A critical threshold of rehabilitation involving brain-derived neurotrophic factor is required for poststroke recovery

A modified rehabilitation paradigm bilaterally increased rat extensor digitorum communis muscle size but did not improve forelimb function after stroke

Malnutrition after stroke may lessen the beneficial effects of rehabilitation on motor recovery through influences on both brain and skeletal muscle. Enriched rehabilitation (ER), a combination of environmental enrichment and forelimb reaching practice, is used preclinically to study recovery of skilled reaching after stroke. However, the chronic food restriction typically used to motivate engagement in reaching practice is a barrier to using ER to investigate interactions between nutritional status and rehabilitation. Thus, our objectives were to determine if a modified ER program comprised of environmental enrichment and skilled reaching practice motivated by a short fast would enhance post-stroke forelimb motor recovery and preserve forelimb muscle size and metabolic fiber type, relative to a group exposed to stroke without ER. At one week after photothrombotic cortical stroke, male, Sprague-Dawley rats were assigned to modified ER or standard care for 2 weeks. Forelimb recovery was assessed in the Montoya staircase and cylinder task before stroke and on days 5-6, 22-23, and 33-34 after stroke. ER failed to improve forelimb function in either task (p > 0.05). Atrophy of extensor digitorum communis (EDC) and triceps brachii long head (TBL) muscles was not evident in the stroke-targeted forelimb on day 35, but the area occupied by hybrid fibers was increased in the EDC muscle (p = 0.038). ER bilaterally increased EDC (p = 0.046), but not TBL, muscle size; EDC muscle fiber type was unchanged by ER. While the modified ER did not promote forelimb motor recovery, it does appear to have utility for studying the role of skeletal muscle plasticity in post-stroke recovery.

Brain-Derived Neurotrophic Factor in Pediatric Acquired Brain Injury and Recovery

We review emerging preclinical and clinical evidence regarding brain-derived neurotrophic factor (BDNF) protein, genotype, and DNA methylation (DNAm) as biomarkers of outcomes in three important etiologies of pediatric acquired brain injury (ABI), traumatic brain injury, global cerebral ischemia, and stroke. We also summarize evidence suggesting that BDNF is (1) involved in the biological embedding of the psychosocial environment, (2) responsive to rehabilitative therapies, and (3) potentially modifiable. BDNF's unique potential as a biomarker of neuroplasticity and neural repair that is reflective of and responsive to both pre- and post-injury environmental influences separates it from traditional protein biomarkers of structural brain injury with exciting potential to advance pediatric ABI management by increasing the accuracy of prognostic tools and informing clinical decision making through the monitoring of therapeutic effects.

Motor Rehabilitation Provides Modest Functional Benefits After Intracerebral Hemorrhage: a Systematic Review and Meta-Analysis of Translational Rehabilitation Studies

Few certainties exist regarding the optimal type, timing, or dosage of rehabilitation after stroke. Despite differing injury mechanisms and recovery patterns following ischemic and hemorrhagic stroke, most translational stroke research is conducted after ischemia. As we enter the era of personalized medicine, exploring subtype-specific treatment efficacy is essential to optimizing recovery. Our objective was to characterize common rehabilitation interventions used after in vivo preclinical intracerebral hemorrhage (ICH) and assess the impact of post-ICH rehabilitation (vs. no-rehabilitation) on recovery of motor function. Following PRISMA guidelines, a systematic review (Academic Search Complete, CINAHL, EMBASE, Medline, PubMed Central) identified eligible articles published up to December 2022. Risk of bias (SYRCLE) and study quality (CAMARADES) were evaluated, and random-effects meta-analysis was used to assess treatment efficacy in recovery of forelimb and locomotor functions. Thirty articles met inclusion criteria, and 48 rehabilitation intervention groups were identified. Most used collagenase to model striatal ICH in young, male rodents. Aerobic exercise, enriched rehabilitation, and constraint-induced movement therapy represented ~ 70% of interventions. Study quality was low (median 4/10, range 2-8), and risk of bias was unclear. Rehabilitation provided modest benefits in skilled reaching, spontaneous impaired forelimb use, and locomotor function; however, effects varied substantially by endpoint, treatment type, and study quality. Rehabilitation statistically improves motor function after preclinical ICH, but whether these effects are functionally meaningful is unclear. Incomplete reporting and variable research quality hinder our capacity to analyze and interpret how treatment factors influence rehabilitation efficacy and recovery after ICH.

Challenges in Translating Regenerative Therapies for Spinal Cord Injury

Regenerating the injured spinal cord is a substantial challenge with many obstacles that need to be overcome to achieve robust functional benefits. This abundance of hurdles can partly explain the limited success when applying regenerative intervention treatments in animal models and/or people. In this article, we elaborate on a few of these obstacles, starting with the applicability of animal models and how they compare to the clinical setting. We then discuss the requirement for combinatorial interventions and the associated problems in experimental design, including the addition of rehabilitative training. The article expands on differences in lesion sizes and locations between humans and common animal models, and how this difference can determine the success or failure of an intervention. An additional and frequently overlooked problem in the translation of interventions that applies beyond the field of neuroregeneration is the reporting bias and the lack of transparency in reporting findings. New data mandates are tackling this problem and will eventually result in a more balanced view of the field. Finally, we will discuss strategies to negotiate the challenging course of successful translation to facilitate successful translation of regeneration promoting interventions.

Performance-Based Robotic Training in Individuals with Subacute Stroke: Differences between Responders and Non-Responders

The high variability of upper limb motor recovery with robotic training (RT) in subacute stroke underscores the need to explore differences in responses to RT. We explored differences in baseline characteristics and the RT dose between responders (ΔFugl-Meyer Assessment (FMA) score ≥ 9 points; n = 20) and non-responders (n = 16) in people with subacute stroke (mean [SD] poststroke time at baseline, 54 (26) days, baseline FMA score, 23 (17) points) who underwent 16 RT sessions combined with conventional therapies. Baseline characteristics were compared between groups. During RT sessions, the actual practice time (%), number of movements performed, and total distance covered (cm) in assisted and unassisted modalities were compared between groups. At baseline, participant characteristics and FMA scores did not differ between groups. During the RT, non-responders increased practice time (+15%; p = 0.02), performed more movements (+285; p = 0.004), and covered more distance (+4037 cm; p < 10^-3), with no difference between physical modalities. In contrast, responders decreased practice time (-21%; p = 0.01) and performed fewer movements (-338; p = 0.03) in the assisted modality while performing more movements (+328; p < 0.05) and covering a greater distance (+4779 cm; p = 0.01) in unassisted modalities. Despite a large amount of motor practice, motor outcomes did not improve in non-responders compared to responders: the difficulty level in RT may have been too low for them. Future studies should combine robot-based parameters to describe the treatment dose, especially in people with severe-to-moderate arm paresis, to optimize the RT and improve the recovery prognosis.

Early, Intense Rehabilitation Fails to Improve Outcome After Intra-Striatal Hemorrhage in Rats

BACKGROUND

The formation and degradation of an intracerebral hemorrhage causes protracted cell death, and an extended window for intervention. Experimental studies find that rehabilitation mitigates late cell death, with accelerated hematoma clearance as a potential mechanism.

OBJECTIVE

We assessed whether early, intense, enriched rehabilitation (ER, environmental enrichment and massed skills training) enhances functional benefit, reduces brain injury, and augments hematoma clearance.

METHODS

In experiment 1, rats (n = 56) were randomized to intervention in the light (-L) or dark phase (-D) of their housing cycle, then to 10 days of ER or control (CON) treatment after collagenase-induced striatal intracerebral hemorrhage (ICH). ER rats were treated from 5 to 14 days after ICH. Behavior and residual hematoma volume was assessed on day 14. In experiment 2, rats (n = 72) were randomized to ER-D10, ER-D20, or CON-D. ER rats completed 10 or 20 days of training in the dark. Rats were euthanized on day 60 for histology. In both experiments, behavioral assessment was completed pre-ICH, pre-ER (day 4 post-ICH), and post-ER (experiment 1: days 13-14; experiment 2: days 16-17 and 30-31).

RESULTS

Reaching intensity was high but similar between ER-D10 and ER-L10. Unlike previous work, rehabilitation did not alter skilled reaching or hematoma resolution. Varying ER duration also did not affect reaching success or lesion volume.

CONCLUSIONS

In contrast to others, and under these conditions, our findings show that striatal ICH was generally unresponsive to rehabilitation. This highlights the difficulty of replicating and extending published work, perhaps owing to small inter-study differences.

Treatment of rat brain ischemia model by NSCs-polymer scaffold transplantation

Neural stem cells (NSCs) transplantation is a promising therapeutic strategy for ischemic stroke. However, significant cell death after transplantation greatly limits its effectiveness. Poly (trimethylene carbonate)15-F127-poly (trimethylene carbonate)15 (PTMC15-F127-PTMC15, PFP) is a biodegradable thermo-sensitive hydrogel biomaterial, which can control drug release and provide permissive substrates for donor NSCs. In our study, we seeded NSCs into PFP polymer scaffold loaded with three neurotrophic factors, including brain-derived neurotrophic factor, nerve growth factor, and Neurotrophin-3. And then we transplanted this NSCs-polymer scaffold in rat brains 14 days after middle cerebral artery occlusion. ELISA assay showed that PFP polymer scaffold sustained releasing three neurotrophic factors for at least 14 days. Western Blot and fluorescence immunostaining revealed that NSCs-polymer scaffold transplantation significantly reduced apoptosis of ischemic penumbra and promoted differentiation of the transplanted NSCs into mature neurons. Furthermore, infarct size was reduced, and neurological performance of the animals were improved by the transplanted NSCs-polymer scaffold. These results demonstrate that PFP polymer scaffold loaded with neurotrophic factors can enhance the effectiveness of stem cell transplantation therapy, which provides a new way for cell transplantation therapy in ischemic stroke.

Revisiting dose and intensity of training: Opportunities to enhance recovery following stroke

PURPOSE

Stroke is a global leading cause of adult disability with survivors often enduring persistent impairments and loss of function. Both intensity and dosage of training appear to be important factors to help restore behavior. However, current practice fails to achieve sufficient intensity and dose of training to promote meaningful recovery. The purpose of this review is to propose therapeutic solutions that can help achieve a higher dose and/or intensity of therapy. Raising awareness of these intensive, high-dose, treatment strategies might encourage clinicians to re-evaluate current practice and optimize delivery of stroke rehabilitation for maximal recovery.

METHODS

Literature that tested and evaluated solutions to increase dose or intensity of training was reviewed. For each therapeutic strategy, we outline evidence of clinical benefit, supporting neurophysiological data (where available) and discuss feasibility of clinical implementation.

RESULTS

Possible therapeutic solutions included constraint induced movement therapy, robotics, circuit therapy, bursts of training, gaming technologies, goal-oriented instructions, and cardiovascular exercise.

CONCLUSION

Our view is that clinicians should evaluate current practice to determine how intensive high-dose training can be implemented to promote greater recovery after stroke.

Intensity matters: protocol for a randomized controlled trial exercise intervention for individuals with chronic stroke

Rationale

Cardiovascular exercise is an effective method to improve cardiovascular health outcomes, but also promote neuroplasticity during stroke recovery. Moderate-intensity continuous cardiovascular training (MICT) is an integral part of stroke rehabilitation, yet it may remain a challenge to exercise at sufficiently high intensities to produce beneficial adaptations to neuroplasticity. High-intensity interval training (HIIT) could provide a viable alternative to achieve higher intensities of exercise by using shorter bouts of intense exercise interspersed with periods of recovery.

Methods and design

This is a two-arm, parallel-group multi-site RCT conducted at the Jewish Rehabilitation Hospital (Laval, Québec, Canada) and McMaster University (Hamilton, Ontario, Canada). Eighty participants with chronic stroke will be recruited at both sites and will be randomly allocated into a HIIT or MICT individualized exercise program on a recumbent stepper, 3 days per week for 12 weeks. Outcomes will be assessed at baseline, at 12 weeks post-intervention, and at an 8-week follow-up.

Outcomes

The primary outcome is corticospinal excitability, a neuroplasticity marker in brain motor networks, assessed with transcranial magnetic stimulation (TMS). We will also examine additional markers of neuroplasticity, measures of cardiovascular health, motor function, and psychosocial responses to training.

Discussion

This trial will contribute novel insights into the effectiveness of HIIT to promote neuroplasticity in individuals with chronic stroke.

Trial registration

ClinicalTrials.govNCT03614585. Registered on 3 August 2018

Supplementary Information

The online version contains supplementary material available at 10.1186/s13063-022-06359-w.

Recovery of Post-Stroke Spatial Memory and Thalamocortical Connectivity Following Novel Glycomimetic and rhBDNF Treatment

Stroke-induced cognitive impairments remain of significant concern, with very few treatment options available. The involvement of glycosaminoglycans in neuroregenerative processes is becoming better understood and recent advancements in technology have allowed for cost-effective synthesis of novel glycomimetics. The current study evaluated the therapeutic potential of two novel glycomimetics, compound A and G, when administered systemically five-days post-photothrombotic stroke to the PFC. As glycosaminoglycans are thought to facilitate growth factor function, we also investigated the combination of our glycomimetics with intracerebral, recombinant human brain-derived neurotrophic factor (rhBDNF). C56BL/6J mice received sham or stroke surgery and experimental treatment (day-5), before undergoing the object location recognition task (OLRT). Four-weeks post-surgery, animals received prelimbic injections of the retrograde tracer cholera toxin B (CTB), before tissue was collected for quantification of thalamo-PFC connectivity and reactive astrogliosis. Compound A or G treatment alone modulated a degree of reactive astrogliosis yet did not influence spatial memory performance. Contrastingly, compound G+rhBDNF treatment significantly improved spatial memory, dampened reactive astrogliosis and limited stroke-induced loss of connectivity between the PFC and midline thalamus. As rhBDNF treatment had negligible effects, these findings support compound A acted synergistically to enhance rhBDNF to restrict secondary degeneration and facilitate functional recovery after PFC stroke.

Virtuous and Vicious Cycles of Arm Use and Function Post-stroke

Large doses of movement practice have been shown to restore upper extremities' motor function in a significant subset of individuals post-stroke. However, such large doses are both difficult to implement in the clinic and highly inefficient. In addition, an important reduction in upper extremity function and use is commonly seen following rehabilitation-induced gains, resulting in "rehabilitation in vain". For those with mild to moderate sensorimotor impairment, the limited spontaneous use of the more affected limb during activities of daily living has been previously proposed to cause a decline of motor function, initiating a vicious cycle of recovery, in which non-use and poor performance reinforce each other. Here, we review computational, experimental, and clinical studies that support the view that if arm use is raised above an effective threshold, one enters a virtuous cycle in which arm use and function can reinforce each other via self-practice in the wild. If not, one enters a vicious cycle of declining arm use and function. In turn, and in line with best practice therapy recommendations, this virtuous/vicious cycle model advocates for a paradigm shift in neurorehabilitation whereby rehabilitation be embedded in activities of daily living such that self-practice with the aid of wearable technology that reminds and motivates can enhance paretic limb use of those who possess adequate residual sensorimotor capacity. Altogether, this model points to a user-centered approach to recovery post-stroke that is tailored to the participant's level of arm use and designed to motivate and engage in self-practice through progressive success in accomplishing meaningful activities in the wild.

Circulating brain-derived neurotrophic factor as a potential biomarker in stroke: a systematic review and meta-analysis

Background

Stroke, an acute cerebrovascular event, is a leading cause of disability, placing a significant psycho-socioeconomic burden worldwide. The adaptation and reorganization process following any neuronal damage is regarded as neuroplasticity. Among many factors believed to attribute to this process, Brain-derived Neurotrophic Factor (BDNF) is a neurotrophin coordinating neuroplasticity after various neurological disorders such as stroke.

Methods

We conducted a systematic search in the main electronic medical databases in January 2021. Primarily we want to compare BDNF levels between patients with stroke and healthy controls (HC). Additional aims included investigation of (1) longitudinal changes in the BDNF levels post-stroke, (2) effects of physical training, (3) repeated transcranial magnetic stimulation (rTMS), and presence of depression on BDNF levels in patients with stroke.

Results

Among 6243 reviewed records from PubMed, Web of Science, and Scopus, 62 studies were eligible for inclusion in our systematic review. Subjects with stroke, n = 1856, showed lower BDNF levels compared to HC, n = 1191 (SMD [95%CI] = − 1.04 [− 1.49 to − 0.58]). No significant difference was detected in the level of BDNF through time points past stroke. BDNF levels were lower in the patients with depression compared to non-depressed subjects (SMD [95%CI] = − 0.60 [− 1.10 to − 0.10]). Physical training had an immediate positive effect on the BDNF levels and not statistically significant effect in the long term; SMD [95%CI] = 0.49 [0.09 to 0.88]) and SMD [95%CI] = 0.02 [− 0.43 to 0.47]). Lastly, rTMS showed no effect on the level of BDNF with 0.00 SMD.

Conclusions

Our study confirms that stroke significantly decreases the level of BDNF in various domains such as cognition, affect, and motor function. As BDNF is the major representative of neuroplasticity within nervous system, it is believed that stroke has a significant impact on the CNS regeneration, which is permanent if left untreated. This effect is intensified with coexisting conditions such as depression which further decrease the BDNF level but the net impact yet needs to be discovered. We also conclude that exercise and some interventions such as different medications could effectively reverse the damage but further studies are crucial to reach the exact modality and dosage for their optimal effect.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12967-022-03312-y.

Safety, Feasibility, and Acceptability of a New Virtual Rehabilitation Platform: A Supervised Pilot Study

Purpose:

Stroke is the leading cause of disability in adults worldwide, with hemiparesis being the most prevalent consequence. The use of video games and movement sensors could contribute to improving patients’ chances of recovery. We performed a supervised pilot study to validate the safety, feasibility, and acceptability of a new virtual rehabilitation platform in patients with chronic post-stroke upper limb hemiparesis.

Methods:

The participants (n = 9) participated in 40 rehabilitation sessions, twice a week, for a period of 20 weeks. Their experiences with the platform were documented using a Likert-scale survey. Changes in motor function were evaluated using the Chedoke Arm and Hand Activity Inventory (CAHAI) and the Wolf Motor Function Test (WMFT).

Results and conclusions:

All participants expressed that they enjoyed the experience and felt comfortable using the platform. Preliminary results showed significant motor recovery (P = .0039) according to the WMFT scores. Patients with significant impairment showed no improvement in upper limb task-oriented motor function after therapy.

The new platform is safe and well-accepted by patients. The improvement in motor function observed in some of the participants should be attributed to the therapy since spontaneous functional recovery is not expected in chronic stroke patients.

Developmental and Interventional Plasticity of Motor Maps after Perinatal Stroke

Within the perinatal stroke field, there is a need to establish preclinical models where putative biomarkers for motor function can be examined. In a mouse model of perinatal stroke, we evaluated motor map size and movement latency following optogenetic cortical stimulation against three factors of post-stroke biomarker utility: (1) correlation to chronic impairment on a behavioral test battery; (2) amenability to change using a skilled motor training paradigm; and (3) ability to distinguish individuals with potential to respond well to training. Thy1-ChR2-YFP mice received a photothrombotic stroke at postnatal day 7 and were evaluated on a battery of motor tests between days 59 and 70. Following a cranial window implant, mice underwent longitudinal optogenetic motor mapping both before and after 3 weeks of skilled forelimb training. Map size and movement latency of both hemispheres were positively correlated with impaired spontaneous forelimb use, whereas only ipsilesional hemisphere map size was correlated with performance in skilled reaching. Map size and movement latency did not show groupwise changes with training; however, mice with the smallest pretraining map sizes and worst impairments demonstrated the greatest expansion of map size in response to skilled forelimb training. Overall, motor map size showed utility as a potential biomarker for impairment and training-induced modulation in specific individuals. Future assessment of the predictive capacity of post-stroke motor representations for behavioral outcome in animal models opens the possibility of dissecting how plasticity mechanisms contribute to recovery following perinatal stroke.SIGNIFICANCE STATEMENT We investigated the utility of two cortical motor representation measures (motor map size and movement onset latency) as potential biomarkers for post-stroke motor recovery in a mouse model of perinatal stroke. Both motor map size and movement latency were associated with functional recovery after perinatal stroke, with map size showing an additional association between training responsiveness and severity of impairment. Overall, both motor map size and movement onset latency show potential as neurophysiological correlates of recovery. As such, future studies of perinatal stroke rehabilitation and neuromodulation should include these measures to help explain neurophysiological changes that might be occurring in response to treatment.

Cholinergic upregulation by optogenetic stimulation of nucleus basalis after photothrombotic stroke in forelimb somatosensory cortex improves endpoint and motor but not sensory control of skilled reaching in mice

A network of cholinergic neurons in the basal forebrain innerve the forebrain and are proposed to contribute to a variety of functions including cortical plasticity, attention, and sensorimotor behavior. This study examined the contribution of the nucleus basalis cholinergic projection to the sensorimotor cortex on recovery on a skilled reach-to-eat task following photothrombotic stroke in the forelimb region of the somatosensory cortex. Mice were trained to perform a single pellet skilled reaching task and their pre and poststroke performance, from Day 4 to Day 28 poststroke, was assessed frame-by-frame by video analysis with endpoint, movement and sensorimotor integration measures. Somatosensory forelimb lesions produced impairments in endpoint and movement component measures of reaching and increased the incidence of fictive eating, a sensory impairment in mistaking a missed reach for a successful reach. Upregulated acetylcholine (ACh) release, as measured by local field potential recording, elicited via optogenetic stimulation of the nucleus basalis improved recovery of reaching and improved movement scores but did not affect sensorimotor integration impairment poststroke. The results show that the mouse cortical forelimb somatosensory region contributes to forelimb motor behavior and suggest that ACh upregulation could serve as an adjunct to behavioral therapy for acute treatment of stroke.

Multidimensional Phase I Dose Ranging Trials for Stroke Recovery Interventions: Key Challenges and How to Address Them

Despite an increase in the amount of published stroke recovery research, interventions have failed to markedly affect the trajectory of recovery poststroke. We argue that early-phase research to systematically investigate dose is an important contributor to advance the science underpinning stroke recovery. In this article, we aim to (a) define the problem of insufficient use of a systematic approach to early-phase, multidimensional dose articulation research and (b) propose a solution that applies this approach to design a multidimensional phase I trial to identify the maximum tolerated dose (MTD). We put forward a design template as a decision support tool to increase knowledge of how to develop a phase I dose-ranging trial for nonpharmaceutical stroke recovery interventions. This solution has the potential to advance the development of efficacious stroke recovery interventions, which include activity-based rehabilitation interventions.

Additional, Mechanized Upper Limb Self-Rehabilitation in Patients With Subacute Stroke: The REM-AVC Randomized Trial

[Figure: see text].

An Exercise Mimetic Approach to Reduce Poststroke Deconditioning and Enhance Stroke Recovery

Evidence supports early rehabilitation after stroke to limit disability. However, stroke survivors are typically sedentary and experience significant cardiovascular and muscular deconditioning. Despite growing consensus that preclinical and clinical stroke recovery research should be aligned, there have been few attempts to incorporate cardiovascular and skeletal muscle deconditioning into animal models of stroke. Here, we demonstrate in rats that a hindlimb sensorimotor cortex stroke results in both cardiovascular and skeletal muscle deconditioning and impairments in gait akin to those observed in humans. To reduce poststroke behavioral, cardiovascular, and skeletal muscle perturbations, we then used a combinatorial intervention consisting of aerobic and resistance exercise in conjunction with administration of resveratrol (RESV), a drug with exercise mimetic properties. A combination of aerobic and resistance exercise mitigated decreases in cardiovascular fitness and attenuated skeletal muscle abnormalities. RESV, beginning 24 hours poststroke, reduced acute hindlimb impairments, improved recovery in hindlimb function, increased vascular density in the perilesional cortex, and attenuated skeletal muscle fiber changes. Early RESV treatment and aerobic and resistance exercise independently provided poststroke benefits, at a time when individuals are rapidly becoming deconditioned as a result of inactivity. Although no additive effects were observed in these experiments, this approach represents a promising strategy to reduce poststroke behavioral impairments and minimize deconditioning. As such, this treatment regime has potential for enabling patients to engage in more intensive rehabilitation at an earlier time following stroke when mechanisms of neuroplasticity are most prevalent.

Types of biomaterials useful in brain repair

Biomaterials is an emerging field in the study of brain tissue engineering and repair or neurogenesis. The fabrication of biomaterials that can replicate the mechanical and viscoelastic features required by the brain, including the poroviscoelastic responses, force dissipation, and solute diffusivity are essential to be mapped from the macro to the nanoscale level under physiological conditions in order for us to gain an effective treatment for neurodegenerative diseases. This research topic has identified a critical study gap that must be addressed, and that is to source suitable biomaterials and/or create reliable brain-tissue-like biomaterials. This chapter will define and discuss the various types of biomaterials, their structures, and their function-properties features which would enable the development of next-generation biomaterials useful in brain repair.

Serum BDNF Levels in Acute Stroke: A Systematic Review and Meta-Analysis

Background and objectives: Brain-derived neurotrophic factor (BDNF) is one of the most studied neurotrophins. Low BDNF concentrations have been noted in patients with traditional cardiovascular disease risk factors and have been associated with the increased risk of stroke/transient ischemic attack (TIA). We aimed to study the correlation of BDNF serum levels with acute stroke severity and its potential role as a biomarker in predicting functional outcome. Materials and methods: We systematically searched PubMed, Web of Science, and the Cochrane database using specific keywords. The endpoints examined were the correlation of BDNF with functional outcome, the National Institute of Health stroke scale (NIHSS) measured at the acute phase, and stroke infarct volume. We also compared serum BDNF levels between stroke patients and healthy controls. Results: Twenty-six records were included from the initial 3088 identified. Twenty-five studies reported NIHSS and BDNF levels on the first day after acute stroke. Nine studies were further meta-analyzed. A statistically significant negative correlation between NIHSS and BDNF levels during the acute phase of stroke was noted (COR: −0.3013, 95%CI: (−0.4725; −0.1082), z = −3.01, p = 0.0026). We also noted that BDNF levels were significantly lower in patients with stroke compared to healthy individuals. Due to the heterogeneity of studies, we only conducted a qualitative analysis regarding serum BDNF and functional outcome, while no correlation between BDNF levels and stroke infarct volume was noted. Conclusions: We conclude that in the acute stroke phase, stroke severity is negatively correlated with BDNF levels. Concurrently, patients with acute stroke have significantly lower BDNF levels in serum compared to healthy controls. No correlations between BDNF and stroke infarct volume or functional outcome at follow-up were noted.

Early-phase dose articulation trials are underutilized for post-stroke motor recovery: A systematic scoping review

BACKGROUND

To enable development of effective interventions, there is a need to complete systematic early-phase dose articulation research. This scoping review aimed to synthesize dose articulation research of behavioral motor interventions for stroke recovery.

METHODS

MEDLINE and EMBASE were systematically searched for dose articulation studies. Preclinical experiments and adult clinical trials were classified based on the discovery pipeline and analyzed to determine which dose dimensions were articulated (time, scheduling or intensity) and how they were investigated (unidimensional vs multidimensional approach). Reporting of dose, safety and efficacy outcomes were summarized. The intervention description, risk of bias, and quality was appraised.

RESULTS

We included 41 studies: 3 of preclinical dose preparation (93 rodents), 2 Phase I dose ranging (21 participants), 9 Phase IIA dose screening (198 participants), and 27 Phase IIB dose finding (1879 participants). All studies adopted a unidimensional approach. Time was the most frequent dimension investigated (53%), followed by intensity (29%), and scheduling (18%). Overall, 95% studies reported an efficacy outcome; however, only 65% reported dose and 45% reported safety. Across studies, 61% were at high risk of bias, and the average percentage reporting of intervention description and quality was 61% and 67%, respectively.

CONCLUSION

This review highlights a need to undertake more high-quality, early-phase studies that systematically articulate intervention doses from a multidimensional perspective in the field of behavioral motor stroke recovery. To address this gap, we need to invest in adapting early phase trial designs, especially Phase I, to support multidimensional dose articulation.

Protection against acute cerebral ischemia/reperfusion injury by Leonuri Herba Total Alkali via modulation of BDNF-TrKB-PI3K/Akt signaling pathway in rats

OBJECTIVE

To observe the brain protective effect of Leonuri Herba Total Alkali (LHA) on cerebral ischemia reperfusion injury in rats, so as to provide basis for clinical research.

METHODS

Adult male SD rats were randomly assigned into sham group, middle cerebral artery occlusion/reperfusion (MCAO/R) group, and LHA + MCAO/R group (25 mg/kg, 50 mg/kg, and 100 mg/kg). Fourteen days before MCAO/R surgery, the rats in treatment groups were orally administered with LHA in ultrapure water once daily for 14 days, while rats in the sham and MCAO groups were given the same amount of saline in advance. After 1 h of administration on the 14th day, MCAO surgery was subjected. The neurological deficits, brain infarct volume, histopathology, immunofluorescence, inflammation indicators and the gene/protein expressions of BDNF-TrKB-PI3K/Akt signaling pathway in the rat brain tissue were evaluated 24 h after the MCAO/R-injury.

RESULTS

It was found that rats in LHA pre-administration group showed significantly reduced neurological deficit scores, infarction volume, the serum levels of NSE and S100β. Meanwhile, the content of Evans Blue (EB) in brain tissue from LHA group was decreased, as well as the levels of inflammatory cytokines and their gene levels. Moreover, LHA pre-administration inhibited the expression of CD44, GFAP, FOXO1 and promoted the expression of BDNF and NeuN. In addition, LHA pre-administration could up-regulate the protein expression of TrkB, p-PI3K, p-Akt, Bcl-2, and down-regulate the protein expression of Bax, and increase the level of Bcl-2/Bax.

CONCLUSIONS

The study demonstrated that LHA pre-administration could regulate the PI3K/Akt pathway by increasing BDNF levels, and play a neuroprotective role in cerebral ischemia-reperfusion injury.

A systematic review of group intervention for acquired dysarthria in adults

PURPOSE

This review aimed to evaluate the evidence for group therapy in improving speech production in adults with acquired dysarthria. Secondary outcomes included communication effectiveness and/or wellbeing.

MATERIALS AND METHODS

A review protocol was prospectively published on PROSPERO. Fourteen electronic databases were searched to identify experimental studies investigating adults with acquired dysarthria participating in group intervention with outcomes related to communication and/or wellbeing. The quality of included studies was assessed using the Mixed Methods Appraisal Tool (MMAT) or the McMaster University's Critical Review Form, and the TIDieR template for intervention description and replication.

RESULTS

21 studies were identified involving 330 individuals with dysarthria, from mostly Parkinson's disease (PD) (97%; n = 321). Treatment approaches included singing therapy (n = 10), loudness therapy (n = 5) and multi-components therapy (including a combination of impairment and/or compensatory approaches) (n = 4). Studies varied in intensity and outcome measures used. Statistically significant improvements to speech production and/or wellbeing were reported following most approaches.

CONCLUSION

There is some preliminary moderate-quality evidence to suggest that group therapy may improve speech production and in some cases communication effectiveness or wellbeing in people with dysarthria following PD, with more consistent improvements being found for loudness approaches. Singing approaches were frequently studied in PD with some improvements to intelligibility evident. Further well-designed controlled studies including individuals with non-progressive aetiologies is warranted to establish the effectiveness of group treatment.IMPLICATIONS FOR REHABILITATIONGroup therapy may be an effective means of improving speech production and/or wellbeing in individuals with dysarthria following Parkinson's disease.Studies' employing loudness-based group therapy for PD demonstrated more consistent improvements to intensity measures.Some controlled studies utilising singing group therapy resulted in improved intelligibility in PD.PROSPERO registration number: CRD42015029374.

Intermittent Skill Training Results in Moderate Improvement in Functional Outcome in a Mouse Model of Ischemic Stroke

BACKGROUND

Stroke is a leading cause of disability worldwide. Focused training of the impaired limb has been shown to improve its functional outcome in animal models. However, most human stroke survivors exhibit persistent motor deficits, likely due to differences in rehabilitation intensity between experimental (animal) and clinical (human) settings.

OBJECTIVE

The current study investigated the effect of training intensity on behavioral outcome in a mouse model of stroke.

METHODS

Mice were trained preoperatively on a skilled reaching task. After training, mice received a unilateral photothrombotic stroke. Postoperatively, animals received either daily rehabilitative training (traditional intensity), intermittent rehabilitative training (every other day), or no rehabilitative training (control). Assessment of the impaired limb occurred after 14 training sessions (14 days for the Traditional group; 28 days for the Intermittent group).

RESULTS

Assessment of the impaired limb illustrated that traditional, daily training resulted in significantly better performance than no training, while intermittent training offered moderate performance gains. Mice receiving intermittent training performed significantly better than control mice but did not exhibit reaching performance as strong as that of animals trained daily.

CONCLUSIONS

The intensity of rehabilitation is important for optimal recovery. Although intermediate intensity offers some benefit, it is not intensive enough to mimic the performance gains traditionally observed in animal models. These results suggest that intensive training, which is often unavailable for human stroke survivors, is necessary to achieve an optimal functional outcome. The lower bounds of training intensity for functional benefit still need to be determined.

Effects of Upper-Extremity Rehabilitation Using Smart Glove in Patients With Subacute Stroke: Results of a Prematurely Terminated Multicenter Randomized Controlled Trial

Background: Although there have been many trials and interventions for reducing upper-extremity impairment in stroke survivors, it remains a challenge. A novel intervention is needed to provide high-repetition task-specific training early after stroke.

Objective: This study aimed to investigate the effect of smart glove training (SGT) for upper-extremity rehabilitation in patients with subacute stroke.

Methods: A prospective, multicenter, randomized, controlled study was conducted in patients with upper-extremity hemiparesis with Brunnstrom stage for arm 2–5 in the subacute phase after stroke. Eligible participants were randomly allocated to the SGT group or the control group. The SGT group underwent 30 min of standard occupational therapy plus 30 min of upper-extremity training with smart glove. The control group underwent standard occupational therapy for 30 min plus upper-extremity self-training (homework tasks at bedside) for 30 min. All participants underwent each intervention 5 days/week for 2 consecutive weeks. They were evaluated before, immediately after, and 4 weeks after the intervention. The primary outcome measure was the change in the score of the Fugl-Meyer assessment of the upper extremity (FMA-UE).

Results: Twenty-three patients were enrolled. Repeated-measures analysis of covariance after controlling for age and disease duration showed significant time × group interaction effects in the FMA-UE, FMA-distal, and FMA-coordination/speed (p = 0.018, p = 0.002, p = 0.006). Repeated-measures analysis of variance showed significant time × group interaction effects in the FMA-UE, FMA-distal, and Box and Block Test (p = 0.034, p = 0.010, p = 0.046). Mann-Whitney U-test showed a statistically higher increase in the FMA-UE and FMA-distal in the SGT group than in the control group (p = 0.023, p = 0.032).

Conclusion: Upper-extremity rehabilitation with a smart glove may reduce upper-extremity impairment in patients with subacute stroke.

Clinical Trial Registration: ClinicalTrials.gov (NCT02592759).

Comparative Enhancement of Motor Function and BDNF Expression Following Different Brain Stimulation Approaches in an Animal Model of Ischemic Stroke

BACKGROUND

Combinatory intervention such as high-frequency (50-100 Hz) excitatory cortical stimulation (ECS) given concurrently with motor rehabilitative training (RT) improves forelimb function, except in severely impaired animals after stroke. Clinical studies suggest that low-frequency (≤1 Hz) inhibitory cortical stimulation (ICS) may provide an alternative approach to enhance recovery. Currently, the molecular mediators of CS-induced behavioral effects are unknown. Brain-derived neurotrophic factor (BDNF) has been associated with improved recovery and neural remodeling after stroke and thus may be involved in CS-induced behavioral recovery.

OBJECTIVE

To investigate whether inhibitory stimulation during RT improves functional recovery of severely impaired rats, following focal cortical ischemia and if this recovery alters BDNF expression (study 1) and depends on BDNF binding to TrkB receptors (study 2).

METHODS

Rats underwent ECS + RT, ICS + RT, or noCS + RT treatment daily for 3 weeks following a unilateral ischemic lesion to the motor cortex. Electrode placement for stimulation was either placed ipsilateral (ECS) or contralateral (ICS) to the lesion. After treatment, BDNF expression was measured in cortical tissue samples (study 1). In study 2, the TrkB inhibitor, ANA-12, was injected prior to treatment daily for 21 days.

RESULTS

ICS + RT treatment significantly improved impaired forelimb recovery compared with ECS + RT and noCS + RT treatment.

CONCLUSION

ICS given concurrently with rehabilitation improves motor recovery in severely impaired animals, and alters cortical BDNF expression; nevertheless, ICS-mediated improvements are not dependent on BDNF binding to TrkB. Conversely, inhibition of TrkB receptors does disrupt motor recovery in ECS + RT treated animals.

The Efficiency, Efficacy, and Retention of Task Practice in Chronic Stroke

In motor skill learning, larger doses of practice lead to greater efficacy of practice, lower efficiency of practice, and better long-term retention. Whether such learning principles apply to motor practice after stroke is unclear. Here, we developed novel mixed-effects models of the change in the perceived quality of arm movements during and following task practice. The models were fitted to data from a recent randomized controlled trial of the effect of dose of task practice in chronic stroke. Analysis of the models' learning and retention rates demonstrated an increase in efficacy of practice with greater doses, a decrease in efficiency of practice with both additional dosages and additional bouts of training, and fast initial decay following practice. Two additional effects modulated retention: a positive "self-practice" effect, and a negative effect of dose. Our results further suggest that for patients with sufficient arm use post-practice, self-practice will further improve use.

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

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

Transplantation of Stem Cells from Human Exfoliated Deciduous Teeth Decreases Cognitive Impairment from Chronic Cerebral Ischemia by Reducing Neuronal Apoptosis in Rats

Stem cells from human exfoliated deciduous teeth (SHED) are a unique postnatal stem cell population with high self-renewal ability that originates from the cranial neural crest. Since SHED are homologous to the central nervous system, they possess superior capacity to differentiate into neural cells. However, whether and how SHED ameliorate degenerative central nervous disease are unclear. Chronic cerebral ischemia (CCI) is a kind of neurological disease caused by long-term cerebral circulation insufficiency and is characterized by progressive cognitive and behavioral deterioration. In this study, we showed that either systemic transplantation of SHED or SHED infusion into the hippocampus ameliorated cognitive impairment of CCI rats in four weeks after SHED treatment by rescuing the number of neurons in the hippocampus area. Mechanistically, SHED transplantation decreased the apoptosis of neuronal cells in the hippocampus area of CCI rats through downregulation of cleaved caspase-3. In summary, SHED transplantation protected the neuronal function and reduced neuronal apoptosis, resulting in amelioration of cognitive impairment from CCI. Our findings suggest that SHED are a promising stem cell source for cell therapy of neurological diseases in the clinic.

Exercise Plus Pharmacological Neuromodulation of Synaptic Inhibition Enhance Motor Function Recovery After Ischemic Stroke

The objective of this study was to examine the interactive effects of exercise and low-level inhibition of GABA_A receptors on the recovery of motor function and BDNF expression in the primary motor cortex (M1) of a stroke rat model. Male Sprague-Dawley rats were divided into five groups: sham (SHAM), control (CON), exercise (EX), bicuculline (BIC), and bicuculline plus exercise (BICEX) groups. All rats, except those in the SHAM group, underwent middle cerebral artery occlusion (MCAO) surgery to induce an ischemic stroke. GABA_A receptor antagonist, bicuculline (0.25 mg/kg, i.p.), was administered to the BIC and BICEX groups. The EX and BICEX groups exercised on a treadmill (11 m/min for 30 min). Each intervention started 3 days after the MCAO surgery and was carried out every day for 2 weeks. Following the intervention, bilateral M1 BDNF mRNA and protein expression levels were assessed using qRT-PCR and ELISA. Marginal recovery was found in the EX and BIC groups, whereas motor function recovery was enhanced with exercise in the presence of BIC administration specifically in the BICEX group. Furthermore, BDNF protein level in the ipsilateral M1 was significantly higher in the BICEX group than in other groups. This study indicated that exercise combined with low-level inhibition of GABA_A receptors after stroke could facilitate the recovery of motor function accompanied by BDNF upregulation in the ipsilateral M1. Therefore, this study provides a novel insight of pharmacological neuromodulation into stroke rehabilitation.

Translating concepts of neural repair after stroke: Structural and functional targets for recovery

Stroke is among the most common causes of adult disability worldwide, and its disease burden is shifting towards that of a long-term condition. Therefore, the development of approaches to enhance recovery and augment neural repair after stroke will be critical. Recovery after stroke involves complex interrelated systems of neural repair. There are changes in both structure (at the molecular, cellular, and tissue levels) and function (in terms of excitability, cortical maps, and networks) that occur spontaneously within the brain. Several approaches to augment neural repair through enhancing these changes are under study. These include identifying novel drug targets, implementing rehabilitation strategies, and developing new neurotechnologies. Each of these approaches has its own array of different proposed mechanisms. Current investigation has emphasized both cellular and circuit-based targets in both gray and white matter, including axon sprouting, dendritic branching, neurogenesis, axon preservation, remyelination, blood brain barrier integrity, blockade of extracellular inhibitory signals, alteration of excitability, and promotion of new brain cortical maps and networks. Herein, we review for clinicians recovery after stroke, basic elements of spontaneous neural repair, and ongoing work to augment neural repair. Future study requires alignment of basic, translational, and clinical research. The field continues to grow while becoming more clearly defined. As thrombolysis changed stroke care in the 1990 s and thrombectomy in the 2010 s, the augmentation of neural repair and recovery after stroke may revolutionize care for these patients in the coming decade.

A Stroke Recovery Trial Development Framework: Consensus-Based Core Recommendations from the Second Stroke Recovery and Rehabilitation Roundtable

A major goal of the Stroke Recovery and Rehabilitation Roundtable (SRRR) is to accelerate development of effective treatments to enhance stroke recovery beyond that expected to occur spontaneously or with current approaches. In this paper, we describe key issues for the next generation of stroke recovery treatment trials and present the Stroke Recovery and Rehabilitation Roundtable Trials Development Framework (SRRR-TDF). An exemplar (an upper limb recovery trial) is presented to demonstrate the utility of this framework to guide the GO, NO-GO decision-making process in trial development.

A stroke recovery trial development framework: Consensus-based core recommendations from the Second Stroke Recovery and Rehabilitation Roundtable

A major goal of the Stroke Recovery and Rehabilitation Roundtable (SRRR) is to accelerate development of effective treatments to enhance stroke recovery beyond that expected to occur spontaneously or with current approaches. In this paper, we describe key issues for the next generation of stroke recovery treatment trials and present the Stroke Recovery and Rehabilitation Roundtable Trials Development Framework (SRRR-TDF). An exemplar (an upper limb recovery trial) is presented to demonstrate the utility of this framework to guide the GO, NO-GO decision-making process in trial development.

Therapeutic Potential of Neurotrophins for Repair After Brain Injury: A Helping Hand From Biomaterials

Stroke remains the leading cause of long-term disability with limited options available to aid in recovery. Significant effort has been made to try and minimize neuronal damage following stroke with use of neuroprotective agents, however, these treatments have yet to show clinical efficacy. Regenerative interventions have since become of huge interest as they provide the potential to restore damaged neural tissue without being limited by a narrow therapeutic window. Neurotrophins, such as brain-derived neurotrophic factor (BDNF), and their high affinity receptors are actively produced throughout the brain and are involved in regulating neuronal activity and normal day-to-day function. Furthermore, neurotrophins are known to play a significant role in both protection and recovery of function following neurodegenerative diseases such as stroke and traumatic brain injury (TBI). Unfortunately, exogenous administration of these neurotrophins is limited by a lack of blood-brain-barrier (BBB) permeability, poor half-life, and rapid degradation. Therefore, we have focused this review on approaches that provide a direct and sustained neurotrophic support using pharmacological therapies and mimetics, physical activity, and potential drug delivery systems, including discussion around advantages and limitations for use of each of these systems. Finally, we discuss future directions of biomaterial drug-delivery systems, including the incorporation of heparan sulfate (HS) in conjunction with neurotrophin-based interventions.

Influences of genetic variants on stroke recovery: a meta-analysis of the 31,895 cases

Background

The influences of genetic variants on functional clinical outcomes following stroke are unclear. In order to reliably quantify these influences, we undertook a comprehensive meta-analysis of outcomes after acute intracerebral haemorrhage (ICH) or ischaemic stroke (AIS) in relation to different genetic variants.

Methods

PubMed, PsycInfo, Embase and Medline electronic databases were searched up to January 2019. Outcomes, defined as favourable or poor, were assessed by validated scales (Barthel index, modified Rankin scale, Glasgow outcome scale and National Institutes of Health stroke scale).

Results

Ninety-two publications comprising 31,895 cases met our inclusion criteria. Poor outcome was observed in patients with ICH who possessed the APOE4 allele: OR =2.60 (95% CI = 1.25–5.41, p = 0.01) and in AIS patients with the GA or AA variant at the BDNF-196 locus: OR = 2.60 (95% CI = 1.25–5.41, p = 0.01) or a loss of function allele of CYP2C19: OR = 2.36 (95% CI = 1.56–3.55, p < 0.0001). Poor outcome was not associated with APOE4: OR = 1.02 (95% CI = 0.81–1.27, p = 0.90) or IL6-174 G/C: OR = 2.21 (95% CI = 0.55–8.86, p = 0.26) in patients with AIS.

Conclusions

We demonstrate that recovery of AIS was unfavourably associated with variants of BDNF and CYP2C19 genes whilst recovery of ICH was unfavourably associated with APOE4 gene.

Electronic supplementary material

The online version of this article (10.1007/s10072-019-04024-w) contains supplementary material, which is available to authorized users.

Can robot-based measurements improve prediction of motor performance after robot-assisted upper-limb rehabilitation in patients with moderate-to-severe sub-acute stroke?

PURPOSE

Patients with moderate-to-severe stroke-related upper limb impairment can benefit from repetitive robot-assisted training. However, predicting motor performance in these patients from baseline measurements, including robot-based parameters would help clinicians to provide optimal treatments for each individual.

METHODS

Forty-six patients with sub-acute stroke underwent a 16-session upper limb rehabilitation combining usual care and robotic therapy. Motor outcomes (Fugl-Meyer Assessment Upper Extremity (FMA) score) were retrospectively analysed and potential predictors of motor outcome (including baseline FMA scores, kinematics and number of repetitions performed in the first session etc.) were determined.

RESULTS

The 16-sessions upper limb combined training program led to significantly improved clinical outcomes (gains of 13.8±11.2 for total FMA score and 7.3±6.7 for FMA Shoulder/Elbow score). For the prediction model, time since stroke poorly explained the FMA total score (R2 < 35%). The model however found that time since stroke and initial value of FMA Shoulder/Elbow score were predictors of the FMA Shoulder/Elbow score: (R2 = 59.6%).

CONCLUSION

This study found that clinical prediction of motor outcomes after moderate-to-severe upper-limb paresis is limited. However, initial proximal motor impairment severity predicted proximal motor performance. The value of baselines kinematics and of the number of repeated movements at initiation in the prediction would need further studies.

Very Early Initiation Reduces Benefits of Poststroke Rehabilitation Despite Increased Corticospinal Projections

Background. Although the effect of rehabilitation is influenced by aspects of the training protocol, such as initiation time and intensity of training, it is unclear whether training protocol modifications affect the corticospinal projections. Objective. The present study was designed to investigate how modification of initiation time (time-dependency) and affected forelimb use (use-dependency) influence the effects of rehabilitation on functional recovery and corticospinal projections. Methods. The time-dependency of rehabilitation was investigated in rats forced to use their impaired forelimb immediately, at 1 day, and 4 days after photothrombotic stroke. The use-dependency of rehabilitation was investigated by comparing rats with affected forelimb immobilization (forced nonuse), unaffected forelimb immobilization (forced use), and a combination of forced use and skilled forelimb training beginning at 4 days after stroke. Results. Although forced use beginning 1 day or 4 days after stroke caused significant functional improvement, immediate forced limb use caused no functional improvement. On the other hand, a combination of forced use and skilled forelimb training boosted functional recovery in multiple tasks compared to simple forced use treatment. Histological examination showed that no treatment caused brain damage. However, a retrograde tracer study revealed that immediate forced use and combination training, including forced use and skilled forelimb training, increased corticospinal projections from the contralesional and ipsilesional motor cortex, respectively. Conclusions. These results indicate that although both very early initiation time and enhanced skilled forelimb use increased corticospinal projections, premature initiation time hampers the functional improvement induced by poststroke rehabilitation.

Delayed exposure to environmental enrichment improves functional outcome after stroke

Stroke is one of the leading causes of long-term disabilities worldwide. Although exposure to an enriched environment (EE) initiated in the acute phase after stroke has neuroprotective effects and improves stroke outcome, it remains unclear whether EE has positive effects when started in a delayed time frame. Here we show that exposure to EE in the delayed phase notably ameliorates the ischemia-induced impairments in neurological functions and spatial learning and memory. In addition, delayed EE exposure after stroke significantly promotes the survival and neuronal fate choice of hippocampal newborn cells, increases synaptic density of hippocampal mature neurons, and enhances the migration of subventricular zone (SVZ)-derived cells towards the ischemic striatum. Histone deacetylase 2 (HDAC2), synapse-associated proteins and brain-derived neurotrophic factor (BDNF) may respectively mediate these roles of delayed EE. Our findings provide the suggestion that exposure to EE initiated in the delayed phase after stroke promotes plastic changes via affecting neurogenesis, synaptogenesis and neuronal migration, and thus improves stroke outcome. Because EE initiated earlier than 24 h is clinically feasible, our work could be introduced into clinical studies of stroke directly and may provide stroke survivors with a new strategy for their functional recovery.

Stroke Induces a BDNF-Dependent Improvement in Cognitive Flexibility in Aged Mice

Stroke remains a leading cause of disability worldwide. Recently, we have established an animal model of stroke that results in delayed impairment in spatial memory, allowing us to better investigate cognitive deficits. Young and aged brains show different recovery profiles after stroke; therefore, we assessed aged-related differences in poststroke cognition. As neurotrophic support diminishes with age, we also investigated the involvement of brain-derived neurotrophic factor (BDNF) in these differences. Young (3-6 months old) and aged (16-21 months old) mice were trained in operant touchscreen chambers to complete a visual pairwise discrimination (VD) task. Stroke or sham surgery was induced using the photothrombotic model to induce a bilateral prefrontal cortex stroke. Five days poststroke, an additional cohort of aged stroke animals were treated with intracerebral hydrogels loaded with the BDNF decoy, TrkB-Fc. Following treatment, animals underwent the reversal and rereversal task to identify stroke-induced cognitive deficits at days 17 and 37 poststroke, respectively. Assessment of sham animals using Cox regression and log-rank analyses showed aged mice exhibit an increased impairment on VD reversal and rereversal learning compared to young controls. Stroke to young mice revealed no impairment on either task. In contrast, stroke to aged mice facilitated a significant improvement in reversal learning, which was dampened in the presence of the BDNF decoy, TrkB-Fc. In addition, aged stroke control animals required significantly less consecutive days and correction trials to master the reversal task, relative to aged shams, an effect dampened by TrkB-Fc. Our findings support age-related differences in recovery of cognitive function after stroke. Interestingly, aged stroke animals outperformed their sham counterparts, suggesting reopening of a critical window for recovery that is being mediated by BDNF.

Repetitive Transcranial Magnetic Stimulation for Upper Extremity Motor Recovery: Does It Help?

PURPOSE OF REVIEW

Repetitive transcranial magnetic stimulation (rTMS) noninvasively modulates brain excitability in humans and influences mediators of plasticity in animals. When applied in humans in the months to years after stroke, potentiation of motor recovery has been limited. Recently, investigators have shifted rTMS administration into the early weeks following stroke, when injury-induced plasticity could be maximally engaged. This article provides an overview of basic mechanisms of rTMS, consideration of its interaction with various forms of neuroplasticity, and a summary of the highest quality clinical evidence for rTMS given early after stroke.

RECENT FINDINGS

Studies of repetitive magnetic stimulation in vitro and in vivo have found modulation of excitatory and inhibitory neurotransmission and induction of cellular mechanisms supporting plasticity. A handful of clinical studies have shown sustained improvements in grip strength and UE motor impairment when rTMS is delivered in the first weeks after stroke. Though in its infancy, recent research suggests a plasticity-enhancing influence and modest motor recovery potentiation when rTMS is delivered early after stroke.

Is Environmental Enrichment Ready for Clinical Application in Human Post-stroke Rehabilitation?

Environmental enrichment (EE) has been widely used as a means to enhance brain plasticity mechanisms (e.g., increased dendritic branching, synaptogenesis, etc.) and improve behavioral function in both normal and brain-damaged animals. In spite of the demonstrated efficacy of EE for enhancing brain plasticity, it has largely remained a laboratory phenomenon with little translation to the clinical setting. Impediments to the implementation of enrichment as an intervention for human stroke rehabilitation and a lack of clinical translation can be attributed to a number of factors not limited to: (i) concerns that EE is actually the "normal state" for animals, whereas standard housing is a form of impoverishment; (ii) difficulty in standardizing EE conditions across clinical sites; (iii) the exact mechanisms underlying the beneficial actions of enrichment are largely correlative in nature; (iv) a lack of knowledge concerning what aspects of enrichment (e.g., exercise, socialization, cognitive stimulation) represent the critical or active ingredients for enhancing brain plasticity; and (v) the required "dose" of enrichment is unknown, since most laboratory studies employ continuous periods of enrichment, a condition that most clinicians view as impractical. In this review article, we summarize preclinical stroke recovery studies that have successfully utilized EE to promote functional recovery and highlight the potential underlying mechanisms. Subsequently, we discuss how EE is being applied in a clinical setting and address differences in preclinical and clinical EE work to date. It is argued that the best way forward is through the careful alignment of preclinical and clinical rehabilitation research. A combination of both approaches will allow research to fully address gaps in knowledge and facilitate the implementation of EE to the clinical setting.

Effect of Inhibition of DNA Methylation Combined with Task-Specific Training on Chronic Stroke Recovery

To develop new rehabilitation therapies for chronic stroke, this study examined the effectiveness of task-specific training (TST) and TST combined with DNA methyltransferase inhibitor in chronic stroke recovery. Eight weeks after photothrombotic stroke, 5-Aza-2'-deoxycytidine (5-Aza-dC) infusion was done on the contralesional cortex for four weeks, with and without TST. Functional recovery was assessed using the staircase test, the cylinder test, and the modified neurological severity score (mNSS). Axonal plasticity and expression of brain-derived neurotrophic factor (BDNF) were determined in the contralateral motor cortex. TST and TST combined with 5-Aza-dC significantly improved the skilled reaching ability in the staircase test and ameliorated mNSS scores and cylinder test performance. TST and TST with 5-Aza-dC significantly increased the crossing fibers from the contralesional red nucleus, reticular formation in medullar oblongata, and dorsolateral spinal cord. Mature BDNF was significantly upregulated by TST and TST combined with 5-Azd-dC. Functional recovery after chronic stroke may involve axonal plasticity and increased mature BDNF by modulating DNA methylation in the contralesional cortex. Our results suggest that combined therapy to enhance axonal plasticity based on TST and 5-Aza-dC constitutes a promising approach for promoting the recovery of function in the chronic stage of stroke.

Constraint-induced movement therapy improves efficacy of task-specific training after severe cortical stroke depending on the ipsilesional corticospinal projections

Descending spinal pathways (corticospinal, rubrospinal, and reticulospinal) are believed to contribute to functional recovery resulting from rehabilitative training after stroke. However, the contribution of each pathway remains unclear. In the current study, we investigated rehabilitation-induced functional recovery and remodelling of the descending spinal pathways after severe cortical stroke in rats followed by 3 weeks of various rehabilitation [constraint-induced movement therapy (CIMT), skilled forelimb reaching, rotarod, and treadmill exercise]. Following photothrombotic stroke, 96% of corticospinal neurons in the ipsilesional motor cortex were destroyed. Despite the preservation of 82% of total spinal projection neurons (e.g. rubrospinal and reticulospinal projection neurons), rats showed persistent and severe disability, especially in skilled motor function. In this severe stroke model, only CIMT promoted functional recovery, associated with increased corticospinal projections from the peri-infarct motor cortex. Rehabilitation-induced recovery was reversed when the restored corticospinal neurons were destroyed by a second stroke. These data indicate that training-induced functional recovery is dependent on ipsilesional corticospinal projections, which highlights the importance of using strategies to enhance survival, axonal remodelling, or regeneration of corticospinal neurons to effectively restore function in severely affected stroke patients.

Capture, learning, and classification of upper extremity movement primitives in healthy controls and stroke patients

There currently exist no practical tools to identify functional movements in the upper extremities (UEs). This absence has limited the precise therapeutic dosing of patients recovering from stroke. In this proof-of-principle study, we aimed to develop an accurate approach for classifying UE functional movement primitives, which comprise functional movements. Data were generated from inertial measurement units (IMUs) placed on upper body segments of older healthy individuals and chronic stroke patients. Subjects performed activities commonly trained during rehabilitation after stroke. Data processing involved the use of a sliding window to obtain statistical descriptors, and resulting features were processed by a Hidden Markov Model (HMM). The likelihoods of the states, resulting from the HMM, were segmented by a second sliding window and their averages were calculated. The final predictions were mapped to human functional movement primitives using a Logistic Regression algorithm. Algorithm performance was assessed with a leave-one-out analysis, which determined its sensitivity, specificity, and positive and negative predictive values for all classified primitives. In healthy control and stroke participants, our approach identified functional movement primitives embedded in training activities with, on average, 80% precision. This approach may support functional movement dosing in stroke rehabilitation.

Does Stroke Rehabilitation Really Matter? Part B: An Algorithm for Prescribing an Effective Intensity of Rehabilitation

Background. The proportional recovery rule suggests that current rehabilitation practices may have limited ability to influence stroke recovery. However, the appropriate intensity of rehabilitation needed to achieve recovery remains unknown. Similarities between rodent and human recovery biomarkers may allow determination of rehabilitation thresholds necessary to activate endogenous biological recovery processes. Objective. We determined the relative influence that clinically relevant biomarkers of stroke recovery exert on functional outcome. These biomarkers were then used to generate an algorithm that prescribes individualized intensities of rehabilitation necessary for recovery of function. Methods. A retrospective cohort of 593 male Sprague-Dawley rats was used to identify biomarkers that best predicted poststroke change in pellet retrieval in the Montoya staircase-reaching task using multiple linear regression. Prospective manipulation of these factors using endothelin-1-induced stroke (n = 49) was used to validate the model. Results. Rehabilitation was necessary to reliably predict recovery across the continuum of stroke severity. As infarct volume and initial impairment increased, more intensive rehabilitation was required to engage recovery. In this model, we prescribed the specific dose of daily rehabilitation required for rats to achieve significant motor recovery using the biomarkers of initial poststroke impairment and infarct volume. Conclusions. Our algorithm demonstrates an individualized approach to stroke rehabilitation, wherein imaging and functional performance measures can be used to develop an optimized rehabilitation paradigm for rats, particularly those with severe impairments. Exploring this approach in human patients could lead to an increase in the proportion of individuals experiencing recovery of lost motor function poststroke.

Rehabilitative skilled forelimb training enhances axonal remodeling in the corticospinal pathway but not the brainstem-spinal pathways after photothrombotic stroke in the primary motor cortex

Task-specific rehabilitative training is commonly used for chronic stroke patients. Axonal remodeling is believed to be one mechanism underlying rehabilitation-induced functional recovery, and significant roles of the corticospinal pathway have previously been demonstrated. Brainstem-spinal pathways, as well as the corticospinal tract, have been suggested to contribute to skilled motor function and functional recovery after brain injury. However, whether axonal remodeling in the brainstem-spinal pathways is a critical component for rehabilitation-induced functional recovery is not known. In this study, rats were subjected to photothrombotic stroke in the caudal forelimb area of the primary motor cortex and received rehabilitative training with a skilled forelimb reaching task for 4 weeks. After completion of the rehabilitative training, the retrograde tracer Fast blue was injected into the contralesional lower cervical spinal cord. Fast blue-positive cells were counted in 32 brain areas located in the cerebral cortex, hypothalamus, midbrain, pons, and medulla oblongata. Rehabilitative training improved motor performance in the skilled forelimb reaching task but not in the cylinder test, ladder walk test, or staircase test, indicating that rehabilitative skilled forelimb training induced task-specific recovery. In the histological analysis, rehabilitative training significantly increased the number of Fast blue-positive neurons in the ipsilesional rostral forelimb area and secondary sensory cortex. However, rehabilitative training did not alter the number of Fast blue-positive neurons in any areas of the brainstem. These results indicate that rehabilitative skilled forelimb training enhances axonal remodeling selectively in the corticospinal pathway, which suggests a critical role of cortical plasticity, rather than brainstem plasticity, in task-specific recovery after subtotal motor cortex destruction.