Non-invasive spinal cord electrical stimulation for arm and hand function in chronic tetraplegia: a safety and efficacy trial.

Cervical spinal cord injury (SCI) leads to permanent impairment of arm and hand functions. Here we conducted a prospective, single-arm, multicenter, open-label, non-significant risk trial that evaluated the safety and efficacy of ARCEX Therapy to improve arm and hand functions in people with chronic SCI. ARCEX Therapy involves the delivery of externally applied electrical stimulation over the cervical spinal cord during structured rehabilitation. The primary endpoints were safety and efficacy as measured by whether the majority of participants exhibited significant improvement in both strength and functional performance in response to ARCEX Therapy compared to the end of an equivalent period of rehabilitation alone. Sixty participants completed the protocol. No serious adverse events related to ARCEX Therapy were reported, and the primary effectiveness endpoint was met. Seventy-two percent of participants demonstrated improvements greater than the minimally important difference criteria for both strength and functional domains. Secondary endpoint analysis revealed significant improvements in fingertip pinch force, hand prehension and strength, upper extremity motor and sensory abilities and self-reported increases in quality of life. These results demonstrate the safety and efficacy of ARCEX Therapy to improve hand and arm functions in people living with cervical SCI. ClinicalTrials.gov identifier: NCT04697472 .

A spinal cord neuroprosthesis for locomotor deficits due to Parkinson's disease.

People with late-stage Parkinson's disease (PD) often suffer from debilitating locomotor deficits that are resistant to currently available therapies. To alleviate these deficits, we developed a neuroprosthesis operating in closed loop that targets the dorsal root entry zones innervating lumbosacral segments to reproduce the natural spatiotemporal activation of the lumbosacral spinal cord during walking. We first developed this neuroprosthesis in a non-human primate model that replicates locomotor deficits due to PD. This neuroprosthesis not only alleviated locomotor deficits but also restored skilled walking in this model. We then implanted the neuroprosthesis in a 62-year-old male with a 30-year history of PD who presented with severe gait impairments and frequent falls that were medically refractory to currently available therapies. We found that the neuroprosthesis interacted synergistically with deep brain stimulation of the subthalamic nucleus and dopaminergic replacement therapies to alleviate asymmetry and promote longer steps, improve balance and reduce freezing of gait. This neuroprosthesis opens new perspectives to reduce the severity of locomotor deficits in people with PD.

Recovery of walking after paralysis by regenerating characterized neurons to their natural target region.

Axon regeneration can be induced across anatomically complete spinal cord injury (SCI), but robust functional restoration has been elusive. Whether restoring neurological functions requires directed regeneration of axons from specific neuronal subpopulations to their natural target regions remains unclear. To address this question, we applied projection-specific and comparative single-nucleus RNA sequencing to identify neuronal subpopulations that restore walking after incomplete SCI. We show that chemoattracting and guiding the transected axons of these neurons to their natural target region led to substantial recovery of walking after complete SCI in mice, whereas regeneration of axons simply across the lesion had no effect. Thus, reestablishing the natural projections of characterized neurons forms an essential part of axon regeneration strategies aimed at restoring lost neurological functions.

Invisible consequences of paralysis.

Neuroprosthetic technologies can control blood pressure and restore walking.

Longitudinal interrogation of sympathetic neural circuits and hemodynamics in preclinical models.

Neurological disorders, including spinal cord injury, result in hemodynamic instability due to the disruption of supraspinal projections to the sympathetic circuits located in the spinal cord. We recently developed a preclinical model that allows the identification of the topology and dynamics through which sympathetic circuits modulate hemodynamics, supporting the development of a neuroprosthetic baroreflex that precisely controls blood pressure in rats, monkeys and humans with spinal cord injuries. Here, we describe the continuous monitoring of arterial blood pressure and sympathetic nerve activity over several months in preclinical models of chronic neurological disorders using commercially available telemetry technologies, as well as optogenetic and neuronal tract-tracing procedures specifically adapted to the sympathetic circuitry. Using a blueprint to construct a negative-pressure chamber, the approach enables the reproduction, in rats, of well-controlled and reproducible episodes of hypotension-mimicking orthostatic challenges already used in humans. Blood pressure variations can thus be directly induced and linked to the molecular, functional and anatomical properties of specific neurons in the brainstem, spinal cord and ganglia. Each procedure can be completed in under 2 h, while the construction of the negative-pressure chamber requires up to 1 week. With training, individuals with a basic understanding of cardiovascular physiology, engineering or neuroscience can collect longitudinal recordings of hemodynamics and sympathetic nerve activity over several months.

Natural and targeted circuit reorganization after spinal cord injury.

A spinal cord injury disrupts communication between the brain and the circuits in the spinal cord that regulate neurological functions. The consequences are permanent paralysis, loss of sensation and debilitating dysautonomia. However, the majority of circuits located above and below the injury remain anatomically intact, and these circuits can reorganize naturally to improve function. In addition, various neuromodulation therapies have tapped into these processes to further augment recovery. Emerging research is illuminating the requirements to reconstitute damaged circuits. Here, we summarize these natural and targeted reorganizations of circuits after a spinal cord injury. We also advocate for new concepts of reorganizing circuits informed by multi-omic single-cell atlases of recovery from injury. These atlases will uncover the molecular logic that governs the selection of 'recovery-organizing' neuronal subpopulations, and are poised to herald a new era in spinal cord medicine.

The neurons that restore walking after paralysis.

A spinal cord injury interrupts pathways from the brain and brainstem that project to the lumbar spinal cord, leading to paralysis. Here we show that spatiotemporal epidural electrical stimulation (EES) of the lumbar spinal cord1-3 applied during neurorehabilitation4,5 (EESREHAB) restored walking in nine individuals with chronic spinal cord injury. This recovery involved a reduction in neuronal activity in the lumbar spinal cord of humans during walking. We hypothesized that this unexpected reduction reflects activity-dependent selection of specific neuronal subpopulations that become essential for a patient to walk after spinal cord injury. To identify these putative neurons, we modelled the technological and therapeutic features underlying EESREHAB in mice. We applied single-nucleus RNA sequencing6-9 and spatial transcriptomics10,11 to the spinal cords of these mice to chart a spatially resolved molecular atlas of recovery from paralysis. We then employed cell type12,13 and spatial prioritization to identify the neurons involved in the recovery of walking. A single population of excitatory interneurons nested within intermediate laminae emerged. Although these neurons are not required for walking before spinal cord injury, we demonstrate that they are essential for the recovery of walking with EES following spinal cord injury. Augmenting the activity of these neurons phenocopied the recovery of walking enabled by EESREHAB, whereas ablating them prevented the recovery of walking that occurs spontaneously after moderate spinal cord injury. We thus identified a recovery-organizing neuronal subpopulation that is necessary and sufficient to regain walking after paralysis. Moreover, our methodology establishes a framework for using molecular cartography to identify the neurons that produce complex behaviours.

Common carotid artery responses to the cold-pressor test are impaired in individuals with cervical spinal cord injury.

Cervical spinal cord injury (SCI) leads to autonomic cardiovascular dysfunction that underlies the three- to fourfold elevated risk of cardiovascular disease in this population. Reduced common carotid artery (CCA) dilatory responsiveness during the cold-pressor test (CPT) is associated with greater cardiovascular disease risk and progression. The cardiovascular and CCA responses to the CPT may provide insight into cardiovascular autonomic dysfunction and cardiovascular disease risk in individuals with cervical SCI. Here, we used CPT to perturb the autonomic nervous system in 14 individuals with cervical SCI and 12 uninjured controls, while measuring cardiovascular responses and CCA diameter. The CCA diameter responses were 55% impaired in those with SCI compared with uninjured controls (P = 0.019). The CCA flow, velocity, and shear response to CPT were reduced in SCI by 100% (P < 0.001), 113% (P = 0.001), and 125% (P = 0.002), respectively. The association between mean arterial pressure and CCA dilation observed in uninjured individuals (r = 0.54, P = 0.004) was absent in the SCI group (r = 0.22, P = 0.217). Steady-state systolic blood pressure (P = 0.020), heart rate (P = 0.003), and cardiac contractility (P < 0.001) were reduced in those with cervical SCI, whereas total peripheral resistance was increased compared with uninjured controls (P = 0.042). Relative cerebral blood velocity responses to CPT were increased in the SCI group and reduced in controls (middle cerebral artery, P = 0.010; posterior cerebral artery, P = 0.026). The CCA and cardiovascular responsiveness to CPT are impaired in those with cervical SCI.NEW & NOTEWORTHY This is the first study demonstrating that CCA responses during CPT are suppressed in SCI. Specifically, CCA diameter, flow, velocity, and shear rate were reduced. The relationship between changes in MAP and CCA dilatation in response to CPT was absent in individuals with SCI, despite similar cardiovascular activation between SCI and uninjured controls. These findings support the notion of elevated cardiovascular disease risk in SCI and that the cardiovascular responses to environmental stimuli are impaired.

Single cell atlas of spinal cord injury in mice reveals a pro-regenerative signature in spinocerebellar neurons.

After spinal cord injury, tissue distal to the lesion contains undamaged cells that could support or augment recovery. Targeting these cells requires a clearer understanding of their injury responses and capacity for repair. Here, we use single nucleus RNA sequencing to profile how each cell type in the lumbar spinal cord changes after a thoracic injury in mice. We present an atlas of these dynamic responses across dozens of cell types in the acute, subacute, and chronically injured spinal cord. Using this resource, we find rare spinal neurons that express a signature of regeneration in response to injury, including a major population that represent spinocerebellar projection neurons. We characterize these cells anatomically and observed axonal sparing, outgrowth, and remodeling in the spinal cord and cerebellum. Together, this work provides a key resource for studying cellular responses to injury and uncovers the spontaneous plasticity of spinocerebellar neurons, uncovering a potential candidate for targeted therapy.

Implanted System for Orthostatic Hypotension in Multiple-System Atrophy.

Orthostatic hypotension is a cardinal feature of multiple-system atrophy. The upright posture provokes syncopal episodes that prevent patients from standing and walking for more than brief periods. We implanted a system to restore regulation of blood pressure and enable a patient with multiple-system atrophy to stand and walk after having lost these abilities because of orthostatic hypotension. This system involved epidural electrical stimulation delivered over the thoracic spinal cord with accelerometers that detected changes in body position. (Funded by the Defitech Foundation.).

A national survey of physical activity after spinal cord injury.

Physical activity is a powerful modifiable risk factor for disease and mortality. Physical activity levels in people with spinal cord injury (SCI) have not been quantified relative to uninjured individuals in a large population-based sample. We aimed to quantify and compare physical activity in people with and without SCI, and to examine the associations between physical activity, lifestyle, and socioeconomic factors. The 2010 Canadian Community Health Survey (n > 57,000) was used, which includes three measures that assess physical activity levels (i.e., leisure time activity frequency, leisure time activity intensity, and transportation time activity intensity). Bivariable and multivariable logistic regressions were performed and odds ratios (ORs) with corresponding 95% confidence intervals (CIs) were estimated. The odds of physical activity in people with SCI were 0.43 (95% CI 0.3-0.61), 0.53 (95% CI 0.36-0.75), and 0.42 (95% CI 0.28-0.61), across the three measures of physical activity, respectively. These differences persisted after adjustment for lifestyle, comorbidities, and socioeconomic factors. Physical activity is reduced in the SCI population compared with the general population. This knowledge is important to direct future research and guide the allocation of health care resources.

National survey of mental health and suicidal thoughts in people with spinal cord injury.

STUDY DESIGN: Retrospective cross-sectional epidemiological study. OBJECTIVES: Previous studies have quantified longitudinal psychological morbidity in individuals with spinal cord injury (SCI) relative to uninjured individuals. However, there is limited information regarding how lifestyle and socioeconomic factors are associated with mental health conditions in individuals with SCI. This study aims to quantify and compare mental health and suicidal thoughts in people with and without SCI, and examine the associations between mental health, suicidal thoughts, sex, age, lifestyle, and socioeconomic factors. SETTING: Canada. METHODS: The 2010 Canadian Community Health Survey (n > 40,000) was used, which includes several measures assessing mental health and suicidal thoughts. Bivariate and multivariate logistic regressions were performed and odds ratios with corresponding 95% confidence intervals were estimated. Sensitivity analyses were performed to evaluate the effect of covariates on reported effect sizes. RESULTS: People with SCI had higher odds of having mood (3.6) and anxiety disorders (2.5), suicidal thoughts (2.3), self-perceived stress (1.9), and depression (4.4); in addition to lower odds of having good self-perceived mental health (0.24) and satisfaction with life (0.25). These differences persisted after adjusting for age, sex, lifestyle, and socioeconomic factors. Lower household income, fruit and vegetable consumption, and physical activity levels, and increased smoking use were associated with poorer mental health in individuals with SCI. CONCLUSIONS: Mental health is poorer in those with SCI when compared with the general population. Those with SCI exhibit a unique profile of lifestyle and socioeconomic factors that are associated with poorer mental health and increased suicidal thoughts.

Spinal cord injury impairs cardiac function due to impaired bulbospinal sympathetic control.

Spinal cord injury chronically alters cardiac structure and function and is associated with increased odds for cardiovascular disease. Here, we investigate the cardiac consequences of spinal cord injury on the acute-to-chronic continuum, and the contribution of altered bulbospinal sympathetic control to the decline in cardiac function following spinal cord injury. By combining experimental rat models of spinal cord injury with prospective clinical studies, we demonstrate that spinal cord injury causes a rapid and sustained reduction in left ventricular contractile function that precedes structural changes. In rodents, we experimentally demonstrate that this decline in left ventricular contractile function following spinal cord injury is underpinned by interrupted bulbospinal sympathetic control. In humans, we find that activation of the sympathetic circuitry below the level of spinal cord injury causes an immediate increase in systolic function. Our findings highlight the importance for early interventions to mitigate the cardiac functional decline following spinal cord injury.

Passive leg cycling increases activity of the cardiorespiratory system in people with tetraplegia.

Individuals with cervical spinal cord injury (SCI) are at an increased risk for cardiovascular disease. Exercise is well-established for preventing cardiovascular disease; however, there are limited straightforward and safe exercise approaches for increasing the activity of the cardiorespiratory system after cervical SCI. The objective of this study was to investigate the cardiorespiratory response to passive leg cycling in people with cervical SCI. Beat-by-beat blood pressure, heart rate, and cerebral blood flow were measured before and throughout 10 minutes of cycling in 11 people with SCI. Femoral artery flow-mediated dilation was also assessed before and immediately after passive cycling. Safety was monitored throughout all study visits. Passive cycling elevated systolic blood pressure (5 ± 2 mm Hg), mean arterial pressure (5 ± 3 mm Hg), stroke volume (2.4 ± 0.8 mL), heart rate (2 ± 1 beats/min) and cardiac output (0.3 ± 0.07 L/min; all p < 0.05). Minute ventilation (0.67 ± 0.23 L/min), tidal volume (70 ± 30 mL) and end-tidal PO2 (2.6 ± 1.23 mm Hg) also increased (all p < 0.05). Endothelial function was improved immediately after exercise (1.62 ± 0.13%, p < 0.01). Passive cycling resulted in an incidence of autonomic dysreflexia. Therefore, passive leg cycling increased the activity of the cardiorespiratory system and improved endothelial function, indicating it may be a beneficial exercise intervention for the cardiovascular and respiratory systems in people with cervical SCI. Novelty: Passive leg cycling increases the activity of the cardiorespiratory system and improves markers of cardiovascular health in cervical SCI. Passive leg cycling exercise is an effective, low-cost, practical, alternative exercise modality for people with cervical SCI.

Engineering spinal cord repair.

Neurological damage caused by spinal cord injury in humans has been observed for over three thousand years and impacts the lives of several hundred thousand people worldwide. Despite this prevalence and its associated consequences, there is no treatment to repair the injured spinal cord. Evidence gathered over the last several decades has provided mechanistic information on the complex cascade of events following traumatic spinal cord injury and this is paving the way towards mechanism based repair strategies. In this review, we summarize state-of-the-art biological and engineering repair strategies and posit that complete repair will be dependent on cataloguing the molecular signatures and growth requirements of the different neuron subpopulations in the brain and spinal cord.

Confronting false discoveries in single-cell differential expression.

Differential expression analysis in single-cell transcriptomics enables the dissection of cell-type-specific responses to perturbations such as disease, trauma, or experimental manipulations. While many statistical methods are available to identify differentially expressed genes, the principles that distinguish these methods and their performance remain unclear. Here, we show that the relative performance of these methods is contingent on their ability to account for variation between biological replicates. Methods that ignore this inevitable variation are biased and prone to false discoveries. Indeed, the most widely used methods can discover hundreds of differentially expressed genes in the absence of biological differences. To exemplify these principles, we exposed true and false discoveries of differentially expressed genes in the injured mouse spinal cord.

Effects of early exercise training on the severity of autonomic dysreflexia following incomplete spinal cord injury in rodents.

Hemodynamic instability and cardiovascular (CV) dysfunction are hallmarks of patients living with cervical and high thoracic spinal cord injuries (SCI). Individuals experience bouts of autonomic dysreflexia (AD) and persistent hypotension which hamper the activities of daily living. Despite the widespread use of exercise training to improve health and CV function after SCI, little is known about how different training modalities impact hemodynamic stability and severity of AD in a model of incomplete SCI. In this study, we used implantable telemetry devices to assess animals with T2 contusions following 3.5 weeks of exercise training initiated 8 days post-injury: passive hindlimb cycling (T2-CYC, n = 5) or active forelimb swimming (T2-SW, n = 6). Uninjured and non-exercised SCI control groups were also included (CON, n = 6; T2-CON, n = 7; T10-CON, n = 6). Five weeks post-injury, both T2-CON and T2-CYC presented with resting hypotension compared to uninjured CON and T10-CON groups; no differences were noted in resting blood pressure in T2-SW versus CON and T10-CON. Furthermore, pressor responses to colorectal distention (AD) were larger in all T2-injured groups compared to T10-CON, and were not attenuated by either form of exercise training. Interestingly, when T2-injured animals were re-stratified based on terminal BBB scores (regardless of training group), animals with limited hindlimb recovery (T2-LOW, n = 7) had more severe AD responses. Our results suggest that the spontaneous recovery of locomotor and autonomic function after severe but incomplete T2 SCI also influences the severity of AD, and that short periods (3.5 weeks) of passive hindlimb cycling or active forelimb swimming are ineffective in this model.

Diversity of Reactive Astrogliosis in CNS Pathology: Heterogeneity or Plasticity?

Astrocytes are essential for the development and homeostatic maintenance of the central nervous system (CNS). They are also critical players in the CNS injury response during which they undergo a process referred to as "reactive astrogliosis." Diversity in astrocyte morphology and gene expression, as revealed by transcriptional analysis, is well-recognized and has been reported in several CNS pathologies, including ischemic stroke, CNS demyelination, and traumatic injury. This diversity appears unique to the specific pathology, with significant variance across temporal, topographical, age, and sex-specific variables. Despite this, there is limited functional data corroborating this diversity. Furthermore, as reactive astrocytes display significant environmental-dependent plasticity and fate-mapping data on astrocyte subsets in the adult CNS is limited, it remains unclear whether this diversity represents heterogeneity or plasticity. As astrocytes are important for neuronal survival and CNS function post-injury, establishing to what extent this diversity reflects distinct established heterogeneous astrocyte subpopulations vs. environmentally dependent plasticity within established astrocyte subsets will be critical for guiding therapeutic development. To that end, we review the current state of knowledge on astrocyte diversity in the context of three representative CNS pathologies: ischemic stroke, demyelination, and traumatic injury, with the goal of identifying key limitations in our current knowledge and suggesting future areas of research needed to address them. We suggest that the majority of identified astrocyte diversity in CNS pathologies to date represents plasticity in response to dynamically changing post-injury environments as opposed to heterogeneity, an important consideration for the understanding of disease pathogenesis and the development of therapeutic interventions.

Markers of susceptibility to cardiac arrhythmia in experimental spinal cord injury and the impact of sympathetic stimulation and exercise training.

Injury to descending autonomic (sympathetic) pathways is common after high-level spinal cord injury (SCI) and associated with abnormal blood pressure and heart rate regulation. In individuals with high-level SCI, abnormal sympathovagal balance (such as during autonomic dysreflexia; paroxysmal hypertension provoked by sensory stimuli below the injury) is proarrhythmogenic. Exercise training is a key component of SCI rehabilitation and management of cardiovascular disease risk, but it is unclear whether exercise training influences susceptibility to cardiac arrhythmia. We aimed to evaluate: (i) whether susceptibility to arrhythmia increases in a rodent-model of SCI; (ii) the impact of the sympathomimetic drug dobutamine (DOB) on arrhythmia risk; (iii) whether exercise training ameliorates arrhythmia risk. Twenty-one Wistar rats were divided into 3 subgroups: T2-contusive SCI (T2, n = 7), T2-contusive SCI completing passive hindlimb cycling training (PHLC, n = 7), and T10-contusive SCI (T10, n = 7). Known electrocardiographic arrhythmia markers and heart rate variability parameters were evaluated before (PRE), 1-week (POST) and 5-weeks post-SCI (TERM) at baseline and during DOB infusion (30 µg/kg/min). Baseline markers of arrhythmia risk were increased in both T2 and T10 animals. DOB decreased R-R interval (p < 0.001), and increased markers of risk for ventricular arrhythmia, particularly in high-level (T2) animals (p < 0.05). Exercise training blunted the exacerbation of markers of arrhythmia risk in the presence of DOB. Markers of risk for cardiac arrhythmia are increased in experimental SCI, and DOB further increases arrhythmia risk in high-level SCI. Exercise training did not improve markers of arrhythmia risk at rest, but did ameliorate markers of arrhythmia risk during sympathetic stimulation.