Stress modulates cortical excitability via α-2 adrenergic and glucocorticoid receptors: As assessed by spreading depression

Insights from triggers and prodromal symptoms on how migraine attacks start: The threshold hypothesis

BACKGROUND

The prodrome or premonitory phase is the initial phase of a migraine attack, and it is considered as a symptomatic phase in which prodromal symptoms may occur. There is evidence that attacks start 24-48 hours before the headache phase. Individuals with migraine also report several potential triggers for their attacks, which may be mistaken for premonitory symptoms and hinder migraine research.

METHODS

This review aims to summarize published studies that describe contributions to understanding the fine difference between prodromal/premonitory symptoms and triggers, give insights for research, and propose a way forward to study these phenomena. We finally aim to formulate a theory to unify migraine triggers and prodromal symptoms. For this purpose, a comprehensive narrative review of the published literature on clinical, neurophysiological and imaging evidence on migraine prodromal symptoms and triggers was conducted using the PubMed database.

RESULTS

Brain activity and network connectivity changes occur during the prodromal phase. These changes give rise to prodromal/premonitory symptoms in some individuals, which may be falsely interpreted as triggers at the same time as representing the early manifestation of the beginning of the attack. By contrast, certain migraine triggers, such as stress, hormone changes or sleep deprivation, acting as a catalyst in reducing the migraine threshold, might facilitate these changes and increase the chances of a migraine attack. Migraine triggers and prodromal/premonitory symptoms can be confused and have an intertwined relationship with the hypothalamus as the central hub for integrating external and internal body signals.

CONCLUSIONS

Differentiating migraine triggers and prodromal symptoms is crucial for shedding light on migraine pathophysiology and improve migraine management.

Glucocorticoid signaling mediates stress-induced migraine-like behaviors in a preclinical mouse model

BACKGROUND

Stress is one of the most common precipitating factors in migraine and is identified as a trigger in nearly 70% of patients. Responses to stress include release of glucocorticoids as an adaptive mechanism, but this may also contribute to migraine attacks. Here, we investigated the role of glucocorticoids on stress-induced migraine-like behaviors.

METHODS

We have shown previously that repeated stress in mice evokes migraine-like behavioral responses and priming to a nitric oxide donor. Metyrapone, mifepristone, and corticosterone (CORT) were used to investigate whether CORT contributes to the stress-induced effects. Facial mechanical hypersensitivity was evaluated by von Frey testing and grimace scoring assessed the presence of non-evoked pain. We also measured serum CORT levels in control, stress, and daily CORT injected groups of both male and female mice.

RESULTS

Metyrapone blocked stress-induced responses and priming in male and female mice. However, repeated CORT injections in the absence of stress only led to migraine-like behaviors in females. Both female and male mice showed similar patterns of serum CORT in response to stress or exogenous administration. Finally, administration of mifepristone, the glucocorticoid receptor antagonist, prior to each stress session blocked stress-induced behavioral responses in male and female mice.

CONCLUSIONS

These findings demonstrate that while CORT synthesis and receptor activation is necessary for the behavioral responses triggered by repeated stress, it is only sufficient in females. Better understanding of how glucocorticoids contribute to migraine may lead to new therapeutic opportunities.

Mifepristone's effects on depression- and anxiety-like behavior in rodents

Mifepristone is a non-selective progesterone (PR), glucocorticoid (GR), and androgen receptor (AR) antagonist with antidepressant and anxiolytic effects. The dose and duration of mifepristone administration vary in rodent preclinical studies to evaluate depression-like and anxiety-like behavior. This review summarizes the findings so far and attempts to reconcile some of the differences in the results. While a few studies assessed basal depression- and anxiety-like behavior, several studies have used mifepristone in conjunction with stress, corticosterone/dexamethasone (after adrenalectomy), or progesterone administration. The effect of mifepristone on depression-like behavior appears to depend not only on the dose and duration of administration but also on the intensity or type of stress. In addition, the anxiolytic effects may depend on the species and strain of the experimental animals. More reports assess antidepressant-like or anxiolytic-like effects following acute than chronic administration. These effects are dependent on the paradigms and the nature of stressors. Most mifepristone studies implicate the role of GRs, yet only two reports have confirmed its role using a genetic approach, whereas none implicate the role of PRs/ARs. There are several novel selective GR antagonists whose effects on depression- and anxiety-like behavior are yet to be studied. Future studies could aim to confirm the role of GRs and evaluate the contribution of PRs/ARs to the effects of mifepristone. Such studies will contribute to a better understanding of depression, anxiety, and other mood disorders and develop novel strategies, particularly for treatment-resistant conditions.

Dysregulation of serum prolactin links the hypothalamus with female nociceptors to promote migraine

Migraine headache results from activation of meningeal nociceptors, however, the hypothalamus is activated many hours before the emergence of pain. How hypothalamic neural mechanisms may influence trigeminal nociceptor function remains unknown. Stress is a common migraine trigger that engages hypothalamic dynorphin/kappa opioid receptor (KOR) signalling and increases circulating prolactin. Prolactin acts at both long and short prolactin receptor isoforms that are expressed in trigeminal afferents. Following downregulation of the prolactin receptor long isoform, prolactin signalling at the prolactin receptor short isoform sensitizes nociceptors selectively in females. We hypothesized that stress may activate the kappa opioid receptor on tuberoinfundibular dopaminergic neurons to increase circulating prolactin leading to female-selective sensitization of trigeminal nociceptors through dysregulation of prolactin receptor isoforms. A mouse two-hit hyperalgesic priming model of migraine was used. Repeated restraint stress promoted vulnerability (i.e. first-hit priming) to a subsequent subthreshold (i.e. second-hit) stimulus from inhalational umbellulone, a TRPA1 agonist. Periorbital cutaneous allodynia served as a surrogate of migraine-like pain. Female and male KORCre; R26lsl-Sun1-GFP mice showed a high percentage of KORCre labelled neurons co-localized in tyrosine hydroxylase-positive cells in the hypothalamic arcuate nucleus. Restraint stress increased circulating prolactin to a greater degree in females. Stress-primed, but not control, mice of both sexes developed periorbital allodynia following inhalational umbellulone. Gi-DREADD activation (i.e. inhibition through Gi-coupled signalling) in KORCre neurons in the arcuate nucleus also increased circulating prolactin and repeated chemogenetic manipulation of these neurons primed mice of both sexes to umbellulone. Clustered regularly interspaced short palindromic repeats-Cas9 deletion of the arcuate nucleus KOR prevented restraint stress-induced prolactin release in female mice and priming from repeated stress episodes in both sexes. Inhibition of circulating prolactin occurred with systemic cabergoline, a dopamine D2 receptor agonist, blocked priming selectively in females. Repeated restraint stress downregulated the prolactin receptor long isoform in the trigeminal ganglia of female mice. Deletion of prolactin receptor in trigeminal ganglia by nasal clustered regularly interspaced short palindromic repeats-Cas9 targeting both prolactin receptor isoforms prevented stress-induced priming in female mice. Stress-induced activation of hypothalamic KOR increases circulating prolactin resulting in trigeminal downregulation of prolactin receptor long and pain responses to a normally innocuous TRPA1 stimulus. These are the first data that provide a mechanistic link between stress-induced hypothalamic activation and the trigeminal nociceptor effectors that produce trigeminal sensitization and migraine-like pain. This sexually dimorphic mechanism may help to explain female prevalence of migraine. KOR antagonists, currently in phase II clinical trials, may be useful as migraine preventives in both sexes, while dopamine agonists and prolactin/ prolactin receptor antibodies may improve therapy for migraine, and other stress-related neurological disorders, in females.

Interaction between endocannabinoids and the adrenergic system before and after stress-exposure

Cold stress-induced analgesia (c-SIA) has been evaluated in male Wistar rats injected with cannabinoid receptors type 1 and a2-adrenergic receptor agonists and antagonists in different combinations before or after stress exposure.

The aim of the study was to evaluate whether the endogenous cannabinoid and the adrenergic systems influenced c-SIA, and the patterns of their potential interaction.

Exogenous administration of anandamide and Clonidine together, before or after stress exposure, increased c-SIA even with differences in the time of manifestation of the effect, its duration and the degree.

The two systems differently contribute to c-SIA pathogenesis and mediation. Administered before stress exposure cannabinoids and the adrenergic system seem to oppose each other: the latter rather potentiates, while cannabinoids suppress c-SIA. Administered after stress exposure, instead, the two systems appear to exert a synergistic effect, and antagonization of each one of them abolishes the analgesic effect.

Electroacupuncture alleviates anxiety and modulates amygdala CRH/CRHR1 signaling in single prolonged stress mice

BACKGROUND

Post-traumatic stress disorder (PTSD) is an anxiety-related psychiatric disorder, manifesting high comorbidity with anxiety disorders. Its underlying neurobiological mechanisms have been associated with hypothalamic-pituitary-adrenal (HPA) axis dysfunction and stress hormones. Corticotropin-releasing hormone (CRH) is a primary stress hormone, expressed in the hypothalamus and amygdala. Electroacupuncture (EA) can improve mood disorders, but its mechanisms have not been fully elucidated. The aim of this study was to observe the effect of EA on PTSD and explore the related mechanisms.

METHODS

We used single prolonged stress (SPS) mice to establish a PTSD model, and EA was performed after SPS or 7 days later for a week. Then we observed their fear and anxiety-like behavior through cue-induced fear condition tests, open field test and the elevated zero maze. CRH and CRH receptor 1 (CRHR1) protein levels in the amygdala were measured in SPS mice after EA intervention.

RESULTS

We found that EA at ST36 and GV20 improved fear and anxiety behavior in SPS mice. The amygdala CRH and CRHR1 protein levels increased in the SPS mice, and this effect was reversed by the EA intervention. CRHR1 inhibition by the CRHR1 antagonist NBI 27914 alleviated anxiety behavior in SPS mice.

CONCLUSION

CRH/CRHR1 signaling in the amygdala may contribute to the anxiolytic effect of EA in SPS mice.

Repetitive stress in mice causes migraine-like behaviors and calcitonin gene-related peptide-dependent hyperalgesic priming to a migraine trigger

Migraine is one of the most disabling disorders worldwide but the underlying mechanisms are poorly understood. Stress is consistently reported as a common trigger of migraine attacks. Here, we show that repeated stress in mice causes migraine-like behaviors that are responsive to a migraine therapeutic. Adult female and male mice were exposed to 2 hours of restraint stress for 3 consecutive days, after which they demonstrated facial mechanical hypersensitivity and facial grimace responses that were resolved by 14 days after stress. Hypersensitivity or grimace was not observed in either control animals or those stressed for only 1 day. After return to baseline, the nitric oxide donor sodium nitroprusside (SNP; 0.1 mg/kg) elicited mechanical hypersensitivity in stressed but not in control animals, demonstrating the presence of hyperalgesic priming. This suggests the presence of a migraine-like state, because nitric oxide donors are reliable triggers of attacks in migraine patients but not controls. The stress paradigm also caused priming responses to dural pH 7.0 treatment. The presence of this primed state after stress is not permanent because it was no longer present at 35 days after stress. Finally, mice received either the calcitonin gene-related peptide monoclonal antibody ALD405 (10 mg/kg) 24 hours before SNP or a coinjection of sumatriptan (0.6 mg/kg). ALD405, but not sumatriptan, blocked the facial hypersensitivity due to SNP. This stress paradigm in mice and the subsequent primed state caused by stress allow further preclinical investigation of mechanisms contributing to migraine, particularly those caused by common triggers of attacks.

Linking atypical depression and insulin resistance-related disorders via low-grade chronic inflammation: Integrating the phenotypic, molecular and neuroanatomical dimensions

Insulin resistance (IR) and related disorders, such as T2DM, increase the risk of major depressive disorder (MDD) and vice versa. Current evidence indicates that psychological stress and overeating can induce chronic low-grade inflammation that can interfere with glutamate metabolism in MDD as well as insulin signaling, particularly in the atypical subtype. Here we first review the interactive role of inflammatory processes in the development of MDD, IR and related metabolic disorders. Next, we describe the role of the anterior cingulate cortex in the pathophysiology of MDD and IR-related disorders. Furthermore, we outline how specific clinical features of atypical depression, such as hyperphagia, are more associated with inflammation and IR-related disorders. Finally, we examine the regional specificity of the effects of inflammation on the brain that show an overlap with the functional and morphometric brain patterns activated in MDD and IR-related disorders.

Chronic Cranial Windows for Long Term Multimodal Neurovascular Imaging in Mice

Chronic cranial windows allow for longitudinal brain imaging experiments in awake, behaving mice. Different imaging technologies have their unique advantages and combining multiple imaging modalities offers measurements of a wide spectrum of neuronal, glial, vascular, and metabolic parameters needed for comprehensive investigation of physiological and pathophysiological mechanisms. Here, we detail a suite of surgical techniques for installation of different cranial windows targeted for specific imaging technologies and their combination. Following these techniques and practices will yield higher experimental success and reproducibility of results.

Therapeutic implications of cortical spreading depression models in migraine

Migraine is among the most common and disabling neurological diseases in the world. Cortical spreading depression (CSD) is a wave of near-complete depolarization of neurons and glial cells that slowly propagates along the cortex creating the perception of aura. Evidence suggests that CSD can trigger migraine headache. Experimental models of CSD have been considered highly translational as they recapitulate migraine-related phenomena and have been validated for screening migraine therapeutics. Here we outline the essential components of validated experimental models of CSD and provide a comprehensive review of potential modulators and targets against CSD. We further focus on novel interventions that have been recently shown to suppress CSD susceptibility that may lead to therapeutic targets in migraine.

Integrating Pathophysiology in Migraine: Role of the Gut Microbiome and Melatonin

BACKGROUND

The pathoetiology and pathophysiology of migraine are widely accepted as unknown.

METHODS

The current article reviews the wide array of data associated with the biological underpinnings of migraine and provides a framework that integrates previously disparate bodies of data.

RESULTS

The importance of alterations in stress- and pro-inflammatory cytokine- induced gut dysbiosis, especially butyrate production, are highlighted. This is linked to a decrease in the availability of melatonin, and a relative increase in the N-acetylserotonin/melatonin ratio, which has consequences for the heightened glutamatergic excitatory transmission in migraine. It is proposed that suboptimal mitochondria functioning and metabolic regulation drive alterations in astrocytes and satellite glial cells that underpin the vasoregulatory and nociceptive changes in migraine.

CONCLUSION

This provides a framework not only for classical migraine associated factors, such as calcitonin-gene related peptide and serotonin, but also for wider factors in the developmental pathoetiology of migraine. A number of future research and treatment implications arise, including the clinical utilization of sodium butyrate and melatonin in the management of migraine.

Genetic mouse models of migraine

Mouse models of rare monogenic forms of migraine provide a unique experimental system to study the cellular and circuit mechanisms of the primary brain dysfunctions causing a migraine disorder. Here, we discuss the migraine-relevant phenotypes and the migraine-relevant functional alterations in the brain of five genetic mouse models of migraine, four of which carry mutations derived from patients with familial hemiplegic migraine (FHM) and the fifth carry a mutation from patients with both phenotypically normal MA and familial advanced sleep phase syndrome (FASPS). We focus on the latter mouse model, in which a ubiquitous serine-threonine kinase is mutated, and on two mouse models of pure FHM, in which a voltage-gated calcium channel controlling neurotransmitter release at most brain synapses and a Na/K ATPase that is expressed mainly in astrocytes in the adult brain are mutated, respectively. First, we describe the behavioral phenotypes of the genetic animal models and review the evidence that an increased susceptibility to experimentally induced cortical spreading depression (CSD) is a key migraine-relevant phenotype common to the five models. Second, we review the synaptic alterations in the cerebral cortex of the genetic models of migraine and discuss the mechanisms underlying their increased susceptibility to CSD. Third, we review the alterations in the trigeminovascular pain pathway and discuss possible implications for migraine pain mechanisms. Finally, we discuss the insights into migraine pathophysiology obtained from the genetic models of migraine, in particular regarding the mechanisms that make the brain of migraineurs susceptible to the ignition of “spontaneous” CSDs. Although the reviewed functional studies support the view of migraine as a disorder of the brain characterized by dysfunctional regulation of the excitatory/inhibitory balance in specific neuronal circuits, much work remains to be done in the genetic mouse models e.g. to identfy the relevant dysfunctional circuits and to establish whether and how the alterations in the function of specific circuits (in the cerebral cortex and/or other brain areas) are state-dependent and may, in certain conditions, favor CSD ignition and the migraine attack.

Relief Following Chronic Stress Augments Spreading Depolarization Susceptibility in Familial Hemiplegic Migraine Mice

Cortical spreading depolarization (CSD) is the electrophysiological substrate of migraine aura, and a putative trigger of trigeminovascular activation and migraine headache. Many migraineurs report stress or relief after a stress triggers an attack. We tested whether various stress conditions might modulate CSD susceptibility and whether this is dependent on genetic factors. Male and female wild type and familial hemiplegic migraine type1 (FHM1) knock-in mice heterozygous for the S218L missense mutation were subjected to acute or chronic stress, or chronic stress followed by relief (36 h). Acute stress was induced by restraint and exposure to bright light and white noise (3 h). Chronic stress was induced for 28 days by two cycles of repeated exposure of mice to a rat (7 days), physical restraint (3 days), and forced swimming (3 days). Electrical CSD threshold and KCl-induced (300 mM) CSD frequency were determined in occipital cortex in vivo at the end of each protocol. Relief after chronic stress reduced the electrical CSD threshold and increased the frequency of KCl-induced CSDs in FHM1 mutants only. Acute or chronic stress without relief did not affect CSD susceptibility in either strain. Stress status did not affect CSD propagation speed, duration or amplitude. In summary, relief after chronic stress, but not acute or chronic stress alone, augments CSD in genetically susceptible mice. Therefore, enhanced CSD susceptibility may explain why, in certain patients, migraine attacks typically occur during a period of stress relief such as weekends or holidays.

Spreading depression as a preclinical model of migraine

Spreading depression (SD) is a slowly propagating wave of near-complete depolarization of neurons and glial cells across the cortex. SD is thought to contribute to the underlying pathophysiology of migraine aura, and possibly also an intrinsic brain activity causing migraine headache. Experimental models of SD have recapitulated multiple migraine-related phenomena and are considered highly translational. In this review, we summarize conventional and novel methods to trigger SD, with specific focus on optogenetic methods. We outline physiological triggers that might affect SD susceptibility, review a multitude of physiological, biochemical, and behavioral consequences of SD, and elaborate their relevance to migraine pathophysiology. The possibility of constructing a recurrent episodic or chronic migraine model using SD is also discussed.

ROS/TRPA1/CGRP signaling mediates cortical spreading depression

Objectives

The transient receptor potential ankyrin A 1 (TRPA1) channel and calcitonin gene-related peptide (CGRP) are targets for migraine prophylaxis. This study aimed to understand their mechanisms in migraine by investigating the role of TRPA1 in cortical spreading depression (CSD) in vivo and exploring how reactive oxygen species (ROS)/TRPA1/CGRP interplay in regulating cortical susceptibility to CSD.

Methods

Immunohistochemistry was used for detecting TRPA1 expression. CSD was induced by K⁺ on the cerebral cortex, monitored using electrophysiology in rats, and intrinsic optical imaging in mouse brain slices, respectively. Drugs were perfused into contralateral ventricle of rats. Lipid peroxidation (malondialdehyde, MDA) analysis was used for indicating ROS level.

Results

TRPA1 was expressed in cortical neurons and astrocytes of rats and mice. TRPA1 deactivation by an anti-TRPA1 antibody reduced cortical susceptibility to CSD in rats and decreased ipsilateral MDA level induced by CSD. In mouse brain slices, H₂O₂ facilitated submaximal CSD induction, which disappeared by the antioxidant, tempol and the TRPA1 antagonist, A-967079; Consistently, TRPA1 activation reversed prolonged CSD latency and reduced magnitude by the antioxidant. Further, blockade of CGRP prolonged CSD latency, which was reversed by H₂O₂ and the TRPA1 agonist, allyl-isothiocyanate, respectively.

Conclusions

ROS/TRPA1/CGRP signaling plays a critical role in regulating cortical susceptibility to CSD. Inhibition ROS and deactivation of TRPA1 channels may have therapeutic benefits in preventing stress-triggered migraine via CGRP.

The Effects of Chronic Stress on Migraine Relevant Phenotypes in Male Mice

Migraine is a disabling neurological disorder affecting 12% of the world’s population. Stress is a major reported trigger and exacerbator of migraine. We evaluated the effects of two chronic stress paradigms on migraine relevant phenotypes in male C57Bl/6 mice.

Methods: Fifty six mice were used in a 14 day social defeat stress (SDS) and twenty three mice were used in a 40 day chronic variable stress (CVS) paradigm. Anxiety measures were evaluated using the open field and elevated plus maze (EPM) tests. Migraine relevant phenotypes were evaluated using the nitroglycerin (NTG) and cortical spreading depression (CSD) models.

Results: Stress sensitive SDS mice and chronically stressed CVS mice showed decreased exploration in the open field and reduced time spent in the open arms of the EPM compared to controls. Stress sensitive and resilient SDS mice had increased serum corticosterone levels, and stressed mice in the CVS paradigm had decreased weight gain compared to controls, providing combined behavioral and physiological evidence of a stress response. In the CVS paradigm but not the SDS paradigm, the stressed group showed a significant decrease in baseline mechanical withdrawal threshold compared to controls. All groups showed a significant reduction in withdrawal threshold after treatment with NTG, but the reduction was not larger in SDS or CVS than in controls. Interestingly, stress resilient SDS mice showed a rapid recovery from NTG effects that was not seen in other groups. No difference in CSD frequency or velocity was seen between stress and control mice in either stress paradigms.

Conclusion: We observed distinct effects of stress on generalized pain response, migraine relevant pain, and migraine relevant excitability. CVS but not SDS was associated with a reduced mechanical withdrawal threshold, consistent with a generalized pain response to chronic stress. Neither SDS nor CVS exacerbated phenotypes considered specifically relevant to migraine - withdrawal to NTG, and susceptibility to CSD. However, the significantly reduced response of stress resilient mice to the NTG stimulus may represent a specific migraine-resistant phenotype.