Experimental Neurology

BackgroundThe entopeduncular nucleus (EP), corresponding to the human globus pallidus internal segment, is a basal ganglia output nucleus, and plays a critical role in motor control. However, the impact of EP damage on skilled motor function and the relationship between its damage in stroke, such as internal capsule hemorrhage (ICH), and motor dysfunction remains unclear. This study aimed to clarify whether EP damage causes motor dysfunction in two disease models. MethodsEP-related motor dysfunction was investigated by inducing localized unilateral EP damage in Long-Evans rats using a stereotactic kainic acid (KA) injection. Motor function was assessed using a single-pellet reaching task pre-injection and on postoperative days 2, 7, 14, 21, and 28. Immunohistochemical staining for NeuN, somatostatin (SST), and parvalbumin was conducted to quantify damage and its correlation with motor outcomes. In addition, unilateral ICH was induced via stereotactic injection of collagenase type IV, which dissolves the vascular basement membrane, into the internal capsule (IC) of Long-Evans rats. Injury sites were classified into the IC, dorsomedial region from the IC, ventral lateral region from the IC, and EP, and their volumes were measured. Measured volumes were analyzed for correlations with motor function assessments. ResultsKA-induced EP damage significantly reduced reaching success rates on postoperative day 2 compared to those in the control group (p<0.05). Immunohistochemical analysis showed that reaching success rates on day 28 positively correlated with the numbers of remaining NeuN-positive and SST-positive neurons (p<0.05). In the ICH experiment, all rats significantly reduced the success rate of the reaching task to 0% on day 2, and the success rate on day 28 correlated positively with the remaining EP volume, but not with total lesion volume. ConclusionsEP damage was strongly associated with motor impairments, highlighting its critical role in motor control and recovery.

Parkinsons disease is characterized by progressive dopaminergic degeneration, yet motor symptoms emerge only after substantial neuronal loss - a dissociation that challenges the sensitivity of conventional behavioral endpoints in preclinical models. Here, we present a proof-of-principle study establishing a graded hemiparkinsonism model in adult male capuchin monkeys (Sapajus apella) through unilateral, MRI-guided stereotaxic injection of 6-hydroxydopamine into the substantia nigra pars compacta. Three toxin concentrations (4, 10, and 40 mg/mL; n = 3) were tested alongside a vehicle-injected sham control (n = 1). Motor function was assessed longitudinally before and after surgery using a three-task battery comprising the Staircase test, Tube test, and Brinkman board, capturing complementary dimensions of motor functions, including gross lateralization, forelimb use asymmetry, and fine digit coordination. Critically, we introduce a novel sequence-deviation metric applied to Brinkman board performance data to quantify disruption in the spatial organization of pellet retrieval independently of task success. Post-surgical tyrosine hydroxylase immunohistochemistry combined with optical fractionator stereology revealed ipsilateral dopaminergic cell losses of 47%, 59%, and 44% relative to the contralateral hemisphere across the three treated animals, with the sham showing no meaningful hemispheric difference. Behavioral impairments were heterogeneous and strategy-dependent: task completion rates were largely preserved, whereas fine motor strategy analysis revealed post-lesion increases in retrieval sequence disorganization in two of three animals. Exploratory regression analyses suggested that strategy-level metrics were more sensitive to nigrostriatal degeneration than global performance measures. These findings demonstrate that capuchin monkeys subjected to unilateral 6-hydroxydopamine lesions reproduce clinically relevant features of hemiparkinsonism and that motor sequence analysis constitutes a sensitive readout of subclinical dopaminergic dysfunction, and can outperform conventional performance-based metrics detecting early motor alterations, therefore a potential biomarker of subclinical dopaminergic dysfunction, with implications for early detection paradigms in Parkinsons disease research.

Electrical stimulation of the nervous system has been employed to enhance the recovery of motor function produced by use-dependent rehabilitation, which is the current gold standard of treatment, following spinal cord injury. However, the therapeutic effects almost always rely on the sustained activation of muscles or neurons, making the benefits largely contingent on continued delivery of stimulation. In the present study, we describe a neuromodulatory intervention that combined intraspinal delivery of serotonergic agonists with use-dependent rehabilitation to restore motor function after a chronic moderate-to-severe cervical contusion in rats that produces impairments in upper-limb movements and dexterity. We show that targeted delivery of quipazine, a broad-spectrum serotonergic agonist, caudal to the lesion increased the effectiveness of physical rehabilitation, leading to substantially improved motor-recovery outcomes in severely-injured, but not moderately-injured, animals. Delivery of quipazine significantly augmented recovery of skilled reach and grasp movements after a severe injury, but moderately-injured animals received no additional benefit from quipazine over physical rehabilitation alone. This difference was perhaps due to a greater loss of serotonin after a severe injury and a resulting environment in which exogenously-applied serotonin can improve circuit function. Our experiments highlight an important role for serotonin in restoration of motor function that is dependent on the severity of the spinal cord injury. They also allude to a potential role for residual serotonin as a biomarker of injury severity. Remarkably, quipazine-mediated behavioral improvements persisted for weeks after termination of neuromodulator delivery, signaling repair of severely-damaged adult spinal circuitry that drives lasting motor recovery. Significance StatementWe describe a neuromodulatory intervention that combined intraspinal delivery of serotonergic agonists with use-dependent physical rehabilitation, which is the current standard of treatment, to promote motor recovery after a chronic moderate-to-severe spinal-contusion injury. Our results show that targeted delivery of serotonergic agonists caudal to the lesion increased the effectiveness of use-dependent rehabilitation, leading to substantially improved motor-recovery outcomes in severely-injured, but not moderately-injured, animals. Notably, therapeutic gains persisted for weeks after termination of neuromodulator delivery--a finding that is both unique and clinically relevant--signaling plasticity induction and repair in chronically-damaged adult spinal circuitry. Our experiments provide important insights into serotonergic modulation of spinal circuitry and highlight a potential role for residual serotonin as a neurochemical biomarker of injury severity.

Neurogenic bladder dysfunction causes urological complications and reduces the quality of life in persons with spinal cord injury (SCI). Glutamatergic signaling via AMPA receptors is fundamentally important to the neural circuits controlling bladder voiding. Ampakines are positive allosteric modulators of AMPA receptors that can enhance the function of glutamatergic neural circuits after SCI. We hypothesized that ampakines can acutely stimulate bladder voiding that has been impaired due to thoracic contusion SCI. Adult female Sprague Dawley rats received a unilateral contusion of the T9 spinal cord (n=10). Bladder function (cystometry) and coordination with the external urethral sphincter (EUS) were assessed five days post-SCI under urethane anesthesia. Data were compared to responses in spinal intact rats (n=8). The "low impact" ampakine CX1739 (5, 10, or 15 mg/kg) or vehicle (HPCD) was administered intravenously. The HPCD vehicle had no discernable impact on voiding. In contrast, following CX1739, the pressure threshold for inducing bladder contraction, voided volume, and the interval between bladder contractions were significantly reduced. These responses occurred in a dose-dependent manner. We conclude that modulating AMPA receptor function using ampakines can rapidly improve bladder voiding capability at sub-acute time points following contusion SCI. These results may provide a new and translatable method for therapeutic targeting of bladder dysfunction acutely after SCI.

Restoring vital motor functions after spinal cord injury (SCI) remains a central challenge in neuroscience and regenerative medicine. Cervical SCI can cause life-threatening respiratory deficits by damaging the phrenic motor network that controls the diaphragm. Cellular transplantation offers a viable means to improve function by providing new neurons that can relay supraspinal drive to denervated spinal phrenic networks, yet the long-term stability of transplants is poorly defined. Here, we examine donor-host neuronal synaptic connectivity in a respiratory model of cervical SCI, 1-year post-transplantation in adult rats. Embryonically-derived spinal cord tissue was transplanted into the lesion cavity one-week post-SCI, and transplant integration and diaphragm function were assessed at 1-month and 1-year post-transplantation. At 1-month, transplant-recipients exhibited significantly greater diaphragm output than injured, vehicle control animals. The extent of recovery at 1-year, however, was significantly less, coinciding with anatomical changes in graft neuronal density and donor-host connectivity, revealed by transneuronal tracing (pseudorabies virus). These results demonstrate that embryonic spinal cord transplants can improve phrenic motor activity after cervical SCI, but that long-term efficacy may be limited by reduced donor-host connectivity. Significance StatementCell transplantation can repair injured spinal cord circuits, but whether donor-host connections persist long term remains unclear. Using a rat model of cervical spinal cord injury, we show that embryonic spinal cord transplants improve diaphragm activity and integrate with the injured phrenic motor network at early time points, but these benefits decline by 1 year after transplantation. This loss of functional recovery is accompanied by reduced transneuronal labeling of donor neurons and changes in graft tissue composition. These results provide important proof of principle that transplant-host connectivity can be evaluated over extended survival times and identify long-term stability of donor-host integration as a critical challenge for achieving durable respiratory repair after spinal cord injury.

Spinal cord injury (SCI) disrupts corticospinal tract (CST) connectivity and impairs skilled voluntary movement. However, most human SCIs are anatomically incomplete, allowing spared CST pathways to engage in rehabilitation-mediated plasticity to promote functional recovery. How voluntary rehabilitation engages and reorganizes the supraspinal targets of the intact CST remains incompletely understood. Here, we combined unilateral pyramidotomy (uPyX) in male and female mice with continuous voluntary complex-wheel running to test whether fine motor-dependent rehabilitation drives supraspinal CST plasticity. uPyX mice rapidly resumed wheel running after a transient deficit. In contrast to lesion-only controls, rehabilitation significantly improved skilled forelimb performance on the horizontal ladder rung task. Immunohistochemical c-Fos labeling confirmed that complex-wheel running robustly activated the intact forelimb CST in motor cortex. Whole-brain CST projection mapping using intersectional viral vector tracing revealed targeted supraspinal reorganization localized to medullary motor nuclei. Three nuclei - the lateral paragigantocellular reticular nucleus (LPGi), gigantocellular reticular nucleus, alpha part (GiA), and ventral medullary reticular nucleus (MdV) - exhibited significant lesion- and/or rehabilitation-induced increases in CST innervation. Rehabilitation-driven CST sprouting correlated with regional c-Fos activation, indicating activity-dependent remodeling. Notably, CST projection density in the MdV, critical for skilled forelimb control, correlated with functional recovery. These findings identify a set of spinally-projecting medullary nuclei as key sites of rehabilitation-induced CST plasticity and highlight the MdV as a potential mediator of restored motor function. This work defines how voluntary rehabilitation reorganizes spared corticospinal pathways and provides targets for optimizing activity-based interventions after SCI. Significance StatementEffective rehabilitation after spinal cord injury (SCI) must harness the plasticity of spared motor pathways, yet the supraspinal circuits that support rehabilitation-mediated recovery remain unknown. Using a model that preserves voluntary motor engagement, we show that continuous fine motor-dependent rehabilitation activates intact corticospinal neurons and drives highly specific remodeling of their supraspinal terminals. Rehabilitation selectively strengthens CST inputs to motor regions of the medulla, particularly the ventral medullary reticular nucleus (MdV), and CST plasticity within this region predicts enhanced behavioral recovery. These findings highlight the MdV as a central locus by which rehabilitation re-establishes descending control of the impaired limb, providing mechanistic insight to guide targeted, circuit-based rehabilitation therapies for incomplete SCI.

The circadian rhythms of gene expression drive diurnal oscillations of physiological processes that determine the acute injury response including immunity, inflammation and hemostasis. While outcomes of various acute injuries are affected by the time of day at which the original insult occurred, such diurnal influences on recovery after spinal cord injury (SCI) are unknown. We report that several key regulators of circadian gene expression are differentially expressed in uninjured spinal cord tissue of naive mice at Zeitgeber time 1 (ZT1) or ZT12, where ZT0 or ZT12 are times when lights are turned on or off, respectively. However, mice that received moderate, T9 contusive SCI at ZT0 or ZT12 showed similar recovery of locomotion as determined using the ladder walking test and the Basso mouse scale (BMS) over a 6 week post-injury period. Consistent with those findings, terminal histological analysis revealed no significant differences in white matter sparing at the injury epicenter. Therefore, locomotor recovery after thoracic contusive SCI is not affected by the time of day at which the neurotrauma occurred at least when comparing the beginning to the end of the mouse active period.

The mechanisms of the spinal cord regeneration after complete spinal cord transection were investigated in spiny mice. In some animals, the appearance of quadrupedal overground stepping together with rewiring of the direct propriospinal projections between the cervical and lumbar enlargements was revealed. In others, no stepping recovery was detected, whereas numerous cells labeled by the neuronal proteins NeuN and {beta}III-tubulin were observed within the injury region. We suggest that depending on trauma severity, different repair mechanisms are elicited: only connectome restoration or both connectome restoration and the activation of neurogenesis. To confirm the high neurogenic potential of spiny mice, a primary culture of bone marrow was established. Unlike in other mammals, bone marrow pluripotent cells in the culture differentiated into neuronal cells without any chemical stimulation. These findings provide strong evidence for the high differentiation potential of spiny mouse stem cells toward neural lineages. GRAPHICAL ABSTRACT O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=180 SRC="FIGDIR/small/739224v1_ufig1.gif" ALT="Figure 1"> View larger version (73K): org.highwire.dtl.DTLVardef@1e6f2c1org.highwire.dtl.DTLVardef@14b88f6org.highwire.dtl.DTLVardef@ce5b5org.highwire.dtl.DTLVardef@bcebd9_HPS_FORMAT_FIGEXP M_FIG C_FIG HIGHLIGHTSO_LITwo regenerative mechanisms are proposed in spiny mice, depending on the severity the spinal cord transection C_LIO_LIRegular transection evoked the emergence of the direct propriospinal projections C_LIO_LISevere transection evoked the neurogenesis within the primary injured region C_LIO_LIPrimary culture of bone marrow cells from spiny mice exhibits neurogenic differentiation without chemical induction C_LI

In response to traumatic brain injury (TBI), the brain increases its generation of new neurons (neurogenesis) within the hippocampus, a brain region critical for learning and memory. Because neurogenesis plays important roles in learning and memory, post-traumatic neurogenesis may represent an adaptive response contributing to cognitive recovery. In contrast to increases in neurogenesis acutely after injury, levels of neurogenesis become impaired long after TBI. And although chronic deficits in neurogenesis after TBI have been reported by multiple groups, it is unknown whether the hippocampus remains capable of eliciting another neurogenic response to a repeated injury. To address this lack of knowledge, we used a closed head injury model that reflects a concussive-like injury or a mild TBI (mTBI) and assessed levels of neurogenesis in male and female adult mice. Mice received one or two mTBI or sham treatments 3 weeks apart. Compared to mice with a single mTBI, proliferation and neurogenesis were blunted in mice that received a second mTBI. This impaired response was unlikely due to a short recovery time between the two mTBIs as the proliferative response to a second mTBI was also impaired when two months were allowed between injuries. We further found that proliferation was impaired in the radial-glia like cells despite an intact pool. The mice that received two mTBIs also had a blunted intensity in their GFAP staining. In contrast to reports of aberrant post-TBI neurogenesis, we found that the neurons born after mTBI had normal dendritic branches. Lastly, we found that impairments in the inability to mount a neurogenic response after a second mTBI were associated with deficits in neurogenesisstrategy flexibility in the reversal water maze task. Our data suggests that a loss in the neurogenic response could in part contribute to worse cognitive recovery after a repeated concussion. These data may expose a novel target to help improve long-term cognitive outcome following repeated brain injury.

The partial crush spinal cord injury (SCI) model enables preclinical testing of experimental therapies in mice, but substantial inter-animal variability in recovery outcomes confounds efficacy assessments. Here, we used open field behavioral data collected during the first 3 days post partial thoracic SCI to generate an Acute Functional Score (AFS) that defined three subgroups with divergent recovery trajectories. Applying latent class growth analysis and growth mixture modeling to open field and grid walk testing data, we demonstrated 83-92% prediction accuracy for AFS-defined recovery trajectories. The three subgroups differed significantly in treadmill kinematics and histological assessments of lesion size and astrocyte bridging. Applying the recovery trajectory framework to mice receiving saline or biomaterial vehicle injections at 3 days post-SCI revealed robust predictive accuracy while exposing disproportionate injury severity distributions between experimental groups. The approach enables individualized post-SCI recovery characterization that can neutralize procedural bias, minimize animal numbers, and provide a probabilistic basis for evaluating whether interventions enhance or suppress wound repair processes. Our findings establish a foundation for improving preclinical SCI study design and accelerating identification of effective therapies.

Traumatic brain injury (TBI) is a major global health concern, affecting more than 40 million people annually. While most cases are mild and present with light symptoms, repeated mild injuries can result in delayed brain pathologies, including cognitive decline, neuropsychiatric complications, and post-traumatic epilepsy (PTE). PTE refers to recurring, unprovoked seizures occurring at least one week after TBI. While the link between moderate to severe TBI and PTE is well established, the epileptogenesis after repetitive mild TBI (rmTBI) is seldom studied. Currently, there are no biomarkers to identify those at risk of developing PTE, and its diagnosis is challenging. Here, we used a rat model to study PTE following rmTBI and assessed human EEG data to identify potential biomarkers for PTE. We employed a closed head TBI model to induce rmTBI, and recorded brain activity using electrocorticography (ECoG) between 2- and 6-months post-injury. Behavioral assessments and post-mortem analysis were also conducted. In humans, we analyzed EEG recordings from the Temple University database to investigate the potential of EEG-derived features for diagnosing PTE. At 6 months post injury, 70% of rmTBI animals developed PTE, compared to 22% in the control group (P=0.01). While neurological assessments following injury did not predict PTE, paroxysmal slow wave events (PSWEs) were found to be a reliable biomarker for PTE prediction. In humans, the percentage time in PSWEs was significantly elevated in PTE patients with epileptiform activity. In conclusion, we suggest PSWEs as a non-invasive, cost-effective biomarker for PTE in rodents and human patients.

Parkinsons disease (PD) is characterized by the degeneration of dopaminergic (DA) neurons in the substantia nigra pars compacta, leading to dopamine depletion in the striatum and the hallmark motor symptoms of the disease. However, non-motor deficits, particularly sensory symptoms, often precede motor manifestations, offering a potential early diagnostic window. The impact of non-motor deficits on sensation behavior and the underlying mechanisms remain poorly understood. In this study, we examined changes in tactile sensation within a parkinsonian state by employing a mouse model of PD induced by 6-hydroxydopamine (6-OHDA) to deplete striatal DA. Leveraging the conserved mouse whisker system as a model for tactile-sensory stimulation, we conducted psychophysical experiments to assess sensory-driven behavioral performance during a tactile detection task in both the healthy and PD-like state. Our findings reveal a range of deficits across subjects following 6-OHDA lesion, including DA loss, motor asymmetry, weight loss, and varying levels of altered tactile sensation behavior. Behavioral changes ranged from no impairments in minor cases to isolated sensory-behavioral deficits in moderate cases and severe motor dysfunction in advanced stages. These results underscore the complex relationship between DA imbalance and sensory-motor processing, emphasizing the need for precise and multifaceted behavioral measurements to accurately capture the diverse manifestations of PD. SIGNIFICANCE STATEMENTThis study explores sensory-motor aspects of Parkinsons disease using a 6-OHDA mouse model. Leveraging the mouse whisker system, we reveal diverse deficits in tactile sensation behavior due to dopamine depletion. Our findings emphasize the importance of sensory assessments in understanding the diverse spectrum of PD symptoms.

Pathogenic variants of the sodium-activated potassium channel KNa1.1, have been reported in multiple epileptic disorders. However, whether and how KNa1.1 channel is involved in epileptogenesis after traumatic brain injury (TBI) remains unknown. Firstly, we used behavioral monitoring and EEG recording to examine physiological property, spontaneous seizure activity, and seizure susceptibility after TBI. We explored the changes of KNa1.1 channel following TBI, including changes of subcellular distribution and expression pattern. Meanwhile, we performed patch-clamp recording to detect the neuronal excitability. Furthermore, we built TBI model using kcnt1-/- mice and compared seizure activity with those on wild- type mice. We found severity-dependent seizure susceptibility in different degree of injured mice. Meanwhile, increased neuronal expression of KNa1.1 channel, especially in inhibitory neurons, around the lesion was also observed following TBI with increased neuronal excitability including reduced firing rate of interneurons and imbalanced excitation and inhibition (E/I). Although the maximum frequency of action potential of kcnt1-/- neurons was increased, kcnt1-/- mice displayed decreased seizure susceptibility to the pentylenetetrazole (PTZ) after TBI. Taken together, this study suggests that pathologically enhanced expression and abnormally distributed KNa1.1 channel after TBI contribute to disputed E/I and seizure susceptibility, which might provide a potential therapeutic target on the epileptogenesis after TBI.

The purpose of this study was to determine if spike-triggered intraspinal microstimulation (ISMS) results in improved motor performance in an ambulatory rat model of spinal cord injury (SCI). Experiments were carried out in adult male Sprague Dawley rats with 175 kdyn moderate T8 contusion injury. Rats were randomly assigned to one of two groups: Control or Activity Dependent Stimulation (ADS) therapy. Four weeks post-SCI, all rats were implanted with a recording electrode in the left hindlimb motor cortex and a fine-wire, custom-made stimulating electrode in the contralateral lumbar spinal cord. Intracortical and intraspinal microstimulation were used to find sites of similar hip representation areas, which were paired together for ADS therapy. In the ADS therapy group, spike-stimulus conditioning was administered for 4 hours/day, 4 days/week, for 4 weeks via a tethered cable in a testing chamber. During therapy sessions, single-unit spikes were discriminated in real time in the hindlimb motor cortex and used to trigger stimulation in the spinal cord ventral horn. The optimal stimulus intensity (50% ISMS movement threshold) and spike-stimulus delay (10ms) determined in preliminary anesthetized preparations were used during ADS. Control rats were similarly implanted with electrodes but did not receive stimulation therapy. Motor performances of each rat were evaluated before SCI contusion, once a week post-SCI for four weeks (prior to electrode implantation), and once a week post-conditioning for four weeks. Behavioral testing included BBB scoring, Ledged Beam walking, Horizontal Ladder walking, treadmill kinematics via the DigiGait and TreadScan system, and open field walking using OptiTrack kinematic analysis. BBB scores were significantly improved in ADS rats compared to Control rats after 1 week of therapy. In the ADS therapy rats, BBB scores were significantly improved after two weeks of ADS therapy when compared to pre-therapy. Foot fault scores on the Horizontal Ladder were significantly lower in ADS rats compared to pre-therapy ADS and Control rats after 1 week of therapy and returned to pre-injury measures after three weeks of ADS therapy. The Ledged Beam test and kinematic analysis using the DigiGait and TreadScan system showed deficits after SCI in both ADS and Control rats but there were no significant differences between groups after 4 weeks of ADS therapy. These results show that activity dependent stimulation after spinal cord injury using spike-triggered ISMS enhances behavioral recovery of locomotor function as measured by the BBB score and the Horizontal Ladder task.

The brain-spinal cord axis generates movement by assembling motor primitives into coordinated sequences. Spinal cord injury (SCI) disrupts this neuroaxis, impairing not only locomotion, but the full repertoire of behavior. Traditional scales for quantifying recovery collapse this complexity into predefined locomotor-focused criteria that obscure heterogeneity in recovery. To quantify the full behavioral repertoire following SCI, we adapted motion sequencing (MoSeq) to identify sub-second behavioral "syllables" and capture their usage and sequential organization without predefined features. We identified biomechanically distinct variants within syllable classes that are shared across injury severities and found that recovery is jointly structured by injury severity and individual mouse identity. Changes in sequences, however, unfold along a conserved temporal trajectory. By compressing behavior into a single metric, we uncovered clusters of coevolving locomotor and non-locomotor behaviors. These results frame SCI recovery with repertoire-level changes, where adaptive strategies emerge from constrained access to motor primitives and their sequences.

Spinal cord injury (SCI) is a devastating condition characterized by impaired motor and sensory function, as well as internal organ pathology and dysfunction. This internal organ dysfunction, particularly gastrointestinal (GI) complications, and neurogenic bowel, can reduce the quality of life of individuals with an SCI and potentially hinder their recovery. The gut microbiome impacts various central nervous system functions and has been linked to a number of health and disease states. An imbalance of the gut microbiome, i.e., gut dysbiosis, contributes to neurological disease and may influence recovery and repair processes after SCI. Here we examine the impact of high cervical SCI on the gut microbiome and find that transient gut dysbiosis with persistent gut pathology develops after SCI. Importantly, probiotic treatment improves gut health and respiratory motor function measured through whole-body plethysmography. Concurrent with these improvements was a systemic decrease in the cytokine tumor necrosis factor-alpha and an increase in neurite sprouting and regenerative potential of neurons. Collectively, these data reveal the gut microbiome as an important therapeutic target to improve visceral organ health and respiratory motor recovery after SCI. Research HighlightsO_LICervical spinal cord injury (SCI) causes transient gut dysbiosis and persistent gastrointestinal (GI) pathology. C_LIO_LITreatment with probiotics after SCI leads to a healthier GI tract and improved respiratory motor recovery. C_LIO_LIProbiotic treatment decreases systemic tumor necrosis factor-alpha and increases the potential for sprouting and regeneration of neurons after SCI. C_LIO_LIThe gut microbiome is a valid target to improve motor function and secondary visceral health after SCI. C_LI

Following a spinal cord injury (SCI), chondroitin sulfate proteoglycans (CSPGs) are up-regulated at the glial scar inhibiting neuroregeneration. Under normal physiological condition, CSPGs interact with hyaluronan (HA) and other extracellular matrix on neuronal surface forming a macromolecular structure called perineuronal nets (PNNs) which regulate neuroplasticity. 4-methylumbelliferone (4-MU) has been used previously to down-regulate HA synthesis but not been tested in SCI. In this study, we have evaluated the effect of 4-MU, an inhibitor of HA, in a chronic contusion model of SCI in rats. At a dose of 1.2 g/kg/day of 4-MU, we observed not only the reduction of HA in the uninjured spinal cords after 60 days of 4-MU administration, but also a down-regulation of CS glycosaminoglycans (CS-GAGs). In order to assess the effect of 4-MU in chronic SCI, rats with T8 spinal contusion injury were fed with 4-MU or placebo for 8 weeks in combination with daily treadmill rehabilitation for 16 weeks to promote neuroplasticity. 4-MU treatment promoted significant sprouting of 5-hydroxytryptamine (5-HT) positive fibres into ventral horns and reduced the HA synthesis by astrocytes around the lesion site. While 4-MU reduced astrogliosis in chronic stage of SCI, the current dose was not sufficient to down-regulate the increased production of CS-GAGs or behavioural performance. Together, these data suggest that oral treatment with 4-MU is able to induce anatomical plasticity but further adjustment on the dosage will be required to benefit functional recovery after SCI.

Spinal cord injury (SCI) triggers secondary pathophysiological cascades, including glutamate excitotoxicity, that result in neuronal loss and impair functional recovery. We have previously shown that lysophosphatidylethanolamine (LPE), a lysophospholipid, promotes neurite outgrowth and protects against glutamate excitotoxicity in cultured cortical neurons. However, whether these effects extend to spinal cord neurons and occur in vivo has remained unclear. In this study, we compared the effects of different LPE species: myristoyl-LPE (14:0 LPE), palmitoyl-LPE (16:0 LPE), stearoyl-LPE (18:0 LPE), and oleoyl-LPE (18:1 LPE) in cultured spinal commissural neurons, and evaluated their effects in vivo using a mouse model of SCI. In cultured neurons, all LPE species promoted neurite outgrowth. Although several species demonstrated a tendency toward neuroprotection, only 16:0 LPE exhibited a statistically significant protective effect against glutamate-induced excitotoxic cell death. Intrathecal administration of 16:0 LPE after SCI reduced TUNEL-positive cells in the acute phase and attenuated lesion expansion at 8 weeks post-injury. Moreover, 5-HT fluorescence intensity was increased in 16:0 LPE-treated mice, suggesting enhanced serotonergic innervation. Furthermore, administration of 16:0 LPE after SCI significantly improved hind-limb motor performance compared with vehicle controls, as assessed by the Basso Mouse Scale. Collectively, these findings suggest that intrathecal administration of 16:0 LPE reduces secondary injury and promotes functional recovery following SCI. Our findings highlight its potential as a therapeutic candidate for SCI.

Spinal cord injury (SCI) can cause long-lasting locomotor deficits, pain, and mood disorders. Anatomical and functional outcomes are exacerbated by inflammation after SCI, which causes secondary damage. One promising target after SCI is manipulating the circadian system, which optimizes biology and behavior for time of day - including neuroimmune responses and mood- related behaviors. Circadian disruption after SCI is likely worsened by a disruptive hospital environment, which typically includes dim light-at-night (dLAN). Here, we hypothesized that mice subjected to SCI, then placed in dLAN, would exhibit worsened locomotor deficits, pain- like behavior, and anxiety-depressive-like symptoms compared to mice maintained in light days with dark nights (LD). C57BL/6J mice received sham surgery or moderate T9 contusion SCI, then were placed permanently in LD or dLAN. dLAN after SCI did not worsen locomotor deficits; rather, SCI-dLAN mice showed slight improvement in open-field locomotion at the final timepoint. Although dLAN did not alter SCI-induced heat hyperalgesia, SCI-dLAN mice exhibited an increase in mechanical allodynia at 13 days post-SCI compared to SCI-LD mice. SCI-LD and SCI-dLAN mice had similar outcomes using sucrose preference (depressive-like) and open-field (anxiety-like) tests. At 21 dpo, SCI-dLAN mice had reduced preference for a novel juvenile compared to SCI-LD, implying that dLAN combined with SCI may worsen this mood-related behavior. Finally, lesion size was similar between SCI-LD and SCI-dLAN mice. Therefore, newly placing C57BL/6J mice in dLAN after SCI had modest effects on locomotor, pain-like, and mood-related behaviors. Future studies should consider whether clinically-relevant circadian disruptors, alone or in combination, could be ameliorated to enhance outcomes after SCI.

Stroke is a leading cause of disability, causing chronic motor impairments in many survivors. Although recovery is correlated with cortical reorganization, the impact of lesion location on post-stroke reorganization is uncertain. We compared movement-related neural activity following experimental infarcts to the motor cortex (M1) or internal capsule in rats. Neural activity was recorded from motor and somatosensory regions during a skilled pellet retrieval task longitudinally during the course of recovery. Cortical lesions resulted in early behavioral recovery accompanied by widespread reductions in neural activity across ipsilesional regions, indicative of large-scale reorganization. In contrast, internal capsule lesions produced delayed recovery with no evidence of long-term ipsilesional cortical reorganization. These findings challenge the relevance of cortical reorganization for recovery from subcortical lesions and indicate that post-stroke recovery mechanisms are lesion-specific and that models targeting subcortical white matter are essential for maximizing translational relevance.