The blood-brain barrier-gatekeeper to neuronal homeostasis: clinical implications in the setting of stroke

The protective effects of Axitinib on blood-brain barrier dysfunction and ischemia-reperfusion injury in acute ischemic stroke

BACKGROUND AND PURPOSE

The pathophysiological features of acute ischemic stroke (AIS) often involve dysfunction of the blood-brain barrier (BBB), characterized by the degradation of tight junction proteins (Tjs) leading to increased permeability. This dysfunction can exacerbate cerebral injury and contribute to severe complications. The permeability of the BBB fluctuates during different stages of AIS and is influenced by various factors. Developing effective therapies to restore BBB function remains a significant challenge in AIS treatment. High levels of vascular endothelial growth factor (VEGF) in the early stages of AIS have been shown to worsen BBB breakdown and stroke progression. Our study aimed to investigate the protective effects of the VEGF receptor inhibitor Axitinib on BBB dysfunction and cerebral ischemia/reperfusion-induced injury.

METHODS

BEnd3 cell exposed to oxygen-glucose deprivation (OGD) model was constructed to estimate pharmacological activity of Axitinib (400 ng/ml) on anti-apoptosis and pathological barrier function recovery. In vivo, rats were subjected to a 1 h transient middle cerebral artery occlusion and 23 h reperfusion (tMCAO/R) to investigate the permeability of BBB and cerebral tissue damage. Axitinib was administered through the tail vein at the beginning of reperfusion. BBB integrity was assessed by Evans blue leakage and the expression levels of Tjs claudin-5 and occludin.

RESULTS

Our research revealed that co-incubation with Axitinib enhanced the cell viability of OGD-insulted bEnd3 cells, decreased LDH leakage rate, and suppressed the expression of apoptosis-related proteins cytochrome C and Bax. Axitinib also mitigated the damage to Tjs and facilitated the restoration of transepithelial electrical resistance in OGD-insulted bEnd.3 cells. In vivo, Axitinib administration reduced intracerebral Evans blue leakage and up-regulated the expression of Tjs in the penumbra brain tissue in tMCAO/R rats. Notably, 10 mg/kg Axitinib exerted a significant anti-ischemic effect by decreasing cerebral infarct volume and brain edema volume, improving neurological function, and reducing pro-inflammatory cytokines IL-6 and TNF-α in the brain.

CONCLUSIONS

Our study highlights Axitinib as a potent protectant of blood-brain barrier function, capable of promoting pathological blood-brain barrier recovery through VEGF inhibition and increased expression of tight junction proteins in AIS. This suggests that VEGF antagonism within the first 24 h post-stroke could be a novel therapeutic approach to enhance blood-brain barrier function and mitigate ischemia-reperfusion injury.

Alterations in brain fluid physiology during the early stages of development of ischaemic oedema

Oedema occurs when higher than normal amounts of solutes and water accumulate in tissues. In brain parenchymal tissue, vasogenic oedema arises from changes in blood-brain barrier permeability, e.g. in peritumoral oedema. Cytotoxic oedema arises from excess accumulation of solutes within cells, e.g. ischaemic oedema following stroke. This type of oedema is initiated when blood flow in the affected core region falls sufficiently to deprive brain cells of the ATP needed to maintain ion gradients. As a consequence, there is: depolarization of neurons; neural uptake of Na+ and Cl- and loss of K+; neuronal swelling; astrocytic uptake of Na+, K+ and anions; swelling of astrocytes; and reduction in ISF volume by fluid uptake into neurons and astrocytes. There is increased parenchymal solute content due to metabolic osmolyte production and solute influx from CSF and blood. The greatly increased [K+]isf triggers spreading depolarizations into the surrounding penumbra increasing metabolic load leading to increased size of the ischaemic core. Water enters the parenchyma primarily from blood, some passing into astrocyte endfeet via AQP4. In the medium term, e.g. after three hours, NaCl permeability and swelling rate increase with partial opening of tight junctions between blood-brain barrier endothelial cells and opening of SUR1-TPRM4 channels. Swelling is then driven by a Donnan-like effect. Longer term, there is gross failure of the blood-brain barrier. Oedema resolution is slower than its formation. Fluids without colloid, e.g. infused mock CSF, can be reabsorbed across the blood-brain barrier by a Starling-like mechanism whereas infused serum with its colloids must be removed by even slower extravascular means. Large scale oedema can increase intracranial pressure (ICP) sufficiently to cause fatal brain herniation. The potentially lethal increase in ICP can be avoided by craniectomy or by aspiration of the osmotically active infarcted region. However, the only satisfactory treatment resulting in retention of function is restoration of blood flow, providing this can be achieved relatively quickly. One important objective of current research is to find treatments that increase the time during which reperfusion is successful. Questions still to be resolved are discussed.

CaMKII activity and metabolic imbalance-related neurological diseases: Focus on vascular dysfunction, synaptic plasticity, amyloid beta accumulation, and lipid metabolism

Metabolic syndrome (MetS) is characterized by insulin resistance, hyperglycemia, excessive fat accumulation and dyslipidemia, and is known to be accompanied by neuropathological symptoms such as memory loss, anxiety, and depression. As the number of MetS patients is rapidly increasing globally, studies on the mechanisms of metabolic imbalance-related neuropathology are emerging as an important issue. Ca2+/calmodulin-dependent kinase II (CaMKII) is the main Ca2+ sensor and contributes to diverse intracellular signaling in peripheral organs and the central nervous system (CNS). CaMKII exerts diverse functions in cells, related to mechanisms such as RNA splicing, reactive oxygen species (ROS) generation, cytoskeleton, and protein-protein interactions. In the CNS, CaMKII regulates vascular function, neuronal circuits, neurotransmission, synaptic plasticity, amyloid beta toxicity, lipid metabolism, and mitochondrial function. Here, we review recent evidence for the role of CaMKII in neuropathologic issues associated with metabolic disorders.

Role of microglia in stroke

Microglia play key roles in the post-ischemic inflammatory response and damaged tissue removal reacting rapidly to the disturbances caused by ischemia and working to restore the lost homeostasis. However, the modified environment, encompassing ionic imbalances, disruption of crucial neuron-microglia interactions, spreading depolarization, and generation of danger signals from necrotic neurons, induce morphological and phenotypic shifts in microglia. This leads them to adopt a proinflammatory profile and heighten their phagocytic activity. From day three post-ischemia, macrophages infiltrate the necrotic core while microglia amass at the periphery. Further, inflammation prompts a metabolic shift favoring glycolysis, the pentose-phosphate shunt, and lipid synthesis. These shifts, combined with phagocytic lipid intake, drive lipid droplet biogenesis, fuel anabolism, and enable microglia proliferation. Proliferating microglia release trophic factors contributing to protection and repair. However, some microglia accumulate lipids persistently and transform into dysfunctional and potentially harmful foam cells. Studies also showed microglia that either display impaired apoptotic cell clearance, or eliminate synapses, viable neurons, or endothelial cells. Yet, it will be essential to elucidate the viability of engulfed cells, the features of the local environment, the extent of tissue damage, and the temporal sequence. Ischemia provides a rich variety of region- and injury-dependent stimuli for microglia, evolving with time and generating distinct microglia phenotypes including those exhibiting proinflammatory or dysfunctional traits and others showing pro-repair features. Accurate profiling of microglia phenotypes, alongside with a more precise understanding of the associated post-ischemic tissue conditions, is a necessary step to serve as the potential foundation for focused interventions in human stroke.

Establishing Co-Culture Blood–Brain Barrier Models for Different Neurodegeneration Conditions to Understand Its Effect on BBB Integrity

The blood–brain barrier (BBB) is a functional interface that provides selective permeability, protection from toxic substances, transport of nutrients, and clearance of brain metabolites. Additionally, BBB disruption has been shown to play a role in many neurodegenerative conditions and diseases. Therefore, the aim of this study was to establish a functional, convenient, and efficient in vitro co-cultured BBB model that can be used for several physiological conditions related to BBB disruption. Mouse brain-derived endothelial (bEnd.3) and astrocyte (C8-D1A) cells were co-cultured on transwell membranes to establish an intact and functional in vitro model. The co-cultured model and its effects on different neurological diseases and stress conditions, including Alzheimer’s disease (AD), neuroinflammation, and obesity, have been examined by transendothelial electrical resistance (TEER), fluorescein isothiocyanate (FITC) dextran, and tight junction protein analyses. Scanning electron microscope images showed evidence of astrocyte end-feet processes passing through the membrane of the transwell. Moreover, the co-cultured model showed effective barrier properties in the TEER, FITC, and solvent persistence and leakage tests when compared to the mono-cultured model. Additionally, the immunoblot results showed that the expression of tight junction proteins such as zonula occludens-1 (ZO-1), claudin-5, and occludin-1 was enhanced in the co-culture. Lastly, under disease conditions, the BBB structural and functional integrity was decreased. The present study demonstrated that the co-cultured in vitro model mimicked the BBB’s structural and functional integrity and, under disease conditions, the co-cultured model showed similar BBB damages. Therefore, the present in vitro BBB model can be used as a convenient and efficient experimental tool to investigate a wide range of BBB-related pathological and physiological studies.

miR-29c-5p knockdown reduces inflammation and blood–brain barrier disruption by upregulating LRP6

Blood–brain barrier participates in the pathological process of ischemic stroke. MicroRNA-29c-5p was highly expressed in clinical samples from patients with ischemic stroke. In this study, oxygen-glucose deprivation (OGD) treatment of astrocytes enhanced the permeability of brain microvascular endothelial cells (BMECs), and the miR-29c-5p expression was elevated in clinical samples from patients with ischemic stroke. For the function of miR-29c-5p in ischemic stroke, the miR-29c-5p knockdown decreased the permeability and the tight junction protein (TJP) destruction of BMECs and ameliorated the inflammation induced by OGD-treated astrocytes. Mechanistically, miR-29c-5p interacted with lipoprotein receptor-related protein 6 (LRP6) and negatively regulated the LRP6 expression in astrocytes. Moreover, the rescue assays indicated that the interference with miR-29c-5p ameliorated the TJP destruction of BMECs and inflammation caused by OGD-treated astrocytes by increasing the LRP6 expression. Together, miR-29c-5p knockdown decreased the high permeability and the TJP destruction of BMECs and ameliorated the inflammation induced by OGD-treated astrocytes by elevating LRP6 expression.

A review of bioeffects induced by focused ultrasound combined with microbubbles on the neurovascular unit

Focused ultrasound combined with circulating microbubbles (FUS+MB) can transiently enhance blood-brain barrier (BBB) permeability at targeted brain locations. Its great promise in improving drug delivery to the brain is reflected by a rapidly growing number of clinical trials using FUS+MB to treat various brain diseases. As the clinical applications of FUS+MB continue to expand, it is critical to have a better understanding of the molecular and cellular effects induced by FUS+MB to enhance the efficacy of current treatment and enable the discovery of new therapeutic strategies. Existing studies primarily focus on FUS+MB-induced effects on brain endothelial cells, the major cellular component of BBB. However, bioeffects induced by FUS+MB expand beyond the BBB to cells surrounding blood vessels, including astrocytes, microglia, and neurons. Together these cell types comprise the neurovascular unit (NVU). In this review, we examine cell-type-specific bioeffects of FUS+MB on different NVU components, including enhanced permeability in endothelial cells, activation of astrocytes and microglia, as well as increased intraneuron protein metabolism and neuronal activity. Finally, we discuss knowledge gaps that must be addressed to further advance clinical applications of FUS+MB.

Effect of NIR light on the permeability of the blood-brain barriers in in vitro models

The blood-brain barrier (BBB) is a dynamic barrier between the blood microcirculation system and the brain parenchyma, which plays an important role in the pathogenesis of a variety of neurological diseases. Meanwhile, a non-invasive therapeutic approach of photobiomodulation (PBM) has emerged as a promising treatment for neurological disorders through irradiation with near infrared (NIR) light. However, despite multiple encouraging results reported for PBM in vitro and in vivo, the mechanisms of its therapeutic effect on brain, especially on the BBB, remain barely known. Herein, the effect of NIR light irradiation on the in vitro BBB models was studied. 808 nm laser irradiation at the doses of 10 and 30 J/cm2 was found to significantly increase the permeability of this BBB model. The results showed that NIR light affected mitochondria of cells in the in vitro BBB models, leading to an increase in the mitochondrial activity, reactive oxygen species (ROS) level and Ca2+ influx. The activity of matrix metalloproteinases and the expression of the tight junction proteins in the endothelial cells were found to be inhibited by the NIR light, resulting in an increase in the BBB permeability. This study suggested a new strategy for drug transport across the BBB in development of treatments for brain disorders.

The Role of the Glycocalyx in the Pathophysiology of Subarachnoid Hemorrhage-Induced Delayed Cerebral Ischemia

The glycocalyx is an important constituent of blood vessels located between the bloodstream and the endothelium. It plays a pivotal role in intercellular interactions in neuroinflammation, reduction of vascular oxidative stress, and provides a barrier regulating vascular permeability. In the brain, the glycocalyx is closely related to functions of the blood-brain barrier and neurovascular unit, both responsible for adequate neurovascular responses to potential threats to cerebral homeostasis. An aneurysmal subarachnoid hemorrhage (aSAH) occurs following rupture of an intracranial aneurysm and leads to immediate brain damage (early brain injury). In some cases, this can result in secondary brain damage, also known as delayed cerebral ischemia (DCI). DCI is a life-threatening condition that affects up to 30% of all aSAH patients. As such, it is associated with substantial societal and healthcare-related costs. Causes of DCI are multifactorial and thought to involve neuroinflammation, oxidative stress, neuroinflammation, thrombosis, and neurovascular uncoupling. To date, prediction of DCI is limited, and preventive and effective treatment strategies of DCI are scarce. There is increasing evidence that the glycocalyx is disrupted following an aSAH, and that glycocalyx disruption could precipitate or aggravate DCI. This review explores the potential role of the glycocalyx in the pathophysiological mechanisms contributing to DCI following aSAH. Understanding the role of the glycocalyx in DCI could advance the development of improved methods to predict DCI or identify patients at risk for DCI. This knowledge may also alter the methods and timing of preventive and treatment strategies of DCI. To this end, we review the potential and limitations of methods currently used to evaluate the glycocalyx, and strategies to restore or prevent glycocalyx shedding.

Neural Stem Cells for Early Ischemic Stroke

Clinical treatments for ischemic stroke are limited. Neural stem cell (NSC) transplantation can be a promising therapy. Clinically, ischemia and subsequent reperfusion lead to extensive neurovascular injury that involves inflammation, disruption of the blood-brain barrier, and brain cell death. NSCs exhibit multiple potentially therapeutic actions against neurovascular injury. Currently, tissue plasminogen activator (tPA) is the only FDA-approved clot-dissolving agent. While tPA’s thrombolytic role within the vasculature is beneficial, tPA’s non-thrombolytic deleterious effects aggravates neurovascular injury, restricting the treatment time window (time-sensitive) and tPA eligibility. Thus, new strategies are needed to mitigate tPA’s detrimental effects and quickly mediate vascular repair after stroke. Up to date, clinical trials focus on the impact of stem cell therapy on neuro-restoration by delivering cells during the chronic stroke stage. Also, NSCs secrete factors that stimulate endogenous repair mechanisms for early-stage ischemic stroke. This review will present an integrated view of the preclinical perspectives of NSC transplantation as a promising treatment for neurovascular injury, with an emphasis on early-stage ischemic stroke. Further, this will highlight the impact of early sub-acute NSC delivery on improving short-term and long-term stroke outcomes.

Carnosine Protects against Cerebral Ischemic Injury by Inhibiting Matrix-Metalloproteinases

Stroke is one of the leading causes of death and disability worldwide. However, treatment options for ischemic stroke remain limited. Matrix-metalloproteinases (MMPs) contribute to brain damage during ischemic strokes by disrupting the blood-brain barrier (BBB) and causing brain edemas. Carnosine, an endogenous dipeptide, was found by us and others to be protective against ischemic brain injury. In this study, we investigated whether carnosine influences MMP activity. Brain MMP levels and activity were measured by gelatin zymography after permanent occlusion of the middle cerebral artery (pMCAO) in rats and in vitro enzyme assays. Carnosine significantly reduced infarct volume and edema. Gelatin zymography and in vitro enzyme assays showed that carnosine inhibited brain MMPs. We showed that carnosine inhibited both MMP-2 and MMP-9 activity by chelating zinc. Carnosine also reduced the ischemia-mediated degradation of the tight junction proteins that comprise the BBB. In summary, our findings show that carnosine inhibits MMP activity by chelating zinc, an essential MMP co-factor, resulting in the reduction of edema and brain injury. We believe that our findings shed new light on the neuroprotective mechanism of carnosine against ischemic brain damage.

Blood-brain barrier opening by intracarotid artery hyperosmolar mannitol induces sterile inflammatory and innate immune responses

Intracarotid arterial hyperosmolar mannitol (ICAHM) blood-brain barrier disruption (BBBD) is effective and safe for delivery of therapeutics for central nervous system malignancies. ICAHM osmotically alters endothelial cells and tight junction integrity to achieve BBBD. However, occurrence of neuroinflammation following hemispheric BBBD by ICAHM remains unknown. Temporal proteomic changes in rat brains following ICAHM included increased damage-associated molecular patterns, cytokines, chemokines, trophic factors, and cell adhesion molecules, indicative of a sterile inflammatory response (SIR). Proteomic changes occurred within 5 min of ICAHM infusion and returned to baseline by 96 h. Transcriptomic analyses following ICAHM BBBD further supported an SIR. Immunohistochemistry revealed activated astrocytes, microglia, and macrophages. Moreover, proinflammatory proteins were elevated in serum, and proteomic and histological findings from the contralateral hemisphere demonstrated a less pronounced SIR, suggesting neuroinflammation beyond regions of ICAHM infusion. Collectively, these results demonstrate ICAHM induces a transient SIR that could potentially be harnessed for neuroimmunomodulation.

Neuropathophysiology of preeclampsia and eclampsia: A review of cerebral hemodynamic principles in hypertensive disorders of pregnancy

Preeclampsia and eclampsia are hypertensive disorders of pregnancy associated with abnormal placental vascular development. The systemic angiogenic imbalance, endothelial dysfunction and proinflammatory state caused by abnormal placental development results in abnormalities in renal, hepatic, pulmonary and neurologic function. Neurosensory symptoms related to pregnancy induced hypertension (PIH), the most devastating of which are intracranial hemorrhage and seizure, are among the leading causes of maternal and perinatal morbidity and mortality globally, yet risk stratification strategies and targeted therapies remain elusive. Current treatment for preeclampsia with severe features is limited to delivery, antihypertensive therapy, and magnesium sulfate seizure prophylaxis. Magnesium sulfate reduces seizure rates among severe preeclamptics, but predisposes patients to weakness, uterine atony, pulmonary edema and respiratory depression. Therefore, this drug should ideally be administered only to the subset of preeclamptics who are at increased risk for neurologic complications. While there are no objective methods validated to predict eclampsia, we hypothesize that measurement of optic nerve sheath diameters, optic disc height and middle cerebral artery transcranial doppler resistance indices may be useful in identifying subclinical cerebral edema, potentially allowing us to recognize those patients at highest risk for seizures. This summary of the current literature provides an initial framework for developing more sophisticated and noninvasive methods for identifying, monitoring and treating parturients who are at highest risk for neurologic complications from preeclampsia.

CXCL6 regulates cell permeability, proliferation, and apoptosis after ischemia-reperfusion injury by modulating Sirt3 expression via AKT/FOXO3a activation

Chemokine (C-X-C motif) ligand 6 (CXCL6), a member of the CXC chemokine family, reportedly mediates several processes such as inflammation, immunoreaction, cell growth, and metastasis through interaction with the chemokine receptors CXCR1 and CXCR2 in humans; further, CXCR1 and CXCR2 can promote repair and regeneration of organs or tissues after ischemia-reperfusion injury (IRI). In this study, we found that HIF-1α, CXCL6, and CXCR2 expression levels were elevated in human brain microvascular endothelial cells (HBMECs) after IRI, whereas silent information regulator of transcription (Sirt) 3 expression level had reduced. HIF-1α inhibition in an IRI model potently promoted HBMEC proliferation, accompanied by increased Sirt3 and decreased CXCL6/CXCR2 expression levels. CXCL6 knockdown in the IRI model significantly decreased HBMEC permeability and promoted HBMEC proliferation, concurrent with a decrease in apoptosis; it also increased Sirt3 expression levels and decreased CXCL6/CXCR2 protein and phosphorylated AKT (p-AKT) and class O of forkhead box (FOXO) 3a (p-FOXO3a) levels. In addition, CXCL6-induced HBMEC permeability and inhibition of HBMEC proliferation were counteracted by Sirt3 overexpression, and the AKT inhibitor LY294002 counteracted the effect of CXCL6 recombinant proteins on Sirt3, p-AKT, and p-FOXO3a expressions. These results suggest that CXCL6 and Sirt3 are downstream of HIF-1α and that CXCL6 regulatesHBMEC permeability, proliferation, and apoptosis after IRI by modulating Sirt3 expression via AKT/FOXO3a activation.

The multifaceted role of ischemia/reperfusion in sickle cell anemia

Sickle cell anemia is a unique disease dominated by hemolytic anemia and vaso-occlusive events. The latter trigger a version of ischemia/reperfusion (I/R) pathobiology that is singular in its origin, cyclicity, complexity, instability, perpetuity, and breadth of clinical consequences. Specific clinical features are probably attributable to local I/R injury (e.g., stroke syndromes) or remote organ injury (e.g., acute chest syndrome) or the systematization of inflammation (e.g., multifocal arteriopathy). Indeed, by fashioning an underlying template of endothelial dysfunction and vulnerability, the robust inflammatory systematization no doubt contributes to all sickle pathology. In this Review, we highlight I/R-targeting therapeutics shown to improve microvascular blood flow in sickle transgenic mice undergoing I/R, and we suggest how such insights might be translated into human therapeutic strategies.

Structural, Molecular, and Functional Alterations of the Blood-Brain Barrier during Epileptogenesis and Epilepsy: A Cause, Consequence, or Both?

The blood-brain barrier (BBB) is a dynamic, highly selective barrier primarily formed by endothelial cells connected by tight junctions that separate the circulating blood from the brain extracellular fluid. The endothelial cells lining the brain microvessels are under the inductive influence of neighboring cell types, including astrocytes and pericytes. In addition to the anatomical characteristics of the BBB, various specific transport systems, enzymes and receptors regulate molecular and cellular traffic across the BBB. While the intact BBB prevents many macromolecules and immune cells from entering the brain, following epileptogenic brain insults the BBB changes its properties. Among BBB alterations, albumin extravasation and diapedesis of leucocytes from blood into brain parenchyma occur, inducing or contributing to epileptogenesis. Furthermore, seizures themselves may modulate BBB functions, permitting albumin extravasation, leading to activation of astrocytes and the innate immune system, and eventually modifications of neuronal networks. BBB alterations following seizures are not necessarily associated with enhanced drug penetration into the brain. Increased expression of multidrug efflux transporters such as P-glycoprotein likely act as a 'second line defense' mechanism to protect the brain from toxins. A better understanding of the complex alterations in BBB structure and function following seizures and in epilepsy may lead to novel therapeutic interventions allowing the prevention and treatment of epilepsy as well as other detrimental neuro-psychiatric sequelae of brain injury.

Theranostic Strategy of Focused Ultrasound Induced Blood-Brain Barrier Opening for CNS Disease Treatment

Focused Ultrasound (FUS) in combination with gaseous microbubbles has emerged as a potential new means of effective drug delivery to the brain. Recent research has shown that, under burst-type energy exposure with the presence of microbubbles, this modality can transiently permeate the blood-brain barrier (BBB). The bioavailability of therapeutic agents is site-specifically augmented only in the zone where the FUS energy is targeted. The non-invasiveness of this approach makes FUS-induced BBB opening a novel and attractive means to perform localized CNS therapeutic agent delivery. Over the past decade, FUS-BBB opening has been preclinically confirmed to successfully enhance CNS penetration of therapeutic agents including chemotherapeutic agents, therapeutic peptides, monoclonal antibodies, and nanoparticles. Recently, a number of clinical human trials have begun to explore clinical utility. This review article, explores this technology through its physical mechanisms, summarizes the existing preclinical findings (including current medical device designs and technical approaches), and summarizes current ongoing clinical trials.

Inhibition of calcium/calmodulin-dependent protein kinase kinase (CaMKK) exacerbates impairment of endothelial cell and blood-brain barrier after stroke

Brain microvascular endothelial cells play an essential role in maintaining blood-brain barrier (BBB) integrity, and disruption of the BBB aggravates the ischemic injury. CaMKK (α and β) is a major kinase activated by elevated intracellular calcium. Previously, we demonstrated that inhibition of CaMKK exacerbated outcomes, conversely, overexpression reduced brain injury after stroke in mice. Interestingly, CaMKK has been shown to activate a key endothelial protector, sirtuin 1 (SIRT1). We hypothesized that CaMKK protects brain endothelial cells via SIRT1 activation after stroke. In this study, Oxygen-Glucose Deprivation (OGD) was performed in human brain microvascular endothelial cells. Stroke was induced by middle cerebral artery occlusion (MCAO) in male mice. Knockdown of CaMKK β using siRNA increased cell death following OGD. Inhibition of CaMKK β by STO-609 significantly and selectively down-regulated levels of phosphorylated SIRT1 after OGD. Changes in the downstream targets of SIRT1 were observed following STO-609 treatment. The effect of STO-609 on cell viability after OGD was absent, when SIRT1 was concurrently inhibited. We also demonstrated that STO-609 increased endothelial expression of the pro-inflammatory proteins ICAM-1 and VCAM-1 and inhibition of CaMKK exacerbated OGD-induced leukocyte-endothelial adhesion. Finally, intracerebroventricular injection of STO-609 exacerbated endothelial apoptosis and reduced BBB integrity after 24-hr reperfusion following MCAO in vivo. Collectively, these results demonstrated that CaMKK inhibition reduced endothelial cell viability, exacerbated inflammatory responses and aggravated BBB impairment after ischemia. CaMKK activation may attenuate ischemic brain injury via protection of the microvascular system and a reduction in the infiltration of pro-inflammatory factors.

The peripheral immune response after stroke-A double edge sword for blood-brain barrier integrity

The blood‐brain barrier (BBB) is a highly regulated interface that separates the peripheral circulation and the brain. It plays a vital role in regulating the trafficking of solutes, fluid, and cells at the blood‐brain interface and maintaining the homeostasis of brain microenvironment for normal neuronal activity. Growing evidence has led to the realization that ischemic stroke elicits profound immune responses in the circulation and the activation of multiple subsets of immune cells, which in turn affect both the early disruption and the later repair of the BBB after stroke. Distinct phenotypes or subsets of peripheral immune cells along with diverse intracellular mechanisms contribute to the dynamic changes of BBB integrity after stroke. This review focuses on the interaction between the peripheral immune cells and the BBB after ischemic stroke. Understanding their reciprocal interaction may generate new directions for stroke research and may also drive the innovation of easy accessible immune modulatory treatment strategies targeting BBB in the pursuit of better stroke recovery.

Neuroinflammatory mechanisms of blood-brain barrier damage in ischemic stroke

As part of the neurovascular unit, the blood-brain barrier (BBB) is a unique, dynamic regulatory boundary that limits and regulates the exchange of molecules, ions, and cells between the blood and the central nervous system. Disruption of the BBB plays an important role in the development of neurological dysfunction in ischemic stroke. Blood-borne substances and cells have restricted access to the brain due to the presence of tight junctions between the endothelial cells of the BBB. Following stroke, there is loss of BBB tight junction integrity, leading to increased paracellular permeability, which results in vasogenic edema, hemorrhagic transformation, and increased mortality. Thus, understanding principal mediators and molecular mechanisms involved in BBB disruption is critical for the development of novel therapeutics to treat ischemic stroke. This review discusses the current knowledge of how neuroinflammation contributes to BBB damage in ischemic stroke. Specifically, we provide an updated overview of the role of cytokines, chemokines, oxidative and nitrosative stress, adhesion molecules, matrix metalloproteinases, and vascular endothelial growth factor as well as the role of different cell types in the regulation of BBB permeability in ischemic stroke.

Prolonged Blood-Brain Barrier Injury Occurs After Experimental Intracerebral Hemorrhage and Is Not Acutely Associated with Additional Bleeding

Intracerebral hemorrhage (ICH) causes blood-brain barrier (BBB) damage along with altered element levels in the brain. BBB permeability was quantified at 3, 7, and 14 days with Evans Blue dye after collagenase-induced ICH in rat. At peak permeability (day 3), a gadolinium (Gd)-based contrast agent was injected to further characterize BBB disruption, and X-ray fluorescence imaging (XFI) was used to map Gd, Fe, Cl, and other elements. XFI revealed that Ca, Cl, Gd, and Fe concentrations were significantly elevated, whereas K was significantly decreased. Therefore, using Gd-XFI, we co-determined BBB dysfunction with alterations in the metallome, including those that contribute to cell death and functional outcome. Warfarin was administered 3 days post-ICH to investigate whether additional or new bleeding occurs during peak BBB dysfunction, and hematoma volume was assessed on day 4. Warfarin administration prolonged bleeding time after a peripheral cut-induced bleed, but warfarin did not worsen hematoma volume. Accordingly, extensive BBB leakage occurred after ICH, but did not appear to affect total hematoma size.

Neural stem cell therapy for subacute and chronic ischemic stroke

Neural stem cells (NSCs) play vital roles in brain homeostasis and exhibit a broad repertoire of potentially therapeutic actions following neurovascular injury. One such injury is stroke, a worldwide leading cause of death and disability. Clinically, extensive injury from ischemic stroke results from ischemia-reperfusion (IR), which is accompanied by inflammation, blood-brain barrier (BBB) damage, neural cell death, and extensive tissue loss. Tissue plasminogen activator (tPA) is still the only US Food and Drug Administration-approved clot-lysing agent. Whereas the thrombolytic role of tPA within the vasculature is beneficial, the effects of tPA (in a non-thrombolytic role) within the brain parenchyma have been reported as harmful. Thus, new therapies are needed to reduce the deleterious side effects of tPA and quickly facilitate vascular repair following stroke. The Stroke Treatment Academic Industry Roundtable (STAIR) recommends that stroke therapies "focus on drugs/devices/treatments with multiple mechanisms of action and that target multiple pathways". Thus, based on multifactorial ischemic cascades in various stroke stages, effective stroke therapies need to focus on targeting and ameliorating early IR injury as well as facilitating angiogenesis, neurogenesis, and neurorestorative mechanisms following stroke. This review will discuss the preclinical perspectives of NSC transplantation as a promising treatment for neurovascular injury and will emphasize both the subacute and chronic phase of ischemic stroke.

Neurofilament as Neuronal Injury Blood Marker in Preeclampsia

Preeclampsia has been shown to be associated with changes in cerebral structure and cognitive function later in life. Nf (neurofilaments) are specific scaffolding proteins of neurons, and their quantification in serum has been proposed as a biomarker for neuroaxonal injury. We performed a prospective, longitudinal, single-center study at the University Hospital of Basel to determine serum Nf concentrations in pregnant women with singleton pregnancies and with high risk of preeclampsia or with early signs of preeclampsia. Enrollment started at 21 weeks of gestation, followed up with multiple visits until delivery. Sixty out of 197 women developed preeclampsia (30.5%). NfL (Nf light chain) was measured with a highly sensitive single molecule array (Simoa) assay, in addition to the established preeclampsia markers sFlt-1 (soluble fms-like tyrosine kinase-1) and PlGF (placental growth factor). The most important independent predictors of NfL were maternal age, number of pregnancies, and proteinuria. NfL levels increased during pregnancy and were significantly higher in women developing preeclampsia. The discriminatory accuracy of NfL, PlGF, and sFlt-1 in receiver operating characteristic curves analysis (area under the curve) of the overall group was 0.68, 0.81, and 0.84, respectively, and in women older than 36 years 0.7, 0.62, and 0.79, respectively. We conclude that increased axonal injury serum marker NfL predicts preeclampsia particularly in older women, with an accuracy similar to the established angiogenic factors. NfL may serve as an early indicator of preeclampsia-induced changes in cerebral structure and may help to stratify disease management.

Cell Type-Specific Mechanisms in the Pathogenesis of Ischemic Stroke: The Role of Apoptosis Signal-Regulating Kinase 1

Stroke has become a more common disease worldwide. Despite great efforts to develop treatment, little is known about ischemic stroke. Cerebral ischemia activates multiple cascades of cell type-specific pathomechanisms. Ischemic brain injury consists of a complex series of cellular reactions in various cell types within the central nervous system (CNS) including platelets, endothelial cells, astrocytes, neutrophils, microglia/macrophages, and neurons. Diverse cellular changes after ischemic injury are likely to induce cell death and tissue damage in the brain. Since cells in the brain exhibit different functional roles at distinct time points after injury (acute/subacute/chronic phases), it is difficult to pinpoint genuine roles of cell types after brain injury. Many experimental studies have shown the association of apoptosis signal-regulating kinase 1 (ASK1) with cellular pathomechanisms after cerebral ischemia. Blockade of ASK1, by either pharmacological or genetic manipulation, leads to reduced ischemic brain injury and subsequent neuroprotective effects. In this review, we present the cell type-specific pathophysiology of the early phase of ischemic stroke, the role of ASK1 suggested by preclinical studies, and the potential use of ASK suppression, either by pharmacologic or genetic suppression, as a promising therapeutic option for ischemic stroke recovery.

Maintenance of Blood-Brain Barrier Integrity in Hypertension: A Novel Benefit of Exercise Training for Autonomic Control

The blood-brain barrier (BBB) is a complex multicellular structure acting as selective barrier controlling the transport of substances between these compartments. Accumulating evidence has shown that chronic hypertension is accompanied by BBB dysfunction, deficient local perfusion and plasma angiotensin II (Ang II) access into the parenchyma of brain areas related to autonomic circulatory control. Knowing that spontaneously hypertensive rats (SHR) exhibit deficient autonomic control and brain Ang II hyperactivity and that exercise training is highly effective in correcting both, we hypothesized that training, by reducing Ang II content, could improve BBB function within autonomic brain areas of the SHR. After confirming the absence of BBB lesion in the pre-hypertensive SHR, but marked fluorescein isothiocyanate dextran (FITC, 10 kD) leakage into the brain parenchyma of the hypothalamic paraventricular nucleus (PVN), nucleus of the solitary tract, and rostral ventrolateral medulla during the established phase of hypertension, adult SHR, and age-matched WKY were submitted to a treadmill training (T) or kept sedentary (S) for 8 weeks. The robust FITC leakage within autonomic areas of the SHR-S was largely reduced and almost normalized since the 2nd week of training (T₂). BBB leakage reduction occurred simultaneously and showed strong correlations with both decreased LF/HF ratio to the heart and reduced vasomotor sympathetic activity (power spectral analysis), these effects preceding the appearance of resting bradycardia (T₄) and partial pressure fall (T₈). In other groups of SHR-T simultaneously infused with icv Ang II or saline (osmotic mini-pumps connected to a lateral ventricle cannula) we proved that decreased local availability of this peptide and reduced microglia activation (IBA1 staining) are crucial mechanisms conditioning the restoration of BBB integrity. Our data also revealed that Ang II-induced BBB lesion was faster within the PVN (T₂), suggesting the prominent role of this nucleus in driven hypertension-induced deficits. These original set of data suggest that reduced local Ang II content (and decreased activation of its downstream pathways) is an essential and early-activated mechanism to maintain BBB integrity in trained SHR and uncovers a novel beneficial effect of exercise training to improve autonomic control even in the presence of hypertension.

Focusing on claudin-5: A promising candidate in the regulation of BBB to treat ischemic stroke

Claudin-5 is a tight junction (TJ) protein in the blood-brain barrier (BBB) that has recently attracted increased attention. Numerous studies have demonstrated that claudin-5 regulates the integrity and permeability of the BBB. Increased claudin-5 expression plays a neuroprotective role in neurological diseases, particularly in cerebral ischemic stroke. Moreover, claudin-5 might be a potential marker for early hemorrhagic transformation detection in ischemic stroke. In light of the distinctive effects of claudin-5 on the nervous system, we present the elaborate network of roles that claudin-5 plays in ischemic stroke. In this review, we first introduce basic knowledge regarding the BBB and the claudin family, the characterization and regulation of claudin-5, and association between claudin-5 and other TJ proteins. Subsequently, we describe BBB dysfunction and neuron-specific drivers of pathogenesis of ischemic stroke, including inflammatory disequilibrium and oxidative stress. Furthermore, we summarize promising ischemic stroke treatments that target the BBB via claudin-5, including modified rt-PA therapy, pharmacotherapy, hormone treatment, receptor-targeted therapy, gene therapy, and physical therapy. This review highlights recent advances and provides a comprehensive summary of claudin-5 in the regulation of the BBB and may be helpful for drug design and clinical therapy for treatment of ischemic stroke.

PKA activation and endothelial claudin-5 breakdown in the schizophrenic prefrontal cortex

Schizophrenia is thought to be caused by a combination of genetic and environmental factors; however, its pathogenesis remains largely unknown. Here, we focus on the endothelial tight-junction protein claudin-5 (CLDN5), because the CLDN5 gene is mapped to the schizophrenia-associated 22q11.2 deletion region, and a single nucleotide polymorphism in the CLDN5 locus is also linked to schizophrenia. We show, by RT-qPCR and immunohistochemistry, that the expressions of CLDN5 mRNA and protein are significantly increased and decreased, respectively, in the schizophrenic prefrontal cortex (PFC) compared with control PFC. These changes were not observed in the schizophrenic visual cortex (VC), and neither the density nor diameter of the CD34-positive microvessels was altered in the schizophrenic PFC or VC. Interestingly, protein kinase A (PKA) was activated in the microvascular and perivascular regions of the schizophrenic PFC, and the pPKA-positive microvascular endothelial cells occasionally exhibited focal loss of CLND5. Since we previously demonstrated that cAMP induced CLDN5 mRNA expression and size-selective loosening of the endothelial barrier in PKA-independent and -dependent manners, respectively, a similar mechanism could contribute to the discrepancy between mRNA and protein expression of CLDN5 in the schizophrenic PFC. Taken collectively, these findings provide novel insights into the pathophysiology of schizophrenia.

Sirt1-Sirt3 axis regulates human blood-brain barrier permeability in response to ischemia

Sirtuin1 (Sirt1) and Sirtuin3 (Sirt3) are two well-characterized members of the silent information regulator 2 (Sir2) family of proteins. Both Sirt1 and Sirt3 have been shown to play vital roles in resistance to cellular stress, but the interaction between these two sirtuins has not been fully determined. In this study, we investigated the role of Sirt1-Sirt3 axis in blood-brain barrier (BBB) permeability after ischemia in vitro. Human brain microvascular endothelial cells and astrocytes were co-cultured to model the BBB in vitro and oxygen and glucose deprivation (OGD) was performed to mimic ischemia. The results of transepithelial electrical resistance (TEER) showed that suppression of Sirt1 via siRNA or salermide significantly decreased BBB permeability, whereas Sirt3 knockdown increased BBB permeability. In addition, Sirt1 was shown to regulate Sirt3 expression after OGD through inhibiting the AMPK-PGC1 pathway. Application of the AMPK inhibitor compound C partially prevented the effects of Sirt1-Sirt3 axis on BBB permeability after OGD. The results of flow cytometry and cytochrome c release demonstrated that Sirt1 and Sirt3 exert opposite effects on OGD-induced apoptosis. Furthermore, suppression of Sirt1 was shown to attenuate mitochondrial reactive oxygen species (ROS) generation, which contribute to the Sirt1-Sirt3 axis-induced regulation of BBB permeability and cell damage. In summary, these findings demonstrate that the Sirt1-Sirt3 axis might act as an important modulator in BBB physiology, and could be a therapeutic target for ischemic stroke via regulating mitochondrial ROS generation.

Spreading depolarization is not an epiphenomenon but the principal mechanism of the cytotoxic edema in various gray matter structures of the brain during stroke

Spreading depolarization (SD) is a phenomenon of various cerebral gray matter structures that only occurs under pathological conditions. In the present paper, we summarize the evidence from several decades of research that SD and cytotoxic edema in these structures are largely overlapping terms. SD/cytotoxic edema is a toxic state that - albeit initially reversible - leads eventually to cellular death when it is persistent. Both hemorrhagic and ischemic stroke are among the most prominent causes of SD/cytotoxic edema. SD/cytotoxic edema is the principal mechanism that mediates neuronal death in these conditions. This applies to gray matter structures in both the ischemic core and the penumbra. SD/cytotoxic edema is often a single terminal event in the core whereas, in the penumbra, a cluster of repetitive prolonged SDs is typical. SD/cytotoxic edema also propagates widely into healthy surrounding tissue as short-lasting, relatively harmless events so that regional electrocorticographic monitoring affords even remote detection of ischemic zones. Ischemia cannot only cause SD/cytotoxic edema but it can also be its consequence through inverse neurovascular coupling. Under this condition, ischemia does not start simultaneously in different regions but spreads in the tissue driven by SD/cytotoxic edema-induced microvascular constriction (= spreading ischemia). Spreading ischemia prolongs SD/cytotoxic edema. Thus, it increases the likelihood for the transition from SD/cytotoxic edema into cellular death. Vasogenic edema is the other major type of cerebral edema with relevance to ischemic stroke. It results from opening of the blood-brain barrier. SD/cytotoxic edema and vasogenic edema are distinct processes with important mutual interactions. This article is part of the Special Issue entitled 'Cerebral Ischemia'.

Epileptiform activity and spreading depolarization in the blood-brain barrier-disrupted peri-infarct hippocampus are associated with impaired GABAergic inhibition and synaptic plasticity

Peri-infarct opening of the blood-brain barrier may be associated with spreading depolarizations, seizures, and epileptogenesis as well as cognitive dysfunction. We aimed to investigate the mechanisms underlying neural network pathophysiology in the blood-brain barrier-dysfunctional hippocampus. Photothrombotic stroke within the rat neocortex was associated with increased intracranial pressure, vasogenic edema, and peri-ischemic blood-brain barrier dysfunction that included the ipsilateral hippocampus. Intrahippocampal recordings revealed electrographic seizures within the first week in two-thirds of animals, accompanied by a reduction in gamma and increase in theta frequency bands. Synaptic interactions were studied in parasagittal hippocampal slices at 24 h and seven days post-stroke. Field potential recordings in CA1 and CA3 uncovered multiple population spikes, epileptiform episodes, and spreading depolarizations at 24 h. Input-output analysis revealed that fEPSP-spike coupling was significantly enhanced at seven days. In addition, CA1 feedback and feedforward inhibition were diminished. Slices generating epileptiform activity at seven days revealed impaired bidirectional long-term plasticity following high and low-frequency stimulation protocols. Microarray and PCR data confirmed changes in expression of astrocyte-related genes and suggested downregulation in expression of GABA_A-receptor subunits. We conclude that blood-brain barrier dysfunction in the peri-infarct hippocampus is associated with early disinhibition, hyperexcitability, and abnormal synaptic plasticity.

Disrupting the blood-brain barrier by focused ultrasound induces sterile inflammation

MRI-guided pulsed focused ultrasound (pFUS) combined with systemic infusion of ultrasound contrast agent microbubbles (MB) causes localized blood-brain barrier (BBB) disruption that is currently being advocated for increasing drug or gene delivery in neurological diseases. The mechanical acoustic cavitation effects of opening the BBB by low-intensity pFUS+MB, as evidenced by contrast-enhanced MRI, resulted in an immediate damage-associated molecular pattern (DAMP) response including elevations in heat-shock protein 70, IL-1, IL-18, and TNFα indicative of a sterile inflammatory response (SIR) in the parenchyma. Concurrent with DAMP presentation, significant elevations in proinflammatory, antiinflammatory, and trophic factors along with neurotrophic and neurogenesis factors were detected; these elevations lasted 24 h. Transcriptomic analysis of sonicated brain supported the proteomic findings and indicated that the SIR was facilitated through the induction of the NFκB pathway. Histological evaluation demonstrated increased albumin in the parenchyma that cleared by 24 h along with TUNEL+ neurons, activated astrocytes, microglia, and increased cell adhesion molecules in the vasculature. Infusion of fluorescent beads 3 d before pFUS+MB revealed the infiltration of CD68+ macrophages at 6 d postsonication, as is consistent with an innate immune response. pFUS+MB is being considered as part of a noninvasive adjuvant treatment for malignancy or neurodegenerative diseases. These results demonstrate that pFUS+MB induces an SIR compatible with ischemia or mild traumatic brain injury. Further investigation will be required before this approach can be widely implemented in clinical trials.

Clinical Trials of Immunomodulation in Ischemic Stroke

Inflammatory mechanisms are currently considered as a prime target for stroke therapy. There is evidence from animal studies that immune signals and mediators can have both detrimental and beneficial effects in particular stages of the disease process. Moreover, several of these mechanisms are turned on with sufficient delay after ischemia onset to make them amenable to therapeutic intervention. Several clinical proof-of concept trials have investigated the efficacy of different immunomodulatory approaches in patients with stroke. Trials targeting the innate immune system have focused on reduction of microglial activation, inhibition of neutrophil migration, and interleukin-1 receptor blockade, suggesting that interleukin-1 receptor blockade may be a promising strategy. Studies aiming at halting T-cell migration have also been undertaken with controversial findings regarding prevention of infarct growth in neuroimaging studies. Consistently, recent proof-of-concept trials targeting lymphocytes with drugs such as natalizumab and fingolimod have yielded some promising results on clinical endpoints, but confirmation in larger trials is needed. At present, the understanding of the role of immune mechanisms in neurorepair and neurodegeneration is limited. Improving long-term brain function by mitigating prolonged neuroinflammation that was triggered by acute brain injury could be a strategy in addition to neuroprotection.

Blood-brain barrier breakdown and neovascularization processes after stroke and traumatic brain injury

PURPOSE OF REVIEW

Angiogenesis or vascular reorganization plays a role in recovery after stroke and traumatic brain injury (TBI). In this review, we have focused on two major events that occur during stroke and TBI from a vascular perspective - what is the process and time course of blood-brain barrier (BBB) breakdown? and how does the surrounding vasculature recover and facilitate repair?

RECENT FINDINGS

Despite differences in the primary injury, the BBB changes overlap between stroke and TBI. Disruption of BBB involves a series of events: formation of caveolae, trans and paracellular disruption, tight junction breakdown and vascular disruption. Confounding factors that need careful assessment and standardization are the severity, duration and extent of the stroke and TBI that influences BBB disruption. Vascular repair proceeds through long-term neovascularization processes: angiogenesis, arteriogenesis and vasculogenesis. Enhancing each of these processes may impart beneficial effects in endogenous recovery.

SUMMARY

Our understanding of BBB breakdown acutely after the cerebrovascular injury has come a long way; however, we lack a clear understanding of the course of BBB disruption and BBB recovery and the evolution of individual cellular events associated with BBB change. Neovascularization responses have been widely studied in stroke for their role in functional recovery but the role of vascular reorganization after TBI in recovery is much less defined.

Vasculoprotection as a Convergent, Multi-Targeted Mechanism of Anti-AD Therapeutics and Interventions

Using a variety of animal models of Alzheimer's disease (AD), there have been a number of recent studies reporting varying degrees of success with anti-AD therapeutics. The efficacies are often discussed in terms of the modulatory effects of the compounds tested on identified or assumed targets among the known (or proposed) pathogenic and neuroprotective mechanisms, largely within the context of the dominant amyloid cascade hypothesis. However, it is clear that several of the relatively more efficacious treatments tend to be multifunctional and target multiple pathological processes associated with AD including most commonly, oxidative and metabolic stress and neuroinflammation. Increasing evidence suggests that vascular and neurodegenerative pathologies often co-exist and that neurovascular dysfunction plays a critical role in the development or progression of AD. In this review, we will discuss the significance of vasculoprotection or neurovascular unit integrity as a common, multi-targeted mechanism underlying the reported efficacy of a majority of anti-AD therapeutics--amyloid-targeted or otherwise--while providing a strong support for future neurovascular-based treatment strategies and interventions.

Computational Pipeline for NIRS-EEG Joint Imaging of tDCS-Evoked Cerebral Responses-An Application in Ischemic Stroke

Transcranial direct current stimulation (tDCS) modulates cortical neural activity and hemodynamics. Electrophysiological methods (electroencephalography-EEG) measure neural activity while optical methods (near-infrared spectroscopy-NIRS) measure hemodynamics coupled through neurovascular coupling (NVC). Assessment of NVC requires development of NIRS-EEG joint-imaging sensor montages that are sensitive to the tDCS affected brain areas. In this methods paper, we present a software pipeline incorporating freely available software tools that can be used to target vascular territories with tDCS and develop a NIRS-EEG probe for joint imaging of tDCS-evoked responses. We apply this software pipeline to target primarily the outer convexity of the brain territory (superficial divisions) of the middle cerebral artery (MCA). We then present a computational method based on Empirical Mode Decomposition of NIRS and EEG time series into a set of intrinsic mode functions (IMFs), and then perform a cross-correlation analysis on those IMFs from NIRS and EEG signals to model NVC at the lesional and contralesional hemispheres of an ischemic stroke patient. For the contralesional hemisphere, a strong positive correlation between IMFs of regional cerebral hemoglobin oxygen saturation and the log-transformed mean-power time-series of IMFs for EEG with a lag of about -15 s was found after a cumulative 550 s stimulation of anodal tDCS. It is postulated that system identification, for example using a continuous-time autoregressive model, of this coupling relation under tDCS perturbation may provide spatiotemporal discriminatory features for the identification of ischemia. Furthermore, portable NIRS-EEG joint imaging can be incorporated into brain computer interfaces to monitor tDCS-facilitated neurointervention as well as cortical reorganization.

Synaptic plasticity in area CA1 of rat hippocampal slices following intraventricular application of albumin

Epileptogenesis following insults to the brain may be triggered by a dysfunctional blood-brain barrier (BBB) associated with albumin extravasation and activation of astrocytes. Using ex vivo recordings from the BBB-disrupted hippocampus after neocortical photothrombotic stroke, we previously demonstrated abnormal activity-dependent accumulation of extracellular potassium with facilitated generation of seizure like events and spreading depolarizations. Similar changes could be observed after intracerebroventricular (icv) application of albumin. We hypothesized that alterations in extracellular potassium and glutamate homeostasis might lead to alterations in synaptic interactions. We therefore assessed the effects of icv albumin on homo- and heterosynaptic plasticity in hippocampal CA1, 24h after a single injection or 7days after continuous infusion of icv albumin. We demonstrate alterations in both homo- and heterosynaptic plasticity compared to control conditions in ex vivo slice studies. Albumin-treated tissue reveals (1) reduced long-term depression following low-frequency stimulation; (2) increased long-term potentiation of population spikes in response to 20Hz stimulation; (3) potentiated responses to Schaffer collateral stimulation following high-frequency stimulation of the direct cortical input and low-frequency stimulation of alveus and finally, (4) TGFβ receptor II (TGFβR-II) involvement in albumin-induced homosynaptic plasticity changes. We conclude that albumin-induced network hyperexcitability is associated with abnormal homo- and heterosynaptic plasticity that could partly be reversed by interference with TGFβR-II-mediated signaling and therefore it might be an important factor in the process of epileptogenesis.

Antidepressant-like effects of sodium butyrate and its possible mechanisms of action in mice exposed to chronic unpredictable mild stress

Sodium butyrate (NaB) has exhibited neuroprotective activity. This study aimed to explore that NaB exerts beneficial effects on chronic unpredictable mild stress (CUMS)-induced depression-like behaviors and its possible mechanisms. The behavioral tests including sucrose preference test (SPT), open field test (OFT), tail suspension test (TST) and forced swimming test (FST) were to evaluate the antidepressant effects of NaB. Then changes of Nissl's body in the hippocampus, brain serotonin (5-HT) concentration, brain-derived neurotrophic factor (BDNF) and tight junctions (TJs) proteins level were assessed to explore the antidepressant mechanisms. Our results showed that CUMS caused significant depression-like behaviors, neuropathological changes, and decreased brain 5-HT concentration, TJs protein levels and BDNF expression in the hippocampus. However, NaB treatment significantly ameliorated behavioral deficits of the CUMS-induced mice, increased 5-HT concentration, increased BDNF expression, and up-regulated Occludin and zonula occludens-1(ZO-1) protein levels in the hippocampus, which demonstrated that NaB could partially restore CUMS-induced blood-brain barrier (BBB) impairments. Besides, the pathologic changes were alleviated. In conclusion, these results demonstrated that NaB significantly improved depression-like behaviors in CUMS-induced mice and its antidepressant actions might be related with, at least in part, the increasing brain 5-HT concentration and BDNF expression and restoring BBB impairments.

Electric stimulation of the ears ameliorated learning and memory impairment in rats with cerebral ischemia-reperfusion injury

Ear acupuncture enhances the secretion of acetylcholine, which has anti-inflammatory effects. Here we want to investigate the effect of electric stimulation (ES) of the ears on learning and memory impairment in rats with cerebral ischemia-reperfusion injury. At 24 h after reperfusion, 2-Hz ES was applied to the ears for 20 min/day (10 min for each ear) for 7 days continuously. The step-through time of the passive avoidance test was greater in the ES group than in the control group (300.0 ± 0.0 s vs 45.0 ± 26.7 s, p < 0.05). Our results showed that neither neurological deficit score nor motor functions were improved after 2-Hz ES (4.0 ± 0 vs 4.5 ± 0.8, p > 0.05). The numbers of nicotinic acetylcholine receptor α4 positively stained cells in the CA2 and dentate gyrus of the hippocampus were 19.0 ± 11.5 and 269.2 ± 79.3, respectively, in the ES group, which were greater than those in the control group (7.0 ± 5.9 and 165.5 ± 30.8, respectively) (both p < 0.05). These results suggested that 2-Hz ES of the ears ameliorated learning and memory impairment in rats with ischemia-reperfusion injury. ES of the ears has neuroprotective effects, which are related to acetylcholine release.

Cerebrovascular Dysfunction in Preeclamptic Pregnancies

Preeclampsia is a hypertensive, multisystem disorder of pregnancy that affects several organ systems, including the maternal brain. Cerebrovascular dysfunction during preeclampsia can lead to cerebral edema, seizures, stroke, and potentially maternal mortality. This review will discuss the effects of preeclampsia on the cerebrovasculature that may adversely affect the maternal brain, including cerebral blood flow (CBF) autoregulation and blood-brain barrier disruption and the resultant clinical outcomes including posterior reversible encephalopathy syndrome (PRES) and maternal stroke. Potential long-term cognitive outcomes of preeclampsia and the role of the cerebrovasculature are also reviewed.

Markers for blood-brain barrier integrity: how appropriate is Evans blue in the twenty-first century and what are the alternatives?

In recent years there has been a resurgence of interest in brain barriers and various roles their intrinsic mechanisms may play in neurological disorders. Such studies require suitable models and markers to demonstrate integrity and functional changes at the interfaces between blood, brain, and cerebrospinal fluid. Studies of brain barrier mechanisms and measurements of plasma volume using dyes have a long-standing history, dating back to the late nineteenth-century. Their use in blood-brain barrier studies continues in spite of their known serious limitations in in vivo applications. These were well known when first introduced, but seem to have been forgotten since. Understanding these limitations is important because Evans blue is still the most commonly used marker of brain barrier integrity and those using it seem oblivious to problems arising from its in vivo application. The introduction of HRP in the mid twentieth-century was an important advance because its reaction product can be visualized at the electron microscopical level, but it also has limitations. Advantages and disadvantages of these markers will be discussed together with a critical evaluation of alternative approaches. There is no single marker suitable for all purposes. A combination of different sized, visualizable dextrans and radiolabeled molecules currently seems to be the most appropriate approach for qualitative and quantitative assessment of barrier integrity.

Increased thrombin activity following reperfusion after ischemic stroke alters synaptic transmission in the hippocampus

Thrombin, a key player in thrombogenesis, affects cells in the brain through activation of its receptors. Low levels of thrombin activity are protective while high levels are toxic. We sought to quantify thrombin activity levels and their spatial distribution in brains of mice following reperfusion after ischemic stroke focusing on infarct, peri-infarct and contralateral areas. In order to find out the contribution of brain-derived thrombin, mRNA levels of both prothrombin and factor X were determined. Furthermore, we assessed the effect of thrombin levels that were measured in the ischemic brain on synaptic transmission. We found that in the brains of mice following transient middle cerebral artery occlusion, thrombin activity is elevated throughout the ischemic hemisphere, including in peri-infarct areas (90 ± 33 and 60 ± 18 mU/mL, in the infarct and peri-infarct areas, respectively, compared to 11 ± 3 and 12 ± 5 mU/mL, in the corresponding contralateral areas; mean ± SE; p < 0.05). Brain mRNA levels of prothrombin and, in particular, factor X are up-regulated in the ischemic core. Hippocampal slices treated with thrombin concentrations as found in the ischemic hemisphere show altered synaptic responses. We conclude that high thrombin activity following reperfusion after ischemic stroke may cause synaptic dysfunction. Following transient middle cerebral artery occlusion in mice, thrombin activity is elevated throughout the ischemic hemisphere, including in peri-infarct areas. Brain mRNA levels of prothrombin and factor X are up-regulated in the ischemic core. Thrombin is known to affect synaptic function in a concentration dependent manner and hippocampal slices treated with the concentrations found in the ischemic hemisphere show altered synaptic responses. We conclude that in ischemic stroke, the high brain thrombin activity found after reperfusion may cause synaptic dysfunction.

Dynamics of T cell responses after stroke

T cells are integral to the pathophysiology of stroke. The initial inflammatory cascade leads to T cell migration, which results in deleterious and protective effects mediated through CD4(+), CD(8)+, γδ T cells and regulatory T cells, respectively. Cytokines are central to the T cell responses, with key roles established for TNF-α, IFN-γ, IL-17, IL-21 and IL-10. Through communication with the systemic immune system via neural and hormonal pathways, there is also transient immunosuppression after severe strokes. With time, the inflammatory process eventually transforms to one more conducive of repair and recovery, though some evidence also suggests ongoing chronic inflammation. The role of antigen-specific T cell responses requires further investigation. As our understanding develops, there is increasing scope to modulate the T cell response after stroke.