The trigeminovascular system and migraine: studies characterizing cerebrovascular and neuropeptide changes seen in humans and cats

Kynurenine aminotransferase in the supratentorial dura mater of the rat: effect of stimulation of the trigeminal ganglion

Electrical stimulation of the trigeminal ganglion has been widely used as a model of nociception, characterizing migraine. This treatment is known to evoke release of neuropeptides and neurotransmitters from nerve fibers of the dura mater. On the basis of immunocytochemical investigations, we found that under normal conditions, surface membranes of Schwann cells surrounding nerve fibers in the supratentorial dura mater display kynurenine aminotransferase-immunoreaction (KAT-IR); also KAT-IR are the granules of mast cells and the cytoplasms of macrophages (histiocytes). In consequence of stimulation of the trigeminal ganglion, Schwann cells in the dura mater became conspicuously swollen while their KAT-IR decreased considerably; also KAT-IR of mast cells and macrophages decreased significantly. At the same time, nitric oxide synthase (NOS)-IR of nerve fibers in the dura mater increased, suggesting release of nitric oxide (NO), this is known to be involved in NMDA receptor activation leading to vasodilation followed by neurogenic inflammation. Because kynurenic acid (KYNA) is an antagonist of NMDA receptors, we hypothesize that KYNA and its synthesizing enzyme, KAT, may play a role in the prevention of migraine attacks.

Regulation of calcitonin gene-related peptide secretion from trigeminal nerve cells by botulinum toxin type A: implications for migraine therapy

OBJECTIVES

To determine the effect of botulinum toxin type A on calcitonin gene-related peptide secretion from cultured trigeminal ganglia neurons.

BACKGROUND

The ability of botulinum toxins to cause muscle paralysis by blocking acetylcholine release at the neuromuscular junction is well known. Previous studies and clinical observations have failed to demonstrate sensory changes related to botulinum toxins or the disease of botulism. Recent studies, however, have suggested that botulinum toxin type A injected into pericranial muscles may have a prophylactic benefit in migraine. This observation has renewed the debate of a mechanism of sensory inhibition mediated by botulinum toxin type A.

METHODS

Primary cultures of rat trigeminal ganglia were utilized to determine whether botulinum toxin type A could directly decrease the release of calcitonin gene-related peptide, a neuropeptide involved in the underlying pathophysiology of migraine. Untreated cultures or cultures stimulated with a depolarizing stimulus (potassium chloride) or capsaicin, an agent known to activate sensory C fibers, were treated for 3, 6, or 24 hours with clinically effective doses of botulinum toxin type A or a control vehicle. The amount of calcitonin gene-related peptide secreted into the culture media following the various treatments was determined using a specific radioimmunoassay.

RESULTS

A high percentage (greater than 90%) of the trigeminal ganglia neurons present in 1- to 3-day-old cultures was shown to express calcitonin gene-related peptide. Treatment with depolarizing stimuli (potassium chloride), a mixture of inflammatory agents, or capsaicin caused a marked increase (4- to 5-fold) in calcitonin gene-related peptide released from the trigeminal neurons. Interestingly, overnight treatment of trigeminal ganglia cultures with therapeutic concentrations of botulinum toxin type A (1.6 or 3.1 units) did not affect the amount of calcitonin gene-related peptide released from these neurons. The stimulated release of calcitonin gene-related peptide following chemical depolarization with potassium chloride or activation with capsaicin, however, was greatly repressed by the botulinum toxin, but not by the control vehicle. A similar inhibitory effect of overnight treatment with botulinum toxin type A was observed with 1.6 and 3.1 units. These concentrations of botulinum toxin type A are well within or below the range of tissue concentration easily achieved with a local injection. Incubation of the cultures with toxin for 24, 6, or even 3 hours was very effective at repressing stimulated calcitonin gene-related peptide secretion when compared to control values.

CONCLUSIONS

These data provide the first evidence that botulinum toxin type A can directly decrease the amount of calcitonin gene-related peptide released from trigeminal neurons. The results suggest that the effectiveness of botulinum toxin type A in the treatment of migraine may be due, in part, to its ability to repress calcitonin gene-related peptide release from activated sensory neurons.

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

We have shown that the development of cutaneous allodynia (exaggerated skin sensitivity) during migraine is detrimental to the anti-migraine action of the 5HT(IB/ID) receptor agonists known is triptans. Because cutaneous allodynia is a manifestation of sensitization of central trigeminovascular neurons, we examined whether triptan treatment can intercept such sensitization before its initiation or after its establishment in our rat model for cutaneous allodynia induced by intracranial pain. Single-unit recordings were obtained from spinal trigeminal neurons that proved to received convergent inputs from the dura and facial skin. The effects of sumatriptan (300 microg/kg i.v.) on central sensitization induced by topical application of inflammatory soup (IS) on the dura were determined when the drug was administered either 2 h after IS (late intervention) or at the same time as IS (early intervention). Late sumatriptan intervention counteracted two aspects of central sensitization: dural receptive fields, which initially expanded by IS, shrunk back after treatment; neuronal response threshold to dural indentation, which initially decreased after IS, increased after sumatriptan. On the other hand, late sumatriptan intervention did not reverse other aspects of central sensitization: spontaneous firing rate and neuronal response magnitude to skin brushing which initially increased after IS, remained elevated after sumatriptan; response threshold to heating of the skin, which initially dropped after IS, remained low after sumatriptan. Early sumatriptan intervention effectively blocked the development of all aspects of central sensitization expected to be induced 2 h after IS application: dural receptive fields did not expand; neuronal response threshold to dural indentation and skin stimulation did not decrease; spontaneous firing rate did not increase. The early treatment results suggest that triptan action provides a powerful means of preventing the initiation of central sensitization triggered by chemical stimulation of meningeal nociceptors. The late treatment results suggest that triptan action is insufficient to counteract an already established central sensitization. Thus, triptan action appears to be exerted directly on peripheral rather than central trigeminovascular neurons.

Calcitonin gene-related peptide receptor antagonist BIBN 4096 BS for the acute treatment of migraine

BACKGROUND

Calcitonin gene-related peptide (CGRP) may have a causative role in migraine. We therefore hypothesized that a CGRP-receptor antagonist might be effective in the treatment of migraine attacks.

METHODS

In an international, multicenter, double-blind, randomized clinical trial of BIBN 4096 BS, a highly specific and potent nonpeptide CGRP-receptor antagonist, 126 patients with migraine received one of the following: placebo or 0.25, 0.5, 1, 2.5, 5, or 10 mg of BIBN 4096 BS intravenously over a period of 10 minutes. A group-sequential adaptive treatment-assignment design was used to minimize the number of patients exposed.

RESULTS

The 2.5-mg dose was selected, with a response rate of 66 percent, as compared with 27 percent for placebo (P=0.001). The BIBN 4096 BS group as a whole had a response rate of 60 percent. Significant superiority over placebo was also observed with respect to most secondary end points: the pain-free rate at 2 hours; the rate of sustained response over a period of 24 hours; the rate of recurrence of headache; improvement in nausea, photophobia, phonophobia, and functional capacity; and the time to meaningful relief. An effect was apparent after 30 minutes and increased over the next few hours. The overall rate of adverse events was 25 percent after the 2.5-mg dose of the drug and 20 percent for the BIBN 4096 BS group as a whole, as compared with 12 percent for placebo. The most frequent side effect was paresthesia. There were no serious adverse events.

CONCLUSIONS

The CGRP antagonist BIBN 4096 BS was effective in treating acute attacks of migraine.

NO-induced migraine attack: strong increase in plasma calcitonin gene-related peptide (CGRP) concentration and negative correlation with platelet serotonin release

The aim of the present study was to investigate changes in the plasma calcitonin gene-related peptide (CGRP) concentration and platelet serotonin (5-hydroxytriptamine, 5-HT) content during the immediate headache and the delayed genuine migraine attack provoked by nitroglycerin. Fifteen female migraineurs (without aura) and eight controls participated in the study. Sublingual nitroglycerin (0.5 mg) was administered. Blood was collected from the antecubital vein four times: 60 min before and after the nitroglycerin application, and 60 and 120 min after the beginning of the migraine attack (mean 344 and 404 min; 12 subjects). In those subjects who had no migraine attack (11 subjects) a similar time schedule was used. Plasma CGRP concentration increased significantly (P<0.01) during the migraine attack and returned to baseline after the cessation of the migraine. In addition, both change and peak, showed significant positive correlations with migraine headache intensity (P<0.001). However, plasma CGRP concentrations failed to change during immediate headache and in the subjects with no migraine attack. Basal CGRP concentration was significantly higher and platelet 5-HT content tended to be lower in subjects who experienced a migraine attack. Platelet serotonin content decreased significantly (P<0.01) after nitroglycerin in subjects with no migraine attack but no consistent change was observed in patients with migraine attack. In conclusion, the fact that plasma CGRP concentration correlates with the timing and severity of a migraine headache suggests a direct relationship between CGRP and migraine. In contrast, serotonin release from platelets does not provoke migraine, it may even counteract the headache and the concomitant CGRP release in this model.

Migraine

Migraine is a very common neurobiological headache disorder that is caused by increased excitability of the CNS. It ranks among the world's most disabling medical illnesses. Diagnosis is based on the headache's characteristics and associated symptoms. The economic and societal effect of migraine is substantial: it affects patients' quality of life and impairs work, social activities, and family life. There are many acute and preventive migraine treatments. Acute treatment is either specific (triptans and ergots) or non-specific (analgesics). Disabling migraine should be treated with triptans. Increased headache frequency is an indication for preventive treatment. Preventive treatment decreases migraine frequency and improves quality of life. More treatments are being developed, which provides hope to the many patients whose migraines remain uncontrolled.

EP4 prostanoid receptor-mediated vasodilatation of human middle cerebral arteries

1. Dilatation of the cerebral vasculature is recognised to be involved in the pathophysiology of migraine. Furthermore, elevated levels of prostaglandin E(2) (PGE(2)) occur in the blood, plasma and saliva of migraineurs during an attack, suggestive of a contributory role. In the present study, we have characterised the prostanoid receptors involved in the relaxation and contraction of human middle cerebral arteries in vitro. 2. In the presence of indomethacin (3 microm) and the TP receptor antagonist GR32191 (1 microM), PGE(2) was found to relax phenylephrine precontracted cerebral arterial rings in a concentration-dependent manner (mean pEC(50) 8.0+/-0.1, n=5). 3. Establishment of a rank order of potency using the EP(4)>EP(2) agonist 11-deoxy PGE(1), and the EP(2)>EP(4) agonist PGE(1)-OH (mean pEC(50) of 7.6+/-0.1 (n=6) and 6.4+/-0.1 (n=4), respectively), suggested the presence of functional EP(4) receptors. Furthermore, the selective EP(2) receptor agonist butaprost at concentrations <1 microM failed to relax the tissues. 4. Blockade of EP(4) receptors with the EP(4) receptor antagonists AH23848 and EP(4)A caused significant rightward displacements in PGE(2) concentration-response curves, exhibiting pA(2) and pK(B) values of 5.7+/-0.1, n=3, and 8.4, n=3, respectively. 5. The IP receptor agonists iloprost and cicaprost relaxed phenylephrine precontracted cerebral arterial rings (mean pEC(50) values 8.3+/-0.1 (n=4) and 8.1+/-0.1 (n=9), respectively). In contrast, the DP and FP receptor agonists PGD(2) and PGF(2 alpha) failed to cause appreciable relaxation or contraction at concentrations of up to 30 microm. In the absence of phenylephrine contraction and GR32191, the TP receptor agonist U46619 caused concentration-dependent contraction of cerebral artery (mean pEC(50) 7.4+/-0.3, n=3). 6. These data demonstrate the presence of prostanoid EP(4) receptors mediating PGE(2) vasodilatation of human middle cerebral artery. IP receptors mediating relaxation and TP receptors mediating contraction were also functionally demonstrated.

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

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

In-depth characterization of CGRP receptors in human intracranial arteries

The purpose of the present study was to characterize the effects of human (h) alpha- and beta-calcitonin gene-related peptide (CGRP) on intracranial arteries from man and to investigate the presence of mRNA for the calcitonin receptor like receptor (CRLR) and the receptor activity modifying proteins (RAMPs) 1, 2 and 3, in cerebral and middle meningeal arteries with and without endothelium, in microvessels and in the endothelial cells isolated from the human basilar artery. Reverse transcriptase-polymerase chain reaction (RT-PCR) revealed the presence of CRLR, RAMP 1, RAMP 2 and RAMP 3 in cerebral and middle meningeal arteries with and without endothelium as well as in microvessels and in the endothelial cells. Human and rat alpha- and beta-CGRP, amylin, adrenomedullin and [acetamidomethyl-Cys(2,7)]human CGRP induced strong concentration-dependent relaxation of human cerebral and middle meningeal arteries. Removal of the endothelium neither changed the maximum relaxant response nor the pIC(50) values for alpha- and beta-CGRP as compared to the responses in arteries with an intact endothelium. Human alpha-CGRP-(8-37) caused a shift of h alpha- and h beta-CGRP-induced relaxations in cerebral and middle meningeal arteries. Calculation of pK(B) values revealed that h alpha-CGRP-(8-37) could not significantly discriminate between relaxations induced by h alpha-CGRP (pK(B) around 6.8) and h beta-CGRP (pK(B) around 5.4). There was no significant difference in pK(B) value of h alpha-CGRP-(8-37) on h beta-CGRP-induced relaxation of human cerebral and middle meningeal arteries with and without endothelium. In conclusion, our molecular and pharmacological data support the existence of a single type of CGRP(1) receptors in the human intracranial circulation.

Immunohistochemical localization of substance P, calcitonin gene-related peptide, galanin and calcium-binding proteins in trigeminal ganglia of goat (Capra hircus)

The objectives of this study was to provide a quantitative analysis of calcium-binding proteins, calbindin (CB), parvalbumin (PA), substance P (SP), calcitonin gene-related peptide (CGRP) and galanin (GAL), in trigeminal ganglia of goats, to establish whether they exhibit coexistence relationships between each other, and to examine possible colocalization with SP, CGRP and GAL, which have been well characterized according to their distributions in an abundance of large and/or small neurones. CB (12.78%), PA (31.91%), SP (24.63%), CGRP (44.44%) and GAL (3.29%) immunoreactive (IR) cells were observed. About 38.37, 8.7 and 0.73% of CGRP-IR neurones in the trigeminal ganglion were also immunoreacted with SP, GAL and CB, respectively. Almost all SP-IR cells are labelled with CGRP (approximately 92.52%), whereas only 16.02 and 0.44% of SP-IR neurones colocalized with GAL and CB. Approximately 4.65 and 1.10% of the CB-IR cells were found to contain CGRP and SP immunoreactivity, respectively. Conversely, no CB-IR cell exhibited GAL immunoreactivity. In addition, all the GAL-IR cells showed CGRP and SP immunoreactivity. The number of CB-, PA-, SP-, CGRP- and GAL-IR neurones in goat trigeminal ganglion are abundant than that of other animals. These results elucidate that the goat differs from other mammalian species in the distribution and localization of neurochemical substances in trigeminal ganglia, and suggest that this difference may be relevant to the morphological characteristics of cerebral vasculatures such as epidural rete mirabile of goat.

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

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

Effects of the CGRP receptor antagonist BIBN4096BS on capsaicin-induced carotid haemodynamic changes in anaesthetised pigs

1. Calcitonin gene-related peptide (CGRP), a potent vasodilator released from capsaicin-sensitive trigeminal sensory nerves, seems to be involved in the pathogenesis of migraine. Hence, CGRP receptor antagonists may serve as a novel treatment for migraine. This study was therefore designed to investigate the effects of BIBN4096BS (100, 300 and 1000 microg kg-1, i.v.), a potent and selective CGRP receptor antagonist, on capsaicin-induced carotid haemodynamic changes in anaesthetised pigs. Both vagosympathetic trunks were cut and phenylephrine was infused into the carotid artery (i.c.) to support carotid vascular tone. 2. Infusions of capsaicin (0.3, 1, 3 and 10 microg kg-1 min-1, i.c.) did not alter the heart rate, but dose-dependently increased the mean arterial blood pressure. This moderate hypertensive effect was not modified by BIBN4096BS. 3. Capsaicin infusion (10 microg kg-1 min-1, i.c.) increased total carotid, arteriovenous anastomotic and tissue blood flows and conductances as well as carotid pulsations, but decreased the difference between arterial and jugular venous oxygen saturations. These responses to capsaicin were dose-dependently blocked by BIBN4096BS. 4. Capsaicin infusion (10 microg kg-1 min-1, i.c.) more than doubled the jugular venous plasma concentration of CGRP. This effect was not blocked, but rather increased, by BIBN4096BS. 5. The above results show that BIBN4096BS behaves as a potent antagonist of capsaicin-induced carotid haemodynamic changes that are mediated via the release of CGRP. Therefore, this compound may prove effective in the treatment of migraine.

2003 Wolff Award: Possible parasympathetic contributions to peripheral and central sensitization during migraine

BACKGROUND

Neurologic signs of increased parasympathetic outflow to the head often accompany migraine attacks. Because increased parasympathetic outflow to the cranial cavity induces vasodilation of cerebral and meningeal blood vessels, it can enhance plasma protein extravasation and the release of proinflammatory mediators that activate perivascular nociceptors. We recently showed that activation of intracranial perivascular nociceptors induces peripheral and central sensitization along the trigeminovascular pathway and proposed that these sensitizations mediate the intracranial hypersensitivity and the cutaneous allodynia of migraine.

METHODS

The present study investigates possible parasympathetic contributions to the generation of peripheral and central sensitization during migraine by applying intranasal lidocaine to reduce cranial parasympathetic outflow through the sphenopalatine ganglion.

RESULTS

In the absence of migraine, patients were pain-free, and their skin sensitivity was normal. Their mean baseline pain thresholds were less than 15 degrees C for cold, more than 45 degrees C for heat, and more than 100 g for mechanical pressure. Their mean pain score was 7.5 of 10 (standard deviation, 1.4) during untreated migraine and 3.5 of 10 (standard deviation, 2.4) after the nasal lidocaine-induced sphenopalatine ganglion block (P <.0001). Most patients developed cutaneous allodynia during migraine, and their mean pain thresholds changed to more than 25 degrees C for cold, less than 40 degrees C for heat, and less than 10 g for mechanical pressure. Following the nasal lidocaine administration (sphenopalatine ganglion block), this allodynia remained unchanged in spite of the pain relief.

CONCLUSION

These findings suggest that cranial parasympathetic outflow contributes to migraine pain by activating or sensitizing (or both) intracranial nociceptors, and that these events induce parasympathetically independent allodynia by sensitizing the central nociceptive neurons in the spinal trigeminal nucleus.

Relationship between pain and autonomic phenomena in headache and other pain conditions

Involvement of the (efferent) autonomic nervous system in the generation of pain is ongoing matter of debate. Based on clinical and experimental observations, there are good arguments that the sympathetic nervous system may be involved in pain following trauma, with and without nerve lesion, at an extremity, such as in complex regional pain syndrome type I and II. However, the mechanisms involved are in many cases still unclear. In various types of headache there is no convincing evidence that the sympathetic nervous system is involved in the generation of pain, although these pains may be accompanied by considerable autonomic reactions which are dependent on activity in sympathetic neurons. Migraine and headaches with autonomic symptoms are accompanied by autonomic reactions which are dependent on activity in cranial parasympathetic neurons. Whether parasympathetic neurons innervating cranial blood vessels are involved in activation or sensitization of trigemino-vascular afferents is discussed and needs experimental verification.

Peripheral and central activation of trigeminal pain pathways in migraine: data from experimental animal models

Animal models for migraine have provided substantial advances on the mechanisms and mediators underlying migraine attacks. The neurogenic inflammation model has helped understanding the perivascular mechanisms underlying the pathophysiology of migraine attacks, the receptors involved and the effect of specific antimigraine drugs. The model based on probing the neuronal effects of nitroglycerin--an organic nitrate known to induce spontaneous-like migraine attacks in predisposed subjects--in the rat has provided interesting insights into the neuroanatomic circuits and neuropharmacological mechanisms involved in the initiation and repetition of migraine attacks [corrected].

Is there a role for botulinum toxin in the treatment of migraine?

In this review, the studies and case reports that are available from reference systems and published congress contributions on the treatment of migraine with botulinum toxin are evaluated. The studies and reports were analyzed with respect to the study design, the efficacy parameters, and the significance of results. One double-blind, placebo-controlled, randomized study with negative (for a 75 U dose of botulinum toxin) and positive (for a 25 U dose of botulinum toxin) evidence of efficacy, one that was a partly positive controlled study (pain intensity, but not attack-frequency improved), and four positive open studies were available. For the acute treatment of migraine with botulinum toxin, only positive case reports were published. As a result of this analysis, there is no sufficient scientific evidence for a treatment recommendation of migraine with botulinum toxin. Further studies are needed for a definite evaluation of subgroups with probable benefit from such a treatment and for the comparison of botulinum toxin with other migraine prophylactic drugs.

New therapeutic target in primary headaches - blocking theCGRP receptor

The primary headaches are among the most prevalent neurological disorders, afflicting up to 16% of the adult population. The associated pain originates from intracranial blood vessels that are innervated by sensory nerves storing several neurotransmitters. In primary headaches, there is a clear association between the headache and the release of calcitonin gene-related peptide (CGRP), but not other neuronal messengers. The specific purpose of this review is to describe CGRP in the human cranial circulation and to elucidate a possible role for a specific antagonist in the treatment of primary headaches. Acute treatment with administration of a 5-HT(1B/1D) agonist (triptan) results in alleviation of the headache and normalisation of the CGRP level. The mechanism of action of triptans involves vasoconstriction of intracranial vessels and a presynaptic inhibitory effect of sensory nerves. The central role of CGRP in migraine and cluster headache pathophysiology has led to the search for small-molecule CGRP antagonists, which are predicted to have fewer cardiovascular side effects in comparison to the triptans. The initial pharmacological profile of such a group of compounds has recently been disclosed. These compounds have high selectivity for human CGRP receptors and are reportedly efficacious in the relief of acute attacks of migraine.

Decreased habituation of the R2 component of the blink reflex in migraine patients

OBJECTIVE

Activation of the trigemino-vascular system as well as of brainstem trigeminal nuclei are thought to play an important role in migraine. The aim of this study was to investigate the habituation phenomenon of the blink reflex in 30 headache-free migraine patients and 30 control subjects.

METHODS

An electromyographic device with a specific habituation test program was used to elicit and record blink reflex responses on both the right and left sides, and to randomly repeat the stimulations at different time intervals in order to induce habituation.

RESULTS

Whereas the R1 and R2 latencies, amplitudes and areas in the basal assessment were similar in patients and control subjects, the blink reflex habituation responses were markedly reduced in migraine patients who had a migraine attack within 72 h after testing (group A). In these patients, the differences between the R2 areas, obtained when stimuli were delivered at subsequent time intervals ranging between 10-5, 5-4, 4-3 and 3-2 s, were statistically different (P<0.001) from those of the patients who had a migraine attack after a longer time interval (group B) and control subjects.

CONCLUSIONS

Our data suggest that the brainstem pathways involved in the blink reflex may be activated in the premonitory phase of migraine attacks, probably through mechanisms that involve dopaminergic function.

Tolerability of the triptans: clinical implications

The triptans represent a relatively new class of compounds effective in the treatment of migraine. The safety and tolerability of these drugs have been extensively investigated since the first triptan (sumatriptan) became commercially available. A report on a very large population of patients tested during clinical trials and in postmarketing studies, confirms that these drugs are safe and well tolerated when correctly used. Adverse events are frequently reported, but are usually mild and only a few patients discontinue therapy because of them. These adverse events include, in particular, the so-called 'triptan symptoms' (tingling, sensation of warmth, etc.). The exact mechanism of chest symptoms reported by 20% of patients with migraine treated with triptans remains unclear, but are exceptionally related to a cardiac mechanism. CNS adverse events (i.e. somnolence) are also reported, but it is a matter of debate whether they are related to the pharmacological properties (i.e. lipophilicity) of the drug or are symptoms of the disease itself. The potential risk for drug overuse must be taken into account when the triptans are given to patients with a high frequency of migraine attacks. Clinical interaction of triptans with other drugs metabolised in the liver may theoretically influence the incidence of adverse events, but there is little evidence to support this assumption. There is no evidence of a teratogenic risk of triptans in pregnant women taking these drugs.

Nociceptin immunoreactivity and receptor mRNA in the human trigeminal ganglion

Nociceptin is a peptide transmitter belonging to the opioid family. Nociceptin has recently attracted considerable interest since it appears to exhibit a number of differences to the other opioids. In the present study, we used a nociceptin antibody to map the distribution of nociceptin in the human trigeminal ganglion. In addition, we studied the nociceptin receptor at mRNA levels by RT-PCR and the vasomotor response to nociceptin in human cerebral vessels using a sensitive in vitro method. About 70% of all neuronal cells in trigeminal ganglia were nociceptin immunopositive. Nociceptin was predominantly (78%) expressed in medium-sized cells (30-60 microm). Nociceptin also distributed in small-sized cells (14% of positive cell bodies; <30 microm) and in large-sized cells (8% of positive cell bodies; >60 microm). Double immunostaining showed that in the human trigeminal ganglion nociceptin colocalized with calcitonin gene-related peptide (CGRP), substance P (SP), nitric oxide synthase (NOS) or pituitary adenylate cyclase activating peptide (PACAP). About 61% of nociceptin positive cells contained CGRP, 54% contained SP, 50% contained NOS and 68% contained PACAP. Immunoreactivity to nociceptin was not detected in human cerebral blood vessels. Reverse transcriptase-polymerase chain reaction detected the expression of nociceptin receptor mRNA in trigeminal ganglia but not in basilar arteries. To further examine whether there are functional nociceptin receptors in human cerebral arteries, a pharmacological study was done, where cerebral arteries revealed strong contractions to 60 mM K(+) and U466166 and strong relaxation to CGRP. Nociceptin failed to elicit contraction or relaxation. In conclusion, nociceptin is expressed in human trigeminal ganglia but not in cerebral blood vessels. Nociceptin is colocalized with CGRP, SP, NOS and PACAP. Nociceptin receptor mRNA is expressed in human trigeminal ganglia but not in basilar arteries. The functional role of nociceptin may be at the presynaptic level.

Stimulation of the calcitonin gene-related peptide enhancer by mitogen-activated protein kinases and repression by an antimigraine drug in trigeminal ganglia neurons

Calcitonin gene-related peptide (CGRP) is involved in the underlying pathophysiology of all vascular headaches, including migraines. Elevated levels of CGRP during migraine are restored to normal coincident with headache relief after treatment with the antimigraine drug sumatriptan. We have used primary cultures of trigeminal neurons under conditions simulating migraine pathology and therapy to study the mechanisms controlling the CGRP promoter. Using reporter genes in transient transfection assays, we demonstrate that an 18 bp enhancer containing a helix-loop-helix element is both necessary and sufficient for full promoter activity. NGF treatment and cotransfection with an upstream activator of the extracellular signal-regulated MAP kinases (MAPKs) activated the enhancer. Treatment with sumatriptan repressed NGF- and MAPK-stimulated CGRP promoter activity. Repression was also observed using a synthetic MAPK-responsive reporter gene. Sumatriptan regulation of CGRP gene expression did not couple to a G(i)/G(o) pathway, but rather caused a prolonged increase in intracellular calcium. The importance of the prolonged calcium signal in repression of MAPK activity was demonstrated by using the ionophore ionomycin to mimic sumatriptan action. We propose that activation of MAPK pathways may increase CGRP gene expression during migraine, and that sumatriptan can diametrically oppose that activation via a prolonged elevation of intracellular calcium.

'Side locked' migraine and trigeminal autonomic cephalgias: evidence for clinical overlap

This paper will discuss evidence which supports a link between 'side locked' migraine (SLM) and the trigeminal autonomic cephalgias (TACs). Recent papers brought strictly unilateral primary headaches into focus, proposing new classification and discussing pathophysiological mechanisms. We reviewed those proposals and present evidence that SLM falls in between the well-defined TACs and side shifting migraine (SSM). It is difficult to differentiate SLM from the recently proposed headache subtype called hemicrania generis incerti (i.e. hemicrania continua unresponsive to indomethacin). We also present cases that may exemplify the considerations made in the paper.

Ergotamine and dihydroergotamine: history, pharmacology, and efficacy

Ergotamine and dihydroergotamine share structural similarities with the adrenergic, dopaminergic, and serotonergic neurotransmitters. As a result, they have wide-ranging effects on the physiologic processes that they mediate. Ergotamine and dihydroergotamine are highly potent at the 5-HT1B and 5-HT1D antimigraine receptors and, as a consequence, the plasma concentrations that are necessary to produce the appropriate therapeutic and physiologic effects are very low. The broad spectrum of activity at other monoamine receptors is responsible for their side effect profile (dysphoria, nausea, emesis, unnecessary vascular effects). Both ergotamine and dihydroergotamine have sustained vasoconstrictor actions. In acute migraine treatment, their mechanisms of action involve constricting the pain-producing intracranial extracerebral blood vessels at the 5-HT1B receptors and inhibiting the trigeminal neurotransmission at the peripheral and central 5-HT1D receptors. The scientific evidence for efficacy is stronger for dihydroergotamine than for ergotamine. Their wide use is based on long-term experience.

Decreased sTNF-RI in migraine patients?

Tumour necrosis factor-alpha (TNF-alpha) and interleukin-6 (IL-6) have recently been found to have a pain-mediating function in addition to their immunological, proinflammatory function. According to the hypothesis of neurovascular inflammation in migraine, these two cytokines could contribute to migraine pain generation. We analysed IL-6 and its soluble receptors sIL-6R and sgp130 as well as TNF-alpha and its soluble receptor sTNF-RI in 27 migraine patients and eight headache-free controls. Migraine patients tended to have less sTNF-RI (794 +/- 158 pg/ml) than controls (945 +/- 137 pg/ml). No differences in cytokine concentrations were observed. If TNF-alpha plays a role in migraine physiopathology, migraine patients may lack sufficient antagonistic sTNF-RI to neutralize hyperalgesic TNF-alpha during a migraine attack.

A locus for migraine without aura maps on chromosome 14q21.2-q22.3

Migraine is a common and disabling neurological disease of unknown origin characterized by a remarkable clinical variability. It shows strong familial aggregation, suggesting that genetic factors are involved in its pathogenesis. Different approaches have been used to elucidate this hereditary component, but a unique transmission model and causative gene(s) have not yet been identified. We report clinical and molecular data from a large Italian pedigree in which migraine without aura (MO) segregates as an autosomal dominant trait. After exclusion of any association between MO and the known familial hemiplegic migraine and migraine with aura loci, we performed a genomewide linkage analysis using 482 polymorphic microsatellite markers. We obtained significant evidence of linkage between the MO phenotype and the marker D14S978 on 14q22.1 (maximum two-point LOD score of 3.70, at a recombination fraction of 0.01). Multipoint parametric analysis (maximum LOD score of 5.25 between markers D14S976 and D14S978) and haplotype construction showed strong evidence of linkage in a region of 10 cM flanked by markers D14S1027 and D14S980 on chromosome 14q21.2-q22.3. These results indicate the first evidence of a genetic locus associated with MO on chromosome 14.

Molecular Mechanisms of Migraine

Migraine is a common complex disorder that affects a large portion of the population and thus incurs a substantial economic burden on society. The disorder is characterized by recurrent headaches that are unilateral and usually accompanied by nausea, vomiting, photophobia, and phonophobia. The range of clinical characteristics is broad and there is evidence of comorbidity with other neurological diseases, complicating both the diagnosis and management of the disorder. Although the class of drugs known as the triptans (serotonin 5-HT(1B/1D) agonists) has been shown to be effective in treating a significant number of patients with migraine, treatment may in the future be further enhanced by identifying drugs that selectively target molecular mechanisms causing susceptibility to the disease.Genetically, migraine is a complex familial disorder in which the severity and susceptibility of individuals is most likely governed by several genes that may be different among families. Identification of the genomic variants involved in genetic predisposition to migraine should facilitate the development of more effective diagnostic and therapeutic applications. Genetic profiling, combined with our knowledge of therapeutic response to drugs, should enable the development of specific, individually-tailored treatment.

Facial migraine in a rhinological setting

This study aims to investigate the incidence of migraine involving the face in a rhinology clinic and to describe its characteristics. It is a study of a cohort of 973 patients consecutively presenting to the outpatient clinic with symptoms of facial pain and/or rhinosinusitis. The study subgroup consisted of patients with facial pain and migraine excluding cluster headache and paroxysmal hemicrania. We studied the features of 51 patients who had facial pain with migraine. The diagnosis was based on the criteria used by the International Headache Society and was also supported by the outcome and response to treatment after a mean of 2 years and 2 months. Of the 973 consecutive patients, 409 (42%) had symptoms of facial pain and/or head pain or pressure. Fifty-one (12%) had migraine. Of these, 39 (76%) had unilateral pain and, in 12 (24%), it was bilateral. The distribution affected the forehead and/or eye or cheek in 32 (63%) patients. Twenty-four (47%) had migraine isolated to the second division of the trigeminal nerve. Twelve per cent of patients attending a rhinology clinic with facial pain had migraine. Of particular interest were the 6% of patients with facial pain who had migraine confined to the second division of the trigeminal nerve. This entity is not widely recognized and has rarely been described in the literature.

The ORL-1 (NOP1) receptor ligand nociceptin/orphanin FQ (N/OFQ) inhibits neurogenic dural vasodilatation in the rat

The effects of the ORL-1 (NOP(1)) receptor ligand nociceptin (N/OFQ) and the nociceptin antagonists [Nphe(1)]N/OFQ-(1-13)-NH(2) (Nphe) and nocistatin (NST) on neurogenic dural vasodilatation (NDV) in the rat dura mater evoked by electrical stimulation of a closed cranial window were studied. The middle meningeal artery was visualised using intravital microscopy, and the vessel diameter analysed using a video dimension analyser. N/OFQ (1, 10, 100 nmol kg(-1); i.v., n=10) significantly and dose-dependently suppressed NDV maximally by 65% (P<0.01). Neither Nphe (100 nmol kg(-1); n=5) nor NST (100 nmol kg(-1); n=4) alone had an effect on NDV (P>0.05). Baseline vessel diameter was not significantly affected by application of N/OFQ, NST or Nphe. Application of the selective N/OFQ antagonist Nphe (10, 100 nmol kg(-1) i.v., n=8) dose-dependently and significantly (P<0.01) reversed the inhibition of NDV induced by application of N/OFQ (10 nmol kg(-1)). NST (10, 100 nmol kg(-1); n=7) failed to reverse the effects elicited by N/OFQ. Application of N/OFQ elicited a dose-dependent transient decrease in arterial blood pressure (P<0.01). Nphe dose-dependently reversed the cardiovascular effects induced by application of N/OFQ (10 nmol kg(-1)) (P<0.01),while NST did not alter the blood pressure reaction elicited by N/OFQ. The results show that N/OFQ inhibits NDV, an effect which is antagonised by Nphe, but not by NST. ORL-1 (NOP(1)) receptors located on trigeminal sensory fibres may be involved in the regulation of dural vessel diameter and hence may play a role in migraine pathophysiology.

Treatment of headache with botulinum toxin A--a review according to evidence-based medicine criteria

The aim of this review is to evaluate the studies available from reference systems and published congress contributions on the prophylactic treatment of idiopathic and cervicogenic headache with botulinum toxin A, and to classify these studies according to evidence-based medicine (EBM) criteria. The studies were analysed with respect to the study design, the number of patients enrolled, the efficacy parameters, and the significance of results. We used the following classification of EBM. I: randomized, controlled study with sufficient number of patients; II: well-designed, controlled study (or randomized, controlled study with insufficient number of patients, no exact diagnosis, missing data of botulinum toxin A dose); III: well-designed, descriptive study; IV: case reports, opinions of experts. For tension-type headache, two studies were found with negative evidence of I with respect to the primary endpoint. There are about as many positive as negative studies with evidence of II or III. For the therapy of migraine, one study with both negative and positive evidence of I, one in part positive study of II, and three positive studies classified as III are available. Two studies on cervicogenic headache with evidence of II and III are contradictory. In addition, we found several positive case reports. For patients with cluster headache, there are positive and negative case reports. We found one positive case report for the treatment of chronic paroxysmal hemicrania. As a result of this analysis, we consider no sufficient positive evidence for a general treatment of idiopathic and cervicogenic headaches with botulinum toxin A to date. Further studies are needed for a definite evaluation of subgroups with benefit from such treatment.

Nitric oxide synthase inhibitors can antagonize neurogenic and calcitonin gene-related peptide induced dilation of dural meningeal vessels

1. The detailed pathophysiology of migraine is beginning to be understood and is likely to involve activation of trigeminovascular afferents. 2. Clinically effective anti-migraine compounds are believed to have actions that include peripheral inhibition of calcitonin gene-related peptide (CGRP) release from trigeminal neurones, or preventing dural vessel dilation, or both. CGRP antagonists can block both neurogenic and CGRP-induced dural vessel dilation. 3. Nitric oxide (NO) can induce headache in migraine patients and often triggers a delayed migraine. The initial headache is thought to be caused via a direct action of the NO-cGMP pathway that causes vasodilation by vascular smooth muscle relaxation, while the delayed headache is likely to be a result of triggering trigeminovascular activation. Nitric oxide synthase (NOS) inhibitors are effective in the treatment of acute migraine. 4. The present studies used intravital microscopy to examine the effects of specific NOS inhibitors on neurogenic dural vasodilation (NDV) and CGRP-induced dilation. 5. The non-specific and neuronal NOS (nNOS) inhibitors were able to partially inhibit NDV, while the non-specific and endothelial NOS (eNOS) inhibitors were able to partially inhibit the CGRP induced dilation. 6. There was no effect of the inducible NOS (iNOS) inhibitor. 7. The data suggest that the delayed headache response triggered by NO donors in humans may be due, in part, to increased nNOS activity in the trigeminal system that causes CGRP release and dural vessel dilation. 8. Further, eNOS activity in the endothelium causes NO production and smooth muscle relaxation by direct activation of the NO-cGMP pathway, and may be involved in the initial headache response.

An immunocytochemical investigation of human trigeminal nucleus caudalis: CGRP, substance P and 5-HT1D-receptor immunoreactivities are expressed by trigeminal sensory fibres

5-HT1D (but not 5-HT1B)-receptor immunoreactivity (i.r.) can be detected on trigeminal fibres within the spinal trigeminal tract of the human brainstem. The present study used immunohistochemical and morphometric techniques to determine the proportions of trigeminal fibres expressing substance P, CGRP or 5-HT1D-receptor immunoreactivities. Co-localization studies between 5-HT1D-receptor and substance P- or CGRP-i.r. were also performed. Brainstem material was obtained with consent (four donors) and the total number of immunoreactive fibres within the trigeminal tract was estimated using random field sampling. A greater proportion of fibres (>1 microm diameter) expressed CGRP-i.r. (80 +/- 6%) compared with substance P-i.r. (46 +/- 7%) or 5-HT1D-receptor-i.r. (25 +/- 1%). 5-HT1D-receptor-i.r. was co-localized on some CGRP- or substance P-i.r. fibres. This suggests that 5-HT1D-receptors can regulate the release of CGRP and substance P and may be relevant to the clinical effectiveness of 5-HT1B/1D-receptor agonists in the treatment of migraine and other cranial pain syndromes.

Review of zolmitriptan and its clinical applications in migraine

Preclinical studies have shown that zolmitriptan is a selective serotonin 5-HT(1B/1D) receptor agonist (triptan). Randomised, placebo-controlled, double-blind trials in patients with migraine have shown that zolmitriptan has good efficacy measured using 2 h response and pain-free rates. Migraine-associated symptoms, including nausea, photophobia and phonophobia, are also improved with zolmitriptan. Oral zolmitriptan (2.5 and 5 mg) has an onset of action within 45 min and efficacy is sustained in most patients who respond at 2 h. The orally-disintegrating zolmitriptan tablet has the advantage that it may be taken immediately, without the need for additional fluids, any time a migraine headache occurs. Patients may benefit in terms of improved efficacy from the convenience of the disintegrating tablet, since there is evidence that taking triptan therapy as early as possible in an attack is advantageous. For similar reasons, as well as improved efficacy, a nasal spray formulation is in development. Zolmitriptan is effective in the treatment of migraine associated with menses and migraine with aura. There is no tachyphylaxis following repeated doses for multiple attacks of migraine over a prolonged period of time. Compared to placebo, the incidence of persistent migraine headache is reduced by zolmitriptan and recurrent migraine headache occurs less frequently. Zolmitriptan has also shown efficacy in the treatment of persistent and/or recurrent migraine headache. Comparative clinical studies have shown overall that zolmitriptan has similar or superior efficacy to sumatriptan in the treatment of migraine. Specifically, zolmitriptan 2.5 mg was significantly more effective than sumatriptan 25 or 50 mg according to a number of end points, including headache response at 2 h. Oral zolmitriptan is also effective in the acute treatment of cluster headache. Zolmitriptan is generally well tolerated, with most adverse events being mild-to-moderate, transient and resolving without intervention or the need for treatment withdrawal. The consistent efficacy in treating all types of migraine and the choice of available formulations make zolmitriptan acceptable to patients and a suitable first-line therapy for the treatment of migraine.

Adenosine A1 receptor agonists inhibit trigeminovascular nociceptive transmission

There is a considerable literature to suggest that adenosine A1 receptor agonists may have anti-nociceptive effects, and we sought to explore the role of adenosine A1 receptors in a model of trigeminovascular nociceptive transmission. Cats were anaesthetized (alpha-chloralose 60 mg/kg, intraperitoneally), and prepared for physiological monitoring. The superior sagittal sinus (SSS) was stimulated electrically, and linked units were recorded in the trigeminocervical complex. Post-stimulus histograms were constructed to analyse the responses and the effect of drug administration. Blood was sampled from the external jugular vein to determine levels of calcitonin gene-related peptide (CGRP) release before and after drug administration. Intravenous administration of the highly selective adenosine A1 receptor agonist, GR79236 (3-100 microg/kg) had a dose-dependent inhibitory effect on SSS-evoked trigeminal activity. The maximal effect (80 +/- 6% reduction in probability of firing) was seen at 100 microg/kg. The neuronal inhibitory effect of GR79236 could be inhibited by the selective adenosine A1 receptor antagonist DPCPX (300 microg/kg; P < 0.05). SSS stimulation increased cranial CGRP levels from 33 +/- 2 pmol/l (n = 6) to 64 +/- 3 pmol/l, an effect substantially reduced by pre-treatment with GR79236 (30 microg/kg; P < 0.01). The selective low efficacy adenosine A1 receptor agonist, GR190178 (30-1000 microg/kg i.v.), also inhibited SSS-evoked neuronal activity in a dose-dependent fashion. In this model of trigeminovascular nociception, adenosine A1 receptor activation leads to neuronal inhibition without concomitant vasoconstriction, suggesting a novel avenue for the treatment of migraine and cluster headache.

Binding properties of the novel, non-peptide CGRP receptor antagonist radioligand, [(3)H]BIBN4096BS

BIBN4096BS [[R-(R,(R*,S*)]-N-[2-[[5-amino-1-[[4-(4-pyridinyl)-1-piperazinyl]carbonyl] pentyl]amino]-1-[(3,5-dibromo-4-hydroxyphenyl)methyl]-2-oxoethyl]-4-(1,4-dihydro-2-oxo-3(2H)-quinazolinyl)-,1-Piperidinecarboxamide] is a selective calcitonin gene-related peptide (CGRP) receptor antagonist with a picomolar affinity to the CGRP receptor in human neuroblastoma SK-N-MC cells. Here, we describe the characterisation of the binding properties of the tritiated radioanalogue of BIBN4096BS in SK-N-MC cells as well as in marmoset tissue. [(3)H]BIBN4096BS showed reversible and saturable binding to SK-N-MC cells with a K(D) of 0.045 nM. In competition experiments, [3(H)]BIBN4096BS is concentration-dependently displaced from SK-N-MC cell membranes by BIBN4096BS as well as by the endogenous ligand CGRP and its analogues with the rank order of affinity BIBN4096BS>human alpha-CGRP=human beta-CGRP>[Cys(Et)(2,7)]human alpha-CGRP>adrenomedullin (high affinity site)=human alpha-CGRP-(8-37)=human beta-CGRP-(8-37)>calcitonin=amylin. In the marmoset cortex, saturable [(3)H]BIBN4096BS binding was observed with a K(D) of 0.077 nM. CGRP showed biphasic competition of [(3)H]BIBN4096BS binding, whilst BIBN4096BS monophasically displaced its radioanalogue with a K(i) of 0.099 nM. These data, using [(3)H]BIBN4096BS, confirm the high affinity of this novel antagonist for the primate CGRP receptor and demonstrate furthermore that this radioligand is a useful tool to study CGRP receptor pharmacology.

Study of an adenosine A1 receptor agonist on trigeminally evoked dural blood vessel dilation in the anaesthetized rat

The purpose of this study was to use intravital microscopy to determine the effect of a selective adenosine A1 receptor agonist, GR79236 (1, 3 and 10 microg/kg i.v.), on neurogenic dural blood vessel dilation in anaesthetized rats. Vasodilation was evoked either by electrical stimulation of perivascular trigeminal nerves or by intravenous CGRP. GR79236 (1-10 microg/kg i.v.) caused a dose-dependent inhibition of neurogenic vasodilation, but had no significant effect on dural vasodilation caused by CGRP. GR79236 (1-3 microg/kg i.v.) had no effect on basal dural vessel diameter, but caused transient dose-dependant bradycardia and hypotension. Bradycardia was more prolonged following 10 microg/kg i.v. GR79236. Pre-treatment with the adenosine A1 receptor antagonist DPCPX (1 mg/kg i.v.) prevented the inhibitory effect of GR79236 (10 microg/kg i.v.) on neurogenic vasodilation as well as GR79236-induced bradycardia and hypotension. These data suggest that the inhibition of neurogenic vasodilation by GR79236 is mediated via the activation of prejunctional adenosine A1 receptors. Provided the systemic cardiovascular effects could be limited, such a mechanism may offer a novel approach to migraine therapy.

Immunohistochemical localization of calcitonin receptor-like receptor and receptor activity-modifying proteins in the human cerebral vasculature

Calcitonin gene-related peptide and adrenomedullin belong to a structurally related neuropeptide family and are potent vasodilators expressed in the trigeminovascular system. The molecular identity of receptors for these proteins has only recently been elucidated. Central to functional binding of these neuropeptides is the G-protein-coupled receptor, the calcitonin receptor-like receptor (CRLR), whose cell surface expression and pharmacology is determined by coexpression of a receptor activity-modifying protein (RAMP). CRLR combined with RAMP binds calcitonin gene-related peptide with high affinity, whereas CRLR coexpression with RAMP2 or -3 confers high-affinity binding of adrenomedullin. The authors investigated the expression of these receptor components in human cerebral vasculature to further characterize neuropeptide receptor content and the potential functions of these receptors. Localization has been carried out using specific antisera raised against immunogenic peptide sequences that were subsequently applied using modern immunohistochemical techniques and confocal microscopy. The results are the first to show the presence of these receptor component proteins in human middle meningeal, middle cerebral, pial, and superficial temporal vessels, and confirm that both calcitonin gene-related peptide and adrenomedullin receptors may arise from the coassembly of RAMPs with CRLR in these vessel types. These novel data advance the understanding of the molecular function of the trigeminovascular system, its potential role in vascular headache disorders such as migraine, and may lead to possible ways in which future synthetic ligands may be applied to manage these disorders.

Receptor activity-modifying protein 1 determines the species selectivity of non-peptide CGRP receptor antagonists

The heterodimeric CGRP receptor requires co-expression of calcitonin receptor-like receptor (CRLR) and an accessory protein called receptor activity-modifying protein (RAMP) 1 (McLatchie, L. M., Fraser, N. J., Main, M. J., Wise, A., Brown, J., Thompson, N., Solari, R., Lee, M. G., and Foord, S. M. (1998) Nature 393, 333-339). Several non-peptide CGRP receptor antagonists have been shown to exhibit marked species selectivity, with >100-fold higher affinities for the human CGRP receptor than for receptors from other species (Doods, H., Hallermayer, G., Wu, D., Entzeroth, M., Rudolf, K., Engel, W., and Eberlein, W. (2000) Br. J. Pharmacol. 129, 420-423; Edvinsson, L., Sams, A., Jansen-Olesen, I., Tajti, J., Kane, S. A., Rutledge, R. Z., Koblan, K. S., Hill, R. G., and Longmore, J. (2001) Eur. J. Pharmacol. 415, 39-44). This observation provided an opportunity to map the determinants of receptor affinity exhibited by BIBN4096BS and the truncated analogs, Compounds 1 and 2. All three compounds exhibited higher affinity for the human receptor, human CRLR/human RAMP1, than for the rat receptor, rat CRLR/rat RAMP1. We have now demonstrated that this species selectivity was directed exclusively by RAMP1. By generating recombinant human/rat CRLR/RAMP1 receptors, we demonstrated that co-expression of human CRLR with rat RAMP1 produced rat receptor pharmacology, and vice versa. Moreover, with rat/human RAMP1 chimeras and site-directed mutants, we have identified a single amino acid at position 74 of RAMP1 that modulates the affinity of small molecule antagonists for CRLR/RAMP1. Replacement of lysine 74 in rat RAMP1 with tryptophan (the homologous amino acid in the human receptor) resulted in a > or =100-fold increase in antagonist affinities, similar to the K(i) values for the human receptor. These observations suggest that important determinants of small molecule antagonist affinity for the CGRP receptor reside within the extracellular region of RAMP1 and provide evidence that this receptor accessory protein may participate in antagonist binding.

Increase in meningeal blood flow by nitric oxide--interaction with calcitonin gene-related peptide receptor and prostaglandin synthesis inhibition

This study addresses possible interactions of the vasodilators nitric oxide (NO), calcitonin gene-related peptide (CGRP) and prostaglandins, which may be implicated in the generation of vascular headaches. Local application of the NO donator diethylamine-NONOate (NONOate) to the exposed dura mater encephali of the rat caused dose-dependent increases in meningeal blood flow recorded by laser Doppler flowmetry. Pre-application of the CGRP receptor antagonist CGRP8-37 significantly attenuated the evoked blood flow increases, while the cyclooxygenase inhibitors acetylsalicylic acid and metamizol were only marginally effective. Stimulation of rat dura mater with NONOate in vitro caused increases in CGRP release. NADPH-diaphorase activity indicating NO production was restricted to the endothelium of dural arterial vessels. We conclude that increases in meningeal blood flow caused by NO depend partly on the release and vasodilatory action of CGRP from dural afferents, while prostaglandins are not significantly involved.

New insights into the molecular actions of serotonergic antimigraine drugs

Migraine is a painful and debilitating neurological disorder that affects approximately 10% of the adult population in Western countries. Sensitization and activation of the trigeminal ganglia nerves that innervate the meningeal blood vessels is believed to play an important role in the initiation and maintenance of migraine pain. In this capacity, release of the neuropeptide calcitonin gene-related peptide (CGRP) and the resultant neurogenic inflammation is thought to underlie the pathophysiology of migraine. Largely due to the success of the serotonin Type 1 migraine drugs such as sumatriptan, migraine pathology and therapy has become a focus of intensive clinical and physiological research during the past decade. The effectiveness of these drugs is thought to be due to their ability to block the stimulated secretion of neuropeptides from trigeminal nerves to break the vicious nociceptive cycle of migraine. A component of this nociceptive cycle involves activation of mitogen-activated protein kinase signaling pathways. Indeed, activation of mitogen-activated protein kinase pathways can increase CGRP neuropeptide synthesis and secretion. Recently, the serotonin Type 1 agonists have been shown to cause a prolonged increase in intracellular Ca(2+) in trigeminal ganglia neurons and an increased phosphatase activity that can repress stimulated CGRP secretion and transcription. Identification of molecular signaling events in migraine pathology and therapy has provided new insight into the pharmacology and signaling mechanisms of sumatriptan and related drugs, and may provide the foundation for development of novel treatments for migraine.

Diagnosis and treatment of migraine

Despite recent advances in understanding the pathophysiology and treatment of migraine, considerable uncertainty remains surrounding the diagnosis and treatment of this disorder. This uncertainty is reflected in studies that show both underdiagnosis and undertreatment of migraine. While the diagnosis can be assisted by criteria from the International Headache Society, other approaches may be useful in clinical practice. Treatment of migraine must be based on an individualized patient strategy that integrates education, patient participation, and effective use of pharmacological interventions. Many patients, despite self-treatment with simple analgesics, continue to suffer considerable disability associated with their migraines. Triptans, which are more effective at relieving migraine symptoms and maintaining patient function than are nonspecific therapies, are used in only a minority of patients with migraine. Treatment goals of rapid, complete relief with no recurrence and minimal adverse effects can be achieved when effective therapy is matched to individual patient goals. For prophylaxis, anticonvulsant drugs emerging as effective options are being added to the armamentarium with traditional compounds such as tricyclic antidepressants and beta-blockers.

Efficacy of the non-peptide CGRP receptor antagonist BIBN4096BS in blocking CGRP-induced dilations in human and bovine cerebral arteries: potential implications in acute migraine treatment

Calcitonin gene-related peptide (CGRP) is a potent vasodilator in brain vessels and it has been implicated in the pathogenesis of migraine headache. Blocking post-junctional CGRP receptors, mediators of trigeminal-induced vasodilation, has been suggested as a potential antimigraine strategy. In this study, we tested the ability of a new non-peptide CGRP receptor antagonist, BIBN4096BS, to inhibit the CGRP-induced dilation in human and/or bovine brain vessels and compared it to that of the antagonist alpha-CGRP(8-37). BIBN4096BS and alpha-CGRP(8-37) both blocked the alpha-CGRP-induced dilation in bovine middle artery segments with respective potency (pK(B) values) of 6.3 and 7.8. In human pial vessels, BIBN4096BS was particularly potent. When tested at 10(-14)-10(-9) M concentrations, it induced a rightward shift in the alpha-CGRP concentration-response curve and yielded a biphasic Schild plot suggesting interaction with more than one receptor population, as was also indicated by the significant best fit of the alpha-CGRP-induced dilation in human brain vessels with a two receptor site interaction. Schild plot analysis in the linear portion of the BIBN4096BS inhibition curve revealed interaction with one high affinity site (pA(2) value approximately 14). In bovine vessels, both alpha-CGRP(8-37) and BIBN4096BS concentration-dependently reversed a pre-established CGRP-induced dilation ( approximately 59 and 85%, respectively), BIBN4096BS being approximately tenfold more potent than alpha-CGRP(8-37) (respective pIC(50) values of 7.5 and 6.75). In human middle cerebral and middle meningeal arteries, BIBN4096BS reversed the alpha-CGRP-induced dilation (> or =70%) by interaction with two different receptor populations: it exhibited a high affinity for one population (pIC(50) value approximately 13) and a lower affinity for the other (pIC(50) value approximately 8). The present data demonstrate that BIBN4096BS is a very potent antagonist that could, depending on its bioavailability and in vivo affinity, be of potential benefit in the acute treatment of migraine headache by blocking and/or reversing the CGRP-mediated dilation of intracranial vessels induced by activation of trigeminovascular afferents.

Etiology and pathogenesis of cluster headache

This last decade has seen remarkable progress made toward unraveling the mystery of primary headache disorders like migraine and cluster. The vascular theory has been superseded by recognition that neurovascular phenomena seem to be the permissive and triggering factors in migraine and cluster headache. This understanding has been achieved through new imaging modalities such as positron emission tomography and functional magnetic resonance imaging. Prior to these imaging techniques it was impossible to study the primary headache disorders because these had no structural basis. There is now an increasing body of evidence that the brain is involved primarily in cluster and migraine and that vessel dilatation is an epiphenomenon.

CGRP may play a causative role in migraine

Calcitonin gene-related peptide (CGRP) has been detected in increased amounts in external jugular venous blood during migraine attacks. However, it is unknown whether this is secondary to migraine or whether CGRP may cause headache. In a double-blind crossover study, the effect of human alphaCGRP (2 microg/min) or placebo infused intravenously for 20 min was studied in 12 patients suffering from migraine without aura. Headache intensity was scored on a scale from 0 to 10. Two patients were excluded due to severe hypotension and one because she had an infection. In the first hour median peak headache score was 1.0 in the halphaCGRP group vs. 0 in the placebo group (P < 0.01). During the following 11 h all patients experienced headaches after halphaCGRP vs. one patient after placebo (P = 0.0004). The median maximal headache score was 4 after CGRP and 0 after placebo (P = 0.006). In three patients after halphaCGRP, but in no patients after placebo, the delayed headache fulfilled the IHS criteria for migraine without aura. As intravenous administration of halphaCGRP causes headache and migraine in migraineurs, our study suggests that the increase in CGRP observed during spontaneous migraine attacks may play a causative role.

Calcitonin gene-related peptide (CGRP) and the pathophysiology of headache: therapeutic implications

Cerebral blood vessels are innervated by sensory nerves that store several neurotransmitters. In primary headaches, there is a clear association between head pain and the release of the neuropeptide calcitonin gene-related peptide (CGRP). Furthermore, when triptan antimigraine agents are administered, headache subsides and the neuropeptide release normalises, in part via a presynaptic effect. The central role of CGRP in primary headaches has led to the search for suitable antagonists of the receptors for this neuropeptide, which it is hoped will have less cardiovascular adverse effects than the triptans. Recently, the initial pharmacological profile of such a group of compounds has been disclosed. These compounds are small molecules with high selectivity for human CGRP receptors. Hypothetically, these agents will be efficacious in the relief of migraine headaches via blockade of the effects of CGRP.

[Recurrent episodes of focal cerebral ischemia in a female patient with mitral valve prolapse and migraine headache]

Migraine is episodic, paroxysmal disorder where the headache represents the central symptom and is followed with different combinations of neurologic, gastrointestinal and vegetative changes. Not until the diagnostic procedures were developed, ischemic lesions were verified even in the patients with ordinary migraine. This is a report of a patient with migraine headache, followed twice by verified episodes of temporary ischemic attacks and verified focal ischemic lesion of cerebral parenchyma. The mitral valve prolapse was also detected. This all imposed the administration of combined prophylactic antimigrainous and anticoagulant therapy as an imperative because of the risk of the development of repeated ischemia of cerebral tissue. This association also confirmed an opinion that migraine is a wider disorder with the dominant dysfunction of limbic system.

Sensory nerves in man and their role in primary headaches

The sensory innervation of intracranial vessels originate in the trigeminal ganglion and comprise the following signal substances; calcitonin gene-related peptide (CGRP), substance P, neurokinin A, pituitary adenylate cyclase activating peptide (PACAP) and nitric oxide (NO). Studies in patients have revealed a clear association between head pain and the release of CGRP. In cluster headache and in a case of chronic paroxysmal headache there is in addition release of vasoactive intestinal peptide (VIP), which was associated with the facial symptoms (nasal congestion, rhinorrhea). In parallel with triptan administration, acting via 5-HT(1B/1D) receptors, head pain subside and neuropeptide release normalise. These data show the involvement of sensory and parasympathetic mechanisms in the pathophysiology of primary headaches.

Characterization of the prostanoid receptor types involved in mediating calcitonin gene-related peptide release from cultured rat trigeminal neurones

1. Prostaglandins and the vasodilator neuropeptide, calcitonin-gene related peptide (CGRP), have both been implicated in the pathogenesis of migraine headache. We have used primary cultures of adult rat trigeminal neurones to examine the effects of prostanoids on CGRP release in vitro. 2. CGRP release was stimulated by prostaglandin E2 (PGE2) and the IP receptor agonist, carbaprostacyclin (cPGI2). These responses were extracellular calcium-dependent, and the PGE2-induced CGRP release was unaltered by inhibition of nitric oxide synthase (NOS), ATP receptor blockade, or the addition of adenosine deaminase. 3. Increases in CGRP levels were also observed in response to prostaglandin D2 (PGD2), and the EP2 receptor selective agonist, butaprost. No increases in CGRP release were observed in response to prostaglandin F2alpha (PGF2alpha) or the TP receptor selective agonist, U46619, or the EP3 receptor selective agonist, GR63799X. 4. The selective DP receptor antagonist, BWA868C, antagonized the PGD2-, but not PGE2- or cPGI2-induced release. Furthermore, the EP1 selective antagonist, ZM325802, failed to antagonize the PGE2-induced CGRP release from these cells. 5. These data indicate that activation of DP, EP and IP receptors can each cause CGRP release from trigeminal neurones, and suggest that the predominant EP receptor subtype involved may be the EP2 receptor. Together with evidence that the cyclo-oxygenase inhibitor, aspirin, particularly when administered intravenously is effective in treating acute migraine, these findings further suggest a role for prostaglandins in migraine pathophysiology.

GABA receptors modulate trigeminovascular nociceptive neurotransmission in the trigeminocervical complex

1. GABA (gamma-aminobutyric acid) receptors involved in craniovascular nociceptive pathways were characterised by in vivo microiontophoresis of GABA receptor agonists and antagonists onto neurones in the trigeminocervical complex of the cat. 2. Extracellular recordings were made from neurones in the trigeminocervical complex activated by supramaximal electrical stimulation of superior sagittal sinus, which were subsequently stimulated with L-glutamate. 3. Cell firing evoked by microiontophoretic application of L-glutamate (n=30) was reversibly inhibited by GABA in every cell tested (n=19), the GABA(A) agonist muscimol (n=10) in all cells tested, or both where tested, but not by iontophoresis of either sodium or chloride ions at comparable ejection currents. Inhibited cells received wide dynamic range (WDR) or nociceptive specific input from cutaneous receptive fields on the face or forepaws. 4. The inhibition of trigeminal neurones by GABA or muscimol could be antagonized by the GABA(A) antagonist N-methylbicuculline, 1(S),9(R) in all but two cells tested (n=16), but not by the GABA(B) antagonist 2-hydroxysaclofen (n=11). 5. R(-)-baclofen, a GABA(B) agonist, inhibited the firing of three out of seven cells activated by L-glutamate. Where tested, this inhibition could be antagonized by 2-hydroxysaclofen. These baclofen-inhibited cells were characterized as having low threshold mechanoreceptor/WDR input. 6. GABA thus appears to modulate nociceptive input to the trigeminocervical complex mainly through GABA(A) receptors. GABA(A) receptors may therefore provide a target for the development of new therapeutic agents for primary headache disorders.