Migraine: New Molecular Mechanisms

Migraine: a disorder of brain excitatory-inhibitory balance?

Migraine is a common disabling brain disorder whose key manifestations are recurrent attacks of unilateral headache and interictal hypersensitivity to sensory stimuli. Migraine arises from a primary brain dysfunction that leads to episodic activation and sensitization of the trigeminovascular pain pathway and as a consequence to headache. Major open issues concern the molecular and cellular mechanisms of the primary brain dysfunction(s) and of migraine pain. We review here our current understanding of these mechanisms, focusing on recent advances regarding migraine genetics, headache mechanisms, and the primary brain dysfunction(s) underlying migraine onset and susceptibility to cortical spreading depression, the neurophysiological correlate of migraine aura. We also discuss insights obtained from the functional analysis of familial hemiplegic migraine mouse models.

Preventive agents for migraine: focus on the antiepileptic drugs

Migraine is among the 10 most disabling disorders worldwide. It is characterized by episodes of moderate or severe headaches with various degree of disability, resulting in a considerable health burden upon the sufferers and their family. The objective of this article is to review the use of prophylaxis with antiepileptic drugs. Particular focus is given to their mechanism of action, metabolism, pharmacokinetics, safety profile, efficacy and to provide a summary of the most relevant clinical studies and patient preference.

Trigeminal satellite cells modulate neuronal responses to triptans: relevance for migraine therapy

In the present paper, we have further developed an in vitro model to study neuronal–glial interaction at trigeminal level by characterizing the effects of conditioned medium (CM) collected from activated primary cultures of satellite glial cells (SGCs) on calcitonin gene-related peptide (CGRP) release from rat trigeminal neurons. Moreover, we investigated whether such release is inhibited by a clinically relevant anti-migraine drug, sumatriptan. CM effects were tested on trigeminal neuronal cultures in different conditions of activation and at different time points. Long-term exposures of trigeminal neurons to CM increased directly neuronal CGRP release, which was further enhanced by the exposure to capsaicin. In this framework, the anti-migraine drug sumatriptan was able to inhibit the evoked CGRP release from naïve trigeminal neuron cultures, as well as from trigeminal cultures pre-exposed for 30 min to CM. On the contrary, sumatriptan failed to inhibit evoked CGRP release from trigeminal neurons after prolonged (4 and 8 h) pre-exposures to CM. These findings were confirmed in co-culture experiments (neurons and SGCs), where activation of SGCs or a bradykinin priming were used. Our data demonstrate that SGCs activation could influence neuronal excitability, and that this event affects the neuronal responses to triptans.

SNP variants within the vanilloid TRPV1 and TRPV3 receptor genes are associated with migraine in the Spanish population

The transient receptor potential (TRP) superfamily of non-selective cationic channels are involved in several processes plausibly relevant to migraine pathophysiology, including multimodal sensory and pain perception, central and peripheral sensitization, and regulation of calcium homeostasis. With the aim of identifying single nucleotide polymorphisms (SNPs) in TRP genes that may confer increased genetic susceptibility to migraine, we carried out a case-control genetic association study with replication, including a total of 1,040 cases and 1,037 controls. We genotyped 149 SNPs covering 14 TRP genes with known brain expression. The two-stage study comprised samples of 555 and 485 Spanish, Caucasian patients, selected according to the ICHD-II criteria for the diagnosis of migraine without aura (MO) or migraine with aura (MA). In the discovery sample, 19 SNPs in ten TRP genes showed nominal association (P < 0.05) with MO, MA, or overall migraine. In the replication sample, nominal association was confirmed for TRPV3 rs7217270 in MA and TRPV1 rs222741 in the overall migraine group. Risk haplotypes were identified for seven of the genes showing nominal association in the discovery set, but none of them was replicated. The present findings suggest that members of the vanilloid TRPV subfamily of receptors contribute to the genetic susceptibility to migraine in the Spanish population.

Identification of cytokines and signaling proteins differentially regulated by sumatriptan/naproxen

OBJECTIVES

The goal of this study was to use protein array analysis to investigate temporal regulation of stimulated cytokine expression in trigeminal ganglia and the spinal trigeminal nucleus in response to co-treatment of sumatriptan and naproxen sodium or individual drug.

BACKGROUND

Activation of neurons and glia in trigeminal ganglia and the spinal trigeminal nucleus leads to increased levels of cytokines that promote peripheral and central sensitization, which are key events in migraine pathology. While recent clinical studies have provided evidence that a combination of sumatriptan and naproxen sodium is more efficacious in treating migraine than either drug alone, it is not well understood why the combination therapy is superior to monotherapy.

METHODS

Male Sprague-Dawley rats were left untreated (control), injected with capsaicin, or pretreated with sumatriptan/naproxen, sumatriptan, or naproxen for 1 hour prior to capsaicin. Trigeminal ganglia and the spinal trigeminal nucleus were isolated 2 and 24 hours after capsaicin or drug treatment, and levels of 90 proteins were determined using a RayBio® Label-Based Rat Antibody Array (RayBiotech, Norcross, GA, USA).

RESULTS

Capsaicin stimulated a >3-fold increase in expression of the majority of cytokines in trigeminal ganglia at 2 hours that was sustained at 24 hours. Significantly, treatment with sumatriptan/naproxen almost completely abolished the stimulatory effects of capsaicin at 2 and 24 hours. Capsaicin stimulated >3-fold expression of more proteins in the spinal trigeminal nucleus at 24 hours when compared to 2 hours. Similarly, sumatriptan/naproxen abolished capsaicin stimulation of proteins in the spinal trigeminal nucleus at 2 hours and greatly suppressed protein expression 24 hours post-capsaicin injection. Interestingly, treatment with sumatriptan alone suppressed expression of different cytokines in trigeminal ganglia and the spinal trigeminal nucleus than repressed by naproxen sodium.

CONCLUSION

We found that the combination of sumatriptan/naproxen was effective in blocking capsaicin stimulation of pro-inflammatory proteins implicated in the development of peripheral and central sensitization in response to capsaicin activation of trigeminal neurons. Based on our findings that sumatriptan and naproxen regulate expression of different proteins in trigeminal ganglia and the spinal trigeminal nucleus, we propose that these drugs function on therapeutically distinct cellular targets to suppress inflammation and pain associated with migraine.

A population-based longitudinal community study of major depression and migraine

OBJECTIVE

To examine whether major depressive episodes (MDEs) are associated with an increased risk of migraine in the general population and to examine whether migraine is associated with an increase risk of MDE.

BACKGROUND

Population-based cross-sectional studies have consistently reported an association between migraine and depression. However, longitudinal studies about this potentially bidirectional association are inconsistent.

METHODS

This retrospective cohort study used 12 years of follow-up data from the Canadian National Population Health Survey (15,254 respondents, age >12). Stratified analysis, logistic regression, and proportional hazard modeling were used to quantify the effect of migraine on subsequent MDE status and vice versa.

RESULTS

After adjusting for sex, age, and other chronic health conditions, respondents with migraine were 60% more likely (HR 1.6, 95% confidence interval 1.3-1.9) to develop MDE compared with those without migraine. Similarly adjusting for sex and age, respondents with MDE were 40% more likely (HR 1.4, 95% confidence interval 1.0-1.9) to develop migraine compared with those without MDE. However, the latter association disappeared after adjustment for stress and childhood trauma.

CONCLUSIONS

The current study provides substantial evidence that migraine is associated with the later development of MDEs, but does not provide strong causal evidence of an association in the other direction. Environmental factors such as childhood trauma and stress may shape the expression of this bidirectional relationship; however, the precise underlying mechanisms are not yet known.

CaV2.1 voltage activated calcium channels and synaptic transmission in familial hemiplegic migraine pathogenesis

Studies on the genetic forms of epilepsy, chronic pain, and migraine caused by mutations in ion channels have given crucial insights into the molecular mechanisms, pathogenesis, and therapeutic approaches to complex neurological disorders. In this review we focus on the role of mutated CaV2.1 (i.e., P/Q-type) voltage-activated Ca2+ channels, and on the ultimate consequences that mutations causing familial hemiplegic migraine type-1 (FHM1) have in neurotransmitter release. Transgenic mice harboring the human pathogenic FHM1 mutation R192Q or S218L (KI) have been used as models to study neurotransmission at several central and peripheral synapses. FHM1 KI mice are a powerful tool to explore presynaptic regulation associated with expression of CaV2.1 channels. Mutated CaV2.1 channels activate at more hyperpolarizing potentials and lead to a gain-of-function in synaptic transmission. This gain-of-function might underlie alterations in the excitatory/ inhibitory balance of synaptic transmission, favoring a persistent state of hyperexcitability in cortical neurons that would increase the susceptibility for cortical spreading depression (CSD), a mechanism believed to initiate the attacks of migraine with aura.

Migraine- and dystonia-related disease-mutations of Na+/K+-ATPases: relevance of behavioral studies in mice to disease symptoms and neurological manifestations in humans

The two autosomal dominantly inherited neurological diseases: familial hemiplegic migraine type 2 (FHM2) and familial rapid-onset of dystonia-parkinsonism (Familial RDP) are caused by in vivo mutations of specific alpha subunits of the sodium-potassium pump (Na(+)/K(+)-ATPase). Intriguingly, patients with classical FHM2 and RDP symptoms additionally suffer from other manifestations, such as epilepsy/seizures and developmental disabilities. Recent studies of FHM2 and RDP mouse models provide valuable tools for dissecting the vital roles of the Na(+)/K(+)-ATPases, and we discuss their relevance to the complex patient symptoms and manifestations. Thus, it is interesting that mouse models targeting a specific α-isoform cause different, although still comparable, phenotypes consistent with classical symptoms and other manifestations observed in FHM2 and RDP patients. This review highlights that use of mouse models have broad potentials for future research concerning migraine and dystonia-related diseases, which will contribute towards understanding the, yet unknown, pathophysiologies.

Reflexive attentional orienting in migraineurs: The behavioral implications of hyperexcitable visual cortex

Introduction: Although migraine is classified as a headache disorder, a key part of migraine pathophysiology is a heightened excitability of visual cortices in between headache events. The goal of our study was to examine the behavioral impact of this visuocortical hyperexcitability, in terms of its effect on reflexive visual attentional orienting.

Methods and results: In Experiment 1, using a non-predictive spatial cuing task that relied on sensory-evoked responses in the visual cortex for triggering attentional orienting, we found that migraineurs had greater attentional enhancement of manual target responses, relative to non-migraine controls. In two control experiments we confirmed that this heightened attention effect in migraineurs is not due to exaggerated reflexive orienting responses in general, but rather, it appears to be specifically associated with sensory-evoked attentional triggers.

Discussion: Taken together, this confirms that the functional consequences of hyperexcitable visual cortex in migraineurs are not just purely sensory in nature, but directly impact at least some forms of reflexive attention. This provides evidence of at least one cognitive implication of hyperexcitable visual cortical responses in migraineurs, namely heightened reflexive visual-spatial orienting specific to sudden-onset peripheral events.

Increased susceptibility to cortical spreading depression in the mouse model of familial hemiplegic migraine type 2

Familial hemiplegic migraine type 2 (FHM2) is an autosomal dominant form of migraine with aura that is caused by mutations of the α2-subunit of the Na,K-ATPase, an isoform almost exclusively expressed in astrocytes in the adult brain. We generated the first FHM2 knock-in mouse model carrying the human W887R mutation in the Atp1a2 orthologous gene. Homozygous Atp1a2^R887/R887 mutants died just after birth, while heterozygous Atp1a2^+/R887 mice showed no apparent clinical phenotype. The mutant α2 Na,K-ATPase protein was barely detectable in the brain of homozygous mutants and strongly reduced in the brain of heterozygous mutants, likely as a consequence of endoplasmic reticulum retention and subsequent proteasomal degradation, as we demonstrate in transfected cells. In vivo analysis of cortical spreading depression (CSD), the phenomenon underlying migraine aura, revealed a decreased induction threshold and an increased velocity of propagation in the heterozygous FHM2 mouse. Since several lines of evidence involve a specific role of the glial α2 Na,K pump in active reuptake of glutamate from the synaptic cleft, we hypothesize that CSD facilitation in the FHM2 mouse model is sustained by inefficient glutamate clearance by astrocytes and consequent increased cortical excitatory neurotransmission. The demonstration that FHM2 and FHM1 mutations share the ability to facilitate induction and propagation of CSD in mouse models further support the role of CSD as a key migraine trigger.

We previously reported that mutations of the α2 subunit of the Na,K-ATPase cause familial hemiplegic migraine type 2 (FHM2), a dominant form of migraine with aura. This paper describes the first animal model of FHM2 and represents the further proceeding in this disease investigation. Homozygous knock-in mutant mice die just after birth, while heterozygous mice show no apparent clinical phenotype. However, in vivo analysis revealed a marked facilitation of cortical spreading depression (CSD), the phenomenon underlying migraine aura. Given the evidence for specific functional coupling between the glial α2 Na,K pump and glutamate transporters, we hypothesize that CSD facilitation in the FHM2 mouse model is sustained by inefficient glutamate clearance by astrocytes and consequent increased cortical excitatory neurotransmission. We finally propose this FHM2 mouse as a valuable in vivo model to investigate migraine mechanisms and, possibly, treatments.

Topiramate: safety and efficacy of its use in the prevention and treatment of migraine

Migraine headaches are typically episodic in nature and may affect nearly 10% of the population. In addition to treatment, prevention of subsequent episodes or progression to a chronic migraine state is an important therapeutic area. Topiramate is a centrally acting medication approved for both the prevention of seizures and migraine headache. At this time, the exact mechanism of how topiramate assists in migraine prevention is unknown. Several large randomized, controlled trials have aided in establishing topiramate's role in migraine prevention. Despite a favorable pharmacokinetic and adverse effect profile established in clinical trials, several additional studies, case reports and toxicology reports have demonstrated topiramate as a cause of cognitive and behavioural changes. The use of topiramate in migraine prevention can improve a patient's quality of life and is a cost-effective option for migraine prevention.

Cortical inhibition at rest and under a focused attention challenge in adults with migraine with and without aura

Objectives: We aimed to further elucidate the functional and attentional regulation of cortical excitability in migraine patients.

Methods: We investigated the cortical silent period (CSP) after transcranial magnetic stimulation as a measure of cortical inhibition under three conditions: resting condition, cortical preactivation during reaction preparation, and during the post-processing of a motor response using a visual contingent negative variation paradigm in adults with migraine with aura, migraine without aura and healthy controls.

Results: CSP was reduced in individuals with migraine with aura and unaffected in those with migraine without aura under resting conditions. Along with the intensity of transcranial magnetic stimulation, CSP increased equally in all groups (equal slopes). Furthermore, the functional challenge by a contingent negative variation task requiring focused sustained attention led to a comparable reduction of CSP duration in all groups.

Discussion: Our data provide further hints towards the conclusion that a specific cortical inhibition deficit in migraine with aura but not migraine without aura is due to a tonic imbalance and not related to increased reactions to phasic stressors. Given that CSP at rest is related to GABA-ergic inhibition whereas the CSP reduction during late contingent negative variation is thought to be related to dopaminergic disinhibition in the basal ganglia, our results point towards reduced GABA-ergic cortical inhibition related to dysfunctional thalamo-cortical loops, especially in migraine with aura.

[Transcranial magnetic stimulation (TMS) in basic and clinical neuroscience research]

INTRODUCTION

Non-invasive brain stimulation methods such as transcranial magnetic stimulation (TMS) are starting to be widely used to make causality-based inferences about brain-behavior interactions. Moreover, TMS-based clinical applications are under development to treat specific neurological or psychiatric conditions, such as depression, dystonia, pain, tinnitus and the sequels of stroke, among others.

BACKGROUND

TMS works by inducing non-invasively electric currents in localized cortical regions thus modulating their activity levels according to settings, such as frequency, number of pulses, train and regime duration and intertrain intervals. For instance, it is known for the motor cortex that low frequency or continuous patterns of TMS pulses tend to depress local activity whereas high frequency and discontinuous TMS patterns tend to enhance it. Additionally, local cortical effects of TMS can result in dramatic patterns in distant brain regions. These distant effects are mediated via anatomical connectivity in a magnitude that depends on the efficiency and sign of such connections.

PERSPECTIVES

An efficient use of TMS in both fields requires however, a deep understanding of its operational principles, its risks, its potential and limitations. In this article, we will briefly present the principles through which non-invasive brain stimulation methods, and in particular TMS, operate.

CONCLUSION

Readers will be provided with fundamental information needed to critically discuss TMS studies and design hypothesis-driven TMS applications for cognitive and clinical neuroscience research.

Epigenetic regulation of the calcitonin gene-related peptide gene in trigeminal glia

BACKGROUND

The neuropeptide calcitonin gene-related peptide (CGRP) plays a key role in migraine. CGRP gene expression involves an enhancer that is active in neurons, yet inactive in glia. In this report, we analyze epigenetic modifications that allow enhancer activation in glia.

METHODS

DNA methylation and histone acetylation states were measured in rat and human- model cell lines and primary cultures of rat trigeminal ganglia glia. The functional consequence of altering the chromatin state was determined by quantitative measurements of both calcitonin (CT) and CGRP mRNAs.

RESULTS

A hypermethylated CpG island flanking the enhancer was identified in glia and non-expressing cell lines. In addition, the chromatin was hypoacetylated. Treatment with the DNA methylation inhibitor 5-aza-2'-deoxycytidine induced CT mRNA ~30-fold in glial cultures. Treatment with a histone deacetylase inhibitor alone had little effect; however, the combination of inhibitors yielded a synergistic ~80-fold increase in CT and ~threefold increase in CGRP mRNA. Treated glia contained CT precursor (pro-CT) immunoreactivity.

CONCLUSIONS

Epigenetic modulation is sufficient to induce the CGRP gene in glia. Because the CGRP gene is systemically activated by inflammatory conditions, this suggests that glial pro-CT may be an unexplored biomarker during migraine.

Central sensitization in the trigeminal nucleus caudalis produced by a conjugate of substance P and the A subunit of cholera toxin

Individuals with chronic craniofacial pain experience symptoms that are consistent with central sensitization. In fact, central sensitization may constitute the major disease process in these conditions, particularly if the original injury has healed or the condition is idiopathic. To understand central sensitization we have developed a conjugate of substance P and cholera toxin (SP-CTA). SP-CTA is selectively taken up by cells that express neurokinin receptors. Twenty-four hours following intracisternal administration of SP-CTA, wild-type rats and mice demonstrated signs of persistent background nociception, but when tested for facial cold sensitivity, they did not differ from controls. However, treating the SP-CTA-injected animals with naloxone exposed cold hypersensitivity in the face. Mu-opioid receptor knockout mice treated with SP-CTA demonstrated hypersensitivity without naloxone treatment. These findings suggest that central sensitization leads to activation of an endogenous opioid system. The data also demonstrate that the intracisternal administration of SP-CTA in rodents is a useful model for studying central sensitization as a disease process without having to induce a peripheral injury.

PERSPECTIVE

Central sensitization is a concern in many craniofacial pain conditions. In this project, we utilize a conjugate of substance P and the catalytic subunit of cholera toxin to induce central sensitization in the nucleus caudalis of rodents. The data indicate that the injected animals become hypersensitive in the face.

Organ culture of the trigeminal ganglion induces enhanced expression of calcitonin gene-related peptide via activation of extracellular signal-regulated protein kinase 1/2

BACKGROUND AND OBJECTIVE

Clinical and experimental studies have revealed a central role of calcitonin gene-related peptide (CGRP) in primary headaches. The role of extracellular signal-regulated kinase 1 and 2 (ERK1/2) in neuronal and glial cell expression of CGRP- immunoreactivity (-ir) in rat trigeminal ganglia was studied with an organ culture method.

EXPERIMENTAL PROCEDURES

Sections of adult rat trigeminal ganglia were cultured for up to 48 hours, examined with immunohistochemistry and quantitative real-time polymerase chain reaction (PCR) assay. Specific antibodies against CGRP, phosphorylated ERK1/2 (pERK1/2), total ERK1/2 (tERK1/2), phosphorylated p38 (pp38), phosphorylated C-Jun-N-terminal protein kinase (pJNK), pro-calcitonin (pro-CT), CGRP receptor activity modifying protein 1 (RAMP1), glutamine synthetase (GS) and pro-CT were used. To explore molecular mechanisms involved in the organ culture-induced CGRP-ir in neurons and glial cells, the effects of the MEK/ERK1/2 inhibitor U0126, its inactive analogue U0124, the p38 inhibitor SB203580 and the JNK inhibitor SP600125 were studied.

RESULTS

In fresh ganglia, small- and medium-sized neurons were CGRP-ir while some larger neurons displayed RAMP1-ir. Glial cells were negative to both. After organ culture, neurons showed enhanced CGRP- and RAMP1-ir. In addition, some glial cells were RAMP1- and CGRP-ir. Isolated glial cells and neurons were found to contain CGRP mRNA, and showed pro-CT-ir, suggestive of local formation of CGRP. Neurons and glial cells showed enhanced pERK1/2-ir already after two hours of organ culture and this remained elevated for 48 hours. There was transient pJNK-ir in neurons at two hours, while pp38-ir was not altered. U0126 reduced the enhanced pERK1/2-ir, while U0124 had no such effect; the CGRP-ir in neurons and glial cells was reduced at 48 hours and in parallel the CGRP mRNA expression was lower at 24 hours.

CONCLUSION

We suggest that in conditions of elevated CGRP expression, inhibition of ERK1/2 might be an option for novel treatment.

Calcitonin gene-related peptide (CGRP) receptor antagonists in the treatment of migraine

Based on preclinical and clinical studies, the neuropeptide calcitonin gene-related peptide (CGRP) is proposed to play a central role in the underlying pathology of migraine. CGRP and its receptor are widely expressed in both the peripheral and central nervous systems by multiple cell types involved in the regulation of inflammatory and nociceptive responses. Peripheral release of CGRP from trigeminal nerve fibres within the dura and from the cell body of trigeminal ganglion neurons is likely to contribute to peripheral sensitization of trigeminal nociceptors. Similarly, the release of CGRP within the trigeminal nucleus caudalis can facilitate activation of nociceptive second-order neurons and glial cells. Thus, CGRP is involved in the development and maintenance of persistent pain, central sensitization and allodynia, events characteristic of migraine pathology. In contrast, CGRP release within the brain is likely to function in an anti-nociceptive capacity. Given the role of CGRP in migraine pathology, the potential of CGRP receptor antagonists in the treatment of migraine has been investigated. Towards this end, the non-peptide CGRP receptor antagonists olcegepant and telcagepant have been shown to be effective in the acute treatment of migraine. While telcagepant is being pursued as a frontline abortive migraine drug in a phase III clinical trial, an oral formulation of a novel CGRP receptor antagonist, BI 44370, is currently in phase II clinical trials. Encouragingly, data from clinical studies on these compounds have clearly demonstrated the potential therapeutic benefit of this class of drugs and support the future development of CGRP receptor antagonists to treat migraine and possibly other types of chronic pain.

Migraine is frequent in patients with systemic lupus erythematosus: A case-control study

Introduction

The objective of this study was to compare the prevalence of primary headaches in systemic lupus erythematosus (SLE) versus healthy subjects, and to determine whether headaches in SLE are associated with MRI- or cere-brospinal fluid (CSF) abnormalitites.

Patients and methods

The case-control study included MRI- and CSF investigations. Headache was classified according to the International Classification of Headache Disorders. Depression and fatigue were measured with Beck Depression Inventory (BDI) and Fatigue Severity Scale (FSS) respectively.

Results

Twenty-four out of 67 SLE patients and 13 out of 67 age- and gender matched healthy subjects had migraine (36% vs 19%, P = 0.03). Nine (13%) SLE patients had migraine with aura vs 4 (6%) in healthy subjects, P = 0.14. The prevalence of tension type headache was equal (60% in patients vs 58% in controls). There was no association between migraine and SLE disease activity, biochemical or immunological markers, cerebral white matter hyperintensities, interleukin-6 in CSF, impairment of the blood-brain barrier, or intrathecal immunoglobulin production. SLE patients had higher BDI- and FSS scores compared with healthy control subjects, and SLE patients with migraine had higher BDI scores than lupus patients without migraine.

Conclusions

Migraine is more prevalent in SLE patients, associated with depression like in the general population, but not associated with disease activity or abnormalities detected on cerebral MRI, in CSF, or any SLE characteristics except from SLE photosensitivity. The inclusion of the migraine item in SLE disease activity instruments remains questionable.

Insights into migraine mechanisms and CaV2.1 calcium channel function from mouse models of familial hemiplegic migraine

Migraine is a very common disabling brain disorder with unclear pathogenesis. A subtype of migraine with aura (familial hemiplegic migraine type 1: FHM1) is caused by mutations in CaV2.1 (P/Q-type) Ca2+ channels. This review describes the functional consequences of FHM1 mutations in knockin mouse models carrying the mild R192Q or severe S218L mutations in the orthologous gene. The FHM1 knockin mice show allele dosage-dependent gain-of-function of neuronal P/Q-type Ca2+ current, reflecting activation of mutant channels at lower voltages, and allele dosage- and sex-dependent facilitation of induction and propagation of cortical spreading depression (CSD), the phenomenon that underlies migraine aura. Gain-of-function of neuronal Ca2+ current, facilitation of CSD and post-CSD motor deficits were larger in S218L than R192Q knockin mice, in correlation with the more severe human S218L phenotype. Enhanced cortical excitatory neurotransmission, due to increased action potential-evoked Ca2+ influx and increased probability of glutamate release at pyramidal cell synapses, but unaltered inhibitory neurotransmission at fast-spiking interneuron synapses, were demonstrated in R192Q knockin mice. Evidence for a causative link between enhanced glutamate release and CSD facilitation was obtained. The data from FHM1 mice strengthen the view of CSD as a key player in the pathogenesis of migraine, give insight into CSD mechanisms and point to episodic disruption of excitation-inhibition balance and neuronal hyperactivity as the basis for vulnerability to CSD ignition in migraine.

BDNF and CGRP interaction: Implications in migraine susceptibility

Objectives: Migraine pathophysiology involves several pathways. Our aims were to explore a possible role of the brain-derived neurotrophic factor gene ( BDNF) in migraine susceptibility; to study, for the first time, the calcitonin gene-related peptide gene ( CGRP); and a possible interaction between the two.

Methods: Using a case-control approach, four tagging single nucleotide polymorphisms (SNPs) (rs7124442, rs6265, rs11030107, and rs2049046) of BDNF and one tagging SNP—rs1553005—of CGRP were analyzed in 188 cases and 287 controls. A multivariable logistic regression was performed, adjusting for gender. Allelic and haplotypic frequencies were estimated. Interaction was assessed by a stepwise multivariable-logistic regression and confirmed by a multifactor dimensionality reduction analysis.

Results: No significant main effects were found; however, a significant interaction was found between BDNF and CGRP, showing an increased risk for the AT-genotype of rs2049046 and the GC-genotype of rs1553005 (odds ratio = 1.88, 95% confidence interval: 1.20–2.93) for migraineurs.

Conclusion: Our data support the hypothesis of an interaction between BDNF and CGRP in migraine susceptibility that should be further explored.

CGRP receptor antagonism and migraine

Calcitonin gene-related peptide (CGRP) is expressed throughout the central and peripheral nervous systems, consistent with control of vasodilatation, nociception, motor function, secretion, and olfaction. alphaCGRP is prominently localized in primary spinal afferent C and ADelta fibers of sensory ganglia, and betaCGRP is the main isoform in the enteric nervous system. In the CNS there is a wide distribution of CGRP-containing neurons, with the highest levels occurring in striatum, amygdala, colliculi, and cerebellum. The peripheral projections are involved in neurogenic vasodilatation and inflammation, and central release induces hyperalgesia. CGRP is released from trigeminal nerves in migraine. Trigeminal nerve activation results in antidromic release of CGRP to cause non-endothelium-mediated vasodilatation. At the central synapses in the trigeminal nucleus caudalis, CGRP acts postjunctionally on second-order neurons to transmit pain signals centrally via the brainstem and midbrain to the thalamus and higher cortical pain regions. Recently developed CGRP receptor antagonists are effective at aborting acute migraine attacks. They may act both centrally and peripherally to attenuate signaling within the trigeminovascular pathway.

Headache-type adverse effects of NO donors: vasodilation and beyond

Although nitrate therapy, used in the treatment of cardiovascular disorders, is frequently associated with side-effects, mainly headaches, the summaries of product characteristics of nitrate-containing medicines do not report detailed description of headaches and even do not highlight the possibility of nitrate-induced migraine. Two different types of nitrate-induced headaches have been described: (i) immediate headaches that develop within the first hour of the application, are mild or medium severity without characteristic symptoms for migraine, and ease spontaneously; and (ii) delayed, moderate or severe migraine-type headaches (occurring mainly in subjects with personal or family history of migraine), that develop 3-6 h after the intake of nitrates, with debilitating, long-lasting symptoms including nausea, vomiting, photo- and/or phono-phobia. These two types of headaches are remarkably different, not only in their timing and symptoms, but also in the persons who are at risk. Recent studies provide evidence that the two headache types are caused by different mechanisms: immediate headaches are connected to vasodilation caused by nitric oxide (NO) release, while migraines are triggered by other actions such as the release of calcitonin gene-related peptide or glutamate, or changes in ion channel function mediated by cyclic guanosine monophosphate or S-nitrosylation. Migraines usually need anti-attack medication, such as triptans, but these drugs are contraindicated in most medical conditions that are treated using nitrates. In conclusion, these data recommend the correction of summaries of nitrate product characteristics, and also suggest a need to develop new types of anti-migraine drugs, effective in migraine attacks, that could be used in patients with risk for angina pectoris.

CaV2.1 channelopathies

Mutations in the CACNA1A gene that encodes the pore-forming alpha1 subunit of human voltage-gated CaV2.1 (P/Q-type) Ca2+ channels cause several autosomal-dominant neurologic disorders, including familial hemiplegic migraine type 1 (FHM1), episodic ataxia type 2, and spinocerebellar ataxia type 6 (SCA6). For each channelopathy, the review describes the disease phenotype as well as the functional consequences of the disease-causing mutations on recombinant human CaV2.1 channels and, in the case of FHM1 and SCA6, on neuronal CaV2.1 channels expressed at the endogenous physiological level in knockin mouse models. The effects of FHM1 mutations on cortical spreading depression, the phenomenon underlying migraine aura, and on cortical excitatory and inhibitory synaptic transmission in FHM1 knockin mice are also described, and their implications for the disease mechanism discussed. Moreover, the review describes different ataxic spontaneous cacna1a mouse mutants and the important insights into the cerebellar mechanisms underlying motor dysfunction caused by mutant CaV2.1 channels that were obtained from their functional characterization.

Calcitonin gene-related peptide differentially regulates gene and protein expression in trigeminal glia cells: findings from array analysis

Calcitonin gene-related peptide (CGRP) is a multifunctional neuropeptide implicated in inflammatory diseases involving trigeminal ganglion nerve activation. Within trigeminal ganglia, satellite glia and Schwann cells are found in close association with neuronal cell bodies and fibers, respectively, and are known to express functional CGRP receptors. The goal of this study was to use array analysis to provide a more comprehensive understanding of CGRP regulation of inflammatory proteins and genes in trigeminal glia. Primary trigeminal ganglia cultures enriched for glia were treated with 500 nM CGRP for 8 or 24h. CGRP caused a >3-fold increase in the level of 19 cytokines 8h after CGRP treatment and the levels of each of these cytokines remained significantly elevated over basal unstimulated levels at 24h. While mRNA levels of many genes involved in mitogen-activated protein (MAP) kinase signaling were increased 8h after CGRP treatment, the number of responsive genes was greatly increased at 24h. Specifically, CGRP was shown to temporally regulate expression of multiple MAP kinases as well as numerous MAP kinase-responsive genes including transcription factors, scaffold/anchoring proteins, and cell cycle proteins. Thus, our data provide evidence of an emerging role of CGRP as an important modulator of trigeminal ganglion glia by stimulating cytokine release as well as inducing expression of a diverse array of proteins involved in MAP kinase signaling.

Shared genetic factors in migraine and depression: evidence from a genetic isolate

OBJECTIVE

To investigate the co-occurrence of migraine and depression and assess whether shared genetic factors may underlie both diseases.

METHODS

Subjects were 2,652 participants of the Erasmus Rucphen Family genetic isolate study. Migraine was diagnosed using a validated 3-stage screening method that included a telephone interview. Symptoms of depression were assessed using the Center for Epidemiologic Studies Depression scale and the depression subscale of the Hospital Anxiety and Depression Scale (HADS-D). The contribution of shared genetic factors in migraine and depression was investigated by comparing heritability estimates for migraine with and without adjustment for symptoms of depression, and by comparing the heritability scores of depression between migraineurs and controls.

RESULTS

We identified 360 migraine cases: 209 had migraine without aura (MO) and 151 had migraine with aura (MA). Odds ratios for depression in patients with migraine were 1.29 (95% confidence interval [CI] 0.98-1.70) for MO and 1.70 (95% CI 1.28-2.24) for MA. Heritability estimates were significant for all migraine (0.56), MO (0.77), and MA (0.96), and decreased after adjustment for symptoms of depression or use of antidepressant medication, in particular for MA. Comparison of the heritability scores for depression between patients with migraine and controls showed a genetic correlation between HADS-D score and MA.

CONCLUSIONS

There is a bidirectional association between depression and migraine, in particular migraine with aura, which can be explained, at least partly, by shared genetic factors.

Headache endocrinological aspects

In this chapter we review the current understanding of how hormones, neurohormones, and neurotransmitters participate in the pain modulation of primary headaches. Stressful conditions and hormones intimately implicated in headache neurobiology are also discussed. With the recent progress in neuroimaging techniques and the development of animal models to study headache mechanisms, the physiopathology of several of the primary headaches is starting to be better understood. Various clinical characteristics of the primary headaches, such as pain, autonomic disturbances, and behavioral changes, are linked to hypothalamic brainstem activation and hormonal influence. Headache is greatly influenced by the circadian circle. Over the millennia the nervous system has evolved to meet changing environmental conditions, including the light-dark cycle, in order to ensure survival and reproduction. The main elements for synchronization between internal biological events and the external environment are the pineal gland and its main secretory product, melatonin. Melatonin is believed to be a significant element in migraine and in other headache disorders, which has implications for treatment. A potential therapeutic use of melatonin has been considered in several headache syndromes. In short, primary headaches are strongly influenced by physiological hormonal fluctuations, when nociceptive and non-nociceptive pathways are differentially activated to modulate the perception of pain.

Biological science of headache channels

Several episodic neurological diseases, including familial hemiplegic migraine (FHM) and different types of epilepsy, are caused by mutations in ion channels, and hence classified as channelopathies. The classification of FHM as a channelopathy has introduced a new perspective in headache research and has strengthened the idea of migraine as a disorder of neural excitability. Here we review recent studies of the functional consequences of mutations in the CACNA1A and SCNA1A genes (encoding the pore-forming subunit of Ca(V)2.1 and Na(V)1.1 channels) and the ATPA1A2 gene (encoding the alpha(2) subunit of the Na(+)/K(+) pump), responsible for FHM1, FHM3, and FHM2, respectively. These studies show that: (1) FHM1 mutations produce gain-of-function of the Ca(V)2.1 channel and, as a consequence, increased glutamate release at cortical synapses and facilitation of induction and propagation of cortical spreading depression (CSD); (2) FHM2 mutations produce loss-of-function of the alpha(2) Na(+)/K(+)-ATPase; and (3) the FHM3 mutation accelerates recovery from fast inactivation of Na(V)1.5 channels. These findings are consistent with the hypothesis that FHM mutations share the ability to render the brain more susceptible to CSD, by causing excessive synaptic glutamate release (FHM1) or decreased removal of K(+) and glutamate from the synaptic cleft (FHM2) or excessive extracellular K(+) (FHM3).

Genetics of headaches

Insight into the molecular mechanisms involved in primary headaches is important to identify drug targets for improving treatment of patients, but essentially lacking. Genetic research is increasingly successful in pinpointing these mechanisms. Most progress has been made for Familial Hemiplegic Migraine, a rare subtype of migraine with aura. Three genes (CACNA1A, ATP1A2 and SCN1A) have been identified that all encode ion transporters. Cellular and transgenic mouse studies suggest that neuronal hyperexcitability and increased susceptibility to cortical spreading depression, the correlate of migraine aura, are important molecular mechanisms in migraine. Investigating monogenic diseases in which migraine is a prominent feature such as CADASIL, which is caused by mutations in the NOTCH3 gene, can help understanding the pathology of migraine. Candidate gene association studies and linkage studies in the common forms of migraine were less successful. Except for the MTHFR gene no gene variant has been identified yet. Convincingly demonstrated genetic findings in other primary headaches such as cluster headache and tension-type headache are even rarer. However, with current technical possibilities of massive genotyping and international efforts to collect large well-phenotyped patient cohorts, the first gene variants for various primary headache types are likely to be discovered in the coming decade.

Pharmacology

Headache treatment has been based primarily on experiences with non-specific drugs such as analgesics, non-steroidal anti-inflammatory drugs, or drugs that were originally developed to treat other diseases, such as beta-blockers and anticonvulsant medications. A better understanding of the basic pathophysiological mechanisms of migraine and other types of headache has led to the development over the past two decades of more target-specific drugs. Since activation of the trigeminovascular system and neurogenic inflammation are thought to play important roles in migraine pathophysiology, experimental studies modeling those events successfully predicted targets for selective development of pharmacological agents to treat migraine. Basically, there are two fundamental strategies for the treatment of migraine, abortive or preventive, based to a large degree on the frequency of attacks. The triptans, which exhibit potency towards selective serotonin (5-hydroxytryptamine, 5-HT) receptors expressed on trigeminal nerves, remain the most effective drugs for the abortive treatment of migraine. However, numerous preventive medications are currently available that modulate the excitability of the nervous system, particularly the cerebral cortex. In this chapter, the pharmacology of commercially available medications as well as drugs in development that prevent or abort headache attacks will be discussed.

Reduced cerebellar inhibition in migraine with aura: a TMS study

Subtle clinical cerebellar alterations have been found in migraine. Moreover, abnormalities in visual and motor cortex excitability consistent with a lack of inhibitory efficiency have been described in migraine, and it is known that cerebellum exerts an inhibitory control on cerebral cortex. Here, we investigated if impairment of cerebellar activity on motor cortex, i.e. reduced inhibitory control, can be found in migraine. Ten migraineurs with aura and seven healthy controls underwent a transcranial magnetic stimulation (TMS) protocol to investigate the cerebellar inhibitory drive on motor cortex: a conditioning pulse on right cerebellar cortex was delivered 5, 7, 10, 15 ms before a test stimulus (TS) on contralateral motor cortex. The cerebellar conditioning stimulus inhibits the size of the motor-evoked potential (MEP) produced by the TS alone by approximately 30-50%. Amplitude of MEP to TS alone showed no significant difference between patients and controls. Cerebellar conditioning TMS showed a significant deficit of cerebellar inhibition in migraine patients as compared to controls at all interstimulus intervals (5-15 ms) tested. Cerebellar inhibition is reduced in migraineurs. This could account, at least in part, for the reduced inhibitory efficiency previously showed in cerebral cortex of these patients.

Mutation I810N in the alpha3 isoform of Na+,K+-ATPase causes impairments in the sodium pump and hyperexcitability in the CNS

In a mouse mutagenesis screen, we isolated a mutant, Myshkin (Myk), with autosomal dominant complex partial and secondarily generalized seizures, a greatly reduced threshold for hippocampal seizures in vitro, posttetanic hyperexcitability of the CA3-CA1 hippocampal pathway, and neuronal degeneration in the hippocampus. Positional cloning and functional analysis revealed that Myk/+ mice carry a mutation (I810N) which renders the normally expressed Na(+),K(+)-ATPase alpha3 isoform inactive. Total Na(+),K(+)-ATPase activity was reduced by 42% in Myk/+ brain. The epilepsy in Myk/+ mice and in vitro hyperexcitability could be prevented by delivery of additional copies of wild-type Na(+),K(+)-ATPase alpha3 by transgenesis, which also rescued Na(+),K(+)-ATPase activity. Our findings reveal the functional significance of the Na(+),K(+)-ATPase alpha3 isoform in the control of epileptiform activity and seizure behavior.

CGRP stimulation of iNOS and NO release from trigeminal ganglion glial cells involves mitogen-activated protein kinase pathways

Clinical and basic science data support an integral role of calcitonin gene-related peptide (CGRP) in the pathophysiology of temporomandibular joint disorders. Recently, we have shown that CGRP can stimulate the synthesis and release of nitric oxide (NO) from trigeminal ganglion glial cells. The goal of this study was to determine the role of mitogen-activated protein kinase (MAPK) signaling pathways in CGRP regulation of iNOS expression and NO release from cultured trigeminal ganglion glial cells from Sprague-Dawley rats. CGRP treatment for 2 h significantly increased activity of the MAPK reporter genes, Elk, ATF-2, and CHOP. In addition, CGRP increased nuclear staining for the active forms of the MAPKs: extracellular signal-regulated kinase, c-Jun amino-terminal kinase, and p38. This stimulatory event was not observed in cultures pre-treated with the CGRP receptor antagonist peptide CGRP(8-37). Similarly, pre-treatment with selective MAPK inhibitors repressed increases in reporter gene activity as well as CGRP-induced increases in iNOS expression and NO release mediated by MAPKs. In addition, over-expression of MAPK kinase 1 (MEK1), MEK3, MEK6, and MEK kinase significantly increased iNOS expression and NO production in glial cells. Results from our study provide evidence that CGRP binding to its receptor can stimulate iNOS gene expression via activation of MAPK pathways in trigeminal ganglion glial cells.

Motor coordination impairment in aged heterozygous rolling Nagoya, Cav2.1 mutant mice

Although rolling Nagoya mice exhibit ataxia and carry a mutation in the alpha1 subunit of the Cav2.1 channel regulating neurotransmitter release, heterozygous mice have not received a great deal of attention. Given the pivotal role of Cav2.1 channels in controlling neurotransmitter release, age-dependent alterations in Cav2.1 channel function may result in aberrant synaptic signaling, leading to motor dysfunction. To examine age-related motor alterations in heterozygous mice, we used a battery of tests (e.g., motor activity, footprint, traction, wire suspension, balance beam, rotating rod, hind-limb extension analysis) in 2- and 22-month-old mice and examined expression patterns of the alpha1 gene in their cerebellum. No significant difference was observed between 2-month-old heterozygous and wild-type mice in the any of the behavioral tests or in the alpha1 expression levels. Although 22-month-old heterozygous and wild-type mice exhibited no significant difference in motor activity, footprint, or traction tests, 22-month-old heterozygous mice showed deficits in the wire hanging, balance beam, and rotating rod tests. Additionally, 22-month-old heterozygous mice displayed clasping behavior in the hind-limb extension test. Expression analysis showed that wild-type Cav2.1alpha(1) mRNA was lower in aged mice than in young mice and that mutant-type Cav2.1alpha(1) mRNA was higher in aged mice than in young mice. These findings suggest that heterozygous mice show age-related motor changes due to mutant-type Cav2.1 and that heterozygous mice may represent a new model for examining motor function.

Tonabersat inhibits trigeminal ganglion neuronal-satellite glial cell signaling

BACKGROUND

Sensitization and activation of trigeminal neurons are implicated in the underlying pathology of migraine, acute sinusitis, and allergic rhinitis. Cell bodies of trigeminal neurons that provide sensory innervation of the dura and nasal mucosa reside in the trigeminal ganglion in association with satellite glial cells where they communicate via gap junctions. Gap junctions, channels formed by connexins, modulate the excitability state of both neurons and glia under pathological conditions. Tonabersat, a compound being tested as an antimigraine drug, is thought to block gap junction activity.

OBJECTIVE

To investigate the cellular events within trigeminal ganglia that may account for the significant comorbidity of migraine and rhinosinusitis and determine the effect of tonabersat on neuron-satellite glia communication.

METHODS

Sprague Dawley rats injected with True Blue were used to localize neuronal cell bodies in the ganglion and study neuron-glia signaling via gap junctions in the trigeminal ganglion. Dye coupling studies were conducted under basal conditions and in response to tumor necrosis factor-alpha injection into the whisker pad and/or capsaicin injection into the eyebrow. Changes in connexin 26 and active p38 levels were determined by immunohistochemistry. In addition, the effect of tonabersat prior to chemical stimulation on gap junction activity and expression of connexins and active p38 was investigated.

RESULTS

Injection of tumor necrosis factor-alpha, a cytokine implicated in the pathology of acute sinusitis and allergic rhinitis, into the V2 region was shown to lower the amount of capsaicin required to stimulate neurons located in the V1 region of the ganglion. While injection of tumor necrosis factor-alpha into the whisker pad or capsaicin injection into the eyebrow alone did not cause increased dye movement, the combination of both stimuli greatly increased neuron-satellite glia communication via gap junctions in both V1 and V2 regions. The change in gap junction activity was accompanied by increased expression of connexin 26 and active p38 levels in both neurons and satellite glia in V1 and V2 regions. Pretreatment with tonabersat inhibited gap junction communication between neurons and satellite glia and blocked the increase in connexin 26 and active p38 levels in response to injection of both tumor necrosis factor-alpha (V2) and capsaicin (V1).

CONCLUSIONS

We propose that increased levels of tumor necrosis factor-alpha, as reported during acute sinusitis and allergic rhinitis, reduces the amount of capsaicin necessary to stimulate V1 neurons that leads to cellular changes in both V1 and V2 regions. The cellular events observed in this study may help to explain, in part, the significant comorbidity reported with migraine and rhinosinusitis. In addition, we have provided evidence to suggest that tonabersat can prevent increased neuron-satellite glia signaling and, thus, may be useful in the treatment of migraine, acute sinusitis, and allergic rhinitis.