Assessment of Bone Mineral Density Over 1 Year in a Cross-Sectional Cohort of Migraine Patients Receiving Anti-CGRP Monoclonal Antibodies

BACKGROUND

Calcitonin gene-related peptide (CGRP), implicated in migraine pain, also possesses bone anabolic properties, which leads to the possibility that monoclonal antibodies targeting CGRP (anti-CGRPs) might increase the risk of bone density abnormalities.

OBJECTIVE

The objective of this study was to explore bone mineral density abnormalities in a cohort of migraine patients treated with anti-CGRPs.

METHODS

This was a single-center, cross-sectional, cohort study including migraine patients who underwent a densitometry assessment during anti-CGRP treatment. We assessed the frequency of osteopenia or osteoporosis (OSTEO+ status), defined as a bone mineral density T-score of -1 to -2.5, and <-2.5 standard deviations from the young female adult mean, respectively. Additionally, the association of OSTEO+ status with anti-CGRP treatment duration and primary osteoporosis' risk factors was investigated using logistic regression models.

RESULTS

Data from 51 patients (43 female, mean age 46 ± 13.9 years) were evaluated. The mean duration of anti-CGRP treatment was 15.7 (±11.8) months. Twenty-seven patients (53%) were OSTEO+ (n = 22 osteopenia; n = 5 osteoporosis). In the final model, menopause [odds ratio 11.641 (95% confidence interval 1.486-91.197), p = 0.019] and anti-seizure drug use [odds ratio 12.825 (95% confidence interval 1.162-141.569), p = 0.037] were associated with OSTEO+ status.

CONCLUSIONS

In our cohort of migraine patients, no evidence of an association between anti-CGRP treatment duration and an increasing risk of bone mineral density abnormalities was found. However, these findings are preliminary and necessitate further longitudinal research with larger cohorts and extended follow-up to be validated.

Migraine headache pathophysiology

In both episodic and chronic migraine, headache is the most disabling symptom that requires medical care. The migraine headache is the most well-studied symptom of migraine pathophysiology. The trigeminal system and the central processing of sensory information transmitted by the trigeminal system are of considerable importance in the pathophysiology of migraine headache. Glutamate is the main neurotransmitter that drives activation of the ascending trigeminal and trigeminothalamic pathways. The neuropeptide, calcitonin gene-related peptide (CGRP) that is released by the trigeminal system, plays a crucial role in the neurobiology of headache. Peripheral and central sensitizations associated with trigeminal sensory processing are neurobiologic states that contribute to both the development of headache during a migraine attack and the maintenance of chronic migraine.

CGRP and CGRP-receptor as targets of migraine therapy: Brain Prize-2021

BACKGROUND

Migraine is a highly prevalent primary headache with an unclear pathomechanism. During the last 40 years numerous hypotheses have arisen, among them the theory of the trigeminovascular system is the primary one. It serves as a skeleton in successful preclinical studies and in the development of effective therapeutic options for migraine headache.

OBJECTIVE

The Brain Prize (awarded annually by the Lundbeck Foundation) is the most prestigious tribute in neuroscience. The winners in 2021 were Lars Edvinsson, Peter Goadsby, Michael Moskowitz and Jes Olesen. They are the fathers of the migraine pathomechanism which led to revolutionary new treatments. This review summarizes their landmark findings.

METHODS

Data related to this topic were reviewed from PubMed records published between 1979 and May 2021. Searches were based on preclinical and clinical studies in the covered field. The findings were listed in chronological order. From a therapeutic perspective, only randomized controlled trials and meta-analysis were discussed.

RESULTS

The calcitonin gene-related peptide-related pathogenesis of migraine is based on the activation of the trigeminovascular system. The therapeutic triad for migraine is triptans, gepants and calcitonin gene-related peptide-targeted monoclonal antibodies.

CONCLUSION

In the past 40 years, the systematic work of leading headache scientists has resulted in robust theoretical and therapeutic knowledge in the preclinical and clinical study of migraine.

Pathophysiology of Migraine: A Disorder of Sensory Processing

Plaguing humans for more than two millennia, manifest on every continent studied, and with more than one billion patients having an attack in any year, migraine stands as the sixth most common cause of disability on the planet. The pathophysiology of migraine has emerged from a historical consideration of the "humors" through mid-20th century distraction of the now defunct Vascular Theory to a clear place as a neurological disorder. It could be said there are three questions: why, how, and when? Why: migraine is largely accepted to be an inherited tendency for the brain to lose control of its inputs. How: the now classical trigeminal durovascular afferent pathway has been explored in laboratory and clinic; interrogated with immunohistochemistry to functional brain imaging to offer a roadmap of the attack. When: migraine attacks emerge due to a disorder of brain sensory processing that itself likely cycles, influenced by genetics and the environment. In the first, premonitory, phase that precedes headache, brain stem and diencephalic systems modulating afferent signals, light-photophobia or sound-phonophobia, begin to dysfunction and eventually to evolve to the pain phase and with time the resolution or postdromal phase. Understanding the biology of migraine through careful bench-based research has led to major classes of therapeutics being identified: triptans, serotonin 5-HT1B/1D receptor agonists; gepants, calcitonin gene-related peptide (CGRP) receptor antagonists; ditans, 5-HT1F receptor agonists, CGRP mechanisms monoclonal antibodies; and glurants, mGlu5 modulators; with the promise of more to come. Investment in understanding migraine has been very successful and leaves us at a new dawn, able to transform its impact on a global scale, as well as understand fundamental aspects of human biology.

Current Understanding on Pain Mechanism in Migraine and Cluster Headache

CONTEXT

Migraine and cluster headache are undoubtedly painful conditions. The respective pathogenesis of these two conditions is incompletely understood. In both cases, the treatments used have largely been empirical and have relied to a much lesser extent on our understanding of the mechanisms causing pain. We hereby review the pain mechanisms in migraine and cluster headache, two of the commonest primary headache disorders.

EVIDENCE ACQUISITION

A review of the English literature was conducted by searching PubMed for studies on pain mechanism in migraine and cluster headache. We entered [migraine] and [pain mechanism] in Pubmed and 488 articles were obtained. Articles were then included according to their relevance to the topic. Similarly, [cluster headache] and [pain mechanism] revealed 79 search results.

RESULTS

There is evidence that the trigeminovascular system and neurogenic inflammation play important roles, together with certain areas of the brain, leading to these conditions being termed 'neurovascular headaches'. Functional imaging findings suggest a possible role of the dorsolateral pons in generating migraine attacks while the role of the hypothalamus in cluster headache is more firmly established.

CONCLUSIONS

Migraine and cluster headache have complex pathophysiologies. The exact mechanism causing pain in both conditions is incompletely understood and more research needs to be undertaken in this area.

Migraine and neuropeptides

Migraine is a common disabling neurovascular primary headache disorder. The pathomechanism is not clear, but extensive preclinical and clinical studies are ongoing. The structural basis of the leading hypothesis is the trigeminovascular system, which includes the trigeminal ganglion, the meningeal vasculature, and the distinct nuclei of the brainstem, the thalamus and the somatosensory cortex. This review covers the effects of sensory (calcitonin gene-related peptide, pituitary adenylate cyclase-activating polypeptide and substance P), sympathetic (neuropeptide Y) and parasympathetic (vasoactive intestinal peptide) migraine-related neuropeptides and the functions of somatostatin, nociceptin and the orexins in the trigeminovascular system. These neuropeptides may take part in neurogenic inflammation (plasma protein extravasation and vasodilatation) of the intracranial vasculature and peripheral and central sensitization of the trigeminal system. The results of human clinical studies are discussed with regard to the alterations in these neuropeptides in the plasma, saliva and cerebrospinal fluid during or between migraine attacks, and the therapeutic possibilities involving migraine-related neuropeptides in the acute and prophylactic treatment of migraine headache are surveyed.

Headache and sleep: shared pathophysiological mechanisms

OBJECTIVE

The objective of the current article is to review the shared pathophysiological mechanisms which may underlie the clinical association between headaches and sleep disorders.

BACKGROUND

The association between sleep and headache is well documented in terms of clinical phenotypes. Disrupted sleep-wake patterns appear to predispose individuals to headache attacks and increase the risk of chronification, while sleep is one of the longest established abortive strategies. In agreement, narcoleptic patients show an increased prevalence of migraine compared to the general population and specific familial sleep disorders have been identified to be comorbid with migraine with aura.

CONCLUSION

The pathophysiology and pharmacology of headache and sleep disorders involves an array of neural networks which likely underlie their shared clinical association. While it is difficult to differentiate between cause and effect, or simply a spurious relationship the striking brainstem, hypothalamic and thalamic convergence would suggest a bidirectional influence.

Pharmacological characterization of VIP and PACAP receptors in the human meningeal and coronary artery

Objective: We pharmacologically characterized pituitary adenylate cyclase–activating polypeptides (PACAPs), vasoactive intestinal peptide (VIP) and the VPAC1, VPAC2 and PAC1 receptors in human meningeal (for their role in migraine) and coronary (for potential side effects) arteries.

Methods: Concentration response curves to PACAP38, PACAP27, VIP and the VPAC1 receptor agonist ([Lys15,Arg16,Leu27]-VIP[1-7]-GRF[8-27]) were constructed in the absence or presence of the PAC1 receptor antagonist PACAP6-38 or the VPAC1 receptor antagonist, PG97269. mRNA expression was measured using qPCR.

Results: PACAP38 was less potent than VIP in both arteries. Both peptides had lower potency and efficacy in meningeal than in coronary arteries, while mRNA expression of VPAC1 receptor was more pronounced in meningeal arteries. PACAP6-38 reduced the Emax of PACAP27, while PG97269 right-shifted the VIP-induced relaxation curve only in the coronary arteries.

Conclusion: The direct vasodilatory effect of VIP and PACAP might be less relevant than the central effect of this compound in migraine pathogenesis.

Animal models of headache: from bedside to bench and back to bedside

In recent years bench-based studies have greatly enhanced our understanding of headache pathophysiology, while facilitating the development of new headache medicines. At present, established animal models of headache utilize activation of pain-producing cranial structures, which for a complex syndrome, such as migraine, leaves many dimensions of the syndrome unstudied. The focus on modeling the central nociceptive mechanisms and the complexity of sensory phenomena that accompany migraine may offer new approaches for the development of new therapeutics. Given the complexity of the primary headaches, multiple approaches and techniques need to be employed. As an example, recently a model for trigeminal autonomic cephalalgias has been tested successfully, while by contrast, a satisfactory model of tension-type headache has been elusive. Moreover, although useful in many regards, migraine models are yet to provide a more complete picture of the disorder.

Therapeutic potential of novel glutamate receptor antagonists in migraine

BACKGROUND

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

OBJECTIVE

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

METHODS

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

RESULTS/CONCLUSIONS

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

The in vivo Effect of VIP, PACAP-38 and PACAP-27 and mRNA Expression of Their Receptors in Rat Middle Meningeal Artery

The parasympathetic nervous system is probably involved in migraine pathogenesis. Its activation releases a mixture of signalling molecules including vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP), which subsequently stimulate VPAC1, VPAC2 and PAC1 receptors. The objective of the present study was to investigate the in vivo effect of VIP, PACAP-27, PACAP-38, the selective VPAC1 agonist ([Lys15, Arg16, Leu27]-VIP(1–7)-GRF(8–27)) and a PAC1 agonist, maxadilan on rat middle meningeal artery (MMA) diameter using the closed cranial window model. Selective antagonists were used for further characterization of the responses. Reverse transcriptase-polymerase chain reaction experiments were also conducted to determine expression of mRNA of PACAP receptors in the MMA. The results showed that VIP, PACAP-38, PACAP-27 and the VPAC1 specific agonist evoked significant dilations with the rank order of potency; VIP = PACAP-38 > PACAP-27 = [Lys15, Arg16, Leu27]-VIP(1–7)-GRF(8–27). Significant inhibition of dilation was only observed for the VPAC1 antagonist PG97–269 on PACAP-38-induced dilation of MMA. The VPAC2 antagonist PG99–465 and PAC1 antagonist PACAP(6–38) did not significantly block VIP- or PACAP-induced dilation. Expression of mRNA of all three receptors was detected in the MMA. In conclusion, the VPAC1 receptor seems to be predominant in mediating MMA dilation. A selective VPAC1 antagonist may be a candidate molecule in the treatment of migraine headache.

Involvement of capsaicin-sensitive afferent nerves in the proteinase-activated receptor 2-mediated vasodilatation in the rat dura mater

Neurogenic inflammation of the dura mater encephali has been suggested to contribute to the mechanisms of meningeal nociception and blood flow regulation. Recent findings demonstrated that the rat dura mater is innervated by trigeminal capsaicin-sensitive peptidergic nociceptive afferent nerves which mediate meningeal vascular responses through activation of the transient receptor potential vanilloid type 1 (TRPV1) receptor. The present work explored the functional significance of the capsaicin-sensitive subpopulation of dural afferent nerves via their contribution to the meningeal vascular responses evoked through activation of the proteinase-activated receptor 2 (PAR-2). The vascular responses of the dura mater were studied by laser Doppler flowmetry in a rat open cranial window preparation. Topical applications of trypsin, a PAR-2-activator, or Ser-Leu-Ile-Gly-Arg-Leu-amide (SLIGRL-NH(2)), a selective PAR-2 agonist peptide, resulted in dose-dependent increases in meningeal blood flow. The SLIGRL-NH(2)-induced vasodilatation was significantly reduced following capsaicin-sensitive afferent nerve defunctionalization by prior systemic capsaicin treatment and by pretreatment of the dura mater with the calcitonin gene-related peptide (CGRP) receptor antagonist CGRP(8-37). Nomega-nitro-L-arginine methyl ester hydrochloride (L-NAME) an unspecific inhibitor of nitric oxide (NO) production, but not 1-(2-trifluoromethylphenyl) imidazole (TRIM), a neuronal NO synthase inhibitor, also inhibited the vasodilator response to SLIGRL-NH(2). The vasodilator responses elicited by very low concentrations of capsaicin (10 nM) were significantly enhanced by prior application of SLIGRL-NH(2). The present findings demonstrate that activation of the PAR-2 localized on capsaicin-sensitive trigeminal nociceptive afferent nerves induces vasodilatation in the dural vascular bed by mechanisms involving NO and CGRP release. The results indicate that the PAR-2-mediated activation and sensitization of meningeal capsaicin-sensitive C-fiber nociceptors may be significantly implicated in the pathophysiology of headaches.

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

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

New Migraine and Pain Research

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

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

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

The relationship between neuropeptide Y expression and headache in pituitary tumours

Patients with pituitary tumours often present with disabling headache but there is no clear relationship between tumour size and headache. Neuropeptide Y (NPY) has been identified in pituitary tumours and may serve as a biochemical marker of the propensity for headache. Using immunohistochemical techniques we examined 27 consecutive pituitary adenoma specimens for NPY (including one normal postmortem control anterior pituitary specimen). A separate observer divided the patients into two groups: headache and non-headache. The association between the presence of NPY and headache was tested. NPY positive immunoreactivity was seen in 13 tumour specimens (50%, 13 of 26 pituitary tumour specimens), characterized by cytoplasmic and nuclear staining patterns. There was no significant association between the presence of NPY and headache (chi(2) = 0.9, P = 0.34). We did not observe NPY in the normal anterior pituitary control specimen. NPY was present in four of five (80%) growth hormone-secreting tumours and two of two (100%) prolactinomas, compared with four of 11 (36%) non-functioning adenomas. The mechanism of many pituitary tumour-associated headaches remains undetermined. The significance of NPY positivity in pituitary tumours is unknown, although the results of this study may implicate this peptide in the control of somatotroph and lactotroph activity. Our data do not support a clear role for NPY pituitary tumour-associated headache.

A human experimental capsaicin model for trigeminal sensitization. Gender-specific differences

Migraine is much more common in women (18%) than in men (6%). Menstrual migraine in female migraineurs also varies from 7 to 19%. The main goals of the present study were (1) to investigate gender specific differences in an experimental capsaicin model of trigeminal sensitization (a proposed mechanism of migraine) and (2) to explore the influence of menstrual cycle phases. Twenty-eight healthy female and male volunteers were studied. Capsaicin (100 microg/0.1 ml) was injected intradermally to the forehead. Pain intensity and distribution together with the visual flare and allodynic area (central sensitization) were assessed for females (during their menstrual and luteal phases) and for males. Pain area significantly changed across the menstrual cycle with 19.2+/-2.0 cm x min at menstrual and 16.4+/-0.9 cm x min at luteal phase (P<0.001). The area was significantly larger in both phases for females compared to males (14.2+/-1.3 cm x min, P<0.0001). Flare area at menstrual phase (69.2+/-4.2 cm(2)) was significantly (P<0.0001) larger than luteal phase (58.6+/-2.1 cm(2)). Females, in both phases, showed larger flare area compared to males (44.9+/-3.6 cm(2), P<0.0001). Area of brush-evoked allodynia was also larger at the menstrual phase compared to the luteal phase (P<0.0001) and males (P<0.0001). A significant difference was found in the capsaicin-evoked pain distribution with a greater response in menstrual phase compared to the luteal phase (P<0.01) and men (P<0.0001). Capsaicin induced trigeminal sensitization and evoked gender specific sensory and vaso-motor responses, with menstruating females generally showing the strongest manifestations. The model may be further applied to explore mechanisms of human trigeminal sensitization.

Orexin 1 Receptor Activation Attenuates Neurogenic Dural Vasodilation in an Animal Model of Trigeminovascular Nociception

The pathophysiology underlying the pulsating quality of the pain of a migraine attack is not fully understood, although trigeminal vascular afferents containing the sensory neuropeptide calcitonin gene-related peptide (CGRP) must have a role. Antimigraine drugs, such as triptans, serotonin 5-hydroxytryptamine(1B/1D) receptor agonists, reproducibly block neurogenic vasodilation associated with CGRP release. We examined the effects of the hypothalamic neuropeptides orexin A and orexin B on neurogenic dural vasodilation, dissecting out the receptor pharmacology with the novel orexin 1 (OX1) receptor antagonist N-(2-methyl-6-benzoxazolyl)-N''-1,5-naphthyridin-4-yl urea (SB-334867). Electrical stimulation of dural afferents (50-300 microA) resulted in reproducible dural vasodilation of 136 +/- 9%. Orexin A 30 microg kg(-1), but not 3 and 10 microg kg(-1), inhibited the dilation brought about by electrical stimulation over 60 min and maximally after 15 min by 60% (t7= 7.138; P < 0.001; n = 8). This response was reversed by pretreatment with the OX1 receptor antagonist SB-334867. Addition of CGRP(8-37) at the point of maximal effect of orexin A produced a further significant decrease in neurogenic dural vasodilation compared with orexin A only. CGRP administration (1 microg kg(-1)) produced a reproducible dural blood vessel dilation of 145 +/- 7% that was not inhibited by intravenous administration of orexin A (30 microg kg(-1)). Orexin B had no significant effect even at the highest dose. The current study demonstrates that orexin A is able to inhibit neurogenic dural vasodilation via activation of the OX1 receptor, resulting in inhibition of prejunctional release of CGRP from trigeminal neurons.

Presence and function of the calcitonin gene-related peptide receptor on rat pial arteries investigated in vitro and in vivo

Calcitonin gene-related peptide (CGRP) and related peptides may be involved in migraine pathogenesis. To understand their vasomotor role in the cerebral circulation, we performed two studies, a pressurized arteriography study of the middle cerebral artery (MCA) and a genuine closed cranial window (gCCW) in vivo study. Using the pressurized arteriography model rat MCAs were mounted on micropipettes, pressurized to 85 mmHg and luminally perfused. The diameter responses to luminally and abluminally applied rat-alphaCGRP, rat-betaCGRP, amylin and adrenomedullin were compared with the resting diameter. Only abluminally applied CGRP induced dilation of the cerebral arteries; E(max) for alphaCGRP and betaCGRP were 35 +/- 0.5% and 10.8 +/- 0.2%. These responses were blocked by CGRP(8-37). The gCCW model allowed videomicroscopic visualization of the pial vessels in anaesthetized rats. Changes in vessel diameter to intravenously administered alphaCGRP and betaCGRP were compared with pre-infusion baseline. Intravenous infusion of alphaCGRP and betaCGRP in the highest dose induced dilation of the cerebral cortical pial arteries/arterioles of 40.3 +/- 7.5% and 49.1 +/- 8.4%, respectively. However, this was probably secondary to a decrease in blood pressure of 44.8 +/- 3.3 mmHg and 49.2 +/- 3.3 mmHg. Our results suggest that CGRP receptors are probably functional on the smooth muscle cells and not on the endothelium of rat cerebral arteries.

Migraine Pathophysiology

A combination of basic science and human physiology, particularly functional neuroimaging, has radically altered our understanding of migraine with a focus on brain mechanisms for this common and disabling disorder. Genetic studies have begun to provide plausible targets for the basic molecular defect in terms of ion channels, albeit thus far in the rare condition of familial hemiplegic migraine (FHM). Migraine pathophysiology involves the trigeminovascular system and central nervous system modulation of the pain-producing structures of the cranium. The degree to which head pain results from the activation of the nociceptors of pain-producing intracranial structures, or to the facilitation or lack of inhibition of afferent signals, is not clear at this time. An understanding of the pain mechanism is likely to provide insights into the mechanisms underlying the more generalized sensory dysfunction that is so typical of migraine.

Local inflammation as a mediator of migraine and tension-type headache

OBJECTIVE

To demonstrate the relationship of migraine and tension-type headache to a localized maxillary gingival inflammation.

BACKGROUND

Intraoral tenderness has been observed consistently in the most common types of primary headache disorders. The laterality and degree of tenderness is related to laterality and severity of reported symptoms, both during headache and in the interictal state.

METHODS

Bilateral posterior maxillary palpation and local temperature recordings were performed during unilateral migraine and tension-type headache. Local anti-inflammatory techniques, ie, local chilling and a topical anti-inflammatory gel, were used in these tender areas in episodic migraine and tension-type headache patients.

RESULTS

Ipsilateral intraoral tenderness and increased local temperature were consistently observed during unilateral migraine and tension-type headache, suggesting local inflammation. Intraoral chilling and topical application of a nonsteroidal anti-inflammatory drug were highly effective for the treatment of migraine and tension-type headache, both in the acute phase and for headache prevention.

CONCLUSION

These results suggest that a local intraoral inflammation may be associated with the pathogenesis of these common headaches.

Calcitonin gene-related peptide (CGRP) modulates nociceptive trigeminovascular transmission in the cat

Calcitonin gene-related peptide (CGRP) is released into the cranial circulation of humans during acute migraine. To determine whether CGRP is involved in neurotransmission in craniovascular nociceptive pathways, we microiontophoresed onto neurons in the trigeminocervical complex and intravenously administered the CGRP receptor antagonists alpha-CGRP-(8-37) and BIBN4096BS. Cats were anaesthetised with alpha-chloralose, and using halothane during surgical preparation. A craniotomy and C1/C2 laminectomy allowed access to the superior sagittal sinus (SSS) and recording site. Recordings of activity in the trigeminocervical complex evoked by electrical stimulation of the SSS were made. Multibarrelled micropipettes incorporating a recording electrode were used for microiontophoresis of test substances. Cells recorded received wide dynamic range (WDR) or nociceptive specific (NS) input from cutaneous receptive fields on the face or forepaws. Cell firing was increased to 25-30 Hz by microiontophoresis of L-glutamate (n = 43 cells). Microiontophoresis of alpha-CGRP excited seven of 17 tested neurons. BIBN4096BS inhibited the majority of units (26 of 38 cells) activated by l-glutamate, demonstrating a non-presynaptic site of action for CGRP. alpha-CGRP-(8-37) inhibited a similar proportion of units (five of nine cells). Intravenous BIBN4096BS resulted in a dose-dependent inhibition of trigeminocervical SSS-evoked activity (ED50 31 microg kg(-1)). The maximal effect observed within 30 min of administration. The data suggest that there are non-presynaptic CGRP receptors in the trigeminocervical complex that can be inhibited by CGRP receptor blockade and that a CGRP receptor antagonist would be effective in the acute treatment of migraine and cluster headache.

Noxious chemical stimulation of rat facial mucosa increases intracranial blood flow through a trigemino-parasympathetic reflex--an experimental model for vascular dysfunctions in cluster headache

Cluster headache is characterized by typical autonomic dysfunctions including facial and intracranial vascular disturbances. Both the trigeminal and the cranial parasympathetic systems may be involved in mediating these dysfunctions. An experimental model was developed in the rat to measure changes in lacrimation and intracranial blood flow following noxious chemical stimulation of facial mucosa. Blood flow was monitored in arteries of the exposed cranial dura mater and the parietal cortex using laser Doppler flowmetry. Capsaicin (0.01-1 mm) applied to oral or nasal mucosa induced increases in dural and cortical blood flow and provoked lacrimation. These responses were blocked by systemic pre-administration of hexamethonium chloride (20 mg/kg). The evoked increases in dural blood flow were also abolished by topical pre-administration of atropine (1 mm) and [Lys1, Pro2,5, Arg3,4, Tyr6]-VIP (0.1 mm), a vasoactive intestinal polypeptide (VIP) antagonist, onto the exposed dura mater. We conclude that noxious stimulation of facial mucosa increases intracranial blood flow and lacrimation via a trigemino-parasympathetic reflex. The blood flow responses seem to be mediated by the release of acetylcholine and VIP within the meninges. Similar mechanisms may be involved in the pathogenesis of cluster headache.

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.

The association between calcitonin gene-related peptide (CGRP), substance P and headache in pituitary tumours

OBJECTIVES

To determine if the differential expression of calcitonin gene-related peptide (CGRP) or substance P (SP) in a range of pituitary tumours was related to the presence or absence of headache.

METHODS

Using recognised immunohistochemical techniques we examined twenty-six consecutive pituitary adenoma specimens for the presence of CGRP and SP. We included one normal post mortem pituitary specimen for comparison. A separate observer divided the patients into two groups: headache and non-headache. The association between the presence of CGRP, SP and headache was observed.

RESULTS

We observed CGRP in seven specimens (27%) and SP in six tumour specimens (23%), with cytoplasmic staining being the predominant morphological picture. CGRP and SP were co-expressed in the same tumour specimen in five cases. There was no significant association between the presence of CGRP and headache (chi(2) 0.86; P = 0.35). We did not observe CGRP or SP in the control specimen. There was no correlation between tumour subtype and the presence of CGRP or SP.

CONCLUSIONS

The mechanism of pituitary tumour-associated headache remains undetermined. The significance of the presence of CGRP and SP in pituitary tumours is unknown but does not appear to be related to headache or endocrine activity of the tumour.

Localization and modulation of calcitonin gene-related peptide-receptor component protein-immunoreactive cells in the rat central and peripheral nervous systems

Calcitonin gene-related peptide (CGRP) is widely distributed in the central and peripheral nervous system. Its highly diverse biological activities are mediated via the G protein-coupled receptor that uniquely requires two accessory proteins for optimal function. CGRP receptor component protein (RCP) is a coupling protein necessary for CGRP-receptor signaling. In this study, we established the anatomical distribution of RCP in the rat central and peripheral nervous system and its relationship to CGRP immunoreactivity. RCP-immunoreactive (IR) perikarya are widely and selectively distributed in the cerebral cortex, septal nuclei, hippocampus, various hypothalamic nuclei, amygdala, nucleus colliculus, periaqueductal gray, parabrachial nuclei, locus coeruleus, cochlear nuclei, dorsal raphe nuclei, the solitary tractus nucleus and gracile nucleus, cerebellar cortex, various brainstem motor nuclei, the spinal dorsal and ventral horns. A sub-population of neurons in the dorsal root ganglia (DRG) and trigeminal ganglia were strongly RCP-IR. Overall, the localization of RCP-IR closely matched with that of CGRP-IR. We also determined whether RCP in DRG and dorsal horn neurons can be modulated by CGRP receptor blockade and pain-related pathological stimuli. The intrathecal injection of the antagonist CGRP(8-37) markedly increased RCP expression in the lumbar DRG and spinal dorsal horn. Carrageenan-induced plantar inflammation produced a dramatic bilateral increase in RCP expression in the dorsal horn while a partial sciatic nerve ligation reduced RCP expression in the ipsilateral superficial dorsal horn. Our data suggest that the distribution of RCP immunoreactivity is closely matched with CGRP immunoreactivity in most of central and peripheral nervous systems. The co-localization of RCP and CGRP in motoneurons and primary sensory neurons suggests that CGRP has an autocrine or paracrine effect on these neurons. Moreover, our data also suggest that RCP expression in DRG and spinal cord can be modulated during CGRP receptor blockade, inflammation or neuropathic pain and this CGRP receptor-associated protein is dynamically regulated.

Capsaicin-sensitive neurogenic sensory vasodilatation in the dura mater of the rat

The neurogenic sensory vascular responses of the dura mater encephali are considered to contribute significantly to the mechanisms of meningeal nociception and headache. Although the fundamental role of capsaicin-sensitive afferent nerves in the development of the neurogenic inflammatory responses of a variety of tissues is well established, their participation in meningeal vascular reactions is unclear. In the present study, the effects of the topical application of capsaicin on the dural blood flow and on the morphology of the dural nerve fibres were examined in control and capsaicin-pretreated rats by means of laser Doppler flowmetry and electron microscopy, respectively. In the control rats, the dural application of capsaicin at concentrations of 50 and 100 nM induced significant increases in blood flow in the branches of the medial meningeal artery. This capsaicin-induced vasodilatation was abolished by capsazepine, a transient receptor potential vanilloid 1 (TRPV1) receptor antagonist, and by hCGRP8-37, a calcitonin gene-related peptide (CGRP) receptor antagonist. Administration of capsaicin at higher concentrations (1 and 10 microM) resulted in marked, dose-dependent decreases in dural blood flow. The capsaicin-induced vasodilatation was abolished, whereas vasoconstriction was augmented, by systemic pretreatment of the animals with capsaicin. Electron microscopy revealed degenerating unmyelinated axons in the dura mater after an acute exposure to capsaicin (10 microM), providing support for the existence and possible functional role of capsaicin-sensitive dural afferent nerves. The results indicate that capsaicin-induced vasodilatation in the rat dura mater is mediated by the release of CGRP from the sensory nerves, whereas the vasoconstrictor response may be attributed to a direct action of capsaicin on the vascular smooth muscle. The present study demonstrates for the first time that capsaicin-sensitive nociceptive afferent nerves contribute significantly to the dural vasodilatory responses and suggests an important role in meningeal nociception.

Preclinical studies characterizing the anti-migraine and cardiovascular effects of the selective 5-HT1D receptor agonist PNU-142633

The present study describes the preclinical pharmacology of a highly selective 5-HT1D receptor agonist PNU-142633. PNU-142633 binds with a Ki of 6 nm at the human 5-HT1D receptor and a Ki of> 18 000 nm at the human 5-HT1B receptor. The intrinsic activity of PNU-142633 at the human 5-HT1D receptor was determined to be 70% that of 5-HT in a cytosensor cell-based assay compared with 84% for that of sumatriptan. PNU-142633 was equally effective as sumatriptan and a half-log more potent than sumatriptan in preventing plasma protein extravasation induced by electrical stimulation of the trigeminal ganglion. Like sumatriptan, PNU-142633 reduced the increase in cat nucleus trigeminal caudalis blood flow elicited by electrical stimulation of the trigeminal ganglion compared with the vehicle control. The direct vasoconstrictor potential of PNU-142633 was evaluated in vascular beds. Sumatriptan increased vascular resistance in carotid, meningeal and coronary arteries while PNU-142633 failed to alter resistance in these vascular beds. These data are discussed in relation to the clinical findings of PNU-142633 in a phase II acute migraine study.

The role of histamine in dural vessel dilation

The pain of migraine is often throbbing suggesting an important role for the cranial blood vessels and their innervation by the trigeminal nerve. It is proposed that clinically effective anti-migraine compounds, such as 5-HT(1B/1D) agonists, have actions that include inhibiting calcitonin gene-related peptide (CGRP) release from trigeminal nerves. Human studies suggest that histamine can induce migraine possibly by activating nitric oxide (NO) synthase to promote endogenous NO production. The present studies investigated the effect of histamine and its antagonists on the cranial blood vessels using intravital microscopy to assess directly the diameter of dural arteries in sodium pentobarbitone anaesthetised rats. Electrical stimulation of a closed cranial window produces, by local depolarisation of nerves, dural vessel dilation that is monitored continuously on-line using video-microscopy and a video dimension analyser. Histamine infusion caused immediate and reproducible dilation of meningeal blood vessels (103.5+/-6%; n=40) that could be blocked by H(1)- (mepyramine) and H(2) (famotidine)-receptor antagonists (P<0.05), as well as a nitric oxide synthase inhibitor (N(G)-nitro-L-arginine methylester; P<0.05). Neurogenic dural vasodilation was not inhibited by H(2)-receptor antagonists, but was significantly inhibited by a H(1)-receptor antagonist at the high dose of 10 mg/kg. The present studies demonstrate that histamine is likely to activate NO synthase to promote NO production. There is also evidence that H(1)-receptors may be present on trigeminal neurones as the H(1)-receptor antagonist inhibited neurogenic vasodilation, albeit at a large dose.

Does nociceptin play a role in pain disorders in man?

Nociceptin-immunoreactive cellbodies were detected in the human trigeminal ganglion, while no such fibers were identified in the temporal artery or in dermal tissue from the neck region. In four healthy subjects receiving nociceptin into the temporal muscle in an open labeled design no pain was detected. In 10 healthy subjects who received 200pmol of nociceptin into tender non-dominant trapezius muscles in a placebo-controlled, randomized, balanced, and double-blinded design local tenderness increased (P=0.025) while no pain was noted. Thus, the action of nociceptin should be searched for in the trigeminal ganglion and/or in the central nervous system (CNS).

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.

Distribution of mRNA for VIP and PACAP receptors in human cerebral arteries and cranial ganglia

The distribution of mRNA for pituitary adenylate cyclase-activating polypeptide (PACAP) type 1 (PAC1) and vasoactive intestinal polypeptide (VIP) types 1 and 2 (VPAC1 and VPAC2, respectively) receptors was examined by reverse transcriptase polymerase chain reaction (RT-PCR) in human cerebral arteries and in trigeminal, otic, sphenopalatine and superior cervical ganglia. RT-PCR products of the expected sizes were detected in the arteries, in both the presence and absence of endothelium. In the majority (80%) of the trigeminal, otic and superior cervical ganglia, mRNA for all three receptors were found (n = 5). However, in the sphenopalatine ganglion neither VPAC2 nor PAC1 was detected (n = 2). This finding indicates the occurrence of both prejunctional (ganglia) and postjunctional (vessels) location of VIP and PACAP receptors.

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.

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.

Neuroimaging in headache

Neuroimaging of primary headache syndromes, such as cluster headache and migraine, has begun to provide a glimpse of the neuroanatomical and physiological basis of the conditions. Although these headache types have been widely described as vascular, there is now considerable imaging and clinical evidence to suggest that they are primarily driven from the brain. The shared anatomical and physiological substrate for both of these clinical problems is the neural innervation of the cranial circulation. Functional imaging with positron emission tomography (PET) has shed light on the genesis of both syndromes, documenting activation in the midbrain and pons in migraine, and in the hypothalamic grey in cluster headache. These areas are involved not simply as a response to first division nociceptive pain impulses but specifically in each syndrome, probably in some permissive or dysfunctional role. In a recent PET study in cluster headache, as well as brain activation, tracer pooled in the region of the major basal arteries. This is likely to be due to vasodilatation of these vessels during the acute pain-attack and represents the first convincing activation of neural vasodilator mechanisms in humans. The author takes the view that the known physiology and pathophysiology of the systems involved dictate that these disorders should be collectively regarded as neurovascular headaches to place emphasis on the interaction between nerves and vessels, which is the underlying characteristic of these syndromes. Understanding this neurovascular relationship facilitates an understanding of the pain mechanisms, while characterising the CNS dysfunction will ultimately allow us to dissect out the basic pathogenesis of these disorders.

An in vivo rat model to study calcitonin gene related peptide release following activation of the trigeminal vascular system

Calcitonin gene related peptide (CGRP) released from the C-fibers projecting from the trigeminal ganglion to the meninges has been suggested to play a crucial role in the pathophysiology of headache, particularly migraine. In humans it has been shown that CGRP is released during migraine-attacks, and this is attenuated by the administration of typical anti-migraine drugs such as dihydroergotamine or sumatriptan. We describe a new rat model which allows the study of CGRP release from the meninges into venous blood following activation of the trigeminal vascular system. The effects of classical and new anti-migraine drugs such as acetylsalicylic acid (ASA), sumatriptan and the new high efficacy 5-HT1B/1D agonist donitriptan (4-[4-[2-(2-aminoethyl)-1H-indol-5-yloxyl]acetyl]piperazinyl-1-yl]benzonitrile) were evaluated in comparison with the established model of neurogenic inflammation in the meninges. Sumatriptan and donitriptan inhibited CGRP release as well as neurogenic inflammation. ASA, however, attenuated neurogenic inflammation, but not CGRP release, confirming the concept of prejunctional inhibition of CGRP release by 5-HT1B/1D receptors. This new model allows the further study of prejunctional pharmacology and mechanisms of neuropeptide release in the trigeminal vascular system, which might be crucial for the further development of potent, more effective anti-migraine drugs.

Tonabersat (SB-220453) a novel benzopyran with anticonvulsant properties attenuates trigeminal nerve-induced neurovascular reflexes

1. The effects of tonabersat (SB-220453) were evaluated on trigeminal nerve ganglion stimulation-induced sensory-autonomic neurovascular reflexes in the anaesthetized cat. Comparisons were made to intravenous administration of carabersat (SB-204269), and to valproate, gabapentin and lamotrigine following intraduodenal administration. 2. There were no effects on resting blood pressure, heart rate, carotid blood flow or carotid vascular resistance for any compound evaluated. 3. Trigeminal nerve ganglion stimulation increased carotid blood flow by 65% and reduced vascular resistance by 41% with minimal effect on blood pressure (< 10%) and no effect on heart rate. Intravenous infusion of tonabersat or carabersat (both 3.4 micromol h(-1)) produced time related reductions in stimulation-induced responses with a maximal inhibition (relative to control) of 30 +/- 7% (n=4), at 240 min for tonabersat and 33+/-4% (n=3) at 180 min for carabersat. Tonabersat (11.5 micromol h(-1)) produced a similar inhibitory effect (32 +/- 9%, n=4) after 120 min of infusion. 4. Following intraduodenal administration of tonabersat, the maximal inhibition of nerve stimulation-induced responses was 55 +/- 4% at 120 min (n=4) for tonabersat 10 mg kg(-1), and 24+/-2% after 180 min for 1 mg kg(-1) (n=4). 5. Intraduodenal administration of sodium valproate (10 or 100 mg kg(-1) n=4/group) had no effect on neurovascular reflexes. Maximal inhibition of nerve ganglion-stimulated reductions in carotid vascular resistance were observed at 150 min for lamotrigine (50 mg kg(-1), 52+/-12%, n=4) and gabapentin (100 mg kg(-1), 17+/-13%, n=3). Lamotrigine 10 mg kg(-1) produced 22+/-11% (n=3) inhibition after 180 min. 6. These data demonstrate blockade of trigeminal parasympathetic reflexes with tonabersat, carabersat and other anticonvulsants. These agents may therefore have therapeutic benefit in conditions where this type of reflex is evident.

Characterisation of the effects of a non-peptide CGRP receptor antagonist in SK-N-MC cells and isolated human cerebral arteries

The cerebral circulation is innervated by calcitonin gene-related peptide (CGRP) containing fibers originating in the trigeminal ganglion. During a migraine attack, there is a release of CGRP in conjunction with the head pain, and triptan administration abolishes both the CGRP release and the pain at the same time. In the search for a novel treatment of migraine, a non-peptide CGRP antagonist has long been sought. Here, we present data on a human cell line and human and guinea-pig isolated cranial arteries for such an antagonist, Compound 1 (4-(2-Oxo-2,3-dihydro-benzoimidazol-1-yl)-piperidine-1-carboxylic acid [1-(3,5-dibromo-4-hydroxy-benzyl)-2-oxo-2-(4-phenyl-piperazin-1-yl)-ethyl]-amide). On SK-N-MC cell membranes, radiolabelled CGRP binding was displaced by both CGRP-(8-37) and Compound 1, yielding pK(i) values of 8.9 and 7.8, respectively. Functional studies with SK-N-MC cells showed that CGRP-induced cAMP production was antagonised by both CGRP-(8-37) and Compound 1 with pA(2) values of 7.8 and 7.7, respectively. Isolated human and guinea pig cerebral arteries were studied with a sensitive myograph technique. CGRP induced a concentration-dependent relaxation in human cerebral arteries which was antagonized by both CGRP-(8-37) and Compound 1 in a competitive manner. In guinea pig basilar arteries, CGRP-(8-37) antagonised the CGRP-induced relaxation while Compound 1 had a weak blocking effect. The clinical studies of non-peptide CGRP antagonists are awaited with great interest.

Neuropeptide localization in the "migraine generator" region of the human brainstem

Evidence from animals and humans suggests that brainstem nuclei such as the raphe nuclei, the locus coeruleus (LC) and the periaqueductal grey matter (PAG), are involved in the pathophysiology of migraine. In order to understand possible neurotransmitters involved we have, by means of indirect immunocytochemistry, analysed these regions for the occurrence and distribution of calcitonin gene-related peptide (CGRP), substance P (SP), pituitary adenylate-cyclase activating peptide (PACAP) and vasoactive intestinal polypeptide (VIP). CGRP-immunoreactive (-ir) cell bodies, but no fibres, were found to occur in high numbers, constituting 80% of all nerve cell bodies in the LC. A smaller number of these nerve cell bodies (40%) in the LC proved to be PACAP-ir. The LC neurones also stored the vesicular monoamine transporter (VMAT)- and the C-terminal flanking peptide of neuropeptide Y (C-PON)-ir, illustrating their adrenergic nature. Double immunostaining revealed that all VMAT-and C-PON-containing neurones, in addition, stored CGRP. Immunoreactive cell bodies were not seen in the nucleus raphe magnus (NRM) or PAG. Numerous SP-ir nerve fibres were observed in the NRM, the LC and the PAG. Few PACAP-ir nerve fibres were detected in the PAG and few VIP-ir nerve fibres were seen in the NRM and the PAG.

Pathophysiology of primary headaches

The cerebral circulation is innervated by sympathetic, parasympathetic, and sensory nerves, which store a considerable number of neurotransmitters. The role of these has been evaluated in primary headaches. A clear association between head pain and the release of calcitonin gene-related peptide was demonstrated. In cluster headache and in a case of chronic paroxysmal headache there was in addition the release of vasoactive intestinal peptide, which was associated with the facial symptoms (nasal congestion, rhinorrhea). In parallel with sumatriptan treatment, head pain subsided and neuropeptide release normalized. These data show the involvement of sensory and parasympathetic mechanisms in the pathophysiology of primary headaches.