limb angles, were measured. Findings indicate that YMPs use a lateral sequence footfall pattern across all speeds. Stride and stance durations decreased with increasing speed whereas swing duration showed no significant change. Across all speeds assessed, no significant differences were noted between hindlimb stepping parameters for bipedal or quadrupedal gait with the exception of distal limb angular kinematics. Specifically, significant differences were observed between locomotor tasks during maximum flexion (quadrupedal > bipedal), total excursion (bipedal > quadrupedal), and the phase relationship between the timing of maximum extension between the right and left hindlimbs (bipedal > quadrupedal). Speed also impacted maximum flexion and right-left phase relationships given that significant differences were found between the fastest speed (3.5 km/h) relative to each of the other speeds. This study establishes a methodology for bipedal and quadrupedal treadmill-based kinematic testing in healthy YMPs. The treadmill approach used was effective in recruiting primarily the spinal circuitry responsible for the basic stepping patterns as has been shown in cats. We recommend 2.5 km/h (0.7 m/sec) as a target walking gait for pre-clinical studies using YMPs, which is similar to that used in cats.

Long ascending propriospinal neurons provide flexible, context-specific control of interlimb coordination.

Within the cervical and lumbar spinal enlargements, central pattern generator (CPG) circuitry produces the rhythmic output necessary for limb coordination during locomotion. Long propriospinal neurons that inter-connect these CPGs are thought to secure hindlimb-forelimb coordination, ensuring that diagonal limb pairs move synchronously while the ipsilateral limb pairs move out-of-phase during stepping. Here, we show that silencing long ascending propriospinal neurons (LAPNs) that inter-connect the lumbar and cervical CPGs disrupts left-right limb coupling of each limb pair in the adult rat during overground locomotion on a high-friction surface. These perturbations occurred independent of the locomotor rhythm, intralimb coordination, and speed-dependent (or any other) principal features of locomotion. Strikingly, the functional consequences of silencing LAPNs are highly context-dependent; the phenotype was not expressed during swimming, treadmill stepping, exploratory locomotion, or walking on an uncoated, slick surface. These data reveal surprising flexibility and context-dependence in the control of interlimb coordination during locomotion.

Nociceptor-dependent locomotor dysfunction after clinically-modeled hindlimb muscle stretching in adult rats with spinal cord injury.

In the course of investigating how common clinical treatments and adaptive technologies affect recovery after spinal cord injury (SCI), we discovered that a clinically-modeled hindlimb stretching protocol dramatically, but transiently, reduces locomotor function. Nociceptive sensory input is capable of altering motor output at the spinal level, and nociceptive neurons are sensitized after SCI. Here we tested the hypotheses that stretch-induced locomotor deficits are dependent on nociceptive afferents by depleting TRPV1+ sensory afferents using capsaicin injections in neonatal rats. Following maturation, animals received 25g-cm contusive SCI at T10. After plateau of locomotor recovery at 6 weeks, daily stretching was performed for 3 weeks, followed by 2 weeks without stretch, and again for two additional weeks. Animals were sacrificed 2 h after the last stretching session for histological assessments. Consistent with previous findings, stretch-induced drops in locomotor function were observed in nociceptor-intact animals but were nearly absent in nociceptor-depleted animals. These functional changes were accompanied by corresponding increases in the number of c-Fos+ nuclei throughout the lumbar enlargement. As expected, nociceptor-depleted animals had very little CGRP+ axonal innervation of the dorsal horn. Nociceptor-intact stretched animals had significantly higher levels of CGRP+ as compared to non-stretched SCI rats, suggesting that stretching promoted intraspinal CGRP+ sprouting. These results indicate that stretch-induced locomotor dysfunction in animals with incomplete SCI involves C-fibers, adding a negative post-SCI role to their adaptive roles (e.g., bladder control), and suggesting that the clinical use of muscle stretching to combat contractures and spasticity may be unintentionally detrimental to locomotor function.

Spinal cord contusion based on precise vertebral stabilization and tissue displacement measured by combined assessment to discriminate small functional differences.

Contusive spinal cord injury (SCI) is the most common type of spinal injury seen clinically. Several rat contusion SCI models have been described, and all have strengths and weaknesses with respect to sensitivity, reproducibility, and clinical relevance. We developed the Louisville Injury System Apparatus (LISA), which contains a novel spine-stabilizing device that enables precise and stable spine fixation, and is based on tissue displacement to determine the severity of injury. Injuries graded from mild to moderately severe were produced using 0.2-, 0.4-, 0.6-, 0.8-, 1.0-, and 1.2-mm spinal cord displacement in rats. Basso, Beattie, and Bresnahan (BBB) and Louisville Swim Score (LSS) could not significantly distinguish between 0.2-mm lesion severities, except those of 0.6- and 0.8-mm BBB scores, but could between 0.4-mm injury differences or if the data were grouped (0.2-0.4, 0.6-0.8, and 1.0-1.2). Transcranial magnetic motor evoked potential (tcMMEP) response amplitudes were decreased 10-fold at 0.2-mm displacement, barely detected at 0.4-mm displacement, and absent with greater displacement injuries. In contrast, somatosensory evoked potentials (SSEPs) were recorded at 0.2- and 0.4-mm displacements with normal amplitudes and latencies but were detected at lower amplitudes at 0.6-mm displacement and absent with more severe injuries. Analyzing combined BBB, tcMMEP, and SSEP results enabled statistically significant discrimination between 0.2-, 0.4-, 0.6-, and 0.8-mm displacement injuries but not the more severe injuries. Present data document that the LISA produces reliable and reproducible SCI whose parameters of injury can be adjusted to more accurately reflect clinical SCI. Moreover, multiple outcome measures are necessary to accurately detect small differences in functional deficits and/or recovery. This is of crucial importance when trying to detect functional improvement after therapeutic intervention to treat SCI.

Benefit of chondroitinase ABC on sensory axon regeneration in a laceration model of spinal cord injury in the rat.

BACKGROUND: Chondroitin sulfate proteoglycans are up-regulated in the spinal cord after SCI, creating a molecular barrier inhibitory to axon growth. Chondroitinase ABC degrades CSPGs in vitro and in vivo. METHODS: We studied whether IT ChABC promotes axonal regeneration in a laceration model of SCI. Three groups of Sprague-Dawley rats were used: control and rats treated with low-dose and high-dose IT ChABC. Chondroitin sulfate proteoglycan breakdown products were measured by 2-B-6 expression, and intact CSPGs by CS-56 expression. Sensory axonal regeneration was traced after CTB injection into the median, ulnar, and sciatic nerves. RESULTS: CS-56 expression was down-regulated and 2-B-6 expression was increased in the groups treated with IT ChABC but not in the control. Laminin and GFAP immunoreactivity was unaltered in the ChABC groups. The number of axons growing into the scar was 3.1 times greater (P < .01) in the high-dose ChABC group and 2.1 times greater (P < .01) in the low-dose group compared with the controls. The length of axonal growth after high- and low-dose ChABC was 9.9 (P < .01) and 8.3 (P < .01) times greater, respectively, than in the control group. Axons extended across the lesion gap and into the distal spinal cord stump in 2 of 8 (low dose) and in 3 of 9 (high dose) rats compared with none in the control group. CONCLUSIONS: Intrathecal ChABC administration caused a slight decrease in CSPGs in the scar after a laceration SCI with a minimal increase in sensory axonal regeneration into and across the laceration gap.

Use of magnetic stimulation to elicit motor evoked potentials, somatosensory evoked potentials, and H-reflexes in non-sedated rodents.

Assessment of locomotor function of rodents may be supplemented using electrophysiological tests which monitor the integrity of ascending and descending tracts as well as the focal circuitry of the spinal cord in non-sedated rodents. Magnetically induced SSEPs (M-SSEPs) were elicited in rats by activating the hindpaw using magnetic stimulation (MS). M-SSEP response latencies were slightly longer than those elicited by electrical stimulation. M-SSEPs were eliminated following selective dorsal column lacerations of the spinal cord, indicating that they were transmitted via this tract. Magnetically induced motor evoked potentials (M-MEPs) were elicited in mice following transcranial MS and recorded from the gastrocnemius muscles. M-MEPs performed on myelin deficient mice demonstrated longer onset latencies and smaller amplitudes than in wild-type mice. Magnetically induced H-reflexes (MH-reflexes) which assess local circuitry in the lumbosacral area of the spinal cord were performed in rats. This response disappeared following an L3 contusion spinal cord injury, however, kainic acid (KA) injection at L3, known to selectively destroy interneurons, caused a shorter latency and an increase in the amplitude of the MH-reflex. M-SSEPs and MH-reflexes in rats and M-MEPs in mice compliment locomotor evaluation in assessing the functional integrity of the spinal cord under normal and pathological conditions in the non-sedated animal.

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.

The Louisville Swim Scale: a novel assessment of hindlimb function following spinal cord injury in adult rats.

The majority of animal studies examining the recovery of function following spinal cord injury use the BBB Open-Field Locomotor Scale as a primary outcome measure. However, it is now well known that rehabilitation strategies can bring about significant improvements in hindlimb function in some animal models. Thus, improvements in walking following spinal cord injury in rats may be influenced by differences in activity levels and housing conditions during the first few weeks post-injury. Swimming is a natural form of locomotion that animals are not normally exposed to in the laboratory setting. We hypothesized that deficits in, and functional recovery of, swimming would accurately represent the locomotor capability of the nervous system in the absence of any retraining effects. To test this hypothesis, we have compared the recovery of walking and swimming in rats following a range of standardized spinal cord injuries and two different retraining strategies. In order to assess swimming, we developed a rating system we call the Louisville Swimming Scale (LSS) that evaluates three characteristics of swimming that are highly altered by spinal cord injury--namely, hindlimb movement, forelimb dependency, and body position. The data indicate that the LSS is a sensitive and reliable method of determining swimming ability and the improvement in hindlimb function after standardized contusion injury of the thoracic spinal cord. Furthermore, the data suggests that when used in conjunction with the BBB Open-field Locomotor Scale, the LSS assesses locomotor capabilities that are not influenced by a retraining effect.

Dural repair reduces connective tissue scar invasion and cystic cavity formation after acute spinal cord laceration injury in adult rats.

This study examined whether duraplasty after acute cervical laceration spinal cord injury (SCI) in a rat model could (1) improve cerebrospinal fluid (CSF) circulation adjacent to the injury; (2) minimize connective tissue scarring; and (3) reduce post-traumatic inflammation and cystic cavitation. Following a transverse dural/arachnoid incision and C5-6 dorsal spinal hemisection, a 5-mm2 cadaveric dura mater allograft was placed over the lesion and fixed with fibrin glue (n=12). Control animals received an identical dural/arachnoid incision and cervical dorsal hemisection without dural repair (n=12). At 1, 5, and 10 weeks post-injury, plain film myelograms were obtained to characterize CSF circulation, and stereological methods were used to compare the extent of tissue sparing between the two groups. Immunohistochemical studies were performed to assess the degree of inflammation (ED-1), connective tissue scarring (laminin and type IV collagen), and reactive astrogliosis (GFAP). Our results indicate that dural allograft can improve CSF flow adjacent to the site of injury, which may be due to reduced meningeal fibrosis/scarring at the lesion site. Stereological analysis demonstrated that duraplasty resulted in a significant reduction in lesion volume at each time-point (p<0.01) associated with a nearly complete attenuation of post-traumatic cystic cavitation (p<0.001). Immunofluorescence studies demonstrated that duraplasty reduced the infiltration of ED-1-positive macrophages/microglia into and surrounding the lesion site, which may be responsible for the marked reduction in secondary injury following duraplasty. We conclude that duraplasty following acute spinal cord laceration may (1) improve CSF flow by limiting meningeal fibrosis; (2) reduce connective tissue scar formation; and (3) attenuate macrophage accumulation and progressive secondary injury.

Effects of swimming on functional recovery after incomplete spinal cord injury in rats.

One of the most promising rehabilitation strategies for spinal cord injury is weight-supported treadmill training. This strategy seeks to re-train the spinal cord below the level of injury to generate a meaningful pattern of movement. However, the number of step cycles that can be accomplished is limited by the poor weight-bearing capability of the neuromuscular system after injury. We have begun to study swimming as a rehabilitation strategy that allows for high numbers of steps and a high step-cycle frequency in a standard rat model of contusive spinal cord injury. The purpose of the present study was to evaluate the effect of swimming as a rehabilitation strategy in rats with contusion injuries at T9. We used a swimming strategy with or without cutaneous feedback based on original work in the chick by Muir and colleagues. Adult female rats (n=27) received moderately-severe contusion injuries at T9. Walking and swimming performance were evaluated using the Open-Field Locomotor Scale (BBB; Basso et al., 1995) and a novel swimming assessment, the Louisville Swimming Scale (LSS). Rats that underwent swim-training with or without cutaneous feedback showed a significant improvement in hindlimb function during swimming compared to untrained animals. Rats that underwent swim-training without cutaneous feedback showed less improvement than those trained with cutaneous feedback. Rats in the non-swimming group demonstrated little improvement over the course of the study. All three groups showed the expected improvement in over-ground walking and had similar terminal BBB scores. These findings suggest that animals re-acquire the ability to swim only if trained and that cutaneous feedback improves the re-training process. Further, these data suggest that the normal course of recovery of over-ground walking following moderately-severe contusion injuries at T9 is the result of a re-training process.