The role of histamine in dural vessel dilation

Hypersensitivity to PACAP-38 in post-traumatic headache: a randomized clinical trial

Pituitary adenylate cyclase-activating polypeptide-38 (PACAP-38), known for its role in migraine pathogenesis, has been identified as a novel drug target. Given the clinical parallels between post-traumatic headache (PTH) and migraine, we explored the possible role of PACAP-38 in the pathogenesis of PTH. To this end, we conducted a randomized, double-blind, placebo-controlled, two-way crossover trial involving adult participants diagnosed with persistent PTH resulting from mild traumatic brain injury. Participants were randomly assigned to receive a 20-min continuous intravenous infusion of either PACAP-38 (10 pmol/kg/min) or placebo (isotonic saline) on two separate experimental days, with a 1-week washout period in between. The primary outcome was the difference in incidence of migraine-like headache between PACAP-38 and placebo during a 12-h observational period post-infusion. The secondary outcome was the difference in the area under the curve (AUC) for baseline-corrected median headache intensity scores during the same 12-h observational period. Of 49 individuals assessed for eligibility, 21 were enrolled and completed the trial. The participants had a mean age of 35.2 years, and 16 (76%) were female. Most [19 of 21 (90%)] had a migraine-like phenotype. During the 12-h observational period, 20 of 21 (95%) participants developed migraine-like headache after intravenous infusion of PACAP-38, compared with two (10%) participants after placebo (P < 0.001). Furthermore, the baseline-corrected AUC values for median headache intensity scores during the 12-h observational period was higher after PACAP-38 than placebo (P < 0.001). These compelling results demonstrate that PACAP-38 is potent inducer of migraine-like headache in people with persistent PTH. Thus, targeting PACAP-38 signalling might be a promising avenue for the treatment of PTH.

Is calcitonin gene-related peptide (CGRP) the missing link in food histamine-induced migraine? A review of functional gut-to-trigeminovascular system connections

Calcitonin gene-related peptide (CGRP) and histamine plasma concentrations increase during migraine attacks. Both mediators are potent vasodilators, and they have been shown to reciprocally contribute to the release of each other in the trigeminovascular system, possibly driving migraine development. A high-histamine-content diet triggers migraine in patients who have histamine degradation deficiency owing to diaminooxidase (DAO) gene mutations. Therefore, studying functional links between exogenous histamine and CGRP seems promising for the understanding of diet-induced migraine generation. Notably, there is a lack of knowledge about the interplay of the enteric nervous system and the spinal/trigeminal somatosensory system with regard to CGRP and histamine. Based on background evidence, we propose that a functional interconnection between exogenous histamine and CGRP contributes to migraine development.

Systemic mastocytosis: The roles of histamine and its receptors in the central nervous system disorders

Mastocytosis is a rare disease of clonal hematological disorders characterized by a pathological accumulation of Mast Cells (MCs) in different tissues, with variable symptomatology and prognosis. Signs and symptoms of Systemic Mastocytosis (SM) are due to pathological infiltration of MCs and to the release of chemical mediators, mainly histamine. Patients with SM may also present with neurological symptoms or complications. The pathophysiology of these neurological disorders remains uncertain to this day, but it can be associated with the infiltration of tissue mastocytes, release of mastocytes' mediators or both. Moreover, there is a lot to understand about the role of neurological symptoms in SM and knowing, for example, what is the real frequency of neurological disorders in SM and if is present a relation between other SM subtypes, because it has been noted that the alteration of the histamine expression may be an initiating factor for susceptibility, gravity and progression of the epigenetic disease. In this review we explain the possible pathophysiological mechanism about neurological symptomatology found in some patients affected by SM, describing the role of histamine and its receptors in the nervous system and, in light of the results, what the future prospects may be for a more specific course of treatment.

Fatigue, Sleep, and Autoimmune and Related Disorders

Profound and debilitating fatigue is the most common complaint reported among individuals with autoimmune disease, such as systemic lupus erythematosus, multiple sclerosis, type 1 diabetes, celiac disease, chronic fatigue syndrome, and rheumatoid arthritis. Fatigue is multi-faceted and broadly defined, which makes understanding the cause of its manifestations especially difficult in conditions with diverse pathology including autoimmune diseases. In general, fatigue is defined by debilitating periods of exhaustion that interfere with normal activities. The severity and duration of fatigue episodes vary, but fatigue can cause difficulty for even simple tasks like climbing stairs or crossing the room. The exact mechanisms of fatigue are not well-understood, perhaps due to its broad definition. Nevertheless, physiological processes known to play a role in fatigue include oxygen/nutrient supply, metabolism, mood, motivation, and sleepiness-all which are affected by inflammation. Additionally, an important contributing element to fatigue is the central nervous system-a region impacted either directly or indirectly in numerous autoimmune and related disorders. This review describes how inflammation and the central nervous system contribute to fatigue and suggests potential mechanisms involved in fatigue that are likely exhibited in autoimmune and related diseases.

Histamine and migraine revisited: mechanisms and possible drug targets

OBJECTIVE

To review the existing literature on histamine and migraine with a focus on the molecule, its receptors, its use in inducing migraine, and antihistamines in the treatment of migraine.

BACKGROUND

Histamine has been known to cause a vascular type headache for almost a hundred years. Research has focused on antihistamines as a possible treatment and histamine as a migraine provoking agent but there has been little interest in this field for the last 25 years. In recent years two additional histamine (H3 and H4) receptors have been discovered and a series of non-sedating antihistamines have been developed. It is therefore timely to review the field again.

METHODS

For this review the PubMed/MEDLINE database was searched for eligible studies. We searched carefully for all articles on histamine, antihistamines and histamine receptors in relation to migraine and the nervous system. The following search terms were used: histamine, migraine disorders, migraine, headache, antihistamines, histamine antagonists, clinical trials, induced headache, histamine H3 receptor, histamine H4 receptor and pharmacology. Four hundred thirty-six titles were read, 135 abstracts were read, 112 articles were read in full and 53 articles were used in this review. Review process resulted in 12 articles added to a total of 65.

FINDINGS

Early studies of H1 and H2 antihistamines lack scientific strength and show conflicting results. Most of the antihistaminic drugs used in these trials bind also to other receptors which makes it difficult to conclude on the antihistaminic effect. Histamine is an efficient inducer of migraine attacks in migraine patients by an H1 mechanism most likely extracerebrally. These findings merit further investigation of antihistamines in clinical drug trials. The H3 and H4 receptors are found in primarily in CNS and immune tissues, respectively. H3 is likely to be involved in antinociception and has been linked with cognitive, neurodegenerative and sleep disorders. The only marketed H3 agent, pitolisant, is a brain penetrant H3 antagonist/inverse agonist which increases central histamine and causes headache. The experimental H3 agonist Nα-methylhistamine has shown promising results as a migraine preventative in studies of uncertain quality. With the current limited knowledge of the H4 receptor it is questionable whether or not the receptor is involved in migraine.

CONCLUSION

There is insufficient support for first generation antihistamines (both H1 and H2) as preventive migraine medications and sedation and weight gain are unacceptable side effects. Non-sedating H1 antihistamines need to be appropriately tested. Central H3 receptors seem to have a role in migraine that merit further investigation. The histaminergic system may be a goal for novel migraine drugs.

Advances in Meningeal Immunity

The central nervous system (CNS) is an immunologically specialized tissue protected by a blood-brain barrier. The CNS parenchyma is enveloped by a series of overlapping membranes that are collectively referred to as the meninges. The meninges provide an additional CNS barrier, harbor a diverse array of resident immune cells, and serve as a crucial interface with the periphery. Recent studies have significantly advanced our understanding of meningeal immunity, demonstrating how a complex immune landscape influences CNS functions under steady-state and inflammatory conditions. The location and activation state of meningeal immune cells can profoundly influence CNS homeostasis and contribute to neurological disorders, but these cells are also well equipped to protect the CNS from pathogens. In this review, we discuss advances in our understanding of the meningeal immune repertoire and provide insights into how this CNS barrier operates immunologically under conditions ranging from neurocognition to inflammatory diseases.

Stimulation of rat cranial dura mater with potassium chloride causes CGRP release into the cerebrospinal fluid and increases medullary blood flow

Primary headaches may be accompanied by increased intracranial blood flow induced by the release of the potent vasodilator calcitonin gene-related peptide (CGRP) from activated meningeal afferents. We aimed to record meningeal and medullary blood flow simultaneously and to localize the sites of CGRP release in rodent preparations in vivo and ex vivo. Blood flow in the exposed rat parietal dura mater and the medulla oblongata was recorded by laser Doppler flowmetry, while the dura was stimulated by topical application of 60mM potassium chloride (KCl). Samples of jugular venous plasma and cerebrospinal fluid (CSF) collected from the cisterna magna were analysed for CGRP concentrations using an enzyme immunoassay. In a hemisected rat skull preparation lined with dura mater the CGRP releasing effect of KCl superfusion was examined. Superfusion of the dura mater with KCl decreased meningeal blood flow unless alpha-adrenoceptors were blocked by phentolamine, whereas the medullary blood flow was increased. The same treatment caused increased CGRP concentrations in jugular plasma and CSF and induced significant CGRP release in the hemisected rat skull preparation. Anaesthesia of the trigeminal ganglion by injection of lidocaine reduced increases in medullary blood flow and CGRP concentration in the CSF upon meningeal KCl application. CGRP release evoked by depolarisation of meningeal afferents is accompanied by increased blood flow in the medulla oblongata but not the dura mater. This discrepancy can be explained by the smooth muscle depolarising effect of KCl and the activation of sympathetic vasoconstrictor mechanisms. The medullary blood flow response is most likely mediated by CGRP released from activated central terminals of trigeminal afferents. Increased blood supply of the medulla oblongata and CGRP release into the CSF may also occur in headaches accompanying vigorous activation of meningeal afferents.

Where are we? The anatomy of the murine cortical meninges revisited for intravital imaging, immunology, and clearance of waste from the brain

Rapid progress is being made in understanding the roles of the cerebral meninges in the maintenance of normal brain function, in immune surveillance, and as a site of disease. Most basic research on the meninges and the neural brain is now done on mice, major attractions being the availability of reporter mice with fluorescent cells, and of a huge range of antibodies useful for immunocytochemistry and the characterization of isolated cells. In addition, two-photon microscopy through the unperforated calvaria allows intravital imaging of the undisturbed meninges with sub-micron resolution. The anatomy of the dorsal meninges of the mouse (and, indeed, of all mammals) differs considerably from that shown in many published diagrams: over cortical convexities, the outer layer, the dura, is usually thicker than the inner layer, the leptomeninx, and both layers are richly vascularized and innervated, and communicate with the lymphatic system. A membrane barrier separates them and, in disease, inflammation can be localized to one layer or the other, so experimentalists must be able to identify the compartment they are studying. Here, we present current knowledge of the functional anatomy of the meninges, particularly as it appears in intravital imaging, and review their role as a gateway between the brain, blood, and lymphatics, drawing on information that is scattered among works on different pathologies.

Interaction of Calcitonin Gene-Related Peptide, Nitric Oxide and Histamine Release in Neurogenic Blood Flow and Afferent Activation in The Rat Cranial Dura Mater

Calcitonin gene-related peptide (CGRP), nitric oxide (NO) and histamine are implicated in primary headaches but their role in vascular and nociceptive events in the dura mater is not well described. In an in vitro preparation of the hemisected rat skull, CGRP and histamine release from the cranial dura was measured using enzyme-linked immunoassays. While the NO donator NONOate (10-4 M) was without effect, CGRP (10-5 M) induced considerable histamine release from the rat cranial dura, which was blocked by the CGRP receptor antagonist CGRP8-37 (10-5 M). Conversely, histamine (10-4 M) did not stimulate CGRP release. In vitro recordings from single rat meningeal afferents showed that only one of 12 mechanically identified units but several mechanically insensitive units responded to histamine (up to 10-5 M). Increases in meningeal blood flow after histamine application (10-4 M) to the rat cranial dura remained unchanged during CGRP receptor blockade with CGRP8-37, inhibition of NO synthesis with L-NAME (20 mg/kg i.v.) and H3 receptor blockade with thioperamide (10-4 M). We conclude that histamine produces direct vasodilatation and activates a subset of largely non-mechanically sensitive, non-CGRP containing afferents in the rat meninges. Histamine is released from meningeal mast cells which are stimulated by CGRP. Similar mechanisms may be involved in the pathogenesis of headaches.

Prophylactic activity of increasing doses of intravenous histamine in refractory migraine: Retrospective observations of a series of patients with migraine without aura

BACKGROUND

Histamine is thought to play a pivotal role in the modulation of peripheral and central pain. The administration of increasing doses of histamine may lead to desensitization of receptors of histamine types 1 and 2, causing meningeal vasodilation, and to depletion of neuropeptides in the trigeminal ganglion, thus inhibiting the initiation of migraine.

OBJECTIVE

In this study, the efficacy and tolerability of increasing doses of IV histamine in migraine prophylaxis were investigated.

METHODS

This single-center, open-label, retrospective, controlled study was conducted at the Headache Center (Department of Internal Medicine, University of Florence, Villa Monna Tessa, Italy). Patients included in the study had 3 to 6 migraines without aura per month that were refractory to common symptomatic and prophylactic agents in the 6 months preceding the study. Patients were treated with IV histamine hydrochloride for 21 days starting with a dosage of 0.5 mg/d and increasing to 4.0 mg/d. To assess the efficacy of the treatment, these patients were matched for age; sex; and frequency, duration, and severity of attacks with untreated migraineurs. Clinical benefit was defined as ⩽ 1 migraine of mild intensity per month. Tolerability was assessed during the hospitalization period, and patients were instructed to contact the Headache Center to report any adverse effects after hospital discharge.

RESULTS

The histamine group comprised 47 patients (40 women, 7 men; mean [SD] age, 42.0 [8.6] years) and the control group comprised 23 patients (20 women, 3 men; mean [SD] age, 38.8 [8.4] years). The histamine-treated patients showed a clinical benefit lasting for a mean of 10.4 (4.2) months, while the patients in the control group showed a clinical benefit of 3.8 (1.9) months. The difference in the duration of the clinical benefit between the 2 groups was 6.6 months (95% CI, 5.15-7.99). Adverse effects consisted of flushing, heat sensation during infusion, headache, and palpitations.

CONCLUSIONS

In this study, histamine showed lasting prophylactic efficacy in migraineurs. If further research confirms this preliminary finding, histamine could be considered when established prophylactic drugs, such as betablockers, calcium antagonists, antidepressants, and antiepileptics, have not been effective.

Comparison of the vasodilator responses of isolated human and rat middle meningeal arteries to migraine related compounds

Background

Migraine attacks occur spontaneously in those who suffer from the condition, but migraine-like attacks can also be induced artificially by a number of substances. Previously published evidence makes the meninges a likely source of migraine related pain. This article investigates the effect of several vasodilators on meningeal arteries in order to find a connection between the effect of a substance on a meningeal vessel and its ability to artificially induce migraine.

Methods

A myograph setup was used to test the vasodilator properties of the substances acetylcholine (ACh), sodium nitroprusside (SNP), sildenafil, prostaglandin E₂ (PGE₂), pituitary adenylate cyclase activating peptide-38 (PACAP-38), calcitonin gene-related peptide (CGRP) and NaCl buffer on meningeal arteries from human and rat. An unpaired t-test was used to statistically compare the mean E_max(%) at the highest concentration of each substance to the E_max(%) of NaCl buffer.

Results

In the human experiments, all substances except PACAP-38 had an E_max (%) higher than the NaCl buffer, but the difference was only significant for SNP and CGRP. For the human samples, clinically tested antimigraine compounds (sumatriptan, telcagepant) were applied to the isolated arteries, and both induced a significant decrease of the effect of exogenously administrated CGRP. In experiments on rat middle meningeal arteries, pre-contracted with PGF_2α, similar tendencies were seen. When the pre-contraction was switched to K⁺ in a separate series of experiments, CGRP and sildenafil significantly relaxed the arteries.

Conclusions

Still no definite answer can be given as to why pain is experienced during an attack of migraine. No clear correlation was found between the efficacy of a substance as a meningeal artery vasodilator in human and the ability to artificially induce migraine or the mechanism of action. Vasodilatation could be an essential trigger, but only in conjunction with other unknown factors. The vasculature of the meninges likely contributes to the propagation of the migrainal cascade of symptoms, but more research is needed before any conclusions can be drawn about the nature of this contribution.

PACAP-38 infusion causes sustained vasodilation of the middle meningeal artery in the rat: possible involvement of mast cells

BACKGROUND

In healthy human volunteers and in migraineurs, pituitary adenylate cyclase-activating polypeptide-38 (PACAP-38) infusion caused sustained vasodilation of the middle meningeal artery (MMA) and an immediate as well as a delayed headache. All the study subjects experienced facial flushing. Mast cells (MCs) might have a role in the long-lasting effect of PACAP-38 infusion. We hypothesized that in mast cell-depleted (MCD) rats the vascular responses to PACAP-38 would be lesser than in control rats because of a lack of vasodilatory products released during MC degranulation.

METHODS

MCs were depleted by chronic treatment with compound 48/80. The effect of 20 minutes' intravenous (i.v.) infusion of calcitonin gene-related peptide (CGRP), PACAP-38, PACAP(6-38) (PAC-1 receptor antagonist) and PACAP-27 on the diameter of the MMA and on mean arterial blood pressure (MABP) in control and MCD rats was recorded by using the genuine closed-cranial window (CCW) model. Vasoactive intestinal polypeptide (VIP) infusion was given only in control rats. A combination of the histamine H1 receptor antagonist mepyramine (4 mg kg(-1) i.v.) and the H2 receptor antagonist famotidine (1 mg kg(-1) i.v.) was given 10 minutes prior to PACAP-38 infusion. Increasing doses of PACAP-38, PACAP-27 and VIP were infused through the intracarotid artery (i.c.) in control and MCD rats to see the direct effects of these peptides on MMA diameter change.

RESULTS

There was no significant change in CGRP-induced MMA diameter increase in control and MCD rats, and the dilated MMA immediately returned back to baseline after stopping the infusion. The delayed MMA dilation induced by PACAP-38 was abolished in MCD and antihistamine (AH)-pretreated rats. Compared to PACAP-38, the PACAP-27 i.v. infusion gave smaller peak dilation of MMA in control rats. In MCD rats, PACAP-27 did not induce any significant dilation. VIP i.v. infusion reduced MABP but did not dilate MMA significantly. PACAP(6-38), which is a potent MC degranulator, also gave a significant delayed dilation of MMA. PACAP-38 i.c. responses (direct receptor mediated response) were not affected by MC depletion. Only the maximum response (% E max) value of PACAP-27 (i.c.) was significantly lower in MCD rats compared to control rats.

CONCLUSIONS

The delayed MMA dilatory responses to PACAP-38 infusion were attenuated in MCD and AH-pretreated rats, indicating a role of the MC mediator-histamine in PACAP-38-induced delayed dilation of MA.

Animal migraine models for drug development: status and future perspectives

Migraine is number seven in WHO's list of all diseases causing disability and the third most costly neurological disorder in Europe. Acute attacks are treatable by highly selective drugs such as the triptans but there is still a huge unmet therapeutic need. Unfortunately, drug development for headache has almost come to a standstill partly because of a lack of valid animal models. Here we review previous models with emphasis on optimal characteristics of a future model. In addition to selection of animal species, the method of induction of migraine-like changes and the method of recording responses elicited by such measures are crucial. The most naturalistic way of inducing attacks is by infusion of endogenous signaling molecules that are known to cause migraine in patients. The most valid response is recording of neural activity in the trigeminal system. The most useful headache related responses are likely to be behavioral, allowing multiple experiments in each individual animal. Distinction is made between acute and prophylactic models and how to validate each of them. Modern insight into neurobiological mechanisms of migraine is so good that it is only a question of resources and efforts that determine when valid models with ability to predict efficacy in migraine will be available.

Chemical mediators of migraine: preclinical and clinical observations

Migraine is a neurovascular disorder, and although the pathophysiology of migraine has not been fully delineated, much has been learned in the past 50 years. This knowledge has been accompanied by significant advancements in the way migraine is viewed as a disease process and in the development therapeutic options. In this review, we will focus on 4 mediators (nitric oxide, histamine, serotonin, and calcitonin gene-related peptide) which have significantly advanced our understanding of migraine as a disease entity. For each mediator we begin by reviewing the preclinical data linking it to migraine pathophysiology, first focusing on the vascular mechanisms, then the neuronal mechanisms. The preclinical data are then followed by a review of the clinical data which support each mediator's role in migraine and highlights the pharmacological agents which target these mediators for migraine therapy.

N-acetylcysteine-induced headache in hospitalized patients with acute acetaminophen overdose

Intravenous N-acetylcysteine (IV-NAC) is usually regarded as a safe antidote to acetaminophen overdose. However, during infusion of the loading dose, adverse drug reactions such as a headache may occur. The objectives of this study were to investigate the prevalence of headache in patients presenting to hospital after acetaminophen overdose and to determine which clinical findings are most predictive of headache among these patients. This is a retrospective cohort study of hospital admissions for acute acetaminophen overdose that was conducted over a period of 4 years from January 1, 2005 to December 31, 2008. Demographic data, clinical characteristics, and predictors of headache were analyzed. spss 15 was used for data analysis. Two-hundred and fifty-five patients were studied; their mean age was 23.1 ± 1.6; 83.9% of them were women and 14.9% had a headache during hospitalization. Headache among patients was significantly associated with IV-NAC administration (P = 0.001), intentional ingestion of drug (P = 0.04), acetaminophen concentration above 'possible toxicity' treatment line (P = 0.04), a high acetaminophen concentration (P = 0.04), and a long hospital stay (P = 0.03). Multiple logistic regression showed a significant risk factor for headache in patients administered IV-NAC (P = 0.04). We recorded a high frequency of headache in patients with acute acetaminophen overdose in our geographical area. This study suggests that among those patients, the use of IV-NAC is associated with an increased risk of headache.

Finding New Drug Targets for the Treatment of Migraine Attacks

No new preventive drugs specific to migraine have appeared for the last 20 years and existing acute therapies need improvement. Unfortunately, no animal models can predict the efficacy of new therapies for migraine. Because migraine attacks are fully reversible and can be aborted by therapy, the headache- or migraine-provoking property of naturally occurring signalling molecules can be tested in a human model. This model has predicted efficacy of nitric oxide synthase inhibition and calcitonin gene-related peptide receptor blockade. The pharmaceutical industry should pay more attention to human models, although methods are different from normal target validation.

Migraine: where and how does the pain originate?

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

Histamine in the nervous system

Histamine is a transmitter in the nervous system and a signaling molecule in the gut, the skin, and the immune system. Histaminergic neurons in mammalian brain are located exclusively in the tuberomamillary nucleus of the posterior hypothalamus and send their axons all over the central nervous system. Active solely during waking, they maintain wakefulness and attention. Three of the four known histamine receptors and binding to glutamate NMDA receptors serve multiple functions in the brain, particularly control of excitability and plasticity. H1 and H2 receptor-mediated actions are mostly excitatory; H3 receptors act as inhibitory auto- and heteroreceptors. Mutual interactions with other transmitter systems form a network that links basic homeostatic and higher brain functions, including sleep-wake regulation, circadian and feeding rhythms, immunity, learning, and memory in health and disease.

Current and prospective pharmacological targets in relation to antimigraine action

Migraine is a recurrent incapacitating neurovascular disorder characterized by unilateral and throbbing headaches associated with photophobia, phonophobia, nausea, and vomiting. Current specific drugs used in the acute treatment of migraine interact with vascular receptors, a fact that has raised concerns about their cardiovascular safety. In the past, alpha-adrenoceptor agonists (ergotamine, dihydroergotamine, isometheptene) were used. The last two decades have witnessed the advent of 5-HT(1B/1D) receptor agonists (sumatriptan and second-generation triptans), which have a well-established efficacy in the acute treatment of migraine. Moreover, current prophylactic treatments of migraine include 5-HT(2) receptor antagonists, Ca(2+) channel blockers, and beta-adrenoceptor antagonists. Despite the progress in migraine research and in view of its complex etiology, this disease still remains underdiagnosed, and available therapies are underused. In this review, we have discussed pharmacological targets in migraine, with special emphasis on compounds acting on 5-HT (5-HT(1-7)), adrenergic (alpha(1), alpha(2,) and beta), calcitonin gene-related peptide (CGRP(1) and CGRP(2)), adenosine (A(1), A(2), and A(3)), glutamate (NMDA, AMPA, kainate, and metabotropic), dopamine, endothelin, and female hormone (estrogen and progesterone) receptors. In addition, we have considered some other targets, including gamma-aminobutyric acid, angiotensin, bradykinin, histamine, and ionotropic receptors, in relation to antimigraine therapy. Finally, the cardiovascular safety of current and prospective antimigraine therapies is touched upon.

Subcutaneous histamine versus topiramate in migraine prophylaxis: a double-blind study

BACKGROUND

Histamine has a selective affinity for H3 receptors and it may specifically inhibit the neurogenic edema response involved in migraine pathophysiology.

OBJECTIVE

To evaluate the therapeutic potential of subcutaneous administration of histamine in migraine prophylaxis, compared with oral administration of topiramate.

METHODS

Ninety patients with migraine were selected in a 12-week double-blind controlled clinical trial to evaluate the efficacy of subcutaneous administration of histamine (1-10 ng twice a week) compared with oral administration of topiramate (100 mg daily dose). The variables studied were: headache intensity, frequency, duration, analgesic intake and Migraine Disability Assessment.

RESULTS

The data collected during the 12 weeks of treatment revealed that headache symptoms improved in both the histamine and topiramate groups, which was evident within the first month after the initiation of treatment, with statistically significant (p < 0.001) reductions in headache frequency (50%), Migraine Disability Assessment score (75%), intensity of pain (51%), duration of migraine attacks (45%), as well as in the use of rescue medication (52%).

CONCLUSION

The present study provides evidence of the efficacy of subcutaneously applied histamine and orally administered topiramate in migraine prophylaxis. Subcutaneously applied histamine may represent a novel and effective therapeutic alternative in resistant migraine patients.

Subcutaneous histamine versus sodium valproate in migraine prophylaxis: a randomized, controlled, double-blind study

Histamine has a selective affinity for H3-receptors and it may specifically inhibit the neurogenic edema response involved in migraine pathophysiology. The objective of this study was to evaluate the therapeutic potential of subcutaneous administration of histamine in migraine prophylaxis, compared with oral administration of sodium valproate, in an open clinical trial. Ninety-two patients with migraine were selected under criteria established by the International Headache Society and enrolled in a 12-week double-blind controlled clinical trial to evaluate the efficacy of subcutaneous administration of histamine (1-10 ng twice a week; n = 46) compared with oral administration of sodium valproate (500 mg daily dose; n = 46). The variables studied were headache intensity, frequency, duration, analgesic intake and migraine disability assessment (MIDAS). Two-tailed Student's t- test was used to compare means and the Mann-Whitney U and anova tests were used. The data collected during the 4th, 8th and 12th weeks of treatment revealed that histamine caused a significantly greater reduction (P < 0.001) in intensity and duration of migraine attacks as well as in analgesic intake. No difference was detected in the frequency of attacks or in MIDAS. The present study provides evidence of the superior efficacy of histamine applied subcutaneously in migraine prophylaxis when compared with sodium valproate taken orally. Subcutaneously applied histamine may represent a novel and effective therapeutic alternative in resistant migraine patients.

Functional serotonin and histamine receptor subtypes in porcine ciliary artery in comparison with middle cerebral artery

Functional serotonin (5-HT) and histamine receptor subtypes were investigated in porcine middle cerebral and ciliary arteries. An H(1) antagonist, mepyramine, antagonized histamine-induced responses with pK(B) values of 8.91-9.10. In the presence of 1 muM mepyramine, however, histamine caused dilation through H(2) receptors in the middle cerebral but not in the ciliary artery. A 5-HT(2A) antagonist, ketanserin, antagonized 5-HT-induced responses, causing rightward shifts in the concentration-response curves with pK(B) values of 8.52-8.71. A 5-HT(1B) antagonist, SB224289, produced rightward shifts of the concentration-response curves to sumatriptan with pK(B) values (6.66) only in the middle cerebral artery. In contrast, a 5-HT(1D) antagonist, BRL15572, had no effect in either artery. An RT-PCR study demonstrated the gene expression of the mRNAs of all three receptors (5HT(1B), 5HT(1D) and 5HT(2A)) in both arteries. These results suggest that histamine-induced contraction is mediated only through functional H(1) receptor in these arteries. Interestingly, there are functional 5-HT(2A) and 5-HT(1B) receptor subtypes in the middle cerebral artery, whereas the only functional receptor is 5-HT(2A) in the ciliary artery. The difference may be important for treatment with 5-HT(1B/1D) agonists (e.g. for migraine) without ocular side effect.

The calcitonin gene-related peptide (CGRP) receptor antagonist BIBN4096BS reduces neurogenic increases in dural blood flow

In an in vivo preparation of the exposed rat cranial dura mater electrical field stimulation causes increases in blood flow that are mainly due to the vasodilatory effect of calcitonin gene-related peptide (CGRP) released from meningeal afferents. In this preparation the effect of BIBN4096BS, a non-peptide competitive antagonist of CGRP receptors, was examined. Additionally, in an in vitro preparation of the hemisected rat skull the effect of BIBN4096BS on CGRP release stimulated by activation of meningeal afferents was analysed. Injection of BIBN4096BS at cumulative doses of 300 microg/kg and 900 microg/kg caused dose-dependent inhibition of the electrically evoked blood flow increases. The basal blood flow and vital parameters were not significantly changed by any dose. In the hemisected skull BIBN4096BS at 10(-6) M did not alter the CGRP release evoked by depolarizing K(+) concentrations or antidromic electrical stimulation of the trigeminal ganglion. We conclude that neurogenic increases in dural blood flow are reduced by BIBN4096BS without changing basal vascular parameters. This peripheral effect may be important with regard to CGRP receptor inhibition as an antimigraine strategy.

Prevalence of migraine headaches in patients with allergic rhinitis

BACKGROUND

Histamine has been implicated in the pathogenesis of migraine headaches. Because allergic rhinitis (AR) is a histamine-driven syndrome and the nasal passage is in close proximity to the central nervous system, we hypothesize that AR may trigger migraine headaches.

OBJECTIVE

To determine the prevalence of migraine headaches in patients with and without AR.

METHODS

Allergic rhinitis was diagnosed based on skin or radioallergosorbent test results, clinical history, and physical examination findings. The diagnosis of migraine headache was made if patients fulfilled the International Headache Society criteria. Surveys were obtained from hospital-based allergy, pediatric, and internal medicine clinics, all serving the same inner-city population.

RESULTS

A total of 294 surveys were completed. Of 76 patients in the AR group, 26 (34%) had headaches meeting the International Headache Society criteria for migraines, and of the 57 patients in the non-AR group, only 2 (4%) had headaches that met the criteria. A Fisher exact test showed P = 8.2 x 10(-6). The odds ratio was 14.3, which signifies that the odds of having migraine headaches is 14.3 times higher in the AR group than in the non-AR group.

CONCLUSIONS

There is a high prevalence of migraine headaches in patients with AR compared with those without AR. We propose that histamine plays a key role in triggering migraines by means of vasodilation and inflammation in the pathogenesis of migraine headaches.

Signal transduction pathways involved in particulate matter induced relaxation in rat aorta--spontaneous hypertensive versus Wistar Kyoto rats

Previously we reported that in vivo exposure to ambient particulate matter (PM) induces vasodilatation in rat aorta. The purpose of the current study was to investigate the intracellular messengers involved in PM-elicited vasodilatation in aortas from spontaneous hypertensive (SHR) and normotensive (WKY) rats.

METHODS

The contribution of three different intracellular pathways, i.e. (1) the NO-cGMP pathway, (2) prostanoids signaling and (3) endothelial hyperpolarisation factors were evaluated by using specific inhibitors (NS2028, Diclofenac and high K-concentration/17-ODYA, respectively). Using antagonists of capsaicin- or histamine receptors we tested potential interactions of PM with these receptors. Particle suspensions (EHC-93), particle filtrates (particle-free) and Cu(2+)- or Zn(2+)-containing solutions were used to obtain cumulative dose-response curves of relaxation in normal and endothelium-denuded rings.

RESULTS

Our present data confirm that PM and its soluble components elicit an endothelium-independent vasodilatation in rat aorta rings. The response is mainly linked to the activation of soluble guanylate cyclase (sGC), since its inhibition by NS2028 almost abolished relaxation. Indeed PM suspensions stimulated cGMP production in purified isolated sGC. Neither the receptor nor their signaling pathways played a significant role in the direct relaxation by PM or metals. Vasodilatation responses were significantly higher in SHR than WKY control rats.

CONCLUSION

Our data demonstrate that PM elicits a dose-dependent vasodilatation via activation of sGC in vascular smooth muscles. PM components, including soluble transition metals play a major role in this response. The stronger effect in SHR rats is in accordance with the observation that acute effects of PM are mainly seen in patients with underlying cardiovascular diseases.

Calcitonin Gene-Related Peptide Antagonists as Treatments of Migraine and Other Primary Headaches

Calcitonin gene-related peptide (CGRP) is a potent neuromodulator that is expressed in the trigeminovascular system and is released into the cranial circulation in various primary headaches. CGRP is released in migraine, cluster headache and paroxysmal hemicrania. The blockade of its release is associated with the successful treatment of acute migraine and cluster headache. CGRP receptor blockade has recently been shown to be an effective acute anti-migraine strategy and is non-vasoconstricting in terms of the mechanism of action. The prospect of a non-vasoconstricting therapy for acute migraine offers a real opportunity to patients, and perhaps more importantly, provides a therapeutic rationale to reinforce migraine as a neurological disorder.

Neurogenic vasodilation of dural blood vessels is not mediated by cholinergic transmission in the anaesthetised rat

Dural vessel dilation induced by activation of trigeminal sensory fibres may be responsible for some component of the migraine attack. The presence in some patients with migraine and cluster headache of clinical features, such as lacrimation, suggests cranial parasympathetic activation and poses the question as to whether neurogenic meningeal dilatation has a cholinergic component. Rats were prepared in order to record on-line the diameter of a middle meningeal artery branch through a closed cranial window using an intravital microscope coupled to a video dimension analyser. Acetylcholine (1 microg, intravenously, i.v.) was administered before and after muscarinic receptor inhibition (n=5) with scopolamine (2 mg/kg, i.v.) or nicotinic receptor inhibition (n=6) with mecamylamine (4 mg/kg, i.v.). Further vasodilation was induced by electrical stimulation of the cranial window surface before and after muscarinic receptor inhibition with i.v. scopolamine (n=8). The mean dural vessel percentage increase caused by acetylcholine stimulation was significantly different before and after muscarinic receptor inhibition (P=0.045). Moreover, there was no difference between the post receptor inhibition values and those obtained after vehicle infusion (P=0.431). In contrast, no difference was detected in the effect of acetylcholine before and after nicotinic receptor inhibition (P=0.688). In the second experiment, where the effect of muscarinic receptor inhibition on the neurogenic dilation model was assessed, no significant difference was demonstrated (P=0.538). Cholinergic dilation of the rat dural arteries is mediated by muscarinic receptors, but this mechanism does not play a significant role in the rat dural vessel dilation induced by closed cranial window electrical stimulation.

Nα-Imidazolylalkyl and Pyridylalkyl Derivatives of Histaprodifen: Synthesis and in Vitro Evaluation of Highly Potent Histamine H1-Receptor Agonists

A novel series of N(alpha)()-imidazolylalkyl and pyridylalkyl derivatives of histaprodifen (6, 2-[2-(3,3-diphenylpropyl)imidazol-4-yl]ethanamine) was synthesized and evaluated as histamine H(1)-receptor agonists. The title compounds displayed partial agonism at contractile H(1)-receptors of guinea pig ileum and were at least equipotent with histamine. Agonist effects of the new derivatives were susceptible to blockade by the H(1)-receptor antagonist mepyramine (2-100 nM). In the imidazole series, suprahistaprodifen (51, [2-[2-(3,3-diphenylpropyl)-1H-imidazol-4-yl]ethyl]-[2-(1H-imidazol-4-yl)ethyl]amine, N(alpha)-2-[(1H-imidazol-4-yl)ethyl]histaprodifen) showed the highest H(1)-receptor agonist potency ever reported in the literature (pEC(50) 8.26, efficacy E(max) 96%). Elongation of the alkyl spacer from ethyl to butyl decreased activity from 3630% (ethyl, 51) to 163% (butyl, 53) of histamine potency. The exchange of the terminal imidazole nucleus for a pyridine ring resulted in compounds with comparably high potency. A decrease in agonist potency and efficacy was observed when the attachment of the alkyl spacer was consecutively changed from the ortho to the meta and the para position, respectively, of the pyridine ring. The pyridine series that contained a butyl chain possessed the highest potency and affinity. N(alpha)-[4-(2-pyridyl)butyl]histaprodifen (56) emerged as a strong partial agonist, being almost equipotent with 51 (pEC(50) 8.16, E(max) 89%). Compounds 51 and 56 also showed potent partial agonism at contractile H(1) receptors in guinea pig aorta and potently activated H(1)-receptor-mediated endothelium-dependent relaxation in the rat aorta. Compounds 51-65 displayed low to moderate affinity at H(2), H(3), and M(3) receptors in functional models of guinea pig. Collectively, N(alpha)-imidazolylalkyl- and N(alpha)-pyridylalkyl-substituted histaprodifens represent a novel class of potent H(1)-receptor agonists. These compounds may be useful to define the (patho)physiological role of the H(1)-receptor and refine molecular models of H(1)-receptor activation.