Cortical Spreading Depression: A Model for Understanding Migraine Biology and Future Drug Targets

Familial hemiplegic migraine type-1 mutated cav2.1 calcium channels alter inhibitory and excitatory synaptic transmission in the lateral superior olive of mice

CaV2.1 Ca(2+) channels play a key role in triggering neurotransmitter release and mediating synaptic transmission. Familial hemiplegic migraine type-1 (FHM-1) is caused by missense mutations in the CACNA1A gene that encodes the α1A pore-forming subunit of CaV2.1 Ca(2+) channels. We used knock-in (KI) transgenic mice harbouring the pathogenic FHM-1 mutation R192Q to study inhibitory and excitatory neurotransmission in the principle neurons of the lateral superior olive (LSO) in the auditory brainstem. We tested if the R192Q FHM-1 mutation differentially affects excitatory and inhibitory synaptic transmission, disturbing the normal balance between excitation and inhibition in this nucleus. Whole cell patch-clamp was used to measure neurotransmitter elicited excitatory (EPSCs) and inhibitory (IPSCs) postsynaptic currents in wild-type (WT) and R192Q KI mice. Our results showed that the FHM-1 mutation in CaV2.1 channels has multiple effects. Evoked EPSC amplitudes were smaller whereas evoked and miniature IPSC amplitudes were larger in R192Q KI compared to WT mice. In addition, in R192Q KI mice, the release probability was enhanced compared to WT, at both inhibitory (0.53 ± 0.02 vs. 0.44 ± 0.01, P = 2.10(-5), Student's t-test) and excitatory synapses (0.60 ± 0.03 vs. 0.45 ± 0.02, P = 4 10(-6), Student's t-test). Vesicle pool size was diminished in R192Q KI mice compared to WT mice (68 ± 6 vs 91 ± 7, P = 0.008, inhibitory; 104 ± 13 vs 335 ± 30, P = 10(-6), excitatory, Student's t-test). R192Q KI mice present enhanced short-term plasticity. Repetitive stimulation of the afferent axons caused short-term depression (STD) of E/IPSCs that recovered significantly faster in R192Q KI mice compared to WT. This supports the hypothesis of a gain-of-function of the CaV2.1 channels in R192Q KI mice, which alters the balance of excitatory/inhibitory inputs and could also have implications in the altered cortical excitability responsible for FHM pathology.

Monoclonal antibodies for migraine: preventing calcitonin gene-related peptide activity

Calcitonin gene-related peptide (CGRP) is a well-studied neuropeptide of relevance for migraine pathophysiology. Jugular levels of CGRP are increased during migraine attacks, and intravenous CGRP administration induces migraine-like headache in most individuals with migraine. Several CGRP receptor antagonists (CGRP-RAs) were shown to be effective for the acute treatment of migraine, validating the target for the treatment of migraine. However, for a number of reasons, including issues of liver toxicity with chronic use, the development of CGRP-RAs has yet to produce a viable clinical therapeutic. Development of monoclonal antibodies (mAbs) targeting the CGRP pathway is an alternative approach that should avoid many of the issues seen with CGRP-RAs. The exquisite target specificity, prolonged half-lives, and reduced potential for hepatotoxicity and drug-drug interactions make mAbs suitable for the preventive treatment of migraine headaches. This manuscript provides an overview of the role of CGRP in the pathophysiology of migraine, followed by a review of the clinical development of CGRP-RAs. Some basic concepts on antibodies are then discussed along with the publicly disclosed information on the development of mAbs targeting the CGRP pathway.

Mathematical approaches to modeling of cortical spreading depression

Migraine with aura (MwA) is a debilitating disease that afflicts about 25%-30% of migraine sufferers. During MwA, a visual illusion propagates in the visual field, then disappears, and is followed by a sustained headache. MwA was conjectured by Lashley to be related to some neurological phenomenon. A few years later, Leão observed electrophysiological waves in the brain that are now known as cortical spreading depression (CSD). CSD waves were soon conjectured to be the neurological phenomenon underlying MwA that had been suggested by Lashley. However, the confirmation of the link between MwA and CSD was not made until 2001 by Hadjikhani et al. [Proc. Natl. Acad. Sci. U.S.A. 98, 4687-4692 (2001)] using functional MRI techniques. Despite the fact that CSD has been studied continuously since its discovery in 1944, our detailed understandings of the interactions between the mechanisms underlying CSD waves have remained elusive. The connection between MwA and CSD makes the understanding of CSD even more compelling and urgent. In addition to all of the information gleaned from the many experimental studies on CSD since its discovery, mathematical modeling studies provide a general and in some sense more precise alternative method for exploring a variety of mechanisms, which may be important to develop a comprehensive picture of the diverse mechanisms leading to CSD wave instigation and propagation. Some of the mechanisms that are believed to be important include ion diffusion, membrane ionic currents, osmotic effects, spatial buffering, neurotransmitter substances, gap junctions, metabolic pumps, and synaptic connections. Discrete and continuum models of CSD consist of coupled nonlinear differential equations for the ion concentrations. In this review of the current quantitative understanding of CSD, we focus on these modeling paradigms and various mechanisms that are felt to be important for CSD.

Presynaptic CaV2.1 calcium channels carrying familial hemiplegic migraine mutation R192Q allow faster recovery from synaptic depression in mouse calyx of Held

Ca(V)2.1 Ca(2+) channels have a dominant and specific role in initiating fast synaptic transmission at central excitatory synapses, through a close association between release sites and calcium sensors. Familial hemiplegic migraine type 1 (FHM-1) is an autosomal-dominant subtype of migraine with aura, caused by missense mutations in the CACNA1A gene that encodes the α(1A) pore-forming subunit of Ca(V)2.1 channel. We used knock-in (KI) transgenic mice harboring the FHM-1 mutation R192Q to study the consequences of this mutation in neurotransmission at the giant synapse of the auditory system formed by the presynaptic calyx of Held terminal and the postsynaptic neurons of the medial nucleus of the trapezoid body (MNTB). Although synaptic transmission seems unaffected by low-frequency stimulation in physiological Ca(2+) concentration, we observed that with low Ca(2+) concentrations (<1 mM) excitatory postsynaptic currents (EPSCs) showed increased amplitudes in R192Q KI mice compared with wild type (WT), meaning significant differences in the nonlinear calcium dependence of nerve-evoked transmitter release. In addition, when EPSCs were evoked by broadened presynaptic action potentials (achieved by inhibition of K(+) channels) via Ca(v)2.1-triggered exocytosis, R192Q KI mice exhibited further enhancement of EPSC amplitude and charge compared with WT mice. Repetitive stimulation of afferent axons to the MNTB at different frequencies caused short-term depression of EPSCs that recovered significantly faster in R192Q KI mice than in WT mice. Faster recovery in R192Q KI mice was prevented by the calcium chelator EGTA-AM, pointing to enlarged residual calcium as a key factor in accelerating the replenishment of synaptic vesicles.

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.

Single-pulse transcranial magnetic stimulation for acute treatment of migraine with aura: a randomised, double-blind, parallel-group, sham-controlled trial

BACKGROUND

Preliminary work suggests that single-pulse transcranial magnetic stimulation (sTMS) could be effective as a treatment for migraine. We aimed to assess the efficacy and safety of a new portable sTMS device for acute treatment of migraine with aura.

METHODS

We undertook a randomised, double-blind, parallel-group, two-phase, sham-controlled study at 18 centres in the USA. 267 adults aged 18-68 years were enrolled into phase one. All individuals had to meet international criteria for migraine with aura, with visual aura preceding at least 30% of migraines followed by moderate or severe headache in more than 90% of those attacks. 66 patients dropped out during phase one. In phase two, 201 individuals were randomly allocated by computer to either sham stimulation (n=99) or sTMS (n=102). We instructed participants to treat up to three attacks over 3 months while experiencing aura. The primary outcome was pain-free response 2 h after the first attack, and co-primary outcomes were non-inferiority at 2 h for nausea, photophobia, and phonophobia. Analyses were modified intention to treat and per protocol. This trial is registered with ClinicalTrials.gov, number NCT00449540.

FINDINGS

37 patients did not treat a migraine attack and were excluded from outcome analyses. 164 patients treated at least one attack with sTMS (n=82) or sham stimulation (n=82; modified intention-to-treat analysis set). Pain-free response rates after 2 h were significantly higher with sTMS (32/82 [39%]) than with sham stimulation (18/82 [22%]), for a therapeutic gain of 17% (95% CI 3-31%; p=0.0179). Sustained pain-free response rates significantly favoured sTMS at 24 h and 48 h post-treatment. Non-inferiority was shown for nausea, photophobia, and phonophobia. No device-related serious adverse events were recorded, and incidence and severity of adverse events were similar between sTMS and sham groups.

INTERPRETATION

Early treatment of migraine with aura by sTMS resulted in increased freedom from pain at 2 h compared with sham stimulation, and absence of pain was sustained 24 h and 48 h after treatment. sTMS could be a promising acute treatment for some patients with migraine with aura.

FUNDING

Neuralieve.

Molecular genetics of migraine

Migraine is an episodic neurovascular disorder that is clinically divided into two main subtypes that are based on the absence or presence of an aura: migraine without aura (MO) and migraine with aura (MA). Current molecular genetic insight into the pathophysiology of migraine predominantly comes from studies of a rare monogenic subtype of migraine with aura called familial hemiplegic migraine (FHM). Three FHM genes have been identified, which all encode ion transporters, suggesting that disturbances in ion and neurotransmitter balances in the brain are responsible for this migraine type, and possibly the common forms of migraine. Cellular and animal models expressing FHM mutations hint toward neuronal hyperexcitability as the likely underlying disease mechanism. Additional molecular insight into the pathophysiology of migraine may come from other monogenic syndromes (for instance cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy, which is caused by NOTCH3 mutations), in which migraine is prominent. Investigating patients with common forms of migraine has had limited successes. Except for 5',10'-methylenetetrahydrolate reductase, an enzyme in folate metabolism, the large majority of reported genetic associations with candidate migraine genes have not been convincingly replicated. Genetic linkage studies using migraine subtypes as an end diagnosis did not yield gene variants thus far. Clinical heterogeneity in migraine diagnosis may have hampered the identification of such variants. Therefore, the recent introduction of more refined methods of phenotyping, such as latent-class analysis and trait component analysis, may be certainly helpful. Combining the new phenotyping methods with genome-wide association studies may be a successful strategy toward identification of migraine susceptibility genes. Likely the identification of reliable biomarkers for migraine diagnosing will make these efforts even more successful.

Migraine in the triptan era: lessons from epidemiology, pathophysiology, and clinical science

The triptan era has been a time of remarkable progress for migraine diagnosis and treatment. In this paper, we review some of the advances achieved in migraine science during this era focusing on 3 themes: lessons from clinical practice, lessons from epidemiology and lessons from pathophysiology. Science has shown that migraine is a disorder of the brain, and that the key events happen in the the trigeminal neuronal pathways, not on blood vessels. Clinical science has led to the observation that migraine sometimes progresses or remits. This in turn led to longitudinal epidemiologic studies focusing on factors that determine migraine prognosis. In addition, these studies raised questions about the mechanisms of migraine progression, including the role of allodynia, obesity, inflammation, and medications as determinants of progression. This in turn opens a new set of scientific questions about the neurobiologic determinants of migraine, as well as of its clinical course, and exciting opportunities to develop new therapies for this highly disabling brain disorder.

Animal models of migraine headache and aura

PURPOSE OF REVIEW

Over the past 30 years, animal models of migraine have led to the identification of novel drug targets and drug treatments as well as helped to clarify a mechanism for abortive and prophylactic drugs. Animal models have also provided translational knowledge and a framework to think about the impact of hormones, genes, and environmental factors on migraine pathophysiology. Although most acknowledge that these animal models have significant shortcomings, promising new drugs are now being developed and brought to the clinic using these preclinical models. Hence, it is timely to provide a short overview examining the ways in which animal models inform us about underlying migraine mechanisms.

RECENT FINDINGS

First generation migraine models mainly focused on events within pain-generating intracranial tissues, for example, the dura mater and large vessels, as well as their downstream consequences within brain. Upstream events such as cortical spreading depression have also been modeled recently and provide insight into mechanisms of migraine prophylaxis. Mouse mutants expressing human migraine mutations have been genetically engineered to provide an understanding of familial hemiplegic migraine and possibly, by extrapolation, may reflect on the pathophysiology of more common migraine subtypes.

SUMMARY

Animal models of migraine reflect distinct facets of this clinically heterogeneous disorder and contribute to a better understanding of its pathophysiology and pharmacology.

Foramen ovale perméable et migraine

Recent epidemiological data suggest a bidirectional link between patent foramen ovale (PFO) and migraine with aura (MA) with a relative risk of 2 for PFO in subjects with MA and for MA in subjects with PFO. There is no evidence for a link between PFO and migraine without aura. This link is not systematic and applies only to subsets of PFO, mostly large ones, and to subsets of patients with MA. Although comorbidity cannot be ruled out, it may be that this link is partly causal and that some large PFOs may favor MA attacks in genetically predisposed subjects, by allowing vasoactive substances, platelet emboli or paradoxical emboli to bypass the lung filter and trigger the cortical spreading depression of the aura. The first double blind randomised trial of PFO closure in refractory MA, "MIST", has failed to show a benefit on the primary efficacy end point: cessation of attacks during the analysis period included between 3 and 6 months after the procedure. There is thus at present no scientific reason to look for PFO or to close PFO in migraine patients.

Topiramate prophylaxis and response to triptan treatment for acute migraine

OBJECTIVE

To evaluate the effect of topiramate migraine prophylaxis on subject responsiveness to triptans used for acute symptomatic migraine treatment.

BACKGROUND

Clinical experience suggests that prophylactic migraine treatment may enhance the efficacy of symptomatic medications used to treat acute migraine attacks.

METHODS

This open-label, single-arm multicenter study consisted of a 6-week baseline period followed by a 16-week topiramate treatment period. Subjects meeting International Headache Society (IHS) criteria for migraine with and without aura signed consent and entered the baseline period. Those with 3 to 12 migraine periods per month during baseline received topiramate prophylactic treatment. Only patients who completed at least 12 weeks of topiramate treatment were included in the data analysis.

RESULTS

Of 55 patients screened, 40 subjects entered the topiramate treatment period and 21 subjects received at least 12 weeks of treatment. Mean final dose of topiramate was 124 mg per day (range 50 to 200 mg per day). During the baseline period, the mean percentage of attacks rendered pain-free at 2 hours for the 21 subjects was 46.9% (SD = 31.9), while during the topiramate treatment period it was 44.6% (SD = 32.2) (P= .8). On topiramate, after the first 8 weeks of dosage titration, patients experienced a mean of 3.68 migraine attacks/month, compared to 4.31 during the baseline period (P < .03). Thirteen subjects discontinued because of adverse events. The most commonly reported adverse events were paresthesia, fatigue, anxiety, and dizziness.

CONCLUSION

Although topiramate prophylaxis did reduce migraine attack frequency, in this pilot study topiramate prophylactic migraine treatment did not increase the proportion of patients pain-free 2 hours after symptomatic triptan therapy.