The anti-migraine 5-HT(1B/1D) agonist rizatriptan inhibits neurogenic dural vasodilation in anaesthetized guinea-pigs

Meningeal brain borders and migraine headache genesis

Migraine is a highly prevalent and disabling pain disorder that affects >1 billion people worldwide. One central hypothesis points to the cranial meninges as a key site underlying migraine headache genesis through complex interplay between meningeal sensory nerves, blood vessels, and adjacent immune cells. How these interactions might generate migraine headaches remains incompletely understood and a subject of much debate. In this review we discuss clinical and preclinical evidence supporting the concept that meningeal sterile inflammation, involving neurovascular and neuroimmune interactions, underlies migraine headache genesis. We examine downstream signaling pathways implicated in the development of migraine pain in response to exogenous events such as infusing migraine-triggering chemical substances. We further discuss cortex-to-meninges signaling pathways that could underlie migraine pain in response to endogenous events, such as cortical spreading depolarization (CSD), and explore future directions for the field.

The 5-HT1F receptor as the target of ditans in migraine - from bench to bedside

Migraine is a leading cause of disability in more than one billion people worldwide, yet it remains universally underappreciated, even by individuals with the condition. Among other shortcomings, current treatments (often repurposed agents) have limited efficacy and potential adverse effects, leading to low treatment adherence. After the introduction of agents that target the calcitonin gene-related peptide pathway, another new drug class, the ditans - a group of selective serotonin 5-HT_1F receptor agonists - has just reached the international market. Here, we review preclinical studies from the late 1990s and more recent clinical research that contributed to the development of the ditans and led to their approval for acute migraine treatment by the US Food and Drug Administration and the European Medicines Agency.

The putative role of neuroinflammation in the complex pathophysiology of migraine: From bench to bedside

The implications of neurogenic inflammation and neuroinflammation in the pathophysiology of migraine have been clearly demonstrated in preclinical migraine models involving several sites relevant in the trigemino-vascular system, including dural vessels and trigeminal endings, the trigeminal ganglion, the trigeminal nucleus caudalis as well as central trigeminal pain processing structures. In this context, a relevant role has been attributed over the years to some sensory and parasympathetic neuropeptides, in particular calcitonin gene neuropeptide, vasoactive intestinal peptide and pituitary adenylate cyclase-activating polypeptide. Several preclinical and clinical lines of evidence also support the implication of the potent vasodilator and messenger molecule nitric oxide in migraine pathophysiology. All these molecules are involved in vasodilation of the intracranial vasculature, as well as in the peripheral and central sensitization of the trigeminal system. At meningeal level, the engagement of some immune cells of innate immunity, including mast-cells and dendritic cells, and their mediators, has been observed in preclinical migraine models of neurogenic inflammation in response to sensory neuropeptides release due to trigemino-vascular system activation. In the context of neuroinflammatory events implicated in migraine pathogenesis, also activated glial cells in the peripheral and central structures processing trigeminal nociceptive signals seem to play a relevant role. Finally, cortical spreading depression, the pathophysiological substrate of migraine aura, has been reported to be associated with inflammatory mechanisms such as pro-inflammatory cytokine upregulation and intracellular signalling. Reactive astrocytosis consequent to cortical spreading depression is linked to an upregulation of these inflammatory markers. The present review summarizes current findings on the roles of immune cells and inflammatory responses in the pathophysiology of migraine and their possible exploitation in the view of innovative disease-modifying strategies.

A critical review of the neurovascular nature of migraine and the main mechanisms of action of prophylactic antimigraine medications

INTRODUCTION

Migraine involves neurovascular, functional, and anatomical alterations. Migraineurs experience an intense unilateral and pulsatile headache frequently accompanied with vomiting, nausea, photophobia, etc. Although there is no ideal preventive medication, frequency in migraine days may be partially decreased by some prophylactics, including antihypertensives, antidepressants, antiepileptics, and CGRPergic inhibitors. However, the mechanisms of action involved in antimigraine prophylaxis remain elusive.

AREAS COVERED

This review recaps some of the main neurovascular phenomena related to migraine and currently available preventive medications. Moreover, it discusses the major mechanisms of action of the recommended prophylactic medications.

EXPERT OPINION

In the last three years, migraine prophylaxis has evolved from nonspecific to specific antimigraine treatments. Overall, nonspecific treatments  mainly involve neural actions, whereas specific pharmacotherapy (represented by CGRP receptor antagonists and CGRPergic monoclonal antibodies) is predominantly mediated by neurovascular mechanisms that may include, among others: (i) reduction in the cortical spreading depression (CSD)-associated events; (ii) inhibition of pain sensitization; (iii) blockade of neurogenic inflammation; and/or (iv) increase in cranial vascular tone. Accordingly, the novel antimigraine prophylaxis promises to be more effective, devoid of significant adverse effects (unlike nonspecific treatments), and more beneficial for the quality of life of migraineurs.

Intra-arterial injection of lidocaine into middle meningeal artery to treat intractable headaches and severe migraine

BACKGROUND AND PURPOSE

We report the results of intra-arterial injection of lidocaine in the middle meningeal artery in patients with intractable headache or status migrainosus.

METHODS

We treated four patients with intra-arterial lidocaine (2 mg/ml) in doses up to 50 mg in each middle meningeal artery via a microcatheter bilaterally (except in one patient). In two patients with intractable headache, the daily maximum intensity of headache (graded by 11-point numeric rating scale) was recorded for 7 days postprocedure. In two patients with status migrainosus, migraine-related disability 3 months prior and after treatment using MIDAS (Migraine Disability Assessment) questionnaire was recorded.

RESULTS

Intra-arterial lidocaine reduced the headache intensity from 8/10 and 10/10 to 0/10 in the two patients with intractable headaches for 2 days (day 0 and day 1) postprocedure. Despite recurrence of headache on day 2, the intensity was less than preprocedure intensity up to the last day recorded (by 3 and 2 points on day 7). In the two patients with status migrainosus, there was immediate reduction in headache intensity following intra-arterial lidocaine. The post treatment 3-month MIDAS score was lower in both patients compared with pretreatment 3-month score; 3 versus 30 and 55 versus 90. Severe disability preprocedure by MIDAS was reduced to little or no disability postprocedure in one patient.

CONCLUSIONS

Intra-arterial lidocaine resulted in amelioration of headache in patients with intractable headache and those with status migrainosus with improvement lasting longer than the short half-life of lidocaine possibly related to central desensitization.

Synthesis, Kinetics, Binding Conformations and Structure-activity Relationship of Potent Tyrosinase Inhibitors: Aralkylated 2-aminothiazole-ethyltriazole Hybrids

Considering the diversified pharmacological importance of thiazole and triazole heterocyclic moieties, a unique series of S-aralkylated bi-heterocyclic hybrids, 7a-l, was synthesized in a convergent manner. The structures of newly synthesized compounds were characterized by ¹H-NMR, ¹³C-NMR, IR, and EI-MS spectral studies. The structure-activity relationship of these compounds was envisaged by analyzing their inhibitory effects against tyrosinase, whereby all these molecules exhibited potent inhibitory potentials relative to the standard used. The Kinetics mechanism was ascertained by Lineweaver-Burk plots, which revealed that 7g inhibited tyrosinase non-competitively by forming an enzyme-inhibitor complex. The inhibition constants K_i calculated from Dixon plots for this compound was 0.0057µM. These bi-heterocyclic molecules also disclosed good binding energy values (kcal /mol) when assessed computationally. So, these molecules can be considered promising medicinal scaffolds for the treatment of skin disorders.

The Influence of Metoclopramide on Trigeminovascular Nociception: Possible Anti-migraine Mechanism of Action

Metoclopramide is widely used as an abortive migraine therapy due to the advantage of having not only antiemetic, but also analgesic properties. Despite the proven clinical efficacy of metoclopramide in acute migraine, the mechanism of its anti-cephalalgic action has not been entirely elucidated. Taking into account the key role of the trigeminovascular system activation in migraine pathophysiology, we aimed to investigate metoclopramide effects on the excitability of central trigeminovascular neurons and neurogenic dural vasodilation using valid electrophysiological and neurovascular models of trigeminovascular nociception. Extracellular recordings of the activity of second-order dura-sensitive neurons were made in the trigeminocervical complex (TCC) of 16 anaesthetised rats. Cumulative metoclopramide infusion (three steps in 30 min intervals, 5 mg/kg i.v. per step, n = 8) significantly and dose-dependently suppressed both ongoing firing of the TCC neurons and their responses to dural electrical stimulation, maximally to 30%[0-49%] (median[Q1-Q3]) and 4%[0-30%] of the initial level, respectively (both p = 0.001, compared to saline (n = 8)). By contrast, the neurogenic dural vasodilation studied in a separate group of 12 rats was not significantly affected by cumulative infusion of metoclopramide (5 mg/kg i.v. per step, n = 6) compared to both baseline values and the vehicle group (n = 6) (all p > 0.05). These results provide evidence that metoclopramide is unable to affect the peripheral response to trigeminovascular activation, but it does suppress the central response, which is highly predictive of anti-migraine action. Thus, here we show the neurophysiological mechanism underlying the therapeutic efficacy of metoclopramide in migraine.

CGRP in Animal Models of Migraine

With the approval of calcitonin gene-related peptide (CGRP) and CGRP receptor monoclonal antibodies by the Federal Drug Administration, a new era in the treatment of migraine patients is beginning. However, there are still many unknowns in terms of CGRP mechanisms of action that need to be elucidated to allow new advances in migraine therapies. CGRP has been studied both clinically and preclinically since its discovery. Here we review some of the preclinical data regarding CGRP in animal models of migraine.

Effects of monoclonal antagonist antibodies on calcitonin gene-related peptide receptor function and trafficking

Background

Monoclonal antibodies against calcitonin gene-related peptide (CGRP) or its receptor are efficacious for the prevention of migraine headaches. The downstream molecular mechanisms following ligand-receptor blockade by which these antibodies prevent CGRP signaling through CGRP receptors have not been demonstrated.

Methods

Here we produced tool monoclonal functional antagonist antibodies against CGRP and its canonical receptor and developed a novel cellular model using fluorogen-activated protein technology that allows detection of CGRP receptor internalization by flow cytometry and, for an extended time course, visualization by confocal microscopy.

Results

Using this cell model we showed that these antagonist antibodies block both CGRP-induced cAMP signaling and CGRP receptor internalization. At least 10-fold higher concentrations of either antibody are necessary to block CGRP receptor internalization compared with cAMP accumulation in our cell model.

Conclusion

These data reinforce our understanding of how monoclonal functional antagonist antibodies interfere with CGRP signaling.

Targeting the central projection of the dural trigeminovascular system for migraine prophylaxis

Migraine abortives likely target both peripheral-dural and central trigeminovascular mechanisms in mediating their therapeutic effects. However, in preclinical assays, many migraine preventives have little success at inhibiting similar trigeminovascular-mediated peripheral changes within the dural microenvironment. In addition, their effects on central trigeminovascular neuronal responses are largely unknown. Using a validated preclinical model of acute dural-intracranial (migraine-like) head pain, using Sprague Dawley rats, we tested whether migraine preventives suppress ongoing firing of central trigeminocervical neurons, and evoked responses to cranial neurovascular activation. Flunarizine, sodium valproate, propranolol, and amitriptyline, all dose-dependently inhibited ongoing spontaneous firing of dural trigeminovascular neurons, and differentially affected neuronal responses to intracranial-dural and extracranial-cutaneous somatosensory stimulation. Lamotrigine, only effective in the treatment of migraine aura, did not affect responses. These data provide a mechanistic rationale for the clinical effects of migraine preventives in the treatment of migraine, via the modulation of dural-responsive central trigeminovascular neurons. Also, given their limited effect on peripheral dural vasdilatory responses, these data also suggest that migraine preventives specifically target central, rather than peripheral, components of trigeminal neurovascular mechanisms involved in migraine pathophysiology, to mediate their preventive action. Finally, these data further validate this preclinical model of central trigeminovascular activation to screen migraine preventives.

Migraine: New Molecular Mechanisms

Migraine is an episodic headache disorder affecting more than 10% of the general population. Migraine arises from a primary brain dysfunction that leads to activation and sensitization of the trigeminovascular system. A major incompletely understood issue in the neurobiology of migraine concerns the molecular and cellular mechanisms that underlie the primary brain dysfunction and lead to activation and sensitization of the trigeminovascular system, thus generating and maintaining migraine pain. Here the author reviews recent discoveries that have advanced our understanding of these mechanisms toward a unifying pathophysiological hypothesis, in which cortical spreading depression (CSD), the phenomenon underlying migraine aura, assumes a key role. In particular, the author discusses the main recent findings in the genetics and neurobiology of familial hemiplegic migraine and the insights they provide into the molecular and cellular mechanisms that may lead to the increased susceptibility of CSD in migraineurs.

Intravital Microscopy on a Closed Cranial Window in Mice: A Model to Study Trigeminovascular Mechanisms Involved in Migraine

The purpose of the study was to develop a mouse model to study trigeminovascular mechanisms using intravital microscopy on a closed cranial window. In addition, we studied exogenous and endogenous calcitonin gene-related peptide (CGRP)-mediated vasodilation in dural arteries. Arteries in C57BL/6Jico mice were constricted with endothelin-1, which reduced the baseline diameter by 65-75%. Subsequently, vasodilation was induced by α-CGRP, capsaicin or transcranial electrical stimulation of perivascular trigeminal nerves in the absence or presence of different concentrations of BIBN4096BS or sumatriptan. Both α-CGRP and capsaicin induced vasodilation in preconstricted arteries. Transcranial electrical stimulation also induced current-dependent relaxation of dural arteries with 100 μA producing maximal dilation in the control group. BIBN4096BS blocked the responses evoked by ä-CGRP and capsaicin, as well as electrical stimulation, whereas sumatriptan attenuated only vasodilation induced by electrical stimulation. This model is likely to prove useful in dissecting elements of the trigeminovascular system and for exploring pathophysiological aspects of migraine, especially in future studies using transgenic mice with mutations relevant to those observed in patients with migraine.

A novel translational animal model of trigeminal autonomic cephalalgias

OVERVIEW

Trigeminal autonomic cephalalgias (TACs) are highly disabling primary headache disorders that involve severe unilateral head pain coupled with significant lateralized cranial autonomic features. Our understanding of these disorders and the development of novel and more effective treatments has been limited by the lack of a suitable animal model to explore their pathophysiology and screen prospective treatments.

DISCUSSION

This review details the development of a novel preclinical model that demonstrates activation of both the trigeminovascular system and parasympathetic projections, thought to be responsible for the severe head pain and autonomic symptoms.

CONCLUSION

This model demonstrates a unique response to TAC specific treatments and highlights the importance of the cranial parasympathetic pathway to the pathophysiology of TACs and as a potential locus of action for treatments. The development of this model opens up opportunities to understand the pathophysiology of these disorders further, the likely involvement of the hypothalamus, as well as providing a preclinical model with which to screen novel compounds.

Effect of intra-arterial injection of lidocaine and methyl-prednisolone into middle meningeal artery on intractable headaches

The present report describes the effect of intra-arterial injection of a dose of 40 mg lidocaine and 20 mg methylprednisolone into the middle meningeal artery of two patients suffering from severe headaches. The effect of injection of lidocaine and methylprednisolone was short lasting with effect manifesting within 5 min and lasting 5-8 h after injection. Both patients reported improvement in headache intensity after 24 h post-procedure. Intra-arterial injection of lidocaine and methylprednisolone may represent another treatment strategy for headaches not responsive to standard treatment.

Modelling headache and migraine and its pharmacological manipulation

Similarities between laboratory animals and humans in anatomy and physiology of the cephalic nociceptive pathways have allowed scientists to create successful models that have significantly contributed to our understanding of headache. They have also been instrumental in the development of novel anti-migraine drugs different from classical pain killers. Nevertheless, modelling the mechanisms underlying primary headache disorders like migraine has been challenging due to limitations in testing the postulated hypotheses in humans. Recent developments in imaging techniques have begun to fill this translational gap. The unambiguous demonstration of cortical spreading depolarization (CSD) during migraine aura in patients has reawakened interest in studying CSD in animals as a noxious brain event that can activate the trigeminovascular system. CSD-based models, including transgenics and optogenetics, may more realistically simulate pain generation in migraine, which is thought to originate within the brain. The realization that behavioural correlates of headache and migrainous symptoms like photophobia can be assessed quantitatively in laboratory animals, has created an opportunity to directly study the headache in intact animals without the confounding effects of anaesthetics. Headache and migraine-like episodes induced by administration of glyceryltrinitrate and CGRP to humans and parallel behavioural and biological changes observed in rodents create interesting possibilities for translational research. Not unexpectedly, species differences and model-specific observations have also led to controversies as well as disappointments in clinical trials, which, in return, has helped us improve the models and advance our understanding of headache. Here, we review commonly used headache and migraine models with an emphasis on recent developments.

Pearls and pitfalls in experimental in vivo models of migraine: dural trigeminovascular nociception

BACKGROUND

Migraine is a disorder of the brain and is thought to involve activation of the trigeminovascular system, which includes the peripheral afferent projection to the nociceptive specific dura mater, as well as the central afferent projection to the trigeminal nucleus caudalis. Stimulation of the blood vessels of the dura mater produces pain in patients that is referred to the head similar to headache. HEADACHE MECHANISMS: The likely reason for the pain is because the vascular structures of the dura mater, including the superior sagittal sinus and middle meningeal artery, are richly innervated by a plexus of largely unmyelinated sensory nerve fibers from the ophthalmic division of the trigeminal ganglion.

METHODOLOGY

Stimulation of these nociceptive specific nerve fibers is painful and produces neuronal activation in the trigeminal nucleus caudalis. Preclinical models of headache have taken advantage of this primarily nociceptive pathway, and various animal models use dural trigeminovascular nociception to assay aspects of head pain. These assays measure responses at the level of the dural vasculature and the central trigeminal nucleus caudalis as a correlate of trigeminovascular activation thought to be involved in headache.

SUMMARY

This review will summarize the history of the development of models of dural trigeminovascular nociception, including intravital microscopy and laser Doppler flowmetry at the level of the vasculature, and electrophysiology and Fos techniques used to observe neuronal activation at the trigeminal nucleus caudalis. It will also describe some of pitfalls of these assays and developments for the future.

Alum catalyzed simple, efficient, and green synthesis of 2-[3-amino-5-methyl-5-(pyridin-3-yl)-1,5-dihydro-4H-1,2,4-triazol-4-yl]propanoic acid derivatives in aqueous media

Alum (KAl(SO4)2 · 12H2O) is an inexpensive, efficient, and nontoxic catalyst used for the synthesis of 2-[3-amino-5-methyl-5-(pyridin-3-yl)-1,5-dihydro-4H-1,2,4-triazol-4-yl]propanoic acid derivatives in aqueous media by the reaction of 3-acetyl pyridine (1), amino acids (2)/(6), and thiosemicarbazide (4) at 80 °C. This methodology offers significant improvements for the synthesis of products with regards to the yield of products, simplicity in operation, and green aspects by avoiding toxic catalysts which uphold the motto of green chemistry. Synthesized compounds have been characterized by FT-IR, (13)C NMR, and (1)HNMR spectroscopy.

mRNA expression of 5-hydroxytryptamine 1B, 1D, and 1F receptors and their role in controlling the release of calcitonin gene-related peptide in the rat trigeminovascular system

Triptans, a family of 5-hydroxytryptamine (5-HT) 1B, 1D, and 1F receptor agonists, are used in the acute treatment of migraine attacks. The site of action and subtypes of the 5-HT(1) receptor that mediate the antimigraine effect have still to be identified. This study investigated the mRNA expression of these receptors and the role of 5-HT(1) receptor subtypes in controlling the release of calcitonin gene-related peptide (CGRP) in rat dura mater, trigeminal ganglion (TG), and trigeminal nucleus caudalis (TNC). The mRNA for each receptor subtype was quantified by quantitative real-time polymerase chain reaction. A high potassium concentration was used to release CGRP from dura mater, isolated TG, and TNC in vitro. The immunoreactive CGRP (iCGRP) release was measured by enzyme-linked immunoassay. The mRNA transcripts of the 3 5-HT(1) receptor subtypes were detected in the trigeminovascular system. Sumatriptan inhibited iCGRP release by 31% in dura mater, 44% in TG, and 56% in TNC. This effect was reversed by a 5-HT(1B/1D) antagonist (GR127395). The 5-HT(1F) agonist (LY-344864) was effective in the dura mater (26% iCGRP inhibition), and the 5-HT(1D) agonist (PNU-142633) had a significant effect in the TNC (48%), whereas the 5-HT(1B) agonist (CP-94253) was unable to reduce the iCGRP release in all tissues studied. We found that sumatriptan reduced the iCGRP release via activation of 5-HT(1D) and 5-HT(1F) receptor subtypes. The 5-HT(1F) receptor agonist was effective only in peripheral terminals in dura mater, whereas the 5-HT(1D) agonist had a preferential effect on central terminals in the TNC.

Can migraine prophylaxis prevent acute mountain sickness at high altitude?

Acute mountain sickness (AMS) develops in people trekking at high altitude. The underlying mechanism is vasodilation due to low pressure of oxygen. However, individual susceptibility for AMS is unknown, thus, one cannot predict when or to whom it happens. Because AMS usually begins with headache, and because migraineurs are more vulnerable to AMS, we studied by the literatures review on the mechanism and clinical features in common, and assessed the treatment modalities for both disorders. This led to us the following hypothesis that, migraine prophylaxis may prevent or delay the onset of AMS at high altitude. Clinical features of AMS include nausea or vomiting when it progresses. Hypobaric hypoxia, dehydration or increased physical exertion trigger or aggravate both disorders. In migraine, cerebral vasodilation can happen following alteration of neuronal activity, whereas the AMS is associated with peripheral vessel dilation. Medications that dilate the vessels worsen both conditions. Acute treatment strategies for migraine overlap with to those of AMS, including drugs such as vasoconstrictors, or other analgesics. To prevent AMS, adaptation to high altitude or pharmacological prophylaxis, i.e., acetazolamide has been recommended. This carbonic anhydrase inhibitor lowers serum potassium level, and thus stabilizes membrane excitability. Acetazolamide is also effective on specific forms of migraine. Taken together, these evidences implicate that migraine prophylaxis may prevent or delay the onset of AMS by elevating the threshold for high altitude.

The relevance of preclinical research models for the development of antimigraine drugs: focus on 5-HT(1B/1D) and CGRP receptors

Migraine is a complex neurovascular syndrome, causing a unilateral pulsating headache with accompanying symptoms. The past four decades have contributed immensely to our present understanding of migraine pathophysiology and have led to the introduction of specific antimigraine therapies, much to the relief of migraineurs. Pathophysiological factors culminating into migraine headaches have not yet been completely deciphered and, thus, pose an additional challenge for preclinical research in the absence of any direct experimental marker. Migraine provocation experiments in humans use a head-score to evaluate migraine, as articulated by the volunteer, which cannot be applied to laboratory animals. Therefore, basic research focuses on different symptoms and putative mechanisms, one at a time or in combination, to validate the hypotheses. Studies in several species, utilizing different preclinical approaches, have significantly contributed to the two antimigraine principles in therapeutics, namely: 5-HT(1B/1D) receptor agonists (known as triptans) and CGRP receptor antagonists (known as gepants). This review will analyze the preclinical experimental models currently known for the development of these therapeutic principles, which are mainly based on the vascular and/or neurogenic theories of migraine pathogenesis. These include models based on the involvement of cranial vasodilatation and/or the trigeminovascular system in migraine. Clearly, the preclinical strategies should involve both approaches, while incorporating the newer ideas/techniques in order to get better insights into migraine pathophysiology.

Calcitonin gene-related peptide (CGRP) receptor antagonists in the treatment of migraine

Based on preclinical and clinical studies, the neuropeptide calcitonin gene-related peptide (CGRP) is proposed to play a central role in the underlying pathology of migraine. CGRP and its receptor are widely expressed in both the peripheral and central nervous systems by multiple cell types involved in the regulation of inflammatory and nociceptive responses. Peripheral release of CGRP from trigeminal nerve fibres within the dura and from the cell body of trigeminal ganglion neurons is likely to contribute to peripheral sensitization of trigeminal nociceptors. Similarly, the release of CGRP within the trigeminal nucleus caudalis can facilitate activation of nociceptive second-order neurons and glial cells. Thus, CGRP is involved in the development and maintenance of persistent pain, central sensitization and allodynia, events characteristic of migraine pathology. In contrast, CGRP release within the brain is likely to function in an anti-nociceptive capacity. Given the role of CGRP in migraine pathology, the potential of CGRP receptor antagonists in the treatment of migraine has been investigated. Towards this end, the non-peptide CGRP receptor antagonists olcegepant and telcagepant have been shown to be effective in the acute treatment of migraine. While telcagepant is being pursued as a frontline abortive migraine drug in a phase III clinical trial, an oral formulation of a novel CGRP receptor antagonist, BI 44370, is currently in phase II clinical trials. Encouragingly, data from clinical studies on these compounds have clearly demonstrated the potential therapeutic benefit of this class of drugs and support the future development of CGRP receptor antagonists to treat migraine and possibly other types of chronic pain.

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.

Review of comorbidities and risk factors for the development of migraine complications (infarct and chronic migraine)

A number of comorbid disorders, behavioural traits and associated risk factors in patients with migraine are known to increase the risk of complications such as ischaemic vascular events and chronic migraine, a syndrome that is more disabling and resistant to treatment with acute and preventative medications than episodic migraine. Reduction of cardiovascular risk factors, smoking cessation and use of non-oestrogen-containing oral contraceptives in female patients are beneficial strategies to reduce the risk of ischaemic events in patients with migraine (especially those with aura). Attack frequency, acute medication overuse, obesity and coexisting depression and anxiety disorders are particularly strong but potentially modifiable independent risk factors for progression to chronic migraine. Identifying and managing comorbidities and associated risk factors for complications of migraine are likely to require an integrated disease management strategy involving several disciplines and allied health services. Such a disease-oriented model of care may potentially interrupt the cycle of progression and disability and improve quality of life for patients with migraine.

Pharmacology

Headache treatment has been based primarily on experiences with non-specific drugs such as analgesics, non-steroidal anti-inflammatory drugs, or drugs that were originally developed to treat other diseases, such as beta-blockers and anticonvulsant medications. A better understanding of the basic pathophysiological mechanisms of migraine and other types of headache has led to the development over the past two decades of more target-specific drugs. Since activation of the trigeminovascular system and neurogenic inflammation are thought to play important roles in migraine pathophysiology, experimental studies modeling those events successfully predicted targets for selective development of pharmacological agents to treat migraine. Basically, there are two fundamental strategies for the treatment of migraine, abortive or preventive, based to a large degree on the frequency of attacks. The triptans, which exhibit potency towards selective serotonin (5-hydroxytryptamine, 5-HT) receptors expressed on trigeminal nerves, remain the most effective drugs for the abortive treatment of migraine. However, numerous preventive medications are currently available that modulate the excitability of the nervous system, particularly the cerebral cortex. In this chapter, the pharmacology of commercially available medications as well as drugs in development that prevent or abort headache attacks will be discussed.

Activation of iGluR5 kainate receptors inhibits neurogenic dural vasodilatation in an animal model of trigeminovascular activation

BACKGROUND AND PURPOSE

Migraine is a disabling neurological disorder involving activation, or the perception of activation, of trigeminovascular afferents containing calcitonin gene-related peptide (CGRP). Released CGRP from peripheral trigeminal afferents causes dilatation of dural blood vessel, and this is used to measure trigeminal nerve activation. Kainate receptors with the GluR5 subunit (iGluR5, ionotropic glutamate receptor) are present in the trigeminal ganglion and may be involved in nociception. We investigated the possible involvement of prejunctional iGluR5 kainate receptors on CGRP release from trigeminal afferents.

EXPERIMENTAL APPROACH

We used neurogenic dural vasodilatation, which involves reproducible vasodilatation in response to CGRP release after electrical stimulation of the dura mater surrounding the middle meningeal artery. The effects of the specific iGluR5 receptor antagonist UBP 302 and agonist (S)-(-)-5-iodowillardiine were investigated on neurogenic and CGRP-induced dural vasodilatation in rats, by using intravital microscopy.

KEY RESULTS

Administration of 10 and 20 mg.kg(-1) of iodowillardiine inhibited electrically induced dural vessel dilatation, an effect blocked by pretreatment with 50 mg.kg(-1) UBP 302. Administration of the iGluR5 receptor antagonist UBP 302 alone had no significant effect. CGRP (1 mg.kg(-1))-induced dural vasodilatation was not inhibited by the iGluR5 receptor agonist iodowillardiine.

CONCLUSIONS AND IMPLICATIONS

This study demonstrates that activation of the iGluR5 kainate receptors with the selective agonist iodowillardiine is able to inhibit neurogenic dural vasodilatation probably by inhibition of prejunctional release of CGRP from trigeminal afferents. Taken together with recent clinical studies the data reinforce CGRP mechanisms in primary headaches and demonstrate a novel role for kainate receptor modulation of trigeminovascular activation.

Migraine

Migraine is a neurovascular disorder which affects one fifth of the general population. Disability due to migraine is severe and involves patients from infancy through senescence and it is aggravated by the fact there is no complete cure. However, various drugs for the symptomatic or prophylactic treatment of the disease are available. Recently, better knowledge of the neurobiological and pharmacological aspects of a subset of trigeminal primary sensory neurons has provided key information for the development of effective molecules that specifically target the activation of the trigeminovascular system and may represent a significant advancement in the treatment of the disease. These novel antagonists block the receptor for the sensory neuropeptide calcitonin gene-related peptide (CGRP), which upon release from peripheral terminals of trigeminal perivascular neurons dilates cranial arterial vessels. Whether neurogenic vasodilatation is the major contributing factor to generate the pain and the associated symptoms of the migraine attack or whether other sites of action of CGRP receptor antagonists are responsible for the antimigraine effect of these compounds is the subject of current and intense research.

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.

Therapeutic use of release-modifying drugs

Presynaptic inhibitory or facilitatory autoreceptors are targets for the endogenous neurotransmitter of the respective neuron, and also for exogenous agonists, partial agonists and antagonists which can produce pharmacological actions through changes in transmitter release. In addition, presynaptic inhibitory or facilitatory heteroreceptors can also be acted upon by exogenous agonists, partial agonists or antagonists to induce changes in transmitter release with useful therapeutic effects. This article summarizes drugs that are known or likely to produce their therapeutic effects through presynaptic modulation of neurotransmitter release. Included are drugs acting on alpha and beta adrenoceptors, dopamine receptors, angiotensin, opioid, cannabinoid, and nicotinic acetylcholine receptors. Also discussed are changes in presynaptic receptor mechanisms produced by drugs that inhibit transmitter re-uptake.

Ethanol causes neurogenic vasodilation by TRPV1 activation and CGRP release in the trigeminovascular system of the guinea pig

Ethanol stimulating transient receptor potential vanilloid 1 (TRPV1) on primary sensory neurons promotes neurogenic inflammation, including calcitonin gene-related peptide (CGRP)-mediated coronary dilation. Alcoholic beverages trigger migraine attacks and activation of trigeminal neurons plays a role in migraine. We have investigated in guinea pigs whether ethanol by TRPV1 stimulation causes neurogenic inflammation in the trigeminovascular system. Ethanol-evoked release of neuropeptides from slices of dura mater was abolished by Ca(2+) removal, capsaicin pretreatment and the TRPV1 antagonist, capsazepine. Intragastric ethanol increased plasma extravasation in dura mater, an effect abolished by capsazepine and the NK1 receptor antagonist, SR140333, and caused vasodilation around the middle meningeal artery, an effect abolished by capsazepine and the CGRP receptor antagonist, BIBN4096BS. Vasodilation of meningeal vessels by TRPV1 activation and CGRP release may be relevant to the mechanism by which alcohol ingestion triggers migraine attacks.

Female sex hormones and rat dural vasodilatation to CGRP, periarterial electrical stimulation and capsaicin

BACKGROUND

The prevalence of migraine is 2 to 3-fold higher in females than in males, and it is intricately related to the levels of female sex hormones. These hormones may regulate the synthesis and receptor expression of calcitonin gene-related peptide (CGRP), which mediates neurogenic dural vasodilatation and is implicated in migraine pathogenesis.

OBJECTIVE

To investigate the effects of the female sex steroids, 17beta-estradiol and progesterone, separately and in combination, on dural vasodilatation induced by alphaCGRP, periarterial electrical stimulation and capsaicin in ovariectomized rats, using intravital microscopy.

METHODS

Sprague-Dawley rats were ovariectomized and, 7 days later, subcutaneously implanted with 21-day release pellets of 17beta-estradiol, progesterone, their combination or placebo. On day 19 to 21, the animals were anesthetized, overlying bone thinned to visualize the middle meningeal artery and vasodilator responses to alphaCGRP (10 to 3000 ng kg(-1)), periarterial electrical stimulation (25 to 125 microA) and capsaicin (0.3 to 18 microg kg(-1)) elicited.

RESULTS

There were no significant differences in the vasodilator potency or efficacy of alphaCGRP or capsaicin in the different groups studied. In contrast, the vasodilator response to electrical stimulation was significantly higher in rats treated with 17beta-estradiol (Emax:157 +/- 19%) as compared to those observed after placebo treatment (Emax:93 +/- 11%).

CONCLUSION

Our results show that, in contrast to CGRP- or capsaicin-induced dural vasodilatation, 17beta-estradiol enhanced neurogenic vasodilatation, suggesting increased CGRP release from perivascular nerves. This may be one of the mechanisms through which 17beta-estradiol exacerbates migraine in women.

New Migraine and Pain Research

An understanding of the pathophysiology and pharmacology of migraine has been driven by astute clinical observations, elegant experimental medicine studies and importantly by the introduction of highly effective selective anti-migraine agents such as the Triptan 5-HT(1B/1D) agonists. New investigational migraine therapies such CGRP antagonists target key components of the trigeminal sensory neuroinflammatory response and show promise for the future. Cutting edge molecular profiling studies looking at gene expression during chronic pain are now being used to reveal the cell biology of pain and new potential therapeutic targets. Translational neuroimaging research can link the laboratory and the clinic and is now being used to help understand the neural systems biology of migraine. Research into migraine has generated sophisticated hypotheses that encompass primary CNS dysfunction, trigeminovascular activation, pain perception and activation of associated neural circuits involved in affective functions providing a rich framework within which to design and test future migraine treatment strategies.

Inhibitory effect of BIBN4096BS, CGRP(8-37), a CGRP antibody and an RNA-Spiegelmer on CGRP induced vasodilatation in the perfused and non-perfused rat middle cerebral artery

BACKGROUND AND PURPOSE

A new concept for the inhibition of CGRP signalling has been developed by interaction with the CGRP molecule per se by using a CGRP antibody or a CGRP binding RNA-Spiegelmer (NOX-C89). We have compared these CGRP scavengers with two known receptor antagonists (CGRP8-37 and BIBN4096BS) on CGRP-induced relaxations in the rat middle cerebral artery (MCA). Furthermore, the role of the endothelial barrier has been studied.

EXPERIMENTAL APPROACH

We used the luminally perfused MCA in an arteriograph, pressurized to 85 mm Hg and myograph studies of isolated ring segments of the MCA.

KEY RESULTS

In myograph studies and in the perfusion system during abluminal application, alphaCGRP and betaCGRP induced concentration-dependent dilatation of the MCA. Given luminally neither peptide was significantly vasodilator. Adrenomedullin and amylin induced weak dilatations. In myograph experiments, relaxation induced by alphaCGRP was prevented by the four CGRP blockers (CGRP8-37, BIBN4096BS, the CGRP antibody and NOX-C89.). In abluminal perfusion experiments, the relaxant response to alphaCGRP was prevented by these agents to a varying degree. Dilatation induced by abluminal application of alphaCGRP was inhibited by luminal CGRP8-37 but not by luminal BIBN4096BS, CGRP antibody or NOX-C89.

CONCLUSIONS AND IMPLICATIONS

alpha or betaCGRP acted on smooth muscle cell CGRP receptors in rat MCA and were effectively prevented from reaching these receptors by the endothelial barrier. The CGRP blockers significantly inhibited alphaCGRP induced relaxation but were also prevented from reaching the CGRP receptors by the arterial endothelium.

Botulinum toxin: Clinical use

Since its development for the use of blepharospasm and strabismus more than 2.5 decades ago, botulinum neurotoxin (BoNT) has become a versatile drug in various fields of medicine. It is the standard of care in different disorders such as cervical dystonia, hemifacial spasm, focal spasticity, hyperhidrosis, ophthalmological and otolaryngeal disorders. It has also found widespread use in cosmetic applications. Many other indications are currently under investigation, including gastroenterologic and urologic indications, analgesic management and migraine. This paper is an extensive review of the spectrum of BoNT clinical applications.

Rizatriptan in the treatment of migraine

Migraine is a common, disabling disorder associated with considerable personal and societal burden. Current guidelines recommend triptans for the acute treatment of migraine unlikely to respond to less effective therapies. Rizatriptan is a second-generation triptan available in tablet or orally disintegrating tablet (wafer) formulations that offers several advantages over other members of its class. Rizatriptan is rapidly absorbed from the gastrointestinal tract and achieves maximum plasma concentrations more quickly than other triptans, providing rapid pain relief. Clinical trials have shown that rizatriptan is at least as effective or superior to other oral migraine-specific agents in the acute treatment of migraine, and has more consistent long-term efficacy across multiple migraine attacks. Rizatriptan has a favorable tolerability profile, and patients have reported greater satisfaction and a preference for rizatriptan over other migraine-specific agents. Improvements in quality of life reported with rizatriptan are consistent with its favorable efficacy and tolerability profiles. Notably, multi-attribute decision models that combine clinical data with patient- and physician-reported treatment preferences have identified rizatriptan as one of three triptans closest to a hypothetical "ideal". The efficacy and tolerability of rizatriptan for the acute treatment of migraine have thus been well established.

Animal models of migraine: looking at the component parts of a complex disorder

Animal models of human disease have been extremely helpful both in advancing the understanding of brain disorders and in developing new therapeutic approaches. Models for studying headache mechanisms, particularly those directed at migraine, have been developed and exploited efficiently in the last decade, leading to better understanding of the potential mechanisms of the disorder and of the action for antimigraine treatments. Model systems employed have focused on the pain-producing cranial structures, the large vessels and dura mater, in order to provide reproducible physiological measures that could be subject to pharmacological exploration. A wide range of methods using both in vivo and in vitro approaches are now employed; these range from manipulation of the mouse genome in order to produce animals with human disease-producing mutations, through sensitive immunohistochemical methods to vascular, neurovascular and electrophysiological studies. No one model system in experimental animals can explain all the features of migraine; however, the systems available have begun to offer ways to dissect migraine's component parts to allow a better understanding of the problem and the development of new treatment strategies.

Topiramate inhibits trigeminovascular activation: an intravital microscopy study

Activation, or the altered perception of activation, of trigeminal nerves that innervate the cranial vasculature is considered to be a pivotal component of the pathophysiology of acute migraine. Calcitonin gene-related peptide (CGRP) levels are increased during migraine and after trigeminal nerve stimulation in the cat. Both CGRP and nitric oxide (NO) infusion causes headache and delayed migraine in migraineurs. Neurogenic stimulation of a cranial window, CGRP and NO injection all cause meningeal artery dilation in the rat when viewed using intravital microscopy. Topiramate is an antiepileptic drug with established efficacy as a migraine preventive, and has recently been shown to inhibit neurons of the trigeminocervical complex after superior sagittal sinus stimulation. In this study, we used intravital microscopy with neurogenic dural vasodilation, and CGRP- and NO-induced dilation to examine whether intravenous topiramate has effects on the trigeminovascular system. Topiramate was able to attentuate neurogenic dural vasodilation maximally after 15 min by 52% at 30 mg kg(-1) (t(5) = 6.78, n = 6); there was no significant inhibition at 10 mg kg(-1). There was also significant attenuation of the NO-induced dilation maximally after 15 min, at both 10 and 30 mg kg(-1) by 21% (t(6) = 6.09, n = 7) and 41% (t(6) = 5.3, n = 7), respectively. CGRP-induced dilation was not inhibited at either dose of topiramate. The study demonstrates that topiramate is likely to inhibit neurogenic dural vasodilation by inhibiting the release of CGRP from prejunctional trigeminal neurons, thus attenuating the dural vasodilation. Topiramate is not able to act postsynaptically at the blood vessels themselves as the CGRP-induced dilation was not attenuated. The data are consistent with an effect of topiramate on trigeminovascular activation which may form part of its preventive antimigraine mechanisms of action.

Phosphodiesterase 5 and effects of sildenafil on cerebral arteries of man and guinea pig

Sildenafil (Viagra), a selective inhibitor of phosphodiesterase 5 (PDE5), induces headache and migraine. Although previously supposed to be a "vascular" headache, no significant cerebral artery dilatation was found in vivo. Thus, we hypothesised that PDE5 may not be present or that sildenafil is less effective on the cGMP hydrolysis in cerebral arteries, and that sildenafil may not be an effective dilator of cerebral arteries under baseline conditions. We evaluated the presence of PDE5 mRNA and protein in human arteries. Furthermore, the effects of two selective PDE5 inhibitors, sildenafil and UK-114,542, and a PDE1 inhibitor UK-90,234 on cGMP hydrolysis were investigated in human and guinea pig cerebral arteries. The vasoactive responses of the compounds were evaluated in guinea pig basilar arteries in vitro, with concomitant measurements of cAMP and cGMP. PDE5 was found in human middle cerebral arteries. Sildenafil and UK-114,542 inhibited cGMP hydrolysis concentration-dependently in both species. In guinea pig arteries, sildenafil induced an endothelium-dependent vasodilatation only at concentrations above 10 nM, which was augmented by sodium nitroprusside and attenuated by reduction of cGMP, but was cGMP independent at high concentrations. UK-114,542 was more and UK-90,234 was less potent than sildenafil. In conclusion, PDE5 is present in human and guinea pig cerebral arteries, and is inhibited by sildenafil at micromolar levels. Sildenafil in vitro is a poor dilator of guinea pig cerebral arteries unless a nitric oxide donor is co-administered, corresponding to the previous findings in vivo.

5-HT1F receptor agonists in acute migraine treatment: a hypothesis

Serotonin-1F receptor (5-HT1F) agonists may relieve acute migraine without vasoconstriction. We conducted a review of preclinical and clinical data that assessed the potential link between migraine and 5-HT1F activation. (i) A high correlation exists between the potency of various 5-HT1 receptor agonists in the guinea pig dural plasma protein extravasation assay and their 5-HT1F receptor binding affinity. (ii) 5-HT1F receptors are on the trigeminal system, and may participate in blocking migraine pain transmission through the trigeminal ganglion and nucleus caudalis. (iii) 5-HT1F receptors are located on glutamate-containing neurones and their activation might inhibit glutamate release; glutamate excess may play a role in migraine. (iv) Selective 5-HT1F receptor agonists (LY334370; LY344864) are effective in preclinical migraine models and are non-vasoconstrictive. (v) LY334370 is effective in acute migraine, and does not cause any symptoms/signs of coronary vasoconstriction. Preclinical experiments and clinical observations argue for a role of selective 5-HT1F agonists in migraine.

Characterization of opioid receptors that modulate nociceptive neurotransmission in the trigeminocervical complex

1. Opioid agonists have been used for many years to treat all forms of headache, including migraine. We sought to characterize opioid receptors involved in craniovascular nociceptive pathways by in vivo microiontophoresis of micro -receptor agonists and antagonists onto neurons in the trigeminocervical complex of the cat. 2. Cats were anaesthetized with alpha-chloralose 60 mg kg(-1), i.p. and 20 mg kg(-1), i.v. supplements after induction and surgical preparation using halothane. Units were identified in the trigeminocervical complex responding to supramaximal electrical stimulation of the superior sagittal sinus, and extracellular recordings of activity made. 3. Seven- or nine-barrelled glass micropipettes incorporating tungsten recording electrodes in their centre barrels were used for microiontophoresis of test substances onto cell bodies. 4. Superior sagittal sinus (SSS)-linked cells whose firing was evoked by microiontophoretic application of L-glutamate (n=8 cells) were reversibly inhibited by microiontophoresis of H(2)N-Tyr-D-Ala-Gly-N-Me-Phe-Gly-ol (DAMGO) (n=12), a selective micro -receptor agonist, in a dose dependent manner, but not by control ejection of sodium or chloride ions from a barrel containing saline. 5. The inhibition by DAMGO of SSS-linked neurons activated with L-glutamate could be antagonized by microiontophoresis of selective micro -receptor antagonists D-Phe-Cys-Tyr-D-Trp-Orn-Thr-Pen-Thr-NH(2) (CTOP) or D-Phe-Cys-Tyr-D-Trp-Arg-Thr-Pen-Thr-NH(2) (CTAP), or both, in all cells tested (n=4 and 6, respectively). 6. Local iontophoresis of DAMGO during stimulation of the superior sagittal sinus resulted in a reduction in SSS-evoked activity. This effect was substantially reversed 10 min after cessation of iontophoresis. The effect of DAMGO was markedly inhibited by co-iontophoresis of CTAP. 7. Thus, we found that micro -receptors modulate nociceptive input to the trigeminocervical complex. Characterizing the sub-types of opioid receptors that influence trigeminovascular nociceptive transmission is an important component to understanding the pharmacology of this synapse, which is pivotal in primary neurovascular headache.

Spotlight on rizatriptan in migraine

Rizatriptan is an orally active serotonin 5-HT(1) receptor agonist that potently and selectively binds to 5-HT(1B/1D) subtypes. Earlier clinical trials demonstrated that rizatriptan 5 or 10mg is more effective than placebo at providing pain relief and a pain-free state, relieving associated symptoms of migraine, normalising functional ability and improving patient quality of life, and showed that rizatriptan provides faster freedom from pain and reduces nausea to a greater extent than oral sumatriptan. More recently, rizatriptan 10mg was shown to be more effective than zolmitriptan 2.5mg or naratriptan 2.5mg at producing a pain-free state 2 hours postdose. Furthermore, compared with naratriptan, significantly more patients who received rizatriptan were pain free or had pain relief from 1 hour onwards. The number of patients with normal functional ability at 2 hours was significantly higher after rizatriptan than after naratriptan or zolmitriptan. Rizatriptan was also generally more effective than zolmitriptan or naratriptan at relieving migraine-associated symptoms. Rizatriptan is generally well tolerated, and adverse events are usually mild and transient. The most common adverse events associated with rizatriptan in recent randomised trials were asthenia/fatigue, dizziness, somnolence and nausea. There was a trend towards a lower incidence of adverse events with rizatriptan compared with zolmitriptan (31.2 vs 38.8%). However, rizatriptan was associated with a significantly higher incidence of adverse events than naratriptan (39 vs 29%). The incidence of chest pain was similar after the administration of rizatriptan, zolmitriptan or naratriptan (2-4%). In conclusion, rizatriptan is an effective drug for the acute treatment of moderate or severe migraine. Oral rizatriptan 5 and 10mg have shown greater efficacy than placebo in providing pain relief, an absence of pain, relief from associated symptoms, normal functional ability and an improvement in patient quality of life. Earlier results showed that rizatriptan provides faster freedom from pain and reduces nausea to a greater extent than oral sumatriptan. More recent studies have shown that rizatriptan 10mg provides faster pain relief and a higher percentage of patients with an absence of pain and normal functional ability at 2 hours than naratriptan 2.5mg or zolmitriptan 2.5mg. The efficacy of rizatriptan is retained when used in the long term, and the drug is generally well tolerated. Although well designed studies comparing rizatriptan with almotriptan, eletriptan and frovatriptan would further define the position of rizatriptan, current data suggest that rizatriptan should be considered as a first-line treatment option in the management of migraine.

The effect of anti-migraine compounds on nitric oxide-induced dilation of dural meningeal vessels

Migraine is characteristically accompanied by a throbbing quality of head pain thought to involve trigeminovascular afferents. Administration of nitric oxide (NO) donors provides the most reliable model of migraine induction in humans. The present studies used intravital microscopy to monitor the effect of local meningeal nerve stimulation and NO on dural blood vessels and any modulation of that effect by anti-migraine compounds. NO caused an immediate and reproducible dilation of meningeal blood vessels that was partially blocked by sumatriptan and indomethacin, while flunarizine and histamine H(1) and H(2) receptor antagonists were unable to block the dilation. Indomethacin also inhibited the neurogenic dilation while flunarizine did not. The present studies demonstrate that NO is unlikely to interact with histamine to produce its dilatory response. Sumatriptan and indomethacin inhibit the NO response by inhibiting trigeminal activation and calcitonin gene-related peptide (CGRP) release. Flunarizine does not modify either the neurogenic vasodilator response or the NO meningeal dilator response at least acutely.

Rizatriptan: an update of its use in the management of migraine

Rizatriptan is an orally active serotonin 5-HT(1) receptor agonist that potently and selectively binds to 5-HT(1B/1D) subtypes. Earlier clinical trials demonstrated that rizatriptan 5 or 10mg is more effective than placebo at providing pain relief and a pain-free state, relieving associated symptoms of migraine, normalising functional ability and improving patient quality of life, and showed that rizatriptan provides faster freedom from pain and reduces nausea to a greater extent than oral sumatriptan. More recently, rizatriptan 10mg was shown to be more effective than zolmitriptan 2.5mg or naratriptan 2.5mg at producing a pain-free state 2 hours postdose. Furthermore, compared with naratriptan, significantly more patients who received rizatriptan were pain free or had pain relief from 1 hour onwards. The number of patients with normal functional ability at 2 hours was significantly higher after rizatriptan than after naratriptan or zolmitriptan. Rizatriptan was also generally more effective than zolmitriptan or naratriptan at relieving migraine-associated symptoms. Rizatriptan is generally well tolerated and adverse events are usually mild and transient. The most common adverse events associated with rizatriptan in recent randomised trials were asthenia/fatigue, dizziness, somnolence and nausea. There was a trend towards a lower incidence of adverse events with rizatriptan compared with zolmitriptan (31.2 vs 38.8%). However, rizatriptan was associated with a significantly higher incidence of adverse events than naratriptan (39 vs 29%). The incidence of chest pain was similar after the administration of rizatriptan, zolmitriptan or naratriptan (2 to 4%).

CONCLUSION

Rizatriptan is an effective drug for the acute treatment of moderate or severe migraine. Oral rizatriptan 5 and 10mg have shown greater efficacy than placebo in providing pain relief, an absence of pain, relief from associated symptoms, normal functional ability and an improvement in patient quality of life. Earlier results showed that rizatriptan provides faster freedom from pain and reduces nausea to a greater extent than oral sumatriptan. More recent studies have shown that rizatriptan 10mg provides faster pain relief and a higher percentage of patients with an absence of pain and normal functional ability at 2 hours than naratriptan 2.5mg or zolmitriptan 2.5mg. The efficacy of rizatriptan is retained when used in the long term and the drug is generally well tolerated. Although well designed studies comparing rizatriptan with almotriptan, eletriptan and frovatriptan would further define the position of rizatriptan, current data suggest rizatriptan should be considered as a first-line treatment option in the management of migraine.