Analgesic triptan action in an animal model of intracranial pain: a race against the development of central sensitization

Central sensitization: a generator of pain hypersensitivity by central neural plasticity

Central sensitization represents an enhancement in the function of neurons and circuits in nociceptive pathways caused by increases in membrane excitability and synaptic efficacy as well as to reduced inhibition and is a manifestation of the remarkable plasticity of the somatosensory nervous system in response to activity, inflammation, and neural injury. The net effect of central sensitization is to recruit previously subthreshold synaptic inputs to nociceptive neurons, generating an increased or augmented action potential output: a state of facilitation, potentiation, augmentation, or amplification. Central sensitization is responsible for many of the temporal, spatial, and threshold changes in pain sensibility in acute and chronic clinical pain settings and exemplifies the fundamental contribution of the central nervous system to the generation of pain hypersensitivity. Because central sensitization results from changes in the properties of neurons in the central nervous system, the pain is no longer coupled, as acute nociceptive pain is, to the presence, intensity, or duration of noxious peripheral stimuli. Instead, central sensitization produces pain hypersensitivity by changing the sensory response elicited by normal inputs, including those that usually evoke innocuous sensations.

PERSPECTIVE

In this article, we review the major triggers that initiate and maintain central sensitization in healthy individuals in response to nociceptor input and in patients with inflammatory and neuropathic pain, emphasizing the fundamental contribution and multiple mechanisms of synaptic plasticity caused by changes in the density, nature, and properties of ionotropic and metabotropic glutamate receptors.

Intracisternal Injection of Inflammatory Soup Activates the Trigeminal Nerve System

The release of calcitonin gene-related peptide (CGRP) and sensitization of the trigeminal nerve system are important elements in migraine pathophysiology. Sensitization can be induced by topical meningeal administration of inflammatory soup (IS). CGRP release is a marker of trigeminal nerve activation. We examined the effect of intracisternal IS administration on CGRP release in rat jugular vein blood at baseline, 2 and 15 min after the beginning of IS infusion. IS administration caused a significant increase of CGRP levels after 2 and 15 min compared with baseline. Daily oral treatment with topiramate for 4 and 8 weeks led to a dose- and time-dependent reduction of IS-induced CGRP release. Sumatriptan also attenuated stimulated neuropeptide release. These results indicate that intracisternal IS administration leads to activation of the trigeminal system. The inhibition of CGRP release by topiramate offers a possible mechanism that may in part account for the preventative antimigraine activity of this drug.

A novel method for modeling facial allodynia associated with migraine in awake and freely moving rats

Migraine is a neurovascular disorder that induces debilitating headaches associated with multiple symptoms including facial allodynia, characterized by heightened responsivity to normally innocuous mechanical stimuli. It is now well accepted that immune activation and immune-derived inflammatory mediators enhance pain responsivity, including the trigeminal system. Nociceptive ("pain" responsive) trigeminal nerves densely innervate the cranial meninges. We have recently proposed that the meninges may serve as a previously unidentified, key interface between the peripheral immune system and the CNS with potential implications for understanding underlying migraine mechanisms. Our focus here is the development of a model for facial allodynia associated with migraine. We developed a model wherein an indwelling catheter is placed between the skull and dura, allowing immunogenic stimuli to be administered over the dura in awake and freely moving rats. Since the catheter does not contact the brain itself, any proinflammatory cytokines induced following manipulation derive from resident or recruited meningeal immune cells. While surgery alone does not alter immune activation markers, TNF or IL6 mRNA and/or protein, it does decrease gene expression and increase protein expression of IL-1 at 4 days after surgery. Using this model we show the induction of facial allodynia in response to supradural administration of either the HIV glycoprotein gp120 or inflammatory soup (bradykinin, histamine, serotonin, and prostaglandin E2), and the induction of hindpaw allodynia in our model after inflammatory soup. This model allows time- and dose-dependent assessment of the relationship between changes in meningeal inflammation and corresponding exaggerated pain behaviors.

Expanding access to triptans: assessment of clinical outcome

OBJECTIVE

To evaluate whether access to more liberal quantities of rizatriptan improves clinical outcome in patients with episodic migraine.

BACKGROUND

Currently many pharmacy benefit programs limit the number of triptan tablets/injections per month based on perceived cost savings and the belief that too-frequent use of triptans may lead to medication overuse headache and headache chronification.

METHODS

This observer-blind, randomized, parallel-group study enrolled 197 subjects with migraine with or without aura. Subjects completed a 3-month baseline period to establish migraine frequency and then were randomly assigned to receive 9 (formulary limit [FL]) or 27 (clinical limit [CL]) tablets of 10 mg rizatriptan orally disintegrating tablet (ODT) per month for 3 months. The primary endpoint was change in the mean number of migraine days from the baseline to treatment period.

RESULTS

There was no statistically significant difference between the FL and CL groups in mean number of migraine days (FL-CL LS mean: -0.08 [-0.39, 0.23]; P = .613). Subjects in the CL group treated attacks at lower headache severity. No CL subjects were reported to have developed chronic migraine despite utilization of greater than 10 rizatriptan ODT tablets per month. Rizatriptan was generally well tolerated by both groups.

CONCLUSION

Providing a greater quantity of rizatriptan ODT 10 mg did not reduce the number of migraine days compared with providing 9 tablets per month for this population with episodic migraine with a frequency of 3-8 migraines per month. Regardless of quantity provided, rizatriptan was generally well tolerated.

Migraine: an overview

The pathophysiology of migraine is not completely understood and continues to be investigated. The complexity of interactions taking place in the sensory neuronal network with the mediation of all different neurotransmitters involved gives the measure of the extreme difficulty connected with the knowledge of migraine pathogenesis and in particular of its cardinal sign. Neuronal components are relevant in migraine pathophysiology: there could be a generalized interictal abnormal excitability of the cerebral cortex in migraine, possibly favoring the occurrence of spreading depression with consequent activation of the trigeminal system. Many theories have been formulated in these last sixty years about the pathogenesis of migraine and other forms of primary headache, but the problem is still far to be fully clarified. The present review is focused on the description of different theories on the migraine pathogenesis. This review is dedicated to the memory of Prof. Alfredo Bianchi.

The effects of the TRPV1 receptor antagonist SB-705498 on trigeminovascular sensitisation and neurotransmission

This report examines the effect of the transient receptor potential vanilloid 1 receptor antagonist SB-705498 on neurotransmission and inflammation-induced sensitisation in the trigeminovascular sensory system. A single-neuron electrophysiological animal model for neurovascular head pain was used to evaluate dural and facial noxious inputs and the effects of SB-705498 administered by intravenous (i.v.) injection. Electrical and mechanical stimulation of the dura mater and the facial skin activated second-order neurons in the trigeminal nucleus caudalis of cats, with A-delta latencies. Intravenous injection of SB-705498 (2 mg kg(-1)) produced a slowly developing and long-lasting suppression of responses to dural and skin stimulation. Maximum suppression occurred by 1 h and reached 41% for dura and 24% for skin. Intravenous injection of drug vehicle did not produce significant suppression of responses to stimulation of either dura or skin. Intravenous injection of SB-705498 produced a brief and small rise in blood pressure and dural blood flow, which both returned to normal before suppression of the responses to stimulation became manifest. Application of "inflammatory soup" to the dura mater produced a pronounced increase in dural blood flow and induced a slowly developing increase in the responses of neurons to both electrical and mechanical stimulations of their facial and dural receptive fields. This sensitisation reached a maximum in 60-90 min, at which time responses had risen to approximately twice that of control levels seen before the application of inflammatory soup. Intravenous injection of SB-705498 subsequent to the development of sensitisation produced a slowly developing, prolonged and statistically significant reversal of the sensitisation induced by inflammatory soup. Maximum reversal of sensitisation to electrical stimulation occurred by 150-180 min, when responses had fallen to, or below, control levels. At 70-85 min following injection of SB-705498, the responses of previously sensitised neurons to mechanical stimulation of dura mater and facial receptive field had also returned to near control levels. SB-705498 was also able to prevent the development of sensitisation; application of inflammatory soup to the dura mater induced a slowly developing increase in the responses of neurons to electrical stimulation of the skin and dura mater in cats which had received an i.v. injection of vehicle for SB-705498 but not in cats which had received the active drug. Blood levels of SB-705498 were maximal immediately following i.v. injection and declined over the following 2 h. Significant brain levels of SB-705498 were maintained for up to 9 h. These results suggest that SB-705498 may be an effective suppressant and reversal agent of the sensitisation to sensory input which follows inflammation in the trigeminovascular sensory distribution but may not be particularly useful in blocking primary pain processes such as migraine headache. SB-705498 could thus potentially prevent, modify or reverse the cutaneous trigeminal allodynia seen in certain migraine conditions, especially "transformed" migraine.

Dynamic mechanical (brush) allodynia in cluster headache: a prevalence study in a tertiary headache clinic

Cutaneous allodynia (CA) has been described in migraine and has been related to treatment failure. There are little data about the incidence of CA in other primary headache syndromes such as cluster headache (CH). The objectives of this study are to evaluate the prevalence of dynamic mechanical (brush) allodynia (BA) in CH patients attending a tertiary headache clinic, and to assess its relation to disease characteristics. Adult patients with episodic or chronic CH were recruited. We obtained demographic data and data on disease characteristics through a structured questionnaire, and tested the patients for brush allodynia BA by applying a 4 x 4 gauze pad over the V1, C2/C3 and C8 skin areas bilaterally. The prevalence of allodynia in the entire study population and in the different sub-groups was calculated. We also examined the association between CA and demographic parameters, and its association with disease characteristics. Forty-one patients were recruited (22 men, 19 women; mean age 44.9 years). Twenty-two had chronic CH (CCH) and 19 had episodic CH (ECH). Mean disease duration was 14.1 years (12.3 the CCH group and 15.7 in the ECH group). Overall, 20 (49%) patients were allodynic. There was no statistically significant association between the presence of allodynia and age, gender, diagnosis (episodic vs. chronic CH), disease duration or disease severity. In conclusion, BA was common in this CH patient sample. The therapeutic implications of the presence of BA in CH need to be further studied.

Genetic enhancement of calcitonin gene-related Peptide-induced central sensitization to mechanical stimuli in mice

Calcitonin gene-related peptide (CGRP) is a key player in migraine. To address the role of CGRP in mechanical allodynia, which is a common feature of migraine, we used CGRP-sensitized transgenic mice. These mice have elevated nervous-system expression of the human receptor activity-modifying protein-1 (hRAMP1) subunit of the CGRP receptor. Under baseline conditions, the nestin/hRAMP1 mice and control littermates had similar hindpaw withdrawal thresholds to von Frey filaments. The effect of CGRP was tested using a filament that elicited a withdrawal response on 20% of its presentations. Following intrathecal injection of 1 nmol CGRP in the nestin/hRAMP1 mice, the response frequency was 80% within 30 minutes. The antagonist CGRP(8-37) blocked the increased response. In control littermates, a 5-fold higher dose of CGRP was required to elicit a similar response. In contrast to intrathecal injection, peripheral CGRP did not increase the mechanical responses. Intraplantar injection of capsaicin was used to test the efficacy of endogenous CGRP. Capsaicin increased mechanical responses in the nestin/hRAMP1 and control mice, although a higher dose was required in controls. In contrast to control mice, there was also a contralateral paw response in nestin/hRAMP1 mice, which is consistent with central sensitization.

PERSPECTIVE

In this study we show central CGRP-induced mechanical allodynia that is enhanced by overexpression of RAMP1 in nervous system. These data suggest that hypersensitivity to CGRP could be a potential mechanism underlying central sensitization in migraine and point to CGRP-receptor antagonists as a possible therapy for other pain disorders.

Acute treatment of migraine

The goals of acute treatment of migraine are cost-effective rapid relief, consistent reduction of disability, and reduced use of rescue medications. Key to acute treatment is matching medication to disability as a surrogate marker for disease severity with a stratified care approach. In the absence of vascular contraindications, triptans are first-line acute treatments for disabling migraine. Acute treatment success can be assessed with use of the paper tool, Migraine-ACT. Opioids and butalbital should be avoided in acute migraine treatment. Triptan type can be selected for patients by differences in speed or effect, formulation, and formulary tier.

What predicts the change from episodic to chronic migraine?

PURPOSE OF REVIEW

Because migraine worsens in a sizeable subgroup of sufferers, but not in most, identifying factors that predict the change from episodic into chronic migraine is of extreme interest and should be seen as a priority in headache research.

RECENT FINDINGS

Potentially remediable risk factors include frequency of migraine attacks, obesity, excessive use of medications containing opioids and barbiturates, caffeine overuse, stressful life events, depression, sleep disorders and cutaneous allodynia.

SUMMARY

While we wait for evidence regarding the benefits of risk factor modifications in the prevention of chronic migraine, several interventions are justifiable based on their other established benefits. For example, decreasing headache frequency with behavioral and pharmacological interventions will decrease current disability even if it does not modify clinical course. Monitoring the body mass index and encouraging maintenance of normal body weight is good practice in patients with and without migraine. Avoiding overuse of caffeine is desirable apart from its potential benefit in preventing progression. Sleep problems should be investigated and treated. Psychiatric comorbidities should be identified and addressed. Medications containing opioids and barbiturates should be reserved for a few selected cases of migraine, and their use should be monitored. For these interventions, the possibility of preventing progression may motivate clinicians to offer good care and patients to engage in the treatment plan.

The triptans

The migraine-specific triptans have revolutionized the treatment of migraine and are currently the drugs of choice to treat a migraine attack in progress. Over the past 15 years, triptans were released in rapid succession, with each one demonstrating some specific pharmacokinetic properties that may be translated into clinical advantages. Triptans share many similarities, but also have important differences from one another. Accordingly, herein we discuss the class of the triptans. We first define the trigeminovascular system and its importance in migraine pain, then discuss the mechanism of action of the triptans and contrast the evidence supporting the use of different triptans. We close with our view of the future and hopes for the next generation of antimigraine therapies.

Excitatory neurotransmitters in brain regions in interictal migraine patients

OBJECTIVE

To examine biochemical differences in the anterior cingulate cortex (ACC) and insula during the interictal phase of migraine patients. We hypothesized that there may be differences in levels of excitatory amino acid neurotransmitters and/or their derivatives in migraine group based on their increased sensitivity to pain.

METHODS

2D J-resolved proton magnetic resonance spectroscopy (1H-MRS) data were acquired at 4.0 Tesla (T) from the ACC and insula in 10 migraine patients (7 women, 3 men, age 43 +/- 11 years) and 8 age gender matched controls (7 women, 3 men, age 41 +/- 9 years).

RESULTS

Standard statistical analyses including analysis of variance (ANOVA) showed no significant metabolite differences between the two subject cohorts in the ACC nor the insula. However, linear discriminant analysis (LDA) introduced a clear separation between subject cohorts based on N-acetyl aspartylglutamate (NAAG) and glutamine (Gln) in the ACC and insula.

CONCLUSION

These results are consistent with glutamatergic abnormalities in the ACC and insula in migraine patients during their interictal period compared to healthy controls. An alteration in excitatory amino acid neurotransmitters and their derivatives may be a contributing factor for migraineurs for a decrease in sensitivity for migraine or a consequence of the chronic migraine state. Such findings, if extrapolated to other regions of the brain would offer new opportunities to modulate central system as interictal or preemptive medications in these patients.

Migraine in the triptan era: progresses achieved, lessons learned and future developments

Triptans, serotonin 5-HT1B/1D receptor agonists, more than revolutionizing the treatment of migraine, stimulated also ground breaking research that provided insights into the anatomy, physiology, and molecular pharmacology of migraine. This knowledge, in turn, is stimulating research on new mechanisms of action for the treatment of migraine. Accordingly, it is opportune to critically review the main advances in migraine science that happened in the triptan era. Herein we first review and conceptualize some of the progresses achieved in migraine science during the triptan era. We then review the class of the triptans - mechanism of action and clinical evidence. We close by briefly discussing the class of CGRP receptor antagonists, which is currently being developed for the acute treatment of migraine.

Is Chronic Migraine One End of a Spectrum of Migraine or a Separate Entity?

Chronic migraine is associated with abnormalities in the periaqueductal grey that may be progressive. The condition is also associated with a greater degree of impairment in cortical processing of sensory stimuli than episodic migraine, perhaps due to more pervasive or persistent cortical hyperexcitability These findings fit with the model of migraine as a spectrum disorder, in which the clinical and pathophysiological features may progress over time. This progression may result from changes in nociceptive thresholds and ensuing central sensitization caused by recurrent migraine in susceptible individuals. This may lead to changes in baseline neurological function between headaches, evident not only in electrophysiological and functional imaging studies, but also as psychological and somatic complaints that occur after years of episodic migraine. From current research and migraine models, a conceptualization of chronic migraine is emerging in which relatively permanent and pervasive central changes have occurred that warrant novel and tolerable treatments.

Fixed-dose sumatriptan and naproxen in poor responders to triptans with a short half-life

OBJECTIVE

To evaluate efficacy and tolerability of a single, fixed-dose tablet of sumatriptan 85 mg/naproxen sodium 500 mg (sumatriptan/naproxen sodium) vs placebo in migraineurs who had discontinued treatment with a short-acting triptan because of poor response or intolerance.

BACKGROUND

Triptan monotherapy is ineffective or poorly tolerated in 1 of 3 migraineurs and in 2 of 5 migraine attacks. In April, 2008, the Food and Drug Administration approved the combination therapy sumatriptan/naproxen sodium, developed specifically to target multiple migraine mechanisms. This combination product offers an alternative migraine therapy for patients who have reported poor response or intolerance to short-acting triptans.

METHODS

Two replicate, randomized, multicenter, double-blind, placebo-controlled, 2-attack crossover trials evaluated migraineurs who had discontinued a short-acting triptan in the past year because of poor response or intolerance. Patients were instructed to treat within 1 hour and while pain was mild.

RESULTS

Patients (n = 144 study 1; n = 139 study 2) had discontinued an average of 3.3 triptans before study entry. Sumatriptan/naproxen sodium was superior (P < .001) to placebo for 2- through 24-hour sustained pain-free response (primary end point) (study 1, 26% vs 8%; study 2, 31% vs 8%) and pain-free response 2 hours post dose (key secondary end point) (study 1, 40% vs 17%; study 2, 44% vs 14%). A similar pattern of results was observed for other end points that evaluated acute (2- or 4-hour), intermediate (8-hour), or 2- through 24-hour sustained response for migraine (ie, pain and associated symptoms), photophobia, phonophobia, or nausea (with the exception of nausea 2 and 4 hours post dose). The percentage of patients with at least 1 adverse event (regardless of causality) was 11% with sumatriptan/naproxen sodium compared with 4% with placebo in study 1 and 9% with sumatriptan/naproxen sodium compared with 5% with placebo in study 2. Only 1 adverse event in 1 study was reported in > or =2% of patients after treatment with sumatriptan/naproxen sodium and reported more frequently with sumatriptan/naproxen than placebo: chest discomfort was reported in 2% of subjects in study 1, and no events met this threshold in study 2. No serious adverse events attributed to study medication were reported in either study.

CONCLUSION

In migraineurs who reported poor response to a short-acting triptan, sumatriptan/naproxen sodium was generally well tolerated and significantly more effective than placebo in conferring initial, intermediate, and sustained efficacy for pain and migraine-associated symptoms of photophobia and phonophobia.

Medullary pain facilitating neurons mediate allodynia in headache-related pain

OBJECTIVE

To develop and validate a model of cutaneous allodynia triggered by dural inflammation for pain associated with headaches. To explore neural mechanisms underlying cephalic and extracephalic allodynia.

METHODS

Inflammatory mediators (IM) were applied to the dura of unanesthetized rats via previously implanted cannulas, and sensory thresholds of the face and hind-paws were characterized.

RESULTS

IM elicited robust facial and hind-paw allodynia, which peaked within 3 hours. These effects were reminiscent of cutaneous allodynia seen in patients with migraine or other primary headache conditions, and were reversed by agents used clinically in the treatment of migraine, including sumatriptan, naproxen, and a calcitonin gene-related peptide antagonist. Consistent with clinical observations, the allodynia was unaffected by a neurokinin-1 antagonist. Having established facial and hind-paw allodynia as a useful animal surrogate of headache-associated allodynia, we next showed that blocking pain-facilitating processes in the rostral ventromedial medulla (RVM) interfered with its expression. Bupivacaine, destruction of putative pain-facilitating neurons, or block of cholecystokinin receptors prevented or significantly attenuated IM-induced allodynia. Electrophysiological studies confirmed activation of pain-facilitating RVM "on" cells and transient suppression of RVM "off" cells after IM.

INTERPRETATION

Facial and hind-paw allodynia associated with dural stimulation is a useful surrogate of pain associated with primary headache including migraine and may be exploited mechanistically for development of novel therapeutic strategies for headache pain. The data also demonstrate the requirement for activation of descending facilitation from the RVM for the expression of cranial and extracranial cutaneous allodynia, and are consistent with a brainstem generator of allodynia associated with headache disorders.

Migraine: where and how does the pain originate?

Migraine is a complex neurological disease with a genetic background. Headache is the most prominent and clinically important symptom of migraine but its origin is still enigmatic. Numerous clinical, histochemical, electrophysiological, molecular and genetical approaches form a puzzle of findings that slowly takes shape. The generation of primary headaches like migraine pain seems to be the consequence of multiple pathophysiological changes in meningeal tissues, the trigeminal ganglion, trigeminal brainstem nuclei and descending inhibitory systems, based on specific characteristics of the trigeminovascular system. This contribution reviews the current discussion of where and how the migraine pain may originate and outlines the experimental work to answer these questions.

Migraine in the triptan era: lessons from epidemiology, pathophysiology, and clinical science

The triptan era has been a time of remarkable progress for migraine diagnosis and treatment. In this paper, we review some of the advances achieved in migraine science during this era focusing on 3 themes: lessons from clinical practice, lessons from epidemiology and lessons from pathophysiology. Science has shown that migraine is a disorder of the brain, and that the key events happen in the the trigeminal neuronal pathways, not on blood vessels. Clinical science has led to the observation that migraine sometimes progresses or remits. This in turn led to longitudinal epidemiologic studies focusing on factors that determine migraine prognosis. In addition, these studies raised questions about the mechanisms of migraine progression, including the role of allodynia, obesity, inflammation, and medications as determinants of progression. This in turn opens a new set of scientific questions about the neurobiologic determinants of migraine, as well as of its clinical course, and exciting opportunities to develop new therapies for this highly disabling brain disorder.

Ten years of rizatriptan: from development to clinical science and future directions

The year 2008 marked the 10th anniversary since rizatriptan was first launched for the acute treatment of migraine. In this article we discuss the concepts that motivated the preclinical and clinical development of rizatriptan, the clinical evidence that has driven its use over the past decade, rizatriptan's overall contribution to the field, and future directions for research.

Sumatriptan does not change calcitonin gene-related peptide in the cephalic and extracephalic circulation in healthy volunteers

Triptans are effective and well tolerated in acute migraine management but their exact mechanism of action is still debated. Triptans might exert their antimigraine effect by reducing the levels of circulating calcitonin gene-related peptide (CGRP). To examine this question, we examined whether sumatriptan modulate the baseline CGRP levels in vivo, under conditions without trigeminovascular system activation. We sampled blood from the internal and external jugular, the cubital veins, and the radial artery before and after administration of subcutaneous sumatriptan in 16 healthy volunteers. Repeated-measure ANOVA showed no interaction between catheter and time of sampling and thus no significant difference in CGRP between the four catheters (P=0.75). CGRP did not change over time in the four compartments (P>0.05). The relative changes in CGRP between baseline and maximal sumatriptan concentration did not differ between the four vascular compartments (P=0.49). It was found that Sumatriptan did not change the levels of circulating CGRP in the intra or extracerebral circulation in healthy volunteers. This speaks against a direct CGRP-reducing effect of sumatriptan in vivo in humans when the trigemino vascular system is not activated.

Migraine, allodynia, and implications for treatment

Allodynia--perception of pain from non-noxious stimuli--is a common clinical feature in various pain syndromes. The significance for migraine has increasingly been recognized and the pathophysiology has been investigated in detail. Allodynia is a marker for sensitization of central trigeminal neurons. Intensity and persistence of allodynic symptoms are a function of duration of migraine attacks, frequency of attacks, and migraine history. It has been hypothesized that treatment success with triptans may be severely impaired in the presence of allodynia. However, randomized controlled trials did not confirm that. Treatment with cyclooxygenase inhibitors and dihydroergotamine does not seem to be limited by allodynia; these medications may be able to reverse allodynia. Data on the new class of calcitonin-gene related-peptide antagonists are not yet available. Additional and more refined randomized controlled trials, focusing on methodological issues pertaining to the determination of allodynia, are warranted to resolve the true relationship between allodynia and treatment response. Regardless--based on available randomized controlled trials--the recommendation prevails to initiate abortive treatment as soon as possible after attack onset when pain is still mild.

Refractory migraine and chronic migraine: pathophysiological mechanisms

Despite increased understanding of primary headaches and their treatment, the underlying causes of refractory migraine remain unknown. This note considers potential genetic, structural, functional and pharmacological factors that could contribute to this relatively intractable condition. Further understanding of refractory migraine will require the use of medical imaging technologies, clinical experimental medicine studies on novel pharmacological agents and astute observations in clinical practice to direct potential novel therapeutic approaches.

Oestrogen increases nociception through ERK activation in the trigeminal ganglion: evidence for a peripheral mechanism of allodynia

The mitogen-activated protein kinase, extracellular signal-regulated kinase (ERK), is activated in experimental models of chronic pain, and is also activated by oestrogen. We used an established model of inflammatory trigeminal pain, injection of Complete Freund's Adjuvant (CFA) into the masseter muscle, to determine whether ERK activation may play a role in hormone-related trigeminal pain disorders. We measured withdrawal responses to stimulation of the masseter (V3, primary allodynia) and whisker pad (V2, secondary allodynia) using graded monofilaments. Oestrogen treatment in the presence of inflammation increased withdrawal response to stimulation of both masseter and whisker pad compared with inflammation alone, indicating an additive effect of inflammation and oestrogen on both primary and secondary allodynia. We examined ERK activation in trigeminal ganglia from each treatment group using western blot and immunohistochemistry. Both masseter inflammation and oestrogen treatment increased ERK activation, and combined treatment had an additive effect. Both masseter inflammation and oestrogen increased the percentage of pERK immunoreactive neurons in divisions 1 and 2 (V1/2), and combined treatment increased pERK immunoreactivity in V1/2 compared with inflammation alone. We stereotactically administered ERK antagonist U0126, or inactive control U0124, to the trigeminal ganglion of CFA+E2-treated rats. U0126 decreased withdrawal responses to mechanical stimulation of the whisker pad compared with U0124-treated rats. Because the secondary allodynia in V2 after inflammation in V3 was reduced by antagonizing ERK activation in the periphery, these data suggest a peripheral component to secondary allodynia mediated through ERK activation.

Von Frey's hairs--a review of their technology and use--a novel automated von Frey device for improved testing for hyperalgesia

We describe a device which allows the mechanical sensitivity of trigeminovascular sensory neurons to be monitored over extended time periods. The device can be used to stimulate either the skin or dura mater and consists of a solenoid-driven plunger to which are fixed interchangeable von Frey hairs. The solenoid can be attached to a stereotaxic carrier and mounted on a stereotaxic frame to allow precise positioning over the receptive field. The device is driven from the synchronization signals of a standard stimulator via TTL circuitry and a relay driver, to allow stimulation by a single or multiple stimuli. The advantages of the device over manual stimulation include the reproducibility of the site of stimulation; the ability to apply a known force for a known time; the ability to measure response latencies to millisecond precision and to compare them to latencies to other stimuli and; easy interface with computer-control. We discuss some of the drawbacks of the von Frey system as usually used and illustrate the use of the new device with results from experiments on peripherally induced sensitization.

Cutaneous allodynia and migraine: another view

The paradigm of early treatment of the migraine attack at mild pain intensity has become one alternative to circumventing the problem of compromised oral absorption of symptomatic drugs due to migraine-induced gastrointestinal dysmotility. Early treatment also has been proposed to be advantageous because most migraineurs could be less responsive to delayed treatment, owing to the development of central sensitization of the trigeminal pain transmission. Ranking the underlying principles, it seems that the improved response to an oral triptan formulation at mild migraine symptom intensity has more to do with less impaired gastrointestinal absorption in the early stage of the attack than decreasing the time and preventing chances for central sensitization and development of cutaneous allodynia. Furthermore, parenteral administration of a triptan is always more likely to provide relief of symptoms than conventional tablets, even when it is used later in the course of the migraine attack. Individually tailored use of the available triptan formulations will increase, without any doubt, the within-migraineur consistency of response. It also will reduce the overall proportion of migraine attacks or migraineurs not responding to triptan treatment. Notwithstanding, the recommendation of early treatment during the migraine attack when the pain is mild remains valid.

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.

Difference in triptan effect in patients with migraine and early allodynia

The aim of this study was to determine whether in migraine patients with and without aura early treatment with various triptans leads to differences in pain reduction after 1 h and in modulating cutaneous allodynia. Thirty-six patients with early manifestation of a clinically recognizable allodynia of the face and non-responders to earlier treatment with sumatriptan 100 mg were included. Patients were randomized to six triptan treatment groups. Significant pain reduction was seen only in the group receiving zolmitriptan nasal spray 5 mg with a mean visual analogue scale (VAS) score of 3.8 (s.d. 1.2) at baseline and 2.4 (s.d. 1.3; P = 0.015) at 1 h after using the triptan and was thus a predictor of a VAS score 3 within 1 h. The study results indicate that migraine headache intensity can be reduced within 1 h by using zolmitriptan 5 mg nasal spray in spite of the presence of early cutaneous allodynia.

Sensitization of meningeal nociceptors: inhibition by naproxen

Migraine attacks associated with throbbing (manifestation of peripheral sensitization) and cutaneous allodynia (manifestation of central sensitization) are readily terminated by intravenous administration of a non-selective cyclooxygenase (COX) inhibitor. Evidence that sensitization of rat central trigeminovascular neurons was also terminated in vivo by non-selective COX inhibition has led us to propose that COX inhibitors may act centrally in the dorsal horn. In the present study, we examined whether COX inhibition can also suppress peripheral sensitization in meningeal nociceptors. Using single-unit recording in the trigeminal ganglion in vivo, we found that intravenous infusion of naproxen, a non-selective COX inhibitor, reversed measures of sensitization induced in meningeal nociceptors by prior exposure of the dura to inflammatory soup (IS): ongoing activity of Adelta- and C-units and their response magnitude to mechanical stimulation of the dura, which were enhanced after IS, returned to baseline after naproxen infusion. Topical application of naproxen or the selective COX-2 inhibitor N-[2-(cyclohexyloxy)-4-nitrophenyl]-methanesulfonamide (NS-398) onto the dural receptive field of Adelta- and C-unit nociceptors also reversed the neuronal hyper-responsiveness to mechanical stimulation of the dura. The findings suggest that local COX activity in the dura could mediate the peripheral sensitization that underlies migraine headache.

Serotonin type 1D receptors (5HTR) are differentially distributed in nerve fibres innervating craniofacial tissues

We tested the hypothesis that the 5HT(1D)R, the primary antinociceptive target of triptans, is differentially distributed in tissues responsible for migraine pain. The density of 5HT(1D)R was quantified in tissues obtained from adult female rats with Western blot analysis. Receptor location was assessed with immunohistochemistry. The density of 5HT(1D)R was significantly greater in tissues known to produce migraine-like pain (i.e. circle of Willis and dura) than in structures in which triptans have no antinociceptive efficacy (i.e. temporalis muscle). 5HT(1D)R-like immunoreactivity was restricted to neuronal fibres, where it colocalized with calcitonin gene-related peptide and tyrosine hydroxylase immunoreactive fibres. These results are consistent with our hypothesis that the limited therapeutic profile of triptans could reflect its differential peripheral distribution and that the antinociceptive efficacy reflects inhibition of neuropeptide release from sensory afferents. An additional site of action at sympathetic efferents is also suggested.

Management of migraine in adolescents

Headaches in children and adolescents are still under-diagnosed. 75% of children are affected by primary headache by the age of 15 with 28% fitting the ICHD2 criteria of migraine. Migraine is considered a chronic disorder that can severely impact a child's daily activities, including schooling and socializing. Early recognition and aggressive therapy, with acute and prophylactic treatments, as well as intensive biobehavioral interventions, are essential to control the migraine attacks and reverse the progression into intractable disabling headache.

Early vs. Non-Early Intervention in Acute Migraine — ‘Act When Mild (AwM)’. A Double-Blind, Placebo-Controlled Trial of Almotriptan

The study was designed to compare the response to almotriptan in migraine patients who take medication early in the course of the attack with that when medication is taken after pain has become moderate or severe. A randomized, four-arm, multicentre, multinational, double-blind, placebo-controlled trial of almotriptan (12.5 mg) comparing treatment administration when pain intensity was mild and within 1 h of headache onset vs. pain that had become moderate or severe was conducted. Of 491 migraineurs enrolled, 403 were evaluable [intention-to-treat population (ITT)]. Their mean age was 38 years, 84% were female and they had a mean of 3.7 attacks/month. Of these patients, 10% did not take medication according to their randomly allocated basal pain intensity (mild or moderate/severe) and were subsequently reassigned to that group for this analysis —'Act when Mild (AwM)' group. In the almotriptan arms, 53% of mild basal pain and 38% of moderate/severe basal pain patients were pain free at 2 h ( P = 0.03; primary end-point). Corresponding proportions in the placebo groups were 25% and 17% (statistically significant vs. respective almotriptan arms). Secondary end-points (ITT) were also significantly in favour of early intervention with almotriptan, both between and across treatment groups, such as sustained pain free: 45.6% vs. 30.5% ( P = 0.02). Adverse events were reported in < 5% of treated patients in all groups (NS), with no serious events. Treatment with almotriptan while migraine pain is still mild provides statistically significant and clinically relevant enhancements in efficacy compared with treatment when pain has reached higher severity levels.

Diagnosing and managing headache in children

Once the correct diagnosis of migraine in a child is established, a treatment plan can be developed. This often entails a combination of acute therapies, preventive therapies, and biobehavioral interventions. Goals of treatment should be clearly established for the patients and parents, and realistic time courses discussed. Overall outcome in terms of disability and quality of life also may need to be addressed and included within the evaluation and management scheme.

Effect of chronic topical exposure to low-dose noxious chemicals and stress on skin sensitivity in mice

It has been suggested that the recent increase in inflammatory diseases is related to an increase in environmental chemicals and psychiatric stress. To investigate the effect of chronic topical exposure to chemicals and isolation stress, low-dose formalin (a mild contact sensitizer and an irritant), 2,4,6-trinitrochlorobenzene (TNCB; a potent contact sensitizer) and sodium lauryl sulphate (SLS; an irritant) were applied to mouse ears at 7-d intervals under no-stress or stress conditions. Skin reactions (ear swelling) elicited by formalin and TNCB increased time dependently. At the chronic stage, a significant skin reaction peaking at 1 h after application was elicited on the formalin-treated sites, while a shift from a delayed-type hypersensitivity to an immediate-type response was observed on the TNCB-treated sites. At the formalin-treated sites, genes related to neurogenic inflammation, i.e., bradykinin (BK) B2 receptor, IL-6, and membrane metallo endopeptidase (NEP) mRNA were upregulated. In the TNCB-treated sites, marked upregulation of IFN-gamma, IL-1beta, IL-4, and IL-6 mRNA was observed in addition to B2 receptor mRNA. Pretreatment with HOE140, the B2 receptor antagonist suppressed these skin reactions. Increased skin sensitivity to an unrelated chemical, ethanol, and thermal stimuli were elicited in formalin and TNCB-treated mice. Cortisol levels in formalin-treated mice and IgE levels in TNCB-treated mice were elevated respectively. Stress markedly amplified the skin reactions and gene expression related to neurogenic inflammation. SLS did not induce any changes. It was concluded that chronic topical exposure to low-dose noxious chemicals and stress could easily induce skin sensitivity relating to the BK-B2 pathway and nociceptive sensitization reflecting neural sensitization.

Treatment of migraine attacks based on the interaction with the trigemino-cerebrovascular system

Primary headaches such as migraine are among the most prevalent neurological disorders, affecting up to one-fifth of the adult population. The scientific work in the last decade has unraveled much of the pathophysiological background of migraine, which is now considered to be a neurovascular disorder. It has been discovered that the trigemino-cerebrovascular system plays a key role in migraine headache pathophysiology by releasing the potent vasodilator calcitonin gene-related peptide (CGRP). This neuropeptide is released in parallel with the pain and its concentration correlates well with the intensity of the headache. The development of drugs of the triptan class has provided relief for the acute attacks but at the cost of, mainly cardiovascular, side effects. Thus, the intention to improve treatment led to the development of small CGRP receptor antagonists such as olcegepant (BIBN4096BS) and MK-0974 that alleviate the acute migraine attack without acute side events. The purpose of this review is to give a short overview of the pathological background of migraine headache and to illustrate the mechanisms behind the actions of triptans and the promising CGRP receptor blockers.

Sensitization, glutamate, and the link between migraine and fibromyalgia

Recent advances have shed insight on the pathophysiologic mechanisms of fibromyalgia and migraine, especially in the chronic form. A growing body of evidence supports the involvement of peripheral and central sensitization disturbances of pain-related processes underlying both disorders. They involve increased glutamate transmission through interaction with its ionotropic and metabotropic receptors. Few studies supporting the implication of this excitatory amino acid in chronic migraine and primary fibromyalgia demonstrated increased levels of glutamate in the cerebrospinal fluid of affected patients. These findings have implications for future therapies directed against glutamate receptors (in particular, N-methyl-D-aspartate receptors). Limited clinical experience in this regard, although promising, does not exclude additional mechanisms contributing to the maintenance of pain, which can be the target of therapeutic approaches in both disorders.

Recognition and treatment of menstrual migraine

BACKGROUND

Menstrual migraine is a chronic disorder affecting approximately 12.6 million women in the United States. In spite of its widespread prevalence, menstrual migraine often goes undiagnosed.

REVIEW SUMMARY

Characteristics of menstrual migraine, which include functional disability, increased headache severity, and lack of aura, are often overlooked, and therefore menstrual migraine is often underdiagnosed. Use of a 3-month diary to record migraine patterns can reveal the predictable patterns associated with menstrual migraine, and a diary is demonstrated to be a useful tool in diagnosis. Optimal treatment of menstrual migraine takes advantage of the predictability of the disorder. Treatment alternatives for menstrual migraine include acute therapy and short- or long-term preventive therapies. Acute therapy is given shortly after the migraine begins. Short-term preventive therapies are effective when administered during the time that menstrual migraine is most likely to occur; the treatment window is typically 2 days prior up to 3 days after the onset of menstruation. Providing triptans, nonsteroidal anti-inflammatory drugs, or estrogen supplements (gel or patches) during this window has been demonstrated to provide effective protection during the days when patients are at greatest risk for menstrual migraine. Alternatively, long-term preventive therapy may be required for recurrent headaches in patients with concomitant medical conditions for whom migraine therapy could serve a dual purpose.

CONCLUSION

By recognizing the patterns associated with menstrual migraine, prompt, acute, or preventive therapy can be used to effectively manage the disorder and reduce its related disability.

Sensitization of central trigeminovascular neurons: blockade by intravenous naproxen infusion

We have previously observed that migraine attacks impervious to triptan therapy were readily terminated by subsequent i.v. administration of the non-steroidal anti-inflammatory drug (NSAID) ketorolac. Since such attacks were associated with periorbital allodynia--a symptom of central sensitization--we examined whether infusion of the NSAID naproxen can block sensitization of central trigeminovascular neurons in the medullary dorsal horn, using in vivo single-unit recording in the rat. Topical exposure of the cerebral dura to inflammatory soup (IS) for 5 min resulted in a short-term burst of activity (<8 min) and a long-lasting (>120 min) neuronal hyper-responsiveness to stimulation of the dura and periorbital skin (group 1). Infusion of naproxen (1 mg/kg) 2 h after IS (group 1) brought all measures of neuronal responsiveness back to the baseline values recorded prior to IS, and depressed ongoing spontaneous activity well below baseline. When given preemptively 1 h before IS (group 2), naproxen blocked the short-term burst of activity and every long-term measure of neuronal hyper-responsiveness that was studied in the central neurons. The same preemptive treatment, however, failed to block IS-induced short-term bursts of activity in C-unit meningeal nociceptors (group 3). The results suggest that parenteral administration of naproxen, unlike triptan therapy, can exert direct inhibition over central trigeminovascular neurons in the dorsal horn. Though impractical as a routine migraine therapy, parenteral NSAID administration should be useful as a non-narcotic rescue therapy for migraine in the setting of the emergency department.

Cutaneous allodynia in transformed migraine patients

BACKGROUND

There is growing evidence that central sensitization plays a role in migraine pathogenesis, and that cutaneous allodynia is its clinical correlate. In headache research, allodynia has largely been studied in episodic migraine. The purpose of this investigation was to determine whether cutaneous allodynia occurs in transformed migraine, using individuals without headaches as controls.

METHODS

Fifteen patients with a diagnosis of transformed migraine and 15 control subjects with no history of headaches were included. All subjects were females between 18 and 50. Similar to the methods of Burstein et al, Von Frey hairs (VFH) were sequentially applied to territories supplied by divisions of the trigeminal nerve, cervical paraspinal muscles, trapezius muscles, ventral forearm, and lower leg to determine a pain threshold. As a milder stimulus, a cotton swab was stroked in the same locations. Each trial was repeated 3 times on 2 occasions. Group comparisons were made using the Student's t-test.

RESULTS

Mean pain thresholds were lower among migraine patients than control subjects across all test areas. The thresholds were statistically significantly lower in migraine patients than in control subjects for the 1st division of the trigeminal nerve (34.0 g versus 115.8 g, P= .035) and for the 2nd division (23.5 g versus 97.6 g, P= .039). Six patients found a cotton swab-stroke painful, compared to zero control subjects. Using a quantitative definition of allodynia, 75% of patients had allodynia to mechanical stimuli.

CONCLUSIONS

This study is the first to demonstrate allodynia in transformed migraine patients using a headache-free control population and supports the hypothesis that central sensitization plays a role in the evolution of transformed migraine.

Dihydroergotamine for Early and Late Treatment of Migraine With Cutaneous Allodynia: An Open-Label Pilot Trial

OBJECTIVE

To explore whether dihydroergotamine (D.H.E. 45) is equally effective and safe for migraine with allodynia, when administered either early or late in an attack.

BACKGROUND

Central sensitization may account for the extracranial tenderness and cutaneous allodynia that can occur with migraine. Once allodynia is established, triptans are less effective. Dihydroergotamine is often effective for patients whose refractory headaches have failed prior triptan therapy.

METHODS

In this single-center, open-label pilot trial, patients with episodic migraine associated with cutaneous allodynia were treated on 2 occasions with dihydroergotamine 1.0 mg intramuscularly. One attack was treated within 2 hours (early) and a second attack at 4 hours (late) after the onset of throbbing pain. Headache pain and any associated symptoms, subjective cutaneous allodynia, and mechanical (brush) allodynia were assessed. All data were analyzed using the Fisher's exact test.

RESULTS

Thirteen patients met the entry criteria; however, data from only 9 patients, those who completed treatment for 2 migraine attacks, were used to evaluate the efficacy and safety of dihydroergotamine. Whether they took dihydroergotamine early or late in the attack, most patients (>55%) had headache relief within 2 hours, and at least 44% of patients achieved headache-free status by 8 hours postdose. Subjective cutaneous allodynia started to decline after 30 minutes postdose in the early treated group and after 120 minutes postdose in the late-treated group. Brush allodynia began to decline after 15 minutes postdose in the early treated group and after 90 minutes postdose in the late-treated group. Six of 9 patients (67%) reported at least 1 adverse event.

CONCLUSIONS

The results of this pilot trial provide proof of concept for the headache-relief benefit of dihydroergotamine in patients with migraine headache and allodynia. A large, placebo-controlled trial of dihydroergotamine in allodynic patients is warranted.

DHE in the pharmacotherapy of migraine: potential for a larger role

Despite a large array of currently marketed, frequently effective drugs for the acute treatment of migraine headache, comprising various classes and formulations, predictably reliable treatment for most headache types is often lacking. Dihydroergotamine mesylate (DHE) is a comparatively safe and effective therapy for migraine headache that could potentially be used for a broader range of headache types than occurs at present. The features of DHE supporting this assertion include (1) effectiveness in terminating severe, long-lasting headaches, (2) rapid onset of action, (3) very low rates of headache recurrence, (4) minimal risk of medication-overuse headache, and (5) in the nasal spray formulation, suitability for outpatients (especially patients who are very nauseated or vomiting, potentially obviating the need for an office or hospital visit for acute care). Conditions or circumstances for which there are data supporting the expanded use of DHE include menstrual migraine, migraine with central sensitization and cutaneous allodynia, medication-overuse headache, migraine recurrence, and status migrainosus. The introduction of the intranasal formulation of DHE provides both pharmacologic and patient-convenience advantages for use in migraine therapy. This article reviews the rationale for the use of DHE in these common, often difficult-to-treat migraine forms.

Clarification of developing and established clinical allodynia and pain-free outcomes

OBJECTIVE

The aim of this study was to determine whether clinical indicators of cutaneous allodynia predict the success of migraine therapy with sumatriptan using a brief questionnaire.

BACKGROUND

Using quantitative sensory testing (QST) recent studies demonstrate that the presence of cutaneous allodynia, a clinical manifestation of central sensitization, can be detrimental to the success of migraine therapy with sumatriptan. QST is costly and requires much time, therefore it is not feasible to use in clinical practice.

METHODS

In this prospective study, migraineurs completed a questionnaire about their skin sensitivity during migraine. Each migraineur treated 2 migraine headaches with sumatriptan (100 mg): 1 headache at the earliest sign of migraine pain (mild, within 1 hour of onset) and 1 headache at least 4 hours after the onset of pain while moderate or severe.

RESULTS

Thirty-six migraine headaches were evaluated in 18 migraineurs. A total of 44% of the headaches were not associated with allodynia at any time. Irrespective of allodynic status, headaches were more likely to become pain-free with early versus late treatment (2 hours; 78% vs. 33%, respectively). Headaches were equally likely to become pain-free when allodynia was reported before treatment but not 2 and 4 hours after treatment (2 hours; 67 vs. 63%, respectively, 4 hours 80 vs. 81%, respectively). However, no headaches were pain-free when allodynia was reported at 2 and 4 hours after treatment.

CONCLUSIONS

Headaches without allodynia were aborted when treated early or late, and headaches with allodynia were aborted only when allodynia was not present after treatment. These findings suggest that different mechanisms account for allodynia before and after treatment; a developing phase in which central sensitization depends on incoming pain signals from the peripheral nociceptors and an established phase in which the sensitization becomes independent of the pain signals that come from the dura.

Identifying cutaneous allodynia in chronic migraine using a practical clinical method

Cutaneous allodynia is common in migraine. In the majority of previous studies on allodynia in migraine, only patients with episodic migraine (EM) were included. Little is known on patterns of allodynia in chronic migraine (CM). Since the presence of allodynia is associated with a poor response to triptans, a clinically practical method to test migraine patients for allodynia would be useful to the clinician. The aim of this study was to assess the prevalence of dynamic mechanical (brush) allodynia (BA) in CM, using a clinically practical method. Eighty-nine CM patients were prospectively recruited. Patients were given a structured questionnaire regarding demographic data and migraine characteristics. Allodynia was tested using a 10 x 10-cm gauze pad to brush various areas of the skin lightly. The prevalence of BA in the entire study population and in different patient subgroups was calculated. BA was present in 42.7% (38/89) of the patients. The presence of allodynia was unrelated to age, disease duration or to the occurrence of an acute headache exacerbation at the time of testing. Allodynia was positively associated with a history of migraine aura. BA was most common in the cephalic area, but was also seen in cervical dermatomes. BA is common in CM and, unlike in EM, is not significantly affected by the occurrence of an acute headache exacerbation. This suggests that central trigeminovascular neurons are chronically sensitized in patients experiencing migraine headache >15 days per month. The testing of BA in the clinical setting is possible using a simple and brief approach. It allows the clinician to determine whether the patient is sensitized, a diagnosis that affects treatment decisions.

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.