The role of spreading depression, spreading depolarization and spreading ischemia in neurological disease

A clinical study of transcranial ultrasound as an adjuvant therapy for progressive cerebral infarction

The present study aimed to investigate the clinical efficacy of transcranial ultrasound as an adjuvant therapy in combination with small doses of urokinase (UK) for the treatment of progressive cerebral infarction. Sixty-one eligible patients with progressive cerebral infarction were successively and randomly assigned into one of the following groups; 30 patients to the treatment group (transcranial ultrasound + small doses of UK) and 31 patients to the control group (single small doses of UK). Based on conventional therapy, patients in the treatment group received transcranial ultrasound. The neural function deficit scale and curative effect scores of the two groups were recorded before treatment and on the 7th and 14th days after treatment. No differences in the neural function deficit scale between the two groups was observed before treatment, however, on the 7th and 14th days after treatment, a significant decrease was evident in the treatment group (P<0.01). The overall response rate was 100% in the treatment group and 74.2% in the control group, with a significant difference (P<0.01). Transcranial ultrasound is able to contribute to the thrombolytic effects of UK and prevent the progression of thrombi, subsequently aiding the recovery of neural functions.

Subarachnoid hemorrhage, spreading depolarizations and impaired neurovascular coupling

Aneurysmal subarachnoid hemorrhage (SAH) has devastating consequences on brain function including profound effects on communication between neurons and the vasculature leading to cerebral ischemia. Physiologically, neurovascular coupling represents a focal increase in cerebral blood flow to meet increased metabolic demand of neurons within active regions of the brain. Neurovascular coupling is an ongoing process involving coordinated activity of the neurovascular unit-neurons, astrocytes, and parenchymal arterioles. Neuronal activity can also influence cerebral blood flow on a larger scale. Spreading depolarizations (SD) are self-propagating waves of neuronal depolarization and are observed during migraine, traumatic brain injury, and stroke. Typically, SD is associated with increased cerebral blood flow. Emerging evidence indicates that SAH causes inversion of neurovascular communication on both the local and global level. In contrast to other events causing SD, SAH-induced SD decreases rather than increases cerebral blood flow. Further, at the level of the neurovascular unit, SAH causes an inversion of neurovascular coupling from vasodilation to vasoconstriction. Global ischemia can also adversely affect the neurovascular response. Here, we summarize current knowledge regarding the impact of SAH and global ischemia on neurovascular communication. A mechanistic understanding of these events should provide novel strategies to treat these neurovascular disorders.

Astroglia in neurological diseases

Astroglia encompass a subset of versatile glial cells that fulfill a major homeostatic role in the mammalian brain. Since any brain disease results from failure in brain homeostasis, astroglial cells are involved in many, if not all, aspects of neurological and/or psychiatric disorders. In this article, the roles of astrocytes as homeostatic cells in healthy and diseased brains are surveyed. These cells can mount the defence response to the insult of the brain, astrogliosis, when and where they display hypertrophy. Interestingly, astrocytes can alternatively display atrophy in some pathological conditions. Various pathologies, including Alexander and Alzheimer's diseases, amyotrophic lateral sclerosis, stroke and epilepsy, to mention a few, are discussed. Astrocytes could represent a novel target for medical intervention in the treatment of brain disorders.

Divergent effects of the T1174S SCN1A mutation associated with seizures and hemiplegic migraine

PURPOSE

To report the identification of the T1174S SCN1A (NaV 1.1) mutation in a three-generation family with both epileptic and familial hemiplegic migraine (FHM) phenotypes and clarify the pathomechanism.

METHODS

The five affected individuals underwent detailed clinical analyses. Mutation analyses was performed by direct sequencing of SCN1A; functional studies by expression in tsA-201 cells. A computational model was used to compare the effects of T1174S with those of a typical FHM mutation (Q1489K).

KEY FINDINGS

The proband had benign occipital epilepsy (BOE); two relatives had simple febrile seizures (FS) and later developed BOE. Two additional relatives had FHM without epilepsy or FS. All affected members and one obliged carrier carried the T1174S mutation. Functional effects were divergent: positive shift of the activation curve and deceleration of recovery from fast inactivation, consistent with loss of function, and increase of persistent current (I(NaP)), consistent with gain of function. The I(NaP) increase was inhibited by dialysis of the cytoplasm, consistent with a modulation. Therefore, as shown by the computational model, T1174S could in some conditions induce overall loss of function, and in others gain of function; Q1489K induced gain of function in all the conditions.

SIGNIFICANCE

Modulation of the properties of T1174S can lead to a switch between overall gain and loss of function, consistent with a switch between promigraine end epileptogenic effect and, thus, with coexistence of epileptic and FHM phenotypes in the same family. These findings may help to shed light on the complex genotype-phenotype relationship of SCN1A mutations.

Electrochemical Failure of the Brain Cortex Is More Deleterious When it Is Accompanied by Low Perfusion

Background and Purpose—

Clinical and experimental evidence suggests that spreading depolarization facilitates neuronal injury when its duration exceeds a certain time point, termed commitment point. We here investigated whether this commitment point is shifted to an earlier period, when spreading depolarization is accompanied by a perfusion deficit.

Methods—

Electrophysiological and cerebral blood flow changes were studied in a rat cranial window model followed by histological and immunohistochemical analyses of cortical damage.

Results—

In group 1, brain topical application of artificial cerebrospinal fluid (ACSF) with high K + concentration ([K + ] ACSF ) for 1 hour allowed us to induce a depolarizing event of fixed duration with cerebral blood flow fluctuations around the baseline (short-lasting initial hypoperfusions followed by hyperemia). In group 2, coapplication of the NO-scavenger hemoglobin ([Hb] ACSF ) with high [K + ] ACSF caused a depolarizing event of similar duration, to which a severe perfusion deficit was coupled (=spreading ischemia). In group 3, intravenous coadministration of the L-type calcium channel antagonist nimodipine with brain topical application of high [K + ] ACSF /[Hb] ACSF caused spreading ischemia to revert to spreading hyperemia. Whereas scattered neuronal injury occurred in the superficial cortical layers in the window areas of groups 1 and 3, necrosis of all layers with partial loss of the tissue texture and microglial activation were observed in group 2.

Conclusions—

The results suggest that electrochemical failure of the cortex is more deleterious when it is accompanied by low perfusion. Thus, the commitment point of the cortex is not a universal value but depends on additional factors, such as the level of perfusion.

Glucose modulation of spreading depression susceptibility

Spreading depression of Leão is an intense spreading depolarization (SD) wave associated with massive transmembrane ionic, water, and neurotransmitter shifts. Spreading depolarization underlies migraine aura, and occurs in brain injury, making it a potential therapeutic target. While susceptibility to SD can be modulated pharmacologically, much less is known about modulation by systemic physiological factors, such as the glycemic state. In this study, we systematically examined modulation of SD susceptibility by blood glucose in anesthetized rats under full physiological monitoring. Hyperglycemia and hypoglycemia were induced by insulin or dextrose infusion (blood glucose ∼40 and 400 mg/dL, respectively). Spreading depolarizations were evoked by direct cortical electrical stimulation to determine the intensity threshold, or by continuous topical KCl application to determine SD frequency. Hyperglycemia elevated the electrical SD threshold and reduced the frequency of KCl-induced SDs, without significantly affecting other SD properties. In contrast, hypoglycemia significantly prolonged individual and cumulative SD durations, but did not alter the electrical SD threshold, or SD frequency, amplitude or propagation speed. These data show that increased cerebral glucose availability makes the tissue resistant to SD.

Phenytoin inhibits the persistent sodium current in neocortical neurons by modifying its inactivation properties

The persistent Na⁺ current (I_NaP) is important for neuronal functions and can play a role in several pathologies, although it is small compared to the transient Na⁺ current (I_NaT). Notably, I_NaP is not a real persistent current because it undergoes inactivation with kinetics in the order of tens of seconds, but this property has often been overlooked. Na⁺ channel blockers, drugs used for treating epilepsy and other diseases, can inhibit I_NaP, but the mechanism of this action and the conditions in which I_NaP can be actually inhibited have not been completely clarified yet. We evaluated the action of phenytoin (PHT), a prototype anti-epileptic Na⁺ channel blocker, on I_NaP inactivation in pyramidal neurons of rat sensorimotor cortical slices at different concentrations, from 5 to 100 µM. PHT did not modify I_NaP evoked with depolarizing voltage ramps of 50 or 100 mVs⁻¹, but decreased I_NaP evoked by slower voltage ramps (10 mVs⁻¹). However, at all of the tested concentrations, PHT decreased I_NaP evoked by faster ramps when they were preceded by inactivating pre-pulses. Moreover, PHT shifted towards negative potentials the voltage-dependence of I_NaP inactivation and accelerated its kinetics of development also at depolarized potentials (+40 mV), not consistently with a simple inactivated state stabilizer. Therefore, our study shows a prominent PHT effect on I_NaP inactivation rather than an open channel block, which is instead often implied. I_NaP is inhibited by PHT only in conditions that induce major I_NaP inactivation. These results highlight the importance of I_NaP inactivation not only for physiological functions but also as drug target, which could be shared by other therapeutic drugs. Through this action PHT can reduce I_NaP-induced long-lasting pathological depolarisations and intracellular sodium overload, whereas shorter I_NaP actions should not be modified. These properties set the conditions of efficacy and the limits of PHT as I_NaP inhibitor.

[Cortical spreading depolarization: an underestimated phenomenon after human brain injury?]

BACKGROUND AND PURPOSE

Cortical spreading depolarization waves (CSD) are massive temporary neuronal depolarizations that slowly propagate through cerebral cortex from brain injured tissue. CSD waves cause temporary brain electrical silence, local tissue hemodynamic responses and metabolic increases required for cellular repolarization. Due to this metabolic imbalance in compromised tissue, CSD could participate in the extension of secondary insults after brain injury. From the analysis of the human literature, we aimed at determine the CSD incidences in brain injured patients.

METHODS

Medline(®) research: "cortical spreading depolarization" and "brain injury", and "human" limits from 1980 to 2011.

RESULTS

Ten original studies were found. CSD occurred in more than 50% of patients monitored for CSD after different brain injury (traumatic, subarachnoid haemorrhage, malignant stroke, spontaneous intracranial haemorrhage). When detected, CSD were associated with a significantly worse neurological outcome. To be identified, CSD required specific devices that directly record cortical electrical depression by a multipolar electrode positioned at the cortex surface or by indirect analysis of hemodynamic and metabolic consequences of the CSD.

CONCLUSIONS

When monitoring tools are available, CSD occur in more than 50% of brain injured patients. Today results come from clinical research. Future studies are necessary to determine the impact of CSD detection on care and potential therapeutics aimed at counteracting these adverse events.

Impaired neurovascular coupling to ictal epileptic activity and spreading depolarization in a patient with subarachnoid hemorrhage: possible link to blood-brain barrier dysfunction

Spreading depolarization describes a sustained neuronal and astroglial depolarization with abrupt ion translocation between intraneuronal and extracellular space leading to a cytotoxic edema and silencing of spontaneous activity. Spreading depolarizations occur abundantly in acutely injured human brain and are assumed to facilitate neuronal death through toxic effects, increased metabolic demand, and inverse neurovascular coupling. Inverse coupling describes severe hypoperfusion in response to spreading depolarization. Ictal epileptic events are less frequent than spreading depolarizations in acutely injured human brain but may also contribute to lesion progression through increased metabolic demand. Whether abnormal neurovascular coupling can occur with ictal epileptic events is unknown. Herein we describe a patient with aneurysmal subarachnoid hemorrhage in whom spreading depolarizations and ictal epileptic events were measured using subdural opto-electrodes for direct current electrocorticography and regional cerebral blood flow recordings with laser-Doppler flowmetry. Simultaneously, changes in tissue partial pressure of oxygen were recorded with an intraparenchymal oxygen sensor. Isolated spreading depolarizations and clusters of recurrent spreading depolarizations with persistent depression of spontaneous activity were recorded over several days followed by a status epilepticus. Both spreading depolarizations and ictal epileptic events where accompanied by hyperemic blood flow responses at one optode but mildly hypoemic blood flow responses at another. Of note, quantitative analysis of Gadolinium-diethylene-triamine-pentaacetic acid (DTPA)-enhanced magnetic resonance imaging detected impaired blood-brain barrier integrity in the region where the optode had recorded the mildly hypoemic flow responses. The data suggest that abnormal flow responses to spreading depolarizations and ictal epileptic events, respectively, may be associated with blood-brain barrier dysfunction.

Clinical review: neuromonitoring - an update

Critically ill patients are frequently at risk of neurological dysfunction as a result of primary neurological conditions or secondary insults. Determining which aspects of brain function are affected and how best to manage the neurological dysfunction can often be difficult and is complicated by the limited information that can be gained from clinical examination in such patients and the effects of therapies, notably sedation, on neurological function. Methods to measure and monitor brain function have evolved considerably in recent years and now play an important role in the evaluation and management of patients with brain injury. Importantly, no single technique is ideal for all patients and different variables will need to be monitored in different patients; in many patients, a combination of monitoring techniques will be needed. Although clinical studies support the physiologic feasibility and biologic plausibility of management based on information from various monitors, data supporting this concept from randomized trials are still required.

Blood-brain barrier opening to large molecules does not imply blood-brain barrier opening to small ions

Neuroimaging of exogenous tracer extravasation has become the technique of choice in preclinical and clinical studies of blood-brain barrier permeability. Such tracers have a larger molecular weight than small ions, neurotransmitters and many drugs. Therefore, it is assumed that tracer extravasation indicates both permeability to these and the cancelation of the electrical polarization across the barrier. Electrophysiological anomalies following intracarotideal administration of dehydrocholate, a bile salt causing extravasation of the albumin-binding tracer Evans blue, seemingly supported this. By contrast, electron microscopic studies suggested a different hierarchical pattern of blood-brain barrier dysfunction, a milder degree of impairment being characterized by increased function of the transcellular pathway and a severe degree by opening of the tight junctions. This would imply that the extravasation of macromolecules can occur before disruption of the electrical barrier. However, functional evidence for this has been lacking. Here, we further investigated the electrophysiological anomalies following intracarotideal application of dehydrocholate in rats and found that it caused focal cerebral ischemia by middle cerebral artery thrombosis, the electrophysiological recordings being characteristic of long-lasting spreading depolarization. These observations indicated that intracarotideal dehydrocholate is not a suitable model to study the isolated dysfunction of the blood-brain barrier. Second, we studied the topical application of dehydrocholate to the brain and the application of mannitol into the carotid artery. In both models, we found significant extravasation of Evans blue but no changes in either extracellular potassium or the CO(2)-dependent intracortical direct current deflection. The latter is assumed to depend on the proton gradient across the barrier in rats which we confirmed in additional experiments in vivo and in vitro. The stability of the extracellular potassium concentration and the CO(2)-dependent direct current deflection are two functional tests which indicate the integrity of the electrical barrier. Hence, our results provide functional evidence that the blood-brain barrier opening to large molecules does not necessarily imply the opening to small ions consistent with the hierarchy of damage in the previous electron microscopic studies.

Ventricular tachycardia during basilar-type migraine attack

Autonomic dysfunction is a characteristic of migraine attacks, rarely, even cardiac repolarization abnormalities have been associated with migraine. We report a case of documented ventricular tachycardia during basilar-type migraine attack. The therapeutic implications of such a co-occurrence as well as a possible relationship between ventricular tachycardia and the underlying biology of basilar-type migraine are discussed.

Criteria for the diagnosis of noninfectious and infectious complications after aneurysmal subarachnoid hemorrhage in DISCHARGE-1

Patients with aneurysmal subarachnoid hemorrhage (aSAH) frequently develop secondary noninfectious and infectious complications that have an important impact on clinical course and outcome. We here report on criteria for the diagnosis of the most important complications after aSAH based on clinical status, neuroimaging, and laboratory tests, including cerebrospinal fluid parameters. These criteria will be used for a retrospective analysis of aSAH patients who were recruited at the Charité Berlin for the CoOperative Study on Brain Injury Depolarisations (COSBID) before the Depolarisations in Ischaemia after Subarachnoid Haemorrhage-1 (DISCHARGE-1) trial started. Moreover, they serve for the survey of complications in DISCHARGE-1. We also report on a customized, Web-based database that has been developed for the documentation of the clinical course after aSAH. This database is used for the COSBID outcome study on aSAH and for DISCHARGE-1.

Cortical spreading depression dynamics can be studied using intrinsic optical signal imaging in gyrencephalic animal cortex

OBJECTIVE

The aim of this study was to co-record electrical changes using electrocorticography (ECoG) and blood volume changes using intrinsic optical signal (IOS) imaging during the induction, propagation, and termination of cortical spreading depolarizations (CSDs).

METHODS

Anesthetized male swine were craniotomized and monitored over 16-20 h. A ten-contact electrode strip was placed on the cortex of one hemisphere for ECoG. An optical imaging recording was implemented using a camera with an optical bandpass filter (564 nm, FWHM:15 nm) and a full spectrum light source. CSDs were induced by mechanical and KCl stimulation. Co-occurrences of ECoG baseline shifts and blood volume changes around electrodes were identified.

RESULTS

A mean of 3 CSDs per hour were induced, in a total of 4 swine during 80 h of recording. The propagation of the CSDs increased progressively over the monitoring time. IOS enabled us to clearly visualize the induction, propagation, and termination of CSDs with a spatial resolution within the sub-millimeter range. Every CSD recorded using ECoG could also be observed in IOS imaging, although some blood volume changes of CSDs were observed that terminated before reaching any of the ECoG electrodes.

CONCLUSION

IOS imaging enables an in vivo evaluation of CSD dynamics over a large surface of gyrencephalic brain.

Decreased cortical spreading depolarizations in neurosurgical patients being given ketamine

Evaluation of: Hertle DN, Dreier JP, Woitzik J et al.; Cooperative Study of Brain Injury Depolarizations (COSBID). Effect of analgesics and sedatives on the occurrence of spreading depolarizations accompanying acute brain injury. Brain 135(Pt 8), 2390–2398 (2012). This retrospective review by the Cooperative Study of Brain Injury Depolarizations group of 115 patients correlates the occurrence of cortical spreading depolarization (SD), measured with cortical electrodes, with the type of sedation used during monitoring in the intensive care unit. SD has recently been implicated in the progression of acute brain injury, and this study represents the first systematic approach to attempt to understand whether the deleterious effects of SD can be impacted with drug therapy. A significantly decreased probability of SD occurrence was documented with ketamine, but none of the five other drugs that were studied. This effect was seen across all days of monitoring and seemed to have a dose-dependent effect. In evaluating clusters of SD (which most likely contribute to injury progression), ketamine remained significantly associated with decreased likelihood of clusters, along with a weaker effect with propofol and a surprising positive association with midazolam. Owing to the retrospective nature of the study, no causal association can be concluded, although the suppressive effect of NMDA receptor antagonists is consistent with prior animal data. This work will provide critical clinical groundwork for carefully designed clinical trials focused on SD suppression and outcome.

Proposed mechanism of cerebral vasospasm: our hypothesis and current topics

Increased vascular contractility plays an important role in the development of cerebral vasospasm following subarachnoid hemorrhage (SAH). Increased vascular contractility can be attributed to either endothelial dysfunction or increased contractility of vascular smooth muscle. Endothelial damage and dysfunction cause impairment of endothelium-dependent vasodilation of the cerebral artery after SAH. In addition to endothelial damage and dysfunction, receptor upregulation in vascular smooth muscle contributes to the induction and enhancement of contractile responses to agonists. Our recent data revealed that feedback regulation of the activity of the G protein-coupled receptor and myofilament Ca(2+) sensitivity is impaired after SAH. This impaired feedback regulation is suggested to cause a sustained contractile response to various agonists, thereby contributing to increased vascular contractility. In addition, three current topics are reviewed: endothelin type A receptor antagonists, 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors for treatment, and cortical spreading depolarization for the mechanism of cerebral vasospasm.

Evaluation of intracranial electrocorticography recording strips and tissue partial pressure of oxygen and temperature probes for radio-frequency-induced heating

Spreading depolarization and subsequent cortical spreading ischemia have been recognized as new mechanisms of ischemic damage in patients with subarachnoid hemorrhage. We are investigating these mechanisms using intracranial implanted devices and perform magnetic resonance imaging (MRI) to monitor for early or delayed ischemia. Before patients undergo MRI with intracranially implanted devices, MR safety with respect to heating induced by radio frequency (RF) needs to be carefully considered. We tested an electrocorticography (ECoG) six-contact electrode strip (Adtech TS06R-SP10X-000) at 1.5 T and a tissue oxygenation/temperature Licox™ probe (model CC1.P1) at 3.0 T for RF-induced heating as MRI safety tests were not available at these field strengths. We observed no relevant temperature increases for the ECoG probe at 1.5 T. For the Licox probe, temperature increased beyond 4°C when measurements were performed at 3.0 T. Our data suggest that MRI can be safely performed in patients with an implanted ECoG electrode strip at 1.5 and 3.0 T. For the Licox probe, MRI can be performed at 1.5 T according to safety regulations, but at 3.0 T, temperature increases pose a significant risk for tissue damage due to RF-induced heating.

Intensive Care Management of Subarachnoid Haemorrhage

Aneurysmal subarachnoid haemorrhage (SAH) is a devastating disease associated with high mortality and poor outcome in many survivors. Aggressive treatment by a comprehensive multidisciplinary team is associated with improved outcome, but the intensive care management of SAH presents significant challenges. Multimodal neuromonitoring may detect secondary insults before irreversible neuronal damage has occurred, and is increasingly being used to guide treatment. This article reviews current trends in the intensive care management of SAH from aspects of initial resuscitation to recent developments in the prevention and management of complications, including delayed cerebral ischaemia. Evidence from clinical trials and recent consensus guidance is reviewed.

Subarachnoid blood converts neurally evoked vasodilation to vasoconstriction in rat brain cortex

The matching of blood flow to regional brain function, called functional hyperemia or neurovascular coupling, involves the coordinated activity of neurons, astrocytes, and parenchymal arterioles. Under physiological conditions, localized neuronal activation leads to elevated astrocyte endfoot Ca(2+) and vasodilation, resulting in an increase in cerebral blood flow. In this study, we examined the impact of subarachnoid hemorrhage (SAH) on neurovascular coupling. SAH model rats received two injections of autologous blood into the cisterna magna 24 h apart. Cortical brain slices from SAH model animals were prepared 4 days after the initial blood injection. Arteriolar diameter and astrocyte endfoot Ca(2+) were simultaneously measured using two-photon microscopy. As expected, neuronal activity evoked by electrical field stimulation (EFS) caused an elevation in endfoot Ca(2+) and vasodilation in brain slices from control animals. However, in brain slices from SAH animals, EFS induced a similar increase in astrocyte endfoot Ca(2+) that caused arteriolar constriction rather than vasodilation. Vasoconstriction was observed in approximately 90% of brain slices from SAH animals in response to EFS, with 40% exhibiting a sustained vasoconstriction, 30% exhibiting a transient vasoconstriction -(diameter restored within 1 min after EFS), and 20% responded with a biphasic response (brief vasodilation followed by -vasoconstriction). This inversion of neurovascular coupling may play a role in the development of neurological deficits following SAH.

Pannexin1 stabilizes synaptic plasticity and is needed for learning

Pannexin 1 (Panx1) represents a class of vertebrate membrane channels, bearing significant sequence homology with the invertebrate gap junction proteins, the innexins and more distant similarities in the membrane topologies and pharmacological sensitivities with gap junction proteins of the connexin family. In the nervous system, cooperation among pannexin channels, adenosine receptors, and K_ATP channels modulating neuronal excitability via ATP and adenosine has been recognized, but little is known about the significance in vivo. However, the localization of Panx1 at postsynaptic sites in hippocampal neurons and astrocytes in close proximity together with the fundamental role of ATP and adenosine for CNS metabolism and cell signaling underscore the potential relevance of this channel to synaptic plasticity and higher brain functions. Here, we report increased excitability and potently enhanced early and persistent LTP responses in the CA1 region of acute slice preparations from adult Panx1^−/− mice. Adenosine application and N-methyl-D-aspartate receptor (NMDAR)-blocking normalized this phenotype, suggesting that absence of Panx1 causes chronic extracellular ATP/adenosine depletion, thus facilitating postsynaptic NMDAR activation. Compensatory transcriptional up-regulation of metabotropic glutamate receptor 4 (grm4) accompanies these adaptive changes. The physiological modification, promoted by loss of Panx1, led to distinct behavioral alterations, enhancing anxiety and impairing object recognition and spatial learning in Panx1^−/− mice. We conclude that ATP release through Panx1 channels plays a critical role in maintaining synaptic strength and plasticity in CA1 neurons of the adult hippocampus. This result provides the rationale for in-depth analysis of Panx1 function and adenosine based therapies in CNS disorders.

Spreading ischemia after aneurysmal subarachnoid hemorrhage

Spreading depolarization (SD) is a wave of mass neuronal and glial depolarization associated with net influx of cations and water. Prolonged SDs facilitate neuronal death. SD induces tone alterations in cerebral resistance arterioles, leading to either transient hyperperfusion (physiological neurovascular coupling) in healthy tissue or hypoperfusion (inverse neurovascular coupling = spreading ischemia) in tissue at risk for progressive damage. Spreading ischemia has been shown experimentally in an animal model replicating the conditions present following aneurysmal subarachnoid hemorrhage (aSAH), in animal models of the ischemic core and penumbra following middle cerebral artery occlusion, and in patients with aSAH. In animals, spreading ischemia produced widespread cortical necrosis. In patients, spreading ischemia occurred in temporal correlation with ischemic lesion development early and late after aSAH. We briefly review important features of SD and spreading ischemia following aSAH.

The roles of early brain injury in cerebral vasospasm following subarachnoid hemorrhage: from clinical and scientific aspects

Cerebral vasospasm research has been focused on investigating the mechanisms of prolonged delayed vasoconstriction of cerebral arteries following subarachnoid hemorrhage (SAH). However, it has been clarified that induction of significant vasodilation of such arteries does not lead to better overall outcomes in SAH patients. On the other hand, early brain injury, such as cortical spreading depression, early cortical depolarization waves, and impairment of neurovascular coupling, is seen acutely after SAH and may play a significant role in early impairment of brain function following SAH. These results clearly indicate that it is time to reconsider what causes this early brain damage and dictates patient outcome following SAH; classical delayed cerebral vasospasm following SAH might be an epiphenomenon. It is of utmost importance to investigate whether early brain injury and delayed cerebral vasospasm correlate with each other following SAH or are independent. Recent results of cerebral vasospasm research indicates future directions, and such investigations would lead to better outcome for SAH patients.

COSBID-M3: a platform for multimodal monitoring, data collection, and research in neurocritical care

Neuromonitoring in patients with severe brain trauma and stroke is often limited to intracranial pressure (ICP); advanced neuroscience intensive care units may also monitor brain oxygenation (partial pressure of brain tissue oxygen, P(bt)O(2)), electroencephalogram (EEG), cerebral blood flow (CBF), or neurochemistry. For example, cortical spreading depolarizations (CSDs) recorded by electrocorticography (ECoG) are associated with delayed cerebral ischemia after subarachnoid hemorrhage and are an attractive target for novel therapeutic approaches. However, to better understand pathophysiologic relations and realize the potential of multimodal monitoring, a common platform for data collection and integration is needed. We have developed a multimodal system that integrates clinical, research, and imaging data into a single research and development (R&D) platform. Our system is adapted from the widely used BCI2000, a brain-computer interface tool which is written in the C++ language and supports over 20 data acquisition systems. It is optimized for real-time analysis of multimodal data using advanced time and frequency domain analyses and is extensible for research development using a combination of C++, MATLAB, and Python languages. Continuous streams of raw and processed data, including BP (blood pressure), ICP, PtiO2, CBF, ECoG, EEG, and patient video are stored in an open binary data format. Selected events identified in raw (e.g., ICP) or processed (e.g., CSD) measures are displayed graphically, can trigger alarms, or can be sent to researchers or clinicians via text message. For instance, algorithms for automated detection of CSD have been incorporated, and processed ECoG signals are projected onto three-dimensional (3D) brain models based on patient magnetic resonance imaging (MRI) and computed tomographic (CT) scans, allowing real-time correlation of pathoanatomy and cortical function. This platform will provide clinicians and researchers with an advanced tool to investigate pathophysiologic relationships and novel measures of cerebral status, as well as implement treatment algorithms based on such multimodal measures.

Cerebral glucose and spreading depolarization in patients with aneurysmal subarachnoid hemorrhage

The pathogenesis of delayed cerebral ischemia (DCI) is multifactorial and not completely elucidated. Our objective was to determine if episodes of spreading depolarization (SD) are reflected in compromised levels of extracellular glucose monitored by bedside microdialysis (MD) in aneurysmal subarachnoid hemorrhage (aSAH) patients. Patients with aSAH, prospectively included in the COSBID (CoOperative Study on Brain Injury Depolarisations) protocol (Berlin, Heidelberg), had hourly monitoring of cerebral glucose by MD and in parallel electrocorticographic (ECoG) monitoring for SD detection on day of admission until days 10-14 after aSAH. Cerebral MD probes were placed in the vascular territory at risk for DCI. Twenty-one aSAH patients (53.3 ± 9.1 years; mean ± standard deviation), classified according to the World Federation of Neurosurgical Societies (WFNS) in low (I-III, 11) and high (IV-V, 10) grades, were studied. Of these, 13 patients (62%) presented with DCI. Median glucose was 1.48 (0.00-8.79). Median occurrence of SD was 7 (0-66)/patients. High WFNS grade (WFNS grades IV-V) patients had more SDs (p = 0.027), while the overall glucose level did not differ. In high-grade SAH patients, SDs were more frequent. Individually, the occurrence of SD was not linked to local deviations (neither high nor low) from the LOWESS (locally weighted scatterplot smoothing) trend curve for extracellular glucose concentrations. Rapid-sampling MD techniques and analyses of SD clusters may elucidate more detail of the relationship between SD and brain energy metabolism.

Full-band electrocorticography of spreading depolarizations in patients with aneurysmal subarachnoid hemorrhage

Cortical spreading depolarizations (CSDs) are a pathologic mechanism occurring in patients with aneurysmal subarachnoid hemorrhage and may contribute to delayed cerebral ischemia. We conducted a pilot study to determine the durations of depolarizations as measured by the negative direct current shifts in electrocorticography. Cortical electrode strips were placed in six patients (aged 35-63 years, Fisher grade 4, World Federation of Neurosurgical Societies [WFNS] 3-4) with ruptured aneurysms treated by clip ligation. Full-band electrocorticography was performed by direct current amplification (g.USBamp, Guger Tec, Graz, Austria) with ±250-mV range, 24-bit digitization, and recording/display with a customized BCI2000 platform. We recorded 191 CSDs in 4 patients, and direct current shifts of CSD (n = 403) were measured at 20 electrodes. Amplitudes were 7.2 mV (median; quartiles 6.2, 7.9), and durations were 2 min 14 s (1:53, 2:45). Ten direct current shifts in two patients with delayed infarcts were longer than 10 min, ranging up to 28 min. Taken together with previous studies, results suggest a threshold of 3-3.5 min to distinguish a normally distributed class of short CSDs with spreading hyperemia from prolonged CSDs with initial spreading ischemia. Results further demonstrate the clinical feasibility of direct current electrocorticography to monitor CSDs and assess their role in the pathology and management of subarachnoid hemorrhage.

Clusters of spreading depolarizations are associated with disturbed cerebral metabolism in patients with aneurysmal subarachnoid hemorrhage

BACKGROUND AND PURPOSE

We studied the dynamics of extracellular brain tissue concentrations of glucose, lactate, pyruvate, and glutamate during the occurrence of spreading depolarizations (SDs) in patients with aneurysmal subarachnoid hemorrhage.

METHODS

In this prospective observational study, patients with aneurysmal subarachnoid hemorrhage received multimodal cerebral monitoring, including intracranial pressure, cerebral microdialysis, and subdural electrocorticography.

RESULTS

Seven of the 17 recruited patients had intracerebral hemorrhage, acute ischemia and severe brain oedema leading to acute ischemic neurological deficits associated with early disturbance of metabolism at the recording site. They displayed a total of 130 SDs. The remaining 10 patients without acute ischemic neurological deficits exhibited 138 single SDs and 68 SDs in clusters. In patients without acute ischemic neurological deficits, clustered SDs were associated with a significant transient decrease in glucose and increase in lactate compared with baseline during the first 140 minutes after SDs. Moreover, the number of clustered SDs correlated with the outcome (R=-0.659; P<0.01).

CONCLUSIONS

SDs can propagate in nonischemic human brain tissue. Clusters of SDs are related to metabolic changes suggestive of ongoing secondary damage in primarily nonischemic brain tissue.

Introducing a nationwide registry: the Swiss study on aneurysmal subarachnoid haemorrhage (Swiss SOS)

BACKGROUND

Aneurysmal subarachnoid haemorrhage (aSAH) is a haemorrhagic form of stroke and occurs in a younger population compared with ischaemic stroke or intracerebral haemorrhage. It accounts for a large proportion of productive life-years lost to stroke. Its surgical and medical treatment represents a multidisciplinary effort. Due to the complexity of the disease, the management remains difficult to standardise and quality of care is accordingly difficult to assess.

OBJECTIVE

To create a registry to assess management parameters of patients treated for aSAH in Switzerland.

METHODS

A cohort study was initiated with the aim to record characteristics of patients admitted with aSAH, starting January 1st 2009. Ethical committee approval was obtained or is pending from the institutional review boards of all centres. In the study period, seven Swiss hospitals (five university [U], two non-university medical centres) harbouring a neurosurgery department, an intensive care unit and an interventional neuroradiology team so far agreed to participate in the registry (Aarau, Basel [U], Bern [U], Geneva [U], Lausanne [U], St. Gallen, Zürich [U]). Demographic and clinical parameters are entered into a common database.

DISCUSSION

This database will soon provide (1) a nationwide assessment of the current standard of care and (2) the outcomes for patients suffering from aSAH in Switzerland. Based on data from this registry, we can conduct cohort comparisons or design diagnostic or therapeutic studies on a national level. Moreover, a standardised registration system will allow healthcare providers to assess the quality of care.

Peri-infarct blood-brain barrier dysfunction facilitates induction of spreading depolarization associated with epileptiform discharges

Recent studies showed that spreading depolarizations (SDs) occurs abundantly in patients following ischemic stroke and experimental evidence suggests that SDs recruit tissue at risk into necrosis. We hypothesized that BBB opening with consequent alterations of the extracellular electrolyte composition and extravasation of albumin facilitates generation of SDs since albumin mediates an astrocyte transcriptional response with consequent disturbance of potassium and glutamate homeostasis. Here we show extravasation of Evans blue-albumin complex into the hippocampus following cortical photothrombotic stroke in the neighboring neocortex. Using extracellular field potential recordings and exposure to serum electrolytes we observed spontaneous SDs in 80% of hippocampal slices obtained from rats 24 h after cortical photothrombosis. Hippocampal exposure to albumin for 24 h through intraventricular application together with serum electrolytes lowered the threshold for the induction of SDs in most slices irrespective of the pathway of stimulation. Exposing acute slices from naive animals to albumin led also to a reduced SD threshold. In albumin-exposed slices the onset of SDs was usually associated with larger stimulus-induced accumulation of extracellular potassium, and preceded by epileptiform activity, which was also observed during the recovery phase of SDs. Application of ifenprodil (3 μM), an NMDA-receptor type 2 B antagonist, blocked stimulus dependent epileptiform discharges and generation of SDs in slices from animals treated with albumin in-vivo. We suggest that BBB opening facilitates the induction of peri-infarct SDs through impaired homeostasis of K+.

Effects of the neurological wake-up test on clinical examination, intracranial pressure, brain metabolism and brain tissue oxygenation in severely brain-injured patients

Introduction

Daily interruption of sedation (IS) has been implemented in 30 to 40% of intensive care units worldwide and may improve outcome in medical intensive care patients. Little is known about the benefit of IS in acutely brain-injured patients.

Methods

This prospective observational study was performed in a neuroscience intensive care unit in a tertiary-care academic center. Twenty consecutive severely brain-injured patients with multimodal neuromonitoring were analyzed for levels of brain lactate, pyruvate and glucose, intracranial pressure (ICP), cerebral perfusion pressure (CPP) and brain tissue oxygen tension (P_btO₂) during IS trials.

Results

Of the 82 trial days, 54 IS-trials were performed as interruption of sedation and analgesics were not considered safe on 28 days (34%). An increase in the FOUR Score (Full Outline of UnResponsiveness score) was observed in 50% of IS-trials by a median of three (two to four) points. Detection of a new neurologic deficit occurred in one trial (2%), and in one-third of IS-trials the trial had to be stopped due to an ICP-crisis (> 20 mmHg), agitation or systemic desaturation. In IS-trials that had to be aborted, a significant increase in ICP and decrease in P_btO₂ (P < 0.05), including 67% with critical values of P_btO₂ < 20 mmHg, a tendency to brain metabolic distress (P < 0.07) was observed.

Conclusions

Interruption of sedation revealed new relevant clinical information in only one trial and a large number of trials could not be performed or had to be stopped due to safety issues. Weighing pros and cons of IS-trials in patients with acute brain injury seems important as related side effects may overcome the clinical benefit.

Sustained NMDA receptor activation by spreading depolarizations can initiate excitotoxic injury in metabolically compromised neurons

Spreading depolarizations (SDs) are slowly propagating waves of near-complete neuronal and glial depolarization. SDs have been recorded in patients with brain injury, and the incidence of SD significantly correlates with outcome severity. Although it is well accepted that the ionic dyshomeostasis of SD presents a severe metabolic burden, there is currently limited understanding of SD-induced injury processes at a cellular level. In the current study we characterized events accompanying SD in the hippocampal CA1 region of murine brain slices, using whole-cell recordings and single-cell Ca(2+) imaging. We identified an excitatory phase that persisted for approximately 2 min following SD onset, and accompanied with delayed dendritic ionic dyshomeostasis. The excitatory phase coincided with a significant increase in presynaptic glutamate release, evidenced by a transient increase in spontaneous EPSC frequency and paired-pulse depression of evoked EPSCs. Activation of NMDA receptors (NMDARs) during this late excitatory phase contributed to the duration of individual neuronal depolarizations and delayed recovery of extracellular slow potential changes. Selectively targeting the NMDAR activation following SD onset (by delayed pressure application of a competitive NMDAR antagonist) significantly decreased the duration of cellular depolarizations. Recovery of dendritic Ca(2+) elevations following SD were also sensitive to delayed NMDA antagonist application. Partial inhibition of neuronal energy metabolism converted SD into an irrecoverable event with persistent Ca(2+) overload and membrane compromise. Delayed NMDAR block was sufficient to prevent these acute injurious events in metabolically compromised neurons. These results identify a significant contribution of a late component of SD that could underlie neuronal injury in pathological circumstances.

Anesthetic effects on susceptibility to cortical spreading depression

Cortical spreading depression (CSD) is a transient neuronal and glial depolarization and disruption of membrane ionic gradients that propagates slowly across the cerebral cortex. Recent clinical and experimental evidence has implicated CSD in the pathophysiology of migraines and neuronal injury states. In the current study, we examined the influence of four different anesthetics (propofol, dexmedetomidine, isoflurane, pentobarbital) on CSD susceptibility in a KCl application animal model. We found that isoflurane and dexmedetomidine suppressed CSD frequency, and tended to reduce the CSD propagation speed. Our data suggest that these anesthetics may be therapeutically beneficial in preventing CSD in diverse neuronal injury states.

Persistent astroglial swelling accompanies rapid reversible dendritic injury during stroke-induced spreading depolarizations

Spreading depolarizations are a key event in the pathophysiology of stroke, resulting in rapid dendritic beading, which represents acute damage to synaptic circuitry. The impact of spreading depolarizations on the real-time injury of astrocytes during ischemia is less clear. We used simultaneous in vivo 2-photon imaging and electrophysiological recordings in adult mouse somatosensory cortex to examine spreading depolarization-induced astroglial structural changes concurrently with signs of neuronal injury in the early periods of focal and global ischemia. Astrocytes in the metabolically compromised ischemic penumbra-like area showed a long lasting swelling response to spontaneous spreading depolarizations despite rapid dendritic recovery in a photothrombotic occlusion model of focal stroke. Astroglial swelling was often facilitated by recurrent depolarizations and the magnitude of swelling strongly correlated with the total duration of depolarization. In contrast, spreading depolarization-induced astroglial swelling was transient in normoxic healthy tissue. In a model of transient global ischemia, the occurrence of a single spreading depolarization elicited by a bilateral common carotid artery occlusion coincided with astroglial swelling alongside dendritic beading. With immediate reperfusion, dendritic beading subsides. Astroglial swelling was either transient during short ischemic periods distinguished by a short-lasting spreading depolarization, or persistent during severe ischemia characterized by a long-lasting depolarization with the ultraslow negative voltage component. We propose that persistent astroglial swelling is initiated and exacerbated during spreading depolarization in brain tissue with moderate to severe energy deficits, disrupting astroglial maintenance of normal homeostatic function thus contributing to the negative outcome of ischemic stroke as astrocytes fail to provide neuronal support.

Adenosine receptor activation is responsible for prolonged depression of synaptic transmission after spreading depolarization in brain slices

Spreading depolarization (SD) is a slowly propagating, coordinated depolarization of brain tissue, which is followed by a transient (5-10min) depression of synaptic activity. The mechanisms for synaptic depression after SD are incompletely understood. We examined the relative contributions of action potential failure and adenosine receptor activation to the suppression of evoked synaptic activity in murine brain slices. Focal micro-injection of potassium chloride (KCl) was used to induce SD and synaptic potentials were evoked by electrical stimulation of Schaffer collateral inputs to hippocampal area Cornu Ammonis area 1 (CA1). SD was accompanied by loss of both presynaptic action potentials (as assessed from fiber volleys) and field excitatory postsynaptic potentials (fEPSPs). Fiber volleys recovered rapidly upon neutralization of the extracellular direct current (DC) potential, whereas fEPSPs underwent a secondary suppression phase lasting several minutes. Paired-pulse ratio was elevated during the secondary suppression period, consistent with a presynaptic mechanism of synaptic depression. A transient increase in extracellular adenosine concentration was detected during the period of secondary suppression. Antagonists of adenosine A1 receptors (8-cyclopentyl-1,3-dipropylxanthine [DPCPX] or 8-cyclopentyl-1,3-dimethylxanthine [8-CPT]) greatly accelerated fEPSP recovery and abolished increases in paired-pulse ratio normally observed after SD. The duration of fEPSP suppression was correlated with both the duration of the DC shift and the area of tissue depolarized, consistent with the model that adenosine accumulates in proportion to the metabolic burden of SD. These results suggest that in brain slices, the duration of the DC shift approximately defined the period of action potential failure, but the secondary depression of evoked responses was in large part due to endogenous adenosine accumulation after SD.

Connexin 36 promotes cortical spreading depolarization and ischemic brain damage

Cortical spreading depolarization (CSD) promotes the progression of neuronal injury after cerebral ischemia. However, the mechanisms of propagation of postischemic CSD events are still unclear. In this study we characterized the role of the main neuronal gap junction protein connexin 36 (Cx36) in generating postischemic CSDs. In Cx36-deficient mice and controls we occluded the distal middle cerebral artery. To detect CSD events we recorded the direct current and laser Doppler flow. In addition, locomotor function and the infarct size were determined. Cx36-deficient mice had significantly fewer and shorter CSD events than wild-type controls. Additionally, Cx36 deletion is neuroprotective, leading to a better functional outcome and decreased infarct size after ischemia. These results suggest a detrimental role for Cx36 after ischemia, possibly by promoting CSD.

Injury and repair in the neurovascular unit

The neurovascular unit provides a conceptual framework for investigating the pathophysiology of how brain cells die after stroke, brain injury, and neurodegeneration. Emerging data now suggest that this concept can be further extended. Cell-cell signaling between neuronal, glial, and vascular elements in the brain not only mediates the mechanisms of acute injury, but integrated responses in these same elements may also be required for recovery as the entire neurovascular unit attempts to reorganize and remodel. Understanding the common signals and substrates of this transition between acute injury and delayed repair in the neurovascular unit may reveal useful paradigms for augmenting neuronal, glial, and vascular plasticity in damaged and diseased brain.

Pathophysiologic cascades in ischemic stroke

Many advances have been achieved in terms of understanding the molecular and cellular mechanisms of ischemic stroke. But thus far, clinically effective neuroprotectants remain elusive. In this minireview, we summarize the basics of ischemic cascades after stroke, covering neuronal death mechanisms, white matter pathophysiology, and inflammation with an emphasis on microglia. Translating promising mechanistic knowledge into clinically meaningful stroke drugs is very challenging. An integrative approach that encompasses the multimodal and multicell signaling phenomenon of stroke will be required to move forward.

Peri-infarct flow transients predict outcome in rat focal brain ischemia

Spreading depolarizations are accompanied by transient changes in cerebral blood flow (CBF). In a post hoc analysis of previously studied control rats we analyzed CBF time courses after middle cerebral artery occlusion in the rat in order to test whether intra-ischemic flow, reperfusion, and different parameters of peri-infarct flow transients (PIFTs) (amplitude, number) can predict outcome. Sprague-Dawley rats anesthetized with either halothane (n=23) or isoflurane (n=32) underwent 90-min filament occlusion of the middle cerebral artery followed by 72 h of reperfusion. The infarct size was determined by 2,3,5-triphenyltetrazolium chloride staining. Relative CBF changes were monitored by laser Doppler flowmetry at 4-5 mm lateral, and 1-2mm posterior to Bregma. An additional filament occlusion study (n=12) was performed to validate that PIFTs were coupled to direct current shifts of spreading depolarization. The PIFT-direct current shift study revealed that every PIFT was associated with a negative direct current shift typical of spreading depolarization. Post-hoc analysis showed that the number of PIFTs, especially with the combination of intra-ischemic level of flow, can predict the development of cortical infarcts. These findings show that PIFTs can serve as an early biomarker in predicting outcome in preclinical animal studies.

Migraine changes the brain: neuroimaging makes its mark

PURPOSE OF REVIEW

This review summarizes key findings of the current literature on functional neuroimaging in migraine and describes how these studies have changed our view of the disorder.

RECENT FINDINGS

Recent studies have started not only to investigate the global cerebral activation pattern during migraine attacks, but to address specific aspects of migraine attacks such as photophobia, osmophobia as well as pain perception with the aim of disentangling the underlying mechanisms. There is also more and more evidence that the migraine brain is abnormal even outside of attacks and that repeated attacks are leading to functional and structural alterations in the brain, which may in turn drive the transformation of migraine to its chronic form. Some new results are pinpointing toward a potential role of interesting new brain areas in migraine pathophysiology such as the temporal cortex or the basal ganglia.

SUMMARY

Neuroimaging studies are beginning to shed light on the mechanisms underlying the development and evolution of migraine and its specific symptoms. Future studies have the potential to also improve our understanding of established and upcoming treatment approaches and to monitor treatment effects in an objective and noninvasive way.

Temporo-spectral imaging of intrinsic optical signals during hypoxia-induced spreading depression-like depolarization

Spreading depression (SD) is characterized by a sustained near-complete depolarization of neurons, a massive depolarization of glia, and a negative deflection of the extracellular DC potential. These electrophysiological signs are accompanied by an intrinsic optical signal (IOS) which arises from changes in light scattering and absorption. Even though the underlying mechanisms are unclear, the IOS serves as non-invasive tool to define the spatiotemporal dynamics of SD in brain slices. Usually the tissue is illuminated by white light, and light reflectance or transmittance is monitored. Using a polychromatic, fast-switchable light source we now performed temporo-spectral recordings of the IOS associated with hypoxia-induced SD-like depolarization (HSD) in rat hippocampal slices kept in an interface recording chamber. Recording full illumination spectra (320–680 nm) yielded distinct reflectance profiles for the different phases of HSD. Early during hypoxia tissue reflectance decreased within almost the entire spectrum due to cell swelling. HSD was accompanied by a reversible reflectance increase being most pronounced at 400 nm and 460 nm. At 440 nm massive porphyrin absorption (Soret band) was detected. Hypotonic solutions, Ca²⁺-withdrawal and glial poisoning intensified the reflectance increase during HSD, whereas hypertonic solutions dampened it. Replacement of Cl^- inverted the reflectance increase. Inducing HSD by cyanide distorted the IOS and reflectance at 340–400 nm increased irreversibly. The pronounced changes at short wavelengths (380 nm, 460 nm) and their cyanide sensitivity suggest that block of mitochondrial metabolism contributes to the IOS during HSD. For stable and reliable IOS recordings during HSD wavelengths of 460–560 nm are recommended.

Blood-brain barrier dysfunction and epilepsy: pathophysiologic role and therapeutic approaches

The blood-brain barrier (BBB) is located within a unique anatomic interface and has functional ramifications to most of the brain and blood cells. In the past, the BBB was considered a pharmacokinetic impediment to antiepileptic drug penetration into the brain; nowadays it is becoming increasingly evident that targeting of the damaged or dysfunctional BBB may represent a therapeutic approach to reduce seizure burden. Several studies have investigated the mechanisms linking the onset and sustainment of seizures to BBB dysfunction. These studies have shown that the BBB is at the crossroad of a multifactorial pathophysiologic process that involves changes in brain milieu, altered neuroglial physiology, development of brain inflammation, leukocyte-endothelial interactions, faulty angiogenesis, and hemodynamic changes leading to energy mismatch. A number of knowledge gaps, conflicting points of view, and discordance between clinical and experimental data currently characterize this field of neuroscience. As more pieces are added to this puzzle, it is apparent that each mechanism needs to be validated in an appropriate clinical context. We now offer a BBB-centric view of seizure disorders, linking several aspects of seizures and epilepsy physiopathology to BBB dysfunction. We have reviewed the therapeutic, antiseizure effect of drugs that promote BBB repair. We also present BBB neuroimaging as a tool to correlate BBB restoration to seizure mitigation. Add-on cerebrovascular drug could be of efficacy in reducing seizure burden when used in association with neuronal antiepileptic drugs.

Enhanced neuronal excitability in adult rat brainstem causes widespread repetitive brainstem depolarizations with cardiovascular consequences

The brainstem of the adult rat is relatively resistant to spreading depolarization (SD) but after enhancement of excitability SD can be evoked by local application of KCl. In the present experiments, we observed that the enhanced excitability even triggers prolonged periods of repetitive depolarizations (RDs), which elicit significant cardiovascular changes. In contrast to KCl-evoked SDs with amplitudes of ∼24 mV and spreading velocity of 4 mm/min, spontaneous RDs had amplitudes of 7 to 12 mV, propagated up to 30 times faster than KCl-evoked SDs, and depolarized larger brainstem areas including the contralateral side. Similarly as SD, RDs depended on glutamatergic neurotransmission and were blocked by MK-801 or by the calcium channel blocker agatoxin. They depended on sodium channels and were blocked by tetrodotoxin. Functionally, the invasion of RDs into the spinal trigeminal and other nuclei evoked bursts of action potentials, indicating that specific neuronal systems are affected. In fact, during episodes of RDs the blood pressure and the local blood flow at the surface of the brainstem and the cortex increased substantially. Brainstem RDs did not propagate into the cerebral cortex. We propose to consider brainstem RPs as a pathophysiological mechanism whose significance for brainstem disease states should be further explored.

Is spreading depolarization characterized by an abrupt, massive release of gibbs free energy from the human brain cortex?

In the evolution of the cerebral cortex, the sophisticated organization in a steady state far away from thermodynamic equilibrium has produced the side effect of two fundamental pathological network events: ictal epileptic activity and spreading depolarization. Ictal epileptic activity describes the partial disruption, and spreading depolarization describes the near-complete disruption of the physiological double Gibbs-Donnan steady state. The occurrence of ictal epileptic activity in patients has been known for decades. Recently, unequivocal electrophysiological evidence has been found in patients that spreading depolarizations occur abundantly in stroke and brain trauma. The authors propose that the ion changes can be taken to estimate relative changes in Gibbs free energy from state to state. The calculations suggest that in transitions from the physiological state to ictal epileptic activity to spreading depolarization to death, the cortex releases Gibbs free energy in a stepwise fashion. Spreading depolarization thus appears as a twilight state close to death. Consistently, electrocorticographic recordings in the core of focal ischemia or after cardiac arrest display a smooth transition from the initial spreading depolarization component to the later ultraslow negative potential, which is assumed to reflect processes in cellular death.