Cortical spreading depression produces increased cGMP levels in cortex and brain stem that is inhibited by tonabersat (SB-220453) but not sumatriptan

OnabotulinumtoxinA affects cortical recovery period but not occurrence or propagation of cortical spreading depression in rats with compromised blood-brain barrier

ABSTRACT

OnabotulinumtoxinA (BoNT-A) is an Food and Drug Administration-approved, peripherally acting preventive migraine drug capable of inhibiting meningeal nociceptors. Expanding our view of how else this neurotoxin attenuates the activation of the meningeal nociceptors, we reasoned that if the stimulus that triggers the activation of the nociceptor is lessened, the magnitude and/or duration of the nociceptors' activation could diminish as well. In the current study, we further examine this possibility using electrocorticogram recording techniques, immunohistochemistry, and 2-photon microscopy. We report (1) that scalp (head) but not lumbar (back) injections of BoNT-A shorten the period of profound depression of spontaneous cortical activity that follows a pinprick-induced cortical spreading depression (CSD); (2) that neither scalp nor lumbar injections prevent the induction, occurrence, propagation, or spreading velocity of a single wave of CSD; (3) that cleaved SNAP25-one of the most convincing tools to determine the anatomical targeting of BoNT-A treatment-could easily be detected in pericranial muscles at the injection sites and in nerve fibers of the intracranial dura, but not within any cortical area affected by the CSD; (4) that the absence of cleaved SNAP25 within the cortex and pia is unrelated to whether the blood-brain barrier is intact or compromised; and (5) that BoNT-A does not alter vascular responses to CSD. To the best of our knowledge, this is the first report of peripherally applied BoNT-A's ability to alter a neuronal function along a central nervous system pathway involved in the pathophysiology of migraine.

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.

Indomethacin-responsive headaches-A narrative review

BACKGROUND

Indomethacin is a nonsteroidal anti-inflammatory drug whose mechanism of action in certain types of headache disorders remains unknown. The so-called indomethacin-responsive headache disorders consist of a group of conditions with a very different presentation that have a particularly good response to indomethacin. The response is so distinct as to be used in the definition of two: hemicrania continua and paroxysmal hemicrania.

METHODS

This is a narrative literature review. PubMed and the Cochrane databases were used for the literature search.

RESULTS

We review the main pharmacokinetic and pharmacodynamics properties of indomethacin useful for daily practice. The proposed mechanisms of action of indomethacin in the responsive headache disorders, including its effect on cerebral blood flow and intracranial pressure, with special attention to nitrergic mechanisms, are covered. The current evidence for its use in primary headache disorders, such as some trigeminal autonomic cephalalgias, cough, hypnic, exertional or sexual headache, and migraine will be covered, as well as its indication for secondary headaches, such as those of posttraumatic origin.

CONCLUSION

Increasing understanding of the mechanism(s) of action of indomethacin will enhance our understanding of the complex pathophysiology that might be shared by indomethacin-sensitive headache disorders.

Therapeutic implications of cortical spreading depression models in migraine

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

Fremanezumab and its isotype slow propagation rate and shorten cortical recovery period but do not prevent occurrence of cortical spreading depression in rats with compromised blood-brain barrier

Most centrally acting migraine preventive drugs suppress frequency and velocity of cortical spreading depression (CSD). The purpose of the current study was to determine how the new class of peripherally acting migraine preventive drug (ie, the anti-CGRP-mAbs) affect CSD-an established animal model of migraine aura, which affects about 1/3 of people with migraine-when allowed to cross the blood-brain barrier (BBB). Using standard electrocorticogram recording techniques and rats in which the BBB was intentionally compromised, we found that when the BBB was opened, the anti-CGRP-mAb fremanezumab did not prevent the induction, occurrence, or propagation of a single wave of CSD induced by a pinprick, but that both fremanezumab and its isotype were capable of slowing down the propagation velocity of CSD and shortening the period of profound depression of spontaneous cortical activity that followed the spreading depolarization. Fremanezumab's inability to completely block the occurrence of CSD in animals in which the BBB was compromised suggests that calcitonin gene-related peptide (CGRP) may not be involved in the initiation of CSD, at least not to the extent that it can prevent its occurrence. Similarly, we cannot conclude that CGRP is involved in the propagation velocity or the neuronal silencing period (also called cortical recovery period) that follows the CSD because similar effects were observed when the isotype was used. These finding call for caution with interpretations of studies that claim to show direct central nervous system effects of CGRP-mAbs.

Yueju-Ganmaidazao Decoction confers rapid antidepressant-like effects and the involvement of suppression of NMDA/NO/cGMP signaling

ETHNOPHARMACOLOGICAL RELEVANCE

Yueju-Ganmaidazao Decoction (YG) is a multiherbal medicine prescribed for treatment of mood disorder, consisting of two classical traditional Chinese herbal medicine Yueju and Ganmaidazao. Yueju and Ganmaidazao both are used for depression treatment. The combined decoction of Yueju and Ganmaidazao is prescribed to achieve optimal clinical outcomes by dealing with different symptoms of depression. Recent studies indicated ethanol extract of Yueju was capable to confer rapid antidepressant-like response. The antidepressant activity of YG decoction with fast-onset feature remains to be investigated.

AIM OF THE STUDY

Rapid and safe antidepressant treatment is urgently needed. This study aimed to assess the rapid antidepressant-like activity of YG and the underlying mechanism, focusing on NMDA/NO/cGMP signaling.

MATERIALS AND METHODS

The optimal doses for immediate and persistent antidepressant-like response were first screened using tail suspension test (TST) and forced swimming test (FST) post a single administration of YG. The rapid action was further confirmed by using the chronic mild stress (CMS) and learned helplessness (LH) paradigms. The expressions of NMDA receptor subunits were evaluated post stress and YG. The contributions of NMDA, NO, and cGMP signaling to the antidepressant effect of YG were investigated systematically using pharmacological interventions.

RESULTS

The optimal dose for immediate and persistent antidepressant potential, evidenced with reduced immobility times in TST or FST from 30 min to 7 days, was determined. The rapid antidepressant-like effect was confirmed in CMS and LH paradigms, including instant normalization of sucrose preference behavior. The expression of NMDA subunit NR1 in the hippocampus was reduced from 30 min to 5 days post YG. In animals subjected to CMS and LH, hippocampal NR1 expression increased, reversed by YG. YG's antidepressant-like effect was blunted by pretreatment with the agonists along the signalings including NMDA (75 mg/kg), L-arginine (750 mg/kg) and sildenafil (5 mg/kg) in TST or FST. Conversely, administration of subeffective dose of individual antagonists, including MK-801 (0.05 mg/kg), 7-nitroindazole (30 mg/kg), methylene blue (10 mg/kg), in combination with a subeffective dose of YG, elicited antidepressant effects.

CONCLUSION

YG conferred rapid antidepressant-like effects, and the antidepressant response was essentially dependent on suppression of NMDA/NO/cGMP signaling.

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

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

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.

Arguments against the role of cortical spreading depression in migraine

Cortical spreading depression (CSD) is a wave of increased electrocortical activity and vasodilation, followed by sustained decreased activity and prolonged vasoconstriction. Although the discovery of CSD has been ascribed to Leão, rather than vasoconstriction, he only observed a depression of neural activity combined with vasodilation, with much weaker stimulation than used by his followers. There is a longstanding belief that CSD underlies migraine aura, with its positive symptoms such as mosaic patterns and its negative symptoms such as scotoma, and a similar propagation speed and vasoreaction pattern. However, there are many arguments against this theory. CSD is difficult to evoke in man, and electroencephalography (EEG) readings are not flattened during migraine (as opposed to EEG during CSD). Moreover, in contrast to CSD, migraine can occur bilaterally, and is not accompanied by a disrupted blood-brain barrier, increased cerebral metabolism, or cerebral cell swelling. Calcitonin gene-related peptide, which is thought to be characteristic of migraine pain, is increased in the blood from the external jugular vein during migraine in humans, but not during CSD in cats or rats. Moreover, CSD does not explain the appearance of premonitory symptoms or allodynia, long before the actual onset of aura. In addition, there is a variation in the pain mechanisms of migraine and CSD, and in their reaction to transcranial magnetic stimulation and several pharmacologic interventions. Finally, the origin of putative CSD in migraine is currently unknown.

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.

Cortical spreading depression in migraine-time to reconsider?

New evidence concerning the pathophysiology of migraine has come from the results of therapeutic transcranial magnetic stimulation (tTMS). The instantaneous responses to single pulses applied during the aura or headache phase, together with a number of other observations, make it unlikely that cortical spreading depression is involved in migraine. tTMS is considered to act by abolishing abnormal impulse activity in cortical pyramidal neurons and a suggestion is made as to how this activity could arise.

Natriuretic hormones in brain function

Natriuretic hormones (NH) include three groups of compounds: the natriuretic peptides (ANP, BNP and CNP), the gastrointestinal peptides (guanylin and uroguanylin), and endogenous cardiac steroids. These substances induce the kidney to excrete sodium and therefore participate in the regulation of sodium and water homeostasis, blood volume, and blood pressure (BP). In addition to their peripheral functions, these hormones act as neurotransmitters or neuromodulators in the brain. In this review, the established information on the biosynthesis, release and function of NH is discussed, with particular focus on their role in brain function. The available literature on the expression patterns of each of the NH and their receptors in the brain is summarized, followed by the evidence for their roles in modulating brain function. Although numerous open questions exist regarding this issue, the available data support the notion that NH participate in the central regulation of BP, neuroprotection, satiety, and various psychiatric conditions, including anxiety, addiction, and depressive disorders. In addition, the interactions between the different NH in the periphery and the brain are discussed.

Efficacy and mechanism of anticonvulsant drugs in migraine

Anticonvulsants represent one of the main substance classes used for the preventive treatment of migraine. Efficacy has been demonstrated in randomized placebo-controlled trials for topiramate and valproic acid including divalproex sodium. In the case of topiramate, efficacy has recently been proven for chronic migraine and even medication overuse headache, questioning the established concept of medication withdrawal. However, preventive treatment with anticonvulsants is frequently hampered by side effects that occasionally require treatment discontinuation. In addition, these data indicate that some anticonvulsant drugs are effective in migraine, while a number are clearly not useful. Effective anticonvulsants, such as topiramate and valproate, target nociceptive trigeminovascular and trigeminothalamic dural pathways or mechanisms involved in cortical spreading depression. Dissecting out how the anticonvulsants that do not work differ mechanistically from those that do will almost certainly provide avenues through which one can develop new treatments to bring to patients with migraine.

Animal migraine models for drug development: status and future perspectives

Migraine is number seven in WHO's list of all diseases causing disability and the third most costly neurological disorder in Europe. Acute attacks are treatable by highly selective drugs such as the triptans but there is still a huge unmet therapeutic need. Unfortunately, drug development for headache has almost come to a standstill partly because of a lack of valid animal models. Here we review previous models with emphasis on optimal characteristics of a future model. In addition to selection of animal species, the method of induction of migraine-like changes and the method of recording responses elicited by such measures are crucial. The most naturalistic way of inducing attacks is by infusion of endogenous signaling molecules that are known to cause migraine in patients. The most valid response is recording of neural activity in the trigeminal system. The most useful headache related responses are likely to be behavioral, allowing multiple experiments in each individual animal. Distinction is made between acute and prophylactic models and how to validate each of them. Modern insight into neurobiological mechanisms of migraine is so good that it is only a question of resources and efforts that determine when valid models with ability to predict efficacy in migraine will be available.

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.

Immunohistochemical characterization of calcitonin gene-related peptide in the trigeminal system of the familial hemiplegic migraine 1 knock-in mouse

Introduction: Familial hemiplegic migraine type 1 (FHM-1) is caused by mutations in the CACNA1A gene, with the R192Q mutation being the most common. Elevated calcitonin gene-related peptide (CGRP) levels in acute migraine and clinical trials using CGRP receptor antagonists suggest CGRP-related mechanisms are important in migraine.

Methods: Wild-type and R192Q knock-in mice were anaesthetized and perfused. Using immunohistochemical staining, the expression of CGRP in the trigeminocervical complex (TCC) and in the trigeminal and dorsal root ganglia was characterized.

Results: There was a 38% reduction in the percentage of CGRP-immunoreactive cells in the trigeminal ganglia ( p < 0.001) of R192Q knock-in mice compared to wild-type animals. The size distribution profile of CGRP-immunoreactive cells within the trigeminal ganglia demonstrated no significant difference in cell diameter between the two groups ( p ≥ 0.56). CGRP expression was also reduced in thoracic ganglia of R192Q knock-in mice (21% vs. 27% in wild-type group; p < 0.05), but not in other ganglia. In addition, decreased CGRP immunoreactivity was observed in the superficial laminae of the TCC in R192Q knock-in mice, when compared to the control group ( p < 0.005).

Conclusion: The data demonstrates that the FHM-1 CACNA1A mutation alters CGRP expression in the trigeminal ganglion and TCC. This suggests further study of these animals is warranted to characterize better the role of these mutations in the neurobiology of migraine.

Verisimilitude (or "truthlikeness") as an alternative to pro and cons: migraine and cluster headache mechanisms

Calculating verisimilitude (or "truthlikeness") ad modum Popper is a quantitative alternative to the usual pros and cons in migraine and cluster headache mechanisms. The following items were evaluated: dilation of large cranial arteries during migraine; CGRP increase during migraine; migraine as a brain disorder; aura and migraine headache; brain stem activation during migraine; rCBF in migraine without aura; NO and pathophysiology of migraine; neurogenic inflammation and migraine; aura in cluster headache; and hypothalamic activation in cluster headache. It is concluded that verisimilitude calculations can be helpful when judging pathophysiological problems in migraine and cluster headache.

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.

Animal models of headache: from bedside to bench and back to bedside

In recent years bench-based studies have greatly enhanced our understanding of headache pathophysiology, while facilitating the development of new headache medicines. At present, established animal models of headache utilize activation of pain-producing cranial structures, which for a complex syndrome, such as migraine, leaves many dimensions of the syndrome unstudied. The focus on modeling the central nociceptive mechanisms and the complexity of sensory phenomena that accompany migraine may offer new approaches for the development of new therapeutics. Given the complexity of the primary headaches, multiple approaches and techniques need to be employed. As an example, recently a model for trigeminal autonomic cephalalgias has been tested successfully, while by contrast, a satisfactory model of tension-type headache has been elusive. Moreover, although useful in many regards, migraine models are yet to provide a more complete picture of the disorder.

Glial cells as sources and targets of natriuretic peptides

Natriuretic peptides and their receptors are widely expressed in mammalian CNS and increasing evidence implicates them in the regulation of neural development, synaptic transmission and processing of information, and neuroprotection. Although the peptides have been mainly localized in neuronal populations they are also produced in glial cells. Astroglia and microglia also express functional natriuretic peptide receptors that can regulate important physiological responses. In this article we review evidence on the localization of natriuretic peptides and their receptors in astroglial and microglial cells and summarize data supporting the participation of this signalling system in neuron-glia and glia-brain blood vessel communication relevant to CNS function.

Migraines with and without aura and their response to preventive therapy with topiramate

Data from the Prolonged Migraine Prevention (PROMPT) with Topiramate trial were evaluated post hoc to determine whether topiramate could prevent migraine auras, and whether its efficacy in preventing migraine headaches was similar in patients with (MA; n = 269) and without (MoA; n = 542) aura. Migraines and auras were recorded during prospective baseline, 6-month open-label (OL) topiramate and 6-month double-blind (DB), placebo-controlled phases. In the last 28 OL days, migraines without aura and migraine auras decreased by 43.1% and 54.1%, respectively, in MA patients. MoA patients experienced a 44.3% reduction in migraines. In the DB phase, increases in migraines with placebo vs. topiramate were similar to the full study, but were generally not statistically significant, probably due to lack of power in the subgroup analysis. Similarly, there were no statistically significant changes in number of auras between groups. Thus, topiramate appears to reduce migraine auras in parallel with headache reductions, which are similar in patients with and without aura.

Pharmacological migraine provocation: a human model of migraine

In vitro studies have contributed to the characterization of receptors in cranial blood vessels and the identification of possible new antimigraine agents. Animal models enable the study of vascular responses, neurogenic inflammation, and peptide release, and thus have provided leads in the search for migraine mechanisms. So far, however, animal models cannot predict the efficacy of new therapies for migraine. Because migraine attacks are fully reversible and can be aborted by therapy, the headache- or migraine-provoking property of naturally occurring signaling molecules can be tested in a human model. If a naturally occurring substance can provoke migraine in human patients, then it is likely, although not certain, that blocking its effect will be effective in the treatment of acute migraine attacks. To this end, a human in vivo model of experimental headache and migraine in humans has been developed. This model has predicted the efficacy of nitric oxide synthase inhibition and calcitonin gene-related peptide receptor blockade, and has been used to examine other endogenous signaling molecules as well as genetic susceptibility factors.

Does sumatriptan cross the blood-brain barrier in animals and man?

Sumatriptan, a relatively hydrophilic triptan, based on several animal studies has been regarded to be unable to cross the blood–brain barrier (BBB). In more recent animal studies there are strong indications that sumatriptan to some extent can cross the BBB. The CNS adverse events of sumatriptan in migraine patients and normal volunteers also indicate a more general effect of sumatriptan on CNS indicating that the drug can cross the BBB in man. It has been discussed whether a defect in the BBB during migraine attacks could be responsible for a possible central effect of sumatriptan in migraine. This review suggests that there is no need for a breakdown in the BBB to occur in order to explain a possible central CNS effect of sumatriptan.

New drugs for migraine

After the triptans, a calcitonin gene-related peptide blocker (telcagepant) is the first acute medicine that has been developed primarily for treatment of acute migraine. Otherwise, the new drugs have been developed first for other purposes, like anticonvulsants, antihypertensives and antidepressants used for migraine prophylaxis. For acute attacks, a new way to administer a traditional drug like dihydroergotamine is under way, and documentation of efficacy in migraine has been gained for some commonly used painkillers and anti-inflammatory drugs, and for some herbal extracts. Based on insights into the basic pathophysiological mechanisms of the disorder, some drugs have been developed which seem promising in early phase II studies (NOS inhibitors and 5HT1F-receptor agonists). In the future, development and enhancements of existing medicines must be accompanied by increased efforts to develop truly new migraine drugs based on knowledge of the pathophysiology if one wishes to reduce substantially the great burden migraine poses on patients and society.

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.

Randomized, Double-Blind, Placebo-Controlled, Proof-of-Concept Study of the Cortical Spreading Depression Inhibiting Agent Tonabersat in Migraine Prophylaxis

Tonabersat is a novel putative migraine prophylactic agent with an unique stereospecific binding site in the brain. Tonabersat has been shown, in animal models, to inhibit experimentally induced cortical spreading depression, the likely underlying mechanism for migraine aura, and cerebrovascular responses to trigeminal nerve stimulation. The aim was to study the potential for tonabersat as a migraine preventive. A randomized, double-blind, placebo-controlled, multicentre, parallel group study recruited patients with migraine with and without aura experiencing between two and six migraine attacks per month. After a 1-month baseline they received tonabersat 20 mg daily for 2 weeks and 40 mg daily for a further 10 weeks. The primary end-point was the change in mean number of migraine headache days between the third month and the baseline period in the intention-to-treat population comparing the placebo ( n = 65) and tonabersat ( n = 58) groups. At the primary end-point there was a 1.0-day (95% confidence interval −0.33, 2.39; P = 0.14) difference in reduction in migraine days between tonabersat and placebo. There were 10 secondary efficacy end-points, of which two were statistically significant. In month 3 of treatment, the responder rate, defined as a 50% reduction in migraine attacks, was 62% for tonabersat and 45% for placebo ( P < 0.05), and the rescue medication use was reduced in the tonabersat group compared with placebo by 1.8 days ( P = 0.02). Placebo responses were particularly high for all end-points. At least one treatment-emergent adverse event was reported in the tonabersat group in 61% of patients compared with 51% in the placebo group; none was worrisome. Placebo responses were unexpectedly high in this trial, complicating straightforward interpretation of the study results. The good tolerability and promising efficacy results support further exploration of higher doses of tonabersat in larger controlled trials.

Effects of tonabersat on migraine with aura: a randomised, double-blind, placebo-controlled crossover study

BACKGROUND

Migraine with aura is thought likely to be caused by cortical spreading depression (CSD). Tonabersat inhibits CSD, and we therefore investigated whether tonabersat has a preventive effect in migraine with aura.

METHODS

In this randomised, double-blind, placebo-controlled crossover trial, 40 mg tonabersat once daily was compared with matched placebo in patients who had at least one aura attack per month during the past 3 months. Randomisation was by computer-generated list. Patients kept a detailed diary to enable objective diagnosis of each attack as migraine with aura, migraine without aura, or other type of headache. Primary endpoints were a reduction in aura attacks with or without headache and a reduction in migraine headache days with or without an aura. Analysis was per protocol. This trial is registered, number NCT00332007.

FINDINGS

39 patients were included in the study, of whom 31 were included in the statistical analysis of efficacy. Median (IQR) attacks of aura were reduced from 3.2 (1.0-5.0) per 12 weeks on placebo to 1.0 (0-3.0) on tonabersat (p=0.01), whereas the other primary outcome measure, median migraine headache days with or without aura, was not significantly different between placebo and tonabersat groups (3.0 days in each group; p=0.09). Tonabersat was well tolerated but overall had more side-effects than placebo.

INTERPRETATION

Tonabersat showed a preventive effect on attacks of migraine aura but no efficacy on non-aura attacks, in keeping with its known inhibitory effect on CSD. The results support the theory that auras are caused by CSD and that this phenomenon is not involved in attacks without aura.

FUNDING

Minster Pharmaceuticals; Lundbeck Foundation.

Advanced neuroimaging of migraine

Advanced neuroimaging has helped to increase our knowledge about migraine pathophysiology. Our perception of migraine has transformed from a vascular, to a neurovascular, and most recently, to a CNS disorder. Functional imaging has confirmed the importance of cortical spreading depression (CSD) as the pathophysiological mechanism of migraine aura in human beings, whereas novel animal studies are unravelling the mechanistic underpinnings of CSD. Altered cerebral blood flow and neurotransmitter systems have been identified during and between headaches in migraine with and without aura. Advanced neuroimaging has identified mechanisms involved in the transformation of migraine from an episodic disorder to one with near continuous symptomatology. Questions regarding the secondary effects of migraine on brain structure and function, possibly related to attack frequency and duration of illness, have been raised. New imaging techniques could lead to novel diagnostic and therapeutic interventions that will help to improve the lives of millions of patients with migraine. In this Review, we summarise the most important findings from current imaging studies of migraine.

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.

[Cortical spreading depression (CSD): a neurophysiological correlate of migraine aura]

Cortical spreading depression (CSD) is a transient (60-120 s) and at 3-5 mm/min propagating depolarization wave of cortical neurons and glial cells and is characterized by a DC shift of 20-35 mV. It is accompanied by massive redistribution of ions between extracellular and intracellular compartments and by a water influx into the cells. Extracellular potassium ion concentration increases up to 60 mM/l. Potassium ions and the excitatory neurotransmitter glutamate essentially contribute to the initiation and propagation of CSD. Both depolarization and disturbance of brain ion homeostasis regenerate within a few minutes while enhancing energy metabolism, but do not cause damage to normally perfused brain tissue. The similar propagation velocity of CSD and visual scotoma during migraine aura led to the assumption that CSD could be the underlying mechanism of migraine aura. The observation of CSD waves in migraine aura patients with the magnet encephalogram (MEG) technique confirmed this theory. Although many data support the relationship between CSD and aura phase in migraine, the role of CSD in migraine headache is still disputed.

Progress report on new antiepileptic drugs: a summary of the Ninth Eilat Conference (EILAT IX)

The Ninth Eilat Conference on New Antiepileptic Drugs (AEDs)-EILAT IX, took place in Sitges, Barcelona from the 15th to 19th of June 2008. Over 300 basic scientists, clinical pharmacologists and neurologists from 25 countries attended the conference, whose main themes included old and new AEDs in generalized epilepsies, novel formulations and routes of administration of AEDs, common targets and mechanisms of action of drugs for treating epilepsy and other central nervous system (CNS) disorders, and opportunities and perspectives in new AED discovery. Consistent with previous formats of this conference, a large part of the programme was devoted to a review of AEDs in development, as well as updates on AEDs introduced since 1989. Unlike previous EILAT manuscripts, the current (EILAT IX) manuscript focuses only on the preclinical and clinical pharmacology of AEDs that are currently in development. These include brivaracetam, carisbamate (RWJ-333369), 2-deoxy-d-glucose, eslicarbazepine acetate (BIA-2-093), ganaxolone, huperzine, JZP-4, lacosamide, NAX-5055, propylisopropylacetamide (PID), retigabine, T-2000, tonabersat, valrocemide and YKP-3089. The CNS efficacy of these compounds in anticonvulsant animal models as well as other disease model systems are presented in first and second tables and their proposed mechanisms of action are summarized in the third table.

Animal models of migraine headache and aura

PURPOSE OF REVIEW

Over the past 30 years, animal models of migraine have led to the identification of novel drug targets and drug treatments as well as helped to clarify a mechanism for abortive and prophylactic drugs. Animal models have also provided translational knowledge and a framework to think about the impact of hormones, genes, and environmental factors on migraine pathophysiology. Although most acknowledge that these animal models have significant shortcomings, promising new drugs are now being developed and brought to the clinic using these preclinical models. Hence, it is timely to provide a short overview examining the ways in which animal models inform us about underlying migraine mechanisms.

RECENT FINDINGS

First generation migraine models mainly focused on events within pain-generating intracranial tissues, for example, the dura mater and large vessels, as well as their downstream consequences within brain. Upstream events such as cortical spreading depression have also been modeled recently and provide insight into mechanisms of migraine prophylaxis. Mouse mutants expressing human migraine mutations have been genetically engineered to provide an understanding of familial hemiplegic migraine and possibly, by extrapolation, may reflect on the pathophysiology of more common migraine subtypes.

SUMMARY

Animal models of migraine reflect distinct facets of this clinically heterogeneous disorder and contribute to a better understanding of its pathophysiology and pharmacology.

Familial hemiplegic migraine type 1 shows no hypersensitivity to nitric oxide

Familial hemiplegic migraine type 1 (FHM-1) is a dominantly inherited subtype of migraine with aura and transient hemiplegia associated with mutations in the CACNA1A gene. FHM-1 shares many phenotypical similarities with common types of migraine, indicating common neurobiological pathways. Experimental studies have established that activation of the nitric oxide-cyclic guanosine monophosphate (NO-cGMP) pathway plays a crucial role in migraine pathophysiology. Therefore, we tested the hypothesis that CACNA1A mutations in patients with FHM-1 are associated with hypersensitivity to NO-cGMP pathway. We included eight FHM-1 patients with R583Q and C1369Y mutations and nine healthy controls, who received intravenous infusions of 0.5 microg kg(-1) min(-1) glyceryl trinitrate (GTN) over 20 min. We recorded: headache intensity on a verbal rating scale; mean flow velocity in the middle cerebral artery (V(meanMCA)) by transcranial Doppler; diameter of the superficial temporal artery (STA) by Dermascan. One patient reported migraine without aura 5 h after start of the GTN infusion. No aura was reported. The AUC(headache) in the immediate phase was more pronounced in patients than in controls (P = 0.01). In the 14 h following GTN infusion, there was no difference in the AUC(headache) between patients and controls (P = 0.17). We found no difference in the AUC(VmeanMCA) (P = 0.12) or AUC(STA) (P = 0.71) between FHM-1 patients and controls. None of the control persons reported migraine-like headache. FHM-1 patients do not show hypersensitivity of the NO-cGMP pathway, as characteristically seen in migraine patients with and without aura. This indicates that the pathophysiological pathways underlying migraine headache in FHM-1 may be different from the common types of migraine.

Effect of eugenol on spreading depression and epileptiform discharges in rat neocortical and hippocampal tissues

Eugenol, an aromatic molecule derived from several plants, has been receiving examination for clinical relevance in epilepsy and headache. To investigate the neurophysiologic properties of the action of eugenol, its effects on epileptiform field potentials elicited by omission of extracellular Mg2+, spreading depression induced by KCl microinjection, electrically evoked field potentials, and long-term potentiation were tested in rat neocortical and hippocampal tissues. Eugenol (10-100 micromol/l) dose-dependently and reversibly suppressed both epileptiform field potentials and spreading depression Eugenol also reversibly decreased the amplitude of the field postsynaptic potentials evoked in CA1 area of hippocampus and the third layer of neocortex. Eugenol significantly reduced the long-term potentiation by approximately 30% compared with controls. Thus, eugenol can suppress epileptiform field potentials and spreading depression, likely via inhibition of synaptic plasticity. The results indicate the potential for eugenol to use in the treatment of epilepsy and cephalic pain.

Plasma levels of cAMP, cGMP and CGRP in sildenafil-induced headache

Sildenafil, a selective inhibitor of the cyclic guanosine monophosphate (cGMP) degrading phosphodiestrase 5 (PDE5), induced migraine without aura in 10 of 12 migraine patients and in healthy subjects it induced significantly more headache than placebo. The aim of the present study was to determine whether the pain-inducing effects of sildenafil would be reflected in plasma levels of important signalling molecules in migraine: cGMP, cyclic adenosine monophosphate (cAMP) and calcitonin gene-related peptide (CGRP). Ten healthy subjects (four women, six men) and 12 patients (12 women) suffering from migraine without aura were included in two separate double-blind, placebo-controlled, cross-over studies in which placebo or sildenafil 100 mg was administered orally. Plasma levels of CGRP, cAMP and cGMP were determined in blood from the antecubital vein. Despite the ability of sildenafil to induce headache and migraine, no significant differences in plasma levels of CGRP, cGMP and cAMP were detected after sildenafil compared with placebo. In conclusion, plasma levels of CGRP, cGMP and cAMP remain normal during sildenafil-induced headache or migraine. However, since previous studies indicate an important role of these signalling molecules, the present study questions whether cAMP and cGMP in peripheral blood can be used for monitoring pathophysiological events in headache and migraine mechanisms.

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.

5-HT(1B/1D) serotonin receptor agonist attenuates nitroglycerin-evoked nitric oxide synthase expression in trigeminal pathway

This study was conducted to investigate the effect of 5-HT(1B/1D) receptor activation on nitroglycerin (NTG)-induced cerebral hyperaemia and neuronal nitric oxide synthase (nNOS) expression in trigeminovascular neurones. NTG (10 mg/kg) was infused intravenously to adult male Wistar rats with or without pretreatment with 5-HT(1B/1D) receptor agonist, sumatriptan (0.4 mg/kg, intravenously). Cortical blood flow and expression of nNOS enzyme in trigeminal ganglia, trigeminal nucleus caudalis and perivascular nerve fibre surrounding superior sagittal sinus were measured. The results showed that pretreatment with sumatriptan could significantly shorten the period of NTG-induced cerebral hyperaemia without compromising the magnitude of hyperaemic peak. Sumatriptan pretreatment also attenuated the NTG-evoked expression of nNOS in all studied areas. Based on these findings, we suggest that 5-HT(1B/1D) receptor has an important role in stabilizing the trigeminovascular system by attenuating the expression of nNOS enzyme, hence reducing nitric oxide production.

Atrial natriuretic peptide expression is increased in rat cerebral cortex following spreading depression: possible contribution to sd-induced neuroprotection

Cortical spreading depression (CSD) is characterised by slowly propagating waves of cellular depolarization and depression and involves transient changes in blood flow, ion balance and metabolism. In cerebral ischaemia, peri-infarct CSD-like depolarization potentiates infarct growth, whereas preconditioning with a CSD episode protects against subsequent ischaemic insult. Thus, many of the long-lasting molecular changes that occur in CSD-affected tissue are presumed to be part of a 'neuroprotective cascade.' 3',5'-Cyclic guanosine monophosphate (cGMP) has been shown to be a neuroprotective mediator and the nitric oxide system, which increases cGMP production by soluble guanylate cyclase, is up-regulated by CSD. Atrial and C-type natriuretic peptide (ANP/CNP) are present in cerebral cortex and their actions are mediated via particulate guanylate cyclase receptors and cGMP production. Therefore, in further efforts to characterise the role of cGMP-related systems in CSD and neuroprotection, this study investigated possible changes in cortical natriuretic peptide expression following acute, unilateral CSD in rats. Using in situ hybridisation, significant 20-80% increases in ANP mRNA were detected in layers II and VI of ipsilateral cortex at 6 h and 1-14 days after CSD. Ipsilateral cortical levels were again equivalent to control contralateral values after 28 days. Assessment of cortical concentrations of ANP immunoreactivity by radioimmunoassay revealed a significant 57% increase at 7 days after CSD. Despite using a sensitive signal-amplification protocol, authentic ANP-like immunostaining was readily detected in subcortical nerve fibres, but was not reliably detected in normal or CSD-affected neocortex, suggesting the presence of very low levels, and/or active or differential processing of the peptide. Cortical CNP mRNA levels are not altered by CSD, indicating the specificity of the observed effects.Overall, these novel findings demonstrate a prolonged increase in cortical ANP expression after an acute episode of CSD. The overlap between the described time course of CSD-induced protection against ischaemic insult and demonstrated increases in ANP levels, suggest that ANP (like nitric oxide) may contribute to CSD-induced neuroprotection, via effects on cGMP production and other signal-transduction pathways.

Pathophysiology, epidemiology, and impact of migraine

Despite a decade of progress, migraine headache remains prevalent, disabling, underdiagnosed, and undertreated in the United States. Migraine affects approximately 12% of the population, and the economic burden in terms of annual cost of labor lost to migraine disability is between $5.6 and $17.2 billion. The threshold for migraine may be genetically determined, although recent genetic and neurophysiologic studies point to migraine as possibly a channelopathy. Cerebral cortical and brain stem changes occur in migraine. Head pain and associated symptoms of migraine can be explained by activation of the trigeminal vascular system. Evidence has also been accumulated that suggests the release of nitric oxide is an important trigger mechanism. Introduction of the triptans has dramatically advanced acute migraine pharmacotherapy, and preventive therapy has greatly improved; however, public health initiatives may be needed to further advance diagnosis and treatment of this common and disabling disorder.

Nitric oxide in primary headaches

The molecular mechanisms that underlie the primary headaches-migraine, cluster headache and tension-type headache-have not yet been clarified. On the basis of studies in headache induced by intravenous infusions of glyceryl trinitrate (an exogenous nitric oxide donor) and histamine (which liberates nitric oxide from vascular endothelium), it has been suggested that nitric oxide is a likely candidate responsible molecule. The present review deals with the biology of this small messenger molecule, and the updated scientific evidence that suggests a key role for this molecule in primary headaches. This evidence suggests that the release of nitric oxide from blood vessels, perivascular nerve endings or from brain tissue is an important molecular trigger mechanism in spontaneous headache pain. Pilot trials have shown efficacy of a nitric oxide synthase inhibitor in both migraine attacks and chronic tension-type headache. These observations suggest new approaches to the pharmacological treatment of headache.