Periinfarct and remote excitability changes after transient middle cerebral artery occlusion

Disentangling neuroplasticity mechanisms in post-stroke language recovery

A major objective in post-stroke aphasia research is to gain a deeper understanding of neuroplastic mechanisms that drive language recovery, with the ultimate goal of enhancing treatment outcomes. Subsequent to recent advances in neuroimaging techniques, we now have the ability to examine more closely how neural activity patterns change after a stroke. However, the way these neural activity changes relate to language impairments and language recovery is still debated. The aim of this review is to provide a theoretical framework to better investigate and interpret neuroplasticity mechanisms underlying language recovery in post-stroke aphasia. We detail two sets of neuroplasticity mechanisms observed at the synaptic level that may explain functional neuroimaging findings in post-stroke aphasia recovery at the network level: feedback-based homeostatic plasticity and associative Hebbian plasticity. In conjunction with these plasticity mechanisms, higher-order cognitive control processes dynamically modulate neural activity in other regions to meet communication demands, despite reduced neural resources. This work provides a network-level neurobiological framework for understanding neural changes observed in post-stroke aphasia and can be used to define guidelines for personalized treatment development.

Patient-specific modeling for guided rehabilitation of stroke patients: the BrainX3 use-case

BrainX3 is an interactive neuroinformatics platform that has been thoughtfully designed to support neuroscientists and clinicians with the visualization, analysis, and simulation of human neuroimaging, electrophysiological data, and brain models. The platform is intended to facilitate research and clinical use cases, with a focus on personalized medicine diagnostics, prognostics, and intervention decisions. BrainX3 is designed to provide an intuitive user experience and is equipped to handle different data types and 3D visualizations. To enhance patient-based analysis, and in keeping with the principles of personalized medicine, we propose a framework that can assist clinicians in identifying lesions and making patient-specific intervention decisions. To this end, we are developing an AI-based model for lesion identification, along with a mapping of tract information. By leveraging the patient's lesion information, we can gain valuable insights into the structural damage caused by the lesion. Furthermore, constraining whole-brain models with patient-specific disconnection masks can allow for the detection of mesoscale excitatory-inhibitory imbalances that cause disruptions in macroscale network properties. Finally, such information has the potential to guide neuromodulation approaches, assisting in the choice of candidate targets for stimulation techniques such as Transcranial Ultrasound Stimulation (TUS), which modulate E-I balance, potentiating cortical reorganization and the restoration of the dynamics and functionality disrupted due to the lesion.

Rethinking Remapping: Circuit Mechanisms of Recovery after Stroke

Stroke is one of the most common causes of disability, and there are few treatments that can improve recovery after stroke. Therapeutic development has been hindered because of a lack of understanding of precisely how neural circuits are affected by stroke, and how these circuits change to mediate recovery. Indeed, some of the hypotheses for how the CNS changes to mediate recovery, including remapping, redundancy, and diaschisis, date to more than a century ago. Recent technological advances have enabled the interrogation of neural circuits with ever greater temporal and spatial resolution. These techniques are increasingly being applied across animal models of stroke and to human stroke survivors, and are shedding light on the molecular, structural, and functional changes that neural circuits undergo after stroke. Here we review these studies and highlight important mechanisms that underlie impairment and recovery after stroke. We begin by summarizing knowledge about changes in neural activity that occur in the peri-infarct cortex, specifically considering evidence for the functional remapping hypothesis of recovery. Next, we describe the importance of neural population dynamics, disruptions in these dynamics after stroke, and how allocation of neurons into spared circuits can restore functionality. On a more global scale, we then discuss how effects on long-range pathways, including interhemispheric interactions and corticospinal tract transmission, contribute to post-stroke impairments. Finally, we look forward and consider how a deeper understanding of neural circuit mechanisms of recovery may lead to novel treatments to reduce disability and improve recovery after stroke.

Multiscale effects of excitatory-inhibitory homeostasis in lesioned cortical networks: A computational study

Stroke-related disruptions in functional connectivity (FC) often spread beyond lesioned areas and, given the localized nature of lesions, it is unclear how the recovery of FC is orchestrated on a global scale. Since recovery is accompanied by long-term changes in excitability, we propose excitatory-inhibitory (E-I) homeostasis as a driving mechanism. We present a large-scale model of the neocortex, with synaptic scaling of local inhibition, showing how E-I homeostasis can drive the post-lesion restoration of FC and linking it to changes in excitability. We show that functional networks could reorganize to recover disrupted modularity and small-worldness, but not network dynamics, suggesting the need to consider forms of plasticity beyond synaptic scaling of inhibition. On average, we observed widespread increases in excitability, with the emergence of complex lesion-dependent patterns related to biomarkers of relevant side effects of stroke, such as epilepsy, depression and chronic pain. In summary, our results show that the effects of E-I homeostasis extend beyond local E-I balance, driving the restoration of global properties of FC, and relating to post-stroke symptomatology. Therefore, we suggest the framework of E-I homeostasis as a relevant theoretical foundation for the study of stroke recovery and for understanding the emergence of meaningful features of FC from local dynamics.

Ischemic stroke rehabilitation through optogenetic modulation of parvalbumin neurons in the contralateral motor cortex

BACKGROUND

Based on the theory of interhemispheric inhibition and the bimodal balance-recovery model in stroke, we explored the effects of excitation/inhibition (E/I) of parvalbumin (PV) neurons in the contralateral primary motor cortex (cM1) connecting the ipsilateral M1 (iM1) via the corpus callosum (cM1-CC-iM1) of ischemic stroke rats by optogenetic stimulation.

METHODS

We tested this by injecting anterograde and retrograde virus in rats with middle cerebral artery occlusion (MCAO), and evaluated the neurological scores, motor behavior, volume of cerebral infarction and the E/I balance of the bilateral M1 two weeks after employing optogenetic treatment.

RESULTS

We found that concentrations of Glu and GABA decreased and increased, respectively, in the iM1 of MCAO rats, and that the former increased in the cM1, suggesting E/I imbalance in bilateral M1 after ischemic stroke. Interestingly, optogenetic stimulation improved M1 E/I imbalance, as illustrated by the increase of Glu in the iM1 and the decrease of GABA in both iM1 and cM1, which were accompanied by an improvement in neurological deficit and motor dysfunction. In addition, we observed a reduced infarct volume, an increase in the expression of the NMDAR and AMPAR, and a decrease in GAD67 in the iM1 after intervention.

CONCLUSIONS

Optogenetic modulation of PV neurons of the iM1-CC-cM1 improve E/I balance, leading to reduced neurological deficit and improved motor dysfunction following ischemic stroke in rats.

Absence of Perilesional Neuroplastic Recruitment in Chronic Poststroke Aphasia

BACKGROUND AND OBJECTIVES

A prominent theory proposes that neuroplastic recruitment of perilesional tissue supports aphasia recovery, especially when language-capable cortex is spared by smaller lesions. This theory has rarely been tested directly and findings have been inconclusive. We tested the perilesional plasticity hypothesis using 2 fMRI tasks in 2 groups of patients with previous aphasia diagnosis.

METHODS

Two cohorts totaling 82 patients with chronic left-hemisphere stroke with previous aphasia diagnosis and 82 control participants underwent fMRI using either a naming task or a reliable semantic decision task. Individualized perilesional tissue was defined by dilating anatomical lesions and language regions were defined using meta-analyses. Mixed modeling examined differences in activity between groups. Relationships with lesion size and aphasia severity were examined.

RESULTS

Patients exhibited reduced activity in perilesional language tissue relative to controls in both tasks. Although a few cortical regions exhibited greater activity irrespective of distance from the lesion, or only when distant from the lesion, no regions exhibited increased activity only when near the lesion. Larger lesions were associated with reduced language activity irrespective of distance from the lesion. Using the reliable fMRI task, reduced language activity was related to aphasia severity independent of lesion size.

DISCUSSION

We found no evidence for neuroplastic recruitment of perilesional tissue in aphasia beyond its typical role in language. Rather, our findings are consistent with alternative hypotheses that changes in left-hemisphere activation during recovery relate to normalization of language network dysfunction and possibly recruitment of alternate cortical processors. These findings clarify left-hemisphere neuroplastic mechanisms supporting language recovery after stroke.

Evaluating the Abnormality of Bilateral Motor Cortex Activity in Subacute Stroke Patients Executing a Unimanual Motor Task With Increasing Demand on Precision

Abnormal contralesional M1 activity is consistently reported in patients with compromised upper limb and hand function after stroke. The underlying mechanisms and functional implications of this activity are not clear, which hampers the development of treatment strategies targeting this brain area. The goal of the present study was to determine the extent to which contralesional M1 activity can be explained by the demand of a motor task, given recent evidence for increasing ipsilateral M1 activity with increasing demand in healthy age-matched controls. We hypothesized that higher activity in contralesional M1 is related to greater demand on precision in a hand motor task. fMRI data were collected from 19 patients with ischemic stroke affecting hand function in the subacute recovery phase and 31 healthy, right-handed, age-matched controls. The hand motor task was designed to parametrically modulate the demand on movement precision. Electromyography data confirmed strictly unilateral task performance by all participants. Patients showed significant impairment relative to controls in their ability to perform the task in the fMRI scanner. However, patients and controls responded similarly to an increase in demand for precision, with better performance for larger targets and poorer performance for smaller targets. Patients did not show evidence of elevated ipsilesional or contralesional M1 blood oxygenation level-dependent (BOLD) activation relative to healthy controls and mean BOLD activation levels were not elevated for patients with poorer performance relative to patients with better task performance. While both patients and healthy controls showed demand-dependent increases in BOLD activation in both ipsilesional/contralateral and contralesional/ipsilateral hemispheres, patients with stroke were less likely to show evidence of a linear relationship between the demand on precision and BOLD activation in contralesional M1 than healthy controls. Taken together, the findings suggest that task demand affects the BOLD response in contralesional M1 in patients with stroke, though perhaps less strongly than in healthy controls. This has implications for the interpretation of reported abnormal bilateral M1 activation in patients with stroke because in addition to contralesional M1 reorganization processes it could be partially related to a response to the relatively higher demand of a motor task when completed by patients rather than by healthy controls.

Selective plasticity of callosal neurons in the adult contralesional cortex following murine traumatic brain injury

Traumatic brain injury (TBI) results in deficits that are often followed by recovery. The contralesional cortex can contribute to this process but how distinct contralesional neurons and circuits respond to injury remains to be determined. To unravel adaptations in the contralesional cortex, we used chronic in vivo two-photon imaging. We observed a general decrease in spine density with concomitant changes in spine dynamics over time. With retrograde co-labeling techniques, we showed that callosal neurons are uniquely affected by and responsive to TBI. To elucidate circuit connectivity, we used monosynaptic rabies tracing, clearing techniques and histology. We demonstrate that contralesional callosal neurons adapt their input circuitry by strengthening ipsilateral connections from pre-connected areas. Finally, functional in vivo two-photon imaging demonstrates that the restoration of pre-synaptic circuitry parallels the restoration of callosal activity patterns. Taken together our study thus delineates how callosal neurons structurally and functionally adapt following a contralateral murine TBI.

Which contralesional circuits adapt after traumatic brain injury (TBI) is unclear. Here the authors used in vivo imaging, retrograde labeling, rabies tracing, clearing and functional imaging to demonstrate that callosal neurons selectively adapt after TBI in mice.

Excitatory-Inhibitory Homeostasis and Diaschisis: Tying the Local and Global Scales in the Post-stroke Cortex

Maintaining a balance between excitatory and inhibitory activity is an essential feature of neural networks of the neocortex. In the face of perturbations in the levels of excitation to cortical neurons, synapses adjust to maintain excitatory-inhibitory (EI) balance. In this review, we summarize research on this EI homeostasis in the neocortex, using stroke as our case study, and in particular the loss of excitation to distant cortical regions after focal lesions. Widespread changes following a localized lesion, a phenomenon known as diaschisis, are not only related to excitability, but also observed with respect to functional connectivity. Here, we highlight the main findings regarding the evolution of excitability and functional cortical networks during the process of post-stroke recovery, and how both are related to functional recovery. We show that cortical reorganization at a global scale can be explained from the perspective of EI homeostasis. Indeed, recovery of functional networks is paralleled by increases in excitability across the cortex. These adaptive changes likely result from plasticity mechanisms such as synaptic scaling and are linked to EI homeostasis, providing a possible target for future therapeutic strategies in the process of rehabilitation. In addition, we address the difficulty of simultaneously studying these multiscale processes by presenting recent advances in large-scale modeling of the human cortex in the contexts of stroke and EI homeostasis, suggesting computational modeling as a powerful tool to tie the meso- and macro-scale processes of recovery in stroke patients.

Functional connectivity drives stroke recovery: shifting the paradigm from correlation to causation

Stroke is a leading cause of disability, with deficits encompassing multiple functional domains. The heterogeneity underlying stroke poses significant challenges in the prediction of post-stroke recovery, prompting the development of neuroimaging-based biomarkers. Structural neuroimaging measurements, particularly those reflecting corticospinal tract injury, are well-documented in the literature as potential biomarker candidates of post-stroke motor recovery. Consistent with the view of stroke as a 'circuitopathy', functional neuroimaging measures probing functional connectivity may also prove informative in post-stroke recovery. An important step in the development of biomarkers based on functional neural network connectivity is the establishment of causality between connectivity and post-stroke recovery. Current evidence predominantly involves statistical correlations between connectivity measures and post-stroke behavioral status, either cross-sectionally or serially over time. However, the advancement of functional connectivity application in stroke depends on devising experiments that infer causality. In 1965, Sir Austin Bradford Hill introduced nine viewpoints to consider when determining the causality of an association: [1] Strength, [2] Consistency [3] Specificity, [4] Temporality, [5] Biological gradient, [6] Plausibility, [7] Coherence, [8] Experiment, and [9] Analogy. Collectively referred to as the Bradford Hill Criteria, these points have been widely adopted in epidemiology. In this review, we assert the value of implementing Bradford Hill's framework to stroke rehabilitation and neuroimaging. We focus on the role of neural network connectivity measurements acquired from task-oriented and resting-state functional magnetic resonance imaging, electroencephalography, magnetoencephalography, and functional near-infrared spectroscopy in describing and predicting post-stroke behavioral status and recovery. We also identify research opportunities within each Bradford Hill tenet to shift the experimental paradigm from correlation to causation.

Rodent models used in preclinical studies of deep brain stimulation to rescue memory deficits

Deep brain stimulation paradigms might be used to treat memory disorders in patients with stroke or traumatic brain injury. However, proof of concept studies in animal models are needed before clinical translation. We propose here a comprehensive review of rodent models for Traumatic Brain Injury and Stroke. We systematically review the histological, behavioral and electrophysiological features of each model and identify those that are the most relevant for translational research.

Evidence for interhemispheric imbalance in stroke patients as revealed by combining transcranial magnetic stimulation and electroencephalography

Interhemispheric interactions in stroke patients are frequently characterized by abnormalities, in terms of balance and inhibition. Previous results showed an impressive variability, mostly given to the instability of motor-evoked potentials when evoked from the affected hemisphere. We aim to find reliable interhemispheric measures in stroke patients with a not-evocable motor-evoked potential from the affected hemisphere, by combining transcranial magnetic stimulation (TMS) and electroencephalography. Ninteen stroke patients (seven females; 61.26 ± 9.8 years) were studied for 6 months after a first-ever stroke in the middle cerebral artery territory. Patients underwent four evaluations: clinical, cortical, corticospinal, and structural. To test the reliability of our measures, the evaluations were repeated after 3 weeks. To test the sensitivity, 14 age-matched healthy controls were compared to stroke patients. In stroke patients, stimulation of the affected hemisphere did not result in any inhibition onto the unaffected. The stimulation of the unaffected hemisphere revealed a preservation of the inhibition mechanism onto the affected. This resulted in a remarkable interhemispheric imbalance, whereas this mechanism was steadily symmetric in healthy controls. This result was stable when cortical evaluation was repeated after 3 weeks. Importantly, patients with a better recovery of the affected hand strength were the ones with a more stable interhemispheric balance. Finally, we found an association between microstructural integrity of callosal fibers, suppression of interhemispheric TMS-evoked activity and interhemispheric connectivity. We provide direct and sensitive cortical measures of interhemispheric imbalance in stroke patients. These measures offer a reliable means of distinguishing healthy and pathological interhemispheric dynamics.

Spreading Depressions and Periinfarct Spreading Depolarizations in the Context of Cortical Plasticity

Studies of cortical function-recovery require a comparison between normal and post-stroke conditions that lead to changes in cortical metaplasticity. Focal cortical stroke impairs experience-dependent plasticity in the neighboring somatosensory cortex and usually evokes periinfarct depolarizations (PiDs) - spreading depression-like waves. Experimentally induced spreading depressions (SDs) affect gene expression and some of these changes persist for at least 30 days. In this study we compare the effects of non-stroke depolarizations that impair cortical experience-dependent plasticity to the effects of stroke, by inducing experience-dependent plasticity in rats with SDs or PiDs by a month of contralateral partial whiskers deprivation. We found that whiskers' deprivation after SDs resulted in normal cortical representation enlargement suggesting that SDs and PiDs depolarization have no influence on experience-dependent plasticity cortical map reorganization. PiDs and the MMP-9, -3, -2 or COX-2 proteins, which are assumed to influence metaplasticity in rats after stroke were compared between SDs induced by high osmolarity KCl solution and the PiDs that followed cortical photothrombotic stroke (PtS). We found that none of these factors directly caused cortical post-stroke metaplasticity changes. The only significant difference between stoke and induced SD was a greater imbalance in interhemispheric activity equilibrium after stroke. The interhemispheric interactions that were modified by stroke may therefore be promising targets for future studies of post-stroke experience-dependent plasticity and of recuperation studies.

Stem Cell Repair of the Microvascular Damage in Stroke

Stroke is a life-threatening disease that leads to mortality, with survivors subjected to long-term disability. Microvascular damage is implicated as a key pathological feature, as well as a therapeutic target for stroke. In this review, we present evidence detailing subacute diaschisis in a focal ischemic stroke rat model with a focus on blood–brain barrier (BBB) integrity and related pathogenic processes in contralateral brain areas. Additionally, we discuss BBB competence in chronic diaschisis in a similar rat stroke model, highlighting the pathological changes in contralateral brain areas that indicate progressive morphological brain disturbances overtime after stroke onset. With diaschisis closely approximating stroke onset and progression, it stands as a treatment of interest for stroke. Indeed, the use of stem cell transplantation for the repair of microvascular damage has been investigated, demonstrating that bone marrow stem cells intravenously transplanted into rats 48 h post-stroke survive and integrate into the microvasculature. Ultrastructural analysis of transplanted stroke brains reveals that microvessels display a near-normal morphology of endothelial cells and their mitochondria. Cell-based therapeutics represent a new mechanism in BBB and microvascular repair for stroke.

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.

Cell Volume Control in Healthy Brain and Neuropathologies

Regulation of cellular volume is a critical homeostatic process that is intimately linked to ionic and osmotic balance in the brain tissue. Because the brain is encased in the rigid skull and has a very complex cellular architecture, even minute changes in the volume of extracellular and intracellular compartments have a very strong impact on tissue excitability and function. The failure of cell volume control is a major feature of several neuropathologies, such as hyponatremia, stroke, epilepsy, hyperammonemia, and others. There is strong evidence that such dysregulation, especially uncontrolled cell swelling, plays a major role in adverse pathological outcomes. To protect themselves, brain cells utilize a variety of mechanisms to maintain their optimal volume, primarily by releasing or taking in ions and small organic molecules through diverse volume-sensitive ion channels and transporters. In principle, the mechanisms of cell volume regulation are not unique to the brain and share many commonalities with other tissues. However, because ions and some organic osmolytes (e.g., major amino acid neurotransmitters) have a strong impact on neuronal excitability, cell volume regulation in the brain is a surprisingly treacherous process, which may cause more harm than good. This topical review covers the established and emerging information in this rapidly developing area of physiology.

Neuroanatomical and electrophysiological recovery in the contralateral intact cortex following transient focal cerebral ischemia in rats

Objectives Focal cerebral ischemia may induce synaptic, electrophysiological, and metabolic dysfunction in remote areas. We have shown that the remote dendritic spine density changes and electrophysiological diaschisis in the acute and subacute stages after stroke previously. Here, we further evaluated electrophysiological outcomes and synapto-dendritic plasticity in long-term recovery in the contralateral cortex following focal cerebral ischemia. Methods Male Sprague-Dawley rats were subjected to intraluminal suture occlusion for 90 min or sham-occlusion. Somatosensory electrophysiological recordings (SSEPs) and neurobehavioral tests were recorded each day for 28 days. Postmortem brains were sectioned and subjected to Nissl staining and Golgi-Cox impregnation through a 28-day period following ischemic stroke. Results In the ipsilateral cortex, infarct size in the cortex and striatum was decreased after the subacute stage; the brains showed reduced swelling in the cortex and stratum 3 days after ischemic insults. Dendritic spine density and SSEP amplitude decreased significantly during a 28-day recovery period. In the contralateral cortex, dendritic spine density and SSEP amplitude decreased significantly for 21 days after ischemic stroke, but recovered to baseline by day 28. The deterioration of the dendritic spine (density reduction) in the ischemic cortex was observed; however, this increased neuroplasticity in the contralateral cortex in the subacute stage. Discussion Focal cerebral ischemia-reperfusion induces time-dependent reduction of dendritic spine density and electrophysiological depression in both the ipsilateral and contralateral cortices and intact brain. This neuroanatomical and electrophysiological evidence suggests that neuroplasticity and functional re-organization in the contralateral cortex is possible following focal cerebral ischemia.

Reactive astrogliosis in stroke: Contributions of astrocytes to recovery of neurological function

Alterations in neuronal connectivity, particularly in the "peri-infarct" tissue adjacent to the region of ischemic damage, are important contributors to the spontaneous recovery of function that commonly follows stroke. Peri-infarct astrocytes undergo reactive astrogliosis and play key roles in modulating the adaptive responses in neurons. This reactive astrogliosis shares many features with that induced by other forms of damage to the central nervous system but also differs in details that potentially influence neurological recovery. A subpopulation of astrocytes within a few hundred micrometers of the infarct proliferate and are centrally involved in the development of the glial scar that separates the damaged tissue in the infarct from surrounding normal brain. The intertwined processes of astrocytes adjacent to the infarct provide the core structural component of the mature scar. Interventions that cause early disruption of glial scar formation typically impede restoration of neurological function. Marked reactive astrogliosis also develops in cells more distant from the infarct but these cells largely remain in the spatial territories they occupied prior to stroke. These cells play important roles in controlling the extracellular environment and release proteins and other molecules that are able to promote neuronal plasticity and improve functional recovery. Treatments manipulating aspects of reactive astrogliosis can enhance neuronal plasticity following stroke. Optimising these treatments for use in human stroke would benefit from a more complete characterization of the specific responses of peri-infarct astrocytes to stroke as well as a better understanding of the influence of other factors including age, sex, comorbidities and reperfusion of the ischemic tissue.

Blood-Spinal Cord Barrier Alterations in Subacute and Chronic Stages of a Rat Model of Focal Cerebral Ischemia

We previously demonstrated blood-brain barrier impairment in remote contralateral brain areas in rats at 7 and 30 days after transient middle cerebral artery occlusion (tMCAO), indicating ischemic diaschisis. Here, we focused on effects of subacute and chronic focal cerebral ischemia on the blood-spinal cord barrier (BSCB). We observed BSCB damage on both sides of the cervical spinal cord in rats at 7 and 30 days post-tMCAO. Major BSCB ultrastructural changes in spinal cord gray and white matter included vacuolated endothelial cells containing autophagosomes, pericyte degeneration with enlarged mitochondria, astrocyte end-feet degeneration and perivascular edema; damaged motor neurons, swollen axons with unraveled myelin in ascending and descending tracts and astrogliosis were also observed. Evans Blue dye extravasation was maximal at 7 days. There was immunofluorescence evidence of reduction of microvascular expression of tight junction occludin, upregulation of Beclin-1 and LC3B immunoreactivities at 7 days and a reduction of the latter at 30 days post-ischemia. These novel pathological alterations on the cervical spinal cord microvasculature in rats after tMCAO suggest pervasive and long-lasting BSCB damage after focal cerebral ischemia, and that spinal cord ischemic diaschisis should be considered in the pathophysiology and therapeutic approaches in patients with ischemic cerebral infarction.

Transition from Initial Hypoactivity to Hyperactivity in Cortical Layer V Pyramidal Neurons after Traumatic Brain Injury In Vivo

Traumatic brain injury (TBI) often results in structural damage and a loss of neurons that is commonly accompanied by early changes in neuronal electrical activity. Loss of neuronal activity has been hypothesized to contribute to post-traumatic epileptogenesis through the regulation of homeostatic plasticity. The existence of activity loss in cortical neurons after TBI and its subsequent transition into hyperactivity over time is not well characterized, however, particularly in models of TBI in vivo. In the current study, changes in neuronal activity in the primary motor cortex after moderate controlled cortical impact (CCI) in mice were studied using a single-unit recording technique in vivo. Recordings were made at different time points after CCI from cortical layer V pyramidal neurons that were within 1-2 mm from the anterior edge of the injured foci. Within 1-4 h after CCI, the frequency of spontaneous single-unit activity depressed significantly, with the mean firing frequency decreasing from 2.59 ± 0.18 Hz in the sham group to 1.05 ± 0.20 Hz of the injured group. The firing frequencies recovered to the normal level at 1 day and 7 days post-CCI, but became significantly higher at 3 days and 14 days post-CCI. The results suggest that TBI caused initial loss of activity in neurons of the perilesional cortical region, which was followed by compensatory recovery and enhancement of activity. These time-dependent changes in neuronal activity may contribute to the development of hyperexcitability through homeostatic activity regulation.

Brain stimulation: Neuromodulation as a potential treatment for motor recovery following traumatic brain injury

There is growing evidence that electrical and magnetic brain stimulation can improve motor function and motor learning following brain damage. Rodent and primate studies have strongly demonstrated that combining cortical stimulation (CS) with skilled motor rehabilitative training enhances functional motor recovery following stroke. Brain stimulation following traumatic brain injury (TBI) is less well studied, but early pre-clinical and human pilot studies suggest that it is a promising treatment for TBI-induced motor impairments as well. This review will first discuss the evidence supporting brain stimulation efficacy derived from the stroke research field as proof of principle and then will review the few studies exploring neuromodulation in experimental TBI studies. This article is part of a Special Issue entitled SI:Brain injury and recovery.

Role of the Contralesional Hemisphere in Post-Stroke Recovery of Upper Extremity Motor Function

Identification of optimal treatment strategies to improve recovery is limited by the incomplete understanding of the neurobiological principles of recovery. Motor cortex (M1) reorganization of the lesioned hemisphere (ipsilesional M1) plays a major role in post-stroke motor recovery and is a primary target for rehabilitation therapy. Reorganization of M1 in the hemisphere contralateral to the stroke (contralesional M1) may, however, serve as an additional source of cortical reorganization and related recovery. The extent and outcome of such reorganization depends on many factors, including lesion size and time since stroke. In the chronic phase post-stroke, contralesional M1 seems to interfere with motor function of the paretic limb in a subset of patients, possibly through abnormally increased inhibition of lesioned M1 by the contralesional M1. In such patients, decreasing contralesional M1 excitability by cortical stimulation results in improved performance of the paretic limb. However, emerging evidence suggests a potentially supportive role of contralesional M1. After infarction of M1 or its corticospinal projections, there is abnormally increased excitatory neural activity and activation in contralesional M1 that correlates with favorable motor recovery. Decreasing contralesional M1 excitability in these patients may result in deterioration of paretic limb performance. In animal stroke models, reorganizational changes in contralesional M1 depend on the lesion size and rehabilitation treatment and include long-term changes in neurotransmitter systems, dendritic growth, and synapse formation. While there is, therefore, some evidence that activity in contralesional M1 will impact the extent of motor function of the paretic limb in the subacute and chronic phase post-stroke and may serve as a new target for rehabilitation treatment strategies, the precise factors that specifically influence its role in the recovery process remain to be defined.

Compromised blood-brain barrier competence in remote brain areas in ischemic stroke rats at the chronic stage

Stroke is a life-threatening disease leading to long-term disability in stroke survivors. Cerebral functional insufficiency in chronic stroke might be due to pathological changes in brain areas remote from the initial ischemic lesion, i.e., diaschisis. Previously, we showed that the damaged blood-brain barrier (BBB) was involved in subacute diaschisis. The present study investigated BBB competence in chronic diaschisis by using a transient middle cerebral artery occlusion (tMCAO) rat model. Our results demonstrated significant BBB damage mostly in the ipsilateral striatum and motor cortex in rats at 30 days after tMCAO. The BBB alterations were also determined in the contralateral hemisphere via ultrastructural and immunohistochemical analyses. Major BBB pathological changes in contralateral remote striatum and motor cortex areas included 1) vacuolated endothelial cells containing large autophagosomes, 2) degenerated pericytes displaying mitochondria with cristae disruption, 3) degenerated astrocytes and perivascular edema, 4) Evans blue extravasation, and 5) appearance of parenchymal astrogliosis. Discrete analyses of striatal and motor cortex areas revealed significantly higher autophagosome accumulation in capillaries of ventral striatum and astrogliosis in dorsal striatum in both cerebral hemispheres. These widespread microvascular alterations in ipsilateral and contralateral brain hemispheres suggest persistent and/or continued BBB damage in chronic ischemia. The pathological changes in remote brain areas likely indicate chronic ischemic diaschisis, which should be considered in the development of treatment strategies for stroke.

A Small Motor Cortex Lesion Abolished Ocular Dominance Plasticity in the Adult Mouse Primary Visual Cortex and Impaired Experience-Dependent Visual Improvements

It was previously shown that a small lesion in the primary somatosensory cortex (S1) prevented both cortical plasticity and sensory learning in the adult mouse visual system: While 3-month-old control mice continued to show ocular dominance (OD) plasticity in their primary visual cortex (V1) after monocular deprivation (MD), age-matched mice with a small photothrombotically induced (PT) stroke lesion in S1, positioned at least 1 mm anterior to the anterior border of V1, no longer expressed OD-plasticity. In addition, in the S1-lesioned mice, neither the experience-dependent increase of the spatial frequency threshold (“visual acuity”) nor of the contrast threshold (“contrast sensitivity”) of the optomotor reflex through the open eye was present. To assess whether these plasticity impairments can also occur if a lesion is placed more distant from V1, we tested the effect of a PT-lesion in the secondary motor cortex (M2). We observed that mice with a small M2-lesion restricted to the superficial cortical layers no longer expressed an OD-shift towards the open eye after 7 days of MD in V1 of the lesioned hemisphere. Consistent with previous findings about the consequences of an S1-lesion, OD-plasticity in V1 of the nonlesioned hemisphere of the M2-lesioned mice was still present. In addition, the experience-dependent improvements of both visual acuity and contrast sensitivity of the open eye were severely reduced. In contrast, sham-lesioned mice displayed both an OD-shift and improvements of visual capabilities of their open eye. To summarize, our data indicate that even a very small lesion restricted to the superficial cortical layers and more than 3mm anterior to the anterior border of V1 compromised V1-plasticity and impaired learning-induced visual improvements in adult mice. Thus both plasticity phenomena cannot only depend on modality-specific and local nerve cell networks but are clearly influenced by long-range interactions even from distant brain regions.

Exploring the Evolution of Cortical Excitability Following Acute Stroke

BACKGROUND

Evolution of changes in intracortical excitability following stroke, particularly in the contralesional hemisphere, is being increasingly recognized in relation to maximizing the potential for functional recovery.

OBJECTIVE

The present study utilized a prospective longitudinal design over a 12-month period from stroke onset, to investigate the evolution of intracortical excitability involving both motor cortices and their relationship to recovery, and whether such changes were influenced by baseline stroke characteristics.

METHODS

Thirty-one patients with acute unilateral ischemic stroke were recruited from a tertiary hospital stroke unit. Comprehensive clinical assessments and cortical excitability were undertaken at stroke onset using a novel threshold-tracking paired-pulse transcranial magnetic stimulation technique, and repeated at 3-, 6-, and 12-month follow-up in 17 patients who completed the longitudinal assessment.

RESULTS

Shortly following stroke, short-interval intracortical inhibition (SICI) was significantly reduced in both lesioned and contralesional hemispheres that correlated with degree of recovery over the subsequent 3 months. Over the follow-up period, ipsilesional SICI remained reduced in all patient groups, while SICI over the contralesional hemisphere remained reduced only in the groups with cortical stroke or more baseline functional impairment.

CONCLUSIONS

The current study has demonstrated that evolution of intracortical excitability, particularly over the contralesional hemisphere, may vary between patients with differing baseline stroke and clinical characteristics, suggesting that ongoing contralesional network recruitment may be necessary for those patients who have significant disruptions to the integrity of ipsilesional motor pathways. Results from the present series have implications for the development of neuromodulatory brain stimulation protocols to harness and thereby facilitate stroke recovery.

The Role of Timing and Intensity of Rehabilitation Therapies

In both animal and clinical studies, motor rehabilitation and training increase cortical representation and improve recovery, whereas lack of training decreases cortical representation for particular motor functions. In animals, delays in providing rehabilitation reduce the impact of therapy with a worsening in motor outcomes and a corresponding reduction in cortical reorganization. In clinical studies, there is an association between earlier admission to rehabilitation and better outcomes that correlates with animal work both in terms of functional gains from chronic stroke deficits and cortical reorganization. There is a likely relationship between therapy intensity and improvements in functional outcomes. Clinically, greater intensity of stroke rehabilitation has been associated with improved outcomes.

Melatonin improves neuroplasticity by upregulating the growth-associated protein-43 (GAP-43) and NMDAR postsynaptic density-95 (PSD-95) proteins in cultured neurons exposed to glutamate excitotoxicity and in rats subjected to transient focal cerebral ischemia even during a long-term recovery period

Recent evidence shows that the NMDAR postsynaptic density-95 (PSD-95), growth-associated protein-43 (GAP-43), and matrix metalloproteinase-9 (MMP-9) protein enhance neuroplasticity at the subacute stage of stroke. Here, we evaluated whether melatonin would modulate the PSD-95, GAP-43, and MMP-9 proteins in cultured neurons exposed to glutamate excitotoxicity and in rats subjected to experimental stroke. Adult male Sprague-Dawley rats were treated with melatonin (5 mg/kg) or vehicle at reperfusion onset after transient occlusion of the right middle cerebral artery (tMCAO) for 90 min. Animals were euthanized for Western immunoblot analyses for the PSD-95 and GAP-43 proteins and gelatin zymography for the MMP-9 activity at 7 days postinsult. Another set of animals was sacrificed for histologic and Golgi-Cox-impregnated sections at 28 days postinsult. In cultured neurons exposed to glutamate excitotoxicity, melatonin significantly upregulated the GAP-43 and PSD-95 expressions and improved dendritic aborizations (P<0.05, respectively). Relative to controls, melatonin-treated stroke animals caused a significant improvement in GAP-43 and PSD-95 expressions as well as the MMP-9 activity in the ischemic brain (P<0.05). Consequently, melatonin also significantly promoted the dendritic spine density and reduced infarction in the ischemic brain, and improved neurobehaviors as well at 28 days postinsult (P<0.05, respectively). Together, melatonin upregulates GAP-43, PSD-95, and MMP-9 proteins, which likely accounts for its actions to improve neuroplasticity in cultured neurons exposed to glutamate excitotoxicity and to enhance long-term neuroprotection, neuroplasticity, and brain remodeling in stroke rats.

Somatosensory cortectomy induces motor cortical hyperexcitability and scoliosis: an experimental study in developing rats

BACKGROUND CONTEXT

Dysfunctions in sensorimotor integration, reminiscent to those described in idiopathic dystonia, have been found in idiopathic scoliosis (IS) and might be involved in its pathogenesis. Studying the effects of experimental disruption of sensory cortex may shed further insight into the etiopathology of IS.

PURPOSE

To evaluate whether disruption of central sensorimotor integration through partial ablation of the somatosensory cortex leads to scoliosis in developing rats and to describe the effects of such an intervention on motor cortico-cortical inhibition and facilitation.

METHODS

Fifty Wistar rats aged 3 weeks were used in the study. Twenty-four rats underwent craniotomy and electrocoagulation of the sensory cortex (PAR1) in the right hemisphere. A second group of 16 rats underwent a sham operation with craniotomy but no electrocoagulation. A third group of 10 rats was used as intact controls. Four weeks after surgery, motor cortical excitability was assessed with paired-pulse electrical cortical stimulation. Neurologic and behavioral examinations were completed serially, and 10 weeks after surgery, X-ray examinations were performed in anesthetized rats to assess spinal curvature. Electromyographic recordings of paravertebral muscle activity were performed in waking rats. At the end of the study, rats were sacrificed, and histologic examinations of brain tissue were performed to confirm the extent of the lesion. A grant from a Government Health Research Fund without salaries assignment financed the study.

RESULTS

Almost half of the animals with somatosensory cortectomy (46%) developed scoliosis, with an average Cobb angle of 23 ± 8°. None of the animals in the sham or control groups developed scoliosis. Despite cortical lesions, no motor or behavioral deficits were apparent in the experimental group, and cortectomized rats were neurologically indistinguishable from sham or control animals, except for the presence of scoliosis. Cortico-cortical inhibition was significantly reduced in the hemisphere of scoliotic concavity in the cortectomized group but was normal in the other groups.

CONCLUSIONS

These findings indicate that altered sensorimotor integration may cause scoliosis without noticeable motor impairment. Reduced cortico-cortical inhibition was observed in cortectomized rats. This finding is consistent with results in adolescents with IS and suggests that alteration of cortical hemispheric balance of sensorimotor integration may play an important role in the pathogenesis of IS.

Alterations in membrane and firing properties of layer 2/3 pyramidal neurons following focal laser lesions in rat visual cortex

Focal cortical injuries are well known to cause changes in function and excitability of the surviving cortical areas but the cellular correlates of these physiological alterations are not fully understood. In the present study we employed a well established ex vivo-in vitro model of focal laser lesions in the rat visual cortex and we studied membrane and firing properties of the surviving layer 2/3 pyramidal neurons. Patch-clamp recordings, performed in the first week post-injury, revealed an increased input resistance, a depolarized spike threshold as well as alterations in the firing pattern of neurons in the cortex ipsilateral to the lesion. Notably, the reported lesion-induced alterations emerged or became more evident when an exciting perfusing solution, known as modified artificial cerebrospinal fluid, was used to increase the ongoing synaptic activity in cortical slices. Conversely, application of glutamatergic or GABAA receptor blockers reduced the observed alterations and GABAB receptor blockers abolished the differences completely. All together the present findings suggest that changes in synaptic receptors function, following focal cortical injuries, can modulate membrane and firing properties of layer 2/3 pyramidal neurons. This previously unknown functional interplay between synaptic and membrane properties may constitute a novel cellular mechanism to explain alterations in neuronal network function and excitability following focal cortical injuries.

Constraint-Induced Movement Therapy Overcomes the Intrinsic Axonal Growth–Inhibitory Signals in Stroke Rats

Background and Purpose—

Constraint-induced movement therapy (CIMT) improves functional outcome in patients with stroke possibly through structural plasticity. We hypothesized that CIMT could enhance axonal growth by overcoming the intrinsic growth–inhibitory signals, leading eventually to improved behavioral performance in stroke rats.

Methods—

Focal cerebral ischemia was induced by intracerebral injection of endothelin-1. Adult Wistar rats were divided into a sham-operated group, an ischemic group, and an ischemic group treated with CIMT. CIMT started at postoperative day 7 and continued for 3 weeks. Biotinylated dextran amine was injected into the contralateral sensorimotor cortex at postoperative day 14 to trace crossing axons at the cervical spinal cord. The expressions of Nogo-A, Nogo receptor, RhoA, and Rho-associated kinase in the peri-infarct cortex, and the expressions of biotinylated dextran amine, growth associated protein-43, synaptophysin, vGlut1, and postsynaptic density-95 in the denervated spinal cord were measured by immunohistochemistry and Western blots. Behavioral recovery was analyzed at postoperative days 29 to 32.

Results—

Infarct volumes were not different between groups after stroke. CIMT significantly increased the length and the number of midline crossings of contralateral corticospinal axons to the denervated cervical spinal cord. CIMT significantly decreased the expressions of Nogo-A/Nogo receptor and RhoA/Rho-associated kinase in the peri-infarct cortex, and increased the expressions of growth associated protein-43, synaptophysin, vGlut1, and postsynaptic density-95 in the denervated cervical spinal cord. Behavioral performances assessed by the beam-walking test and the water maze test were improved significantly by CIMT.

Conclusions—

CIMT promoted poststroke synaptic plasticity and axonal growth at least partially by overcoming the intrinsic growth–inhibitory signaling, leading to improved behavioral outcome.

Blood-brain barrier alterations provide evidence of subacute diaschisis in an ischemic stroke rat model

BACKGROUND

Comprehensive stroke studies reveal diaschisis, a loss of function due to pathological deficits in brain areas remote from initial ischemic lesion. However, blood-brain barrier (BBB) competence in subacute diaschisis is uncertain. The present study investigated subacute diaschisis in a focal ischemic stroke rat model. Specific focuses were BBB integrity and related pathogenic processes in contralateral brain areas.

METHODOLOGY/PRINCIPAL FINDINGS

In ipsilateral hemisphere 7 days after transient middle cerebral artery occlusion (tMCAO), significant BBB alterations characterized by large Evans Blue (EB) parenchymal extravasation, autophagosome accumulation, increased reactive astrocytes and activated microglia, demyelinization, and neuronal damage were detected in the striatum, motor and somatosensory cortices. Vascular damage identified by ultrastuctural and immunohistochemical analyses also occurred in the contralateral hemisphere. In contralateral striatum and motor cortex, major ultrastructural BBB changes included: swollen and vacuolated endothelial cells containing numerous autophagosomes, pericyte degeneration, and perivascular edema. Additionally, prominent EB extravasation, increased endothelial autophagosome formation, rampant astrogliosis, activated microglia, widespread neuronal pyknosis and decreased myelin were observed in contralateral striatum, and motor and somatosensory cortices.

CONCLUSIONS/SIGNIFICANCE

These results demonstrate focal ischemic stroke-induced pathological disturbances in ipsilateral, as well as in contralateral brain areas, which were shown to be closely associated with BBB breakdown in remote brain microvessels and endothelial autophagosome accumulation. This microvascular damage in subacute phase likely revealed ischemic diaschisis and should be considered in development of treatment strategies for stroke.

Influence of inflammation on poststroke plasticity

Age-related brain injuries including stroke are a leading cause of morbidity and mental disability worldwide. Most patients who survive stroke experience some degree of recovery. The restoration of lost functions can be explained by neuronal plasticity, understood as brain ability to reorganize and remodel itself in response to changed environmental requirements. However, stroke triggers a cascade of events which may prevent the normal development of the plastic changes. One of them may be inflammatory response initiated immediately after stroke, which has been found to contribute to neuronal injury. Some recent evidence though has suggested that inflammatory reaction can be also neuroprotective. This paper attempts to discuss the influence of poststroke inflammatory response on brain plasticity and stroke outcome. We also describe the recent anti-inflammatory strategies that have been effective for recovery in experimental stroke.

Abnormal corticospinal excitability in patients with disorders of consciousness

BACKGROUND

Transcranial magnetic stimulation (TMS) has been frequently used to explore changes in the human motor cortex in different conditions, while the extent of motor cortex reorganization in patients in vegetative state (VS) (now known as unresponsive wakefulness syndrome, UWS) and minimally conscious (MCS) states due to severe brain damage remains largely unknown.

OBJECTIVE/HYPOTHESIS

It was hypothesized that cortical motor excitability would be decreased and would correlate to the level of consciousness in patients with disorders of consciousness.

METHODS

Corticospinal excitability was assessed in 47 patients (24 VS/UWS and 23 MCS) and 14 healthy controls. The test parameters included maximal peak-to-peak M-wave (Mmax), F-wave persistence, peripheral and central motor conduction times, sensory (SEP) and motor evoked (MEP) potential latencies and amplitudes, resting motor threshold (RMT), stimulus/response curves, and short latency afferent inhibition (SAI). TMS measurements were correlated to the level of consciousness (assessed using the Coma Recovery Scale-Revised).

RESULTS

On average, the patient group had lower Mmax, lower MEP and SEP amplitudes, higher RMTs, narrower stimulus/response curves, and reduced SAI compared to the healthy controls (P < 0.05). The SAI alterations were correlated to the level of consciousness (P < 0.05).

CONCLUSIONS

The findings demonstrated the impairment of the cortical inhibitory circuits in patients with disorders of consciousness. Moreover, the significant relationship was found between cortical inhibition and clinical consciousness dysfunction.

Stroke induces long-lasting deficits in the temporal fidelity of sensory processing in the somatosensory cortex

Recovery from stroke is rarely complete as humans and experimental animals typically show lingering deficits in sensory function. One explanation for limited recovery could be that rewired cortical networks do not process sensory stimuli with the same temporal precision as they normally would. To examine how well peri-infarct and more distant cortical networks process successive vibro-tactile stimulations of the affected forepaw (a measure of temporal fidelity), we imaged cortical depolarizations with millisecond temporal resolution using voltage-sensitive dyes. In control mice, paired forepaw stimulations (ranging from 50 to 200 milliseconds apart) induced temporally distinct depolarizations in primary forelimb somatosensory (FLS1) cortex, and to a lesser extent in secondary FLS (FLS2) cortex. For mice imaged 3 months after stroke, the first forepaw stimulus reliably evoked a strong depolarization in the surviving region of FLS1 and FLS2 cortex. However, depolarizations to subsequent forepaw stimuli were significantly reduced or completely absent (for stimuli ≤100 milliseconds apart) in the FLS1 cortex, whereas FLS2 responses were relatively unaffected. Our data reveal that stroke induces long-lasting impairments in how well the rewired FLS1 cortex processes temporal aspects of sensory stimuli. Future therapies directed at enhancing the temporal fidelity of cortical circuits may be necessary for achieving full recovery of sensory functions.

Shift from phasic to tonic GABAergic transmission following laser-lesions in the rat visual cortex

Reduction in the strength of GABAergic neurotransmission has often been reported following brain lesions. This weakened inhibition is believed to influence neurological deficits, neuronal hyperexcitability and functional recovery after brain injuries. Uncovering the mechanisms underlying the altered inhibition is therefore crucial. In the present study we used an ex vivo-in vitro model of laser lesions in the rat visual cortex to characterize the cellular correlates of changes in GABAergic transmission in the tissue adjacent to the injury. In the first week post-injury the number of VGAT positive GABAergic terminals as well as the expression level of the GABA synthesizing enzymes GAD67 and GAD65 remained unaltered. However, a reduced frequency of miniature inhibitory postsynaptic currents (mIPSCs) together with an increased paired-pulse ratio (PPR) of evoked IPSCs suggested a functional reduction of phasic GABA release. In parallel, we found an enhancement in the GABAA receptor-mediated tonic inhibition. On the basis of these findings, we propose that cortical lesions provoke a shift in GABAergic transmission, decreasing the phasic and reinforcing the tonic component. We therefore suggest that it is not, as traditionally assumed, the overall inhibitory strength to be primarily compromised by a cortical lesion but rather the temporal accuracy of the GABAergic synaptic signaling.

Influence of intra- and extracellular acidification on free radical formation and mitochondria membrane potential in rat brain synaptosomes

Brain ischemia is accompanied by lowering of intra- and extracellular pH. Stroke often leads to irreversible damage of synaptic transmission by unknown mechanism. We investigated an influence of lowering of pH(i) and pH(o) on free radical formation in synaptosomes. Three models of acidosis were used: (1) pH(o) 6.0 corresponding to pH(i) decrease down to 6.04; (2) pH(o) 7.0 corresponding to the lowering of pH(i) down to 6.92: (3) 1 mM amiloride corresponding to pH(i) decrease down to 6.65. We have shown that both types of extracellular acidification, but not intracellular acidification, increase 2',7'-dichlorodihydrofluorescein diacetate fluorescence that reflects free radical formation. These three treatments induce the rise of the dihydroethidium fluorescence that reports synthesis of superoxide anion. However, the impact of amiloride on superoxide anion synthesis was less than that induced by moderate extracellular acidification. Superoxide anion synthesis at pH(o) 7.0 was almost completely eliminated by mitochondrial uncoupler carbonyl cyanide 4-(trifluoromethoxy)phenylhydrazone. Furthermore, using fluorescent dyes JC-1 and rhodamine-123, we confirmed that pH(o) lowering, but not intracellular acidification, led to depolarization of intrasynaptosomal mitochondria. We have shown that pH(o) but not pH(i) lowering led to oxidative stress in neuronal presynaptic endings that might underlie the long-term irreversible changing in synaptic transmission.

Longitudinal plasticity across the neural axis in acute stroke

BACKGROUND

With the advent of novel brain stimulation techniques aimed at improving functional outcome, understanding poststroke plasticity becomes critical for the appropriate selection of patients and optimal timing to introduce neuromodulatory interventions.

OBJECTIVE

To better define the temporal evolution of central and peripheral neuroplastic changes in the first 3 months after stroke and their clinical implications.

METHODS

Transcranial magnetic stimulation, peripheral nerve excitability, and clinical assessments were undertaken longitudinally in 31 acute stroke patients, comprising a total of 384 clinical studies.

RESULTS

During the hyperacute phase (<7 days), short-interval intracortical inhibition (SICI) was significantly reduced in lesioned (4.3% ± 1.3%) and contralesional hemispheres (3.6% ± 1.9%) compared with controls (11.4% ± 1.3%, P = .001). There were also significant alterations in accommodative properties of motor axons in the affected limb. At follow-up, SICI remained suppressed in both hemispheres in the context of significant clinical improvement.

CONCLUSION

Simultaneous assessment of central and peripheral motor pathways has identified bilateral plastic changes that develop throughout the neural axis in acute stroke patients. It is proposed that these changes represent an adaptive response and that the persistent bihemispheric reduction in SICI may act to promote stroke recovery through cortical reorganization.

Selective vulnerability of synaptic signaling and metabolism to nitrosative stress

SIGNIFICANCE

Nitric oxide (NO) plays diverse physiological roles in the central nervous system, where it modulates neuronal communication, regulates blood flow, and contributes to the innate immune responses. In a number of brain pathologies, the excessive production of NO also leads to the formation of reactive and toxic intermediates generically termed reactive nitrogen species (RNS). RNS cause irreversible or poorly reversible damage to brain cells.

RECENT ADVANCES

Recent work in the field focused on the ability of NO and RNS to yield protein modifications, including the S-nitrosation of cysteine residues, which, in many instances, impact cellular functions and viability.

CRITICAL ISSUES

The vast majority of neuropathological studies focus on the loss of cell viability, but nitrosative stress may also strongly impair the functions of neuronal processes: axonal projections and dendritic trees. The functional integrity of axons and dendrites critically depends on local metabolism and effective delivery of metabolic enzymes and organelles. Here, we summarize the existing literature describing the effects of nitrosative stress on the major pathways of energetic metabolism: glycolysis, tricarboxylic acid cycle, and mitochondrial respiration, with the emphasis on modifications of protein thiols.

FUTURE DIRECTIONS

We propose that axons and dendrites are highly vulnerable to nitrosative stress because of their low glycolytic capacity and high dependence on timely delivery of metabolic enzymes and organelles from the cell body. Thus, supplementation with the end products of glycolysis, pyruvate or lactate, may help preserve metabolism in distal neuronal processes and protect or restore synaptic function in the ailing brain.

Ischemic cerebral damage: an appraisal of synaptic failure

In the human brain, ≈30% of the energy is spent on synaptic transmission. Disappearance of synaptic activity is the earliest consequence of cerebral ischemia. The changes of synaptic function are generally assumed to be reversible and persistent damage is associated with membrane failure and neuronal death. However, there is overwhelming experimental evidence of isolated, but persistent, synaptic failure resulting from mild or moderate cerebral ischemia. Early failure results from presynaptic damage with impaired transmitter release. Proposed mechanisms include dysfunction of adenosine triphosphate-dependent calcium channels and a disturbed docking of glutamate-containing vesicles resulting from impaired phosphorylation. We review energy distribution among neuronal functions, focusing on energy usage of synaptic transmission. We summarize the effect of ischemia on neurotransmission and the evidence of long-lasting synaptic failure as a cause of persistent symptoms in patients with cerebral ischemia. Finally, we discuss the implications of synaptic failure in the diagnosis of cerebral ischemia, including the limited sensitivity of diffusion-weighted MRI in those cases in which damage is presumably limited to the synapses.

Cinnamophilin offers prolonged neuroprotection against gray and white matter damage and improves functional and electrophysiological outcomes after transient focal cerebral ischemia

OBJECTIVE

We have previously shown that cinnamophilin ([8R, 8'S]-4, 4'-dihydroxy-3, 3'-dimethoxy-7-oxo-8, 8'-neolignan) exhibited potent antioxidant, radical-scavenging, and anti-inflammatory actions and reduced acute ischemic brain damage, even when it was given up to 6 hrs postinsult. Here, we characterized the long-lasting neuroprotection of cinnamophilin against gray and white matter damage and its beneficial effects on electrophysiological and functional outcomes in a model of stroke.

DESIGN

Prospective laboratory animal study.

SETTING

Research laboratory in a university teaching hospital.

SUBJECTS

Adult male Sprague-Dawley rats (240-290 g).

INTERVENTIONS

Under controlled conditions of normoxia, normocarbia, and normothermia, spontaneously breathing, halothane-anesthetized (1.0-1.5%) rats were subjected to transient middle cerebral artery occlusion for 90 mins. Cinnamophilin (80 mg/kg) or vehicle was given intravenously at reperfusion onset.

MEASUREMENTS AND MAIN RESULTS

Physiological parameters, including arterial blood gases and cortical blood perfusion, somatosensory-evoked potentials, and neurobehavioral outcomes, were serially examined. Animals were euthanized at 7 days or 21 days postinsult. Gray matter and white matter (axonal and myelin) damage were then evaluated by quantitative histopathology and immunohistochemistry against phosphorylated component-H neurofilaments and myelin basic protein, respectively. After the follow-up period of 7 and 21 days, our results showed that cinnamophilin significantly decreased gray matter damage by 31.6% and 34.9% (p < .05, respectively) without notable adverse effects. Additionally, cinnamophilin effectively reduced axonal and myelin damage by 46.3-68.6% (p < .05) and 25.2-28.1% (p < .05), respectively. Furthermore, cinnamophilin not only improved the ipsilateral field potentials (p < .05, respectively), but also reduced the severity of contralateral electrophysiological diaschisis (p < .05). Consequently, cinnamophilin improved sensorimotor outcomes up to 21 days postinsult (p < .05, respectively).

CONCLUSIONS

Administration with cinnamophilin provides long-lasting neuroprotection against gray and white matter damage and improves functional and electrophysiological outcomes after ischemic stroke. The results suggest a need for further studies to characterize the potential of cinnamophilin in the field of ischemic stroke.