Cortical spreading depression and migraine

The Enlightened Brain: Novel Imaging Methods Focus on Epileptic Networks at Multiple Scales

Epilepsy research is rapidly adopting novel fluorescence optical imaging methods to tackle unresolved questions on the cellular and circuit mechanisms of seizure generation and evolution. State of the art two-photon microscopy and wide-field fluorescence imaging can record the activity in epileptic networks at multiple scales, from neuronal microcircuits to brain-wide networks. These approaches exploit transgenic and viral technologies to target genetically encoded calcium and voltage sensitive indicators to subclasses of neurons, and achieve genetic specificity, spatial resolution and scalability that can complement electrophysiological recordings from awake animal models of epilepsy. Two-photon microscopy is well suited to study single neuron dynamics during interictal and ictal events, and highlight the differences between the activity of excitatory and inhibitory neuronal classes in the focus and propagation zone. In contrast, wide-field fluorescence imaging provides mesoscopic recordings from the entire cortical surface, necessary to investigate seizure propagation pathways, and how the unfolding of epileptic events depends on the topology of brain-wide functional connectivity. Answering these questions will inform pre-clinical studies attempting to suppress seizures with gene therapy, optogenetic or chemogenetic strategies. Dissecting which network nodes outside the seizure onset zone are important for seizure generation, propagation and termination can be used to optimize current and future evaluation methods to identify an optimal surgical strategy.

PhD AM, Burstein R. Activation of pial and dural macrophages and dendritic cells by cortical spreading depression

OBJECTIVE

Cortical spreading depression (CSD) has long been implicated in migraine attacks with aura. The process by which CSD, a cortical event that occurs within the blood-brain barrier (BBB), results in nociceptor activation outside the BBB is likely mediated by multiple molecules and cells. The objective of this study was to determine whether CSD activates immune cells inside the BBB (pia), outside the BBB (dura), or in both, and if so, when.

METHODS

Investigating cellular events in the meninges shortly after CSD, we used in vivo two-photon imaging to identify changes in macrophages and dendritic cells (DCs) that reside in the pia, arachnoid, and dura and their anatomical relationship to TRPV1 axons.

RESULTS

We found that activated meningeal macrophages retract their processes and become circular, and that activated meningeal DCs stop migrating. We found that CSD activates pial macrophages instantaneously, pial, subarachnoid, and dural DCs 6-12 minutes later, and dural macrophages 20 minutes later. Dural macrophages and DCs can appear in close proximity to TRPV1-positive axons.

INTERPRETATION

The findings suggest that activation of pial macrophages may be more relevant to cases where aura and migraine begin simultaneously, that activation of dural macrophages may be more relevant to cases where headache begins 20 to 30 minutes after aura, and that activation of dural macrophages may be mediated by activation of migratory DCs in the subarachnoid space and dura. The anatomical relationship between TRPV1-positive meningeal nociceptors, and dural macrophages and DCs supports a role for these immune cells in the modulation of head pain. Ann Neurol 2018;83:508-521.

Understanding Spreading Depression from Headache to Sudden Unexpected Death

Spreading depression (SD) is a neurophysiological phenomenon characterized by abrupt changes in intracellular ion gradients and sustained depolarization of neurons. It leads to loss of electrical activity, changes in the synaptic architecture, and an altered vascular response. Although SD is often described as a unique phenomenon with homogeneous characteristics, it may be strongly affected by the particular triggering event and by genetic background. Furthermore, SD may contribute differently to the pathogenesis of widely heterogeneous clinical conditions. Indeed, clinical disorders related to SD vary in their presentation and severity, ranging from benign headache conditions (migraine syndromes) to severely disabling events, such as cerebral ischemia, or even death in people with epilepsy. Although the characteristics and mechanisms of SD have been dissected using a variety of approaches, ranging from cells to human models, this phenomenon remains only partially understood because of its complexity and the difficulty of obtaining direct experimental data. Currently, clinical monitoring of SD is limited to patients who require neurosurgical interventions and the placement of subdural electrode strips. Significantly, SD events recorded in humans display electrophysiological features that are essentially the same as those observed in animal models. Further research using existing and new experimental models of SD may allow a better understanding of its core mechanisms, and of their differences in different clinical conditions, fostering opportunities to identify and develop targeted therapies for SD-related disorders and their worst consequences.

Serum apolipoprotein E may be a novel biomarker of migraine

Migraine attacks alter various molecules that might be related to the pathophysiology of migraine, such as serotonin, calcitonin gene-related peptide, and nitric oxide. The underlying pathophysiology of migraine is as yet unclear. We explored key proteins related to the pathogenesis of migraine here. Serum was collected from two patients with migraine with aura (MA) and seven patients with migraine without aura (MO) during attack-free periods and migraine attacks. Samples were analyzed using 2-dimensional gel electrophoresis. Nineteen protein spots were altered between the attack-free versus migraine attack periods. Mass spectrometric analysis was performed to identify the proteins within each of the 19 altered spots. Thirty-six proteins were significantly altered in samples collected during attack-free periods versus migraine attacks. The protein with the statistically most significant MASCOT/Mowse score (268±112) among lipoproteins was apolipoprotein (ApoE). In the MA and MO groups, ApoE protein levels were significantly higher during migraine attack than during the attack-free period (p<0.05). ApoE protein levels were also significantly increased in the MA group during the attack-free period compared to healthy controls and patients with tension type headaches (p<0.01). Migraine alters ApoE levels, especially in MA. ApoE might play an important role in the pathophysiology of migraine, and may act as a diagnostic biomarker of migraine.

The Delta Opioid Receptor in Pain Control

Nowadays, the delta opioid receptor (DOPr) represents a promising target for the treatment of chronic pain and emotional disorders. Despite the fact that they produce limited antinociceptive effects in healthy animals and in most acute pain models, DOPr agonists have shown efficacy in various chronic pain models. In this chapter, we review the progresses that have been made over the last decades in understanding the role played by DOPr in the control of pain. More specifically, the distribution of DOPr within the central nervous system and along pain pathways is presented. We also summarize the literature supporting a role for DOPr in acute, tonic, and chronic pain models, as well as the mechanisms regulating its activity under specific conditions. Finally, novel compounds that have make their way to clinical trials are discussed.

Headache

Headache, an almost universal human experience, is one of the most common complaints encountered in medicine and neurology. Described and categorized since antiquity, with the first classification by Aretaeus of Cappadocia, other classifications followed. The evaluation of this condition may be straightforward or challenging, and, though often benign, headache may prove to be an ominous symptom. This review discusses the current diagnosis and classification of headache disorders and principles of management, with a focus on migraine, tension-type headache, trigeminal autonomic cephalgias, and various types of daily headache.

Association between headache and temporomandibular disorder

Headaches are one of the most common conditions associated with temporomandibular disorder (TMD). In the present paper, we evaluated the relationship between headache and TMD, determined whether headache influences the symptoms of TMD, and reported two cases of TMD accompanied by headache. Our practical experience and a review of the literature suggested that headache increases the frequency and intensity of pain parameters, thus complicating dysfunctional diseases in both diagnostic and treatment phases. Therefore, early and multidisciplinary treatment of TMD is necessary to avoid the overlap of painful events that could result in pain chronicity.

Heterogenous migraine aura symptoms correlate with visual cortex functional magnetic resonance imaging responses

OBJECTIVE

Migraine aura is sparsely studied due to the highly challenging task of capturing patients during aura. Cortical spreading depression (CSD) is likely the underlying phenomenon of aura. The possible correlation between the multifaceted phenomenology of aura symptoms and the effects of CSD on the brain has not been ascertained.

METHODS

Five migraine patients were studied during various forms of aura symptoms induced by hypoxia, sham hypoxia, or physical exercise with concurrent photostimulation. The blood oxygenation level-dependent (BOLD) functional magnetic resonance imaging (fMRI) signal response to visual stimulation was measured in retinotopic mapping-defined visual cortex areas V1 to V4.

RESULTS

We found reduced BOLD response in patients reporting scotoma and increased response in patients who only experienced positive symptoms. Furthermore, patients with bilateral visual symptoms had corresponding bihemispherical changes in BOLD response.

INTERPRETATION

These findings suggest that different aura symptoms reflect different types of cerebral dysfunction, which correspond to specific changes in BOLD signal reactivity. Furthermore, we provide evidence of bilateral CSD recorded by fMRI during bilateral aura symptoms. Ann Neurol 2017;82:925-939.

Delayed Cerebral Ischemia after Subarachnoid Hemorrhage: Beyond Vasospasm and Towards a Multifactorial Pathophysiology

PURPOSE OF REVIEW

Delayed cerebral ischemia (DCI) is common after subarachnoid hemorrhage (SAH) and represents a significant cause of poor functional outcome. DCI was mainly thought to be caused by cerebral vasospasm; however, recent clinical trials have been unable to confirm this hypothesis. Studies in humans and animal models have since supported the notion of a multifactorial pathophysiology of DCI. This review summarizes some of the main mechanisms under investigation including cerebral vascular dysregulation, microthrombosis, cortical spreading depolarizations, and neuroinflammation.

RECENT FINDINGS

Recent guidelines have differentiated between DCI and angiographic vasospasm and have highlighted roles of the microvasculature, coagulation and fibrinolytic systems, cortical spreading depressions, and the contribution of the immune system to DCI. Many therapeutic interventions are underway in both preclinical and clinical studies to target these novel mechanisms as well as studies connecting these mechanisms to one another. Clinical trials to date have been largely unsuccessful at preventing or treating DCI after SAH. The only successful pharmacologic intervention is the calcium channel antagonist, nimodipine. Recent studies have provided evidence that cerebral vasospasm is not the sole contributor to DCI and that additional mechanisms may play equal if not more important roles.

Connexin43- and Pannexin-Based Channels in Neuroinflammation and Cerebral Neuropathies

Connexins (Cx) are largely represented in the central nervous system (CNS) with 11 Cx isoforms forming intercellular channels. Moreover, in the CNS, Cx43 can form hemichannels (HCs) at non-junctional membrane as does the related channel-forming Pannexin1 (Panx1) and Panx2. Opening of Panx1 channels and Cx43 HCs appears to be involved in inflammation and has been documented in various CNS pathologies. Over recent years, evidence has accumulated supporting a link between inflammation and cerebral neuropathies (migraine, Alzheimer’s disease (AD), Parkinson’s disease (PD), major depressive disorder, autism spectrum disorder (ASD), epilepsy, schizophrenia, bipolar disorder). Involvement of Panx channels and Cx43 HCs has been also proposed in pathophysiology of neurological diseases and psychiatric disorders. Other studies showed that following inflammatory injury of the CNS, Panx1 activators are released and prolonged opening of Panx1 channels triggers neuronal death. In neuropsychiatric diseases, comorbidities are frequently present and can aggravate the symptoms and make therapeutic management more complex. The high comorbidity between some neuropathies can be partially understood by the fact that these diseases share a common etiology involving inflammatory pathways and Panx1 channels or Cx43 HCs. Thus, anti-inflammatory therapy opens perspectives of targets for new treatments and could have real potential in controlling a cerebral neuropathy and some of its comorbidities. The purpose of this mini review is to provide information of our knowledge on the link between Cx43- and Panx-based channels, inflammation and cerebral neuropathies.

Migraine and risk of stroke: a national population-based twin study

Numerous studies have indicated an increased risk for stroke in patients with migraine, especially migraine with aura; however, many studies used self-reported migraine and only a few controlled for familial factors. We aimed to investigate migraine as a risk factor for stroke in a Swedish population-based twin cohort, and whether familial factors contribute to an increased risk. The study population included twins without prior cerebrovascular disease who answered a headache questionnaire during 1998 and 2002 for twins born 1935-58 and during 2005-06 for twins born between 1959 and 1985. Migraine with and without aura and probable migraine was defined by an algorithm mapping on to clinical diagnostic criteria according to the International Classification of Headache Disorders. Stroke diagnoses were obtained from the national patient and cause of death registers. Twins were followed longitudinally, by linkage of national registers, from date of interview until date of first stroke, death, or end of study on 31 Dec 2014. In total, 8635 twins had any migraineous headache, whereof 3553 had migraine with aura and 5082 had non-aura migraineous headache (including migraine without aura and probable migraine), and 44 769 twins had no migraine. During a mean follow-up time of 11.9 years we observed 1297 incident cases of stroke. The Cox proportional hazards model with attained age as underlying time scale was used to estimate hazard ratios with 95% confidence intervals for stroke including ischaemic and haemorrhagic subtypes related to migraine with aura, non-aura migraineous headache, and any migraineous headache. Analyses were adjusted for gender and cardiovascular risk factors. Where appropriate; within-pair analyses were performed to control for confounding by familial factors. The age- and gender-adjusted hazard ratio for stroke related to migraine with aura was 1.27 (95% confidence interval 1.00-1.62), P = 0.05, and 1.07 (95% confidence interval 0.91-1.26), P = 0.39 related to any migraineous headache. Multivariable adjusted analyses showed similar results. When stratified by gender and attained age of ≤50 or >50 years, the estimated hazard ratio for stroke was higher in twins younger than 50 years and in females; however, non-significant. In the within-pair analysis, the hazard ratio for stroke related to migraine with aura was attenuated [hazard ratio 1.09 (95% confidence interval 0.81-1.46), P = 0.59]. In conclusion, we observed no increased stroke risk related to migraine overall but there was a modestly increased risk for stroke related to migraine with aura, and within-pair analyses suggested that familial factors might contribute to this association.

Intranasally administered IGF-1 inhibits spreading depression in vivo

Spreading depression (SD) is a wave of cellular depolarization that travels slowly through susceptible gray matter brain areas. SD is the most likely cause of migraine aura and perhaps migraine pain, and is a well-accepted animal model of migraine. Identification of therapeutics that can prevent SD may have clinical relevance toward migraine treatment. Here we show that insulin-like growth factor-1 (IGF-1) significantly inhibited neocortical SD in vivo after intranasal delivery to rats. A single dose of IGF-1 inhibited SD within an hour, and continued to protect for at least seven days thereafter. A two-week course of IGF-1, administered every third day, further decreased SD susceptibility and showed no aberrant effects on glial activation, nasal mucosa, or serum markers of toxicity. SD begets SD in vitro by mechanisms that involve microglial activation. We add to this relationship by showing that recurrent SD in vivo increased susceptibility to subsequent SD, and that intervention with IGF-1 significantly interrupted this pathology. These findings support nasal administration of IGF-1 as a novel intervention capable of mitigating SD susceptibility, and as a result, potentially migraine.

Initiation of spreading depression by synaptic and network hyperactivity: Insights into trigger mechanisms of migraine aura

Background

Cortical spreading depression (SD) is thought to underlie migraine aura but mechanisms of triggering SD in the structurally normal, well-nourished cortex of migraine patients remain unknown. Synaptic and network dysfunctions appear to underlie episodic neurological disorders, including migraine. The narrative review summarizes old and recent experimental evidence for triggering SD by synaptic/network mechanisms and discusses the relevance of the data to migraine pathogenesis. Our hypothesis is that under some conditions synaptic/network hyperactivity may reliably ignite SD, and this mechanism may underlie triggering migraine aura in patients.

Findings

High-frequency tetanic stimulation of the cortex reliably triggers SD in synaptically connected regions; SD is a reliable cortical response to acute hyperexcitability (epileptic seizures), though chronic epilepsy prevents triggering SD; in the hyperexcitable cortex, SD may be triggered by sensory stimulation; compromised glutamatergic transmission plays the critical role in triggering SD.

Conclusion

SD may be triggered by dynamic network instability produced by dysfunction of calcium-dependent glutamate release. Synaptic drive from subcortical sensory processing structures (brainstem and/or thalamocortical networks) is able to evoke depolarization of hyperexcitable cortical neurons sufficient to initiate the regenerative SD process. Studying SD initiation by synaptic/network hyperexcitability may provide insights into basic mechanisms underlying SD generation in migraine brain.

Gap junctions, pannexins and pain

Enhanced expression and function of gap junctions and pannexin (Panx) channels have been associated with both peripheral and central mechanisms of pain sensitization. At the level of the sensory ganglia, evidence includes augmented gap junction and pannexin1 expression in glial cells and neurons in inflammatory and neuropathic pain models and increased synchrony and enhanced cross-excitation among sensory neurons by gap junction-mediated coupling. In spinal cord and in suprapinal areas, evidence is largely limited to increased expression of relevant proteins, although in several rodent pain models, hypersensitivity is reduced by treatment with gap junction/Panx1 channel blocking compounds. Moreover, targeted modulation of Cx43 expression was shown to modulate pain thresholds, albeit in somewhat contradictory ways, and mice lacking Panx1 expression globally or in specific cell types show depressed hyperalgesia. We here review the evidence for involvement of gap junctions and Panx channels in a variety of animal pain studies and then discuss ways in which gap junctions and Panx channels may mediate their action in pain processing. This discussion focusses on spread of signals among satellite glial cells, in particular intercellular Ca²⁺ waves, which are propagated through both gap junction and Panx1-dependent routes and have been associated with the phenomenon of spreading depression and the malady of migraine headache with aura.

Frequency-Dependent Habituation Deficit of the Nociceptive Blink Reflex in Aura With Migraine Headache. Can Migraine Aura Modulate Trigeminal Excitability?

OBJECTIVE

To study the influence of the migraine aura on the trigeminal nociception, we investigated the habituation of the nociceptive blink reflex (nBR) R2 responses in aura with migraine headache (AwMH) and comparatively in migraine without aura (MWoA) and healthy subjects (HS).

BACKGROUND

A clear deficit of habituation in trigeminal nociceptive responses has been documented in MWoA; however, similar data in MWA are lacking.

METHODS

Seventeen AwMH, 29 MWoA, and 30 HS were enrolled and a nonrandomized clinical neurophysiological study examining nBR habituation by clinical diagnosis was devised. We delivered a series of 26 electrical stimuli, at different stimulation frequencies (SF) (0.05, 0.1, 0.2, 0.3, 0.5, and 1 Hz), subsequently subdivided in five blocks of five responses for each SF. The mean area values of the second to the fifth block expressed as the percentage of the mean area value of the first block were taken as an index of habituation for each SF.

RESULTS

A significant lower mean percentage decrease of the R2 area across all blocks was found at 1, 0.5, 0.3, and 0.2 Hz SF in MWoA and at 0.3 and 0.2 Hz SF in AwMH, when compared to HS. In the most representative fifth block of responses, we found in MWoA vs HS at 1 Hz, 57.0 ± 27.8 vs 30.6 ± 12.0; at 0.5 Hz, 54.8 ± 26.1 vs 32.51 ± 17.7; at 0.3 Hz, 44.7 ± 21.6 vs 27.6 ± 13.2; at 0.2 Hz, 61.3 ± 29.5 vs 32.6 ± 18.0, and in AwMH vs HS at 0.3 Hz, 52.7 ± 24.7 vs 27.6 ± 13.2; at 0.2 Hz, 69.3 ± 38.6 vs 32.6 ± 18.0 as mean ± SD of the R2 area percentage of the first block, respectively. Interestingly, AwMH subjects did not show differences in mean percentage decrease of the R2 area at 1 and 0.5 Hz SF when compared to HS. No differences between groups were found at 0.1 and 0.05 Hz SF.

CONCLUSIONS

We demonstrated in AwMH a deficit of habituation of the nBR R2 responses after repeated stimulations, although less pronounced than that observed in MWoA of comparable clinical severity. We hypothesize that AwMH and MWoA share some pathogenetic aspects, and also that migraine aura physiopathology may play a modulating role on the excitability of the nociceptive trigeminal pathways.

Recording, analysis, and interpretation of spreading depolarizations in neurointensive care: Review and recommendations of the COSBID research group

Spreading depolarizations (SD) are waves of abrupt, near-complete breakdown of neuronal transmembrane ion gradients, are the largest possible pathophysiologic disruption of viable cerebral gray matter, and are a crucial mechanism of lesion development. Spreading depolarizations are increasingly recorded during multimodal neuromonitoring in neurocritical care as a causal biomarker providing a diagnostic summary measure of metabolic failure and excitotoxic injury. Focal ischemia causes spreading depolarization within minutes. Further spreading depolarizations arise for hours to days due to energy supply-demand mismatch in viable tissue. Spreading depolarizations exacerbate neuronal injury through prolonged ionic breakdown and spreading depolarization-related hypoperfusion (spreading ischemia). Local duration of the depolarization indicates local tissue energy status and risk of injury. Regional electrocorticographic monitoring affords even remote detection of injury because spreading depolarizations propagate widely from ischemic or metabolically stressed zones; characteristic patterns, including temporal clusters of spreading depolarizations and persistent depression of spontaneous cortical activity, can be recognized and quantified. Here, we describe the experimental basis for interpreting these patterns and illustrate their translation to human disease. We further provide consensus recommendations for electrocorticographic methods to record, classify, and score spreading depolarizations and associated spreading depressions. These methods offer distinct advantages over other neuromonitoring modalities and allow for future refinement through less invasive and more automated approaches.

Optogenetic induction of cortical spreading depression in anesthetized and freely behaving mice

Cortical spreading depression, which plays an important role in multiple neurological disorders, has been studied primarily with experimental models that use highly invasive methods. We developed a relatively non-invasive optogenetic model to induce cortical spreading depression by transcranial stimulation of channelrhodopsin-2 ion channels expressed in cortical layer 5 neurons. Light-evoked cortical spreading depression in anesthetized and freely behaving mice was studied with intracortical DC-potentials, multi-unit activity and/or non-invasive laser Doppler flowmetry, and optical intrinsic signal imaging. In anesthetized mice, cortical spreading depression induction thresholds and propagation rates were similar for invasive (DC-potential) and non-invasive (laser Doppler flowmetry) recording paradigms. Cortical spreading depression-related vascular and parenchymal optical intrinsic signal changes were similar to those evoked with KCl. In freely behaving mice, DC-potential and multi-unit activity recordings combined with laser Doppler flowmetry revealed cortical spreading depression characteristics comparable to those under anesthesia, except for a shorter cortical spreading depression duration. Cortical spreading depression resulted in a short increase followed by prolonged reduction of spontaneous active behavior. Motor function, as assessed by wire grip tests, was transiently and unilaterally suppressed following a cortical spreading depression. Optogenetic cortical spreading depression induction has significant advantages over current models in that multiple cortical spreading depression events can be elicited in a non-invasive and cell type-selective fashion.

Increased intrinsic brain connectivity between pons and somatosensory cortex during attacks of migraine with aura

The neurological disturbances of migraine aura are caused by transient cortical dysfunction due to waves of spreading depolarization that disrupt neuronal signaling. The effects of these cortical events on intrinsic brain connectivity during attacks of migraine aura have not previously been investigated. Studies of spontaneous migraine attacks are notoriously challenging due to their unpredictable nature and patient discomfort. We investigated 16 migraine patients with visual aura during attacks and in the attack-free state using resting state fMRI. We applied a hypothesis-driven seed-based approach focusing on cortical visual areas and areas involved in migraine pain, and a data-driven independent component analysis approach to detect changes in intrinsic brain signaling during attacks. In addition, we performed the analyses after mirroring the MRI data according to the side of perceived aura symptoms. We found a marked increase in connectivity during attacks between the left pons and the left primary somatosensory cortex including the head and face somatotopic areas (peak voxel: P = 0.0096, (x, y, z) = (-54, -32, 32), corresponding well with the majority of patients reporting right-sided pain. For aura-side normalized data, we found increased connectivity during attacks between visual area V5 and the lower middle frontal gyrus in the symptomatic hemisphere (peak voxel: P = 0.0194, (x, y, z) = (40, 40, 12). The present study provides evidence of altered intrinsic brain connectivity during attacks of migraine with aura, which may reflect consequences of cortical spreading depression, suggesting a link between aura and headache mechanisms. Hum Brain Mapp 38:2635-2642, 2017. © 2017 Wiley Periodicals, Inc.

Current and novel insights into the neurophysiology of migraine and its implications for therapeutics

Migraine headache and its associated symptoms have plagued humans for two millennia. It is manifest throughout the world, and affects more than 1/6 of the global population. It is the most common brain disorder, and is characterized by moderate to severe unilateral headache that is accompanied by vomiting, nausea, photophobia, phonophobia, and other hypersensitive symptoms of the senses. While there is still a clear lack of understanding of its neurophysiology, it is beginning to be understood, and it seems to suggest migraine is a disorder of brain sensory processing, characterized by a generalized neuronal hyperexcitability. The complex symptomatology of migraine indicates that multiple neuronal systems are involved, including brainstem and diencephalic systems, which function abnormally, resulting in premonitory symptoms, ultimately evolving to affect the dural trigeminovascular system, and the pain phase of migraine. The migraineur also seems to be particularly sensitive to fluctuations in homeostasis, such as sleep, feeding and stress, reflecting the abnormality of functioning in these brainstem and diencephalic systems. Implications for therapeutic development have grown out of our understanding of migraine neurophysiology, leading to major drug classes, such as triptans, calcitonin gene-related peptide receptor antagonists, and 5-HT1F receptor agonists, as well as neuromodulatory approaches, with the promise of more to come. The present review will discuss the current understanding of the neurophysiology of migraine, particularly migraine headache, and novel insights into the complex neural networks responsible for associated neurological symptoms, and how interaction of these networks with migraine pain pathways has implications for the development of novel therapeutics.

Postoperative Hemiplegic Migraine After a Laparoscopic Cholecystectomy: A Case Report

We report the case of a 35-year-old woman who developed severe right-sided hemiplegia and hemisensory loss shortly after emergence from general anesthesia for a laparoscopic cholecystectomy. Her medical history was significant for migraine with aura and a family history of transient hemiparesis thought to be a result of a transient ischemic attack. The patient's deficits slowly resolved, and she was ultimately diagnosed with familial hemiplegic migraine after a negative workup for cerebrovascular accidents.

Cortical Spreading Depression Closes Paravascular Space and Impairs Glymphatic Flow: Implications for Migraine Headache

Functioning of the glymphatic system, a network of paravascular tunnels through which cortical interstitial solutes are cleared from the brain, has recently been linked to sleep and traumatic brain injury, both of which can affect the progression of migraine. This led us to investigate the connection between migraine and the glymphatic system. Taking advantage of a novel in vivo method we developed using two-photon microscopy to visualize the paravascular space (PVS) in naive uninjected mice, we show that a single wave of cortical spreading depression (CSD), an animal model of migraine aura, induces a rapid and nearly complete closure of the PVS around surface as well as penetrating cortical arteries and veins lasting several minutes, and gradually recovering over 30 min. A temporal mismatch between the constriction or dilation of the blood vessel lumen and the closure of the PVS suggests that this closure is not likely to result from changes in vessel diameter. We also show that CSD impairs glymphatic flow, as indicated by the reduced rate at which intraparenchymally injected dye was cleared from the cortex to the PVS. This is the first observation of a PVS closure in connection with an abnormal cortical event that underlies a neurological disorder. More specifically, the findings demonstrate a link between the glymphatic system and migraine, and suggest a novel mechanism for regulation of glymphatic flow.SIGNIFICANCE STATEMENT Impairment of brain solute clearance through the recently described glymphatic system has been linked with traumatic brain injury, prolonged wakefulness, and aging. This paper shows that cortical spreading depression, the neural correlate of migraine aura, closes the paravascular space and impairs glymphatic flow. This closure holds the potential to define a novel mechanism for regulation of glymphatic flow. It also implicates the glymphatic system in the altered cortical and endothelial functioning of the migraine brain.

Deletion of Aquaporin-4 Curtails Extracellular Glutamate Elevation in Cortical Spreading Depression in Awake Mice

Cortical spreading depression (CSD) is a phenomenon that challenges the homeostatic mechanisms on which normal brain function so critically depends. Analyzing the sequence of events in CSD holds the potential of providing new insight in the physiological processes underlying normal brain function as well as the pathophysiology of neurological conditions characterized by ionic dyshomeostasis. Here, we have studied the sequential progression of CSD in awake wild-type mice and in mice lacking aquaporin-4 (AQP4) or inositol 1,4,5-triphosphate type 2 receptor (IP3R2). By the use of a novel combination of genetically encoded sensors that a novel combination - an unprecedented temporal and spatial resolution, we show that CSD leads to brisk Ca2+ signals in astrocytes and that the duration of these Ca2+ signals is shortened in the absence of AQP4 but not in the absence of IP3R2. The decrease of the astrocytic, AQP4-dependent Ca2+ signals, coincides in time and space with a decrease in the duration of extracellular glutamate overflow but not with the initial peak of the glutamate release suggesting that in CSD, extracellular glutamate accumulation is extended through AQP4-dependent glutamate release from astrocytes. The present data point to a salient glial contribution to CSD and identify AQP4 as a new target for therapy.

Cortical Spreading Depression Promotes Persistent Mechanical Sensitization of Intracranial Meningeal Afferents: Implications for the Intracranial Mechanosensitivity of Migraine

Migraine is one of the most common and disabling diseases in the world. A major feature of migraine headache is its aggravation by maneuvers that momentarily increase intracranial pressure. A key hypothesis implicates mechanical sensitization of trigeminal afferents that innervate the intracranial meninges in mediating this feature of migraine. However, whether such pain-related neural response actually develops under endogenous conditions that are linked specifically to migraine remains to be established. Single-unit recordings in the trigeminal ganglion of anesthetized male rats were combined with quantitative mechanical stimulation of the cranial dura mater to determine whether cortical spreading depression (CSD), an endogenous migraine-triggering event, affects the mechanosensitivity of meningeal afferents. CSD gave rise to an almost threefold increase in the magnitude of the responses to mechanical stimuli in 17 of 23 of the afferents tested. CSD-evoked meningeal afferent mechanosensitization occurred with a delay of 23.1 ± 2.2 min and lasted 64.1 ± 6.8 min in recording sessions that lasted for 90 min and for 177.5 ± 22.1 min in recording sessions that were extended for 240 min. Some of the sensitized afferents also developed a shorter-lasting increase in their ongoing discharge rate that was not correlated with the increase in their mechanosensitivity, suggesting that CSD-evoked meningeal afferent sensitization and increase in ongoing activity are independent phenomena. These novel findings support the notion that mechanical sensitization of meningeal afferents serves as a key nociceptive process that underlies the worsening of migraine headache during conditions that momentarily increase intracranial pressure.

Neurovascular contributions to migraine: Moving beyond vasodilation

Migraine is the third most common disease worldwide, the most common neurological disorder, and one of the most common pain conditions. Despite its prevalence, the basic physiology and underlying mechanisms contributing to the development of migraine are still poorly understood and development of new therapeutic targets is long overdue. Until recently, the major contributing pathophysiological event thought to initiate migraine was cerebral and meningeal arterial vasodilation. However, the role of vasodilation in migraine is unclear and recent findings challenge its necessity. While vasodilation itself may not contribute to migraine, it remains possible that vessels play a role in migraine pathophysiology in the absence of vasodilation. Blood vessels consist of a variety of cell types that both release and respond to numerous mediators including growth factors, cytokines, adenosine triphosphate (ATP), and nitric oxide (NO). Many of these mediators have actions on neurons that can contribute to migraine. Conversely, neurons release factors such as norepinephrine and calcitonin gene-related peptide (CGRP) that act on cells native to blood vessels. Both normal and pathological events occurring within and between vascular cells could thus mediate bi-directional communication between vessels and the nervous system, without the need for changes in vascular tone. This review will discuss the potential contribution of the vasculature, specifically endothelial cells, to current neuronal mechanisms hypothesized to play a role in migraine. Hypothalamic activity, cortical spreading depression (CSD), and dural afferent input from the cranial meninges will be reviewed with a focus on how these mechanisms can influence or be impacted by blood vessels. Together, the data discussed will provide a framework by which vessels can be viewed as important potential contributors to migraine pathophysiology, even in light of the current uncertainty over the role of vasodilation in this disorder.

Sex differences in the epidemiology, clinical features, and pathophysiology of migraine

Migraine is two to three times more prevalent in women than men, and women report a longer attack duration, increased risk of headache recurrence, greater disability, and a longer period of time required to recover. Conditions recognised to be comorbid with migraine include asthma, anxiety, depression, and other chronic pain conditions, and these comorbidities add to the amount of disability in both sexes. Migraine-specifically migraine with aura-has been identified as a risk factor for vascular disorders, particularly in women, but because of the scarcity of data, the comparative risk in men has yet to be established. There is evidence implicating the role of female sex hormones as a major factor in determining migraine risk and characteristics, which accounts for sex differences, but there is also evidence to support underlying genetic variance. Although migraine is often recognised in women, it is underdiagnosed in men, resulting in suboptimal management and less participation of men in clinical trials.

Diagnosing migraine

Migraine is a common headache disorder, particularly in women. It usually starts during the teens and twenties, a time when many women are seeking contraception advice. Migraine without aura is the most prevalent type of migraine, affecting up to 70% of people with migraine, while the remainder experience attacks with and/or without aura. Aura is a phase of focal neurological symptoms, typically visual. An increasing body of evidence identifies aura as a marker of increased risk of ischaemic stroke and its presence is a contraindication to the use of combined hormonal contraception (CHC). However, aura is often confused with more generalised premonitory visual symptoms of migraine that may precede attacks of migraine with and without aura, which are not associated with stroke risk. Diagnostic confidence is needed so that CHC is not withheld unnecessarily.

Ischemia-induced spreading depolarization in the retina

Cortical spreading depolarization is a metabolically costly phenomenon that affects the brain in both health and disease. Following severe stroke, subarachnoid hemorrhage, or traumatic brain injury, cortical spreading depolarization exacerbates tissue damage and enlarges infarct volumes. It is not known, however, whether spreading depolarization also occurs in the retina in vivo. We report now that spreading depolarization episodes are generated in the in vivo rat retina following retinal vessel occlusion produced by photothrombosis. The properties of retinal spreading depolarization are similar to those of cortical spreading depolarization. Retinal spreading depolarization waves propagate at a velocity of 3.0 ± 0.1 mm/min and are associated with a negative shift in direct current potential, a transient cessation of neuronal spiking, arteriole constriction, and a decrease in tissue O2 tension. The frequency of retinal spreading depolarization generation in vivo is reduced by administration of the NMDA antagonist MK-801 and the 5-HT(1D) agonist sumatriptan. Branch retinal vein occlusion is a leading cause of vision loss from vascular disease. Our results suggest that retinal spreading depolarization could contribute to retinal damage in acute retinal ischemia and demonstrate that pharmacological agents can reduce retinal spreading depolarization frequency after retinal vessel occlusion. Blocking retinal spreading depolarization generation may represent a therapeutic strategy for preserving vision in branch retinal vein occlusion patients.

How does spreading depression spread? Physiology and modeling

Spreading depression (SD) is a wave phenomenon in gray matter tissue. Locally, it is characterized by massive redistribution of ions across cell membranes. As a consequence, there is sustained membrane depolarization and tissue polarization that depress any normal electrical activity. Despite these dramatic events, SD remains difficult to observe in humans noninvasively, which, for long, has slowed advances in this field. The growing appreciation of its clinical importance in migraine and stroke is therefore consistent with an increasing need for computational methods that tackle the complexity of the problem at multiple levels. In this review, we focus on mathematical tools to investigate the question of spread and its two complementary aspects: What are the physiological mechanisms and what is the spatial extent of SD in the cortex? This review discusses two types of models used to study these two questions, namely, Hodgkin-Huxley type and generic activator-inhibitor models, and the recent advances in techniques to link them.

The effects of acute and preventive migraine therapies in a mouse model of chronic migraine

Background The development of novel migraine therapies has been slow, in part because of the small number of clinically relevant animal models. We have recently developed a new mouse model of chronic migraine using chronic intermittent nitroglycerin, a known human migraine trigger. The objective of this study was to validate this model by testing known and potential migraine-preventive treatments. Methods Migraine therapies were administered to male and female mice for 11 days. On day 3, mice were tested with nitroglycerin every second day for nine days. Basal and nitroglycerin-evoked mechanical hypersensitivity was evaluated using von Frey filaments. Results Chronic intermittent nitroglycerin produced acute hyperalgesia with each administration, and progressive and sustained basal hypersensitivity. The established preventive migraine therapy propranolol effectively blocked the development of acute and chronic nitroglycerin-induced hyperalgesia, while valproate had no effect. Potential migraine-preventive therapies were also tested: Amiloride inhibited nitroglycerin-induced acute and chronic hyperalgesia; while memantine was ineffective. We also tested the acute migraine therapy sumatriptan, which did not alter nitroglycerin-induced hyperalgesia, but instead resulted in acute and chronic hyperalgesia similar to that observed following nitroglycerin administration. Conclusions This study establishes the chronic nitroglycerin model as an additional screening tool to test novel migraine-preventive therapies.

Isostable reduction with applications to time-dependent partial differential equations

Isostables and isostable reduction, analogous to isochrons and phase reduction for oscillatory systems, are useful in the study of nonlinear equations which asymptotically approach a stationary solution. In this work, we present a general method for isostable reduction of partial differential equations, with the potential power to reduce the dimensionality of a nonlinear system from infinity to 1. We illustrate the utility of this reduction by applying it to two different models with biological relevance. In the first example, isostable reduction of the Fokker-Planck equation provides the necessary framework to design a simple control strategy to desynchronize a population of pathologically synchronized oscillatory neurons, as might be relevant to Parkinson's disease. Another example analyzes a nonlinear reaction-diffusion equation with relevance to action potential propagation in a cardiac system.

Involvement of CGRP receptors in retinal spreading depression

BACKGROUND

Cortical spreading depression (CSD) is a transient propagating excitation of synaptic activity followed by depression, which is implicated in migraine with aura and is regarded as the underlying cause of migraine. Calcitonin-gene related peptide (CGRP) receptors play a crucial role in mediating the magnitude of CSD in rat cortical slice. This study aimed to examine whether CGRP receptors are involved in retinal spreading depression (RSD) in chicks.

METHODS

Western blot was used for detection of calcitonin-receptor like receptor (CALCRL) and intrinsic optical imaging was used for pharmacological investigation.

RESULTS

We found that the key component of CGRP receptor, CALCRL, is expressed in the chick retina. Using an in vitro migraine RSD model, we demonstrated that BIBN4096, a potent antagonist for CGRP receptors, markedly reduced the magnitude of RSD induced by K(+), but also the propagation rate.

CONCLUSIONS

The data suggest that CGRP receptors mediate RSD propagation involving neuronal mechanism and approve that RSD is an efficient in vitro approach for assessing anti-migraine drugs targeting CGRP receptors.

The Revolution in Migraine Genetics: From Aching Channels Disorders to a Next-Generation Medicine

Channelopathies are a heterogeneous group of neurological disorders resulting from dysfunction of ion channels located in cell membranes and organelles. The clinical scenario is broad and symptoms such as generalized epilepsy (with or without fever), migraine (with or without aura), episodic ataxia and periodic muscle paralysis are some of the best known consequences of gain- or loss-of-function mutations in ion channels. We review the main clinical effects of ion channel mutations associated with a significant impact on migraine headache. Given the increasing and evolving use of genetic analysis in migraine research-greater emphasis is now placed on genetic markers of dysfunctional biological systems-we also show how novel information in rare monogenic forms of migraine might help to clarify the disease mechanisms in the general population of migraineurs. Next-generation sequencing (NGS) and more accurate and precise phenotyping strategies are expected to further increase understanding of migraine pathophysiology and genetics.

Clinical and electroencephalographic abnormalities during the full duration of a sporadic hemiplegic migraine attack

Electroencephalographic (EEG) abnormalities have been reported during migraine attacks but their spatial and temporal distributions are not well known. We report the temporospatial dynamics of EEG during the full duration of a migraine attack with aura in a 19-year-old woman. She experienced episodes of hemiplegic migraine since the age of 2.5 years, with right hemibody paralysis preceded by visual symptoms. She reported severe pain of the right hemibody just before hemiplegia that was enventually suggestive of possible epileptic seizure, justifying diagnostic video-EEG monitoring. Sporadic hemiplegic migraine was diagnosed in the absence of family history. EEG was normal at the beginning of visual aura. After 15minutes, posterior slow waves appeared over the migrainous hemisphere, spreading progressively towards anterior regions: first the central region (5minutes after onset of contralateral hemiplegia), then the frontal region and over both hemispheres. A new de novo mutation was identified in the SCN1A gene.

Neurostimulation in the treatment of primary headaches

There is increasing interest in using neurostimulation to treat headache disorders. There are now several non-invasive and invasive stimulation devices available with some open-label series and small controlled trial studies that support their use. Non-invasive stimulation options include supraorbital stimulation (Cefaly), vagus nerve stimulation (gammaCore) and single-pulse transcranial magnetic stimulation (SpringTMS). Invasive procedures include occipital nerve stimulation, sphenopalatine ganglion stimulation and ventral tegmental area deep brain stimulation. These stimulation devices may find a place in the treatment pathway of headache disorders. Here, we explore the basic principles of neurostimulation for headache and overview the available methods of neurostimulation.

Does Migraine Increase the Risk of Glaucoma?: A Population-Based Cohort Study

This study investigated whether migraine influences the risk of primary open-angle glaucoma (POAG) and primary angle-closure glaucoma (PACG) in Taiwan.We retrieved the data analyzed in this study from the National Health Insurance Research Database in Taiwan. We included 17,606 newly diagnosed migraine patients without preexisting glaucoma and randomly selected and matched 70,423 subjects without migraine as the comparison cohort. The same exclusion criteria were also applied to comparison subjects. Multivariate Cox proportion-hazards regression model was used to assess the effects of migraines on the risk of glaucoma after adjusting for demographic characteristics and comorbidities.The cumulative incidence of POAG was higher in the migraine cohort than that in the comparison cohort (log-rank P = 0.04). The overall incidence of POAG (per 10,000 person-years) was 9.62 and 7.69, respectively, for migraine cohort and nonmigraine cohort (crude hazard ratio [HR] = 1.24, 95% confidence interval [CI] = 1.01-1.54). After adjusting the covariates, the risk of POAG was not significantly higher in the migraine cohort than in the comparison cohort (adjusted HR [aHR] = 1.15, 95% CI = 0.93-1.42). The cumulative incidence of PACG did not differ between the migraine cohort and the comparison cohort (log-rank test P = 0.53). The overall incidence of PACG was not significantly higher in the migraine cohort than that in the comparison cohort (7.42 vs 6.84 per 10,000 person-years), with an aHR of 1.04 (95% CI = 0.82-1.32).This study shows that migraines are not associated with a higher risk either in POAG or in PACG.

Altered kynurenine pathway metabolites in serum of chronic migraine patients

Background

Activation of glutamate (Glu) receptors plays a key role in the pathophysiology of migraine. Both NMDA and metabotropic Glu receptors are activated or inhibited by metabolites of the kynurenine pathway, such as kynureninic acid (KYNA), quinolinic acid (QUINA), and xanthurenic acid (XA). In spite of the extensive research carried out on KYNA and other kynurenine metabolites in experimental models of migraine, no studies have ever been carried out in humans. Here, we measured all metabolites of the kynurenine pathway in the serum of patients affected by chronic migraine (CM) and age- and gender-matched healthy controls.

Methods

We assessed serum levels of tryptophan (Trp), L-kynurenine (KYN), KYNA, anthranilic acid (ANA), 3-hydroxyanthranilic acid (3-HANA), 3-hydroxykynirenine (3-HK), XA, QUINA, and 5-hydroxyindolacetic acid (5-HIAA) in 119 patients affected by CM (ICHD-3beta criteria) and 84 age-matched healthy subjects.

Patients with psychiatric co-morbidities, systemic inflammatory, endocrine or neurological disorders, and mental retardation were excluded. Serum levels of all metabolites were assayed using liquid chromatography/tandem mass spectrometry (LC-MS/MS).

Results

LC-MS/MS analysis of kynurenine metabolites showed significant reductions in the levels of KYN (−32 %), KYNA (−25 %), 3-HK (−49 %), 3-HANA (−63 %), 5-HIAA (−36 %) and QUINA (−80 %) in the serum of the CM patients, as compared to healthy controls. Conversely, levels of Trp, ANA and XA were significantly increased in CM patients (+5 %, +339 % and +28 %, respectively).

Conclusions

These findings suggest that in migraine KYN is unidirectionally metabolized into ANA at expenses of KYNA and 3-HK. The reduction in the levels of KYNA, which behaves as a competitive antagonist of the glycine site of NMDA receptors, is consistent with the hypothesis that NMDA receptors are overactive in migraine. The increase in XA, a putative activator of Glu2 receptors, may represent a compensatory event aimed at reinforcing endogenous analgesic mechanisms. The large increase in the levels of ANA encourages research aimed at establishing whether ANA has any role in the regulation of nociceptive transmission.

Evidence-Based Treatments for Adults with Migraine

Migraine, a significantly disabling condition, is treated with acute and preventive medications. However, some individuals are refractory to standard treatments. Although there is a host of alternative management options available, these are not always backed by strong evidence. In fact, most of the drugs used in migraine were initially designed for other purposes. Whilst effective, the benefits from these medications are modest, reflecting the need for newer and migraine-specific therapeutic agents. In recent years, we have witnessed the emergence of novel treatments, of which noninvasive neuromodulation appears to be the most attractive given its ease of use and excellent tolerability profile. This paper reviews the evidence behind the available treatments for migraine.

Novel imaging techniques in cerebral small vessel diseases and vascular cognitive impairment

Dementia is a global growing concern, affecting over 35 million people with a global economic impact of over $604 billion US. With an ageing population the number of people affected is expected double over the next two decades. Vascular cognitive impairment can be caused by various types of cerebrovascular disease, including cortical and subcortical infarcts, and the more diffuse white matter injury due to cerebral small vessel disease. Although this type of cognitive impairment is usually considered the second most common form of dementia after Alzheimer's disease, there is increasing recognition of the vascular contribution to neurodegeneration, with both pathologies frequently coexisting. The aim of this review is to highlight the recent advances in the understanding of vascular cognitive impairment, with a focus on small vessel diseases of the brain. We discuss recently identified small vessel imaging markers that have been associated with cognitive impairment, namely cerebral microbleeds, enlarged perivascular spaces, cortical superficial siderosis, and microinfarcts. We will also consider quantitative techniques including diffusion tensor imaging, magnetic resonance perfusion imaging with arterial spin labelling, functional magnetic resonance imaging and positron emission tomography. As well as potentially shedding light on the mechanism by which cerebral small vessel diseases cause dementia, these novel imaging biomarkers are also of increasing relevance given their ability to guide diagnosis and reflect disease progression, which may in the future be useful for therapeutic interventions. This article is part of a Special Issue entitled: Vascular Contributions to Cognitive Impairment and Dementia edited by M. Paul Murphy, Roderick A. Corriveau and Donna M. Wilcock.

Magnetic Resonance Imaging of Pediatric Neurologic Emergencies

Although computed tomography is often the first line of imaging in the emergency setting, magnetic resonance imaging (MRI) is of increasing importance in the evaluation of central nervous system emergencies in the pediatric population. As such, it is necessary to understand the indications for which MRI may be necessary. This article reviews the unique pathophysiologic entities affecting the pediatric population and the associated MRI findings. Specifically, utility of emergent MRI and characteristic appearances of traumatic brain injury, traumatic spinal injury, nonaccidental trauma, arterial ischemic stroke, cerebral sinovenous thrombosis, stroke mimics, and central nervous system infections are described.

From migraine genes to mechanisms

Migraine is a common multifactorial episodic brain disorder with strong genetic basis. Monogenic subtypes include rare familial hemiplegic migraine, cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy, familial advanced sleep-phase syndrome (FASPS), and retinal vasculopathy with cerebral leukodystrophy. Functional studies of disease-causing mutations in cellular and/or transgenic models revealed enhanced (glutamatergic) neurotransmission and abnormal vascular function as key migraine mechanisms. Common forms of migraine (both with and without an aura), instead, are thought to have a polygenic makeup. Genome-wide association studies have already identified over a dozen genes involved in neuronal and vascular mechanisms. Here, we review the current state of molecular genetic research in migraine, also with respect to functional and pathway analyses. We will also discuss how novel experimental approaches for the identification and functional characterization of migraine genes, such as next-generation sequencing, induced pluripotent stem cell, and optogenetic technologies will further our understanding of the molecular pathways involved in migraine pathogenesis.

Visual evoked potentials in subgroups of migraine with aura patients

Background

Patients suffering from migraine with aura can have either pure visual auras or complex auras with sensory disturbances and dysphasia, or both. Few studies have searched for possible pathophysiological differences between these two subgroups of patients.

Methods

Methods - Forty-seven migraine with aura patients were subdivided in a subgroup with exclusively visual auras (MA, N = 27) and another with complex neurological auras (MA+, N = 20). We recorded pattern-reversal visual evoked potentials (VEP: 15 min of arc cheques, 3.1 reversal per second, 600 sweeps) and measured amplitude and habituation (slope of the linear regression line of amplitude changes from the 1st to 6th block of 100 sweeps) for the N1-P1 and P1-N2 components in patients and, for comparison, in 30 healthy volunteers (HV) of similar age and gender distribution.

Results

VEP N1-P1 habituation, i.e. amplitude decrement between 1st and 6th block, which was obvious in most HV (mean slope −0.50), was deficient in both MA (slope +0.01, p = 0.0001) and MA+ (−0.0049, p = 0.001) patients. However, VEP N1-P1 amplitudes across blocks were normal in MA patients, while they were significantly greater in MA+ patients than in HVs.

Conclusions

Our findings suggest that in migraine with aura patients different aura phenotypes may be underpinned by different pathophysiological mechanisms. Pre-activation cortical excitability could be higher in patients with complex neurological auras than in those having pure visual auras or in healthy volunteers.

Advances in the understanding of delayed cerebral ischaemia after aneurysmal subarachnoid haemorrhage

Delayed cerebral ischaemia has been described as the single most important cause of morbidity and mortality in patients who survive the initial aneurysmal subarachnoid haemorrhage. Our understanding of the pathophysiology of delayed cerebral ischaemia is meagre at best and the calcium channel blocker nimodipine remains the only intervention to consistently improve functional outcome after aneurysmal subarachnoid haemorrhage. There is substantial evidence to support cerebral vessel narrowing as a causative factor in delayed cerebral ischaemia, but contemporary research demonstrating improvements in vessel narrowing has failed to show improved functional outcomes. This has encouraged researchers to investigate other potential causes of delayed cerebral ischaemia, such as early brain injury, microthrombosis, and cortical spreading depolarisation. Adherence to a common definition of delayed cerebral ischaemia is needed in order to allow easier assessment of studies using multiple different terms. Furthermore, improved recognition of delayed cerebral ischaemia would not only allow for faster treatment but also better assessment of interventions. Finally, understanding nimodipine's mechanism of action may allow us to develop similar agents with improved efficacy.

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.