Anesthetic effects on susceptibility to cortical spreading depression

Isoflurane lowers the cerebral metabolic rate of oxygen and prevents hypoxia during cortical spreading depolarization in vitro: An integrative experimental and modeling study

Cortical spreading depolarization (SD) imposes a massive increase in energy demand and therefore evolves as a target for treatment following acute brain injuries. Anesthetics are empirically used to reduce energy metabolism in critical brain conditions, yet their effect on metabolism during SD remains largely unknown. We investigated oxidative metabolism during SD in brain slices from Wistar rats. Extracellular potassium ([K+]o), local field potential and partial tissue oxygen pressure (ptiO2) were measured simultaneously. The cerebral metabolic rate of oxygen (CMRO2) was calculated using a reaction-diffusion model. By that, we tested the effect of clinically relevant concentrations of isoflurane on CMRO2 during SD and modeled tissue oxygenation for different capillary pO2 values. During SD, CMRO2 increased 2.7-fold, resulting in transient hypoxia in the slice core. Isoflurane decreased CMRO2, reduced peak [K+]o, and prolonged [K+]o clearance, which indicates reduced synaptic transmission and sodium-potassium ATPase inhibition. Modeling tissue oxygenation during SD illustrates the need for increased capillary pO2 levels to prevent hypoxia. In the absence thereof, isoflurane could improve tissue oxygenation by lowering CMRO2. Therefore, isoflurane is a promising candidate for pre-clinical studies on neuronal survival in conditions involving SD.

Ketamine improves neuronal recovery following spreading depolarization in peri-infarct tissues

Spreading depolarization (SD) has emerged as an important contributor to the enlargement of acute brain injuries. We previously showed that the N-methyl-D-aspartate receptor antagonist ketamine was able to prevent deleterious consequences of SD in brain slices, under conditions of metabolic compromise. The current study aimed to extend these observations into an in vivo stroke model, to test whether gradients of metabolic capacity lead to differential accumulation of calcium (Ca2+) following SD. In addition, we tested whether ketamine protects vulnerable tissuewhile allowing SD to propagate through surrounding undamaged tissue. Focal lesions were generated using a distal middle cerebral artery occlusion in mice, and clusters of SD were generated at 20 min intervals with remote microinjection of potassium chloride. SDs invading peri-infarct regions had significantly different consequences, depending on the distance from the infarct core. Proximal to the lesion, Ca2+ transients were extended, as compared with responses in better-perfused tissue more remote from the lesion. Extracellular potential shifts were also longer and hyperemia responses were reduced in proximal regions following SDs. Consistent with in vitro studies, ketamine, at concentrations that did not abolish the propagation of SD, reduced the accumulation of intracellular Ca2+ in proximal regions following an SD wave. These findings suggest that deleterious consequences of SD can be targeted in vivo, without requiring outright block of SD initiation and propagation.

Different vulnerability of fast and slow cortical oscillations to suppressive effect of spreading depolarization: state-dependent features potentially relevant to pathogenesis of migraine aura

BACKGROUND

Spreading depolarization (SD), underlying mechanism of migraine aura and potential activator of pain pathways, is known to elicit transient local silencing cortical activity. Sweeping across the cortex, the electrocorticographic depression is supposed to underlie spreading negative symptoms of migraine aura. Main information about the suppressive effect of SD on cortical oscillations was obtained in anesthetized animals while ictal recordings in conscious patients failed to detect EEG depression during migraine aura. Here, we investigate the suppressive effect of SD on spontaneous cortical activity in awake animals and examine whether the anesthesia modifies the SD effect.

METHODS

Spectral and spatiotemporal characteristics of spontaneous cortical activity following a single unilateral SD elicited by amygdala pinprick were analyzed in awake freely behaving rats and after induction of urethane anesthesia.

RESULTS

In wakefulness, SD transiently suppressed cortical oscillations in all frequency bands except delta. Slow delta activity did not decline its power during SD and even increased it afterwards; high-frequency gamma oscillations showed the strongest and longest depression under awake conditions. Unexpectedly, gamma power reduced not only during SD invasion the recording cortical sites but also when SD occupied distant subcortical/cortical areas. Contralateral cortex not invaded by SD also showed transient depression of gamma activity in awake animals. Introduction of general anesthesia modified the pattern of SD-induced depression: SD evoked the strongest cessation of slow delta activity, milder suppression of fast oscillations and no distant changes in gamma activity.

CONCLUSION

Slow and fast cortical oscillations differ in their vulnerability to SD influence, especially in wakefulness. In the conscious brain, SD produces stronger and spatially broader depression of fast cortical oscillations than slow ones. The frequency-specific effects of SD on cortical activity of awake brain may underlie some previously unexplained clinical features of migraine aura.

The NMDA receptor antagonists memantine and ketamine as anti-migraine agents

Migraine is a debilitating disorder affecting females more frequently than males. There is some evidence that drugs targeting glutamate receptors: memantine and ketamine might be beneficial in the therapy of this entity. Therefore, the purpose of this work is to present NMDA receptor antagonists, memantine and ketamine, as potential anti-migraine agents. We searched PubMed/MEDLINE, Embase, and clinical trials submitted to ClinicalTrials.gov to find publications describing eligible trials published between database inception and December 31, 2021. This comprehensive literature review summarizes data on the use of the NMDA receptor antagonists memantine and ketamine in the pharmacotherapy of migraine. Results from 20 previous and recent preclinical experiments are discussed and correlated with 19 clinical trials (including case series, open-label, and randomized placebo-controlled trials). For the purposes of this review, the authors hypothesized that the propagation of SD is a major mechanism in the pathophysiology of migraine. In several animal studies and in vitro studies, memantine and ketamine inhibited or reduced propagation of the SD. In addition, the results of clinical trials suggest that memantine or ketamine may be an effective treatment option for migraine. However, most studies on these agents lack control group. Although further clinical trials are needed, the results suggest that ketamine or memantine may be promising molecules for the treatment of severe migraine. Particular attention should be paid to people who have a treatment-resistant form of migraine with aura or have exhausted existing treatment options. For them, the drugs under discussion could represent an interesting alternative in the future.

Role of Dexmedetomidine in Aneurysmal Subarachnoid Hemorrhage: A Comprehensive Scoping Review

Dexmedetomidine (DEX), an α2-adrenergic agonist, has been widely used for anesthesia, pain control, and intensive care unit sedation. Besides sleep-like sedation, DEX has many other beneficial effects, such as anti-inflammation, antioxidation, and anticell death. Subarachnoid hemorrhage (SAH), a severe and potentially fatal form of stroke, is a complex disease that is divided into 2 phases: early brain injury and delayed cerebral ischemia. In each phase, several pathologic changes are involved, including disturbed intracranial homeostasis, metabolic failure, blood-brain barrier damage, vasospasm, microthrombosis, and cortical spreading depolarization. DEX has been shown to have an effect on these SAH-related pathologic processes. Research shows that DEX could serve as a protective therapy for patients with SAH due to its ability to maintain stable intracerebral homeostasis, balance coagulation-fibrinolysis, repair a damaged blood-brain barrier as well as prevent vasospasm and suppress cortical spreading depolarization by anti-inflammatory, antioxidative, antiapoptotic, and vasoconstriction-dilation effects. In this scoping review, we critically assess the existing data on the potential protective effect of DEX after SAH. So far, only 1 retrospective clinical trial assessing the effect of DEX on clinical outcomes after SAH has been performed. Hence, more trials are still needed as well as translational research bringing results from bench to bedside.

Electrophysiological and pharmacological characterization of spreading depolarization in the adult zebrafish tectum

Spreading depolarization (SD) is a slowly propagating wave of neuronal and glial depolarization. A growing number of studies show that SD and SD-like phenomena play a role in neurological disorders such as migraine, stroke, and traumatic brain injury. Despite the clinical importance of SD, its underlying molecular and cellular mechanisms remain elusive, possibly because of insufficient animal model allowing genetic manipulation. Such a model would also allow high-throughput screening for SD-suppressing drug development. To address this, we developed a novel experimental system to study SD using zebrafish. Electrophysiological recordings in the immobilized adult zebrafish revealed that increasing extracellular potassium concentration elicited SD with a large and long-lasting negative shift of direct current (DC) potential in the optic tectum. It also reduced the oscillatory activity in the extracellular field potential and increased the expression of the immediate early gene c-fos. Pharmacological blocking of the N-methyl-d-aspartate (NMDA) glutamate receptor attenuated the propagation of SD, suggesting that glutamatergic neurotransmission mediated tectal SD in zebrafish. Our analyses revealed that the zebrafish tectum and rodent cortex had similar SD kinetics. The current study provides electrophysiological and pharmacological evidence that zebrafish SD and mammal SD are comparable. This zebrafish SD model is suitable for genetic manipulation and cost-effective high-throughput screening. It could pave the way to novel diagnostic and therapeutic methods applicable to SD-associated neurological disorders.NEW & NOTEWORTHY Previous studies have implicated spreading depolarization (SD) in stroke and migraine. Here, we demonstrate SD, for the first time, in the adult zebrafish tectum showing waveform kinetics, c-fos expression, and attenuation by N-methyl-d-aspartate glutamate receptor blocker as observed in the rodent cortex. Since the zebrafish is an animal model amenable to genetic manipulation and chemical screening, this result could pave the way to novel diagnostic and therapeutic methods applicable to SD-associated neurological disorders.

Updated review on the link between cortical spreading depression and headache disorders

INTRODUCTION

Experimental animal studies have revealed mechanisms that link cortical spreading depression (CSD) to the trigeminal activation mediating lateralized headache. However, conventional CSD as seen in lissencephalic brain is insufficient to explain some clinical features of aura and migraine headache.

AREAS COVERED

The importance of CSD in headache development including dysfunction of the thalamocortical network, neuroinflammation, calcitonin gene-related peptide, transgenic models, and the role of CSD in migraine triggers, treatment options, neuromodulation and future directions are reviewed.

EXPERT OPINION

The conventional understanding of CSD marching across the hemisphere is invalid in gyrencephalic brains. Thalamocortical dysfunction and interruption of functional cortical network systems by CSD, may provide alternative explanations for clinical manifestations of migraine phases including aura. Not all drugs showing CSD blocking properties in lissencephalic brains, have efficacy in migraine headache and monoclonal antibodies against CGRP ligand/receptors which are effective in migraine treatment, have no impact on aura in humans or CSD properties in rodents. Functional networks and molecular mechanisms mediating and amplifying the effects of limited CSD in migraine brain remain to be investigated to define new targets.

CVN-AD Alzheimer's mice show premature reduction in neurovascular coupling in response to spreading depression and anoxia compared to aged controls

We compared the efficacy of neurovascular coupling and substrate supply in cerebral cortex during severe metabolic challenges in transgenic Alzheimer's [CVN-AD] and control [C57Bl/6] mice, to evaluate the hypothesis that metabolic insufficiency is a critical component of degeneration leading to dementia. We analyzed cerebral blood flow and metabolic responses to spreading depression (induced by K⁺ applied to the cortex) and anoxia across aging in CVN-AD + C57Bl/6 genotypes. In the CVN-AD genotype progression to histological and cognitive hallmarks of dementia is a stereotyped function of age. We correlated physiology and imaging of the cortex with the blood flow responses measured with laser doppler probes. The results show that spreading depression resulted in a hyperemic blood flow response that was dramatically reduced (24% in amplitude, 70% in area) in both middle-aged and aged CVN-AD mice compared to C57Bl/6 age-matched controls. However, spreading depression amplitude and conduction velocity (≈6 mm/min) did not differ among groups. Anoxia (100% N₂ ) showed significantly decreased (by 62%) reactive blood flow and autoregulation in aged AD-CVN mice compared to aged control animals. Significantly reduced neurovascular coupling occurred prematurely with aging in CVN-AD mice. Abbreviated physiological hyperemia and decreased resilience to anoxia may enhance early-onset metabolic deficiency through decreased substrate supply to the brain. Metabolic deficiency may contribute significantly to the degeneration associated with dementia as a function of aging and regions of the brain involved.

The role of spreading depolarizations and electrographic seizures in early injury progression of the rat photothrombosis stroke model

Spreading depolarization (SD) and seizures are pathophysiological events associated with cerebral ischemia. Here, we investigated their role for injury progression in the cerebral cortex. Cerebral ischemia was induced in anesthetized male Wistar rats using the photothrombosis (PT) stroke model. SD and spontaneous neuronal activity were recorded in the presence of either urethane or ketamine/xylazine anesthesia. Blood-brain barrier (BBB) permeability, cerebral perfusion, and cellular damage were assessed through a cranial window and repeated intravenous injection of fluorescein sodium salt and propidium iodide until 4 h after PT. Neuronal injury and early lesion volume were quantified by stereological cell counting and manual and automated assessment of ex vivo T2-weighted magnetic resonance imaging. Onset SDs originated at the thrombotic core and invaded neighboring cortex, whereas delayed SDs often showed opposite propagation patterns. Seizure induction by 4-aminopyridine caused no increase in lesion volume or neuronal injury in urethane-anesthetized animals. Ketamine/xylazine anesthesia was associated with a lower number of onset SDs, reduced lesion volume, and neuronal injury despite a longer duration of seizures. BBB permeability increase inversely correlated with the number of SDs at 3 and 4 h after PT. Our results provide further evidence that ketamine may counteract the early progression of ischemic injury.

Loss of GFAP and Vimentin Does Not Affect Peri-Infarct Depolarizations after Focal Cerebral Ischemia

Peri-infarct depolarization (PID), one kind of spreading depolarization, contributes to infarct volume enlargement after ischemic stroke. Astrocytes participate in PIDs by various mechanisms. The roles of glial fibrillary acidic protein (GFAP) and vimentin (Vim), intermediate filament proteins in astrocytes, however, in PIDs induction and propagation remain unknown. Middle cerebral artery occlusion (MCAO) model was made in 9 GFAP-/-Vim-/- and 9 wild-type (WT) C57BL/6 mice. Using 4-wavelength optical intrinsic signal imaging (OIS), we identified PIDs as consistent, red and blue interaction waves in the cortical reflectance that slowly propagated peripherally from the origin site. Five propagation patterns of PIDs were observed after MCAO in mice, namely, latero-medial, medial-lateral, rostro-caudal, caudo-rostral, and collision. Additionally, the frequency, propagation velocity, and duration of PIDs between GFAP-/-Vim-/- and WT mice were not significantly different (p > 0.05). Furthermore, no significant difference was found in infarct volume and brain edema between the two groups. In conclusion, the 4-wavelength OIS system allows acquisition of high temporal-spatial resolution color images for analyzing temporal-spatial characteristics of PIDs in detail. GFAP and Vim in astrocytes are not involved in PIDs after MCAO in mice.

Acute sleep deprivation enhances susceptibility to the migraine substrate cortical spreading depolarization

BACKGROUND

Migraine is a common headache disorder, with cortical spreading depolarization (CSD) considered as the underlying electrophysiological event. CSD is a slowly propagating wave of neuronal and glial depolarization. Sleep disorders are well known risk factors for migraine chronification, and changes in wake-sleep pattern such as sleep deprivation are common migraine triggers. The underlying mechanisms are unknown. As a step towards developing an animal model to study this, we test whether sleep deprivation, a modifiable migraine trigger, enhances CSD susceptibility in rodent models.

METHODS

Acute sleep deprivation was achieved using the "gentle handling method", chosen to minimize stress and avoid confounding bias. Sleep deprivation was started with onset of light (diurnal lighting conditions), and assessment of CSD was performed at the end of a 6 h or 12 h sleep deprivation period. The effect of chronic sleep deprivation on CSD was assessed 6 weeks or 12 weeks after lesioning of the hypothalamic ventrolateral preoptic nucleus. All experiments were done in a blinded fashion with respect to sleep status. During 60 min of continuous topical KCl application, we assessed the total number of CSDs, the direct current shift amplitude and duration of the first CSD, the average and cumulative duration of all CSDs, propagation speed, and electrical CSD threshold.

RESULTS

Acute sleep deprivation of 6 h (n = 17) or 12 h (n = 11) duration significantly increased CSD frequency compared to controls (17 ± 4 and 18 ± 2, respectively, vs. 14 ± 2 CSDs/hour in controls; p = 0.003 for both), whereas other electrophysiological properties of CSD were unchanged. Acute total sleep deprivation over 12 h but not over 6 h reduced the electrical threshold of CSD compared to controls (p = 0.037 and p = 0.095, respectively). Chronic partial sleep deprivation in contrast did not affect CSD susceptibility in rats.

CONCLUSIONS

Acute but not chronic sleep deprivation enhances CSD susceptibility in rodents, possibly underlying its negative impact as a migraine trigger and exacerbating factor. Our findings underscore the importance of CSD as a therapeutic target in migraine and suggest that headache management should identify and treat associated sleep disorders.

Therapeutic implications of cortical spreading depression models in migraine

Migraine is among the most common and disabling neurological diseases in the world. Cortical spreading depression (CSD) is a wave of near-complete depolarization of neurons and glial cells that slowly propagates along the cortex creating the perception of aura. Evidence suggests that CSD can trigger migraine headache. Experimental models of CSD have been considered highly translational as they recapitulate migraine-related phenomena and have been validated for screening migraine therapeutics. Here we outline the essential components of validated experimental models of CSD and provide a comprehensive review of potential modulators and targets against CSD. We further focus on novel interventions that have been recently shown to suppress CSD susceptibility that may lead to therapeutic targets in migraine.

Propofol for Treatment of Acute Migraine in the Emergency Department: A Systematic Review

OBJECTIVES

Propofol has not been extensively studied as an acute migraine therapy; however, based on the limited evidence from outpatient and inpatient settings, propofol has been proposed as an option for patients who present to the emergency department (ED). The purpose of this review was to evaluate the existing literature regarding the safety and efficacy of propofol for acute migraine treatment in the ED.

METHODS

A systematic review of clinical studies of propofol treatment for acute migraine in the ED was performed using Preferred Reporting Items for Systematic Review and Meta-Analysis (PRISMA) guidelines. Trials were identified through PubMed, Google Scholar, clinical trial registries, research registries, and key journals through May 2019. A modified Jadad scoring system was used to assess the methodologic quality of the included randomized controlled trials, and the Newcastle-Ottawa Scale was used for the retrospective cohort study.

RESULTS

Nine studies, including five case reports or series, one retrospective cohort study, and three randomized controlled trials, consisting of 290 patients, were reviewed. All studies in adults reported propofol to be an effective therapy for migraine, but the strength of these results was limited by dosing variations, small sample sizes, and limited generalizability. Pediatric studies produced mixed results.

CONCLUSIONS

Propofol may be an effective rescue therapy for patients presenting to the ED for acute migraine, but its place in therapy based on the limited available evidence is unknown. The safety of propofol for migraine management in the ED has not been adequately examined.

Brainstem spreading depolarization and cortical dynamics during fatal seizures in Cacna1a S218L mice

Sudden unexpected death in epilepsy (SUDEP) is a fatal complication of epilepsy in which brainstem spreading depolarization may play a pivotal role, as suggested by animal studies. However, patiotemporal details of spreading depolarization occurring in relation to fatal seizures have not been investigated. In addition, little is known about behavioural and neurophysiological features that may discriminate spontaneous fatal from non-fatal seizures. Transgenic mice carrying the missense mutation S218L in the α1A subunit of Cav2.1 (P/Q-type) Ca2+ channels exhibit enhanced excitatory neurotransmission and increased susceptibility to spreading depolarization. Homozygous Cacna1aS218L mice show spontaneous non-fatal and fatal seizures, occurring throughout life, resulting in reduced life expectancy. To identify characteristics of fatal and non-fatal spontaneous seizures, we compared behavioural and electrophysiological seizure dynamics in freely-behaving homozygous Cacna1aS218L mice. To gain insight on the role of brainstem spreading depolarization in SUDEP, we studied the spatiotemporal distribution of spreading depolarization in the context of seizure-related death. Spontaneous and electrically-induced seizures were investigated by video monitoring and electrophysiological recordings in freely-behaving Cacna1aS218L and wild-type mice. Homozygous Cacna1aS218L mice showed multiple spontaneous tonic-clonic seizures and died from SUDEP in adulthood. Death was preceded by a tonic-clonic seizure terminating with hindlimb clonus, with suppression of cortical neuronal activity during and after the seizure. Induced seizures in freely-behaving homozygous Cacna1aS218L mice were followed by multiple spreading depolarizations and death. In wild-type or heterozygous Cacna1aS218L mice, induced seizures and spreading depolarization were never followed by death. To identify temporal and regional features of seizure-induced spreading depolarization related to fatal outcome, diffusion-weighted MRI was performed in anaesthetized homozygous Cacna1aS218L and wild-type mice. In homozygous Cacna1aS218L mice, appearance of seizure-related spreading depolarization in the brainstem correlated with respiratory arrest that was followed by cardiac arrest and death. Recordings in freely-behaving homozygous Cacna1aS218L mice confirmed brainstem spreading depolarization during spontaneous fatal seizures. These data underscore the value of the homozygous Cacna1aS218L mouse model for identifying discriminative features of fatal compared to non-fatal seizures, and support a key role for cortical neuronal suppression and brainstem spreading depolarization in SUDEP pathophysiology.

Aura and Head pain: relationship and gaps in the translational models

Migraine is a complex brain disorder and initiating events for acute attacks still remain unclear. It seems difficult to explain the development of migraine headache with one mechanism and/or a single anatomical location. Cortical spreading depression (CSD) is recognized as the biological substrate of migraine aura and experimental animal studies have provided mechanisms that possibly link CSD to the activation of trigeminal neurons mediating lateralized head pain. However, some CSD features do not match the clinical features of migraine headache and there are gaps in translating CSD to migraine with aura. Clinical features of migraine headache and results from research are critically evaluated; and consistent and inconsistent findings are discussed according to the known basic features of canonical CSD: typical SD limited to the cerebral cortex as it was originally defined. Alternatively, arguments related to the emergence of SD in other brain structures in addition to the cerebral cortex or CSD initiated dysfunction in the thalamocortical network are proposed. Accordingly, including thalamus, particularly reticular nucleus and higher order thalamic nuclei, which functions as a hub connecting the visual, somatosensory, language and motor cortical areas and subjects to modulation by brain stem projections into the CSD theory, would greatly improve our current understanding of migraine.

Cortical spreading depolarizations induced by surgical field blood in a mouse model of neurosurgery

OBJECTIVE

Cortical spreading depolarization (CSD) has been linked to poor clinical outcomes in the setting of traumatic brain injury, malignant stroke, and subarachnoid hemorrhage. There is evidence that electrocautery during neurosurgical procedures can also evoke CSD waves in the brain. It is unknown whether blood contacting the cortical surface during surgical bleeding affects the frequency of spontaneous or surgery-induced CSDs. Using a mouse neurosurgical model, the authors tested the hypothesis that electrocautery can induce CSD waves and that surgical field blood (SFB) is associated with more CSDs. The authors also investigated whether CSD can be reliably observed by monitoring the fluorescence of GCaMP6f expressed in neurons.

METHODS

CSD waves were monitored by using confocal microscopy to detect fluorescence increases at the cortical surface in mice expressing GCaMP6f in CamKII-positive neurons. The cortical surface was electrocauterized through an adjacent burr hole. SFB was simulated by applying a drop of tail vein blood to the brain through the same burr hole.

RESULTS

CSD waves were readily detected in GCaMP6f-expressing mice. Monitoring GCaMP6f fluorescence provided far better sensitivity and spatial resolution than detecting CSD events by observing changes in the intrinsic optical signal (IOS). Forty-nine percent of the CSD waves identified by GCaMP6f had no corresponding IOS signal. Electrocautery evoked CSD waves. On average, 0.67 ± 0.08 CSD events were generated per electrocautery episode, and multiple CSD waves could be induced in the same mouse by repeated cauterization (average, 7.9 ± 1.3 events; maximum number in 1 animal, 13 events). In the presence of SFB, significantly more spontaneous CSDs were generated (1.35 ± 0.37 vs 0.13 ± 0.16 events per hour, p = 0.002). Ketamine effectively decreased the frequency of spontaneous CSD waves (1.35 ± 0.37 to 0.36 ± 0.15 CSD waves per hour, p = 0.016) and electrocautery-stimulated CSD waves (0.80 ± 0.05 to 0.18 ± 0.08 CSD waves per electrocautery, p = 0.00002).

CONCLUSIONS

CSD waves are detected with far greater sensitivity and fidelity by monitoring GCaMP6f signals in neurons than by monitoring IOSs. Electrocautery reliably evokes CSD waves, and the frequency of spontaneous CSD waves is increased when blood is applied to the cortical surface. These experimental conditions recapitulate common scenarios in the neurosurgical operating room. Ketamine, a clinically available pharmaceutical agent, can block stimulated and spontaneous CSDs. More research is required to understand the clinical importance of intraoperative CSD.

Spreading Depolarization Waves in Neurological Diseases: A Short Review about its Pathophysiology and Clinical Relevance

Lesion growth following acutely injured brain tissue after stroke, subarachnoid hemorrhage and traumatic brain injury is an important issue and a new target area for promising therapeutic interventions. Spreading depolarization or peri-lesion depolarization waves were demonstrated as one of the significant contributors of continued lesion growth. In this short review, we discuss the pathophysiology for SD forming events and try to list findings detected in neurological disorders like migraine, stroke, subarachnoid hemorrhage and traumatic brain injury in both human as well as experimental studies. Pharmacological and non-pharmacological treatment strategies are highlighted and future directions and research limitations are discussed.

The effect of anesthetic agents on cerebral vasospasms after subarachnoid hemorrhage: A retrospective study

Cerebral vasospasm is the most important cause of morbidity after an aneurysm clipping in the early postoperative period. The aim of this retrospective study was to evaluate whether the incidence of vasospasms differs when using propofol or desflurane for an emergent aneurysm clipping.The data from 102 patients (50 in the propofol group, 52 in the desflurane group) were analyzed. The occurrence of vasospasm based on daily transcranial Doppler, angiography, and cerebral infarction during 14 days after surgery were compared by anesthetic agents. Postoperative data including Glasgow Coma Scale (GCS) score on day 14 after surgery, and the Glasgow Outcome Scale (GOS) score at 3 months were documented.Patients that intraoperatively received propofol for anesthesia maintenance, had higher incidence of transcranial Doppler (TCD)-evident vasospasm than those that received desflurane (54% vs 30.8%, P = .027). The occurrence of TCD-evident vasospasm was still higher (odds ratio: 2.84; 95% confidence interval: 1.12-7.20) in the propofol group than in the desflurane group after adjusting for confounding factors. However, the incidence of angiographic vasospasm, cerebral infarction, and interventions to treat cerebral vasospasms were similar between both groups. GCS score on day 14 after surgery and the GOS score at 3 months were similar between groups.No effect of anesthetic agents on angiographic vasospasm, cerebral infarction, or clinical outcome was observed, whereas desflurane anesthesia was associated with a lower incidence of TCD-evident vasospasms compared to propofol anesthesia. Our study provides a basis for further randomized controlled studies in a larger patient population to clarify the effects of anesthetic agents on the occurrence of cerebral vasospasms.

Systematic review of the pharmacological agents that have been tested against spreading depolarizations

Spreading depolarization (SD) occurs alongside brain injuries and it can lead to neuronal damage. Therefore, pharmacological modulation of SD can constitute a therapeutic approach to reduce its detrimental effects and to improve the clinical outcome of patients. The major objective of this article was to produce a systematic review of all the drugs that have been tested against SD. Of the substances that have been examined, most have been shown to modulate certain SD characteristics. Only a few have succeeded in significantly inhibiting SD. We present a variety of strategies that have been proposed to overcome the notorious harmfulness and pharmacoresistance of SD. Information on clinically used anesthetic, sedative, hypnotic agents, anti-migraine drugs, anticonvulsants and various other substances have been compiled and reviewed with respect to the efficacy against SD, in order to answer the question of whether a drug at safe doses could be of therapeutic use against SD in humans.

Comparison of volatile anesthetic-induced preconditioning in cardiac and cerebral system: molecular mechanisms and clinical aspects

Volatile anesthetic-induced preconditioning (APC) has shown to have cardiac and cerebral protective properties in both pre-clinical models and clinical trials. Interestingly, accumulating evidences demonstrate that, except from some specific characters, the underlying molecular mechanisms of APC-induced protective effects in myocytes and neurons are very similar; they share several major intracellular signaling pathways, including mediating mitochondrial function, release of inflammatory cytokines and cell apoptosis. Among all the experimental results, cortical spreading depolarization is a relative newly discovered cellular mechanism of APC, which, however, just exists in central nervous system. Applying volatile anesthetic preconditioning to clinical practice seems to be a promising cardio-and neuroprotective strategy. In this review, we also summarized and discussed the results of recent clinical research of APC. Despite all the positive experimental evidences, large-scale, long-term, more precisely controlled clinical trials focusing on the perioperative use of volatile anesthetics for organ protection are still needed.

Novel Therapeutic Targets Against Spreading Depression

Migraine is among the most prevalent and disabling neurological diseases in the world. Cortical spreading depression (SD) is an intense wave of neuronal and glial depolarization underlying migraine aura, and a headache trigger, which has been used as an experimental platform for drug screening in migraine. Here, we provide an overview of novel therapeutic targets that show promise to suppress SD, such as acid-sensing ion channels, casein kinase Iδ, P2X7-pannexin 1 complex, and neuromodulation, and outline the experimental models and essential quality measures for rigorous and reproducible efficacy testing.

Acute cardiac support with intravenous milrinone promotes recovery from early brain injury in a murine model of severe subarachnoid haemorrhage

Early brain injury/ischaemia (EBI) is a serious complication early after subarachnoid haemorrhage (SAH) that contributes to development of delayed cerebral ischaemia (DCI). This study aimed to determine the role of inotropic cardiac support using milrinone (MIL) on restoring acute cerebral hypoperfusion attributable to EBI and improving outcomes after experimental SAH. Forty-three male C57BL/6 mice were assigned to either sham surgery (SAH-sham), SAH induced by endovascular perforation plus postconditioning with 2% isoflurane (Control), or SAH plus isoflurane combined with MIL with and without hypoxia-inducible factor inhibitor (HIF-I) pretreatment. Cardiac output (CO) during intravenous MIL infusion (0.25-0.75 μg/kg/min) between 1.5 and 2.5 hours after SAH induction was monitored with Doppler echocardiography. Magnetic resonance imaging (MRI)-continuous arterial spin labelling was used for quantitative cerebral blood flow (CBF) measurements. Neurobehavioral function was assessed daily by neurological score and open field test. DCI was analyzed 3 days later by determining infarction on MRI. Mild reduction of cardiac output (CO) and global cerebral blood flow (CBF) depression were notable early after SAH. MIL increased CO in a dose-dependent manner (P<.001), which was accompanied by improved hypoperfusion, incidence of DCI and functional recovery than Control (P<.05). The neuroprotective effects afforded by MIL or Control were attenuated by hypoxia-inducible factor (HIF) inhibition (P<.05). These results suggest that MIL improves acute hypoperfusion by its inotropic effect, leading to neurobehavioral improvement in mice after severe SAH, in which HIF may be acting as a critical mediator.

Anesthesia in Experimental Stroke Research

Anesthetics have enabled major advances in development of experimental models of human stroke. Yet, their profound pharmacologic effects on neural function can confound the interpretation of experimental stroke research. Anesthetics have species-, drug-, and dose-specific effects on cerebral blood flow and metabolism, neurovascular coupling, autoregulation, ischemic depolarizations, excitotoxicity, inflammation, neural networks, and numerous molecular pathways relevant for stroke outcome. Both preconditioning and postconditioning properties have been described. Anesthetics also modulate systemic arterial blood pressure, lung ventilation, and thermoregulation, all of which may interact with the ischemic insult as well as the therapeutic interventions. These confounds present a dilemma. Here, we provide an overview of the anesthetic mechanisms of action and molecular and physiologic effects on factors relevant to stroke outcomes that can guide the choice and optimization of the anesthetic regimen in experimental stroke.

Propofol in the treatment of refractory migraine headaches

INTRODUCTION

Refractory/intractable migraine headaches are associated with chronic pain that does not respond to standard care of treatment. Propofol(2,6-diisopropylphenol) in sub-anesthetic doses has been reported to be beneficial in such patients. The present article describes the complete drug profile of propofol in the management of these super-refractory migraine headaches.

AREAS COVERED

The article covers different preclinical and clinical studies available in the literature. Expert commentary: Propofol is useful as an off-label drug molecule in an emergency situation of refractory migraines where it has been found to reduce the pain intensity. The molecule with a narrow therapeutic index and high abuse potential is prescribed only when conventional drugs fail to deliver any relief. There are not adequate double-blind crossover studies that substantiate the effectiveness of propofol in the treatment of migraine headaches. Furthermore, long-term outcomes for the use of propofol in migraine headaches requires an extensive investigation.

Insights into the Pathology of the α2-Na(+)/K(+)-ATPase in Neurological Disorders; Lessons from Animal Models

A functional Na⁺/K⁺-ATPase consists of a catalytic α subunit and a regulatory β subunit. Four α isoforms of the Na⁺/K⁺-ATPase are found in mammals, each with a unique expression pattern and catalytic activity. The α₂ isoform, encoded by the ATP1A2 gene, is primarily found in the central nervous system (CNS) and in heart-, skeletal- and smooth muscle tissues. In the CNS, the α₂ isoform is mainly expressed in glial cells. In particular, the α₂ isoform is found in astrocytes, important for astrocytic K⁺ clearance and, consequently, the indirect uptake of neurotransmitters. Both processes are essential for proper brain activity, and autosomal dominantly mutations in the ATP1A2 gene cause the neurological disorder Familial hemiplegic migraine type 2 (FHM2). FHM2 is a severe subtype of migraine with aura including temporary numbness or weakness, and affecting only one side of the body. FHM2 patients often suffer from neurological comorbidities such as seizures, sensory disturbances, cognitive impairment, and psychiatric manifestations. The functional consequences of FHM2 disease mutations leads to a partial or complete loss of function of pump activity; however, a clear phenotype-genotype correlation has yet to be elucidated. Gene-modified mouse models targeting the Atp1a2 gene have proved instrumental in the understanding of the pathology of FHM2. Several Atp1a2 knockout (KO) mice targeting different exons have been reported. Homozygous Atp1a2 KO mice die shortly after birth due to respiratory malfunction resulting from abnormal Cl⁻ homeostasis in brainstem neurons. Heterozygous KO mice are viable, but display altered behavior and neurological deficits such as altered spatial learning, decreased motor activity and enhanced fear/anxiety compared to wild type mice. FHM2 knock-in (KI) mouse models carrying the human in vivo disease mutations W887R and G301R have also been reported. Both models display altered cortical spreading depression (CSD) and point to deficits in the glutamatergic system as the main underlying mechanism of FHM2.

Glutamate-system defects behind psychiatric manifestations in a familial hemiplegic migraine type 2 disease-mutation mouse model

Migraine is a complex brain disorder, and understanding the complexity of this prevalent disease could improve quality of life for millions of people. Familial Hemiplegic Migraine type 2 (FHM2) is a subtype of migraine with aura and co-morbidities like epilepsy/seizures, cognitive impairments and psychiatric manifestations, such as obsessive-compulsive disorder (OCD). FHM2 disease-mutations locate to the ATP1A2 gene encoding the astrocyte-located α₂-isoform of the sodium-potassium pump (α₂Na⁺/K⁺-ATPase). We show that knock-in mice heterozygous for the FHM2-associated G301R-mutation (α₂^+/G301R) phenocopy several FHM2-relevant disease traits e.g., by mimicking mood depression and OCD. In vitro studies showed impaired glutamate uptake in hippocampal mixed astrocyte-neuron cultures from α₂^G301R/G301R E17 embryonic mice, and moreover, induction of cortical spreading depression (CSD) resulted in reduced recovery in α₂^+/G301R male mice. Moreover, NMDA-type glutamate receptor antagonists or progestin-only treatment reverted specific α₂^+/G301R behavioral phenotypes. Our findings demonstrate that studies of an in vivo relevant FHM2 disease knock-in mouse model provide a link between the female sex hormone cycle and the glutamate system and a link to co-morbid psychiatric manifestations of FHM2.

Episodic Aphasia Associated With Cortical Spreading Depression After Subdural Hemorrhage Evacuation

Cortical spreading depression (CSD) has been associated with many pathological entities including migraine, trauma, hemorrhage, and mitochondrial disease. The clinical diagnosis remains challenging without the other concomitant features such as headache because CSD can mimic seizure or acute stroke. Wereport of a 77 year-old right handed man with a left subdural hematoma evacuation that subsequently developed episodic aphasia, slurred speech, right nasolabial fold flattening, and right pronator drift. In this case report, we discuss our multimodal diagnostic approach and treatment in a patient with episodic aphasia and neurological deficits in order to propose the diagnosis of cortical spreading depression. CSD should be considered when focal deficits in brief episodes occur after stroke and seizures have been ruled out. Treatment choices as illustrated by this case report can have an impact on outcome and resolution of episodes.

Dynamics of Ionic Shifts in Cortical Spreading Depression

Cortical spreading depression is a slowly propagating wave of near-complete depolarization of brain cells followed by temporary suppression of neuronal activity. Accumulating evidence indicates that cortical spreading depression underlies the migraine aura and that similar waves promote tissue damage in stroke, trauma, and hemorrhage. Cortical spreading depression is characterized by neuronal swelling, profound elevation of extracellular potassium and glutamate, multiphasic blood flow changes, and drop in tissue oxygen tension. The slow speed of the cortical spreading depression wave implies that it is mediated by diffusion of a chemical substance, yet the identity of this substance and the pathway it follows are unknown. Intercellular spread between gap junction-coupled neurons or glial cells and interstitial diffusion of K(+) or glutamate have been proposed. Here we use extracellular direct current potential recordings, K(+)-sensitive microelectrodes, and 2-photon imaging with ultrasensitive Ca(2+) and glutamate fluorescent probes to elucidate the spatiotemporal dynamics of ionic shifts associated with the propagation of cortical spreading depression in the visual cortex of adult living mice. Our data argue against intercellular spread of Ca(2+) carrying the cortical spreading depression wavefront and are in favor of interstitial K(+) diffusion, rather than glutamate diffusion, as the leading event in cortical spreading depression.

Spreading Depression, Spreading Depolarizations, and the Cerebral Vasculature

Spreading depression (SD) is a transient wave of near-complete neuronal and glial depolarization associated with massive transmembrane ionic and water shifts. It is evolutionarily conserved in the central nervous systems of a wide variety of species from locust to human. The depolarization spreads slowly at a rate of only millimeters per minute by way of grey matter contiguity, irrespective of functional or vascular divisions, and lasts up to a minute in otherwise normal tissue. As such, SD is a radically different breed of electrophysiological activity compared with everyday neural activity, such as action potentials and synaptic transmission. Seventy years after its discovery by Leão, the mechanisms of SD and its profound metabolic and hemodynamic effects are still debated. What we did learn of consequence, however, is that SD plays a central role in the pathophysiology of a number of diseases including migraine, ischemic stroke, intracranial hemorrhage, and traumatic brain injury. An intriguing overlap among them is that they are all neurovascular disorders. Therefore, the interplay between neurons and vascular elements is critical for our understanding of the impact of this homeostatic breakdown in patients. The challenges of translating experimental data into human pathophysiology notwithstanding, this review provides a detailed account of bidirectional interactions between brain parenchyma and the cerebral vasculature during SD and puts this in the context of neurovascular diseases.

GluN2A/B ratio elevation induced by cortical spreading depression: electrophysiological and quantitative studies of the hippocampus

Cortical spreading depression (CSD), an underlying mechanism of migraine aura, propagates to the hippocampus, and might explain hippocampusassociated symptoms during migraine attack. We hypothesised that this process is, some parts, mediated by NMDA receptors. By using a rat model, CSD was elicited by solid KCl for 45 minutes prior to electrophysiological and quantitative analyses. The result from electrophysiological study was the ratio of glutamate NMDA receptor 2A and 2B subunits (GluN2A/B). Total NMDA receptor response was isolated using an AMPA antagonist, prior to a GluN2B receptor antagonist. The GluN2A/B ratio was calculated by dividing the remaining NMDA-mediated field-excitatory synaptic potentials (fEPSP) with the subtracted difference of NMDAmediated fEPSP. Western blot analysis of the hippocampus was performed to confirm the quantitative change of GluN2A/B ratio. In hippocampal slice study (n = 12), the GluN2A/B ratio of hippocampal fEPSP was significantly increased in CSD group. Western blot analysis (n = 30) revealed an increase in GluN2A subunits and a decrease in GluN2B subunits in the hippocampus ipsilateral to the CSD induction. Our current study revealed that GluN2A/B ratio was shown to be elevated following CSD stimulation by increasing the total number of GluN2A while reducing the total number of GluN2B subunits. This ratio was demonstrated to be associated with synaptic plasticity of the hippocampus in numerous studies. In conclusion, we showed that CSD increased GluN2A/B ratio, in turn, would result in altered synaptic plasticity. Our findings provide a probable implication on the correlation of migraine aura and hippocampusassociated symptoms.

Measurement of distinctive features of cortical spreading depolarizations with different MRI contrasts

Growing clinical evidence suggests critical involvement of spreading depolarizations (SDs) in the pathophysiology of neurological disorders such as migraine and stroke. MRI provides powerful tools to detect and assess co-occurring cerebral hemodynamic and cellular changes during SDs. This study reports the feasibility and advantages of two MRI scans, based on balanced steady-state free precession (b-SSFP) and diffusion-weighted multi-spin-echo (DT2), heretofore unexplored for monitoring SDs. These were compared with gradient-echo MRI. SDs were induced by KCl application in rat brain. Known for high SNR, the T2- and T1-based b-SSFP contrast was hypothesized to provide higher spatiotemporal specificity than T2*-based gradient-echo scanning. DT2 scanning was designed to provide simultaneous T2 and apparent diffusion coefficient (ADC) measurements, thus enabling combined quantitative assessment of hemodynamic and cellular changes during SDs. Procedures were developed to automate identification of SD-induced responses in all the scans. These responses were analyzed to determine detection sensitivity and temporal characteristics of signals from each scanning method. Cluster analysis was performed to elucidate unique temporal patterns for each contrast. All scans allowed detection of SD-induced responses. b-SSFP scans showed significantly larger relative intensity changes, narrower peak widths and greater spatial specificity compared with gradient-echo MRI. SD-induced effects on ADC, calculated from DT2 scans, showed the most pronounced signal changes, displaying about 20% decrease, as against 10-15% signal increases observed with b-SSFP and gradient-echo scanning. Cluster analysis revealed additional temporal sub-patterns, such as an initial dip on gradient-echo scans and temporally shifted T2 and proton density changes in DT2 data. To summarize, b-SSFP and DT2 scanning provide distinct information on SDs compared with gradient-echo MRI. DT2 scanning, with its potential to simultaneously provide cellular and hemodynamic information, can offer unique information on the inter-relationship between these processes in pathologic brain, which may improve monitoring of spreading depolarizations in (pre)clinical settings.

Anesthetic agents modulate ECoG potentiation after spreading depression, and insulin-induced hypoglycemia does not modify this effect

Cortical spreading depression (CSD) is characterized by reversible reduction of spontaneous and evoked electrical activity of the cerebral cortex. Experimental evidence suggests that CSD may modulate neural excitability and synaptic activity, with possible implications for long-term potentiation. Systemic factors like anesthetics and insulin-induced hypoglycemia can influence CSD propagation. In this study, we examined whether the post-CSD ECoG potentiation can be modulated by anesthetics and insulin-induced hypoglycemia. We found that awake adult rats displayed increased ECoG potentiation after CSD, as compared with rats under urethane+chloralose anesthesia or tribromoethanol anesthesia. In anesthetized rats, insulin-induced hypoglycemia did not modulate ECoG potentiation. Comparison of two cortical recording regions in awake rats revealed a similarly significant (p<0.05) potentiation effect in both regions, whereas in the anesthetized groups the potentiation was significant only in the recording region nearer to the stimulating point. Our data suggest that urethane+chloralose and tribromoethanol anesthesia modulate the post-CSD potentiation of spontaneous electrical activity in the adult rat cortex, and insulin-induced hypoglycemia does not modify this effect. Data may help to gain a better understanding of excitability-dependent mechanisms underlying CSD-related neurological diseases.

Pharmacological modulation of spreading depolarizations

Spreading depolarization (SD) is a wave of almost complete depolarization of the neuronal and glial cells. Nowadays there is sufficient evidence demonstrating its pathophysiological effect in migraine with aura, transient global amnesia, stroke, subarachnoid hemorrhage, intracerebral hemorrhage, and traumatic brain injury. In these cases, occurrence of SD has been associated with functional neuronal damage, neuronal necrosis, neurological degeneration, and poor clinical outcome. Animal models show that SD can be modulated by drugs that interfere with its initiation and propagation. There are many pharmacological targets that may help to suppress SD occurrence, such as Na⁺, K⁺, Cl⁻, and Ca²⁺ channels; Na⁺/K⁺ -ATPase; gap junctions; and ligand-based receptors, for example, adrenergic, serotonin, sigma-1, calcitonin gene-related peptide, GABAA, and glutamate receptors. In this regard, N-methyl-d-aspartate (NMDA) receptor blockers, in particular, ketamine, have shown promising results. Therefore, theoretically pharmacologic modulation of SD could help diminish its pathological effects.

Characterization of inhibitory GABA-A receptor activation during spreading depolarization in brain slice

Spreading depolarization (SD) is a slowly propagating wave of near complete depolarizations of neurons and glia. Previous studies have reported large GABA releases during SD, but there is limited understanding of how GABA release and receptor activation are regulated and influence the propagating SD wavefront, as well as an excitatory phase immediately following the passage of SD. The present study characterized GABA-A type receptor (GABA_AR) currents during SD generated by KCl microinjection in acute hippocampal slices from adult mice. Spontaneous GABA_AR-mediated currents (sIPSCs) were initially enhanced, and were followed by a large outward current at the wavefront. sIPSC were then transiently supressed during the late SD phase, resulting in a significant reduction of the sIPSC/sEPSC ratio. The large outward current generated during SD was eliminated by the GABA_AR antagonist gabazine, but the channel potentiator/agonist propofol failed to potentiate the current, likely because of a ceiling effect. Extracellular Cl⁻ decreases recorded during SD were reduced by the antagonist but were not increased by the potentiator. Together with effects of GABA_AR modulators on SD propagation rate, these results demonstrate a significant inhibitory role of the initial GABA_AR activation and suggest that intracellular Cl⁻ loading is insufficient to generate excitatory GABA_AR responses during SD propagation. These results provide a mechanistic explanation for facilitating effects of GABA_AR antagonists, and the lack of inhibitory effect of GABA_AR potentiators on SD propagation. In addition, selective suppression of GABA transmission in the late SD period and the lack of effect of GABA_A modulators on the duration of SD suggests that GABA modulation may not be effective approach to protect neurons during the vulnerable phase of SD.

Radial, spiral and reverberating waves of spreading depolarization occur in the gyrencephalic brain

OBJECTIVES

The detection of the hemodynamic and propagation patterns of spreading depolarizations (SDs) in the gyrencephalic brain using intrinsic optical signal imaging (IOS).

METHODS

The convexity of the brain surface was surgically exposed in fourteen male swine. Within the boundaries of this window, brains were immersed and preconditioned with an elevated K(+) concentration (7 mmol/l) in the standard Ringer lactate solution for 30-40 min. SDs were triggered using 3-5 μl of 1 mol/l KCl solution. Changes in tissue absorbency or reflection were registered with a CCD camera at a wavelength of 564 nm (14 nm FWHM), which was mounted 25 cm above the exposed cortex. Additional monitoring by electrocorticography and laser-Doppler was used in a subset of animals (n=7) to validate the detection of SD.

RESULTS

Of 198 SDs quantified in all of the experiments, 187 SDs appeared as radial waves that developed semi-planar fronts. The morphology was affected by the surface of the gyri, the sulci and the pial vessels. Other SD patterns such as spirals and reverberating waves, which have not been described before in gyrencephalic brains, were also observed. Diffusion gradients created in the cortex surface (i.e., KCl concentrations), sulci, vessels and SD-SD interactions make the gyrencephalic brain prone to the appearance of irregular SD waves.

CONCLUSION

The gyrencephalic brain is capable of irregular SD propagation patterns. The irregularities of the gyrencephalic brain cortex may promote the presence of re-entrance waves, such as spirals and reverberating waves.

Cortical spreading depression as a target for anti-migraine agents

Spreading depression (SD) is a slowly propagating wave of neuronal and glial depolarization lasting a few minutes, that can develop within the cerebral cortex or other brain areas after electrical, mechanical or chemical depolarizing stimulations. Cortical SD (CSD) is considered the neurophysiological correlate of migraine aura. It is characterized by massive increases in both extracellular K⁺ and glutamate, as well as rises in intracellular Na⁺ and Ca²⁺. These ionic shifts produce slow direct current (DC) potential shifts that can be recorded extracellularly. Moreover, CSD is associated with changes in cortical parenchymal blood flow. CSD has been shown to be a common therapeutic target for currently prescribed migraine prophylactic drugs. Yet, no effects have been observed for the antiepileptic drugs carbamazepine and oxcarbazepine, consistent with their lack of efficacy on migraine. Some molecules of interest for migraine have been tested for their effect on CSD. Specifically, blocking CSD may play an enabling role for novel benzopyran derivative tonabersat in preventing migraine with aura. Additionally, calcitonin gene-related peptide (CGRP) antagonists have been recently reported to inhibit CSD, suggesting the contribution of CGRP receptor activation to the initiation and maintenance of CSD not only at the classic vascular sites, but also at a central neuronal level. Understanding what may be lying behind this contribution, would add further insights into the mechanisms of actions for "gepants", which may be pivotal for the effectiveness of these drugs as anti-migraine agents. CSD models are useful tools for testing current and novel prophylactic drugs, providing knowledge on mechanisms of action relevant for migraine.