Topiramate inhibits trigeminovascular activation: an intravital microscopy study

Voltage-gated Calcium Channels as Potential Therapeutic Targets in Migraine

Migraine is a complex and highly incapacitating neurological disorder that affects around 15% of the general population with greater incidence in women, often at the most productive age of life. Migraine physiopathology is still not fully understood, but it involves multiple mediators and events in the trigeminovascular system and the central nervous system. The identification of calcitonin gene-related peptide as a key mediator in migraine physiopathology has led to the development of effective and highly selective antimigraine therapies. However, this treatment is neither accessible nor effective for all migraine sufferers. Thus, a better understanding of migraine mechanisms and the identification of potential targets are still clearly warranted. Voltage-gated calcium channels (VGCCs) are widely distributed in the trigeminovascular system, and there is accumulating evidence of their contribution to the mechanisms associated with headache pain. Several drugs used in migraine abortive or prophylactic treatment target VGCCs, which probably contributes to their analgesic effect. This review aims to summarize the current evidence of VGGC contribution to migraine physiopathology and to discuss how current pharmacological options for migraine treatment interfere with VGGC function. PERSPECTIVE: Calcitonin gene-related peptide (CGRP) represents a major migraine mediator, but few studies have investigated the relationship between CGRP and VGCCs. CGRP release is calcium channel-dependent and VGGCs are key players in familial migraine. Further studies are needed to determine whether VGCCs are suitable molecular targets for treating migraine.

Menthol dural application alters meningeal arteries tone and enhances excitability of trigeminocervical neurons in rats

Headaches, including migraines, can have a causal relationship to exposure to cold, and this relationship may be both positive and negative, as cold can both provoke and alleviate cephalgia. The role of thermoreceptors responsible for transduction of low temperatures belongs to the transient receptor potential cation channel subfamily melastatin member 8 (TRPM8). These channels mediate normal cooling sensation and have a role in both cold pain and cooling-mediated analgesia; they are seen as a potential target for principally new anti-migraine pharmaceuticals. Using a validated animal migraine models, we evaluated effects of menthol, the TRPM8-agonist, on trigeminovascular nociception. In acute experiments on male rats, effects of applied durally menthol solution in various concentrations on the neurogenic dural vasodilatation (NDV) and firing rate of dura-sensitive neurons of the trigeminocervical complex (TCC) were assessed. Application of menthol solution in concentrations of 5 % and 10 % was associated with NDV suppression, however amplitude reduction of the dilatation response caused not by the vascular dilatation degree decrease, but rather due to the significant increase of the meningeal arterioles' basal tone. In electrophysiological experiments the 1 % and 30 % menthol solutions intensified TCC neuron responses to the dural electrical stimulation while not changing their background activity. Revealed in our study excitatory effects of menthol related to the vascular as well as neuronal branches of the trigeminovascular system indicate pro-cephalalgic effects of TRPM8-activation and suggest feasibility of further search for new anti-migraine substances among TRPM8-antagonists.

Migraine Comorbidities

Novel knowledge about the interrelationships and reciprocal effects of migraine and epilepsy, migraine and mood disorders, or migraine and irritable bowel syndrome has emerged in recent decades. Over time, comorbid pathologies associated with migraine that share common physiopathological mechanisms were studied. Among these studied pathologies is epilepsy, a disorder with common ion channel dysfunctions as well as dysfunctions in glutamatergic transmission. A high degree of neuronal excitement and ion channel abnormalities are associated with epilepsy and migraine and antiepileptic drugs are useful in treating both disorders. The coexistence of epilepsy and migraine may occur independently in the same individual or the two may be causally connected. The relationship between cortical spreading depression (CSD) and epileptic foci has been suggested by basic and clinical neuroscience research. The most relevant psychiatric comorbidities associated with migraine are anxiety and mood disorders, which influence its clinical course, treatment response, and clinical outcome. The association between migraine and major depressive disorder can be explained by a robust molecular genetic background. In addition to its role as a potent vasodilator, CGRP is also involved in the transmission of nociception, a phenomenon inevitably linked with the stress and anxiety caused by frequent migraine attacks. Another aspect is the role of gut microbiome in migraine's pathology and the gut-brain axis involvement. Irritable bowel syndrome patients are more likely to suffer migraines, according to other studies. There is no precise explanation for how the gut microbiota contributes to neurological disorders in general and migraines in particular. This study aims to show that migraines and comorbid conditions, such as epilepsy, microbiota, or mood disorders, can be connected from the bench to the bedside. It is likely that these comorbid migraine conditions with common pathophysiological mechanisms will have a significant impact on best treatment choices and may provide clues for future treatment options.

Acetazolamide and topiramate lower intracranial pressure through differential mechanisms: The effect of acute and chronic administration

BACKGROUND AND PURPOSE

Diseases of raised intracranial pressure (ICP) cause severe morbidity and mortality. Multiple drugs are utilised to lower ICP including acetazolamide and topiramate. However, the evidence for their use is unclear. We aimed to assess the ICP modulatory effects and molecular effects at the choroid plexus (CP) of acetazolamide and topiramate.

EXPERIMENTAL APPROACH

Female rats were implanted with telemetric ICP probes for physiological, freely moving 24/7 ICP recordings. Randomised cross-over studies were performed, where rats received acute (24 h) high doses of acetazolamide and topiramate, and chronic (10 days) clinically equivalent doses of acetazolamide and topiramate, all via oral gavage. Cerebrospinal fluid (CSF) secretion assays, and RT-qPCR and western blots on in vitro and in vivo CP, were used to investigate drug actions.

KEY RESULTS

We demonstrate that acetazolamide and topiramate achieved maximal ICP reduction within 120 min of administration, and in combination doubled the ICP reduction over a 24-h period. Chronic administration of acetazolamide or topiramate lowered ICP by 25%. Topiramate decreased CSF secretion by 40%. Chronic topiramate increased the gene expression of Slc12a2 and Slc4a10 and protein expression of the sodium-dependent chloride/bicarbonate exchanger (NCBE), whereas chronic acetazolamide did not affect the expression of assessed genes.

CONCLUSIONS AND IMPLICATIONS

Acetazolamide and topiramate are effective at lowering ICP at therapeutic levels. We provide the first evidence that topiramate lowers CSF secretion and that acetazolamide and topiramate may lower ICP via distinct molecular mechanisms. Thus, the combination of acetazolamide and topiramate may have utility for treating raised ICP.

Role of Atogepant in the Treatment of Episodic Migraines: Clinical Perspectives and Considerations

Advances in molecular biology and neuroscience have led to the discovery of calcitonin gene-related peptide (CGRP), a 37 amino-acid neuropeptide that plays a critical role in the pathogenesis of migraine. CGRP receptor antagonist, also known as gepant, is an oral medication that inhibits the CGRP-related nociceptive signaling pathway. To date, three gepants are approved by the FDA for migraine treatment. Atogepant is a 2nd-generation gepant that non-competitively antagonizes CGRP receptors inhibiting neurogenic inflammation and pain sensitization. With its long half-life and minimal cardiovascular or liver toxicity, it is the first in its class approved primarily for migraine prevention. This article will discuss the evidence, safety, and rationale of atogepant for use in clinical practice.

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.

Pharmacological treatment of migraine: Drug classes, mechanisms of action, clinical trials and new treatments

Migraine is the sixth most prevalent disease globally, a major cause of disability, and it imposes an enormous personal and socioeconomic burden. Migraine treatment is often limited by insufficient therapy response, leading to the need for individually adjusted treatment approaches. In this review, we analyse historical and current pharmaceutical development approaches in acute and chronic migraine based on a comprehensive and systematic analysis of Food and Drug Administration (FDA)-approved drugs and those under investigation. The development of migraine therapeutics has significantly intensified during the last 3 years, as shown by our analysis of the trends of drug development between 1970 and 2020. The spectrum of drug targets has expanded considerably, which has been accompanied by an increase in the number of specialised clinical trials. This review highlights the mechanistic implications of FDA-approved and currently investigated drugs and discusses current and future therapeutic options based on identified drug classes of interest.

Relationships between migraine and epilepsy: Pathophysiological mechanisms and clinical implications

Migraine and epilepsy are distinct neurological diseases with specific clinical features and underlying pathophysiological mechanisms. However, numerous studies have highlighted the complex and multifaceted relationships between the two conditions. The relationships between headache and epilepsy manifest themselves in different ways. Firstly, the clinical diagnosis of these disorders may be challenging in view of possible overlapping. While post-ictal headache is a frequent condition, ictal epileptic headache is a rare but challenging diagnosis. Both situations raise the question of the pathophysiological mechanism of headache triggered by seizures. Migraine aura and epilepsy can also exhibit overlapping symptoms leading to their misdiagnosis, in particular in the case of visual aura. Secondly, migraine with aura and epilepsy can occur as a co-morbid condition, particularly in familial hemiplegic migraine (FHM). From a pathophysiological perspective, the identification of genetic mutations in FHM has brought significant advances in the understanding of dysfunctions of neuronal networks leading to hyperexcitability. The purpose of this review is to present clinical situations encompassing headache and epilepsy that can be challenging in neurological practice and to discuss the underlying pathophysiological mechanism of such interactions.

Cluster headache pathophysiology - insights from current and emerging treatments

Cluster headache is a debilitating primary headache disorder that affects approximately 0.1% of the population worldwide. Cluster headache attacks involve severe unilateral pain in the trigeminal distribution together with ipsilateral cranial autonomic features and a sense of agitation. Acute treatments are available and are effective in just over half of the patients. Until recently, preventive medications were borrowed from non-headache indications, so management of cluster headache is challenging. However, as our understanding of cluster headache pathophysiology has evolved on the basis of key bench and neuroimaging studies, crucial neuropeptides and brain structures have been identified as emerging treatment targets. In this Review, we provide an overview of what is known about the pathophysiology of cluster headache and discuss the existing treatment options and their mechanisms of action. Existing acute treatments include triptans and high-flow oxygen, interim treatment options include corticosteroids in oral form or for greater occipital nerve block, and preventive treatments include verapamil, lithium, melatonin and topiramate. We also consider emerging treatment options, including calcitonin gene-related peptide antibodies, non-invasive vagus nerve stimulation, sphenopalatine ganglion stimulation and somatostatin receptor agonists, discuss how evidence from trials of these emerging treatments provides insights into the pathophysiology of cluster headache and highlight areas for future research.

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.

Current Status of Antiepileptic Drugs as Preventive Migraine Therapy

BACKGROUND

Antiepileptic drugs (AEDs) are an important class of agents used in the treatment of migraine, a neurological disorder that imparts significant socioeconomic burden. It is important for neurologists to understand the rationale for AEDs in migraine-preventive treatment, as well as each agent's efficacy and tolerability profile, in order to best determine clinical care.

PURPOSE OF THIS REVIEW

This article specifically provides the following: (1) a review of the mechanism of action, efficacy, and tolerability of topiramate and divalproex sodium/sodium valproate, the most widely used AEDs for migraine prevention, (2) a discussion on emerging evidence regarding the efficacy of zonisamide and levetiracetam, and (3) comments on gabapentin, pregabalin, carbamazepine, oxcarbazepine, and lamotrigine, AEDs which have insufficient evidence for use in migraine prevention.

RECENT FINDINGS

The potential role for new extended-release formulations of topiramate in migraine prevention is discussed. There is substantial evidence supporting the use of AEDs in migraine prevention. Specific agents should be chosen based on their efficacy and tolerability profiles. Further studies are needed to determine the efficacy of the newer AEDs, zonisamide and levetiracetam, in migraine prevention and to clarify the role of gabapentinoids in headache management.

Age-Dependent Anti-migraine Effects of Valproic Acid and Topiramate in Rats

Background: Valproic acid (VPA) and topiramate (TPM), initially developed as antiepileptics, are approved for migraine prophylaxis in adults but not children. The differences in their antimigraine mechanism(s) by age remain unclear.

Methods: A migraine model induced by intra-cisternal (i.c.) capsaicin instillation in pediatric (4–5 weeks) and adult (8–9 weeks) rats was pretreated with VPA (30, 100 mg/kg) or TPM (10, 30, 100 mg/kg). Noxious meningeal stimulation by the irritant capsaicin triggered trigeminovascular system (TGVS) activation mimicking migraine condition, which were assessed peripherally by the depletion of calcitonin gene-related peptide (CGRP) in sensory nerve fibers of the dura mater, the increased CGRP immunoreactivity at trigeminal ganglia (TG) and centrally by the number of c-Fos-immunoreactive (c-Fos-ir) neurons in the trigeminocervical complex (TCC). Peripherally, CGRP released from dural sensory nerve terminals of TG triggered pain signal transmission in the primary afferent of trigeminal nerve, which in turn caused central sensitization of the TGVS due to TCC activation and hence contributed to migraine.

Results: In the VPA-treated group, the central responsiveness expressed by reducing the number of c-Fos-ir neurons, which had been increased by i.c. capsaicin, was significant in pediatric, but not adult, rats. Inversely, VPA was effective in peripheral inhibition of elevated CGRP immunoreactivity in the TG and CGRP depletion in the dura mater of adult, but not pediatric, rats. In TPM group, the central responsiveness was significant in both adult and pediatric groups. Peripherally, TPM significantly inhibited capsaicin-induced CGRP expression of TG in adult, but not pediatric, rats. Interestingly, the capsaicin-induced depletion of CGRP in dura was significantly rescued by TPM at high doses in adults, but at low dose in pediatric group.

Conclusion: These results suggest VPA exerted peripheral inhibition in adult, but central suppression in pediatric migraine-rats. In contrast, TPM involves both central and peripheral inhibition of migraine with an optimal therapeutic window in both ages. These findings may clarify the age-dependent anti-migraine mechanism of VPA and TPM, which may guide the development of new pediatric anti-migraine drugs in the future.

The α6 subunit-containing GABAA receptor: A novel drug target for inhibition of trigeminal activation

Novel treatments against migraine are an urgent medical requirement. The α6 subunit-containing GABA_A receptors (α6GABA_ARs) are expressed in trigeminal ganglia (TG), the hub of the trigeminal vascular system (TGVS) that is involved in the pathogenesis of migraine. Here we reveal an unprecedented role of α6GABA_ARs in ameliorating TGVS activation using several pharmacological approaches in an animal model mimicking pathological changes in migraine. TGVS activation was induced by intra-cisternal (i.c.) instillation of capsaicin in Wistar rats. Centrally, i.c. capsaicin activated the trigeminal cervical complex (TCC) measured by the increased number of c-Fos-immunoreactive (c-Fos-ir) TCC neurons. Peripherally, it elevated calcitonin gene-related peptide immunoreactivity (CGRP-ir) in TG and depleted CGRP-ir in the dura mater. Pharmacological approaches included a recently identified α6GABA_AR-selective positive allosteric modulator (PAM), the pyrazoloquinolinone Compound 6, two α6GABA_AR-active PAMs (Ro15-4513 and loreclezole), an α6GABA_AR-inactive benzodiazepine (diazepam), an α6GABA_AR-selective antagonist (furosemide), and a clinically effective antimigraine agent (topiramate). We examined effects of these compounds on both central and peripheral TGVS responses induced by i.c. capsaicin. Compound 6 (3-10 mg/kg, i.p.) significantly attenuated the TCC neuronal activation and TG CGRP-ir elevation, and dural CGRP depletion induced by capsaicin. All these effects of Compound 6 were mimicked by topiramate, Ro15-4513 and loreclezole, but not by diazepam. The brain-impermeable furosemide antagonized the peripheral, but not central, effects of Compound 6. These results suggest that the α6GABA_AR in TG is a novel drug target for TGVS activation and that α6GABA_AR-selective PAMs have the potential to be developed as a novel pharmacotherapy for migraine.

Chronic and intermittent administration of systemic nitroglycerin in the rat induces an increase in the gene expression of CGRP in central areas: potential contribution to pain processing

Background

Calcitonin gene related peptide (CGRP) is a key neuropeptide involved in the activation of the trigeminovascular system and it is likely related to migraine chronification. Here, we investigated the role of CGRP in an animal model that mimics the chronic migraine condition via repeated and intermittent nitroglycerin (NTG) administration. We also evaluated the modulatory effect of topiramate on this experimental paradigm. Male Sprague-Dawley rats were injected with NTG (5 mg/kg, i.p.) or vehicle, every 2 days over a 9-day period (5 total injections). A group of animals was injected with topiramate (30 mg/kg, i.p.) or saline every day for 9 days. Twenty-four hours after the last administration of NTG or vehicle, animals underwent tail flick test and orofacial Von Frey test. Rats were subsequently sacrificed to evaluate c-Fos and CGRP gene expression in medulla-pons region, cervical spinal cord and trigeminal ganglia.

Results

NTG administration induced spinal hyperalgesia and orofacial allodynia, together with a significant increase in the expression of CGRP and c-Fos genes in trigeminal ganglia and central areas. Topiramate treatment prevented NTG-induced changes by reversing NTG-induced hyperalgesia and allodynia, and inhibiting CGRP and c-Fos gene expression in all areas evaluated.

Conclusions

These findings point to the role of CGRP in the processes underlying migraine chronification and suggest a possible interaction with gamma-aminobutyrate (GABA) and glutamate transmission to induce/maintain central sensitization and to contribute to the dysregulation of descending pain system involved in chronic migraine.

Topiramate in Migraine Prevention: A 2016 Perspective

BACKGROUND

In evidence-based guidelines published in 2000, topiramate was a third-tier migraine preventive with no scientific evidence of efficacy; recommendation for its use reflected consensus opinion and clinical experience. Its neurostabilizing activity, coupled with its favorable weight profile, made topiramate an attractive alternative to other migraine preventives that caused weight gain. When guidelines for migraine prevention in episodic migraine were published in 2012, topiramate was included as a first-line option based on double-blind, randomized controlled trials involving nearly 3000 patients. The scientific and clinical interest in topiramate has generated a large body of data from randomized controlled trials, meta-analyses, patient registries, cohort studies, and claims data analyses that have more fully characterized its role as a migraine preventive.

AIM

This article will review the profile of topiramate that has emerged out of the past decade of research and clinical use in migraine prophylaxis. It will also address the rationale for extended-release (XR) formulations in optimizing topiramate therapy in migraine.

SUMMARY

Topiramate has activity at multiple molecular targets, which may account for why it is effective in migraine and most other, more specific, anticonvulsants are not. Based on randomized controlled trials, topiramate reduces migraine frequency and acute medication use, improves quality of life, and reduces disability in patients with episodic migraine and in those with chronic migraine with or without medication overuse headache. Its efficacy in chronic migraine is not improved by the addition of propranolol. Topiramate's ability to prevent progression from high-frequency episodic migraine to chronic migraine remains unclear. Consistent with clinicians' perceptions, migraineurs are more sensitive to topiramate-associated side effects than patients with epilepsy. Paresthesia is a common occurrence early in treatment but is rarely cause for terminating topiramate treatment. Cognitive problems occur much less frequently than paresthesia but are more troublesome in terms of treatment discontinuation. Cognitive complaints can often be managed by slowly increasing the topiramate dose in small increments to allow habituation. As with other carbonic anhydrase inhibitors, topiramate has metabolic effects that favor the development of metabolic acidosis and possibly renal stones. Because migraineurs have an increased risk of renal stones independent of topiramate exposure, clinicians should counsel all migraine patients to maintain hydration. Abrupt onset of blurring, other visual disturbances, and/or ocular pain following topiramate's initiation should be evaluated promptly since this may indicate rare but potentially sight-threatening idiosyncratic events. Postmarketing evidence has shown that first-trimester exposure to topiramate monotherapy is associated with increased occurrence of cleft lip with or without cleft palate (Pregnancy Category D). Even though topiramate's long half-life would seemingly support q.d. dosing, randomized controlled migraine trials used b.i.d. administration of immediate-release (IR) topiramate, which has more favorable plasma concentration-time profile (ie, lower peak concentrations and higher trough concentrations) than q.d. IR dosing. Given the sensitivity of migraineurs to topiramate-related adverse events, particularly cognitive effects, pharmacokinetic profiles should be considered when optimizing migraine outcomes. The extended-release (XR) formulations Qudexy^® XR (Upsher-Smith Laboratories) and Trokendi XR^® (Supernus Pharmaceuticals) were specifically designed to achieve the adherence benefits of q.d. dosing but with more favorable (ie, more constant) steady-state plasma concentrations over the 24-hour dosing interval vs IR topiramate b.i.d. Intriguing results from a study in healthy volunteers showed consistently less impairment in neuropsychometric tests of verbal fluency and mental processing speed with an XR topiramate formulation (Trokendi XR) vs IR topiramate b.i.d. These findings suggest a pharmacodynamic effect associated with significantly reducing plasma concentration fluctuation when topiramate absorption is slowed. Results of retrospective studies in migraineurs treated with XR topiramate appear to support a clinically meaningful benefit of XR topiramate vs IR topiramate in terms of significantly fewer cognitive effects, improved adherence, and overall better outcomes of migraine prophylaxis with topiramate.

Modulation of nociceptive dural input to the trigeminocervical complex through GluK1 kainate receptors

Migraine is a common and disabling neurologic disorder, with important psychiatric comorbidities. Its pathophysiology involves activation of neurons in the trigeminocervical complex (TCC). Kainate receptors carrying the glutamate receptor subunit 5 (GluK1) are present in key brain areas involved in migraine pathophysiology. To study the influence of kainate receptors on trigeminovascular neurotransmission, we determined the presence of GluK1 receptors within the trigeminal ganglion and TCC with immunohistochemistry. We performed in vivo electrophysiologic recordings from TCC neurons and investigated whether local or systemic application of GluK1 receptor antagonists modulated trigeminovascular transmission. Microiontophoretic application of a selective GluK1 receptor antagonist, but not of a nonspecific ionotropic glutamate receptor antagonist, markedly attenuated cell firing in a subpopulation of neurons activated in response to dural stimulation, consistent with selective inhibition of postsynaptic GluK1 receptor-evoked firing seen in all recorded neurons. In contrast, trigeminovascular activation was significantly facilitated in a different neuronal population. The clinically active kainate receptor antagonist LY466195 attenuated trigeminovascular activation in all neurons. In addition, LY466195 demonstrated an N-methyl-d-aspartate receptor-mediated effect. This study demonstrates a differential role of GluK1 receptors in the TCC, antagonism of which can inhibit trigeminovascular activation through postsynaptic mechanisms. Furthermore, the data suggest a novel, possibly presynaptic, modulatory role of trigeminocervical kainate receptors in vivo. Differential activation of kainate receptors suggests unique roles for this receptor in pro- and antinociceptive mechanisms in migraine pathophysiology.

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.

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.

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.

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.

Suppressive effect of chronic peroral topiramate on potassium-induced cortical spreading depression in rats

OBJECTIVE

To evaluate the chronic effect of topiramate (TPM) on cortical spreading depression (CSD), which is thought to be related to migraine aura.

METHODS

Male rats (n = 30) were randomized to once-daily peroral treatment with TPM (50, 100, 200 or 600 mg/kg) or vehicle for 6 weeks. We evaluated the characteristics of CSD induced by topical application of KCl under isoflurane anesthesia and the changes in plasma level of TPM in each group. The effect of single administration of TPM on CSD was also evaluated.

RESULTS

After the final administration of TPM, when the plasma level of TPM was high, KCl-induced CSD frequency and CSD propagation velocity were dose-dependently reduced and the interval between CSD episodes was elongated, compared with the vehicle control. However, before the final administration of TPM, when the plasma level was very low, the KCl-induced CSD profile was the same as that in the vehicle control. Single administration of TPM did not alter the CSD profile. Local cerebral blood flow was not significantly altered by chronic administration of TPM.

CONCLUSION

TPM suppressed the frequency and propagation of CSD along the cerebral cortex, and might be a candidate for relief of migraine.

Topiramate in the treatment of migraine: A kainate (glutamate) receptor antagonist within the trigeminothalamic pathway

Background: The development of new agents for the preventive treatment of migraine is the greatest unmet need in the therapeutics of primary headaches. Topiramate, an anticonvulsant drug, is an effective anti-migraine preventive whose mechanism of action is not fully elucidated. Since glutamate plays a major role in migraine pathophysiology, the potential action of topiramate through glutamatergic mechanisms is of considerable interest.

Methods: Recordings of neurons in the trigeminocervical complex (TCC) and the ventroposteromedial thalamic nucleus (VPM) of anesthetized rats were made using electrophysiological techniques. The effects of intravenous or microiontophorezed topiramate on trigeminovascular activation of second- and third-order neurons in the trigeminothalamic pathway were characterized. The potential interactions of topiramate with the ionotropic glutamate receptors were studied using microiontophoresis.

Results: Both intravenous and microiontophorized topiramate significantly inhibited trigeminovascular activity in the TCC and VPM. In both nuclei microiontophoretic application of topiramate significantly attenuated kainate receptor-evoked firing but had no effect on N-methyl-d-aspartic acid or α-amino-3-hydroxyl-5-methyl-4-isoxazole-propionate receptor activation.

Conclusion: The data demonstrate for the first time that topiramate modulates trigeminovascular transmission within the trigeminothalamic pathway with the kainate receptor being a potential target. Understanding the mechanism of action of topiramate may help in the design of new medications for migraine prevention, with the data pointing to glutamate-kainate receptors as a fruitful target to pursue.

Effects of ionotropic glutamate receptor antagonists on rat dural artery diameter in an intravital microscopy model

BACKGROUND AND PURPOSE

During migraine, trigeminal nerves may release calcitonin gene-related peptide (CGRP), inducing cranial vasodilatation and central nociception; hence, trigeminal inhibition or blockade of craniovascular CGRP receptors may prevent this vasodilatation and abort migraine headache. Several preclinical studies have shown that glutamate receptor antagonists affect the pathophysiology of migraine. This study investigated whether antagonists of NMDA (ketamine and MK801), AMPA (GYKI52466) and kainate (LY466195) glutamate receptors affected dural vasodilatation induced by alpha-CGRP, capsaicin and periarterial electrical stimulation in rats, using intravital microscopy.

EXPERIMENTAL APPROACH

Male Sprague-Dawley rats were anaesthetized and the overlying bone was thinned to visualize the dural artery. Then, vasodilator responses to exogenous (i.v. alpha-CGRP) and endogenous (released by i.v. capsaicin and periarterial electrical stimulation) CGRP were elicited in the absence or presence of the above antagonists.

KEY RESULTS

alpha-CGRP, capsaicin and periarterial electrical stimulation increased dural artery diameter. Ketamine and MK801 inhibited the vasodilator responses to capsaicin and electrical stimulation, while only ketamine attenuated those to alpha-CGRP. In contrast, GYKI52466 only attenuated the vasodilatation to exogenous alpha-CGRP, while LY466195 did not affect the vasodilator responses to endogenous or exogenous CGRP.

CONCLUSIONS AND IMPLICATIONS

Although GYKI52466 has not been tested clinically, our data suggest that it would not inhibit migraine via vascular mechanisms. Similarly, the antimigraine efficacy of LY466195 seems unrelated to vascular CGRP-mediated pathways and/or receptors. In contrast, the cranial vascular effects of ketamine and MK801 may represent a therapeutic mechanism, although the same mechanism might contribute, peripherally, to cardiovascular side effects.

New drugs in migraine treatment and prophylaxis: telcagepant and topiramate

Although the triptan drugs provide effective relief from migraine for many patients, a substantial number of affected individuals are unresponsive to these compounds, and such therapy can also lead to a range of adverse effects. Telcagepant represents a new class of antimigraine drug-the calcitonin gene-related peptide receptor blockers. This compound exerts its effects by blocking receptors for the calcitonin-gene-related peptide at several sites in the trigeminal and central nervous systems, resulting in pain relief. Telcagepant does not cause vasoconstriction, a major limitation in the use of triptans. Comparisons with triptans in clinical trials for acute treatment of migraine attacks revealed clinical effects similar to those of triptans but better than those of placebo. Telcagepant might provide hope for those who have a poor response to, or are unable to use, older drugs. In patients who need prophylaxis because of frequent attacks of migraine, topiramate is a first-line drug for migraine prevention in many countries; it is generally safe and reasonably well tolerated. Data suggest that topiramate could aid reversion of chronic migraine to episodic migraine.

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.

Epidemiology, risk factors, and treatment of chronic migraine: a focus on topiramate

The term chronic daily headache refers to a heterogeneous group of headache disorders characterized by a frequency of headaches on > or = 15 days per month. Chronic migraine is a subtype of chronic daily headache. The prevalence of chronic migraine is approximately 1%. Baseline attack frequency and acute medication overuse have been identified as potential risk factors for the progression of migraine from an episodic disorder to a chronic condition. There is an unmet patient need for effective and safe treatments for patients with chronic migraine, but data from rigorous controlled trials are limited. Previous studies have demonstrated that topiramate is an effective and safe preventive treatment for episodic migraine. In addition, pilot studies have suggested the utility of topiramate for the prevention of chronic migraine. Two randomized, double-blind, placebo-controlled, multicenter trials investigating the efficacy and safety of topiramate in the treatment of patients with chronic migraine have recently been completed. This review presents comparative data from these 2 clinical trials, which suggest that topiramate at a dose of 100 mg daily is effective and generally well tolerated in chronic migraine.

Therapeutic potential of novel glutamate receptor antagonists in migraine

BACKGROUND

Migraine is a common and disabling neurological disorder. Although the pharmacotherapy of migraine has advanced in parallel with our understanding of the pathophysiology of the disease, there is still a considerable unmet need to find more effective treatments. Migraine pathophysiology involves activation or the perception of activation of the trigeminovascular system. Glutamate, the major excitatory neurotransmitter in the CNS, is implicated in elements of the pathophysiology of the disorder, including trigeminovascular activation, central sensitization and cortical spreading depression.

OBJECTIVE

The aim of this article is to review the potential use of glutamate receptor antagonists as innovative neuronally targeted treatments of migraine.

METHODS

A systematic search of peer-reviewed publications was performed in PubMed on glutamate and migraine/trigeminovascular activation, and important references providing an insight into migraine pathophysiology are included. The results of unpublished trials were obtained from presentations at national and international meetings.

RESULTS/CONCLUSIONS

The preclinical and clinical data argue strongly for a role of glutamatergic receptor activation in migraine. The pharmacology of glutamatergic trigeminovascular responses in brain areas involved in migraine pathophysiology is relevant to the development of new therapies for this disabling condition. Glutamate receptors represent a promising target for a valuable, non-vasoconstrictor, and perhaps more importantly neuronal-specific therapeutic approach to the treatment of migraine.

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.

Antiepileptic Drugs on Calcium Currents Recorded from Cortical and PAG Neurons: Therapeutic Implications for Migraine

Cortex and periaqueductal grey (PAG) play a major role in the pathophysiology of migraine. Some antiepileptic drugs (AEDs) influence the activity of these structures by modulating high-voltage-activated (HVA) Ca2+ channels and are effective in migraine prevention. The aim of the present study was to investigate the expression of total HVA Ca2+ channels in cortical and PAG neurons and to study the differential action of AEDs on these channels. Isolated neurons were visually identified based on morphological criteria. HVA currents were recorded by whole-cell patch-clamp technique. The distribution ratio of L-, N-, P-, Q- and R-type HVA Ca2+ channels was different between cortical and PAG neurons. In particular, we found that P- and Q-type HVA Ca2+ channels were more expressed in PAG neurons than in cortical cells, whereas L- and R-type HVA Ca2+ channels showed an opposite distribution. Interestingly, N-type HVA Ca2+ channels were equally distributed in these two neuronal populations. A differential sensitivity to AEDs of HVA Ca2+ channels located on cortical and PAG neurons was observed for topiramate (TPM), but not for lamotrigine (LTG) or levetiracetam (LEV). In fact, whereas both LTG and LEV were equally effective and potent in inhibiting HVA Ca2+ currents in the two neuronal populations, TPM showed a much higher potency and efficacy in blocking these currents in PAG neurons than in cortical pyramidal cells. TPM, in fact, inhibited N-, P- and L-type channels in PAG neurons, whereas in cortical neurons this AED modulated only P- and L-type channels. Unlike the other AEDs investigated, valproic acid did not affect HVA Ca2+ currents in cortical and PAG neurons. The negative modulation of specific subtypes of HVA Ca2+ channels by various AEDs can restore normal electrical activity in target brain areas such as cortex and PAG, providing interesting therapeutic approaches in migraine prevention.

CGRP function-blocking antibodies inhibit neurogenic vasodilatation without affecting heart rate or arterial blood pressure in the rat

BACKGROUND AND PURPOSE

Calcitonin gene-related peptide (CGRP) receptor antagonists effectively abort migraine headache and inhibit neurogenic vasodilatation in humans as well as rat models. Monoclonal antibodies typically have long half-lives, and we investigated whether or not function-blocking CGRP antibodies would inhibit neurogenic vasodilatation with a long duration of action and therefore be a possible approach to preventive therapy of migraine. During chronic treatment with anti-CGRP antibodies, we measured cardiovascular function, which might be a safety concern of CGRP inhibition.

EXPERIMENTAL APPROACH

We used two rat blood flow models that measure electrically stimulated vasodilatation in the skin or in the middle meningeal artery (MMA). These vasomotor responses are largely dependent on the neurogenic release of CGRP from sensory afferents. To assess cardiovascular function during chronic systemic anti-CGRP antibody treatment, we measured heart rate and blood pressure in conscious rats.

KEY RESULTS

Treatment with anti-CGRP antibodies inhibited skin vasodilatation or the increase in MMA diameter to a similar magnitude as treatment with CGRP receptor antagonists. Although CGRP antibody treatment had a slower onset of action than the CGRP receptor antagonists, the inhibition was still evident 1 week after dosing. Chronic treatment with anti-CGRP antibodies had no detectable effects on heart rate or blood pressure.

CONCLUSIONS AND IMPLICATIONS

We showed for the first time that anti-CGRP antibodies exert a long lasting inhibition of neurogenic vasodilatation in two different rat models of arterial blood flow. We have provided strong preclinical evidence that anti-CGRP antibody may be a suitable drug candidate for the preventive treatment of migraine.

Molecular pharmacodynamics, clinical therapeutics, and pharmacokinetics of topiramate

Topiramate (TPM; TOPAMAX) is a broad-spectrum antiepileptic drug (AED) that is approved in many world markets for preventing or reducing the frequency of epileptic seizures (as monotherapy or adjunctive therapy), and for the prophylaxis of migraine. TPM, a sulfamate derivative of the naturally occurring sugar D-fructose, possesses several pharmacodynamic properties that may contribute to its clinically useful attributes, and to its observed adverse effects. The sulfamate moiety is essential, but not sufficient, for its pharmacodynamic properties. In this review, we discuss the known pharmacodynamic and pharmacokinetic properties of TPM, as well as its various clinically beneficial and adverse effects.

New insights into migraine pathophysiology

PURPOSE OF REVIEW

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

RECENT FINDINGS

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

SUMMARY

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

Cerebrospinal fluid sodium increases in migraine

BACKGROUND

Pharmaceuticals with calcium- or sodium-channel-blocking activity have proven useful for migraine prophylaxis, and calcium channel, sodium transporter, and sodium channel gene mutations have been found in familial hemiplegic migraine. However, it is not known whether calcium or sodium homeostasis is altered in migraine.

OBJECTIVE

To compare levels of sodium, calcium, potassium, and magnesium in cerebrospinal fluid (CSF) and blood plasma between migraineurs and controls.

METHODS

We recruited 20 migraineurs without aura and 11 controls prospectively, and studied migraineurs in sick (MH(+)) and well (MH(-)) states. We collected lumbar CSF and venous blood plasma, quantified elements with ion-selective electrodes or colorimetry, and determined osmolality by depression of freezing point. We compared levels of Na(+), Ca(2+), K(+), and Mg among and also within subjects who were studied in both MH(+) and MH(-) states.

RESULTS

Mean CSF Na(+) levels were increased by 3 mmol/L in MH(+) compared with MH(-) and by 4 mmol/L compared to controls (P < 0.005). In 4 subjects who were sampled in both MH(+) and MH(-) states, mean CSF Na(+) concentration increased by 2 mmol/L in the MH(+) state compared with the MH(-) state (P < 0.05). Simultaneous plasma Na(+) levels did not differ among the 3 clinical groups, nor did osmolality, total Ca and Ca(2+), K(+), and total Mg levels in CSF.

CONCLUSIONS

Compared to both controls and the MH(-) state, CSF Na(+) concentration increased in MH(+) independently from other clinical or pharmacological fluctuations, CSF concentrations of Ca(2+), Mg, and K(+), and blood plasma Na(+) levels. These results implicate a deviation of Na(+) homeostasis in migraine. The modestly elevated extracellular Na(+) in MH(+) may cause the neural changes that underlie clinical features of migraine.

Effects of current and prospective antimigraine drugs on the porcine isolated meningeal artery

Vasoconstriction to agonists at serotonin (5-hydroxytryptamine; 5-HT) receptors and alpha-adrenoceptors, as well as vasodilatation induced by alpha-CGRP, have been well described in the porcine carotid circulation in vivo. The present study sets out to investigate the effects of current and prospective antimigraine drugs on porcine meningeal artery segments in vitro. Sumatriptan, ergotamine, dihydroergotamine, isometheptene and clonidine failed to contract the meningeal artery, but 5-HT, noradrenaline and phenylephrine induced concentration-dependent contractions. The contractions to 5-HT were competitively antagonized by the 5-HT(2A) receptor antagonist ketanserin, whilst those to noradrenaline were antagonized by alpha(1)-(prazosin), alpha(2)-(rauwolscine and yohimbine) and alpha(2C/2B)-(OPC-28326) adrenoceptor antagonists. Whilst dobutamine and salbutamol were ineffective, alpha-CGRP produced concentration-dependent relaxations that were antagonized by the CGRP(1) receptor antagonist olcegepant. In agreement with their lack of contractile effect, sumatriptan and ergotamine failed to influence forskolin-stimulated cyclic AMP accumulation in the porcine meningeal artery; in contrast, both compounds decreased forskolin-stimulated cyclic AMP accumulation in the human isolated saphenous vein, where they induced contractions. Finally, using RT-PCR, we could demonstrate the presence of mRNAs encoding for several 5-HT receptors (5-HT(1B), 5-HT(1D), 5-HT(1F), 5-HT(2A) and 5-HT(7)) and adrenoceptors (alpha(1A), alpha(1B), alpha(1D), alpha(2A), alpha(2B), alpha(2C), beta(1) and beta(2)), as well as that for the calcitonin receptor like receptor, a component of the CGRP(1) receptor. These results suggest that: (i) the porcine meningeal artery may not be involved in the vasoconstriction of the carotid vascular bed elicited by antimigraine drugs in anaesthetized pigs, and (ii) the mismatch between the presence of receptor mRNA and the lack of response to sumatriptan, dobutamine and salbutamol implies that mRNAs for the 5-HT(1B) receptor and beta(1)- and beta(2)-adrenoceptors are probably unstable, or that their density is too low for being translated as receptor protein in sufficient quantities.

Topiramate and Triptans Revert Chronic Migraine With Medication Overuse to Episodic Migraine

OBJECTIVE

This is a randomized, double-blind versus placebo study aimed at evaluating the efficacy of topiramate (TPM) in reducing the number of days with headache and the amount of acute medication taken monthly in patients with chronic migraine with medication overuse. We also studied the efficacy of single triptans available in Italy in interrupting headache crises during preventive treatment.

METHODS

The studied sample was made up of 50 subjects: 30 patients were randomized for treatment with TPM, 100 mg/d, and 20 for placebo. Subjects treated with TPM were further randomized to evaluate, in double-blind versus placebo, the efficacy of single triptans available in Italy. The double-blind phase consisted of a titration phase (4 weeks) and of a maintenance phase (8 weeks).

OUTCOME MEASURES

The reduction in the number of days with headache per 28 days and the reduction in the amount of acute medication taken per 28 days throughout the clinical trial in the TPM group were compared with those of the placebo group; the number of patients who were pain-free at 2 hours after the triptan intake and the headache recurrence rate in the 22 hours after the pain-free condition in the triptan group were compared with those of the placebo group. We also looked at tolerability profile.

RESULTS

The group treated with TPM had a significant reduction in the number of days with headache (P < 0.0001 vs placebo) and in the mean amount of acute medication taken (P < 0.0001 vs placebo); all triptans were superior to placebo; there were no significant differences between different triptans; the analgesic effect of triptans increased throughout the trial.

CONCLUSIONS

Topiramate proved to be well tolerated and effective in reverting chronic migraine with medication overuse to episodic migraine.

Repression of Stimulated Calcitonin Gene-Related Peptide Secretion by Topiramate

OBJECTIVE

The goal of the proposed research was to determine the effect of topiramate on basal and stimulated release of calcitonin gene-related peptide (CGRP) from trigeminal ganglia neurons.

BACKGROUND

CGRP is implicated in migraine headaches. Clinical evidence supports topiramate as an effective migraine prophylactic. In this study, the connection between topiramate and CGRP expression was investigated.

METHODS

Primary cultures of rat trigeminal ganglia were utilized to determine the effects of topiramate on CGRP release stimulated by a depolarizing stimulus (KCl), nitric oxide, and/or protons. The amount of CGRP secreted into the culture media was determined using a CGRP-specific radioimmunoassay.

RESULTS

Treatment of trigeminal cultures with KCl, nitric oxide donor S-nitroso-N-acetylpenicillamine, or protons (pH 5.5 media) caused a marked increase (3 to 5 fold) in the amount of CGRP release. Topiramate treatment repressed KCl-stimulated CGRP release in a time- and concentration-dependent manner. However, topiramate did not alter the amount of unstimulated or basal CGRP released from trigeminal neurons. In addition, topiramate inhibited nitric oxide and proton mediated CGRP secretion.

CONCLUSIONS

Findings from these studies demonstrate that topiramate can directly repress the stimulated release of CGRP from sensory trigeminal neurons. We propose that topiramate's ability to prevent migraine attacks may involve inhibition of CGRP secretion from trigeminal neurons.