Migraine is a complex disorder characterized by recurrent episodes of headache, and is one of the most prevalent and disabling neurological disorders. A key feature of migraine is that various factors can trigger an attack, and this phenomenon provides a unique opportunity to investigate disease mechanisms by experimentally inducing migraine attacks. In this Review, we summarize the existing experimental models of migraine in humans, including those that exploit nitric oxide, histamine, neuropeptide and prostaglandin signalling. We describe the development and use of these models in the discovery of molecular pathways that are responsible for initiation of migraine attacks. Combining experimental human models with advanced imaging techniques might help to identify biomarkers of migraine, and in the ongoing search for new and better migraine treatments, human models will have a key role in the discovery of future targets for more-specific and more-effective mechanism-based antimigraine drugs.

Human models of migraine - short-term pain for long-term gain.

Migraine is a highly prevalent and disabling neurological disorder which is commonly linked with a broad range of psychiatric comorbidities, especially among subjects with migraine with aura or chronic migraine. Defining the exact nature of the association between migraine and psychiatric disorders and bringing out the pathophysiological mechanisms underlying the comorbidity with psychiatric conditions are relevant issues in the clinical practice. A systematic review of the most relevant studies about migraine and psychiatric comorbidity was performed using “PubMed”, “Scopus”, and “ScienceDirect” electronic databases from 1 January 1998 to 15 July 2018. Overall, 178 studies met our inclusion criteria and were included in the current review. According to the most relevant findings of our overview, the associations with psychiatric comorbidities are complex, with a bidirectional association of major depression and panic disorder with migraine. Importantly, optimizing the pharmacological and non-pharmacological treatment of either migraine or its psychiatric comorbidities might help clinicians to attenuate the burden of both these conditions. The available data highlight the need for a comprehensive evaluation of psychiatric disorders in migraine in order to promote an integrated model of care and carefully address the burden and psychosocial impairment related to psychiatric comorbidities in migraine.

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Understanding the nature of psychiatric comorbidity in migraine: a systematic review focused on interactions and treatment implications.

Migraine, with and without aura (MA and MO), is a prevalent and complex neurovascular disorder that is likely to be influenced by multiple genes some of which may be capable of causing vascular changes leading to disease onset. This study was conducted to determine whether the ACE I/D gene variant is involved in migraine risk and whether this variant might act in combination with the previously implicated MTHFR C677T genetic variant in 270 migraine cases and 270 matched controls. Statistical analysis of the ACE I/D variant indicated no significant difference in allele or genotype frequencies (P > 0.05). However, grouping of genotypes showed a modest, yet significant, over-representation of the DD/ID genotype in the migraine group (88%) compared to controls (81%) (OR of 1.64, 95% CI: 1.00–2.69, P = 0.048). Multivariate analysis, including genotype data for the MTHFR C677T, provided evidence that the MTHFR (TT) and ACE (ID/DD) genotypes act in combination to increase migraine susceptibility (OR = 2.18, 95% CI: 1.15–4.16, P = 0.018). This effect was greatest for the MA subtype where the genotype combination corresponded to an OR of 2.89 (95% CI:1.47–5.72, P = 0.002). In Caucasians, the ACE D allele confers a weak independent risk to migraine susceptibility and also appears to act in combination with the C677T variant in the MTHFR gene to confer a stronger influence on the disease.

Genetic variants of angiotensin converting enzyme and methylenetetrahydrofolate reductase may act in combination to increase migraine susceptibility

Toll-like receptor 4 (TLR4) recognizes exogenous pathogen-associated molecular patterns (PAMPs) and endogenous danger-associated molecular patterns (DAMPs) and initiates the innate immune response. Opioid receptors (μ, δ, and κ) activate inhibitory G-proteins and relieve pain. This review summarizes the following types of TLR4/opioid receptor pathway crosstalk: (a) Opioid receptor agonists non-stereoselectively activate the TLR4 signaling pathway in the central nervous system (CNS), in the absence of lipopolysaccharide (LPS). Opioids bind to TLR4, in a manner parallel to LPS, activating TLR4 signaling, which leads to nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) expression and the production of the pro-inflammatory cytokines tumor necrosis factor (TNF)-α, interleukin (IL)-1β, and IL-6. (b) Opioid receptor agonists inhibit the LPS-induced TLR4 signaling pathway in peripheral immune cells. Opioids operate as pro-inflammatory cytokines, resulting in neuroinflammation in the CNS, but they mediate immunosuppressive effects in the peripheral immune system. It is apparent that TLR4/opioid receptor pathway crosstalk varies dependent on the cell type and activating stimulus. (c) Both the TLR4 and opioid receptor pathways activate the mitogen-activated protein kinase (MAPK) pathway. This crosstalk is located downstream of the TLR4 and opioid receptor signaling pathways. Furthermore, the classic opioid receptor can also produce pro-inflammatory effects in the CNS via MAPK signaling and induce neuroinflammation. (d) Opioid receptor agonists induce the production of high mobility group box 1 (HMGB1), an endogenous TLR4 agonist, supporting intercellular (neuron-to-glia or glia-to-neuron) interactions. This review also summarizes the potential effects of TLR4/opioid receptor pathway crosstalk on opioid analgesia, immune function, and gastrointestinal motility. Opioids non-stereoselectively activate the TLR4 pathway, and together with the subsequent release of pro-inflammatory cytokines such as IL-1 by glia, this TLR4 signaling initiates the central immune signaling response and modifies opioid pharmacodynamics. The DAMP HMGB1 is associated with the development of neuropathic pain. To explain morphine-induced persistent sensitization, a positive feedback loop has been proposed; this involves an initial morphine-induced amplified release of IL-1β and a subsequent exacerbated release of DAMPs, which increases the activation of TLR4 and the purinergic receptor P2X7R. Opioid receptor (μ, δ, and κ) agonists are involved in many aspects of immunosuppression. The intracellular TLR4/opioid receptor signaling pathway crosstalk induces the formation of the β-arrestin-2/TNF receptor-associated factor 6 (TRAF6) complex, which contributes to morphine-induced inhibition of LPS-induced TNF-α secretion in mast cells. A possible molecular mechanism is that the TLR4 pathway initially triggers the formation of the β-arrestin-2/TRAF6 complex, which is amplified by opioid receptor signaling, suggesting that β-arrestin-2 acts as a functional component of the TLR4 pathway.

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Toll-Like Receptor 4 (TLR4)/Opioid Receptor Pathway Crosstalk and Impact on Opioid Analgesia, Immune Function, and Gastrointestinal Motility.

Animal models have provided a growing body of information about the pathophysiology of headaches and novel therapeutic targets. In recent years, experiments in awake animals have gained attention as more relevant headache models. Pain can be assessed in animals using behavioral alterations, which includes sensory-discriminative, affective-emotional and cognitive aspects. Spontaneous behavioral alterations such as increased grooming, freezing, eye blinking, wet dog shake and head shake and decreased locomotion, rearing, food or water consumption observed during pain episodes are oftentimes easy to translate into clinical outcomes, but are giving little information about the localization and modality of the pain. Evoked pain response such as tactile and thermal hypersensitivity measures are less translatable but gives more insight into mechanisms of action. Mechanical allodynia is usually assessed with von Frey monofilaments and dynamic aesthesiometer, and thermal allodynia can be evaluated with acetone evaporation test and Hargreaves’ test in animal models. Anxiety and depression are the most frequent comorbid diseases in headache disorders. Anxiety-like behaviors are evaluated with the open-field, elevated plus-maze or light/dark box tests. Interpretation of the latter test is challenging in migraine models, as presence of photophobia or photosensitivity can also be measured in light/dark boxes. Depressive behavior is assessed with the forced-swim or tail suspension tests. The majority of headache patients complain of cognitive symptoms and migraine is associated with poor cognitive performance in clinic-based studies. Cluster headache and tension type headache patients also exhibit a reversible cognitive dysfunction during the headache attacks. However, only a limited number of animal studies have investigated cognitive aspects of headache disorders, which remains a relatively unexplored aspect of these pathologies. Thus, the headache field has an excellent and growing selection of model systems that are likely to yield exciting advances in the future.

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Behavioral and cognitive animal models in headache research.

Background: Many studies investigated the association between angiotensin-converting enzyme (ACE) insertion/deletion (I/D) polymorphism and migraine, with controversial results. Thus, we performed a meta-analysis to better evaluate the correlation of this polymorphism and migraine. Methods: We retrieved studies published up to September 2014 about the ACE gene polymorphism and migraine from electronic database. Pooled odds ratios (ORs) with 95% confidence interval (CI) were calculated to examine the strength of association between the ACE I/D polymorphism and migraine, using random-effects models. Results: We identified 14 separate studies, in which 7334 migraineurs and 22 990 healthy controls were eligible for the meta-analysis. The results showed no relationship between the ACE I/D polymorphism and any migraine. Stratification revealed a protective effect in the Turkish population against migraine with aura for the II genotype model (II vs. DD: pooled OR = 0.366, 95% CI = 0.137–0.980; II vs. DI + DD: po...

Association between angiotensin-converting enzyme insertion/deletion polymorphism and migraine: a meta-analysis.

Voxel-based morphometry is used to detect structural brain changes in patients with migraine However, the relevance of migraine and structural changes is not clear This study investigated structural brain abnormalities based on voxel-based morphometry using a rat model of recurrent headache The rat model was established by infusing an inflammatory soup through supradural catheters in conscious male rats Rats were subgrouped according to the frequency and duration of the inflammatory soup infusion Tactile sensory testing was conducted prior to infusion of the inflammatory soup or saline The periorbital tactile thresholds in the high-frequency inflammatory soup stimulation group declined persistently from day 5 Increased white matter volume was observed in the rats three weeks after inflammatory soup stimulation, brainstem in the in the low-frequency inflammatory soup-infusion group and cortex in the high-frequency inflammatory soup-infusion group After six weeks' stimulation, rats showed gray matter volume changes The brain structural abnormalities recovered after the stimulation was stopped in the low-frequency inflammatory soup-infused rats and persisted even after the high-frequency inflammatory soup stimulus stopped The changes of voxel-based morphometry in migraineurs may be the result of recurrent headache Cognition, memory, and learning may play an important role in the chronification of migraines Reducing migraine attacks has the promise of preventing chronicity of migraine

https://journals.sagepub.com/doi/pdf/10.1177/1744806918756466

Volumetric abnormalities of the brain in a rat model of recurrent headache

BackgroundATP1A2 has been identified as the genetic cause of familial hemiplegic migraine type 2. Over 80 ATP1A2 mutations have been reported, but no data from Chinese family studies has been inclu...

A Chinese family with familial hemiplegic migraine type 2 due to a novel missense mutation in ATP1A2.

BackgroundThe existence of an association between migraine and essential tremor has long been controversial. The prevalence of migraine in essential tremor patients was surveyed to explore the association between the two diseases.MethodsA case–control clinical study was conducted to investigate the prevalence of migraine in 150 consecutive essential tremor patients and in 150 matched controls without tremor. Detailed information about essential tremor and migraine was obtained using a structured questionnaire at a face-to-face interview. Moreover, a functional variant of the dopamine receptor D3 gene (Ser9Gly, rs6280) was studied in 46 essential tremor patients with and without migraine using direct sequencing analysis.ResultsThe prevalence of lifetime migraine in essential tremor patients was significantly higher than that in controls (22.0% vs. 12.7%; p = 0.035; odds ratio = 1.95; 95% confidence interval = 1.05–3.60). No significant difference was found in the migraine features between the essential tre...

Higher prevalence of migraine in essential tremor: a case-control study.

Pituitary adenylate cyclase-activating polypeptide (PACAP) plays several important roles in vasodilation, neurotransmission, neuromodulation and neurotrophy, as well as activation of the trigeminovascular system. The aim of the present study was to explore the relationship between altered PACAP levels in peripheral blood and different types of headache. The present study enrolled 101 outpatients with headache and 35 healthy control volunteers. Blood samples were collected from the cubital vein and peripheral blood mononuclear cells (PBMCs) were separated. Total mRNA in the PBMCs was extracted and the expression of PACAP mRNA was analyzed by quantitative-polymerase chain reaction (Q-PCR). There was a significant decrease in PACAP mRNA expression in the PBMCs of the migraine (M) group relative to the healthy control group. However, there were no significant differences in PACAP mRNA expression between the control group and tension-type headache (TTH), cluster headache (CH), or medication overuse headache (MOH) groups. The PBMC levels of patients with migraine, but not other commonly seen headache types, exhibited a significant reduction in PACAP mRNA expression compared with healthy control subjects.

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Wenjing Tang

Papers

Association between angiotensin-converting enzyme insertion/deletion polymorphism and migraine: a meta-analysis.

Volumetric abnormalities of the brain in a rat model of recurrent headache

A Chinese family with familial hemiplegic migraine type 2 due to a novel missense mutation in ATP1A2.

Higher prevalence of migraine in essential tremor: a case-control study.

Pituitary adenylate cyclase-activating polypeptide expression in peripheral blood mononuclear cells of migraineurs.