Diffusion-weighted MRI used to detect in vivo modulation of cortical spreading depression: comparison of sumatriptan and tonabersat

Aberrant CHCHD2-associated mitochondriopathy in Kii ALS/PDC astrocytes

Amyotrophic Lateral Sclerosis/Parkinsonism-Dementia Complex (ALS/PDC), a rare and complex neurological disorder, is predominantly observed in the Western Pacific islands, including regions of Japan, Guam, and Papua. This enigmatic condition continues to capture medical attention due to affected patients displaying symptoms that parallel those seen in either classical amyotrophic lateral sclerosis (ALS) or Parkinson's disease (PD). Distinctly, postmortem examinations of the brains of affected individuals have shown the presence of α-synuclein aggregates and TDP-43, which are hallmarks of PD and classical ALS, respectively. These observations are further complicated by the detection of phosphorylated tau, accentuating the multifaceted proteinopathic nature of ALS/PDC. The etiological foundations of this disease remain undetermined, and genetic investigations have yet to provide conclusive answers. However, emerging evidence has implicated the contribution of astrocytes, pivotal cells for maintaining brain health, to neurodegenerative onset, and likely to play a significant role in the pathogenesis of ALS/PDC. Leveraging advanced induced pluripotent stem cell technology, our team cultivated multiple astrocyte lines to further investigate the Japanese variant of ALS/PDC (Kii ALS/PDC). CHCHD2 emerged as a significantly dysregulated gene when disease astrocytes were compared to healthy controls. Our analyses also revealed imbalances in the activation of specific pathways: those associated with astrocytic cilium dysfunction, known to be involved in neurodegeneration, and those related to major neurological disorders, including classical ALS and PD. Further in-depth examinations revealed abnormalities in the mitochondrial morphology and metabolic processes of the affected astrocytes. A particularly striking observation was the reduced expression of CHCHD2 in the spinal cord, motor cortex, and oculomotor nuclei of patients with Kii ALS/PDC. In summary, our findings suggest a potential reduction in the support Kii ALS/PDC astrocytes provide to neurons, emphasizing the need to explore the role of CHCHD2 in maintaining mitochondrial health and its implications for the disease.

Cx43 hemichannels contribute to astrocyte-mediated toxicity in sporadic and familial ALS

Our results demonstrate that connexin 43 hemichannels are the conduits for amyotrophic lateral sclerosis (ALS) astrocyte-mediated motor neuron toxicity and disease spread, acting as a common mechanism that can target both familial ALS and sporadic ALS populations. Furthermore, our present work provides proof of principle that tonabersat, as a drug already studied in clinical trials for other indications, could serve as a potential ALS therapeutic.

Connexin 43 (Cx43) gap junctions and hemichannels mediate astrocyte intercellular communication in the central nervous system under normal conditions and contribute to astrocyte-mediated neurotoxicity in amyotrophic lateral sclerosis (ALS). Here, we show that astrocyte-specific knockout of Cx43 in a mouse model of ALS slows disease progression both spatially and temporally, provides motor neuron (MN) protection, and improves survival. In addition, Cx43 expression is up-regulated in human postmortem tissue and cerebrospinal fluid from ALS patients. Using human induced pluripotent stem cell–derived astrocytes (hiPSC-A) from both familial and sporadic ALS, we establish that Cx43 is up-regulated and that Cx43-hemichannels are enriched at the astrocyte membrane. We also demonstrate that the pharmacological blockade of Cx43-hemichannels in ALS astrocytes using GAP 19, a mimetic peptide blocker, and tonabersat, a clinically tested small molecule, provides neuroprotection of hiPSC-MN and reduces ALS astrocyte-mediated neuronal hyperexcitability. Extending the in vitro application of tonabersat with chronic administration to SOD1^G93A mice results in MN protection with a reduction in reactive astrocytosis and microgliosis. Taking these data together, our studies identify Cx43 hemichannels as conduits of astrocyte-mediated disease progression and a pharmacological target for disease-modifying ALS therapies.

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.

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.

17-β-Estradiol induces spreading depression and pain behavior in alert female rats

AIMS

Test the putative contribution of 17-β-estradiol in the development of spreading depression (SD) events and head pain in awake, non-restrained rats.

MAIN METHODS

Female, Sprague-Dawley rats were intact or underwent ovariectomy followed one week later by surgery to place electrodes onto the dura to detect epidural electroencephalographic activity (dEEG). dEEG activity was recorded two days later for 12 hours after systemic administration of 17-β-estradiol (180 μg/kg, i.p.). A separate set of rats were observed for changes in exploratory, ambulatory, fine, and rearing behaviors; periorbital allodynia was also assessed.

KEY FINDINGS

A bolus of 17-β-estradiol significantly elevated serum estrogen levels, increased SD episodes over a 12-hour recording period and decreased rearing behaviors in ovariectomized rats. Pre-administration of ICI 182,780, an estrogen receptor antagonist, blocked 17-β-estradiol-evoked SD events and pain behaviors; similar results were observed when the antimigraine therapeutic sumatriptan was used.

SIGNIFICANCE

These data indicate that an estrogen receptor-mediated mechanism contributes to SD events in ovariectomized rats and pain behaviors in both ovariectomized -and intact- rats. This suggests that estrogen plays a different role in each phenomenon of migraine where intense fluctuations in concentration may influence SD susceptibility. This is the first study to relate estrogen peaks to SD development and pain behaviors in awake, freely moving female rats, establishing a framework for future preclinical migraine studies.

Nitroglycerin enhances the propagation of cortical spreading depression: comparative studies with sumatriptan and novel kynurenic acid analogues

Background

The complex pathophysiology of migraine is not yet clearly understood; therefore, experimental models are essential for the investigation of the processes related to migraine headache, which include cortical spreading depression (CSD) and NO donor-induced neurovascular changes. Data on the assessment of drug efficacy in these models are often limited, which prompted us to investigate a novel combined migraine model in which an effective pharmacon could be more easily identified.

Materials and methods

In vivo electrophysiological experiments were performed to investigate the effect of nitroglycerin (NTG) on CSD induced by KCl application. In addition, sumatriptan and newly synthesized neuroactive substances (analogues of the neuromodulator kynurenic acid [KYNA]) were also tested.

Results

The basic parameters of CSDs were unchanged following NTG administration; however, propagation failure was decreased compared to the controls. Sumatriptan decreased the number of CSDs, whereas propagation failure was as minimal as in the NTG group. On the other hand, both of the KYNA analogues restored the ratio of propagation to the control level.

Discussion

The ratio of propagation appeared to be the indicator of the effect of NTG. This is the first study providing direct evidence that NTG influences CSD; furthermore, we observed different effects of sumatriptan and KYNA analogues. Sumatriptan changed the generation of CSDs, whereas the analogues acted on the propagation of the waves. Our experimental design overlaps with a large spectrum of processes present in migraine pathophysiology, and it can be a useful experimental model for drug screening.

New therapeutic approaches for the prevention and treatment of migraine

The management of patients with migraine is often unsatisfactory because available acute and preventive therapies are either ineffective or poorly tolerated. The acute treatment of migraine attacks has been limited to the use of analgesics, combinations of analgesics with caffeine, ergotamines, and the triptans. Successful new approaches for the treatment of acute migraine target calcitonin gene-related peptide (CGRP) and serotonin (5-hydroxytryptamine, 5-HT1F) receptors. Other approaches targeting the transient receptor potential vanilloid (TRPV1) receptor, glutamate, GABAA receptors, or a combination of 5-HT1B/1D receptors and neuronal nitric oxide synthesis have been investigated but have not been successful in clinical trials thus far. In migraine prevention, the most promising new approaches are humanised antibodies against CGRP or the CGRP receptor. Non-invasive and invasive neuromodulation approaches also show promise as both acute and preventive therapies, although further studies are needed to define appropriate candidates for these therapies and optimum protocols for their use.

Involvement of gap junction channels in the pathophysiology of migraine with aura

Migraine is a common, recurrent, and disabling primary headache disorder with a genetic component which affects up to 20% of the population. One third of all patients with migraine experiences aura, a focal neurological disturbance that manifests itself as visual, sensitive or motor symptoms preceding the headache. In the pathophysiology of migraine with aura, activation of the trigeminovascular system from the meningeal vessels mediates migraine pain via the brainstem and projections ascend to the thalamus and cortex. Cortical spreading depression (CSD) was proposed to trigger migraine aura and to activate perivascular trigeminal nerves in the cortex. Quinine, quinidine and the derivative mefloquine are able to inhibit CSD suggesting an involvement of neuronal connexin36 channels in CSD propagation. More recently, CSD was shown to induce headache by activating the trigeminovascular system through the opening of stressed neuronal Pannexin1 channels. A novel benzopyran compound, tonabersat, was selected for clinical trial on the basis of its inhibitory activity on CSD and neurogenic inflammation in animal models of migraine. Interestingly, in the time course of animal model trials, tonabersat was shown to inhibit trigeminal ganglion (TGG) neuronal-glial cell gap junctions, suggesting that this compound could prevent peripheral sensitization within the ganglion. Three clinical trials aimed at investigating the effectiveness of tonabersat as a preventive drug were negative, and conflicting results were obtained in other trials concerning its ability to relieve attacks. In contrast, in another clinical trial, tonabersat showed a preventive effect on attacks of migraine with aura but had no efficacy on non-aura attacks. Gap junction channels seem to be involved in several ways in the pathophysiology of migraine with aura and emerge as a new promising putative target in treatment of this disorder.

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.

Pharmacological targeting of spreading depression in migraine

Migraine, particularly with aura, is a genetically heterogeneous disorder of ion channels, pumps or transporters associated with increased cortical excitability. Spreading depression, as one reflection of hyperexcitability, is the electrophysiological event underlying aura symptoms and a trigger for headache. Endogenous (e.g., genes and hormones) and exogenous factors (e.g., drugs) modulating migraine susceptibility have also been shown to modulate spreading depression susceptibility concordantly, suggesting that spreading depression can be a relevant therapeutic target in migraine. In support of this, several migraine prophylactic drugs used in clinical practice have been shown to suppress spreading depression susceptibility as a probable mechanism of action, despite belonging to widely different pharmacological classes. Hence, susceptibility to spreading depression can be a useful preclinical model with good positive and negative predictive value for drug screening.

Oxcarbazepine does not suppress cortical spreading depression

BACKGROUND

Cortical spreading depression is the electrophysiological substrate of migraine aura, and may trigger headache. Recently, chronic treatment with five migraine prophylactic drugs was shown to suppress cortical spreading depression, implicating spreading depression as a common therapeutic target in migraine prophylaxis.

MATERIALS AND METHODS

In order to assess the negative predictive value of spreading depression susceptibility as a preclinical drug screening tool, we tested oxcarbazepine, an anti-epileptic ineffective in migraine prophylaxis. Valproate served as the positive control. Cortical spreading depression susceptibility was measured in rats using topical KCl or electrical stimulation.

RESULTS

Oxcarbazepine did not suppress spreading depression either after a single dose or after daily treatment for 5 weeks. As previously shown, valproate suppressed spreading depression susceptibility after chronic dosing, while a single dose was ineffective.

CONCLUSIONS

These data provide further support for spreading depression as a relevant target in migraine prophylaxis, and demonstrate the predictive utility of employed spreading depression models.

Cortical spreading depression triggers migraine attack: pro

More than 60 years ago Aristides Leão coined the term spreading depression (SD) to describe a transient "depression" of electrocorticographic activity that lasts up to several minutes and slowly "spreads" in all directions in cortex by way of gray matter contiguity.(1) Today we know that SD is an intrinsic electrophysiological property of central nervous systems, evolutionarily preserved from locust to man.(2-7) Largely based on the similarities between the symptomatology of migraine aura and the electrophysiological features of SD, a causal relationship between the two has long been hypothesized.(8-10) Recently, the SD theory of migraine gained momentum by evidence emerging from both clinical and experimental studies despite being challenged by alternative mechanisms and hypotheses. Here, I will review the accumulated evidence supporting a causal relationship between SD and migraine aura and headache, and discuss the contested notion that SD may also be involved in migraine attacks without a "perceived" aura.

Migraine preventive treatment

Migraine is a chronic neurological disease. Preventive therapy is given in an attempt to reduce the frequency, duration, or severity of attacks. Circumstances that might warrant preventive treatment include recurring migraine attacks that significantly interfere with the patient's daily routines, despite appropriate acute treatment; frequent headaches; contraindication to, failure of, overuse of, or intolerance to acute therapies; patient preference; frequent, very long, or uncomfortable auras; and presence of uncommon migraine conditions. The major medication groups for preventive migraine treatment include beta-adrenergic blockers, antidepressants, calcium channel antagonists, serotonin antagonists, and anticonvulsants. The choice of preventive treatment depends on the individual drug's efficacy and adverse events, the patient's clinical features, frequency, and response to prior treatment, and the presence of any comorbid or coexistent disease.

Cortical spreading depression-new insights and persistent questions

Since its original extensive description by Leao in 1944, thousands of publications have characterized the phenomenon of cortical spreading depression (CSD). Despite the attention that CSD has received over more than six decades, however, many fundamental questions regarding its initiation, propagation, functional consequences, and relationship to migraine and other human disorders remain unanswered. Advances in genetics and cellular imaging have led to important insights into the basic mechanisms of CSD, with increasing attention focused on specific neuronal ion channels, neurotransmitters and neuromodulators. In addition, there is growing recognition that astrocytes and the vasculature may play an active, rather than simply a passive or reactive role in CSD. Several recent descriptions of CSD in humans in the setting of brain injury provide definitive evidence that this phenomenon can occur and have important functional consequences in the human brain. Although the exact role of CSD in migraine has yet to be conclusively established, there is strong evidence that the investigation of CSD in animal models can provide meaningful information about migraine that can be translated into the clinical setting. This review will briefly address the extensive work that has been done on CSD over more than half a century, but focus primarily on more recent studies with a particular emphasis on relevance to migraine.

Spreading depression: from serendipity to targeted therapy in migraine prophylaxis

Despite the relatively well-characterized headache mechanisms in migraine, upstream events triggering individual attacks are poorly understood. This lack of mechanistic insight has hampered a rational approach to prophylactic drug discovery. Unlike targeted abortive and analgesic interventions, mainstream migraine prophylaxis has been largely based on serendipitous observations (e.g. propranolol) and presumed class effects (e.g. anticonvulsants). Recent studies suggest that spreading depression is the final common pathophysiological target for several established or investigational migraine prophylactic drugs. Building on these observations, spreading depression can now be explored for its predictive utility as a preclinical drug screening paradigm in migraine prophylaxis.

Neurological mechanisms of migraine: potential of the gap-junction modulator tonabersat in prevention of migraine

Migraine is a neurovascular disorder characterized by recurrent episodic headaches, and is caused by abnormal processing of sensory information due to peripheral and/or central sensitization. The exact pathophysiological mechanism underlying migraine is not fully understood; however, cortical spreading depression (CSD) is thought to provide the basis for migraine aura and may serve as a trigger of migraine pain. CSD depends on neuronal-glial cell communication, which is mediated by intercellular transfer of messengers through connexin-containing gap junctions, as well as messengers released into the extracellular space by non-junctional connexin-containing hemichannels. These processes are believed to be important in peripheral sensitization within the trigeminal ganglion and to lead to central sensitization. The novel benzopyran compound tonabersat binds selectively to a unique site in the brain. In preclinical studies, tonabersat markedly reduced CSD and CSD-associated events and inhibited gap-junction communication between neurons and satellite glial cells in the trigeminal ganglion. Together, these findings suggest that tonabersat should have clinical application in preventing migraine attacks.

Tonabersat inhibits trigeminal ganglion neuronal-satellite glial cell signaling

BACKGROUND

Sensitization and activation of trigeminal neurons are implicated in the underlying pathology of migraine, acute sinusitis, and allergic rhinitis. Cell bodies of trigeminal neurons that provide sensory innervation of the dura and nasal mucosa reside in the trigeminal ganglion in association with satellite glial cells where they communicate via gap junctions. Gap junctions, channels formed by connexins, modulate the excitability state of both neurons and glia under pathological conditions. Tonabersat, a compound being tested as an antimigraine drug, is thought to block gap junction activity.

OBJECTIVE

To investigate the cellular events within trigeminal ganglia that may account for the significant comorbidity of migraine and rhinosinusitis and determine the effect of tonabersat on neuron-satellite glia communication.

METHODS

Sprague Dawley rats injected with True Blue were used to localize neuronal cell bodies in the ganglion and study neuron-glia signaling via gap junctions in the trigeminal ganglion. Dye coupling studies were conducted under basal conditions and in response to tumor necrosis factor-alpha injection into the whisker pad and/or capsaicin injection into the eyebrow. Changes in connexin 26 and active p38 levels were determined by immunohistochemistry. In addition, the effect of tonabersat prior to chemical stimulation on gap junction activity and expression of connexins and active p38 was investigated.

RESULTS

Injection of tumor necrosis factor-alpha, a cytokine implicated in the pathology of acute sinusitis and allergic rhinitis, into the V2 region was shown to lower the amount of capsaicin required to stimulate neurons located in the V1 region of the ganglion. While injection of tumor necrosis factor-alpha into the whisker pad or capsaicin injection into the eyebrow alone did not cause increased dye movement, the combination of both stimuli greatly increased neuron-satellite glia communication via gap junctions in both V1 and V2 regions. The change in gap junction activity was accompanied by increased expression of connexin 26 and active p38 levels in both neurons and satellite glia in V1 and V2 regions. Pretreatment with tonabersat inhibited gap junction communication between neurons and satellite glia and blocked the increase in connexin 26 and active p38 levels in response to injection of both tumor necrosis factor-alpha (V2) and capsaicin (V1).

CONCLUSIONS

We propose that increased levels of tumor necrosis factor-alpha, as reported during acute sinusitis and allergic rhinitis, reduces the amount of capsaicin necessary to stimulate V1 neurons that leads to cellular changes in both V1 and V2 regions. The cellular events observed in this study may help to explain, in part, the significant comorbidity reported with migraine and rhinosinusitis. In addition, we have provided evidence to suggest that tonabersat can prevent increased neuron-satellite glia signaling and, thus, may be useful in the treatment of migraine, acute sinusitis, and allergic rhinitis.

Translational imaging studies of cortical spreading depression in experimental models for migraine aura

This perspective discusses cortical spreading depression (CSD) phenomena and their translational significance for human migraine aura and the peri-infarct events following cerebral ischemia and injury. They begin with interstitial K(+) release and accumulation following neuronal stimulation, and a buffering astrocytic K(+) influx and remote liberation propagating waves of neuronal hyperexcitability and depression. Diffusion-weighted echoplanar MRI demonstrates CSD features in gyrencephalic brains recapitulating human migraine aura, spatial and temporal features of single primary events and multiple secondary events, their stimulus dependence, pharmacological properties, and their relationship to blood oxygenation level-dependent signals and late cerebrovascular changes. The article finally explores prospects for physiological studies of CSD gaining fuller insights both into mechanisms underlying the pathology of the corresponding human condition and possible approaches to management.

Is there hope for chronic pain and headache?

Currently the clinical needs for pain and headache management are not met. Despite the numerous and exciting recent advances in understanding the molecular and cellular mechanisms that originate pain, we cannot yet fully explain the mechanism underlying the biology of chronic pain. Pain is a natural mechanism preserving our species survival; however, when the protective quality is lost, physiologic changes to the peripheral and central nervous systems result in the formation of chronic pain states. Once we understand how this chronic pain state is created, either through genetic, environmental, therapeutic, or other triggers we may be able to enhance our species existence, limiting maladaptive pain and suffering. The future therapeutic targets will need to address the genetics, neurophysiologic changes of the neurons and brain as well as help control immune systems including the glia. The key to successful headache and pain therapy is research aimed at prevention and minimizing the plastic changes triggering chronic pain.

Simulating the propagation of spreading cortical depression (SCD) wavefront on human brain surface

Spreading cortical depression (SCD) is a slowly spreading supression of electroencephalogram (EEG) activity that was first observed in anaesthetized rabbits in 1944. Since then, the spatial properties of propagation have been investigated on numerous animal experiments. In the folded and complex human cortex, both the occurrence of SCD and the relationship between SCD and migraine have been discussed controversially. This study proposes a software tool to simulate the possible wavefront motion on the surface of human brain. The SCD wavefront motion has been simulated up to an affected surface region of roughly 150 cm(2) and validated by clinical experts.

New insights into migraine pathophysiology

PURPOSE OF REVIEW

This article will review new and exciting developments in migraine research, with particular emphasis on mutations associated with familial hemiplegic migraine and the role of cortical spreading depression in its pathophysiology and treatment.

RECENT FINDINGS

The recent discovery of multiple point mutations in familial hemiplegic migraine has led to the suggestion that migraine and its variants may be due to a paroxysmal disturbance in ion-translocating mechanisms. Mutations associated with familial hemiplegic migraine render the brain more susceptible to prolonged cortical spreading depression caused by either excessive synaptic glutamate release or decreased removal of glutamate and potassium from the synaptic cleft, or persistent sodium influx. Suppression of cortical spreading depression has become an interesting target for preventive migraine treatment. Prolonged treatment with beta-blockers, valproate, topiramate, methysergide or amitriptyline reduced the number of potassium-evoked cortical spreading depressions and elevated the electrical stimulation threshold for the induction of cortical spreading depression in rats. Recent imaging studies in patients suffering from migraine without aura also point to the presence of silent cortical spreading depression as an underlying mechanism. Repeated waves of cortical spreading depression may have deleterious effects on brain function, and perhaps cause silent ischaemic lesions in vulnerable brain regions such as the cerebellum in susceptible individuals.

SUMMARY

This review emphasizes several neurobiological aspects of migraine that reveal paroxysmal disturbances in neuronal and vascular function, that in turn reflect disturbances in the maintenance of ionic gradients.

Suppression of cortical spreading depression in migraine prophylaxis

OBJECTIVE

Topiramate, valproate, propranolol, amitriptyline, and methysergide have been widely prescribed for migraine prophylaxis, but their mechanism or site of action is uncertain. Cortical spreading depression (CSD) has been implicated in migraine and as a headache trigger and can be evoked in experimental animals by electrical or chemical stimulation. We hypothesized that migraine prophylactic agents suppress CSD as a common mechanism of action.

METHODS

Rats were treated either acutely or chronically over weeks and months, with one of the above migraine prophylactic drugs, vehicle, or D-propranolol, a clinically ineffective drug. The impact of treatment was determined on the frequency of evoked CSDs after topical potassium application or on the incremental cathodal stimulation threshold to evoke CSD.

RESULTS

Chronic daily administration of migraine prophylactic drugs dose-dependently suppressed CSD frequency by 40 to 80% and increased the cathodal stimulation threshold, whereas acute treatment was ineffective. Longer treatment durations produced stronger CSD suppression. Chronic D-propranolol treatment did not differ from saline control.

INTERPRETATION

Our data suggest that CSD provides a common therapeutic target for widely prescribed migraine prophylactic drugs. Assessing CSD threshold may prove useful for developing new prophylactic drugs and improving upon existing ones.

Sensitivity and specificity of the new international diagnostic criteria for migraine with aura

OBJECTIVES

Since 1998, migraine with aura (MA) has been diagnosed according to the operational diagnostic criteria of the International Headache Society (ICHD-1). Here we present the data underlying the new criteria for MA in the ICHD-2 classification.

METHODS

Sensitivity of the new criteria was tested in patients with MA and specificity in patients with reversible non-aura visual disturbances. The diagnoses in both groups of patients were made in a validated semistructured physician-conducted interview. We tested five sets of criteria for sensitivity and specificity comparing with the diagnosis according to the ICHD-1 in 200 patients and the selected set of criteria in 274 additional patients.

RESULTS

Four sets of criteria had sensitivity/specificity of 46%/100%, 71%/100%, 62%/95%, and 99%/76%. Sensitivity of the selected set of criteria was 84% (95% CI 79% to 90%) and specificity 97% (95% CI 95% to 99%). According to these criteria at least two of the following should be fulfilled: homonymous visual or unilateral sensory symptoms; at least one aura symptom develops gradually over > or =5 minutes and/or different symptoms occur in succession over > or =5 minutes; each symptom lasts > or =5 and < or =60 minutes. In the additional sample sensitivity of the selected criteria was 90% (95% CI 86% to 94%) and specificity 96% (95% CI 91% to 100%).

CONCLUSIONS

The diagnostic criteria for MA selected for ICHD-2 had high sensitivity and specificity. The ICHD-2 criteria are more operational and probably delineate a more homogeneous sample of patients than the ICHD-1. The ICHD-2 for MA is intended equally for research and clinical practice and can be used at different levels of specialisation.

Emerging drugs in migraine treatment

Ergot alkaloids have been the mainstay of acute migraine therapy for most of the 20th century. They have been supplanted by sumatriptan-like drugs ('triptans'), which, while keeping some of the ergotś mechanisms of action, show improved safety profiles due to their increased receptor selectivity. However, triptans are still far from being perfect drugs: they can constrict human coronary arteries at therapeutic doses and, therefore, are contra-indicated in the presence of cardiovascular disease. Another problem with these agents is recurrence of moderate-to-severe pain within 24 h of initial headache relief. While mechanism-driven drug design has led to the development of various novel, albeit still imperfect, acute antimigraine medications, only a few new prophylactic agents have been made available to migraine clinicians. The efficacy of most, if not all of them has been discovered serendipitously. This is probably due to the fact that, while the pathophysiology of a migraine attack is now reasonably understood, the mechanisms leading to an attack are still mostly unknown. This update analyses the profile of some antimigraine drugs in clinical trials, their mode of action and their potential advantages or drawbacks over already available agents.

Cortical spreading depression: Its role in migraine pathogenesis and possible therapeutic intervention strategies

Cortical spreading depression (CSD) is a well-characterized phenomenon in experimental animals. Recent data show that CSD actually can occur in the injured human brain and compelling evidence is accumulating to support the concept that CSD is responsible for migraine aura. The aim of this review is to highlight recent key advances regarding our understanding of CSD in animal and human studies and its relevance to the pathophysiology of migraine and its potential treatment options.

Migraine aura: new information on underlying mechanisms

PURPOSE OF REVIEW

Since the initial description of cortical spreading depression by Leao, evidence that cortical spreading depression is the underlying pathomechanism of migraine aura has increased. The purpose of this review is to describe the ultimate genetic and molecular mechanisms of migraine aura.

RECENT FINDINGS

It has been debated how a primarily cortical phenomenon (aura phase) may activate trigeminal fibres (headache phase). Recent data have demonstrated a link between cortical events and activation of the pain-sensitive structures of the dura mater. The initial cortical hyperperfusion in cortical spreading depression is partly mediated by the release of trigeminal and parasympathetic neurotransmitters from perivascular nerve fibres, whereas delayed meningeal blood flow increase is mediated by a trigeminal-parasympathetic brainstem connection. With regard to molecular mechanisms, cortical spreading depression upregulates a variety of genes coding for COX-2, TNF-alpha and IL-1beta, galanin or metalloproteinases. The activation of metalloproteinases leads to leakage of the blood-brain barrier, allowing potassium, nitric oxide, adenosine and other products released by cortical spreading depression to reach and sensitize the dural perivascular trigeminal afferents. In familial hemiplegic migraine, new mutations have been described in chromosome 1q23, leading to a haploinsufficiency of the sodium/potassium pump, producing an increase in intracellular calcium, similar to the CACNA1A mutation.

SUMMARY

Recent studies have helped unravel the basic mechanisms involved in migraine aura. Far from being a simple phenomenon, a sequence of events leads from the cortex to the activation of pain-sensitive structures. The role of the brainstem is still poorly described. The identification of target molecules may provide new therapies.

A delayed class of BOLD waveforms associated with spreading depression in the feline cerebral cortex can be detected and characterised using independent component analysis (ICA)

An application of independent component analysis to blood oxygenation level- dependent MRI (BOLD-MRI) results was used to detect cerebrovascular changes that followed the initiation of cortical spreading depression (CSD) in feline brain. The cortical images were obtained from a horizontal plane at 28 s intervals before, and for 1.4-1.75 h after, KCl dissolved in agar (KCl/agar) had been directly applied to the left suprasylvian gyrus of 13 anesthetized cats for 10 min. It successfully resolved, for the first time, a novel class of prolonged, and delayed, biphasic BOLD waveforms. These were larger in amplitude ( approximately 20%), longer lasting and more delayed in onset (13-33 min) than the brief propagating (90 s) BOLD increase ( approximately 4%) already known to be associated with CSD on earlier occasions. Furthermore, such changes occurred in localized regions on the hemisphere ipsilateral to the site of stimulus application in 4 out of 5 control subjects rather than themselves generating propagating waves. Finally, the biphasic waveforms were consistently abolished in the 4 experimental animals studied following the i.v. administration of sumatriptan (0.3 mg kg(-1)), an antimigraine 5-HT(1B/1D) agonist, 15 min before the application of the transient stimulus. They were abolished in 2 out of 4 animals following the intraperitoneal (i.p.) administration of SB-220453 (tonabersat: 10 mg kg(-1), 90 min before stimulus application), a novel anticonvulsant that has recently been reported to inhibit CSD. ICA has thus been successful in detecting a novel localized, as opposed to propagating, signal of potential physiological significance hidden in complex BOLD- MRI data, whose sensitivity to sumatriptan may relate it to the cerebrovascular changes reported in the headache phase of migraine.