Memantine enhances recovery from stroke

Argon neuroprotection in ischemic stroke and its underlying mechanism

Ischemic stroke (IS), primarily caused by cerebrovascular obstruction, results in severe neurological deficits and has emerged as a leading cause of death and disability worldwide. Recently, there has been increasing exploration of the neuroprotective properties of the inert gas argon. Argon has exhibited impressive neuroprotection in many in vivo and ex vivo experiments without signs of adverse effects, coupled with the advantages of being inexpensive and easily available. However, the efficient administration strategy and underlying mechanisms of neuroprotection by argon in IS are still unclear. This review summarizes current research on the neuroprotective effects of argon in IS with the goal to provide effective guidance for argon application and to elucidate the potential mechanisms of argon neuroprotection. Early and appropriate argon administration at as high a concentration as possible offers favorable neuroprotection in IS. Argon inhalation has been shown to provide some long-term protection benefits. Argon provides the anti-oxidative stress, anti-inflammatory and anti-apoptotic cytoprotective effects mainly around Toll-like receptor 2/4 (TLR2/4), mediated by extracellular signal-regulated kinase 1/2 (ERK1/2), nuclear factor (erythroid-derived 2)-like 2 (Nrf2), nuclear factor kappa-B (NF-ĸB) and B-cell leukemia/lymphoma 2 (Bcl-2). Therefore, argon holds significant promise as a novel clinical neuroprotective gas agent for ischemic stroke after further researches to identify the optimal application strategy and elucidate the underlying mechanism.

Activation of cerebral Ras-related C3 botulinum toxin substrate (Rac) 1 promotes post-ischemic stroke functional recovery in aged mice

Brain functional impairment after stroke is common; however, the molecular mechanisms of post-stroke recovery remain unclear. It is well-recognized that age is the most important independent predictor of poor outcomes after stroke as older patients show poorer functional outcomes following stroke. Mounting evidence suggests that axonal regeneration and angiogenesis, the major forms of brain plasticity responsible for post-stroke recovery, diminished with advanced age. Previous studies suggest that Ras-related C3 botulinum toxin substrate (Rac) 1 enhances stroke recovery as activation of Rac1 improved behavior recovery in a young mice stroke model. Here, we investigated the role of Rac1 signaling in long-term functional recovery and brain plasticity in an aged (male, 18 to 22 months old C57BL/6J) brain after ischemic stroke. We found that as mice aged, Rac1 expression declined in the brain. Delayed overexpression of Rac1, using lentivirus encoding Rac1 injected day 1 after ischemic stroke, promoted cognitive (assessed using novel object recognition test) and sensorimotor (assessed using adhesive removal tests) recovery on days 14-28. This was accompanied by the increase of neurite and proliferative endothelial cells in the peri-infarct zone assessed by immunostaining. In a reverse approach, pharmacological inhibition of Rac1 by intraperitoneal injection of Rac1 inhibitor NSC23766 for 14 successive days after ischemic stroke worsened the outcome with the reduction of neurite and proliferative endothelial cells. Furthermore, Rac1 inhibition reduced the activation of p21-activated kinase 1, the protein level of brain-derived neurotrophic factor, and increased the protein level of glial fibrillary acidic protein in the ischemic brain on day 28 after stroke. Our work provided insight into the mechanisms behind the diminished plasticity after cerebral ischemia in aged brains and identified Rac1 as a potential therapeutic target for improving functional recovery in the older adults after stroke.

Extrasynaptic NMDA receptors in acute and chronic excitotoxicity: implications for preventive treatments of ischemic stroke and late-onset Alzheimer's disease

Stroke and late-onset Alzheimer's disease (AD) are risk factors for each other; the comorbidity of these brain disorders in aging individuals represents a significant challenge in basic research and clinical practice. The similarities and differences between stroke and AD in terms of pathogenesis and pathophysiology, however, have rarely been comparably reviewed. Here, we discuss the research background and recent progresses that are important and informative for the comorbidity of stroke and late-onset AD and related dementia (ADRD). Glutamatergic NMDA receptor (NMDAR) activity and NMDAR-mediated Ca²⁺ influx are essential for neuronal function and cell survival. An ischemic insult, however, can cause rapid increases in glutamate concentration and excessive activation of NMDARs, leading to swift Ca²⁺ overload in neuronal cells and acute excitotoxicity within hours and days. On the other hand, mild upregulation of NMDAR activity, commonly seen in AD animal models and patients, is not immediately cytotoxic. Sustained NMDAR hyperactivity and Ca²⁺ dysregulation lasting from months to years, nevertheless, can be pathogenic for slowly evolving events, i.e. degenerative excitotoxicity, in the development of AD/ADRD. Specifically, Ca²⁺ influx mediated by extrasynaptic NMDARs (eNMDARs) and a downstream pathway mediated by transient receptor potential cation channel subfamily M member (TRPM) are primarily responsible for excitotoxicity. On the other hand, the NMDAR subunit GluN3A plays a "gatekeeper" role in NMDAR activity and a neuroprotective role against both acute and chronic excitotoxicity. Thus, ischemic stroke and AD share an NMDAR- and Ca²⁺-mediated pathogenic mechanism that provides a common receptor target for preventive and possibly disease-modifying therapies. Memantine (MEM) preferentially blocks eNMDARs and was approved by the Federal Drug Administration (FDA) for symptomatic treatment of moderate-to-severe AD with variable efficacy. According to the pathogenic role of eNMDARs, it is conceivable that MEM and other eNMDAR antagonists should be administered much earlier, preferably during the presymptomatic phases of AD/ADRD. This anti-AD treatment could simultaneously serve as a preconditioning strategy against stroke that attacks ≥ 50% of AD patients. Future research on the regulation of NMDARs, enduring control of eNMDARs, Ca²⁺ homeostasis, and downstream events will provide a promising opportunity to understand and treat the comorbidity of AD/ADRD and stroke.

Memantine as a neuroprotective agent in ischemic stroke: Preclinical and clinical analysis

The primary mechanism for neuron death after an ischemic stroke is excitotoxic injury. Excessive depolarization leads to NMDA-mediated calcium entry to the neuron and, subsequently, cellular death. Therefore, the inhibition of the NMDA channel has been proposed as a neuroprotective measure in ischemic stroke. The high morbimortality associated with stroke warrants new therapies that can improve the functional prognosis of patients. Memantine is a non-competitive NMDA receptor antagonist which has gained attention as a potential drug for ischemic stroke. Here we analyze the available preclinical and clinical evidence concerning the use of memantine following an ischemic stroke. Preclinical evidence shows inhibition of the excitotoxic cascade, as well as improved outcomes in terms of motor and sensory function with the use of memantine. The available clinical trials of high-dose memantine in patients poststroke have found that it can improve patients' NIHSS and Barthel index and help patients with poststroke aphasia and intracranial hemorrhage. These results suggest that memantine has a clinically relevant neuroprotective effect; however, small sample sizes and other study shortcomings limit the impact of these findings. Even so, current studies show promising results that should serve as a basis to promote future research to conclusively determine if memantine does improve the outcomes of patients' post-ischemic stroke. We anticipate that future trials will fill current gaps in knowledge, and these latter results will broaden the therapeutic arsenal for clinicians looking to improve the prognosis of patients poststroke.

Pathophysiology and Current Drug Treatments for Post-Stroke Depression: A Review

Post-stroke depression (PSD) is a biopsychosocial disorder that affects individuals who have suffered a stroke at any point. PSD has a 20 to 60 percent reported prevalence among stroke survivors. Its effects are usually adverse, can lead to disability, and may increase mortality if not managed or treated early. PSD is linked to several other medical conditions, including anxiety, hyper-locomotor activity, and poor functional recovery. Despite significant awareness of its adverse impacts, understanding the pathogenesis of PSD has proved challenging. The exact pathophysiology of PSD is unknown, yet its complexity has been definitively shown, involving mechanisms such as dysfunction of monoamine, the glutamatergic systems, the gut-brain axis, and neuroinflammation. The current effectiveness of PSD treatment is about 30-40 percent of all cases. In this review, we examined different pathophysiological mechanisms and current pharmacological and non-pharmacological approaches for the treatment of PSD.

Understanding Acquired Brain Injury: A Review

Any type of brain injury that transpires post-birth is referred to as Acquired Brain Injury (ABI). In general, ABI does not result from congenital disorders, degenerative diseases, or by brain trauma at birth. Although the human brain is protected from the external world by layers of tissues and bone, floating in nutrient-rich cerebrospinal fluid (CSF); it remains susceptible to harm and impairment. Brain damage resulting from ABI leads to changes in the normal neuronal tissue activity and/or structure in one or multiple areas of the brain, which can often affect normal brain functions. Impairment sustained from an ABI can last anywhere from days to a lifetime depending on the severity of the injury; however, many patients face trouble integrating themselves back into the community due to possible psychological and physiological outcomes. In this review, we discuss ABI pathologies, their types, and cellular mechanisms and summarize the therapeutic approaches for a better understanding of the subject and to create awareness among the public.

BDNF Therapeutic Mechanisms in Neuropsychiatric Disorders

Brain-derived neurotrophic factor (BDNF) is the most abundant neurotrophin in the adult brain and functions as both a primary neurotrophic signal and a neuromodulator. It serves essential roles in neuronal development, maintenance, transmission, and plasticity, thereby influencing aging, cognition, and behavior. Accumulating evidence associates reduced central and peripheral BDNF levels with various neuropsychiatric disorders, supporting its potential utilization as a biomarker of central pathologies. Subsequently, extensive research has been conducted to evaluate restoring, or otherwise augmenting, BDNF transmission as a potential therapeutic approach. Promising results were indeed observed for genetic BDNF upregulation or exogenous administration using a multitude of murine models of neurological and psychiatric diseases. However, varying mechanisms have been proposed to underlie the observed therapeutic effects, and many findings indicate the engagement of disease-specific and other non-specific mechanisms. This is because BDNF essentially affects all aspects of neuronal cellular function through tropomyosin receptor kinase B (TrkB) receptor signaling, the disruptions of which vary between brain regions across different pathologies leading to diversified consequences on cognition and behavior. Herein, we review the neurophysiology of BDNF transmission and signaling and classify the converging and diverging molecular mechanisms underlying its therapeutic potentials in neuropsychiatric disorders. These include neuroprotection, synaptic maintenance, immunomodulation, plasticity facilitation, secondary neuromodulation, and preservation of neurovascular unit integrity and cellular viability. Lastly, we discuss several findings suggesting BDNF as a common mediator of the therapeutic actions of centrally acting pharmacological agents used in the treatment of neurological and psychiatric illness.

Targeting organic cation transporters at the blood-brain barrier to treat ischemic stroke in rats

Drug discovery and development for stroke is challenging as evidenced by few drugs that have advanced beyond a Phase III clinical trial. Memantine is a N-methyl-d-aspartate (NMDA) receptor antagonist that has been shown to be neuroprotective in various preclinical studies. We have identified an endogenous BBB uptake transport system for memantine: organic cation transporters 1 and 2 (Oct1/Oct2). Our goal was to evaluate Oct1/Oct2 as a required BBB mechanism for memantine neuroprotective effects. Male Sprague-Dawley rats (200-250 g) were subjected to middle cerebral artery occlusion (MCAO) for 90 min followed by reperfusion. Memantine (5 mg/kg, i.v.) was administered 2 h following intraluminal suture removal. Specificity of Oct-mediated transport was evaluated using cimetidine (15 mg/kg, i.v.), a competitive Oct1/Oct2 inhibitor. At 2 h post-MCAO, [³H]memantine uptake was increased in ischemic brain tissue. Cimetidine inhibited blood-to-brain uptake of [³H]memantine, which confirmed involvement of an Oct-mediated transport mechanism. Memantine reduced post-MCAO infarction and brain edema progression as well as improved neurological outcomes during post-stroke recovery. All positive effects of memantine were attenuated by co-administration of cimetidine, which demonstrates that Oct1/Oct2 transport is required for memantine to exert neuroprotective effects in ischemic stroke. Furthermore, Oct1/Oct2-mediated transport was shown to be the dominant mechanism for memantine brain uptake in the MCAO model despite a concurrent increase in paracellular "leak." These novel and translational findings provide mechanistic evidence for the critical role of BBB transporters in CNS delivery of stroke therapeutics, information that can help such drugs advance in clinical trials.

Non-invasive brain stimulation as therapeutic approach for ischemic stroke: Insights into the (sub)cellular mechanisms

Although spontaneous recovery can occur following ischemic stroke due to endogenous neuronal reorganization and neuroplastic events, the degree of functional improvement is highly variable, causing many patients to remain permanently impaired. In the last decades, non-invasive brain stimulation (NIBS) techniques have emerged as potential add-on interventions to the standard neurorehabilitation programs to improve post-stroke recovery. Due to their ability to modulate cortical excitability and to induce neuroreparative processes in the brain, multiple studies have assessed the safety, efficacy and (sub)cellular mechanisms of NIBS following ischemic stroke. In this review, an overview will be provided of the different NIBS techniques that are currently being investigated in (pre)clinical stroke studies. The NIBS therapies that will be discussed include transcranial magnetic stimulation, transcranial direct current stimulation and extremely low frequency electromagnetic stimulation. First, an overview will be given of the cellular mechanisms induced by NIBS that are associated with enhanced stroke outcome in preclinical models. Furthermore, the current knowledge on safety and efficacy of these NIBS techniques in stroke patients will be reviewed.

Clavulanic Acid: A Novel Potential Agent in Prevention and Treatment of Scopolamine-Induced Alzheimer's Disease

Background and Aim: Alzheimer's disease (AD) is the most common form of dementia in the elderly. It is characterized as a multifaced disorder with a greater genetic contribution. The contribution of many genes such as BDNF, Sirtuin 6, and Seladin 1 has been reported in the pathogenesis of AD. Current therapies include acetylcholinesterase inhibitors and N-methyl-d-aspartate receptor antagonists, which are only temporarily beneficial. Therefore, it seems that more studies should be conducted to determine the exact mechanisms of drugs to deal with the diseases' multifactorial features that we face. Methods: In this study, 42 adult rats were randomly divided into 7 groups and received drugs intraperitoneally and orally according to the protocol as follows: scopolamine group, clavulanic acid group, memantine group, scopolamine + memantine group, clavulanic acid pre- and post-treatment, and normal saline group. The Morris water maze method was performed to evaluate the spatial memory of animals, and the terminal deoxynucleotidyl transferase dUTP nick end labeling assay and real-time polymerase chain reaction were performed to study neuronal cell apoptosis and gene expression, respectively. Results: Significant differences were observed in the spatial memory of rats that received clavulanic acid prophylactically compared to the Alzheimer's model on the day of the test. Moreover, the results obtained during the training showed that both memantine and clavulanic acid improved spatial memory by increasing the time of rats present in the platform position and by reducing the swimming time in the scopolamine-induced Alzheimer's group. Besides, rats that received clavulanic acid and memantine had a greater percentage of healthy cells in comparison with the scopolamine-induced Alzheimer's group; however, the results were more significant for clavulanic acid. Furthermore, the expressions of BDNF, Seladin 1, and Sirtuin 6 as neuroprotective target genes were modified after clavulanic acid and memantine administrations; similarly, the results obtained from clavulanic acid were more significant. Conclusion: The results show that the administration of clavulanic acid before and after the use of scopolamine can reduce the percentage of apoptotic cells in the hippocampus and also improve the parameters related to learning and spatial memory; however, its effect in the prophylactic state was stronger. The results obtained from memantine revealed that it has neuroprotective potency against AD; however, clavulanic acid had a greater effect. Also, with increased expression of the neuroprotective genes, clavulanic acid could be considered as an option in the upcoming preclinical and clinical research about Alzheimer's disease.

Brain-Derived Neurotrophic Factor and Nerve Growth Factor Therapeutics for Brain Injury: The Current Translational Challenges in Preclinical and Clinical Research

Ischemic stroke and traumatic brain injury (TBI) are among the leading causes of death and disability worldwide with impairments ranging from mild to severe. Many therapies are aimed at improving functional and cognitive recovery by targeting neural repair but have encountered issues involving efficacy and drug delivery. As a result, therapeutic options for patients are sparse. Neurotrophic factors are one of the key mediators of neural plasticity and functional recovery. Neurotrophic factors such as brain-derived neurotrophic factor (BDNF) and nerve growth factor (NGF) serve as potential therapeutic options to increase neural repair and recovery as they promote neuroprotection and regeneration. BDNF and NGF have demonstrated the ability to improve functional recovery in preclinical and to a lesser extent clinical studies. Direct and indirect methods to increase levels of neurotrophic factors in animal models have been successful in improving postinjury outcome measures. However, the translation of these studies into clinical trials has been limited. Preclinical experiments have largely failed to result in significant impacts in clinical research. This review will focus on the administration of these neurotrophic factors in preclinical and clinical stroke and TBI and the challenges in translating these therapies from the bench to the clinic.

Post-stroke treatment with argon preserved neurons and attenuated microglia/macrophage activation long-termly in a rat model of transient middle cerebral artery occlusion (tMCAO)

In a previous study from our group, argon has shown to significantly attenuate brain injury, reduce brain inflammation and enhance M₂ microglia/macrophage polarization until 7 days after ischemic stroke. However, the long-term effects of argon have not been reported thus far. In the present study, we analyzed the underlying neuroprotective effects and potential mechanisms of argon, up to 30 days after ischemic stroke. Argon administration with a 3 h delay after stroke onset and 1 h after reperfusion demonstrated long-term neuroprotective effect by preserving the neurons at the ischemic boundary zone 30 days after stroke. Furthermore, the excessive microglia/macrophage activation in rat brain was reduced by argon treatment 30 days after ischemic insult. However, long-lasting neurological improvement was not detectable. More sensorimotor functional measures, age- and disease-related models, as well as further histological and molecular biological analyses will be needed to extend the understanding of argon’s neuroprotective effects and mechanism of action after ischemic stroke.

[CRMP2 binding compound accelerates functional recovery from central nervous system damage]

Brain injury causes temporary or permanent impairment of brain function due to an accident or circulation disorders. Even after rehabilitation training, there are often persistent functional impairments. Recent advances in our understanding of the repair mechanisms of neural circuits after brain injury have led to the possibility that these mechanisms may offer potential therapeutic targets for drugs that promote functional recovery after brain injury. Neuroplasticity is believed to be important for the recovery process after brain injury in the brain regions associated with injured region for compensation. The effectiveness of drugs for restoring brain function after stroke investigated in a variety of animal models and clinical trials has been focused on drugs that act on the monoamine system to modulate neuroplasticity, as well as other targets such as NMDA receptors and CCR5. Recently, we focused on novel small compound, edonerpic maleate, as a drug which facilitates experience-dependent synaptic delivery of AMPA receptor. We found that edonerpic maleate binds to Collapsin-response mediator protein 2, a downstream molecule of Semaphorin and enhance synaptic plasticity by facilitating synaptic delivery of AMPA receptors, thereby promoting functional recovery in a rehabilitation-dependent manner after brain injury in rodents and non-human primates. Further investigations is needed to seek more appropriate drug targets from both preclinical animal studies and clinical trials, and to translate preclinical results into successful clinical trials.

Therapeutic time windows of compounds against NMDA receptors signaling pathways for ischemic stroke

Much evidence has proved that excitotoxicity induced by excessive release of glutamate contributes largely to damage caused by ischemia. In view of the key role played by NMDA receptors in mediating excitotoxicity, compounds against NMDA receptors signaling pathways have become the most promising type of anti-stroke candidate compounds. However, the limited therapeutic time window for neuroprotection is a key factor preventing NMDA receptor-related compounds from showing efficacy in all clinical trials for ischemic stroke. In this perspective, the determination of therapeutic time windows of these kinds of compounds is useful in ensuring a therapeutic effect and accelerating clinical application. This mini-review discussed the therapeutic time windows of compounds against NMDA receptors signaling pathways, described related influence factors and the status of clinical studies. The purpose of this review is to look for compounds with wide therapeutic time windows and better clinical application prospect.

Memantine Improves Recovery After Spreading Depolarization in Brain Slices and can be Considered for Future Clinical Trials

BACKGROUND

Spreading depolarization (SD) has been identified as a key mediator of secondary lesion progression after acute brain injuries, and clinical studies are beginning to pharmacologically target SDs. Although initial work has focused on the N-Methyl-D-aspartate receptor antagonist ketamine, there is also interest in alternatives that may be better tolerated. We recently showed that ketamine can inhibit mechanisms linked to deleterious consequences of SD in brain slices. The present study tested the hypothesis that memantine improves recovery of brain slices after SD and explored the effects of memantine in a clinical case targeting SD.

METHODS

For mechanistic studies, electrophysiological and optical recordings were made from hippocampal area CA1 in acutely prepared brain slices from mice. SDs were initiated by localized microinjection of K+ in conditions of either normal or reduced metabolic substrate availability. Memantine effects were assessed from intrinsic optical signals and extracellular potential recordings. For the clinical report, a subdural strip electrode was used for continuous electrocorticographic recording after the surgical evacuation of a chronic subdural hematoma.

RESULTS

In brain slice studies, memantine (10-300 µM) did not prevent the initiation of SD, but impaired SD propagation rate and recovery from SD. Memantine reduced direct current (DC) shift duration and improved recovery of synaptic potentials after SD. In brain slices with reduced metabolic substrate availability, memantine reduced the evidence of structural disruption after the passage of SD. In our clinical case, memantine did not noticeably immediately suppress SD; however, it was associated with a significant reduction of SD duration and a reduction in the electrocorticographic (ECoG) suppression that occurs after SD. SD was completely suppressed, with improvement in neurological examination with the addition of a brief course of ketamine.

CONCLUSIONS

These data extend recent work showing that N-Methyl-D-aspartate receptor antagonists can improve recovery from SD. These results suggest that memantine could be considered for future clinical trials targeting SD, and in some cases as an adjunct or alternative to ketamine.

Transcriptomic signatures of treatment response to the combination of escitalopram and memantine or placebo in late-life depression

Drugs that target glutamate neuronal transmission, such as memantine, offer a novel approach to the treatment of late-life depression, which is frequently comorbid with cognitive impairment. The results of our recently published double-blind, randomized, placebo-controlled trial of escitalopram or escitalopram/memantine in late-life depression with subjective memory complaints (NCT01902004) indicated no differences between treatments in depression remission, but additional benefits in cognition at 12-month follow-up with combination treatment. To identify pathways and biological functions uniquely induced by combination treatment that may explain cognitive improvements, we generated transcriptional profiles of remission compared with non-remission from whole blood samples. Remitters to escitalopram compared with escitalopram/memantine combination treatment display unique patterns of gene expression at baseline and 6 months after treatment initiation. Functional enrichment analysis demonstrates that escitalopram-based remission associates to functions related to cellular proliferation, apoptosis, and inflammatory response. Escitalopram/memantine-based remission, however, is characterized by processes related to cellular clearance, metabolism, and cytoskeletal dynamics. Both treatments modulate inflammatory responses, albeit via different effector pathways. Additional research is needed to understand the implications of these results in explaining the observed superior effects of combination treatment on cognition observed with prolonged treatment.

Differential effects of the cell cycle inhibitor, olomoucine, on functional recovery and on responses of peri-infarct microglia and astrocytes following photothrombotic stroke in rats

Background

Following stroke, changes in neuronal connectivity in tissue surrounding the infarct play an important role in both spontaneous recovery of neurological function and in treatment-induced improvements in function. Microglia and astrocytes influence this process through direct interactions with the neurons and as major determinants of the local tissue environment. Subpopulations of peri-infarct glia proliferate early after stroke providing a possible target to modify recovery. Treatment with cell cycle inhibitors can reduce infarct volume and improve functional recovery. However, it is not known whether these inhibitors can influence neurological function or alter the responses of peri-infarct glia without reducing infarction. The present study aimed to address these issues by testing the effects of the cell cycle inhibitor, olomoucine, on recovery and peri-infarct changes following photothrombotic stroke.

Methods

Stroke was induced by photothrombosis in the forelimb sensorimotor cortex in Sprague-Dawley rats. Olomoucine was administered at 1 h and 24 h after stroke induction. Forelimb function was monitored up to 29 days. The effects of olomoucine on glial cell responses in peri-infarct tissue were evaluated using immunohistochemistry and Western blotting.

Results

Olomoucine treatment did not significantly affect maximal infarct volume. Recovery of the affected forelimb on a placing test was impaired in olomoucine-treated rats, whereas recovery in a skilled reaching test was substantially improved. Olomoucine treatment produced small changes in aspects of Iba1 immunolabelling and in the number of CD68-positive cells in cerebral cortex but did not selectively modify responses in peri-infarct tissue. The content of the astrocytic protein, vimentin, was reduced by 30% in the region of the lesion in olomoucine-treated rats.

Conclusions

Olomoucine treatment modified functional recovery in the absence of significant changes in infarct volume. The effects on recovery were markedly test dependent, adding to evidence that skilled tasks requiring specific training and general measures of motor function can be differentially modified by some interventions. The altered recovery was not associated with specific changes in key responses of peri-infarct microglia, even though these cells were considered a likely target for early olomoucine treatment. Changes detected in peri-infarct reactive astrogliosis could contribute to the altered patterns of functional recovery.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-021-02208-w.

The pros and cons of motor, memory, and emotion-related behavioral tests in the mouse traumatic brain injury model

Traumatic brain injury (TBI) is a medical emergency with high morbidity and mortality. Motor, memory, and emotion-related deficits are common symptoms following TBI, yet treatment is very limited. To develop new drugs and find new therapeutic avenues, a wide variety of TBI models have been established to mimic the heterogeneity of TBI. In this regard, along with histologic measures, behavioral functional outcomes provide valuable insight into the underlying neuropathology and guide neurorehabilitation efforts for neuropsychiatric impairment after TBI. Development, characterization, and application of behavioral tests that can assess functional neurologic deficits are essential to the development of translational therapies. This comprehensive review aims to summarize 19 common behavioral tests from three aspects (motor, memory, and emotion-related) that are associated with TBI pathology. Discussion covers the apparatus, the test steps, the evaluation indexes, data collection and analysis, animal performance and applications, advantages and disadvantages as well as precautions to eliminate bias wherever possible. We discussed recent studies on TBI-related preconditioning, biomarkers, and optimized behavioral protocols. The neuropsychologic tests employed in clinics were correlated with those used in mouse TBI models. In summary, this review provides a comprehensive, up-to-date reference for TBI researchers to choose the right neurobehavioral protocol according to the research objectives of their translational investigation.

The effects of memantine on the serum concentrations of matrix metalloproteinases and neurologic function of patients with ischemic stroke

Memantine was suggested as a promising treatment for stroke due to its neuroprotective property and efficacy in reducing ischemic brain injury and improving post-ischemic neurological recovery. This pilot, open-label, randomized clinical trial was conducted to investigate the impact of memantine on serum concentrations of matrix metalloproteinases (MMP)-2 and MMP-9, as neuronal damage biomarkers, and neurologic function evaluated by the National Institute of Health Stroke Scale(NIHSS) and Barthelindex(BI) in patients with ischemic stroke. Admitted patients with mild to moderate ischemic stroke were assessed for eligibility, and eligible patients were randomized to the intervention or control group. Enrolled patients in the intervention group received 20 mg memantine every 8 h for five days and then 20 mg daily for three months. Both groups managed with the standard treatments. From 77 randomized patients, 29 participants in the control group and 24 patients in the intervention group completed the study. Data showed that the increase in the serum concentrations of MMP-9 within the first 5 days of the study was significantly lower in the intervention group (P = 0.005). This effect of memantine on the MMP-2 was not significant (P = 0.448). memantine also could significantly improve the neurologic function of the patients according to NIHSS (P < 0.0001) and BI (P = 0.002) during hospitalization and after that. In conclusion, memantine could be considered as a neuroprotective agent in patients with mild to moderate ischemic stroke, based on its significant effects on reducing brain damage and improving neurologic function of the patients.

Behavioral Assessment of Sensory, Motor, Emotion, and Cognition in Rodent Models of Intracerebral Hemorrhage

Intracerebral hemorrhage (ICH) is the second most common type of stroke and has one of the highest fatality rates of any disease. There are many clinical signs and symptoms after ICH due to brain cell injury and network disruption resulted from the rupture of a tiny artery and activation of inflammatory cells, such as motor dysfunction, sensory impairment, cognitive impairment, and emotional disturbance, etc. Thus, researchers have established many tests to evaluate behavioral changes in rodent ICH models, in order to achieve a better understanding and thus improvements in the prognosis for the clinical treatment of stroke. This review summarizes existing protocols that have been applied to assess neurologic function outcomes in the rodent ICH models such as pain, motor, cognition, and emotion tests. Pain tests include mechanical, hot, and cold pain tests; motor tests include the following 12 types: neurologic deficit scale test, staircase test, rotarod test, cylinder test, grid walk test, forelimb placing test, wire hanging test, modified neurologic severity score, beam walking test, horizontal ladder test, and adhesive removal test; learning and memory tests include Morris water maze, Y-maze, and novel object recognition test; emotion tests include elevated plus maze, sucrose preference test, tail suspension test, open field test, and forced swim test. This review discusses these assessments by examining their rationale, setup, duration, baseline, procedures as well as comparing their pros and cons, thus guiding researchers to select the most appropriate behavioral tests for preclinical ICH research.

Delayed Treatment with Human Dental Pulp Stem Cells Accelerates Functional Recovery and Modifies Responses of Peri-Infarct Astrocytes Following Photothrombotic Stroke in Rats

Dental pulp contains multipotent mesenchymal stem cells that improve outcomes when administered early after temporary middle cerebral artery occlusion in rats. To further assess the therapeutic potential of these cells, we tested whether functional recovery following stroke induced by photothrombosis could be modified by a delayed treatment that was initiated after the infarct attained maximal volume. Photothrombosis induces permanent focal ischemia resulting in tissue changes that better reflect key aspects of the many human strokes in which early restoration of blood flow does not occur. Human dental pulp stem cells (approximately 400 × 10³ viable cells) or vehicle were injected into the infarct and adjacent brain tissue of Sprague-Dawley rats at 3 days after the induction of unilateral photothrombotic stroke in the sensorimotor cortex. Forepaw function was tested up to 28 days after stroke. Cellular changes in peri-infarct tissue at 28 days were assessed using immunohistochemistry. Rats treated with the stem cells showed faster recovery compared with vehicle-treated animals in a test of forelimb placing in response to vibrissae stimulation and in first attempt success in a skilled forelimb reaching test. Total success in the skilled reaching test and forepaw use during exploration in a Perspex cylinder were not significantly different between the 2 groups. At 28 days after stroke, rats treated with the stem cells showed decreased immunolabeling for glial fibrillary acidic protein in tissue up to 1 mm from the infarct, suggesting decreased reactive astrogliosis. Synaptophysin, a marker of synapses, and collagen IV, a marker of capillaries, were not significantly altered at this time by the stem-cell treatment. These results indicate that dental pulp stem cells can accelerate recovery without modifying initial infarct formation. Decreases in reactive astrogliosis in peri-infarct tissue could have contributed to the change by promoting adaptive responses in neighboring neurons.

Qingda granule exerts neuroprotective effects against ischemia/reperfusion-induced cerebral injury via lncRNA GAS5/miR-137 signaling pathway

Background: Ischemic stroke is the second leading cause of death and disability worldwide, which needs to develop new pharmaceuticals for its prevention and treatment. Qingda granule (QDG), a traditional Chinese medicine formulation, could improve angiotensin II-induced brain injury and decrease systemic inflammation. In this study, we aimed to evaluate the neuroprotective effect of QDG against ischemia/reperfusion-induced cerebral injury and illustrate the potential mechanisms. Methods: The middle cerebral artery occlusion/reperfusion (MCAO/R) surgery in vivo and oxygen-glucose deprivation/reoxygenation (OGD/R) in vitro models were established. Ischemic infarct volume was quantified using magnetic resonance imaging (MRI). Neurobehavioral deficits were assessed using a five-point scale. Cerebral histopathology was determined by hematoxylin-eosin (HE) staining. Neuronal apoptosis was evaluated by TUNEL and immunostaining with NeuN antibodies. The protective effect of QDG on OGD/R-injured HT22 cells was determined by MTT assay and Hoechst 33258 staining. The expression of lncRNA GAS5, miR-137 and apoptosis-related proteins were investigated in MCAO/R-injured rats and in OGD/R-injured HT22 cells using RT-qPCR and western blot analysis. Results: QDG significantly reduced the ischemic infarct volume, which was accompanied with improvements in neurobehavioral deficits. Additionally, QDG significantly ameliorated cerebral histopathological changes and reduced neuron loss in MCAO/R-injured rats. Moreover, QDG improved growth and inhibited apoptosis of HT22 cells injured by OGD/R in vitro. Finally, QDG significantly decreased the expression of lncRNA GAS5, Bax and cleaved caspase3, whereas it increased miR-137 and Bcl-2 expression in MCAO/R-injured rats and in OGD/R-injured HT22 cells. Conclusion: QDG plays a neuroprotective role in ischemic stroke via regulation of the lncRNA GAS5/miR-137 signaling pathway.

Physiopathology of ischemic stroke and its modulation using memantine: evidence from preclinical stroke

Ischemic stroke is the most common type of cerebrovascular disease and is caused by an interruption of blood flow in the brain. In this disease, two different damage areas are identifying: the lesion core, in which cells quickly die; and the penumbra (surrounding the lesion core), in which cells are functionally weakened but may recover and restore their functions. The currently approved treatments for ischemic stroke are the recombinant tissue plasminogen activator and endovascular thrombectomy, but they have a short therapeutic window (4.5 and 6 hours after stroke onset, respectively) and a low percentage of stroke patients actually receive these treatments. Memantine is an approved drug for the treatment of Alzheimer’s disease. Memantine is a noncompetitive, low affinity and use-dependent antagonist of N-methyl-D-aspartate glutamate receptor. Memantine has several advantages over developing a new drug to treat focal ischemic stroke, but the most important is that it has sufficient safe probes in preclinical models and humans, and if the preclinical studies provide more evidence about pharmacological actions in tissue protection and repair, this could help to increase the number of clinical trials. The present review summarizes the physiopathology of isquemic stroke and the pharmacological actions in neuroprotection and neuroplasticity of memantine in the post stroke stage of preclinical stroke models, to illustrate their potential to improve functional recovery in human patients.

The Role of Glutamate in Language and Language Disorders - Evidence from ERP and Pharmacologic Studies

Current models of language processing do not address mechanisms at the neurotransmitter level, nor how pharmacologic agents may improve language function(s) in seemingly disparate disorders. L-Glutamate, the primary excitatory neurotransmitter in the human brain, is extensively involved in various higher cortical functions. We postulate that the physiologic role of L-Glutamate neurotransmission extends to the regulation of language access, comprehension, and production, and that disorders in glutamatergic transmission and circuitry contribute to the pathogenesis of neurodegenerative diseases and sporadic-onset language disorders such as the aphasic stroke syndromes. We start with a review of basic science data pertaining to various glutamate receptors in the CNS and ways that they may influence the physiological processes of language access and comprehension. We then focus on the dysregulation of glutamate neurotransmission in three conditions in which language dysfunction is prominent: Alzheimer's Disease, Fragile X-associated Tremor/Ataxia Syndrome, and Aphasic Stroke Syndromes. Finally, we review the pharmacologic and electrophysiologic (event related brain potential or ERP) data pertaining to the role glutamate neurotransmission plays in language processing and disorders.

BDNF rs6265 Polymorphism and Its Methylation in Patients with Stroke Undergoing Rehabilitation

Brain-Derived Neurotrophic Factor (BDNF) and its rs6265 single nucleotide polymorphism (SNP) play an important role in post-stroke recovery. We investigated the correlation between BDNF rs6265 SNP and recovery outcome, measured by the modified Barthel index, in 49 patients with stroke hospitalized in our rehabilitation center at baseline (T0) and after 30 sessions of rehabilitation treatment (T1); moreover, we analyzed the methylation level of the CpG site created or abolished into BDNF rs6265 SNP. In total, 11 patients (22.4%) were heterozygous GA, and 32 (65.3%) and 6 (12.2%) patients were homozygous GG and AA, respectively. The univariate analysis showed a significant relationship between the BDNF rs6265 SNP and the modified Barthel index cut-off (χ²(1, N = 48) = 3.86, p = 0.049), considering patients divided for carrying (A+) or not carrying (A−) the A allele. A higher percentage of A− patients obtained a favorable outcome, as showed by the logistic regression model corrected by age and time since the stroke onset, compared with the A+ patients (OR: 5.59). At baseline (T0), the percentage of BDNF methylation was significantly different between GG (44.6 ± 1.1%), GA (39.5 ± 2.8%) and AA (28.5 ± 1.7%) alleles (p < 0.001). After rehabilitation (T1), only patients A− showed a significant increase in methylation percentages (mean change = 1.3, CI: 0.4–2.2, p = 0.007). This preliminary study deserves more investigation to confirm if BDNF rs6265 SNP and its methylation could be used as a biological marker of recovery in patients with stroke undergoing rehabilitation treatment.

Activation of neuronal Ras-related C3 botulinum toxin substrate 1 (Rac1) improves post-stroke recovery and axonal plasticity in mice

Long-term disability after stroke is common but the mechanisms of post-stroke recovery remain unclear. Cerebral Ras-related C3 botulinum toxin substrate (Rac) 1 contributes to functional recovery after ischemic stroke in mice. As Rac1 plays divergent roles in individual cell types after central neural system injury, we herein examined the specific role of neuronal Rac1 in post-stroke recovery and axonal regeneration. Young male mice were subjected to 60-min of middle cerebral artery occlusion (MCAO). Inducible deletion of neuronal Rac1 by daily intraperitoneal injection of tamoxifen (2 mg/40 g) into Thy1-creER/Rac1-floxed mice day 7-11 after MCAO worsened cognitive (assayed by novel object recognition test) and sensorimotor (assayed by adhesive removal and pellet reaching tests) recovery day 14-28 accompanied with the reduction of neurofilament-L (NFL) and myelin basic protein (MBP) and the elevation of glial fibrillary acidic protein (GFAP) in the peri-infarct zone assessed by immunostaining. Whereas the brain tissue loss was not altered assayed by cresyl violet staining. In another approach, delayed overexpression of neuronal Rac1 by injection of lentivirus encoding Rac1 with neuronal promotor into both the cortex and striatum (total 4 μl at 1 × 10⁹ transducing units/mL) of stroke side in C57BL/6J mice day 7 promoted stroke outcome, NFL and MBP regrowth and alleviated GFAP invasion. Furthermore, neuronal Rac1 over-expression led to the activation of p21 activating kinases (PAK) 1, mitogen-activated protein kinase kinase (MEK) 1/2 and extracellular signal-regulated kinase (ERK) 1/2, and the elevation of brain-derived neurotrophic factor (BDNF) day 14 after stroke. Finally, we observed higher counts of neuronal Rac1 in the peri-infarct zone of subacute/old ischemic stroke subjects. This work identified a neuronal Rac1 signaling in improving functional recovery and axonal regeneration after stroke, suggesting a potential therapeutic target in the recovery stage of stroke.

A Window of Vascular Plasticity Coupled to Behavioral Recovery after Stroke

Stroke causes remodeling of vasculature surrounding the infarct, but whether and how vascular remodeling contributes to recovery are unclear. We established an approach to monitor and compare changes in vascular structure and blood flow with high spatiotemporal precision after photothrombotic infarcts in motor cortex using longitudinal 2-photon and multiexposure speckle imaging in mice of both sexes. A spatially graded pattern of vascular structural remodeling in peri-infarct cortex unfolded over the first 2 weeks after stroke, characterized by vessel loss and formation, and selective stabilization of a subset of new vessels. This vascular structural plasticity was coincident with transient activation of transcriptional programs relevant for vascular remodeling, reestablishment of peri-infarct blood flow, and large improvements in motor performance. Local vascular plasticity was strongly predictive of restoration of blood flow, which was in turn predictive of behavioral recovery. These findings reveal the spatiotemporal evolution of vascular remodeling after stroke and demonstrate that a window of heightened vascular plasticity is coupled to the reestablishment of blood flow and behavioral recovery. Our findings support that neovascularization contributes to behavioral recovery after stroke by restoring blood flow to peri-infarct regions. These findings may inform strategies for enhancing recovery from stroke and other types of brain injury.SIGNIFICANCE STATEMENT An improved understanding of neural repair could inform strategies for enhancing recovery from stroke and other types of brain injury. Stroke causes remodeling of vasculature surrounding the lesion, but whether and how the process of vascular remodeling contributes to recovery of behavioral function have been unclear. Here we used longitudinal in vivo imaging to track vascular structure and blood flow in residual peri-infarct cortex after ischemic stroke in mice. We found that stroke created a restricted period of heightened vascular plasticity that was associated with restoration of blood flow, which was in turn predictive of recovery of motor function. Therefore, our findings support that vascular remodeling facilitates behavioral recovery after stroke by restoring blood flow to peri-infarct cortex.

Neuroprotective Methodologies of Co-Enzyme Q10 Mediated Brain Hemorrhagic Treatment: Clinical and Pre-Clinical Findings

Cerebral brain hemorrhage is associated with the highest mortality and morbidity despite only constituting approximately 10-15% of all strokes classified into intracerebral and intraventricular hemorrhage where most of the patients suffer from impairment in memory, weakness or paralysis in arms or legs, headache, fatigue, gait abnormality and cognitive dysfunctions. Understanding molecular pathology and finding the worsening cause of hemorrhage will lead to explore the therapeutic interventions that could prevent and cure the disease. Mitochondrial ETC-complexes dysfunction has been found to increase neuroinflammatory cytokines, oxidative free radicals, excitotoxicity, neurotransmitter and energy imbalance that are the key neuropathological hallmarks of cerebral hemorrhage. Coenzyme Q10 (CoQ10), as a part of the mitochondrial respiratory chain can effectively restore these neuronal dysfunctions by preventing the opening of mitochondrial membrane transition pore, thereby counteracting cell death events as well as exerts an anti-inflammatory effect by influencing the expression of NF-kB1 dependent genes thus preventing the neuroinflammation and energy restoration. Due to behavior and biochemical heterogeneity in post cerebral brain hemorrhagic pattern different preclinical autologous blood injection models are required to precisely investigate the forthcoming therapeutic strategies. Despite emerging pre-clinical research and resultant large clinical trials for promising symptomatic treatments, there are very less pharmacological interventions demonstrated to improve post operative condition of patients where intensive care is required. Therefore, in current review, we explore the disease pattern, clinical and pre-clinical interventions under investigation and neuroprotective methodologies of CoQ10 precursors to ameliorate post brain hemorrhagic conditions.

Roles of glutamate receptors in a novel in vitro model of early, comorbid cerebrovascular, and Alzheimer's diseases

Systemic multimorbidity is highly prevalent in the elderly and, remarkably, coexisting neuropathological markers of Alzheimer's (AD) and cerebrovascular (CVD) diseases are found at autopsy in most brains of patients clinically diagnosed as AD. Little is known on neurodegeneration peculiar to comorbidities, especially at early stages when pathogenesis may propagate at subclinical levels. We developed a novel in vitro model of comorbid CVD/AD in organotypic hippocampal cultures, by combining oxygen-glucose deprivation (OGD) and exposure to amyloid-Aβ oligomers (AβOs), both applied at levels subtoxic to neurons when used in isolation. We focused on synaptic proteins and the roles of glutamate receptors, which have been implicated in many basic and clinical approaches to either CVD or AD. Subtoxic insults by OGD and AβOs synergized to reduce levels of synaptophysin (SYP) and PSD-95 without cell death, while effects of antagonists of either metabotropic or ionotropic glutamate receptors were distinct from reports in models of isolated CVD or AD. In particular, modulation of glutamate receptors differentially impacted SYP and PSD-95, and antagonists of a single receptor subtype had distinct effects when either isolated or combined. Our findings highlight the complexity of CVD/AD comorbidity, help understand variable responses to glutamate receptor antagonists in patients diagnosed with AD and may contribute to future development of therapeutics based on investigation of the pattern of progressive comorbidity.

Memantine ameliorates motor impairments and pathologies in a mouse model of neuromyelitis optica spectrum disorders

Background

Neuromyelitis optica spectrum disorders (NMOSD) are central nervous system (CNS) autoimmune inflammatory demyelinating diseases characterized by recurrent episodes of acute optic neuritis and transverse myelitis. Aquaporin-4 immunoglobulin G (AQP4-IgG) autoantibodies, which target the water channel aquaporin-4 (AQP4) on astrocytic membrane, are pathogenic in NMOSD. Glutamate excitotoxicity, which is triggered by internalization of AQP4-glutamate transporter complex after AQP4-IgG binding to astrocytes, is involved in early NMOSD pathophysiologies. We studied the effects of memantine, a N-methyl-D-aspartate (NMDA) receptor antagonist, on motor impairments and spinal cord pathologies in mice which received human AQP4-IgG.

Methods

Purified IgG from AQP4-IgG-seropositive NMOSD patients were passively transferred to adult C57BL/6 mice with disrupted blood-brain barrier. Memantine was administered by oral gavage. Motor impairments of the mice were assessed by beam walking test. Spinal cords of the mice were assessed by immunofluorescence and ELISA.

Results

Oral administration of memantine ameliorated the motor impairments induced by AQP4-IgG, no matter the treatment was initiated before (preventive) or after (therapeutic) disease flare. Memantine profoundly reduced AQP4 and astrocyte loss, and attenuated demyelination and axonal loss in the spinal cord of mice which had received AQP4-IgG. The protective effects of memantine were associated with inhibition of apoptosis and suppression of neuroinflammation, with decrease in microglia activation and neutrophil infiltration and reduction of increase in levels of proinflammatory cytokines including interleukin-1β (IL-1β), interleukin-6 (IL-6), and tumor necrosis factor-α (TNF-α). In addition, memantine elevated growth factors including brain-derived neurotrophic factor (BDNF), glial cell line-derived neurotrophic factor (GDNF), and vascular endothelial growth factor (VEGF) in the spinal cord.

Conclusions

Our findings support that glutamate excitotoxicity and neuroinflammation play important roles in complement-independent pathophysiology during early development of NMOSD lesions, and highlight the potential of oral memantine as a therapeutic agent in NMOSD acute attacks.

Transporter-Mediated Delivery of Small Molecule Drugs to the Brain: A Critical Mechanism That Can Advance Therapeutic Development for Ischemic Stroke

Ischemic stroke is the 5th leading cause of death in the United States. Despite significant improvements in reperfusion therapies, stroke patients still suffer from debilitating neurocognitive deficits. This indicates an essential need to develop novel stroke treatment paradigms. Endogenous uptake transporters expressed at the blood-brain barrier (BBB) provide an excellent opportunity to advance stroke therapy via optimization of small molecule neuroprotective drug delivery to the brain. Examples of such uptake transporters include organic anion transporting polypeptides (OATPs in humans; Oatps in rodents) and organic cation transporters (OCTs in humans; Octs in rodents). Of particular note, small molecule drugs that have neuroprotective properties are known substrates for these transporters and include 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors (i.e., statins) for OATPs/Oatps and 1-amino-3,5-dimethyladamantane (i.e., memantine) for OCTs/Octs. Here, we review current knowledge on specific BBB transporters that can be targeted for improvement of ischemic stroke treatment and provide state-of-the-art perspectives on the rationale for considering BBB transport properties during discovery/development of stroke therapeutics.

Memantine Protects From Exacerbation of Ischemic Stroke and Blood Brain Barrier Disruption in Mild But Not Severe Hyperhomocysteinemia

Background Hyperhomocysteinemia is a risk factor for ischemic stroke; however, a targeted treatment strategy is lacking partly because of limited understanding of the causal role of homocysteine in cerebrovascular pathogenesis. Methods and Results In a genetic model of cystathionine beta synthase (CBS) deficiency, we tested the hypothesis that elevation in plasma total homocysteine exacerbates cerebrovascular injury and that memantine, a N-methyl-D-aspartate receptor antagonist, is protective. Mild or severe elevation in plasma total homocysteine was observed in Cbs+/- (6.1±0.3 μmol/L) or Cbs-/- (309±18 μmol/L) mice versus Cbs+/+ (3.1±0.6 μmol/L) mice. Surprisingly, Cbs-/- and Cbs+/- mice exhibited similar increases in cerebral infarct size following middle cerebral artery ischemia/reperfusion injury, despite the much higher total homocysteine levels in Cbs-/- mice. Likewise, disruption of the blood brain barrier was observed in both Cbs+/- and Cbs-/- mice. Administration of the N-methyl-D-aspartate receptor antagonist memantine protected Cbs+/- but not Cbs-/- mice from cerebral infarction and blood brain barrier disruption. Our data suggest that the differential effect of memantine in Cbs+/- versus Cbs-/- mice may be related to changes in expression of N-methyl-D-aspartate receptor subunits. Cbs-/-, but not Cbs+/- mice had increased expression of NR2B subunit, which is known to be relatively insensitive to homocysteine. Conclusions These data provide experimental evidence that even a mild increase in plasma total homocysteine can exacerbate cerebrovascular injury and suggest that N-methyl-D-aspartate receptor antagonism may represent a strategy to prevent reperfusion injury after acute ischemic stroke in patients with mild hyperhomocysteinemia.

Gamma radiation preparation of chitosan nanoparticles for controlled delivery of memantine

The purpose of the current study is to prepare chitosan nanoparticles by gamma radiation as a new brain delivery system for memantine to improve its therapeutic efficiency. Fourier-transform infrared analysis of chitosan nanoparticles showed the characteristic peaks of chitosan and the reduction of particle size induced by irradiation at doses 10, 20 and 30 kGy. The solubility of chitosan nanoparticles was tested using different solvents and exhibited good solubility in both water and 1% acetic acid than other tested solvents at 80°C. Different formulations containing memantine -loaded chitosan nanoparticles were evaluated for brain targeting on aluminum-induced Alzheimer’s disease in rats. Memory deficit was evaluated using the Morris water maze test. The levels of amyloid-β peptide, tumour necrosis factor alpha, interleukin-1β and interleukin-6 in brain tissues as well as the serum level of brain-derived neurotrophic factor were assayed. Data demonstrated that memantine -loaded chitosan nanoparticles 1:1 transported memantine effectively into the brain compared to free memantine as evidenced by better behaviour performance and biochemical amelioration and confirmed by histopathological examination in Alzheimer’s disease rats. Interestingly, the therapeutic effect of memantine -loaded chitosan nanoparticles 1:1 was superior to memantine -loaded chitosan nanoparticles 1:2 and memantine -loaded chitosan nanoparticles 2:1. Based on these findings, it is reasonable to suggest that memantine -loaded chitosan nanoparticles 1:1 could be a promising approach for Alzheimer’s disease.

Role of cerebral glutamate in post-stroke epileptogenesis

Stroke is one of the most important causes of acquired epilepsy in the adult population. While factors such as cortical involvement and haemorrhage have been associated with increased seizure risk, the mechanisms underlying the development of epilepsy after stroke remain unclear. One hypothesised mechanism is an excitotoxic effect of abnormal glutamate release following a stroke. Cerebral extracellular glutamate levels are known to rise in the setting of acute stroke, and numerous studies have implicated glutamate in the pathogenesis of seizures and epilepsy, both through direct measurement of glutamate from the epileptic brain and by analysis of receptors and transporters central to glutamate homeostasis. While experimental evidence suggests the cellular injury induced by glutamate exposure may lead to development of an epileptic phenotype, there is little direct data linking the rise in glutamate during stroke with the later development of epilepsy. Clinical research in this field has been hampered by the lack of non-invasive methods to measure cerebral glutamate. However, with the increasing availability of 7T MRI technology, Magnetic Resonance Spectroscopy is able to better resolve glutamate from other chemical species at this field strength, and Glutamate Chemical Exchange Saturation Transfer (GluCEST) imaging has been applied to localise epileptic foci in non-lesional focal epilepsy. This review outlines the evidence implicating a pivotal role for cerebral glutamate in the development of post-stroke epilepsy, and exploring the role of MRI in studying glutamate as a biomarker and therefore its suitability as a molecular target for anti-epileptogenic therapies. We hypothesise that the rise in glutamate levels in the setting of acute stroke is a clinically relevant biomarker for the development of post-stroke epilepsy.

Paired Associative Stimulation as a Tool to Assess Plasticity Enhancers in Chronic Stroke

Background and Purpose

The potential for adaptive plasticity in the post-stroke brain is difficult to estimate, as is the demonstration of central nervous system (CNS) target engagement of drugs that show promise in facilitating stroke recovery. We set out to determine if paired associative stimulation (PAS) can be used (a) as an assay of CNS plasticity in patients with chronic stroke, and (b) to demonstrate CNS engagement by memantine, a drug which has potential plasticity-modulating effects for use in motor recovery following stroke.

Methods

We examined the effect of PAS in fourteen participants with chronic hemiparetic stroke at five time-points in a within-subjects repeated measures design study: baseline off-drug, and following a week of orally administered memantine at doses of 5, 10, 15, and 20 mg, comprising a total of seventy sessions. Each week, MEP amplitude pre and post-PAS was assessed in the contralesional hemisphere as a marker of enhanced or diminished plasticity. Strength and dexterity were recorded each week to monitor motor-specific clinical status across the study period.

Results

We found that MEP amplitude was significantly larger after PAS in baseline sessions off-drug, and responsiveness to PAS in these sessions was associated with increased clinical severity. There was no observed increase in MEP amplitude after PAS with memantine at any dose. Motor threshold (MT), strength, and dexterity remained unchanged during the study.

Conclusion

Paired associative stimulation successfully induced corticospinal excitability enhancement in chronic stroke subjects at the group level. However, this response did not occur in all participants, and was associated with increased clinical severity. This could be an important way to stratify patients for future PAS-drug studies. PAS was suppressed by memantine at all doses, regardless of responsiveness to PAS off-drug, indicating CNS engagement.

The flavonoid, 2'-methoxy-6-methylflavone, affords neuroprotection following focal cerebral ischaemia

Tonic inhibitory currents, mediated by extrasynaptic GABA_A receptors, are elevated at a delay following stroke. Flavonoids minimise the extent of cellular damage following stroke, but little is known about their mode of action. We demonstrate that the flavonoid, 2'-methoxy-6-methylflavone (0.1-10 µM; 2'MeO6MF), increases GABA_A receptor tonic currents presumably via δ-containing GABA_A receptors. Treatment with 2'MeO6MF 1-6 h post focal ischaemia dose dependently decreases infarct volume and improves functional recovery. The effect of 2'MeO6MF was attenuated in δ^-/- mice, indicating that the effects of the flavonoid were mediated via δ-containing GABA_A receptors. Further, as flavonoids have been shown to have multiple modes of action, we investigated the anti-inflammatory effects of 2'MeO6MF. Using a macrophage cell line, we show that 2'MeO6MF can dampen an LPS-induced elevation in NFkB activity. Assessment of vehicle-treated stroke animals revealed a significant increase in circulating IL1β, TNFα and IFγ levels. Treatment with 2'MeO6MF dampened the stroke-induced increase in circulating cytokines, which was blocked in the presence of the pan-AKT inhibitor, GSK690693. These studies support the hypothesis that compounds that potentiate tonic inhibition via δ-containing GABA_A receptors soon after stroke can afford neuroprotection.

Post-stroke treatment with argon attenuated brain injury, reduced brain inflammation and enhanced M2 microglia/macrophage polarization: a randomized controlled animal study

BACKGROUND

In recent years, argon has been shown to exert neuroprotective effects in an array of models. However, the mechanisms by which argon exerts its neuroprotective characteristics remain unclear. Accumulating evidence imply that argon may exert neuroprotective effects via modulating the activation and polarization of microglia/macrophages after ischemic stroke. In the present study, we analyzed the underlying neuroprotective effects of delayed argon application until 7 days after reperfusion and explored the potential mechanisms.

METHODS

Twenty-one male Wistar rats underwent transient middle cerebral artery occlusion or sham surgery randomly for 2 h using the endoluminal thread model. Three hours after transient middle cerebral artery occlusion induction and 1 h after reperfusion, animals received either 50% vol Argon/50% vol O2 or 50% vol N2/50% vol O2 for 1 h. The primary outcome was the 6-point neuroscore from 24 h to d7 after reperfusion. Histological analyses including infarct volume, survival of neurons (NeuN) at the ischemic boundary zone, white matter integrity (Luxol Fast Blue), microglia/macrophage activation (Iba1), and polarization (Iba1/Arginase1 double staining) on d7 were conducted as well. Sample size calculation was performed using nQuery Advisor + nTerim 4.0. Independent t test, one-way ANOVA and repeated measures ANOVA were performed, respectively, for statistical analysis (SPSS 23.0).

RESULTS

The 6-point neuroscore from 24 h to d7 after reperfusion showed that tMCAO Ar group displayed significantly improved neurological performance compared to tMCAO N2 group (p = 0.026). The relative numbers of NeuN-positive cells in the ROIs of tMCAO Ar group significantly increased compared to tMCAO N2 group (p = 0.010 for cortex and p = 0.011 for subcortex). Argon significantly suppressed the microglia/macrophage activation as revealed by Iba1 staining (p = 0.0076) and promoted the M2 microglia/macrophage polarization as revealed by Iba1/Arginase 1 double staining (p = 0.000095).

CONCLUSIONS

Argon administration with a 3 h delay after stroke onset and 1 h after reperfusion significantly alleviated neurological deficit within the first week and preserved the neurons at the ischemic boundary zone 7 days after stroke. Moreover, argon reduced the excessive microglia/macrophage activation and promoted the switch of microglia/macrophage polarization towards the anti-inflammatory M2 phenotype. Studies making efforts to further elucidate the protective mechanisms and to benefit the translational application are of great value.

Neuroprotective effect ofPanax ginsengextract against cerebral ischemia–reperfusion-injury-induced oxidative stress in middle cerebral artery occlusion models

The present study investigated the in vivo neuroprotective role of Panax ginseng extract (PGE) pretreatment against transient cerebral ischemia in a middle cerebral artery occlusion (MCAO) model. Rats were randomly divided as follows: group I, control; group II, sham-operated; group III, where animals were subjected to MCAO surgery; and group IV, where animals were orally administered 10 mL PGE per day (200 mg/kg of body weight per day) for 30 d followed by MCAO induction at day 31. Following 24 h of reperfusion, blood and tissue (brain, liver, and kidney) samples were collected for biochemical and histopathological examination. Biochemical testing included lipid profile, liver enzymes, kidney function tests, C-reactive protein (CRP), lactate dehydrogenase (LDH), glucose, and total protein estimation. Tissue antioxidants (catalase, superoxide dismutase, and glutathione) were assessed in brain, liver, and kidney tissues. MCAO-induced histopathological changes were also examined in the tissues. Pretreatment with PGE showed significant improvement in tissue antioxidant status in brain, liver and kidney tissues. PGE treatment maintains plasma lipid profile, liver enzymes, kidney function, and CRP, LDH, and glucose levels. Histologically, monocytes and macrophage infiltration were observed in the tissues of MCAO animals, whereas PGE treatment preserved tissue architecture and minimal monocyte infiltration. PGE supplementation showed a neuroprotective effect against ischemia–reperfusion injury by effectively increasing endogenous antioxidant enzyme activity.

Kallmes D. Memantine for the treatment of ischemic stroke: experimental benefits and clinical lack of studies

Stroke is an important cause of mortality and disability worldwide. Immediately after stroke onset, the ischemic cascade initiates and deleteriously affects neural cells. Time to reperfusion therapy is a critical determinant of functional recovery in stroke patients. Although recent trials have shown the significant efficacy of endovascular thrombectomy, either alone or with intravenous tissue plasminogen activator, in improving the functional outcomes of stroke patients with large vessel occlusion, hours can pass before patients receive reperfusion therapy. Moreover, many patients do not meet the eligibility criteria to receive reperfusion treatments. Therefore, an adjunct and alternative agent that can protect ischemic neuronal tissue during the hyperacute phase until reperfusion therapy can be administered may prevent further brain damage and enhance functional recovery. Memantine is a US Food and Drug Administration approved drug for the treatment of Alzheimer’s disease. Memantine blocks overstimulated N-methyl-d-aspartate receptors and prevents neurotoxicity caused by massive glutamate release. Preclinical studies show that memantine decreases infarction volume and improves neurologic outcomes. However, few clinical studies have evaluated the safety and efficacy of memantine in stroke patients. This review article summarizes the current evidence for the role of memantine in the treatment of ischemic stroke and highlights areas for future research.

GAT3 selective substrate l-isoserine upregulates GAT3 expression and increases functional recovery after a focal ischemic stroke in mice

Ischemic stroke triggers an elevation in tonic GABA inhibition that impairs the ability of the brain to form new structural and functional cortical circuits required for recovery. This stroke-induced increase in tonic inhibition is caused by impaired GABA uptake via the glial GABA transporter GAT3, highlighting GAT3 as a novel target in stroke recovery. Using a photothrombotic stroke mouse model, we show that GAT3 protein levels are decreased in peri-infarct tissue from 6 h to 42 days post-stroke. Prior studies have shown that GAT substrates can increase GAT surface expression. Therefore, we aimed to assess whether the GAT3 substrate, L-isoserine, could increase post-stroke functional recovery. L-Isoserine (38 µM or 380 µM) administered directly into the infarct from day 5 to 32 post-stroke, significantly increased motor performance in the grid-walking and cylinder tasks in a concentration-dependent manner, without affecting infarct volumes. Additionally, L-isoserine induced a lasting increase in GAT3 expression in peri-infarct regions accompanied by a small decrease in GFAP expression. This study is the first to show that a GAT3 substrate can increase GAT3 expression and functional recovery after focal ischemic stroke following a delayed long-term treatment. We propose that enhancing GAT3-mediated uptake dampens tonic inhibition and promotes functional recovery after stroke.

Evaluation of temperature induction in focal ischemic thermocoagulation model

The thermocoagulation model, which consists of focal cerebral ischemia with craniectomy, is helpful in studying permanent ischemic brain lesions and has good reproducibility and low mortality. This study analyzed the best conditions for inducing a focal ischemic lesion by thermocoagulation. We investigated parameters such as temperature and thermal dissipation in the brain tissue during induction and analyzed real-time blood perfusion, histological changes, magnetic resonance imaging (MRI), and motor behavior in a permanent ischemic stroke model. We used three-month-old male Wistar rats, weighing 300–350 g. In the first experiment, the animals were divided into four groups (n = 5 each): one sham surgery group and three ischemic lesion groups having thermocoagulation induction (TCI) temperatures of 200°C, 300°C, and 400°C, respectively, with blood perfusion (basal and 30 min after TCI) and 2,3,5-Triphenyl-tetrazolium chloride (TTC) evaluation at 2 h after TCI. In the second experiment, five groups (n = 5 each) were analyzed by MRI (basal and 24 h after TCI) and behavioral tests (basal and seven days after TCI) with the control group added for the surgical effects. The MRI and TTC analyses revealed that ischemic brain lesions expressively evolved, especially at TCI temperatures of 300°C and 400°C, and significant motor deficits were observed as the animals showed a decrease frequency of movement and an asymmetric pattern. We conclude that a TCI temperature of 400°C causes permanent ischemic stroke and motor deficit.

N-methyl-D-aspartate receptor-mediated calcium influx connects amyloid-β oligomers to ectopic neuronal cell cycle reentry in Alzheimer's disease

INTRODUCTION

Alzheimer's disease (AD) symptoms reflect synaptic dysfunction and neuron death. Amyloid-β oligomers (AβOs) induce excess calcium entry into neurons via N-methyl-D-aspartate receptors (NMDARs), contributing to synaptic dysfunction. The study described here tested the hypothesis that AβO-stimulated calcium entry also drives neuronal cell cycle reentry (CCR), a prelude to neuron death in AD.

METHODS

Pharmacologic modulators of calcium entry and gene expression knockdown were used in cultured neurons and AD model mice.

RESULTS

In cultured neurons, AβO-stimulated CCR was blocked by NMDAR antagonists, total calcium chelation with 1,2-Bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid tetrakis(acetoxymethyl ester) (BAPTA-AM), or knockdown of the NMDAR subunit, NR1. NMDAR antagonists also blocked the activation of calcium-calmodulin-dependent protein kinase II and treatment of Tg2576 AD model mice with the NMDAR antagonist, memantine, prevented CCR.

DISCUSSION

This study demonstrates a role for AβO-stimulated calcium influx via NMDAR and CCR in AD and suggests the use of memantine as a disease-modifying therapy for presymptomatic AD.

Memantine treatment of juvenile rats with kaolin-induced hydrocephalus

Memantine is a selective, non-competitive N-methyl-D-aspartate (NMDA) receptor antagonist that has previously been shown to have neuroprotective qualities in some animal models of neurologic disease. We hypothesized that memantine therapy would improve behavioral, neuropathological, and/or biochemical outcomes in juvenile rats with kaolin-induced hydrocephalus. Three-week old rats received an injection of kaolin (aluminum silicate) into the cisterna magna. Magnetic resonance imaging was performed one week later to assess ventricle size and stratify rats to three treatment groups. Rats were blindly treated daily for three weeks with saline or 10 or 30 mg/kg/day memantine. Behavior measures were performed weekly. Histologic and biochemical evaluations were performed at termination. Hydrocephalic rats showed no differences in weight among treatment groups. Memantine treatment stabilized ventricular enlargement in both low and high dose groups. The high dose group exhibited increased motor activity in open field chambers compared to the vehicle-treated group. However, there were no significant differences between the three hydrocephalic treatment groups for other behavioral tasks. Ventriculomegaly was associated with periventricular white matter damage. Glial fibrillary acidic protein (GFAP) content was higher in the low dose memantine group compared to vehicle-treated group, but there were no differences in GFAP-immunoreactive astrocytes or Iba-1- immunoreactive microglia between groups. Memantine therapy stabilized ventricular expansion and improved some behavioral measures but did not reduce brain tissue changes in juvenile rats with kaolin-induced hydrocephalus.