Spreading Diffusion-Restriction Events in the Gyrencephalic Brain After Subarachnoid Hemorrhage Revealed by Continuous Magnetic Resonance Imaging

BACKGROUND

How widely spreading depolarizations (SDs) propagate through the gyrencephalic brain, including sulci and deeper cortical areas, remains an important clinical question. Here, we investigated SDs that occur spontaneously after subarachnoid placement of autologous blood clots in sulci of the juvenile swine brain.

METHODS

To investigate the three-dimensional spread of waves, animals underwent continuous diffusion-weighted magnetic resonance imaging (DW-MRI) for up to 6 h following clot placement. SD is the mechanism of the cytotoxic edema of developing infarction that is diagnosed by DW-MRI, and DW-MRI also captures transient diffusion restriction caused by SD in less injured or healthy brains. Here, images (b = 0, 375, and 750) were acquired across five coronal slices with 1.25 × 1.25-mm in-plane resolution and 5-mm slice thickness, and the protocol was repeated every 6.83-9.15 s. Spatial drift correction, temporal smoothing, and signal intensity normalization were applied to generate videos of diffusion signal intensity changes for each coronal slice.

RESULTS

Review of video data from five animals revealed ten discrete events consisting of focal diffusion restriction that propagated through cerebral cortex. All events originated in the cortex surrounding the sulcal clot, either in the gyrus (n = 4) or in the sulcal depth (n = 6). In six cases, two to three independent waves spread simultaneously in medial, lateral, and antero-posterior directions. Waves traveled within sulcal walls, traversed the depths of sulci to re-emerge on the adjacent gyrus, and, in three cases, spread fully around the dorsolateral convexity. One event spread deep to olfactory regions along midline cortex, and no events were observed contralateral to the subarachnoid clot.

CONCLUSIONS

Together, these results suggest that SDs in the injured gyrencephalic brain originate near the injury focus and can spread extensively through the cortex to wide and deep uninjured regions. These findings have implications for transient neurologic deficits in the neurocritically ill patient and relevance to patient monitoring and therapeutics.

Oxygen-Induced and pH-Induced Direct Current Artifacts on Invasive Platinum/Iridium Electrodes for Electrocorticography

BACKGROUND

Spreading depolarization (SD) and the initial, still reversible phase of neuronal cytotoxic edema in the cerebral gray matter are two modalities of the same process. SD may thus serve as a real-time mechanistic biomarker for impending parenchyma damage in patients during neurocritical care. Using subdural platinum/iridium (Pt/Ir) electrodes, SD is observed as a large negative direct current (DC) shift. Besides SD, there are other causes of DC shifts that are not to be confused with SD. Here, we systematically analyzed DC artifacts in ventilated patients by observing changes in the fraction of inspired oxygen. For the same change in blood oxygenation, we found that negative and positive DC shifts can simultaneously occur at adjacent Pt/Ir electrodes.

METHODS

Nurses and intensivists typically increase blood oxygenation by increasing the fraction of inspired oxygen at the ventilator before performing manipulations on the patient. We retrospectively identified 20 such episodes in six patients via tissue partial pressure of oxygen (p_tiO₂) measurements with an intracortical O₂ sensor and analyzed the associated DC shifts. In vitro, we compared Pt/Ir with silver/silver chloride (Ag/AgCl) to assess DC responses to changes in pO₂, pH, or 5-min square voltage pulses and investigated the effect of electrode polarization on pO₂-induced DC artifacts.

RESULTS

Hyperoxygenation episodes started from a p_tiO₂ of 37 (30-40) mmHg (median and interquartile range) reaching 71 (50-97) mmHg. During a total of 20 episodes on each of six subdural Pt/Ir electrodes in six patients, we observed 95 predominantly negative responses in six patients, 25 predominantly positive responses in four patients, and no brain activity changes. Adjacent electrodes could show positive and negative responses simultaneously. In vitro, Pt/Ir in contrast with Ag/AgCl responded to changes in either pO₂ or pH with large DC shifts. In response to square voltage pulses, Pt/Ir falsely showed smaller DC shifts than Ag/AgCl, with the worst performance under anoxia. In response to pO₂ increase, Pt/Ir showed DC positivity when positively polarized and DC negativity when negatively polarized.

CONCLUSIONS

The magnitude of pO₂-induced subdural DC shifts by approximately 6 mV was similar to that of SDs, but they did not show a sequential onset at adjacent recording sites, could be either predominantly negative or positive in contrast with the always negative DC shifts of SD, and were not accompanied by brain activity depression. Opposing polarities of pO₂-induced DC artifacts may result from differences in baseline electrode polarization or subdural p_tiO₂ inhomogeneities relative to subdermal p_tiO₂ at the quasi-reference.

Spreading Depolarization After Chronic Subdural Hematoma Evacuation: Associated Clinical Risk Factors and Influence on Clinical Outcome

BACKGROUND

Chronic subdural hematoma (cSDH) is a common neurosurgical condition responsible for excess morbidity, particularly in the geriatric population. Recovery after evacuation is complicated by fluctuating neurological deficits in a high proportion of patients. We previously demonstrated that spreading depolarizations (SDs) may be responsible for some of these events. In this study, we aim to determine candidate risk factors for probable SD and assess the influence of probable SD on outcome.

METHODS

We used two cohorts who underwent surgery for cSDH. The first cohort (n = 40) had electrocorticographic monitoring to detect SD. In the second cohort (n = 345), we retrospectively identified subjects with suspected SD based on the presence of transient neurological symptoms not explained by structural etiology or ictal activity on electroencephalography. We extracted standard demographic and outcome variables for comparisons and modeling.

RESULTS

Of 345 subjects, 80 (23%) were identified in the retrospective cohort as having probable SD. Potential risk factors included history of hypertension, worse clinical presentation on the Glasgow Coma Scale, and lower Hounsfield unit density and volume of the preoperative subdural hematoma. Probable SD was associated with multiple worse-outcome measures, including length of stay and clinical outcomes, but not increased mortality. On a multivariable analysis, probable SD was independently associated with worse outcome, determined by the Glasgow Outcome Scale score at the first clinic follow-up (odds ratio 1.793, 95% confidence interval 1.022-3.146) and longer hospital length of stay (odds ratio 7.952, 95% confidence interval 4.062-15.563).

CONCLUSIONS

Unexplained neurological deficits after surgery for cSDH occur in nearly a quarter of patients and may be explained by SD. We identified several potential candidate risk factors. Patients with probable SD have worse outcomes, independent of other baseline risk factors. Further data with gold standard monitoring are needed to evaluate for possible predictors of SD to target therapies to a high-risk population.

Neuronal Swelling: A Non-osmotic Consequence of Spreading Depolarization

An acute reduction in plasma osmolality causes rapid uptake of water by astrocytes but not by neurons, whereas both cell types swell as a consequence of lost blood flow (ischemia). Either hypoosmolality or ischemia can displace the brain downwards, potentially causing death. However, these disorders are fundamentally different at the cellular level. Astrocytes osmotically swell or shrink because they express functional water channels (aquaporins), whereas neurons lack functional aquaporins and thus maintain their volume. Yet both neurons and astrocytes immediately swell when blood flow to the brain is compromised (cytotoxic edema) as following stroke onset, sudden cardiac arrest, or traumatic brain injury. In each situation, neuronal swelling is the direct result of spreading depolarization (SD) generated when the ATP-dependent sodium/potassium ATPase (the Na+/K+ pump) is compromised. The simple, and incorrect, textbook explanation for neuronal swelling is that increased Na+ influx passively draws Cl- into the cell, with water following by osmosis via some unknown conduit. We first review the strong evidence that mammalian neurons resist volume change during acute osmotic stress. We then contrast this with their dramatic swelling during ischemia. Counter-intuitively, recent research argues that ischemic swelling of neurons is non-osmotic, involving ion/water cotransporters as well as at least one known amino acid water pump. While incompletely understood, these mechanisms argue against the dogma that neuronal swelling involves water uptake driven by an osmotic gradient with aquaporins as the conduit. Promoting clinical recovery from neuronal cytotoxic edema evoked by spreading depolarizations requires a far better understanding of molecular water pumps and ion/water cotransporters that act to rebalance water shifts during brain ischemia.

Aneurysmal Subarachnoid Hemorrhage: Review of the Pathophysiology and Management Strategies

PURPOSE OF REVIEW

Aneurysmal subarachnoid hemorrhage remains a devastating disease process despite medical advances made over the past 3 decades. Much of the focus was on prevention and treatment of vasospasm to reduce delayed cerebral ischemia and improve outcome. In recent years, there has been a shift of focus onto early brain injury as the precursor to delayed cerebral ischemia. This review will focus on the most recent data surrounding the pathophysiology of aneurysmal subarachnoid hemorrhage and current management strategies.

RECENT FINDINGS

There is a paucity of successful trials in the management of subarachnoid hemorrhage likely related to the targeting of vasospasm. Pathophysiological changes occurring at the time of aneurysmal rupture lead to early brain injury including cerebral edema, inflammation, and spreading depolarization. These events result in microvascular collapse, vasospasm, and ultimately delayed cerebral ischemia. Management of aneurysmal subarachnoid hemorrhage has remained the same over the past few decades. No recent trials have resulted in new treatments. However, our understanding of the pathophysiology is rapidly expanding and will advise future therapeutic targets.

N,N-Dimethyltryptamine attenuates spreading depolarization and restrains neurodegeneration by sigma-1 receptor activation in the ischemic rat brain

Dimethyltryptamine (DMT), an endogenous ligand of sigma-1 receptors (Sig-1Rs), acts against systemic hypoxia, but whether DMT may prevent cerebral ischemic injury is unexplored. Here global forebrain ischemia was created in anesthetized rats and aggravated with the induction of spreading depolarizations (SDs) and subsequent short hypoxia before reperfusion. Drugs (DMT, the selective Sig-1R agonist PRE-084, the Sig-1R antagonist NE-100, or the serotonin receptor antagonist asenapine) were administered intravenously alone or in combination while physiological variables and local field potential from the cerebral cortex was recorded. Neuroprotection and the cellular localization of Sig-1R were evaluated with immunocytochemistry. Plasma and brain DMT content was measured by 2D-LC-HRMS/MS. The affinity of drugs for cerebral Sig-1R was evaluated with a radioligand binding assay. Both DMT and PRE-084 mitigated SDs, counteracted with NE-100. Further, DMT attenuated SD when co-administered with asenapine, compared to asenapine alone. DMT reduced the number of apoptotic and ferroptotic cells and supported astrocyte survival. The binding affinity of DMT to Sig-1R matched previously reported values. Sig-1Rs were associated with the perinuclear cytoplasm of neurons, astrocytes and microglia, and with glial processes. According to these data, DMT may be considered as adjuvant pharmacological therapy in the management of acute cerebral ischemia.

Specific activation of GluN1-N2B NMDA receptors underlies facilitation of cortical spreading depression in a genetic mouse model of migraine with reduced astrocytic glutamate clearance

Migraine is a common but poorly understood sensory circuit disorder. Mouse models of familial hemiplegic migraine (FHM, a rare monogenic form of migraine with aura) show increased susceptibility to cortical spreading depression (CSD, the phenomenon that underlies migraine aura and can activate migraine headache mechanisms), allowing an opportunity to investigate the mechanisms of CSD and migraine onset. In FHM type 2 (FHM2) knock-in mice with reduced expression of astrocytic Na⁺, K⁺-ATPases, the reduced rate of glutamate uptake into astrocytes can account for the facilitation of CSD initiation. Here, we investigated the underlying mechanisms and show that the reduced rate of glutamate clearance in FHM2 mice results in increased amplitude and slowing of rise time and decay of the NMDA receptor (NMDAR) excitatory postsynaptic current (EPSC) elicited in layer 2/3 pyramidal cells by stimulation of neuronal afferents in somatosensory cortex slices. The relative increase in NMDAR activation in FHM2 mice is activity-dependent, being larger after high-frequency compared to low-frequency afferent activity. Inhibition of GluN1-N2B NMDARs, which hardly affected the NMDAR EPSC in wild-type mice, rescued the increased and prolonged activation of NMDARs as well as the facilitation of CSD induction and propagation in FHM2 mice. Our data suggest that the enhanced susceptibility to CSD in FHM2 is mainly due to specific activation of extrasynaptic GluN1-N2B NMDARs and point to these receptors as possible therapeutic targets for prevention of CSD and migraine.

Comparative analysis of spreading depolarizations in brain slices exposed to osmotic or metabolic stress

BACKGROUND

Recurrent spreading depolarizations (SDs) occur in stroke and traumatic brain injury and are considered as a hallmark of injury progression. The complexity of conditions associated with SD in the living brain encouraged researchers to study SD in live brain slice preparations, yet methodological differences among laboratories complicate integrative data interpretation. Here we provide a comparative evaluation of SD evolution in live brain slices, in response to selected SD triggers and in various media, under otherwise standardized experimental conditions.

METHODS

Rat live coronal brain slices (350 μm) were prepared (n = 51). Hypo-osmotic medium (Na+ content reduced from 130 to 60 mM, HM) or oxygen-glucose deprivation (OGD) were applied to cause osmotic or ischemic challenge. Brain slices superfused with artificial cerebrospinal fluid (aCSF) served as control. SDs were evoked in the control condition with pressure injection of KCl or electric stimulation. Local field potential (LFP) was recorded via an intracortical glass capillary electrode, or intrinsic optical signal imaging was conducted at white light illumination to characterize SDs. TTC and hematoxylin-eosin staining were used to assess tissue damage.

RESULTS

Severe osmotic stress or OGD provoked a spontaneous SD. In contrast with SDs triggered in aCSF, these spontaneous depolarizations were characterized by incomplete repolarization and prolonged duration. Further, cortical SDs under HM or OGD propagated over the entire cortex and occassionally invaded the striatum, while SDs in aCSF covered a significantly smaller cortical area before coming to a halt, and never spread to the striatum. SDs in HM displayed the greatest amplitude and the most rapid propagation velocity. Finally, spontaneous SD in HM and especially under OGD was followed by tissue injury.

CONCLUSIONS

While the failure of Na+/K+ ATP-ase is thought to impair tissue recovery from OGD-related SD, the tissue swelling-related hyper excitability and the exhaustion of astrocyte buffering capacity are suggested to promote SD evolution under osmotic stress. In contrast with OGD, SD propagating under hypo-osmotic condition is not terminal, yet it is associated with irreversible tissue injury. Further investigation is required to understand the mechanistic similarities or differences between the evolution of SDs spontaneously occurring in HM and under OGD.

Which Spreading Depolarizations Are Deleterious To Brain Tissue?

Spreading depolarizations (SDs) are profound disruptions of cellular homeostasis that slowly propagate through gray matter and present an extraordinary metabolic challenge to brain tissue. Recent work has shown that SDs occur commonly in human patients in the neurointensive care setting and have established a compelling case for their importance in the pathophysiology of acute brain injury. The International Conference on Spreading Depolarizations (iCSD) held in Boca Raton, Florida, in September of 2018 included a discussion session focused on the question of "Which SDs are deleterious to brain tissue?" iCSD is attended by investigators studying various animal species including invertebrates, in vivo and in vitro preparations, diseases of acute brain injury and migraine, computational modeling, and clinical brain injury, among other topics. The discussion included general agreement on many key issues, but also revealed divergent views on some topics that are relevant to the design of clinical interventions targeting SDs. A draft summary of viewpoints offered was then written by a multidisciplinary writing group of iCSD members, based on a transcript of the session. Feedback of all discussants was then formally collated, reviewed and incorporated into the final document. It is hoped that this report will stimulate collection of data that are needed to develop a more nuanced understanding of SD in different pathophysiological states, as the field continues to move toward effective clinical interventions.

Spreading depolarization occurs in repeating, recognizable, patient-specific patterns after human brain injury

Background and Objective: Electrocorticographic (ECoG) measurement of spreading depolarization (SD) has led to significant advances in understanding of injury progression in neuro ICU patients.  However, SD can be difficult to recognize in ECoG regions with high artifact. Heuristics for ECoG analysis within these regions would be highly valuable.Methods: Patients requiring craniotomy following subarachnoid hemorrhage, malignant hemispheric stroke, or traumatic brain injury were enrolled in this study. ECoG leads were placed intraoperatively and scoring of SDs was completed twice; once using traditional criteria and again with the intention of finding SD patterns. Utilizing covariance structures, graphical overlay and various measures surrounding DC shift, SDs were evaluated for patterns.Results: SD patterns were consistently observed and were unique to each patient and lead placement. No more than five different patterns were noted for any given patient, and statistical analysis utilizing covariance structures revealed high intra-pattern consistency.Conclusion: This validation of internal patient specific patterns offers more insight into ECoG readings of high artifact regions. This, in addition to traditional SD scoring heuristics, offers another scoring tool for the neuro-ICU care of patient experiencing SD. Furthermore, description of neurologic disease by its SD patterns may offer a new direction for precision medicine.

Remote and Persistent Alterations in Glutamate Receptor Subunit Composition Induced by Spreading Depolarizations in Rat Brain

Spreading depolarizations (SDs) are massive breakdowns of ion homeostasis in the brain's gray matter and are a necessary pathologic mechanism for lesion development in various injury models. However, injury-induced SDs also propagate into remote, healthy tissue where they do not cause cell death, yet their functional long-term effects are unknown. Here we induced SDs in uninjured cortex and hippocampus of Sprague-Dawley rats to study their impact on glutamate receptor subunit expression after three days. We find that both cortical and hippocampal tissue exhibit changes in glutamate receptor subunit expression, including GluA1 and GluN2B, suggesting that SDs in healthy brain tissue may have a role in plasticity. This study is the first to show prolonged effects of SDs on glutamate signaling and has implications for neuroprotection strategies aimed at SD suppression.

Association of cortical spreading depression and seizures in patients with medically intractable epilepsy

OBJECTIVE

Monitoring of the ultra-low frequency potentials, particularly cortical spreading depression (CSD), is excluded in epilepsy monitoring due to technical barriers imposed by the scalp ultra-low frequency electroencephalogram (EEG). As a result, clinical studies of CSD have been limited to invasive EEG. Therefore, the occurrence of CSD and its interaction with epileptiform field potentials (EFP) require investigation in epilepsy monitoring.

METHODS

Using a novel AC/DC-EEG approach, the occurrence of DC potentials in patients with intractable epilepsy presenting different symptoms of aura was investigated during long-term video-EEG monitoring.

RESULTS

Various forms of slow potentials, including simultaneous negative direct current (DC) potentials and prolonged EFP, propagated negative DC potentials, and non-propagated single negative DC potentials were recorded from the scalp of the epileptic patients. The propagated and single negative DC potentials preceded the prolonged EFP with a time lag and seizure appeared at the final shoulder of some instances of the propagated negative DC potentials. The slow potential deflections had a high amplitude and prolonged duration and propagated slowly through the brain. The high-frequency EEG was suppressed in the vicinity of the negative DC potential propagations.

CONCLUSIONS

The study is the first to report the recording of the propagated and single negative DC potentials with EFP at the scalp of patients with intractable epilepsy. The negative DC potentials preceded the prolonged EFP and may trigger seizures. The propagated and single negative DC potentials may be considered as CSD.

SIGNIFICANCE

Recordings of CSD may serve as diagnostic and prognostic monitoring tools in epilepsy.

Intravascular Endothelin-1 does not trigger or increase susceptibility to Spreading Depolarizations

Objectives

Spreading depolarizations (SD) likely manifest as aura in migraineurs. Triggers are unknown although vascular events have been implicated. Direct carotid puncture has been reported to trigger migraine with aura. The potent vasoconstrictor endothelin-1 (ET-1), which can be released from the endothelium under pathological conditions, may play a role. Here, we tested whether intracarotid ET-1 infusion triggers SD and whether systemic ET-1 infusion increases the susceptibility to SD.

Methods

Carotid infusions were performed in mice (C57BL/6, male) through a catheter placed at the carotid bifurcation via the external carotid artery. Intracarotid ET-1 (1.25 nmol/ml) was infused at various rates (2–16 μl/min) with or without heparin in the catheter and compared with vehicle infusion (PBS with 0.01% acetic acid) or sham-operated mice (n = 5). Systemic infusions ET-1 (1 nmol/kg, n = 7) or vehicle (n = 7) infusions were performed in rats (Sprague-Dawley, male) via the tail vein. Electrical SD threshold and KCl-induced SD frequency were measured after the infusion.

Results

Intracarotid infusion of saline (n = 19), vehicle (n = 7) or ET-1 (n = 12) all triggered SDs at various proportions (21%, 14% and 50%, respectively). These were often associated with severe hypoperfusion prior to SD onset. Heparinizing the infusion catheter completely prevented SD occurrence during the infusions (n = 8), implicating microembolization from carotid thrombi as the trigger. Sham-operated mice never developed SD. Systemic infusion of ET-1 did not affect the electrical SD threshold or KCl-induced SD frequency.

Conclusion

Intravascular ET-1 does not trigger or increase susceptibility to SD. Microembolization was the likely trigger for migraine auras in patients during carotid puncture.

NMDA receptors sustain but do not initiate neuronal depolarization in spreading depolarization

Spreading depolarization (SD) represents a neurological process characterized by a massive, self-sustaining wave of brain cell depolarization. Understanding its mechanism is important for treating ischemic or hemorrhagic stroke and migraine with aura. Many believed that ion fluxes through NMDA receptors (NMDARs) are responsible for neuronal transmembrane currents of SD. However, the explicit role of NMDARs remains ambiguous. This is in part due to the limitation of traditional pharmacological approaches in resolving the contribution of NMDARs in different intercellular and intracellular processes of SD. Here, we applied single-cell blockade and genetic deletion methods to remove functional NMDARs from individual hippocampal CA1 neurons in order to examine the role of NMDARs in the depolarization mechanism without affecting the propagation of SD. We analyzed neuronal membrane potential changes to demonstrate that NMDARs are not required for initiating the depolarization. Consistently, neuronal input resistance (R_N) revealed a sharp decline at the start of SD, which was unaffected by blocking NMDARs. Instead, the recovery of both membrane potential and R_N during the late phase of SD was facilitated by inhibition of NMDARs, indicating that NMDARs are responsible for sustaining the depolarization. Our results strongly indicate that NMDAR activation is not a determinant of the initiation of depolarization but is important for sustaining transmembrane ion fluxes during SD.

Effects of brief chilling and desiccation on ion homeostasis in the central nervous system of the migratory locust, Locusta migratoria

In insects, chilling, anoxia, and dehydration are cues to trigger rapid physiological responses enhancing stress tolerance within minutes. Recent evidence suggests that responses elicited by different cues are mechanistically distinct from each other, though these differences have received little attention. Further, the effects are not well studied in neural tissue. In this study, we examined how brief exposure to desiccation and chilling affect ion homeostatic mechanisms in metathoracic ganglion of the migratory locust, Locusta migratoria. Both desiccation and chilling enhanced resistance to anoxia, though only chilling hastened recovery from anoxic coma. Similarly, only chilling enhanced resistance to pharmacological perturbation of neuronal ion homeostasis. Our results indicate that chilling and desiccation trigger mechanistically distinct responses and, while both may be important for neuronal ion homeostasis, chilling has a larger effect on this tissue. SUMMARY STATEMENT: This is one of few studies to demonstrate the importance of the central nervous system in rapid acclimatory responses in insects.

Role of adenosine in functional recovery following anoxic coma in Locusta migratoria

When exposed to prolonged anoxia insects enter a reversible coma during which neural and muscular systems temporarily shut down. Nervous system shut down is a result of spreading depolarization throughout neurons and glial cells. Upon return to normoxia, recovery occurs following the restoration of ion gradients. However, there is a delay in the functional recovery of synaptic transmission following membrane repolarization. In mammals, the build-up of extracellular adenosine following spreading depolarization contributes to this delay. Adenosine accumulation is a marker of metabolic stress and it has many downstream effects through the activation of adenosine receptors, including the inhibition of cAMP production. Here we demonstrate that adenosine lengthens the time to functional recovery following anoxic coma in locusts. Caffeine, used as an adenosine receptor antagonist, decreased the time to recovery in intact animals and lengthened the time to recovery in semi-intact animals. A cAMP inhibitor, NKH 477, delayed recovery time in male animals. Our results show that the rate of recovery in insect systems is affected by the presence of adenosine.

Spreading depolarizations in the rat endothelin-1 model of focal cerebellar ischemia

Focal brain ischemia is best studied in neocortex and striatum. Both show highly vulnerable neurons and high susceptibility to spreading depolarization (SD). Therefore, it has been hypothesized that these two variables generally correlate. However, this hypothesis is contradicted by findings in cerebellar cortex, which contains highly vulnerable neurons to ischemia, the Purkinje cells, but is said to be less susceptible to SD. Here, we found in the rat cerebellar cortex that elevated K⁺ induced a long-lasting depolarizing event superimposed with SDs. Cerebellar SDs resembled those in neocortex, but negative direct current (DC) shifts and regional blood flow responses were usually smaller. The K⁺ threshold for SD was higher in cerebellum than in previous studies in neocortex. We then topically applied endothelin-1 (ET-1) to the cerebellum, which is assumed to cause SD via vasoconstriction-induced focal ischemia. Although the blood flow decrease was similar to that in previous studies in neocortex, the ET-1 threshold for SD was higher. Quantitative cell counting found that the proportion of necrotic Purkinje cells was significantly higher in ET-1-treated rats than sham controls even if ET-1 had not caused SDs. Our results suggest that ischemic death of Purkinje cells does not require the occurrence of SD.

The role of Toll-like receptor signaling pathways in cerebrovascular disorders: the impact of spreading depolarization

Cerebral vascular diseases (CVDs) are a group of disorders that affect the blood supply to the brain and lead to the reduction of oxygen and glucose supply to the neurons and the supporting cells. Spreading depolarization (SD), a propagating wave of neuroglial depolarization, occurs in different CVDs. A growing amount of evidence suggests that the inflammatory responses following hypoxic-ischemic insults and after SD plays a double-edged role in brain tissue injury and clinical outcome; a beneficial effect in the acute phase and a destructive role in the late phase. Toll-like receptors (TLRs) play a crucial role in the activation of inflammatory cascades and subsequent neuroprotective or harmful effects after CVDs and SD. Here, we review current data regarding the pathophysiological role of TLR signaling pathways in different CVDs and discuss the role of SD in the potentiation of the inflammatory cascade in CVDs through the modulation of TLRs.

Na+/K+-ATPase α isoform deficiency results in distinct spreading depolarization phenotypes

Compromised Na⁺/K⁺-ATPase function is associated with the occurrence of spreading depolarization (SD). Mutations in ATP1A2, the gene encoding the α2 isoform of the Na⁺/K⁺-ATPase, were identified in patients with familial hemiplegic migraine type 2 (FHM2), a Mendelian model disease for SD. This suggests a distinct role for the α2 isoform in modulating SD susceptibility and raises questions about underlying mechanisms including the roles of other Na⁺/K⁺-ATPase α isoforms. Here, we investigated the effects of genetic ablation and pharmacological inhibition of α1, α2, and α3 on SD using heterozygous knock-out mice. We found that only α2 heterozygous mice displayed higher SD susceptibility when challenged with prolonged extracellular high potassium concentration ([K⁺]_o), a pronounced post SD oligemia and higher SD speed in-vivo. By contrast, under physiological [K⁺]_o, α2 heterozygous mice showed similar SD susceptibility compared to wild-type littermates. Deficiency of α3 resulted in increased resistance against electrically induced SD in-vivo, whereas α1 deficiency did not affect SD. The results support important roles of the α2 isoform in SD. Moreover, they suggest that specific experimental conditions can be necessary to reveal an inherent SD phenotype by driving a (meta-) stable system into decompensation, reminiscent of the episodic nature of SDs in various diseases.

Effect of Locally Delivered Nimodipine Microparticles on Spreading Depolarization in Aneurysmal Subarachnoid Hemorrhage

BACKGROUND

Recurrent spreading depolarizations (SDs) occur in patients after aneurysmal subarachnoid hemorrhage (aSAH), resulting in metabolic stress to brain. These events are closely associated with delayed cerebral ischemia. Preclinical data suggest that the beneficial effect of nimodipine demonstrated in clinical trials may be related to inhibition of SD rather than limitation of large artery vasospasm.

METHODS

Subjects enrolled in a phase 3 trial of intraventricularly delivered, sustained-release nimodipine (EG-1962) versus standard of care oral nimodipine (NEWTON 2) who required surgical clipping had subdural strip electrodes implanted for monitoring of SD. SD was then scored blinded to NEWTON 2 allocation.

RESULTS

Five subjects underwent electrocorticography monitoring of SD. Three of five patients had SD. There were fewer SDs, a lower rate of SD, and shorter depression durations in subjects treated with EG-1962 compared to standard of care. Outcomes were worse in the standard of care group, though there were baseline imbalances.

CONCLUSIONS

These results are consistent with a beneficial effect of locally delivered nimodipine (EG-1962) on SD after aSAH in more severely injured patients who are at risk of delayed cerebral ischemia related to SD. Larger studies are warranted to test this effect.

The antagonism of prostaglandin FP receptors inhibits the evolution of spreading depolarization in an experimental model of global forebrain ischemia

Spontaneous, recurrent spreading depolarizations (SD) are increasingly more appreciated as a pathomechanism behind ischemic brain injuries. Although the prostaglandin F2α - FP receptor signaling pathway has been proposed to contribute to neurodegeneration, it has remained unexplored whether FP receptors are implicated in SD or the coupled cerebral blood flow (CBF) response. We set out here to test the hypothesis that FP receptor blockade may achieve neuroprotection by the inhibition of SD. Global forebrain ischemia/reperfusion was induced in anesthetized rats by the bilateral occlusion and later release of the common carotid arteries. An FP receptor antagonist (AL-8810; 1 mg/bwkg) or its vehicle were administered via the femoral vein 10 min later. Two open craniotomies on the right parietal bone served the elicitation of SD with 1 M KCl, and the acquisition of local field potential. CBF was monitored with laser speckle contrast imaging over the thinned parietal bone. Apoptosis and microglia activation, as well as FP receptor localization were evaluated with immunohistochemistry. The data demonstrate that the antagonism of FP receptors suppressed SD in the ischemic rat cerebral cortex and reduced the duration of recurrent SDs by facilitating repolarization. In parallel, FP receptor antagonism improved perfusion in the ischemic cerebral cortex, and attenuated hypoemic CBF responses associated with SD. Further, FP receptor antagonism appeared to restrain apoptotic cell death related to SD recurrence. In summary, the antagonism of FP receptors (located at the neuro-vascular unit, neurons, astrocytes and microglia) emerges as a promising approach to inhibit the evolution of SDs in cerebral ischemia.

Chemogenetics-mediated acute inhibition of excitatory neuronal activity improves stroke outcome

BACKGROUND AND PURPOSE

Ischemic stroke significantly perturbs neuronal homeostasis leading to a cascade of pathologic events causing brain damage. In this study, we assessed acute stroke outcome after chemogenetic inhibition of forebrain excitatory neuronal activity.

METHODS

We generated hM4Di-TG transgenic mice expressing the inhibitory hM4Di, a Designer Receptors Exclusively Activated by Designer Drugs (DREADD)-based chemogenetic receptor, in forebrain excitatory neurons. Clozapine-N-oxide (CNO) was used to activate hM4Di DREADD. Ischemic stroke was induced by transient occlusion of the middle cerebral artery. Neurologic function and infarct volumes were evaluated. Excitatory neuronal suppression in the hM4Di-TG mouse forebrain was assessed electrophysiologically in vitro and in vivo, based on evoked synaptic responses, and in vivo based on occurrence of potassium-induced cortical spreading depolarizations.

RESULTS

Detailed characterization of hM4Di-TG mice confirmed that evoked synaptic responses in both in vitro hippocampal slices and in vivo motor cortex were significantly reduced after CNO-mediated activation of the inhibitory hM4Di DREADD. Further, CNO treatment had no obvious effects on physiology and motor function in either control or hM4Di-TG mice. Importantly, hM4Di-TG mice treated with CNO at either 10 min before ischemia or 30 min after reperfusion exhibited significantly improved neurologic function and smaller infarct volumes compared to CNO-treated control mice. Mechanistically, we showed that potassium-induced cortical spreading depression episodes were inhibited, including frequency and duration of DC shift, in CNO-treated hM4Di-TG mice.

CONCLUSIONS

Our data demonstrate that acute inhibition of a subset of excitatory neurons after ischemic stroke can prevent brain injury and improve functional outcome. This study, together with the previous work in optogenetic neuronal modulation during the chronic phase of stroke, supports the notion that targeting neuronal activity is a promising strategy in stroke therapy.

Cholinergic modulation inhibits cortical spreading depression in mouse neocortex through activation of muscarinic receptors and decreased excitatory/inhibitory drive

Cortical spreading depression (CSD) is a wave of transient network hyperexcitability leading to long lasting depolarization and block of firing, which initiates focally and slowly propagates in the cerebral cortex. It causes migraine aura and it has been implicated in the generation of migraine headache. Cortical excitability can be modulated by cholinergic actions, leading in neocortical slices to the generation of rhythmic synchronous activities (UP/DOWN states). We investigated the effect of cholinergic activation with the cholinomimetic agonist carbachol on CSD triggered with 130 mM KCl pulse injections in acute mouse neocortical brain slices, hypothesizing that the cholinergic-induced increase of cortical network excitability during UP states could facilitate CSD. We observed instead an inhibitory effect of cholinergic activation on both initiation and propagation of CSD, through the action of muscarinic receptors. In fact, carbachol-induced CSD inhibition was blocked by atropine or by the preferential M1 muscarinic antagonist telenzepine; the preferential M1 muscarinic agonist McN-A-343 inhibited CSD similarly to carbachol, and its effect was blocked by telenzepine. Recordings of spontaneous excitatory and inhibitory post-synaptic currents in pyramidal neurons showed that McN-A-343 induced overall a decrease of the excitatory/inhibitory ratio. This inhibitory action may be targeted for novel pharmacological approaches in the treatment of migraine with muscarinic agonists.

Migraine aura, a predictor of near-death experiences in a crowdsourced study

Background

Near-death experiences (NDE) occur with imminent death and in situations of stress and danger but are poorly understood. Evidence suggests that NDE are associated with rapid eye movement (REM) sleep intrusion, a feature of narcolepsy. Previous studies further found REM abnormalities and an increased frequency of dream-enacting behavior in migraine patients, as well as an association between migraine with aura and narcolepsy. We therefore investigated if NDE are more common in people with migraine aura.

Methods

We recruited 1,037 laypeople from 35 countries and five continents, without any filters except for English language and age ≥18 years, via a crowdsourcing platform. Reports were validated using the Greyson NDE Scale.

Results

Eighty-one of 1,037 participants had NDE (7.8%; CI [6.3-9.7%]). There were no significant associations between NDE and age (p > 0.6, t-test independent samples) or gender (p > 0.9, Chi-square test). The only significant association was between NDE and migraine aura: 48 (6.1%) of 783 subjects without migraine aura and 33 (13.0%) of 254 subjects with migraine aura had NDE (p < 0.001, odds ratio (OR) = 2.29). In multiple logistic regression analysis, migraine aura remained significant after adjustment for age (p < 0.001, OR = 2.31), gender (p < 0.001, OR = 2.33), or both (p < 0.001, OR = 2.33).

Conclusions

In our sample, migraine aura was a predictor of NDE. This indirectly supports the association between NDE and REM intrusion and might have implications for the understanding of NDE, because a variant of spreading depolarization (SD), terminal SD, occurs in humans at the end of life, while a short-lasting variant of SD is considered the pathophysiological correlate of migraine aura.

Cortical Spreading Depression in the Setting of Traumatic Brain Injury

Cortical spreading depression (CSD) is a pathophysiologic phenomenon that describes an expanding wave of depolarization within the cortical gray matter. Originally described over 70 years ago, this spreading depression disrupts neuronal and glial ionic equilibrium, leading to increased energy demands that can cause a metabolic crisis. This results in secondary insult, further perpetuating brain injury and neuronal death. Initially not thought to be of clinical significance, the view of CSD was modified with the advent of intracranial electroencephalography, or electrocorticography. With these improved monitoring techniques, CSD has been identified as a major mechanism by which traumatic brain injury (TBI) imparts its negative sequalae. TBI is a heterogenous disease process that runs the gamut of clinical presentations. This includes concussion, epidural and subdural hematoma, diffuse axonal injury, and subarachnoid hemorrhage. Nonetheless, CSD appears to be frequently occurring among the various types of TBI, thus allowing for the potential development of targeted therapies in an otherwise ill-fated patient cohort. Although a complete understanding of the interplay between CSD and TBI has not yet been achieved, the authors recount the efforts that have been employed over the last several decades in an effort to bridge this gap. In addition, our current understanding of the role neuroimmune cells play in CSD is discussed in the context of TBI. Finally, current therapeutic strategies using CSD as a pharmacologic target are explored with respect to their clinical use in patients with TBI.