Compensatory Relearning Following Stroke: Cellular and Plasticity Mechanisms in Rodents

Small extracellular vesicles derived from cerebral endothelial cells with elevated microRNA 27a promote ischemic stroke recovery

JOURNAL/nrgr/04.03/01300535-202501000-00030/figure1/v/2024-05-14T021156Z/r/image-tiff Axonal remodeling is a critical aspect of ischemic brain repair processes and contributes to spontaneous functional recovery. Our previous in vitro study demonstrated that exosomes/small extracellular vesicles (sEVs) isolated from cerebral endothelial cells (CEC-sEVs) of ischemic brain promote axonal growth of embryonic cortical neurons and that microRNA 27a (miR-27a) is an elevated miRNA in ischemic CEC-sEVs. In the present study, we investigated whether normal CEC-sEVs engineered to enrich their levels of miR-27a (27a-sEVs) further enhance axonal growth and improve neurological outcomes after ischemic stroke when compared with treatment with non-engineered CEC-sEVs. 27a-sEVs were isolated from the conditioned medium of healthy mouse CECs transfected with a lentiviral miR-27a expression vector. Small EVs isolated from CECs transfected with a scramble vector (Scra-sEVs) were used as a control. Adult male mice were subjected to permanent middle cerebral artery occlusion and then were randomly treated with 27a-sEVs or Scra-sEVs. An array of behavior assays was used to measure neurological function. Compared with treatment of ischemic stroke with Scra-sEVs, treatment with 27a-sEVs significantly augmented axons and spines in the peri-infarct zone and in the corticospinal tract of the spinal grey matter of the denervated side, and significantly improved neurological outcomes. In vitro studies demonstrated that CEC-sEVs carrying reduced miR-27a abolished 27a-sEV-augmented axonal growth. Ultrastructural analysis revealed that 27a-sEVs systemically administered preferentially localized to the pre-synaptic active zone, while quantitative reverse transcription-polymerase chain reaction and Western Blot analysis showed elevated miR-27a, and reduced axonal inhibitory proteins Semaphorin 6A and Ras Homolog Family Member A in the peri-infarct zone. Blockage of the Clathrin-dependent endocytosis pathway substantially reduced neuronal internalization of 27a-sEVs. Our data provide evidence that 27a-sEVs have a therapeutic effect on stroke recovery by promoting axonal remodeling and improving neurological outcomes. Our findings also suggest that suppression of axonal inhibitory proteins such as Semaphorin 6A may contribute to the beneficial effect of 27a-sEVs on axonal remodeling.

Neuroprotective Therapeutic Potential of microRNA-149-5p against Murine Ischemic Stroke

Ischemic stroke resulting from blockade of brain vessels lacks effective treatments, prompting exploration for potential therapies. Among promising candidates, microRNA-149 (miR-149) has been investigated for its role in alleviating oxidative stress, inflammation, and neurodegeneration associated with ischemic conditions. To evaluate its therapeutic effect, male Wistar rats were categorized into five groups, each consisting of 27 rats: sham, MCAO, lentiviral control, lentiviral miR-149, and miR149-5p mimic. Treatments were microinjected intracerebroventricularly (ICV) (right side), and ischemia was induced using middle cerebral artery occlusion (MCAO) procedure. Post-MCAO, neurological function, histopathological changes, blood-brain barrier (BBB) permeability, cerebral edema, and mRNA levels of Fas ligand (Faslg) and glutamate ionotropic NMDA receptor 1 (GRIN1) were assessed, alongside biochemical assays. MiR-149 administration improved neurological function, reduced brain damage, preserved BBB integrity, and attenuated cerebral edema. Upregulation of miR149-5p decreased Faslg and GRIN1 expression in ischemic brain regions. MiR-149 also reduced oxidative stress, enhanced antioxidant activity, decreased caspase-1 and - 3 activity, and modulated inflammatory factors in ischemic brain regions. Moreover, DNA fragmentation as an index of cell death decreased following miR-149 treatment. In conclusion, the study underscores miR-149 potential as a neuroprotective agent against ischemic stroke, showcasing its efficacy in modulating various mechanisms and supporting its candidacy as a promising therapeutic target for innovative strategies in stroke treatment.

Vagus nerve stimulation during training fails to improve learning in healthy rats

Learning new skills requires neuroplasticity. Vagus nerve stimulation (VNS) during sensory and motor events can increase neuroplasticity in networks related to these events and might therefore serve to facilitate learning on sensory and motor tasks. We tested if VNS could broadly improve learning on a wide variety of tasks across different skill domains in healthy, female adult rats. VNS was paired with presentation of stimuli or on successful trials during training, strategies known to facilitate plasticity and improve recovery in models of neurological disorders. VNS failed to improve either rate of learning or performance for any of the tested tasks, which included skilled forelimb motor control, speech sound discrimination, and paired-associates learning. These results contrast recent findings from multiple labs which found VNS pairing during training produced learning enhancements across motor, auditory, and cognitive domains. We speculate that these contrasting results may be explained by key differences in task designs, training timelines and animal handling approaches, and that while VNS may be able to facilitate rapid and early learning processes in healthy subjects, it does not broadly enhance learning for difficult tasks.

Differential impact of unilateral stroke on the bihemispheric motor cortex representation of the jaw and tongue muscles in young and aged rats

Introduction

Dysphagia commonly occurs after stroke, yet the mechanisms of post-stroke corticobulbar plasticity are not well understood. While cortical activity associated with swallowing actions is bihemispheric, prior research has suggested that plasticity of the intact cortex may drive recovery of swallowing after unilateral stroke. Age may be an important factor as it is an independent predictor of dysphagia after stroke and neuroplasticity may be reduced with age. Based on previous clinical studies, we hypothesized that cranial muscle activating volumes may be expanded in the intact hemisphere and would contribute to swallowing function. We also hypothesized that older age would be associated with limited map expansion and reduced function. As such, our goal was to determine the impact of stroke and age on corticobulbar plasticity by examining the jaw and tongue muscle activating volumes within the bilateral sensorimotor cortices.

Methods

Using the middle cerebral artery occlusion rat stroke model, intracortical microstimulation (ICMS) was used to map regions of sensorimotor cortex that activate tongue and jaw muscles in both hemispheres. Young adult (7 months) and aged (30 months) male F344 × BN rats underwent a stroke or sham-control surgery, followed by ICMS mapping 8 weeks later. Videofluoroscopy was used to assess oral-motor functions.

Results

Increased activating volume of the sensorimotor cortex within the intact hemisphere was found only for jaw muscles, whereas significant stroke-related differences in tongue activating cortical volume were limited to the infarcted hemisphere. These stroke-related differences were correlated with infarct size, such that larger infarcts were associated with increased jaw representation in the intact hemisphere and decreased tongue representation in the infarcted hemisphere. We found that both age and stroke were independently associated with swallowing differences, weight loss, and increased corticomotor thresholds. Laterality of tongue and jaw representations in the sham-control group revealed variability between individuals and between muscles within individuals.

Conclusion

Our findings suggest the role of the intact and infarcted hemispheres in the recovery of oral motor function may differ between the tongue and jaw muscles, which may have important implications for rehabilitation, especially hemisphere-specific neuromodulatory approaches. This study addressed the natural course of recovery after stroke; future work should expand to focus on rehabilitation.

Crossed Corticostriatal Projections in the Macaque Brain

In nonhuman primates, major input to the striatum originates from ipsilateral cortex and thalamus. The striatum is a target also of crossed corticostriatal (CSt) projections from the contralateral hemisphere, which have been so far somewhat neglected. In the present study, based on neural tracer injections in different parts of the striatum in macaques of either sex, we analyzed and compared qualitatively and quantitatively the distribution of labeled CSt cells in the two hemispheres. The results showed that crossed CSt projections to the caudate and the putamen can be relatively robust (up to 30% of total labeled cells). The origin of the direct and the crossed CSt projections was not symmetrical as the crossed ones originated almost exclusively from motor, prefrontal, and cingulate areas and not from parietal and temporal areas. Furthermore, there were several cases in which the contribution of contralateral areas tended to equal that of the ipsilateral ones. The present study is the first detailed description of this anatomic pathway of the macaque brain and provides the substrate for bilateral distribution of motor, motivational, and cognitive signals for reinforcement learning and selection of actions or action sequences, and for learning compensatory motor strategies after cortical stroke.SIGNIFICANCE STATEMENT In nonhuman primates the striatum is a target of projections originating from the contralateral hemisphere (crossed CSt projections), which have been so far poorly investigated. The present study analyzed qualitatively and quantitatively in the macaque brain the origin of the crossed CSt projections compared with those originating from the ipsilateral hemisphere. The results showed that crossed CSt projections originate mostly from frontal and rostral cingulate areas and in some cases their contribution tended to equal that from ipsilateral areas. These projections could provide the substrate for bilateral distribution of motor, motivational, and cognitive signals for reinforcement learning and action selection, and for learning compensatory motor strategies after cortical stroke.

Motor Cortex Plasticity During Functional Recovery Following Brain Damage

Although brain damage causes functional impairment, it is often followed by partial or total recovery of function. Recovery is believed to occur primarily because of brain plasticity. Both human and animal studies have significantly contributed to uncovering the neuronal basis of plasticity. Recent advances in brain imaging technology have enabled the investigation of plastic changes in living human brains. In addition, animal experiments have revealed detailed changes at the neural and genetic levels. In this review, plasticity in motor-related areas of the cerebral cortex, which is one of the most well-studied areas of the neocortex in terms of plasticity, is reviewed. In addition, the potential of technological interventions to enhance plasticity and promote functional recovery following brain damage is discussed. Novel neurorehabilitation technologies are expected to be established based on the emerging research on plasticity from the last several decades.

Post-Stroke Hemiplegic Rodent Evaluation: A Framework for Assessing Forelimb Movement Quality Using Kinematics

Kinematics is the gold-standard method for measuring detailed joint motions. Recent research demonstrates that post-stroke kinematic analysis in rats reveals reaching abnormalities similar to those seen in humans after stroke. Nonetheless, behavioral neuroscientists have failed to incorporate kinematic methods for assessing movement quality in stroke models. The availability of a user-friendly method to assess multi-segment forelimb kinematics models should greatly increase uptake of this approach. Here, we present a framework for multi-segment forelimb analysis in rodents after stroke. This method greatly enhances the understanding of post-stroke forelimb motor recovery by including several movement quality metrics often used in human clinical work, such as upper-limb linear and angular kinematics, movement smoothness and kinetics, abnormal synergies, and compensations. These metrics may constitute a preclinical surrogate for the Fugl-Meyer assessment of hemiplegic patients. The data obtained using this method are 83 outputs of linear and angular kinematics and kinetics. The outputs also include 24 time series of continuous data, which afford a graphical representation of the kinematics and kinetics of the reaching cycle. We show that post-stroke rodents displayed many features resembling those seen in humans after stroke that are evident only when multi-segment kinematics models are considered. This method expands the knowledge derived from methods constrained to paw movements to a multi-segment forelimb movement quality framework. Moreover, it highlights the need for preclinical work to consider more sensitive measures of sensorimotor impairment and recovery as a means to enhance the interpretation of true recovery and compensation. © 2022 Wiley Periodicals LLC. Basic Protocol: Recording and data analysis of rodents performing the Montoya staircase task.

The Emergence of Stereotyped Kinematic Synergies when Mice Reach to Grasp Following Stroke

Reaching tasks are commonly used in preclinical and clinical studies to assess the acquisition of fine motor skills and recovery of function following stroke. These tasks are often used to assess functional deficits in the absence of quantifying the quality of movement which requires kinematic analysis. To meet this need, this study uses a kinematic analysis in mice performing the Montoya staircase task at 5 and 14 days following a cortical photothrombosis-induced stroke. Following stroke, the mice had reaching impairments associated with sustained deficits including longer, unsmooth, and less individuated paw trajectories. Two weeks after stroke we also detected the emergence of abnormal elbow and shoulder angles, flexion/extensions, and stereotyped kinematic synergies. These data suggest that proximal and distal segments acting in concert is paramount during post-stroke reaching and encourage further analysis of synergies within the translational pipeline of preclinical to clinical studies.

Long-term monitoring of chronic demyelination and remyelination in a rat ischemic stroke model using macromolecular proton fraction mapping

Remyelination is a key process enabling post-stroke brain tissue recovery and plasticity. This study aimed to explore the feasibility of demyelination and remyelination monitoring in experimental stroke from the acute to chronic stage using an emerging myelin imaging biomarker, macromolecular proton fraction (MPF). After stroke induction by transient middle cerebral artery occlusion, rats underwent repeated MRI examinations during 85 days after surgery with histological endpoints for the animal subgroups on the 7th, 21st, 56th, and 85th days. MPF maps revealed two sub-regions within the infarct characterized by distinct temporal profiles exhibiting either a persistent decrease by 30%-40% or a transient decrease followed by return to nearly normal values after one month of observation. Myelin histology confirmed that these sub-regions had nearly similar extent of demyelination in the sub-acute phase and then demonstrated either chronic demyelination or remyelination. The remyelination zones also exhibited active axonal regrowth, reconstitution of compact fiber bundles, and proliferation of neuronal and oligodendroglial precursors. The demyelination zones showed more extensive astrogliosis from the 21st day endpoint. Both sub-regions had substantially depleted neuronal population over all endpoints. These results histologically validate MPF mapping as a novel approach for quantitative assessment of myelin damage and repair in ischemic stroke.

A First Step Toward the Operationalization of the Learned Non-Use Phenomenon: A Delphi Study

BACKGROUND

The negative discrepancy between residual functional capacity and reduced use of the contralesional hand, frequently observed after a brain lesion, has been termed Learned Non-Use (LNU) and is thought to depend on the interaction of neuronal mechanisms during recovery and learning-dependent mechanisms.

OBJECTIVE

Albeit the LNU phenomenon is generally accepted to exist, currently, no transdisciplinary definition exists. Furthermore, although therapeutic approaches are implemented in clinical practice targeting LNU, no standardized diagnostic routine is described in the available literature. Our objective was to reach consensus regarding a definition as well as synthesize knowledge about the current diagnostic procedures.

METHODS

We used a structured group communication following the Delphi method among clinical and scientific experts in the field, knowledge from both, the work with patient populations and with animal models.

RESULTS

Consensus was reached regarding a transdisciplinary definition of the LNU phenomenon. Furthermore, the mode and strategy of the diagnostic process, as well as the sources of information and outcome parameters relevant for the clinical decision making, were described with a wide range showing the current lack of a consistent universal diagnostic approach.

CONCLUSIONS

The need for the development of a structured diagnostic procedure and its implementation into clinical practice is emphasized. Moreover, it exists a striking gap between the prevailing hypotheses regarding the mechanisms underlying the LNU phenomenon and the actual evidence. Therefore, basic research is needed to bridge between bedside and bench and eventually improve clinical decision making and further development of interventional strategies beyond the field of stroke rehabilitation.

Experimental cortical stroke induces aberrant increase of sharp-wave-associated ripples in the hippocampus and disrupts cortico-hippocampal communication

The functional consequences of ischemic stroke in the remote brain regions are not well characterized. The current study sought to determine changes in hippocampal oscillatory activity that may underlie the cognitive impairment observed following distal middle cerebral artery occlusion (dMCAO) without causing hippocampal structural damage. Local field potentials were recorded from the dorsal hippocampus and cortex in urethane-anesthetized rats with multichannel silicon probes during dMCAO and reperfusion, or mild ischemia induced by bilateral common carotid artery occlusion (CCAO). Bilateral change of brain state was evidenced by reduced theta/delta amplitude ratio and shortened high theta duration following acute dMCAO but not CCAO. An aberrant increase in the occurrence of sharp-wave-associated ripples (150-250 Hz), crucial for memory consolidation, was only detected after dMCAO reperfusion, coinciding with an increased occurrence of high-frequency discharges (250-450 Hz). dMCAO also significantly affected the modulation of gamma amplitude in the cortex coupled to hippocampal theta phase, although both hippocampal theta and gamma power were temporarily decreased during dMCAO. Our results suggest that MCAO may disrupt the balance between excitatory and inhibitory circuits in the hippocampus and alter the function of cortico-hippocampal network, providing a novel insight in how cortical stroke affects function in remote brain regions.

First Person - Gustavo Balbinot and Clarissa Pedrini Schuch

First Person is a series of interviews with the first authors of a selection of papers published in Biology Open, helping early-career researchers promote themselves alongside their papers. Gustavo Balbinot and Clarissa Pedrini Schuch are first authors on ‘Mechanical and energetic determinants of impaired gait following stroke: segmental work and pendular energy transduction during treadmill walking’, published in BiO.

Gustavo Balbinot is a postdoctoral fellow at KITE - Toronto Rehabilitation Institute, University Health Network, Toronto, Canada. Clarissa Pedrini Schuch is a postdoctoral fellow at the Graduate Program in Rehabilitation Sciences, Federal University of Health Sciences of Porto Alegre (UFCSPA), Brazil.

Mechanical and energetic determinants of impaired gait following stroke: segmental work and pendular energy transduction during treadmill walking

Systems biology postulates the balance between energy production and conservation in optimizing locomotion. Here, we analyzed how mechanical energy production and conservation influenced metabolic energy expenditure in stroke survivors during treadmill walking at different speeds. We used the body center of mass (BCoM) and segmental center of mass to calculate mechanical energy production: external and each segment's mechanical work (W_seg). We also estimated energy conservation by applying the pendular transduction framework (i.e. energy transduction within the step; R_int). Energy conservation was likely optimized by the paretic lower-limb acting as a rigid shaft while the non-paretic limb pushed the BCoM forward at the slower walking speed. W_seg production was characterized by greater movements between the limbs and body, a compensatory strategy used mainly by the non-paretic limbs. Overall, W_seg production following a stroke was characterized by non-paretic upper-limb compensation, but also by an exaggerated lift of the paretic leg. This study also highlights how post-stroke subjects may perform a more economic gait while walking on a treadmill at preferred walking speeds. Complex neural adaptations optimize energy production and conservation at the systems level, and may fundament new insights onto post-stroke neurorehabilitation.

This article has and associated First Person interview with the first author of the paper.

Summary: Walking after a stroke may be energetically consuming. Here, we show how compensations and asymmetries may contribute to increasing the amount of work needed to walk following a stroke.

Graph theoretical quantification of white matter reorganization after cortical stroke in mice

Stroke is a devastating disease leading to cell death and disconnection between neurons both locally and remote, often resulting in severe long-term disability. Spontaneous reorganization of areas and pathways not primarily affected by ischemia is, however, associated with albeit limited recovery of function. Quantitative mapping of whole-brain changes of structural connectivity concerning the ischemia-induced sensorimotor deficit and recovery thereof would help to target structural plasticity in order to improve rehabilitation. Currently, only in vivo diffusion MRI can extract the structural whole-brain connectome noninvasively. This approach is, however, used primarily in human studies. Here, we applied atlas-based MRI analysis and graph theory to DTI in wild-type mice with cortical stroke lesions. Using a DTI network approach and graph theory, we aimed at gaining insights into the dynamics of the spontaneous reorganization after stroke related to the recovery of function. We found evidence for altered structural integrity of connections of specific brain regions, including the breakdown of connections between brain regions directly affected by stroke as well as long-range rerouting of intra- and transhemispheric connections related to improved sensorimotor behavior.

Effect of Rehabilitation with Extremely Low Frequency Electromagnetic Field on Molecular Mechanism of Apoptosis in Post-Stroke Patients

Apoptosis in acute stroke is associated with a negative prognosis and is correlated with the severity of the neurological deficit. However, there is no evidence that indicates that, in the subacute phase of the stroke, the apoptosis process might activate neuroplasticity. Therefore, in this study, we investigated the effect of an extremely low frequency electromagnetic field (ELF-EMF) on the molecular mechanism of apoptosis, as used in the rehabilitation of post-stroke patients. Patients with moderate stroke severity (n = 48), 3–4 weeks after incident, were enrolled in the analysis and divided into ELF-EMF and non-ELF-EMF group. The rehabilitation program in both groups involves the following: kinesiotherapy—30 min; psychological therapy—15 min; and neurophysiological routines—60 min. Additionally, the ELF-EMF group was exposed to an ELF-EMF (40 Hz, 5 mT). In order to assess the apoptosis gene expression level, we measured the mRNA expression of BAX, BCL-2, CASP8, TNFα, and TP53. We found that ELF-EMF significantly increased the expression of BAX, CASP8, TNFα, and TP53, whereas the BCL-2 mRNA expression after ELF-EMF exposition remained at a comparable level in both groups. Thus, we suggest that increasing the expression of pro-apoptotic genes in post-stroke patients promotes the activation of signaling pathways involved in brain plasticity processes. However, further research is needed to clarify this process.

Lesion Size- and Location-Dependent Recruitment of Contralesional Thalamus and Motor Cortex Facilitates Recovery after Stroke in Mice

Brain lesions caused by cerebral ischemia or hemorrhage lead to a local breakdown of energy homeostasis followed by irreversible cell death and long-term impairment. Importantly, local brain lesions also generate remote functional and structural disturbances, which contribute to the behavioral deficit but also impact the recovery of function. While spontaneous recovery has been associated with endogenous repair mechanisms at the vascular, neural, and immune cell levels, the impact of structural plasticity on sensory-motor dysfunction and recovery thereof remains to be elucidated by longitudinal imaging in a mouse model. Here, we applied behavioral assessments, in vivo fiber tracking, and histological validation in a photothrombotic stroke mouse model. Atlas-based whole-brain structural connectivity analysis and ex vivo histology revealed secondary neurodegeneration in the ipsilesional brain areas, mostly in the dorsal sensorimotor area of the thalamus. Furthermore, we describe for the first time a lesion size-dependent increase in structural connectivity between the contralesional primary motor cortex and thalamus with the ipsilesional cortex. The involvement of the contralesional hemisphere was associated with improved functional recovery relative to lesion size. This study highlights the importance of in vivo fiber tracking and the role of the contralesional hemisphere during spontaneous functional improvement as a potential novel stroke biomarker and therapeutic targets.