Lack of asymmetry of middle cerebral artery blood velocity in unilateral migraine

The human NTG model of migraine in drug discovery and development

INTRODUCTION

Various triggers can originate a migraine attack. In healthy volunteers and patients with migraine, the nitroglycerin (NTG) provocation model induces a headache that resembles migraine in pain characteristics and vascular manifestations. This headache is reversible and treatable in monitored conditions, providing an opportunity to test novel antimigraine medications in early clinical development.

AREAS COVERED

This perspective covers the main characteristics and applications of the human NTG model of migraine with effective and ineffective antimigraine therapies.

EXPERT OPINION

The NTG model represents a potential de-risking strategy to test novel hypotheses for antimigraine mechanisms in humans. Considering previous studies conducted with effective and ineffective antimigraine therapies, the sensitivity of the model was 71% while the specificity was 100%. The probability that following an analgesic effect, that compound would truly be efficacious in individuals with migraine was 100%. Following a negative result, the probability that such compound would truly be ineffective in patients with individuals was 33%. A clinical trial testing the analgesic properties of novel compounds after a sublingual and/or intravenous NTG challenge in migraine patients may support a subsequent phase 2 trial for the treatment of migraine.

Cerebrovascular function in tension-type headache and migraine with or without aura: Transcranial Doppler study

The aim of the current study was to determine whether tension-type headache (TTH) and migraine with or without aura have altered anterior and posterior circulation compared with normal volunteers as assessed by Transcranial Doppler (TCD) ultrasonography. The study included 24 patients with chronic TTH and 37 patients with migraine (16 with aura and 21 without aura) classified according to the diagnostic criteria of the International Headache Society 2018. They were compared with a control group of 50 age- and sex-matched healthy volunteers. Each participant was examined with TCD ultrasonography of the middle, anterior and posterior cerebral and vertebral arteries (MCA, ACA, PCA, and VA) at rest. Patients in the TTH group had a significantly lower peak systolic velocity (PSV) and mean flow velocity (MFV) in the MCA compared with controls, whereas EDV and MFV in the ACA were significantly higher in the migraine without aura group than controls. Within the 3 groups of patients, the TTH group had significantly lower PSV in the MCA and PCA than the group of migraine with aura. In addition, the TTH group had significantly lower PSV and MFV in the MCA and a lower EDV in the VA than migraine patients without aura. In conclusion, the possibility of cerebrovascular changes is confirmed in the present study in both TTH and migraine without aura. The former has a low MFV in the MCA whereas the latter has a high MFV in the ACA.

Cerebral hemodynamics in the different phases of migraine and cluster headache

Headache is one of the most common ailments; migraine is one of the most prevalent and disabling neurological disorders and cluster headache presents as one of the most excruciating pain disorders. Both are complex disorder characterized by recurrent episodes of headache. A key feature is that various triggers can set off an attack providing the opportunity to explore disease mechanisms by experimentally inducing attacks. This review summarizes neuroimaging and hemodynamic studies in human in provoked and spontaneous attacks of migraine and cluster headache. Cerebral hemodynamics during different phases of the migraine attack demonstrate alterations in cerebral blood flow and perfusion, vessel caliber, cortical and sub-cortical function, underscoring that migraine pathophysiology is highly complex. Migraine attacks might begin in diencephalic and brainstem areas, whereas migraine aura is a cortical phenomenon. In cluster headache pathophysiology, the hypothalamus might also play a pivotal role, whereas the pattern of cerebral blood flood differs from migraine. For both disorders, alterations of arterial blood vessel diameter might be more an epiphenomenon of the attack than a causative trigger. Studying cerebral hemodynamics in provocation models are important in the search for specific biomarkers in the hope to discover future targets for more specific and effective mechanism-based anti-headache treatment.

Cerebral Hemodynamic Changes During Migraine Attacks and After Triptan Treatments

Introduction

Migraine has been known for many years, but its mechanism remains unclear. Different cerebral hemodynamic changes have been observed at different stages of a migraine attack. Published results on cerebral hemodynamics are contradictory. For this reason, we aimed to investigate cerebral hemodynamic changes during attacks as well as the effects of frovatriptan and rizatriptan.

Methods

Forty migraine patients with aura using rizatriptan (n=20) and frovatriptan (n=20) and 20 healthy individuals were included in our study. Cerebral blood flow velocities and breath-holding indices were recorded bilaterally from middle and posterior cerebral arteries. All procedures were repeated one hour after treatments and one week after attacks.

Results

We observed similar values of cerebral blood flow velocities and breath holding indices in all patients with migraine during the attack-free period compared to the control group. All cerebral vascular structures in migraine patients had significantly lower cerebral blood flow velocities and higher values in breath-holding indices during attacks. After taking rizatriptan and frovatriptan for an attack, the changes in hemodynamics disappeared.

Conclusion

During attacks of migraineurs with aura, vasodilatation develops. In addition, higher vasomotor reactivity during attacks supports hypersensitivity in migraine pathophysiology. Triptans, acting as vasoconstrictor agents, were able to stop over-vasodilatation during attacks. In other words, it is possible that triptans show their effects by eliminating vascular hypersensitivity during acute attacks.

Cerebral blood flow velocity in migraine and chronic tension-type headache patients

Introduction

The present study seeks to use transcranial Doppler ultrasound to evaluate cerebral blood flow velocities in anterior and posterior circulation arteries, during an attack-free episode in migraine patients, with and without aura, as well as in chronic tension-type headache patients who were not receiving prophylactic medication.

Methods

A total of 50 patients (35 female, 15 male) were evaluated during a headache-free episode: 30 migraine patients without aura (mean age: 32±8 years), 10 migraine patients with aura (mean age: 34±4 years), and 10 patients with chronic tension-type headache (mean age: 34±5 years).

Results

No significant difference was present between anterior, middle, and posterior cerebral and vertebral arteries' blood flow velocities between migraine patients, with and without aura, or in patients with a tension-type headache, and normal controls (p>0.05). However, a significant increase in basilar artery cerebral blood flow velocities relative to controls was present in patients with a tension-type headache (p>0.001).

Conclusion

It is difficult to predict the main reason for the significant increase in basilar artery blood flow velocities in patients with chronic tension-type headache. It may be due to constriction of conductance or the dilatation of the resistance vessels.

Longitudinal changes in cerebral blood flow velocities in different clinical courses of migraine

Objective To assess longitudinal changes in cerebral blood flow velocities (ΔCBFVs) according to the clinical course of migraine. Methods We retrospectively included migraine patients with two or more attacks per month at baseline who were followed up within 2 years with transcranial Doppler in a tertiary headache clinic. ΔCBFVs were analyzed in relation to clinical courses, defined as remission (0-1 headache days/month), persistence (2-14/month), or progression (≥15/month) in episodic migraine (EM), and conversion to EM (<15/month) and persistence (≥15/month) in chronic migraine (CM). Results A total of 166 patients (90 EM and 76 CM) were included. In EM, the remission group ( n = 30) showed a decrease in CBFV in the middle cerebral artery (MCA) and the basilar artery (BA). The progression group ( n = 10) showed increasing CBFVs in the bilateral MCAs. Patients with the persistence course ( n = 50) showed generally unchanged CBFVs. In CM, ΔCBFVs decreased in the BA and increased in the posterior cerebral artery (PCA) after conversion to EM ( n = 61), whereas they remained unchanged in the persistence group ( n = 15). In all patients, % change in headache days was positively correlated with the %ΔCBFVs of the bilateral MCAs and the BA. Conclusions CBFV changes are associated with the different clinical courses of migraine. The association is more prominent in EM than CM.

Reduced breath holding index in patients with chronic migraine

Migraine is a neurovascular disorder characterized by autonomic nervous system dysfunction and severe headache attacks. Studies have shown that changes in the intracranial vessels during migraine have an important role in the pathophysiology. Many studies have been conducted on the increased risk of stroke in patients with migraine, but insufficient data are available on the mechanism underlying the increase. This study aimed to evaluate basal cerebral blood flow velocity and vasomotor reactivity in patients with chronic migraine. We evaluated 38 patients with chronic migraine. Three of them were excluded because they had auras and four of them were excluded because of their use of medication that can affect cerebral blood flow velocity and breath holding index (beta or calcium channel blockers). Our study population consisted of 31 patients with chronic migraine without aura and 29 age- and gender-matched healthy individuals who were not taking any medication. The mean blood flow velocity and breath holding index were measured on both sides from the middle cerebral artery and posterior cerebral artery, with temporal window insonation. The breath holding index for middle cerebral artery and posterior cerebral artery was significantly lower in the migraine group compared to that of the control group (p < 0.05).The vasomotor reactivity indicates the dilatation potential of a vessel, and it is closely related to autoregulation. According to our results, the vasodilator response of cerebral arterioles to hypercapnia was lower in patients with chronic migraine. These findings showed the existence of impairments in the harmonic cerebral hemodynamic mechanisms in patients with chronic migraine. This finding also supports the existing idea of an increased risk of stroke in patients with chronic migraine due to impaired vasomotor reactivity.

A nitric oxide donor (nitroglycerin) triggers genuine migraine attacks

Supersensitivity to induction of headache and arterial dilatation by a donor of nitric oxide (nitroglycerin) has recently been demonstrated in migraine sufferers. The aims of the present study were to examine whether the nitric oxide donor nitroglycerin may induce a typical migraine attack, to exclude placebo-related effects and to describe the relation between middle cerebral artery dilatation and provoked migraine. Nitroglycerin (0.5 μg/kg/min for 20 min) or placebo was infused into 12 migraine patients in a double-blind cross-over trial. Blood velocity in the middle cerebral artery was measured with transcranial Doppler and characteristics of headache and accompanying symptoms were recorded frequently. Headache occurred during the nitroglycerin infusion as previously described but peak headache intensity did first occur 5.5 h after infusion. At this time the induced headaches in 8 of 10 completing patients fulfilled the diagnostic criteria for migraine without aura of the International Headache Society. Furthermore, all patients who normally had unilateral spontaneous migraine attacks also had unilateral headaches after nitroglycerin. Only one subject developed migraine after placebo (p < 0.03). The time pattern of headache and estimated middle cerebral artery dilatation corresponded well. The study therefore demonstrates that activation of the nitric oxide cGMP pathway may cause typical migraine attacks.

Structural and functional neuroimaging in migraine: insights from 3 decades of research

Modern imaging methods provide unprecedented insights into brain structure, perfusion, metabolism, and neurochemistry, both during and between migraine attacks. Neuroimaging investigations conducted in recent decades bring us closer to uncovering migraine as a multifaceted, primarily central nervous system disorder. Three main categories of structural and functional brain changes are described in this review, corresponding to the migrainous aura, ictal headache, and interictal states. These changes greatly advance our understanding of multiple pathophysiologic underpinnings of migraine, from central "migraine generating" loci, to cortical spreading depression, intimate mechanisms underlying activation of neuronal pain pathways in vulnerable patients, central sensitization, and chronification. Structural imaging begins to explain the complex connections between migraine and cerebral vascular events, white matter lesions, grey matter density alterations, iron deposition, and microstructural brain damage. Selected structural and functional alterations of brain structures, as identified with imaging methods, may represent the foundation of new diagnostic strategies and serve as markers of therapeutic efficacy.

Pituitary adenylate cyclase-activating polypeptide (PACAP) potently dilates middle meningeal arteries: implications for migraine

Migraine is a debilitating neurological disorder characterized by mild to severe headache that is often accompanied by aura and other neurological symptoms. Among proposed mechanisms, dilation of the dural vasculature especially the middle meningeal artery (MMA) has been implicated as one component underlying this disorder. Several regulatory peptides from trigeminal sensory and sphenopalatine postganglionic parasympathetic fibers innervating these vessels have been implicated in the process including pituitary adenylate cyclase-activating polypeptide (PACAP). Although PACAP has been well described as a potent dilator in many vascular beds, the effects of PACAP on the dural vasculature are unclear. In the current study, we examined the ability of PACAP to dilate MMAs that were isolated from rats and pressurized ex vivo. PACAP38 potently dilated pressurized MMAs with an EC(50) of 1 pM. The PAC1 receptor antagonist, PACAP(6-38), abolished MMA dilation caused by picomolar concentrations of PACAP. In contrast, cerebellar arteries isolated from the brain surface were ~1,000-fold less sensitive to PACAP than MMAs. Although cerebellar arteries expressed transcripts for all three PACAP receptor subtypes (PAC1, VPAC1, and VPAC2 receptors) by RT-PCR analyses, MMA demonstrated only PAC1 and VPAC2 receptor expression. Further, multiple variants of the PAC1 receptor were identified in the MMA. The expression of PAC1 receptors and the high potency of PACAP to induce MMA vasodilation are consistent with their potential roles in the etiology of migraine.

Antidromic vasodilatation and the migraine mechanism

Despite the fact that an unprecedented series of new discoveries in neurochemistry, neuroimaging, genetics and clinical pharmacology accumulated over the last 20 years has significantly increased our current knowledge, the underlying mechanism of the migraine headache remains elusive. The present review article addresses, from early evidence that emerged at the end of the nineteenth century, the role of ‘antidromic vasodilatation’ as part of the more general phenomenon, currently defined as neurogenic inflammation, in the unique type of pain reported by patients suffering from migraine headaches. The present paper describes distinctive orthodromic and antidromic properties of a subset of somatosensory neurons, the vascular- and neurobiology of peptides contained in these neurons, and the clinical–pharmacological data obtained in recent investigations using provocation tests in experimental animals and human beings. Altogether, previous and recent data underscore that antidromic vasodilatation, originating from the activation of peptidergic somatosensory neurons, cannot yet be discarded as a major contributing mechanism of the throbbing head pain and hyperalgesia of migraine.

Evidence for a vascular factor in migraine

OBJECTIVE

It has been suggested that migraine is caused by neural dysfunction without involvement of vasodilatation. Because dismissal of vascular mechanisms seemed premature, we examined diameter of extra- and intracranial vessels in migraine without aura patients.

METHODS

A novel high-resolution direct magnetic resonance angiography imaging technique was used to measure arterial circumference of the extracranial middle meningeal artery (MMA) and the intracranial middle cerebral artery (MCA). Data were obtained at baseline, during migraine attack, and after treatment with the migraine abortive drug sumatriptan (a 5-hydroxytryptamine agonist).

RESULTS

We found dilatation of both MMA and MCA during migraine attack (p = 0.001). Sumatriptan administration caused amelioration of headache (p < 0.001) and contraction of MMA (p < 0.001), but MCA remained unchanged (p = 0.16). Exploratory analysis revealed that in migraine attacks with half-sided headache, there was only dilatation on the headache side of MMA of 12.49% (95% confidence interval [CI], 4.16-20.83%) and of MCA of 12.88% (95% CI, 3.49-22.27%) and no dilatation on the non headache side of MMA (95% CI, -4.27 to 11.53%) and MCA (95% CI, -6.7 to 14.28%). In double-sided headache we found bilateral vasodilatation of both MMA and MCA (p < 0.001).

INTERPRETATION

These data show that migraine without aura is associated with dilatation of extra- and intracerebral arteries and that the headache location is associated with the location of the vasodilatation. Furthermore, contraction of extracerebral and not intracerebral arteries is associated with amelioration of headache. Collectively, these data suggest that vasodilatation and perivascular release of vasoactive substances is an integral mechanism of migraine pathophysiology.

Lack of correlation between vasodilatation and pharmacologically induced immediate headache in healthy subjects

BACKGROUND

The causal relationship between experimental headache and vasodilatation has not been fully clarified. In the present study, we combined headache and vascular data from eight experimental studies and conducted detailed statistical analyses. Given that substances used in all these experiments were vasodilators we examined a possible correlation between headache scores and increases in arterial diameter.

METHODS

We identified nine studies and retrieved raw data in 89 healthy subjects (46 females, 43 males), mean age 27 years (range 18-59 years). The following variables were collected: maximal median headache intensity scores on a verbal rating scale (VRS) during immediate headache (0-120 minutes); the mean velocity of blood flow in the middle cerebral artery (V(meanMCA)); and the diameter of the frontal branch of the superficial temporal artery (STA) during the maximal median headache intensity.

RESULTS

The scatter plots show no relationship between maximal headache score and the relative changes in V(meanMCA) and diameter of the STA. The main analyses of covariance showed a significant effect only of heart rate on headache (p = .014). The interaction tests were insignificant for all variables.

CONCLUSIONS

The major outcome is a finding of no linear relationship between experimental immediate headache and dilatation of the MCA or STA.

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

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

Advanced neuroimaging of migraine

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

Increased cerebral vasomotor reactivity in migraine with aura: an autoregulation disorder? A transcranial Doppler and near-infrared spectroscopy study

Migraine with aura (MA) is associated with changes in cerebral blood flow (CBF), whereas the role of cerebral autoregulation is uncertain. This study aimed to evaluate basal CBF, cerebral blood volume (CBV) and vasomotor reactivity (VMR) in MA patients. Twenty-one controls and 16 MA patients (eight with side predominance) underwent simultaneous examination of flow velocity in the middle cerebral arteries by transcranial Doppler (TCD) and of near-infrared spectroscopy (NIRS) parameters [oxygen haemoglobin saturation: oxygen%, and total haemoglobin content (THC)] at rest and after hypercapnia. Cerebral VMR, THC and oxygen% increases were significantly greater on the predominant compared with the non-predominant migraine side, with both sides of patients without side predominance and with controls. These findings suggest altered autoregulation in MA patients, possibly secondary to impaired cerebrovascular autonomic control. Simultaneous TCD and NIRS investigation could represent a non-invasive approach to evaluate cerebral haemodynamics at the cortical and subcortical level.

Transcranial Doppler measurements in migraine and nitroglycerin headache

The objective of this study was to examine the cerebral circulation during spontaneous migraine attacks and to compare changes to an experimental headache model induced by nitroglycerin (NTG) infusion. This prospective study was carried out in a tertiary care hospital on migraineurs with or without aura. Healthy volunteers served as controls. There were no interventions. Flow velocity (FV) and pulsatility index (PI) were measured in migraineurs between and during headache attacks. In controls, FV and PI of the middle cerebral arteries were performed at baseline and after each IV infusion of 0.125, 0.25 and 0.5 microg/kg/min of NTG. In migraineurs, a significant increase in the mean flow velocity (MFV) in the left vertebral artery (VA) and the PI of the right VA during spontaneous migraine headache was found. In controls, all FV significantly decreased after infusion of NTG. The NTG model produces expected and substantially different vascular effects than those seen with spontaneous migraine headache.

Color Doppler sonography of orbital and vertebral arteries in migraineurs without aura

PURPOSE

The objective of this study was to investigate whether the retrobulbar hemodynamics in the ophthalmic (OA), posterior ciliary (PCA), central retinal (CRA), and vertebral (VA) arteries are affected in migraineurs without aura.

METHODS

The eyes of migraineurs without aura and those of healthy control subjects were evaluated during both headache and headache-free periods. Retrobulbar and vertebral blood flow velocities in the OA, PCA, CRA, and the extracranial part of the VA were measured bilaterally using color Doppler sonography. The peak systolic and end-diastolic flow velocities and the pulsatility (PI) and resistance (RI) indices were determined for all arteries.

RESULTS

In total, we enrolled 30 migraineurs and 31 healthy control subjects. Statistically significant differences between headache-free migraineurs and control subjects were observed in the PI and RI of both right and left PCAs and in the RI of both right and left CRAs. The PI and RI of the left VA of the migraineurs were significantly lower during both headache and headache-free periods than were those of the control subjects. Among the migraineurs, the peak systolic and end-diastolic velocities of the left VA were increased during headache periods relative to those found during the headache-free periods.

CONCLUSIONS

The retrobulbar circulation and flow hemodynamics in the left VA may be altered in both headache and headache-free periods in migraineurs without aura. The differences found between migraineurs and control subjects may implicate autonomic dysfunction in migraineurs.

Blood flow velocity and pulsatility index differences in patients with unilateral migraine

OBJECTIVE

To evaluate blood flow velocity and pulsatility in unilateral migraine without aura during the headache-free period using transcranial Doppler (TCD) sonography.

METHODS

Patients with unilateral headache were recruited during the headache-free period. Maximum mean flow velocity (MFV) and pulsatility index (PI) were measured in the middle cerebral (MCA) and basilar arteries. Controls were headache-free individuals without cerebrovascular disease.

RESULTS

Twenty-five patients with right-sided migraine, 25 patients with left-sided migraine, and 19 controls were studied. The MCA PI was higher on the right headache side versus the left headache side (0.97 +/- 0.2 versus 0.86 +/- 0.1 cm/s, P =.02) and versus controls (0.9 +/- 0.2 cm/s, NS). The basilar artery MFV was higher in patients with right-sided headache versus left-sided headache (39.5 +/- 5.6 versus 34.7 +/- 8.2 cm/s, P =.02) and versus controls (38.2 +/- 8 cm/s, NS). No decrease in MFV with age was observed in patients with migraine.

CONCLUSIONS

Middle cerebral artery flow pulsatility and basilar artery velocity are higher in patients with right-sided migraine compared with left-sided migraineurs, during the headache-free period. Although these parameters were similar to controls, the differences found during the headache-free period in migraineurs may indicate vascular involvement predisposing to the unilateral headache recurrence.

Neurogenic inflammation in the context of migraine

Despite considerable research into the pathogenesis of idiopathic headaches, such as migraine, the pathophysiological mechanisms underlying them remain poorly understood. Although it is well established that the trigeminal nerve becomes activated during migraine, the consequences of this activation remain controversial. One theory, based on preclinical observations, is that activation of trigeminal sensory fibers leads to a painful neurogenic inflammation within the meningeal (dural) vasculature mediated by neuropeptide release from trigeminal sensory fibres and characterized by plasma protein extravasation, vasodilation, and mast cell degranulation. Effective antimigraine agents such as ergots, triptans, opioids, and valproate inhibit preclinical neurogenic dural extravasation, suggesting that this activity may be a predictor of potential clinical efficacy of novel agents. However, several clinical trials with other agents that inhibit this process preclinically have failed to show efficacy in the acute treatment of migraine in man. Alternatively, it has been proposed that painful neurogenic vasodilation of meningeal blood vessels could be a key component of the inflammatory process during migraine headache. This view is supported by the observation that jugular plasma levels of the potent vasodilator, calcitonin gene-related peptide (CGRP) are elevated during the headache and normalized by successful sumatriptan treatment. Preclinically, activation of trigeminal sensory fibers evokes a CGRP-mediated neurogenic dural vasodilation, which is blocked by dihydroergotamine, triptans, and opioids but unaffected by NK1 receptor antagonists that failed in clinical trials. These observations suggest that CGRP release with associated neurogenic dural vasodilation may be important in the generation of migraine pain, a theory that would ultimately be tested by the clinical testing of a CGRP receptor antagonist.

Dipyridamole dilates large cerebral arteries concomitant to headache induction in healthy subjects

Dipyridamole is used for secondary prophylaxis in ischemic stroke and as a vasodilator agent in myocardial scintigraphy. An important side effect to administering dipyridamole is headache. The aim of the current study was to investigate the effects of dipyridamole on cerebral blood flow, large artery diameter, and headache induction. Twelve healthy subjects were included in this single-blind placebo-controlled study in which placebo (0.9% NaCl) and dipyridamole 0.142 mg/kg x min were administered intravenously over 4 minutes 1 hour apart. Blood flow velocity in the middle cerebral artery (Vmax) was recorded by transcranial Doppler and regional cerebral blood flow in the middle cerebral artery (rCBFmca) was measured using single photon emission computed tomography and 133Xenon-inhalation. Blood pressure, heart rate, and pCO2 were measured repeatedly. Headache response was scored every 10 minutes on a verbal scale from 0 to 10 (10 = worst). Dipyridamole caused a decrease in pCO2 (P < 0.001). pCO2 corrected rCBFmca was 41.7 +/- 6.9 mL/100 g x min after placebo versus 41.2 +/- 6.9 after dipyridamole (P > or = 0.05). pCO2 corrected Vmca decreased 8.4% +/- 11.7 (P < 0.001) after dipyridamole, indicating a mean 5.6% +/- 6.7 (P = 0.005) relative increase of the arterial diameter. After dipyridamole the median peak headache score was 2 (range 0 to 7) compared with 0 (range 0 to 3) after placebo (P = 0.02). Dilatation of the middle cerebral artery outlasted the headache response. In conclusion, dipyridamole causes a modest pCO2 independent dilatation of the MCA, which is time-linked to the onset, but not to the cessation, of headache.

Serotonin in migraine: theories, animal models and emerging therapies

A role for serotonin in migraine has been supported by changes in circulating levels of serotonin and its metabolites during the phases of a migraine attack, along with the ability of serotonin-releasing agents to induce migraine-like symptoms. The development of serotonin receptor agonists with efficacy in the clinic for the alleviation of migraine pain further implicates serotonin as a key molecule in migraine. Several theories regarding the etiology of migraine have been proposed. The vasodilatory theory of migraine suggested that extracranial arterial dilation during an attack was related to migraine pain; a theory supported when vasoconstrictors such as sumatriptan alleviated migraine pain. The neurological theory of migraine proposed that migraine resulted from abnormal firing in brain neurons. Cortical spreading depression, one facet of the neurological theory, could explain the prodrome of migraine. The neurogenic dural inflammation theory of migraine supposed that the dural membrane surrounding the brain became inflamed and hypersensitive due to release of neuropeptides from primary sensory nerve terminals. Substance P, calcitonin gene related peptide and nitric oxide are all though to play a role in the dural inflammatory cascade. Animal models of migraine have been utilized to study the physiology of migraine and develop new pharmaceutical therapies. One model measures the shunting of blood to arteriovenous anastomoses based on a proposal that migraine primarily involves cranial arteriovenous vasodilation. Another model utilizes electrical stimulation of the trigeminal ganglion to induce neurogenic dural inflammation quantified by the resulting extravasation of proteins. Pharmacological agents such as meta-chlorophenylpiperazine (mCPP) and nitroglycerin have also been used to induce dural extravasation in animals. Both compounds also induce migraine attacks in individuals with a history of migraine. In addition, Fos, a protein produced by activation of the c-fos gene, has been measured as an index of migraine-like pain transmission to the CNS following chemical or electrical stimulation of the trigeminal nerve. A role for serotonin in migraine is further supported by the efficacy of serotonin receptor ligands. Sumatriptan is an agonist at 5-HT1D and 5-HT1B receptor subtypes, and effective in treating migraine pain and associated symptoms. Recently, selective 5-HT1F agonists have been proposed for the treatment of migraine, without the side effects associated with the present 5-HT1D and 5-HT1B receptor agonists. A role for 5-HT2B receptors has also been suggested the initiation of migraine, supporting use of selective 5-HT2B receptor antagonists in migraine. Thus, agents that modulate 5-HT1B, 5-HT1D, 5-HT1F and 5-HT2B receptors either have or may have clinical utility in the therapy of migraine headache.

Cranial vascular effects of zolmitriptan, a centrally active 5-HT1B/1D receptor partial agonist for the acute treatment of migraine

The anti-migraine drug zolmitriptan is a novel 5-HT1B/1D receptor partial agonist which, unlike sumatriptan, has been shown to cross the intact blood-brain barrier. In this study we examined whether or not the ability to access the cerebro-vascular intima affects the way in which a centrally-active 5-HT1B/1D receptor agonist influences cranial haemodynamics. The effects of zolmitriptan on carotid arterial blood flow distribution were studied in anaesthetised cats using radiolabelled microspheres. Zolmitriptan (10-1000 microg kg(-1) i.v.) selectively reduced arteriovenous-anastomotic (AVA) conductance producing a maximum decrease of 92.5+/-2.3%. The drug also produced a modest reduction in extra-cerebral conductance (23.9+/-6.5% maximum reduction at 30 microg kg(-1), i.v.), but was without effect on cerebral conductance. Using laser doppler flowmetry in anaesthetised cats, zolmitriptan (1-30 microg kg(-1), i.v.) produced dose-dependent decreases in ear microvascular conductance (15+/-5 to 60+/-6%) which mirrored decreases in carotid arterial conductance (12+/-11 to 61+/-5%). By contrast, zolmitriptan at doses up to 1000 microg kg(-1) was without effect on cerebral microvascular conductance. Although zolmitriptan crosses the blood-brain barrier and can therefore access the cerebro-vascular intima, this study suggests that this property does not adversely affect cerebrovascular function.

Nitric oxide synthase inhibition: a new principle in the treatment of migraine attacks

Glyceryl trinitrate, an exogenous nitric oxide (NO) donor, and histamine, which causes NO formation in vascular endothelium, have been shown to trigger migraine attacks. However, it remains uncertain whether NO is involved in the subsequent phase of migraine attacks. To answer this question we studied the effect of L-NGmethylarginine hydrochloride (546C88), a NO-synthase inhibitor, on spontaneous migraine attacks. In a double-blind study design, 18 patients with migraine without aura randomly received 546C88 (6 mg/kg) or placebo (5% dextrose) i.v. given over 15 min for a single migraine attack (546C88:placebo, 15:3). Furthermore, 11 placebo-treated patients from previous double-blind trials with almost identical design were added to the placebo group in the statistical evaluation. Two hours after the infusion, 10 of 15 L-NGmethylarginine hydrochloride-treated patients experienced headache relief compared to 2 of 14 placebo-treated patients (p = 0.01). Symptoms such as phono- and photophobia were also significantly improved. A similar trend for nausea was not significant. We conclude that NO may be involved in the pain mechanisms throughout the course of spontaneous migraine attacks.

Investigations into the role of nitric oxide and the large intracranial arteries in migraine headache

Previous studies suggest that nitric oxide (NO) is involved in headaches induced by i.v. infusion of the vasodilator and NO donor glyceryl trinitrate (GTN) in healthy subjects. Extending these studies to sufferers of migraine without aura, it was found that migraineurs experienced a stronger headache than non-migraineurs. In addition, most migraineurs experienced a delayed migraine attack at variable times (mean 5.5 h) after GTN provocation. This biphasic headache response in migraineurs may be linked to hypersensitivity in the NO-cGMP pathway. Thus, compared to controls, migraineurs were found to be more sensitive to GTN-induced intracranial arterial dilatation, which is known to be mediated via liberation of NO and subsequent synthesis of cGMP Furthermore, histamine infusions in migraineurs induced headache responses and intracranial arterial responses resembling those induced by GTN in migraineurs. Histamine is known to liberate NO from the endothelium via stimulation of the H1 receptor, which is present in the large intracranial arteries in man. Because both immediate histamine-induced headache and intracranial arterial dilatation and delayed histamine-induced migraine are blocked by H1-receptor blockade, a likely common pathway for GTN and histamine-induced headaches/migraines and intracranial arterial responses may be via activation of the NO-cGMP pathway. The delay in the development of these experimental migraines may reflect activation of multiple physiological processes. The intracranial arteries of migraineurs were found supersensitive to the vasodilating effect of GTN (exogenous NO). This relates to clinical findings suggesting dilatation of the large intracranial arteries on the headache side during spontaneous migraine attacks. The function of arterial regulatory mechanisms involving NO in migraine was therefore studied. In peripheral arteries, no endothelial dysfunction of NO was found and cardiovascular and intracranial arterial sympathetic function was normal. A mild parasympathetic dysfunction may be involved and may, via denervation supersensitivity, be responsible for the observed supersensitivity to NO. Another possibility is that NO initiates a perivascular neurogenic inflammation with liberation of vasoactive peptides. NO also mediates a variety of other physiological phenomena. One of these, the pain-modulating effect observed in animals, was evaluated in a human study using GTN infusion and measurements of pain thresholds. No definite effects of GTN were demonstrated. The precise mechanisms involved in NO-triggered migraines and which part of the NO-activated cascade that is involved remain to be determined. The possibilities for pharmacological stimulation and/or inhibition of several steps of the NO-activated cascade increase rapidly and soon may be available for human studies.

Plasma protein extravasation induced in the rat dura mater by stimulation of the parasympathetic sphenopalatine ganglion

It has been proposed that migraine could result from a neurogenic inflammation of the dura mater. According to this theory, inflammation could be initiated by an axon reflex of nociceptive nerve fibers, but the trigger of this axon reflex remains poorly understood. Previous works have shown that parasympathetic agonists can activate mast cells and/or sensory C-fibers, inducing pain and inflammation. The aim of the present work was to determine whether the activation of intracranial parasympathetic nerve fibers could trigger an inflammatory mechanism within the rat dura mater. Activation of the intracranial parasympathetic system was achieved by electrical stimulation of the sphenopalatine ganglion (SPG). The development of a neurogenic inflammation was estimated either by microscopic examination or by quantitative measurement of plasma protein extravasation (PPE) in the dura. To determine the respective roles of the parasympathetic and sensory innervations, two groups of rats were pretreated either with atropine or with capsaicin. Stimulation of the SPG induced a PPE increase of about 200% in the stimulated side on the dura mater. Extravasated material was mainly concentrated around small blood vessels. This extravasation was significantly reduced by capsaicin pretreatment and completely abolished by atropine. Infusion of carbachol in the common carotid artery induced PPE in the ipsilateral dura comparable to that induced by electrical stimulation of the SPG. This extravasation was also blocked by atropine infusion. These data indicate for the first time that the parasympathetic nervous system can trigger a neurogenic inflammation in the dura via muscarinic cholinergic receptors. Sensory C-fibers seem to play a role in this phenomenon. With respect to the potential autonomic imbalance described in the etiology of various types of vascular headaches, such a mechanism could be important in inducing attacks.

Headache induced by a nitric oxide donor (nitroglycerin) responds to sumatriptan. A human model for development of migraine drugs

Experimental "vascular" headache in humans may be used in characterizing new migraine drugs. The effects of sumatriptan on nitroglycerin-(NTG)-induced headache and arterial responses were therefore studied. Following a double-blind randomized crossover design, 10 healthy volunteers received sumatriptan 6 mg s.c. or placebo succeeded by 20 min NTG (0.12 microgram/kg/min) infusion. Headache was rated on a 10 points scale. Temporal and radial artery diameters and velocity in the middle cerebral artery (MCA) were measured with ultrasound. Sumatriptan reduced the NTG-induced headache, median score 1.5 versus 4 after placebo (p < 0.01) and decreased temporal and radial artery diameters 75 +/- 3 and 86 +/- 3% of baseline respectively (p < 0.05). Blood velocity in the MCA was unaffected. The NTG model may prove to be a valuable tool in the development of future migraine drugs. The results suggest that NTG headache in non-migraineurs may share mechanisms with migraine headache.

Sumatriptan: vasoactive effect on human dural vessels, demonstrated by subselective angiography

Sumatriptan, a selective 5-hydroxytryptamine (5HT1D)-receptor agonist, has recently been introduced in the pharmacotherapy of acute migrane attacks. The potential vasoactive effect of sumatriptan on human dural vessels in vivo, however, is still a matter of controversy. We investigated the effects of sumatriptan on dural vessels after subcutaneous or intra-arterial injection. During interventional angiography, the middle meningeal artery (MMA) of nine patients was catheterized with a microcatheter using the transfemoral route. Three MMA were entirely normal, two supplied a dural arteriovenous fistula (AVF) and four were transdural feeders to a brain arteriovenous malformation (AVM). Sumatriptan was injected either into the subcutaneous tissue of the right shoulder (6 mg, two patients) or into the catheterized MMA (2 mg, six patients). The substance caused a marked vasoconstriction of the three normal MMA, visible angiographically and confirmed by intravascular Doppler ultrasonography. Vasoconstriction was still present in the last angiogram obtained 15 min post-injection. Slightly hypertrophied feeders to dural AVF and to brain AVM showed some vasoconstriction in one and four patients, respectively. In two patients with markedly hypertrophied dural feeders to a dural AVF and to a brain AVM, respectively, rapid shunting probably prevented obvious vasoactive effects of sumatriptan. The data obtained by angiography and intravascular Doppler ultrasonography provide strong evidence that sumatriptan has a vasoconstrictive effect on normal as well as hypertrophied dural vessels.

Migraine and cluster headache--their management with sumatriptan: a critical review of the current clinical experience

Sumatriptan is a potent and selective agonist at the vascular 5HT1 receptor which mediates constriction of certain large cranial blood vessels and/or inhibits the release of vasoactive neuropeptides from perivascular trigeminal axons in the dura mater following activation of the trigeminovascular system. The mode of action of this drug in migraine and cluster headache is discussed. On the basis of a detailed review of all published trials and available data from post-marketing studies, the efficacy, safety, tolerability and the place of oral and subcutaneous sumatriptan in the treatment of both conditions are assessed. A number of double-blind clinical trials have demonstrated that sumatriptan 100 mg administered orally is clearly superior to placebo in the acute treatment of migraine headache and achieves significantly greater response rates than ergotamine or aspirin. In other studies, 70 to 80% of patients receiving sumatriptan 6 mg sc experienced relief of migraine headaches by 1 or 2 h after administration, and patients consistently required less rescue medication for unresolved symptoms. Sumatriptan was also effective in relieving associated migraine symptoms like nausea and vomiting. Sumatriptan was equally effective regardless of migraine type or duration of migraine symptoms. Overall, approximately 40% of patients who initially responded to oral or subcutaneous sumatriptan experienced recurrence of their headache usually within 24 h, effectively treated by a further dose of this drug. In 75% of patients with cluster headache treated with sumatriptan 6 mg sc, relief was achieved within 15 min. Based on pooled study data, sumatriptan is generally well tolerated and most adverse events are transient. Adverse events following oral administration include nausea, vomiting, malaise, fatigue and dizziness. With the subcutaneous injection, injection site reactions occur in approximately 30%. Chest syumptoms are reported in 3 to 5% but have been associated with myocardial ischaemia only in rare isolated cases. The recommended dosage of sumatriptan at the onset of migraine symptoms is 100 mg orally or 6 mg subcutaneously. The recommended dosage for cluster headache is 6 mg sumatriptan sc. Sumatriptan must not be given together with vasoconstrictive substances, e.g., ergotamines, or with migraine prophylactics with similar properties, e.g., methysergide. Sumatriptan should not be given during the migraine aura. It is contraindicated in patients with ischaemic heart disease, previous myocardial infarction, Prinzmetal (variant) angina and uncontrolled hypertension.

Cerebral blood flow velocities are reduced during attacks of unilateral migraine without aura

It has been disputed whether or not large intracranial arteries are dilated during migraine attacks. In order to answer this question the present transcranial Doppler study focused on side-to-side differences of middle cerebral artery blood velocity during unilateral attacks of migraine without aura in 25 patients. Blood velocity in the middle cerebral artery was lower on the headache side (59 cm/s) than on the non-headache side (65 cm/s) during the migraine attack. No such difference was found outside of attack (65 cm/s both sides). The difference (headache side minus non-headache side) was on average -6.1 cm/s during attack compared to -0.4 cm/s outside of attack (p = 0.01). Assuming that rCBF is unchanged during attacks of migraine without aura, our results suggest a 9% increase in middle cerebral artery lumen (cross-sectional area) on the affected side during unilateral attacks of migraine without aura. The findings, however, do not necessarily mean that arterial dilatation is the only or even the most significant cause of pain.