Synchronous neuronal activity is a signal for axonal sprouting after cortical lesions in the adult

Collateral Sprouting of Peripheral Sensory Neurons Exhibits a Unique Transcriptomic Profile

Peripheral nerve injuries result in motor and sensory dysfunction which can be recovered by compensatory or regenerative processes. In situations where axonal regeneration of injured neurons is hampered, compensation by collateral sprouting from uninjured neurons contributes to target reinnervation and functional recovery. Interestingly, this process of collateral sprouting from uninjured neurons has been associated with the activation of growth-associated programs triggered by Wallerian degeneration. Nevertheless, the molecular alterations at the transcriptomic level associated with these compensatory growth mechanisms remain to be fully elucidated. We generated a surgical model of partial sciatic nerve injury in mice to mechanistically study degeneration-induced collateral sprouting from spared fibers in the peripheral nervous system. Using next-generation sequencing and Ingenuity Pathway Analysis, we described the sprouting-associated transcriptome of uninjured sensory neurons and compare it with the activated by regenerating neurons. In vitro approaches were used to functionally assess sprouting gene candidates in the mechanisms of axonal growth. Using a novel animal model, we provide the first description of the sprouting transcriptome observed in uninjured sensory neurons after nerve injury. This collateral sprouting-associated transcriptome differs from that seen in regenerating neurons, suggesting a molecular program distinct from axonal growth. We further demonstrate that genetic upregulation of novel sprouting-associated genes activates a specific growth program in vitro, leading to increased neuronal branching. These results contribute to our understanding of the molecular mechanisms associated with collateral sprouting in vivo. The data provided here will therefore be instrumental in developing therapeutic strategies aimed at promoting functional recovery after injury to the nervous system.

Experimental and Computational Study on Motor Control and Recovery After Stroke: Toward a Constructive Loop Between Experimental and Virtual Embodied Neuroscience

Being able to replicate real experiments with computational simulations is a unique opportunity to refine and validate models with experimental data and redesign the experiments based on simulations. However, since it is technically demanding to model all components of an experiment, traditional approaches to modeling reduce the experimental setups as much as possible. In this study, our goal is to replicate all the relevant features of an experiment on motor control and motor rehabilitation after stroke. To this aim, we propose an approach that allows continuous integration of new experimental data into a computational modeling framework. First, results show that we could reproduce experimental object displacement with high accuracy via the simulated embodiment in the virtual world by feeding a spinal cord model with experimental registration of the cortical activity. Second, by using computational models of multiple granularities, our preliminary results show the possibility of simulating several features of the brain after stroke, from the local alteration in neuronal activity to long-range connectivity remodeling. Finally, strategies are proposed to merge the two pipelines. We further suggest that additional models could be integrated into the framework thanks to the versatility of the proposed approach, thus allowing many researchers to achieve continuously improved experimental design.

Competing Roles of Slow Oscillations and Delta Waves in Memory Consolidation versus Forgetting

Sleep has been implicated in both memory consolidation and forgetting of experiences. However, it is unclear what governs the balance between consolidation and forgetting. Here, we tested how activity-dependent processing during sleep might differentially regulate these two processes. We specifically examined how neural reactivations during non-rapid eye movement (NREM) sleep were causally linked to consolidation versus weakening of the neural correlates of neuroprosthetic skill. Strikingly, we found that slow oscillations (SOs) and delta (δ) waves have dissociable and competing roles in consolidation versus forgetting. By modulating cortical spiking linked to SOs or δ waves using closed-loop optogenetic methods, we could, respectively, weaken or strengthen consolidation and thereby bidirectionally modulate sleep-dependent performance gains. We further found that changes in the temporal coupling of spindles to SOs relative to δ waves could account for such effects. Thus, our results indicate that neural activity driven by SOs and δ waves have competing roles in sleep-dependent memory consolidation.

Effects of bone marrow mononuclear cells on induction of axonal sprouting in cortico-cortical and cortico-striatal pathways in an animal model of cortical ablation

OBJECTIVES

Many therapies have been proposed in order to investigate the mechanisms of neural repair associated with neurological diseases, including bone marrow mononuclear cells (BMMC) transplantation. However, there is evidence that some encephalic injuries are less responsive to neural repair, such as, for example, cortical ablation. On the other hand, some models of cortical ablation have shown functional recovery after BMMC transplantation. Thus, it is relevant to expand the knowledge of BMMC transplantation-induced neuroplasticity in animal models, considering a promising approach for the rehabilitation of patients with neurological diseases. Using an experimental model of cerebral cortex ablation in adult male Wistar rats, which is known to be poorly responsive to neuroplasticity, the aim of this study was to investigate the effects of BMMC on axonal sprouting in cortico-cortical and cortico-striatal pathways synaptic fields. An anterograde neurotracer was used to evaluate the distribution of axonal fibres.

RESULTS

The results showed that BMMC were not able to significantly induce axonal sprouting in the evaluated synaptic fields. Our results reinforced the idea that cortical ablation may be less responsive to neuroplasticity and the beneficial effects of BMMC therapy depend on the particularities of a neural microenvironment intrinsic to a given cortical lesion.

Combinational Approach of Genetic SHP-1 Suppression and Voluntary Exercise Promotes Corticospinal Tract Sprouting and Motor Recovery Following Brain Injury

Background. Brain injury often causes severe motor dysfunction, leading to difficulties with living a self-reliant social life. Injured neural circuits must be reconstructed to restore functions, but the adult brain is limited in its ability to restore neuronal connections. The combination of molecular targeting, which enhances neural plasticity, and rehabilitative motor exercise is an important therapeutic approach to promote neuronal rewiring in the spared circuits and motor recovery. Objective. We tested whether genetic reduction of Src homology 2-containing phosphatase-1 (SHP-1), an inhibitor of brain-derived neurotrophic factor (BDNF)/tropomyosin receptor kinase B (TrkB) signaling, has synergistic effects with rehabilitative training to promote reorganization of motor circuits and functional recovery in a mouse model of brain injury. Methods. Rewiring of the corticospinal circuit was examined using neuronal tracers following unilateral cortical injury in control mice and in Shp-1 mutant mice subjected to voluntary exercise. Recovery of motor functions was assessed using motor behavior tests. Results. We found that rehabilitative exercise decreased SHP-1 and increased BDNF and TrkB expression in the contralesional motor cortex after the injury. Genetic reduction of SHP-1 and voluntary exercise significantly increased sprouting of corticospinal tract axons and enhanced motor recovery in the impaired forelimb. Conclusions. Our data demonstrate that combining voluntary exercise and SHP-1 suppression promotes motor recovery and neural circuit reorganization after brain injury.

Phosphodiesterase 10A Inhibition Leads to Brain Region-Specific Recovery Based on Stroke Type

Stroke is the leading cause of adult disability. Recovery of function after stroke involves signaling events that are mediated by cAMP and cGMP pathways, such as axonal sprouting, neurogenesis, and synaptic plasticity. cAMP and cGMP are degraded by phosphodiesterases (PDEs), which are differentially expressed in brain regions. PDE10A is highly expressed in the basal ganglia/striatum. We tested a novel PDE10A inhibitor (TAK-063) for its effects on functional recovery. Stroke was produced in mice in the cortex or the striatum. Behavioral recovery was measured to 9 weeks. Tissue outcome measures included analysis of growth factor levels, angiogenesis, neurogenesis, gliogenesis, and inflammation. TAK-063 improved motor recovery after striatal stroke in a dose-related manner, but not in cortical stroke. Recovery of motor function correlated with increases in striatal brain-derived neurotrophic factor. TAK-063 treatment also increased motor system axonal connections. Stroke affects distinct brain regions, with each comprising different cellular and molecular elements. Inhibition of PDE10A improved recovery of function after striatal but not cortical stroke, consistent with its brain localization. This experiment is the first demonstration of brain region-specific enhanced functional recovery after stroke, and indicates that differential molecular signaling between brain regions can be exploited to improve recovery based on stroke subtype.

Activity in grafted human iPS cell-derived cortical neurons integrated in stroke-injured rat brain regulates motor behavior

Stem cell transplantation can improve behavioral recovery after stroke in animal models but whether stem cell-derived neurons become functionally integrated into stroke-injured brain circuitry is poorly understood. Here we show that intracortically grafted human induced pluripotent stem (iPS) cell-derived cortical neurons send widespread axonal projections to both hemispheres of rats with ischemic lesions in the cerebral cortex. Using rabies virus-based transsynaptic tracing, we find that at 6 mo after transplantation, host neurons in the contralateral somatosensory cortex receive monosynaptic inputs from grafted neurons. Immunoelectron microscopy demonstrates myelination of the graft-derived axons in the corpus callosum and that their terminals form excitatory, glutamatergic synapses on host cortical neurons. We show that the stroke-induced asymmetry in a sensorimotor (cylinder) test is reversed by transplantation. Light-induced inhibition of halorhodopsin-expressing, grafted neurons does not recreate the impairment, indicating that its reversal is not due to neuronal activity in the graft. However, we find bilateral decrease of motor performance in the cylinder test after light-induced inhibition of either grafted or endogenous halorhodopsin-expressing cortical neurons, located in the same area, and after inhibition of endogenous halorhodopsin-expressing cortical neurons by exposure of their axons to light on the contralateral side. Our data indicate that activity in the grafted neurons, probably mediated through transcallosal connections to the contralateral hemisphere, is involved in maintaining normal motor function. This is an example of functional integration of efferent projections from grafted neurons into the stroke-affected brain's neural circuitry, which raises the possibility that such repair might be achievable also in humans affected by stroke.

Toward Functional Restoration of the Central Nervous System: A Review of Translational Neuroscience Principles

Injury to the central nervous system (CNS) can leave patients with devastating neurological deficits that may permanently impair independence and diminish quality of life. Recent insights into how the CNS responds to injury and reacts to critically timed interventions are being translated into clinical applications that have the capacity to drastically improve outcomes for patients suffering from permanent neurological deficits due to spinal cord injury, stroke, or other CNS disorders. The translation of such knowledge into practical and impactful treatments involves the strategic collaboration between neurosurgeons, clinicians, therapists, scientists, and industry. Therefore, a common understanding of key neuroscientific principles is crucial. Conceptually, current approaches to CNS revitalization can be divided by scale into macroscopic (systems-circuitry) and microscopic (cellular-molecular). Here we review both emerging and well-established tenets that are being utilized to enhance CNS recovery on both levels, and we explore the role of neurosurgeons in developing therapies moving forward. Key principles include plasticity-driven functional recovery, cellular signaling mechanisms in axonal sprouting, critical timing for recovery after injury, and mechanisms of action underlying cellular replacement strategies. We then discuss integrative approaches aimed at synergizing interventions across scales, and we make recommendations for the basis of future clinical trial design. Ultimately, we argue that strategic modulation of microscopic cellular behavior within a macroscopic framework of functional circuitry re-establishment should provide the foundation for most neural restoration strategies, and the early involvement of neurosurgeons in the process will be crucial to successful clinical translation.

Post-stroke remodeling processes in animal models and humans

After cerebral ischemia, events like neural plasticity and tissue reorganization intervene in lesioned and non-lesioned areas of the brain. These processes are tightly related to functional improvement and successful rehabilitation in patients. Plastic remodeling in the brain is associated with limited spontaneous functional recovery in patients. Improvement depends on the initial deficit, size, nature and localization of the infarction, together with the sex and age of the patient, all of them affecting the favorable outcome of reorganization and repair of damaged areas. A better understanding of cerebral plasticity is pivotal to design effective therapeutic strategies. Experimental models and clinical studies have fueled the current understanding of the cellular and molecular processes responsible for plastic remodeling. In this review, we describe the known mechanisms, in patients and animal models, underlying cerebral reorganization and contributing to functional recovery after ischemic stroke. We also discuss the manipulations and therapies that can stimulate neural plasticity. We finally explore a new topic in the field of ischemic stroke pathophysiology, namely the brain-gut axis.

Long-Term Motor Deficit and Diffuse Cortical Atrophy Following Focal Cortical Ischemia in Athymic Rats

Development of new stroke therapies requires animal models that recapitulate the pathophysiological and functional consequences of ischemic brain damage over time-frames relevant to the therapeutic intervention. This is particularly relevant for the rapidly developing area of stem cell therapies, where functional replacement of circuitry will require maturation of transplanted human cells over months. An additional challenge is the establishment of models of ischemia with stable behavioral phenotypes in chronically immune-suppressed animals to allow for long-term survival of human cell grafts. Here we report that microinjection of endothelin-1 into the sensorimotor cortex of athymic rats results in ischemic damage with a sustained deficit in function of the contralateral forepaw that persists for up to 9 months. The histological post-mortem analysis revealed chronic and diffuse atrophy of the ischemic cortical hemisphere that continued to progress over 9 months. Secondary atrophy remote to the primary site of injury and its relationship with long-term cognitive and functional decline is now recognized in human populations. Thus, focal cortical infarction in athymic rats mirrors important pathophysiological and functional features relevant to human stroke, and will be valuable for assessing efficacy of stem cell based therapies.

Ginsenoside Rb1 Promotes Motor Functional Recovery and Axonal Regeneration in Post-stroke Mice through cAMP/PKA/CREB Signaling Pathway

The central nervous system (CNS) has a poor self-repairing capability after injury because of the inhibition of axonal regeneration by many myelin-associated inhibitory factors. Therefore, ischemic stroke usually leads to disability. Previous studies reported that Ginsenoside Rb1 (GRb1) plays a role in neuronal protection in acute phase after ischemic stroke, but its efficacy in post-stroke and the underlying mechanism are not clear. Recent evidences demonstrated GRb1 promotes neurotransmitter release through the cAMP-depend protein kinase A (PKA) pathway, which is related to axonal regeneration. The present study aimed to determine whether GRb1 improves long-term motor functional recovery and promotes cortical axon regeneration in post-stroke. Adult male C57BL/6 mice were subjected to distal middle cerebral artery occlusion (dMCAO). GRb1 solution (5 mg/ml) or equal volume of normal saline was injected intraperitoneally for the first time at 24 h after surgery, and then daily injected until day 14. Day 3, 7, 14 and 28 after dMCAO were used as observation time points. Motor functional recovery was assessed with Rota-rod test and grid walking task. The expression of growth-associated protein 43 (GAP43) and biotinylated dextran amine (BDA) was measured to evaluate axonal regeneration. The levels of cyclic AMP (cAMP) and PKA were measured by Elisa, PKAc and phosphorylated cAMP response element protein (pCREB) were determined by western blot. Our results shown that GRb1 treatment improved motor function and increased the expression of GAP43 and BDA in ipsilesional and contralateral cortex. GRb1 significantly elevated cAMP and PKA, increased the protein expression of PKAc and pCREB. However, the effects of GRb1 were eliminated by H89 intervention (a PKA inhibitor). These results suggested that GRb1 improved functional recovery in post-stroke by stimulating axonal regeneration and brain repair. The underlying mechanism might be up-regulating the expression of cAMP/PKA/CREB pathway.

Low-intensity contralesional electrical theta burst stimulation modulates ipsilesional excitability and enhances stroke recovery

Targeting interhemispheric inhibition using brain stimulation has shown potential for enhancing stroke recovery. Following stroke, increased inhibition originating from the contralesional hemisphere impairs motor activation in ipsilesional areas. We have previously reported that low-intensity electrical theta burst stimulation (TBS) applied to an implanted electrode in the contralesional rat motor cortex reduces interhemispheric inhibition, and improves functional recovery when commenced three days after cortical injury. Here we apply this approach at more clinically relevant later time points and measure recovery from photothrombotic stroke, following three weeks of low-intensity intermittent TBS (iTBS), continuous TBS (cTBS) or sham stimulation applied to the contralesional motor cortex. Interhemispheric inhibition and cellular excitability were measured in the same rats from single pyramidal neurons in the peri-infarct area, using in vivo intracellular recording. A minimal dose of iTBS did not enhance motor function when applied beginning one month after stroke. However both a high and a low dose of iTBS improved recovery to a similar degree when applied 10 days after stroke, with the degree of recovery positively correlated with ipsilesional excitability. The final level of interhemispheric inhibition was negatively correlated with excitability, but did not independently correlate with functional recovery. In contrast, contralesional cTBS left recovery unaltered, but decreased ipsilesional excitability. These data support focal contralesional iTBS and not cTBS as an intervention for enhancing stroke recovery and suggest that there is a complex relationship between functional recovery and interhemispheric inhibition, with both independently associated with ipsilesional excitability.

Plasticity and recovery of function

The frontal lobe plays a crucial role in human motor behavior. It is one of the last areas of the brain to mature, especially the prefrontal regions. After a brief historical perspective on the perceived dichotomy between the view of the brain as a static organ and that of a plastic, constantly changing structure, we discuss the stability/plasticity dilemma including examples of documented cortical reorganization taking place at multiple spatial and temporal scales. We pose that while plasticity is needed for motor learning, stability of the system is necessary for storage and maintenance of memorized skills. We discuss how this plasticity/stability dilemma is resolved along the life span and after a brain injury. We then examine the main challenges that clinicians have to overcome to promote recovery of function in patients with brain lesions, including attempts to use neurostimulation techniques as adjuvant to training-based customary neurorehabilitation.

Power spectrum slope is related to motor function after focal cerebral ischemia in the rat

Electroencephalography (EEG) changes across vigilance states have been observed after ischemic stroke in patients and experimental stroke models, but their relation to functional recovery remains unclear. Here, we evaluate motor function, as measured by single pellet reaching (SPR), as well as local EEG changes in nonrapid eye movement (NREM), rapid eye movement (REM), and wakefulness during a 30 day recovery period after middle cerebral artery occlusion or sham surgery in rats. Small cortical infarcts resulted in poor SPR performance and induced widespread changes in EEG spectra in the ipsilesional hemisphere in all vigilance states, without causing major changes in sleep-wake architecture. Ipsilesional 1-4 Hz power was increased after stroke, whereas power in higher frequencies was reduced, resulting in a steeper slope of the power spectrum. Microelectrode array analysis of ipsilesional M1 showed that these spectral changes were present on the microelectrode level throughout M1 and were not related to increased synchronization between electrodes. Spectrum slope was significantly correlated with poststroke motor function and may thus be a useful readout of recovery-related plasticity.

Homeostatic activity regulation as a mechanism underlying the effect of brain stimulation

Hyperexcitability of the neural network often occurs after brain injuries or degeneration and is a key pathophysiological feature in certain neurological diseases such as epilepsy, neuropathic pain, and tinnitus. Although the standard approach of pharmacological treatments is to directly suppress the hyperexcitability through reducing excitation or enhancing inhibition, different techniques for stimulating brain activity are often used to treat refractory neurological conditions. However, it is unclear why stimulating brain activity would be effective for controlling hyperexcitability. Recent studies suggest that the pathogenesis in these disorders exhibits a transition from an initial activity loss after acute injury or progressive neurodegeneration to subsequent development of hyperexcitability. This process mimics homeostatic activity regulation and may contribute to developing network hyperexcitability that underlies neurological symptoms. This hypothesis also predicts that stimulating brain activity should be effective in reducing hyperexcitability due to homeostatic activity regulation and in relieving symptoms. Here we review current evidence of homeostatic plasticity in the development of hyperexcitability in some neurological diseases and the effects of brain stimulation. The homeostatic plasticity hypothesis may provide new insights into the pathophysiology of neurological diseases and may guide the use of brain stimulation techniques for treating them.

Neuronal activity and microglial activation support corticospinal tract and proprioceptive afferent sprouting in spinal circuits after a corticospinal system lesion

Spared corticospinal tract (CST) and proprioceptive afferent (PA) axons sprout after injury and contribute to rewiring spinal circuits, affecting motor recovery. Loss of CST connections post-injury results in corticospinal signal loss and associated reduction in spinal activity. We investigated the role of activity loss and injury on CST and PA sprouting. To understand activity-dependence after injury, we compared CST and PA sprouting after motor cortex (MCX) inactivation, produced by chronic MCX muscimol microinfusion, with sprouting after a CST lesion produced by pyramidal tract section (PTx). Activity suppression, which does not produce a lesion, is sufficient to trigger CST axon outgrowth from the active side to cross the midline and to enter the inactivated side of the spinal cord, to the same extent as PTx. Activity loss was insufficient to drive significant CST gray matter axon elongation, an effect of PTx. Activity suppression triggered presynaptic site formation, but less than PTx. Activity loss triggered PA sprouting, as PTx. To understand injury-dependent sprouting further, we blocked microglial activation and associated inflammation after PTX by chronic minocycline administration after PTx. Minocycline inhibited myelin debris phagocytosis contralateral to PTx and abolished CST axon elongation, formation of presynaptic sites, and PA sprouting, but not CST axon outgrowth from the active side to cross the midline. Our findings suggest sprouting after injury has a strong activity dependence and that microglial activation after injury supports axonal elongation and presynaptic site formation. Combining spinal activity support and inflammation control is potentially more effective in promoting functional restoration than either alone.

Brain networks and their relevance for stroke rehabilitation

Stroke has long been regarded as focal disease with circumscribed damage leading to neurological deficits. However, advances in methods for assessing the human brain and in statistics have enabled new tools for the examination of the consequences of stroke on brain structure and function. Thereby, it has become evident that stroke has impact on the entire brain and its network properties and can therefore be considered as a network disease. The present review first gives an overview of current methodological opportunities and pitfalls for assessing stroke-induced changes and reorganization in the human brain. We then summarize principles of plasticity after stroke that have emerged from the assessment of networks. Thereby, it is shown that neurological deficits do not only arise from focal tissue damage but also from local and remote changes in white-matter tracts and in neural interactions among wide-spread networks. Similarly, plasticity and clinical improvements are associated with specific compensatory structural and functional patterns of neural network interactions. Innovative treatment approaches have started to target such network patterns to enhance recovery. Network assessments to predict treatment response and to individualize rehabilitation is a promising way to enhance specific treatment effects and overall outcome after stroke.

Promoting Brain Repair and Regeneration After Stroke: a Plea for Cell-Based Therapies

PURPOSE OF REVIEW

After decades of hype, cell-based therapies are emerging into the clinical arena for the purposes of promoting recovery after stroke. In this review, we discuss the most recent science behind the role of cell-based therapies in ischemic stroke and the efforts to translate these therapies into human clinical trials.

RECENT FINDINGS

Preclinical data support numerous beneficial effects of cell-based therapies in both small and large animal models of ischemic stroke. These benefits are driven by multifaceted mechanisms promoting brain repair through immunomodulation, trophic support, circuit reorganization, and cell replacement. Cell-based therapies offer tremendous potential for improving outcomes after stroke through multimodal support of brain repair. Based on recent clinical trials, cell-based therapies appear both feasible and safe in all phases of stroke. Ongoing translational research and clinical trials will further refine these therapies and have the potential to transform the approach to stroke recovery and rehabilitation.

Compensatory Relearning Following Stroke: Cellular and Plasticity Mechanisms in Rodents

von Monakow’s theory of diaschisis states the functional ‘standstill’ of intact brain regions that are remote from a damaged area, often implied in recovery of function. Accordingly, neural plasticity and activity patterns related to recovery are also occurring at the same regions. Recovery relies on plasticity in the periinfarct and homotopic contralesional regions and involves relearning to perform movements. Seeking evidence for a relearning mechanism following stroke, we found that rodents display many features that resemble classical learning and memory mechanisms. Compensatory relearning is likely to be accompanied by gradual shaping of these regions and pathways, with participating neurons progressively adapting cortico-striato-thalamic activity and synaptic strengths at different cortico-thalamic loops – adapting function relayed by the striatum. Motor cortex functional maps are progressively reinforced and shaped by these loops as the striatum searches for different functional actions. Several cortical and striatal cellular mechanisms that influence motor learning may also influence post-stroke compensatory relearning. Future research should focus on how different neuromodulatory systems could act before, during or after rehabilitation to improve stroke recovery.

Inflammation and neural repair after ischemic brain injury

Stroke causes neuronal cell death and destruction of neuronal circuits in the brain and spinal cord. Injury to the brain tissue induces sterile inflammation triggered by the extracellular release of endogenous molecules, but cerebral inflammation after stroke is gradually resolved within several days. In this pro-resolving process, inflammatory cells adopt a pro-resolving or repairing phenotype in the injured brain, activating endogenous repairing programs. Although the mechanisms involved in the transition from inflammation to neural repair after stroke remain largely unknown to date, some of the mechanisms for inflammation and neural repair have been clarified in detail. This review focuses on the molecular or cellular mechanisms involved in sterile inflammation and neural repair after stroke. This accumulation of evidence may be helpful for speculating about the endogenous repairing mechanisms in the brain and identifying therapeutic targets for improving the functional prognoses of stroke patients.

A systematic review and meta-analysis of sleep architecture and chronic traumatic brain injury

Sleep quality appears to be altered by traumatic brain injury (TBI). However, whether persistent post-injury changes in sleep architecture are present is unknown and relatively unexplored. We conducted a systematic review and meta-analysis to assess the extent to which chronic TBI (>6 months since injury) is characterized by changes to sleep architecture. We also explored the relationship between sleep architecture and TBI severity. In the fourteen included studies, sleep was assessed with at least one night of polysomnography in both chronic TBI participants and controls. Statistical analyses, performed using Comprehensive Meta-Analysis software, revealed that chronic TBI is characterized by relatively increased slow wave sleep (SWS). A meta-regression showed moderate-severe TBI is associated with elevated SWS, reduced stage 2, and reduced sleep efficiency. In contrast, mild TBI was not associated with any significant alteration of sleep architecture. The present findings are consistent with the hypothesis that increased SWS after moderate-severe TBI reflects post-injury cortical reorganization and restructuring. Suggestions for future research are discussed, including adoption of common data elements in future studies to facilitate cross-study comparability, reliability, and replicability, thereby increasing the likelihood that meaningful sleep (and other) biomarkers of TBI will be identified.

Modified structural network backbone in the contralesional hemisphere chronically after stroke in rat brain

Functional outcome after stroke depends on the local site of ischemic injury and on remote effects within connected networks, frequently extending into the contralesional hemisphere. However, the pattern of large-scale contralesional network remodeling remains largely unresolved. In this study, we applied diffusion-based tractography and graph-based network analysis to measure structural connectivity in the contralesional hemisphere chronically after experimental stroke in rats. We used the minimum spanning tree method, which accounts for variations in network density, for unbiased characterization of network backbones that form the strongest connections in a network. Ultrahigh-resolution diffusion MRI scans of eight post-mortem rat brains collected 70 days after right-sided stroke were compared against scans from 10 control brains. Structural network backbones of the left (contralesional) hemisphere, derived from 42 atlas-based anatomical regions, were found to be relatively stable across stroke and control animals. However, several sensorimotor regions showed increased connection strength after stroke. Sensorimotor function correlated with specific contralesional sensorimotor network backbone measures of global integration and efficiency. Our findings point toward post-stroke adaptive reorganization of the contralesional sensorimotor network with recruitment of distinct sensorimotor regions, possibly through strengthening of connections, which may contribute to functional recovery.

Theta-Band Oscillations as an Indicator of Mild Traumatic Brain Injury

Mild traumatic brain injury (mTBI) patients continue to pose a diagnostic challenge due to their diverse symptoms without trauma-specific changes in structural imaging. We addressed here the possible early changes in spontaneous oscillatory brain activity after mTBI, and their feasibility as an indicator of injury in clinical evaluation. We recorded resting-state magnetoencephalography (MEG) data in both eyes-open and eyes-closed conditions from 26 patients (11 females and 15 males, aged 20–59) with mTBI 6 days–6 months after the injury, and compared their spontaneous oscillatory activity to corresponding data from 139 healthy controls. Twelve of the patients underwent a follow-up measurement at 6 months. Ten of all patients were without structural lesions in MRI. At single-subject level, aberrant 4–7 Hz (theta) band activity exceeding the + 2 SD limit of the healthy subjects was visible in 7 out of 26 patients; three out of the seven patients with abnormal theta activity were without any detectable lesions in MRI. Of the patients that participated in the follow-up measurements, five showed abnormal theta activity in the first recording, but only two in the second measurement. Our results suggest that aberrant theta-band oscillatory activity can provide an early objective sign of brain dysfunction after mTBI. In 3/7 patients, the slow-wave activity was transient and visible only in the first recording, urging prompt timing for the measurements in clinical settings.

Gabapentin Prevents Progressive Increases in Excitatory Connectivity and Epileptogenesis Following Neocortical Trauma

Neocortical injury initiates a cascade of events, some of which result in maladaptive epileptogenic reorganization of surviving neural circuits. Research focused on molecular and organizational changes that occur following trauma may reveal processes that underlie human post-traumatic epilepsy (PTE), a common and unfortunate consequence of traumatic brain injury. The latency between injury and development of PTE provides an opportunity for prophylactic intervention, once the key underlying mechanisms are understood. In rodent neocortex, injury to pyramidal neurons promotes axonal sprouting, resulting in increased excitatory circuitry that is one important factor promoting epileptogenesis. We used laser-scanning photostimulation of caged glutamate and whole-cell recordings in in vitro slices from injured neocortex to assess formation of new excitatory synapses, a process known to rely on astrocyte-secreted thrombospondins (TSPs), and to map the distribution of maladaptive circuit reorganization. We show that this reorganization is centered principally in layer V and associated with development of epileptiform activity. Short-term blockade of the synaptogenic effects of astrocyte-secreted TSPs with gabapentin (GBP) after injury suppresses the new excitatory connectivity and epileptogenesis for at least 2 weeks. Results reveal that aberrant circuit rewiring is progressive in vivo and provide further rationale for prophylactic anti-epileptogenic use of gabapentinoids following cortical trauma.

Cortical Reorganization of Sensorimotor Systems and the Role of Intracortical Circuits After Spinal Cord Injury

The plasticity of sensorimotor systems in mammals underlies the capacity for motor learning as well as the ability to relearn following injury. Spinal cord injury, which both deprives afferent input and interrupts efferent output, results in a disruption of cortical somatotopy. While changes in corticospinal axons proximal to the lesion are proposed to support the reorganization of cortical motor maps after spinal cord injury, intracortical horizontal connections are also likely to be critical substrates for rehabilitation-mediated recovery. Intrinsic connections have been shown to dictate the reorganization of cortical maps that occurs in response to skilled motor learning as well as after peripheral injury. Cortical networks incorporate changes in motor and sensory circuits at subcortical or spinal levels to induce map remodeling in the neocortex. This review focuses on the reorganization of cortical networks observed after injury and posits a role of intracortical circuits in recovery.

The effect of a single dose of escitalopram on sensorimotor networks

INTRODUCTION

Serving as a pilot study of poststroke pharmacotherapy, the present investigation was intended to establish the effect of a single dose of escitalopram on motor task performance in normal volunteers.

METHODS

Ten healthy volunteers of median age 63 years including four females performed a well-studied tactile manipulation task in two fMRI sessions using a double-blind cross-over design. The sessions began approximately three hours after ingestion of 20 mg escitalopram or placebo presented in pseudorandom order. The fMRI image sequences were submitted to principal component analysis (PCA).

RESULTS

Based on volume correlations of task-related principal components with the mean component images derived in our previous study, we established the reproducibility of two networks of sensorimotor activity proposed there. The network reflecting motor control (cerebral pattern I) appeared invariably in placebo and verum conditions. In contrast, the other network, attributed to diminished motor control due to distracting mental processing (cerebral pattern II), emerged less regularly and exhibited more variability. Second-level PCAs of both conditions confirmed the findings of the initial analysis. Specifically, it validated the dominant and invariable expression of cerebral pattern I after application of a single dose of escitalopram. Dynamic causal modeling confirmed enhanced motor output as a result of a significantly increased connectivity between primary motor cortex and dorsal premotor cortex.

CONCLUSION

This pilot study suggests the promise of stimulation by a specific serotonin reuptake inhibitor in regard to recovery and preservation of motor control after stroke.

Preservation of interhemispheric cortical connections through corpus callosum following intravenous infusion of mesenchymal stem cells in a rat model of cerebral infarction

Systemic administration of mesenchymal stem cells (MSCs) following cerebral infarction exerts functional improvements. Previous research has suggested potential therapeutic mechanisms that promote neuroprotection and synaptogenesis. These include secretion of neurotrophic factors, remodeling of neural circuits, restoration of the blood brain barrier, reduction of inflammatory infiltration and demyelination, and elevation of trophic factors. In addition to these mechanisms, we hypothesized that restored interhemispheric bilateral motor cortex connectivity might be an additional mechanism of functional recovery. In the present study, we have shown, with both MRI diffusion tensor imaging (DTI) and neuroanatomical tracing techniques using an adeno-associated virus (AAV) expressing GFP, that there was anatomical restoration of cortical interhemispheric connections through the corpus callosum after intravenous infusion of MSCs in a rat middle cerebral artery occlusion (MCAO) stroke model. Moreover, the degree of connectivity was greater in the MSC-treated group than in the vehicle-infused group. In accordance, both the thickness of corpus callosum and synaptic puncta in the contralateral (non-infarcted) motor cortex connected to the corpus callosum were greater in the MSC-treated group than in the vehicle group. Together, these results suggest that distinct preservation of interhemispheric cortical connections through corpus callosum was promoted by intravenous infusion of MSCs. This anatomical preservation of the motor cortex in the contralateral hemisphere may contribute to functional improvements following MSC therapy for cerebral stroke.

Motor Improvement of Skilled Forelimb Use Induced by Treatment with Growth Hormone and Rehabilitation Is Dependent on the Onset of the Treatment after Cortical Ablation

We previously demonstrated that the administration of GH immediately after severe motor cortex injury, in rats, followed by rehabilitation, improved the functionality of the affected limb and reexpressed nestin in the contralateral motor cortex. Here, we analyze whether these GH effects depend on a time window after the injury and on the reexpression of nestin and actin. Injured animals were treated with GH (0.15 mg/kg/day) or vehicle, at days 7, 14, and 35 after cortical ablation. Rehabilitation was applied at short and long term (LTR) after the lesion and then sacrificed. Nestin and actin were analyzed by immunoblotting in the contralateral motor cortex. Giving GH at days 7 or 35 after the lesion, but not 14 days after it, led to a remarkable improvement in the functionality of the affected paw. Contralateral nestin and actin reexpression was clearly higher in GH-treated animals, probably because compensatory brain plasticity was established. GH and immediate rehabilitation are key for repairing brain injuries, with the exception of a critical time period: GH treatment starting 14 days after the lesion. Our data also indicate that there is not a clear plateau in the recovery from a brain injury in agreement with our data in human patients.

Recovery of the 20 Hz Rebound to Tactile and Proprioceptive Stimulation after Stroke

Sensorimotor integration is closely linked to changes in motor-cortical excitability, observable in the modulation of the 20 Hz rhythm. After somatosensory stimulation, the rhythm transiently increases as a rebound that reflects motor-cortex inhibition. Stroke-induced alterations in afferent input likely affect motor-cortex excitability and motor recovery. To study the role of somatosensory afferents in motor-cortex excitability after stroke, we employed magnetoencephalographic recordings (MEG) at 1–7 days, one month, and 12 months in 23 patients with stroke in the middle cerebral artery territory and 22 healthy controls. The modulation of the 20 Hz motor-cortical rhythm was evaluated to two different somatosensory stimuli, tactile stimulation, and passive movement of the index fingers. The rebound strengths to both stimuli were diminished in the acute phase compared to the controls and increased significantly during the first month after stroke. However, only the rebound amplitudes to tactile stimuli fully recovered within the follow-up period. The rebound strengths in the affected hemisphere to both stimuli correlated strongly with the clinical scores across the follow-up. The results show that changes in the 20 Hz rebound to both stimuli behave similarly and occur predominantly during the first month. The 20 Hz rebound is a potential marker for predicting motor recovery after stroke.

Objective Sleep Measures in Inpatients With Subacute Stroke Associated With Levels and Improvements in Activities of Daily Living

OBJECTIVE

To investigate whether objective polysomnographic measures of prevalent sleep problems such as sleep-disordered-breathing (SDB) and insomnia are associated with activities of daily living levels in inpatients at rehabilitation units.

DESIGN

Retrospective and observational study.

SETTING

Single rehabilitation center.

PARTICIPANTS

Inpatients with subacute stroke (N=123) (61.6±13.1 years; 23.8±3.4 kg/m²; 33% women; 90.5±36.7 days post-stroke) underwent a 1-night polysomnographic study and a 1-month inpatient rehabilitation program.

MAIN OUTCOME MEASURES

Admission and discharge Barthel Index (BI) scores and its change scores.

RESULTS

One hundred three (92%) patients had moderate-to-severe SDB (46.7±25.1 events/h in the apnea-hypopnea index), and 24 (19.5%) patients had acceptable continuous positive airway pressure adherence. Diverse values were found for total sleep time (259±71 min), sleep efficiency (69.5%±19.3%), sleep latency (24.3±30.9 min), and wakefulness after sleep onset (93.1±74.2 min). Admission BI scores and the BI change scores were 33.8±23.2 and 10.1±9.2, respectively. The National Institutes of Health Stroke Scale (NIHSS, 10.2±5.6), available in 57 (46%) patients, was negatively associated with admission levels and gains in BI change scores (P<.001, =0.002, respectively) in a univariate analysis. In regression models with backward selection, excluding NIHSS score, both age (P=.025) and wakefulness after sleep onset (P<.001) were negatively associated (adjusted R²=0.260) with admission BI scores. Comorbidity of hypertension; sleep latency percentage of stage 1, non-rapid eye movement sleep; and desaturation events ≥4% (P<.001, 0.001, 0.021, and 0.043, respectively; adjusted R²=0.252) were negatively associated with BI score gains.

CONCLUSIONS

Based on objective sleep measures, insomnia rather than SDB in inpatients with subacute stroke was associated negatively with admission levels of activity of daily living and its improvement after a 1-month rehabilitation course.

Longitudinal Structural and Functional Differences Between Proportional and Poor Motor Recovery After Stroke

BACKGROUND

Evolution of motor function during the first months after stroke is stereotypically bifurcated, consisting of either recovery to about 70% of maximum possible improvement ("proportional recovery, PROP") or in little to no improvement ("poor recovery, POOR"). There is currently no evidence that any rehabilitation treatment will prevent POOR and favor PROP.

OBJECTIVE

To perform a longitudinal and multimodal assessment of functional and structural changes in brain organization associated with PROP.

METHODS

Fugl-Meyer Assessments of the upper extremity and high-density electroencephalography (EEG) were obtained from 63 patients, diffusion tensor imaging from 46 patients, at 2 and 4 weeks (T0) and at 3 months (T1) after stroke onset.

RESULTS

We confirmed the presence of 2 distinct recovery patterns (PROP and POOR) in our sample. At T0, PROP patients had greater integrity of the corticospinal tract (CST) and greater EEG functional connectivity (FC) between the affected hemisphere and rest of the brain, in particular between the ventral premotor and the primary motor cortex. POOR patients suffered from degradation of corticocortical and corticofugal fiber tracts in the affected hemisphere between T0 and T1, which was not observed in PROP patients. Better initial CST integrity correlated with greater initial global FC, which was in turn associated with less white matter degradation between T0 and T1.

CONCLUSIONS

These findings suggest links between initial CST integrity, systems-level cortical network plasticity, reduction of white matter atrophy, and clinical motor recovery after stroke. This identifies candidate treatment targets.

Optogenetically stimulating intact rat corticospinal tract post-stroke restores motor control through regionalized functional circuit formation

Current neuromodulatory strategies to enhance motor recovery after stroke often target large brain areas non-specifically and without sufficient understanding of their interaction with internal repair mechanisms. Here we developed a novel therapeutic approach by specifically activating corticospinal circuitry using optogenetics after large strokes in rats. Similar to a neuronal growth-promoting immunotherapy, optogenetic stimulation together with intense, scheduled rehabilitation leads to the restoration of lost movement patterns rather than induced compensatory actions, as revealed by a computer vision-based automatic behavior analysis. Optogenetically activated corticospinal neurons promote axonal sprouting from the intact to the denervated cervical hemi-cord. Conversely, optogenetically silencing subsets of corticospinal neurons in recovered animals, results in mistargeting of the restored grasping function, thus identifying the reestablishment of specific and anatomically localized cortical microcircuits. These results provide a conceptual framework to improve established clinical techniques such as transcranial magnetic or transcranial direct current stimulation in stroke patients.

Existing methods to improve motor function after stroke include non-specific neuromodulatory approaches. Here the authors use an automated method of analysis of reaching behaviour in rodents to show that optogenetic stimulation of intact corticospinal tract fibres leads to restoration of prior motor functions, rather than compensatory acquisition of new movements.

Retinoic acid protects from experimental cerebral infarction by upregulating GAP-43 expression

The aim of this study was to investigate whether exogenous retinoic acid (RA) can upregulate the mRNA and protein expression of growth-associated protein 43 (GAP-43), thereby promoting brain functional recovery in a rat distal middle cerebral artery occlusion (MCAO) model of ischemia. A total of 216 male Sprague Dawley rats weighing 300–320 g were divided into 3 groups: sham-operated group, MCAO+vehicle group and MCAO+RA group. Focal cortical infarction was induced with a distal MCAO model. The expression of GAP-43 mRNA and protein in the ipsilateral perifocal region was assessed using qPCR and immunocytochemistry at 1, 3, 7, 14, 21, and 28 days after distal MCAO. In addition, an intraperitoneal injection of RA was given 12 h before MCAO and continued every day until the animal was sacrificed. Following ischemia, the expression of GAP-43 first increased considerably and then decreased. Administration of RA reduced infarction volume, promoted neurological functional recovery and upregulated expression of GAP-43. Administration of RA can ameliorate neuronal damage and promote nerve regeneration by upregulating the expression of GAP-43 in the perifocal region after distal MCAO.

Functional remodeling of subtype-specific markers surrounding implanted neuroprostheses

Microelectrode arrays implanted in the brain are increasingly used for the research and treatment of intractable neurological disease. However, local neuronal loss and glial encapsulation are known to interfere with effective integration and communication between implanted devices and brain tissue, where these observations are typically based on assessments of broad neuronal and astroglial markers. However, both neurons and astrocytes comprise heterogeneous cellular populations that can be further divided into subclasses based on unique functional and morphological characteristics. In this study, we investigated whether or not device insertion causes alterations in specific subtypes of these cells. We assessed the expression of both excitatory and inhibitory markers of neurotransmission (vesicular glutamate and GABA transporters, VGLUT1 and VGAT, respectively) surrounding single-shank Michigan-style microelectrode arrays implanted in the motor cortex of adult rats by use of quantitative immunohistochemistry. We found a pronounced shift from significantly elevated VGLUT1 within the initial days following implantation to relatively heightened VGAT by the end of the 4-wk observation period. Unexpectedly, we observed VGAT positivity in a subset of reactive astrocytes during the first week of implantation, indicating heterogeneity in early-responding encapsulating glial cells. We coupled our VGLUT1 data with the evaluation of a second marker of excitatory neurons (CamKiiα); the results closely paralleled each other and underscored a progression from initially heightened to subsequently weakened excitatory tone in the neural tissue proximal to the implanted electrode interface (within 40 μm). Our results provide new evidence for subtype-specific remodeling surrounding brain implants that inform observations of suboptimal integration and performance.NEW & NOTEWORTHY We report novel changes in the local expression of excitatory and inhibitory synaptic markers surrounding microelectrode arrays implanted in the motor cortex of rats, where a progressive shift toward increased inhibitory tone was observed over the 4-wk observation period. The result was driven by declining glutamate transporter expression (VGLUT1) in parallel with increasing GABA transporter expression (VGAT) over time, where a reactive VGAT+ astroglial subtype made an unexpected contribution to our findings.

PEGylated insulin-like growth factor-I affords protection and facilitates recovery of lost functions post-focal ischemia

Insulin-like growth factor-I (IGF-I) is involved in the maturation and maintenance of neurons, and impaired IGF-I signaling has been shown to play a role in various neurological diseases including stroke. The aim of the present study was to investigate the efficacy of an optimized IGF-I variant by adding a 40 kDa polyethylene glycol (PEG) chain to IGF-I to form PEG-IGF-I. We show that PEG-IGF-I has a slower clearance which allows for twice-weekly dosing to maintain steady-state serum levels in mice. Using a photothrombotic model of focal stroke, dosing from 3 hrs post-stroke dose-dependently (0.3–1 mg/kg) decreases the volume of infarction and improves motor behavioural function in both young 3-month and aged 22–24 month old mice. Further, PEG-IGF-I treatment increases GFAP expression when given early (3 hrs post-stroke), increases Synaptophysin expression and increases neurogenesis in young and aged. Finally, neurons (P5–6) cultured in vitro on reactive astrocytes in the presence of PEG-IGF-I showed an increase in neurite length, indicating that PEG-IGF-I can aid in sprouting of new connections. This data suggests a modulatory role of IGF-I in both protective and regenerative processes, and indicates that therapeutic approaches using PEG-IGF-I should be given early and where the endogenous regenerative potential is still high.

The role of sleep in recovery following ischemic stroke: A review of human and animal data

Despite advancements in understanding the pathophysiology of stroke and the state of the art in acute management of afflicted patients as well as in subsequent neurorehabilitation training, stroke remains the most common neurological cause of long-term disability in adulthood. To enhance stroke patients' independence and well-being it is necessary, therefore, to consider and develop new therapeutic strategies and approaches. We postulate that sleep might play a pivotal role in neurorehabilitation following stroke. Over the last two decades compelling evidence for a major function of sleep in neuroplasticity and neural network reorganization underlying learning and memory has evolved. Training and learning of new motor skills and knowledge can modulate the characteristics of subsequent sleep, which additionally can improve memory performance. While healthy sleep appears to support neuroplasticity resulting in improved learning and memory, disturbed sleep following stroke in animals and humans can impair stroke outcome. In addition, sleep disorders such as sleep disordered breathing, insomnia, and restless legs syndrome are frequent in stroke patients and associated with worse recovery outcomes. Studies investigating the evolution of post-stroke sleep changes suggest that these changes might also reflect neural network reorganization underlying functional recovery. Experimental and clinical studies provide evidence that pharmacological sleep promotion in rodents and treatment of sleep disorders in humans improves functional outcome following stroke. Taken together, there is accumulating evidence that sleep represents a "plasticity state" in the process of recovery following ischemic stroke. However, to test the key role of sleep and sleep disorders for stroke recovery and to better understand the underlying molecular mechanisms, experimental research and large-scale prospective studies in humans are necessary. The effects of hospital conditions, such as adjusting light conditions according to the patients' sleep-wake rhythms, or sleep promoting drugs and non-invasive brain stimulation to promote neuronal plasticity and recovery following stroke requires further investigation.

Stroke Lesions in a Large Upper Limb Rehabilitation Trial Cohort Rarely Match Lesions in Common Preclinical Models

BACKGROUND

Stroke patients with mild-moderate upper extremity motor impairments and minimal sensory and cognitive deficits provide a useful model to study recovery and improve rehabilitation. Laboratory-based investigators use lesioning techniques for similar goals.

OBJECTIVE

To determine whether stroke lesions in an upper extremity rehabilitation trial cohort match lesions from the preclinical stroke recovery models used to drive translational research.

METHODS

Clinical neuroimages from 297 participants enrolled in the Interdisciplinary Comprehensive Arm Rehabilitation Evaluation (ICARE) study were reviewed. Images were characterized based on lesion type (ischemic or hemorrhagic), volume, vascular territory, depth (cortical gray matter, cortical white matter, subcortical), old strokes, and leukoaraiosis. Lesions were compared with those of preclinical stroke models commonly used to study upper limb recovery.

RESULTS

Among the ischemic stroke participants, median infarct volume was 1.8 mL, with most lesions confined to subcortical structures (61%) including the anterior choroidal artery territory (30%) and the pons (23%). Of ICARE participants, <1% had lesions resembling proximal middle cerebral artery or surface vessel occlusion models. Preclinical models of subcortical white matter injury best resembled the ICARE population (33%). Intracranial hemorrhage participants had small (median 12.5 mL) lesions that best matched the capsular hematoma preclinical model.

CONCLUSIONS

ICARE subjects are not representative of all stroke patients, but they represent a clinically and scientifically important subgroup. Compared with lesions in general stroke populations and widely studied animal models of recovery, ICARE participants had smaller, more subcortically based strokes. Improved preclinical-clinical translational efforts may require better alignment of lesions between preclinical and human stroke recovery models.

Enhancing Nervous System Recovery through Neurobiologics, Neural Interface Training, and Neurorehabilitation

After an initial period of recovery, human neurological injury has long been thought to be static. In order to improve quality of life for those suffering from stroke, spinal cord injury, or traumatic brain injury, researchers have been working to restore the nervous system and reduce neurological deficits through a number of mechanisms. For example, neurobiologists have been identifying and manipulating components of the intra- and extracellular milieu to alter the regenerative potential of neurons, neuro-engineers have been producing brain-machine and neural interfaces that circumvent lesions to restore functionality, and neurorehabilitation experts have been developing new ways to revitalize the nervous system even in chronic disease. While each of these areas holds promise, their individual paths to clinical relevance remain difficult. Nonetheless, these methods are now able to synergistically enhance recovery of native motor function to levels which were previously believed to be impossible. Furthermore, such recovery can even persist after training, and for the first time there is evidence of functional axonal regrowth and rewiring in the central nervous system of animal models. To attain this type of regeneration, rehabilitation paradigms that pair cortically-based intent with activation of affected circuits and positive neurofeedback appear to be required-a phenomenon which raises new and far reaching questions about the underlying relationship between conscious action and neural repair. For this reason, we argue that multi-modal therapy will be necessary to facilitate a truly robust recovery, and that the success of investigational microscopic techniques may depend on their integration into macroscopic frameworks that include task-based neurorehabilitation. We further identify critical components of future neural repair strategies and explore the most updated knowledge, progress, and challenges in the fields of cellular neuronal repair, neural interfacing, and neurorehabilitation, all with the goal of better understanding neurological injury and how to improve recovery.

Disrupted mitochondrial genes and inflammation following stroke

AIMS

Determine the subacute time course of mitochondria disruption, cell death, and inflammation in a rat model of unilateral motor cortical ischemic stroke.

MAIN METHODS

Rats received unilateral ischemia of the motor cortex and were tested on behavioral tasks to determine impairments. Animals were euthanized at 24h, 72h and 144h and mRNA expression of key mitochondria proteins and indicators of inflammation, apoptosis and potential regenerative processes in ipsilesion cortex and striatum, using RT-qPCR. Mitochondrial proteins were examined at 144h using immunoblot analysis.

KEY FINDINGS

Rats with stroke induced-behavioral deficits had sustained, 144h post-lesion, decreases in mitochondrial-encoded electron transport chain proteins NADH dehydrogenase subunit-1 and cytochrome c oxidase subunit-1 (mRNA and protein) and mitochondrial DNA content in perilesion motor and sensory cortex. Uncoupling-protein-2 gene expression, but not superoxide dismutase-2, remained elevated in ipsilateral cortex and striatum at this time. Cortical inflammatory cytokine, interleukin-6, was increased early and was followed by increased macrophage marker F4/80 after stroke. Cleaved caspase-3 activation was elevated in cortex and growth associated protein-43 was elevated in the cortex and striatum six days post-lesion.

SIGNIFICANCE

We identified a relationship between three disrupted pathways, (1) sustained loss of mitochondrial proteins and mitochondrial DNA copy number in the cortex linked to decreased mitochondrial gene transcription; (2) early inflammatory response mediated by interleukin- 6 followed by macrophages; (3) apoptosis in conjunction with the activation of regenerative pathways. The stroke-induced spatial and temporal profiles lay the foundation to target pharmacological therapeutics to these three pathways.