Changes in Brainstem Pain Modulation Circuitry Function over the Migraine Cycle

Pituitary cyclase-activating polypeptide targeted treatments for the treatment of primary headache disorders

OBJECTIVE

Migraine is a complex and disabling neurological disorder. Recent years have witnessed the development and emergence of novel treatments for the condition, namely those targeting calcitonin gene-related peptide (CGRP). However, there remains a substantial need for further treatments for those unresponsive to current therapies. Targeting pituitary adenylate cyclase-activating polypeptide (PACAP) as a possible therapeutic strategy in the primary headache disorders has gained interest over recent years.

METHODS

This review will summarize what we know about PACAP to date: its expression, receptors, roles in migraine and cluster headache biology, insights gained from preclinical and clinical models of migraine, and therapeutic scope.

RESULTS

PACAP shares homology with vasoactive intestinal polypeptide (VIP) and is one of several vasoactive neuropeptides along with CGRP and VIP, which has been implicated in migraine neurobiology. PACAP is widely expressed in areas of interest in migraine pathophysiology, such as the thalamus, trigeminal nucleus caudalis, and sphenopalatine ganglion. Preclinical evidence suggests a role for PACAP in trigeminovascular sensitization, while clinical evidence shows ictal release of PACAP in migraine and intravenous infusion of PACAP triggering attacks in susceptible individuals. PACAP leads to dural vasodilatation and secondary central phenomena via its binding to different G-protein-coupled receptors, and intracellular downstream effects through cyclic adenosine monophosphate (cAMP) and phosphokinase C (PKC). Targeting PACAP as a therapeutic strategy in headache has been explored using monoclonal antibodies developed against PACAP and against the PAC1 receptor, with initial positive results.

INTERPRETATION

Future clinical trials hold considerable promise for a new therapeutic approach using PACAP-targeted therapies in both migraine and cluster headache.

Pathophysiology of Migraine

OBJECTIVE

This article provides an overview of the current understanding of migraine pathophysiology through insights gained from the extended symptom spectrum of migraine, neuroanatomy, migraine neurochemistry, and therapeutics.

LATEST DEVELOPMENTS

Recent advances in human migraine research, including human experimental migraine models and functional neuroimaging, have provided novel insights into migraine attack initiation, neurochemistry, neuroanatomy, and therapeutic substrates. It has become clear that migraine is a neural disorder, in which a wide range of brain areas and neurochemical systems are implicated, producing a heterogeneous clinical phenotype. Many of these neural pathways are monoaminergic and peptidergic, such as those involving calcitonin gene-related peptide and pituitary adenylate cyclase-activating polypeptide. We are currently witnessing an exciting era in which specific drugs targeting these pathways have shown promise in treating migraine, including some studies suggesting efficacy before headache has even started.

ESSENTIAL POINTS

Migraine is a brain disorder involving both headache and altered sensory, limbic, and homeostatic processing. A complex interplay between neurotransmitter systems, physiologic systems, and pain processing likely occurs. Targeting various therapeutic substrates within these networks provides an exciting avenue for future migraine therapeutics.

Effects of somatostatin, a somatostatin agonist, and an antagonist, on a putative migraine trigger pathway

OBJECTIVE

To determine whether somatostatin (SST) could be a cortico-brainstem neurotransmitter involved in producing the headache of migraine.

BACKGROUND

There is evidence to support the idea that a cortico-brainstem-trigeminal nucleus neuraxis might be responsible for producing migraine headache; we have suggested that SST may be one of the neurotransmitters involved.

METHODS

Rats were anesthetised and prepared for recording neurons in either the periaqueductal gray matter (PAG) or nucleus raphe magnus (NRM), as well as the trigeminal nucleus caudalis (TNC). The dura mater and facial skin were stimulated electrically or mechanically. SST, the SST agonist L054264 and the SST antagonist CYN54806 were injected intravenously, by microinjection, or by iontophoresis into the PAG or NRM. Cortical neuronal activity was provoked by cortical spreading depression (CSD) or light flash (LF) and was monitored by recording cortical blood flow (CBF).

RESULTS

Intravenous injection of SST: (a) selectively decreased the responses of TNC neurons to stimulation of the dura, but not skin, for up to 5 h; (b) decreased the ongoing discharge rate of TNC neurons while simultaneously increasing the discharge rate of neurons in either brainstem nucleus and; (c) prevented, or reversed, the effect of CSD and LF on brainstem and trigeminal neuron discharge rates. CSD and LF decreased the discharge rate of neurons in both brainstem nuclei and increased the discharge rate of TNC neurons. These effects were reversed by L054264 and mimicked by CYN54806. Injections of L054264 into the PAG or NRM reduced the response of TNC neurons to dural stimulation and skin stimulation differentially, depending on the nucleus injected. Injections of CYN54806 into either brainstem nucleus potentiated the responses of TNC neurons to dural and skin stimulation, but without a marked differential effect.

CONCLUSIONS

These results imply that SST could be a neurotransmitter in a pathway responsible for migraine pain.

Vesicular HMGB1 release from neurons stressed with spreading depolarization enables confined inflammatory signaling to astrocytes

The role of high mobility group box 1 (HMGB1) in inflammation is well characterized in the immune system and in response to tissue injury. More recently, HMGB1 was also shown to initiate an "inflammatory signaling cascade" in the brain parenchyma after a mild and brief disturbance, such as cortical spreading depolarization (CSD), leading to headache. Despite substantial evidence implying a role for inflammatory signaling in prevalent neuropsychiatric disorders such as migraine and depression, how HMGB1 is released from healthy neurons and how inflammatory signaling is initiated in the absence of apparent cell injury are not well characterized. We triggered a single cortical spreading depolarization by optogenetic stimulation or pinprick in naïve Swiss albino or transgenic Thy1-ChR2-YFP and hGFAP-GFP adult mice. We evaluated HMGB1 release in brain tissue sections prepared from these mice by immunofluorescent labeling and immunoelectron microscopy. EzColocalization and Costes thresholding algorithms were used to assess the colocalization of small extracellular vesicles (sEVs) carrying HMGB1 with astrocyte or microglia processes. sEVs were also isolated from the brain after CSD, and neuron-derived sEVs were captured by CD171 (L1CAM). sEVs were characterized with flow cytometry, scanning electron microscopy, nanoparticle tracking analysis, and Western blotting. We found that HMGB1 is released mainly within sEVs from the soma of stressed neurons, which are taken up by surrounding astrocyte processes. This creates conditions for selective communication between neurons and astrocytes bypassing microglia, as evidenced by activation of the proinflammatory transcription factor NF-ĸB p65 in astrocytes but not in microglia. Transmission immunoelectron microscopy data illustrated that HMGB1 was incorporated into sEVs through endosomal mechanisms. In conclusion, proinflammatory mediators released within sEVs can induce cell-specific inflammatory signaling in the brain without activating transmembrane receptors on other cells and causing overt inflammation.

Trigeminocervical pain sensitivity during the migraine cycle depends on headache frequency

OBJECTIVE

This experimental study aimed to assess pain sensitivity in low-frequency episodic migraine (LFEM), high-frequency episodic migraine (HFEM), and chronic migraine (CM) patients across the different phases of the migraine cycle.

METHOD

In this observational, experimental study, clinical characteristics (diary and time from the last/next headache attack), and quantitative sensory testing (QST) (wind-up pain ratio (WUR) and pressure pain threshold (PPT) from the trigeminal area and PPT from the cervical spine) was performed. LFEM, HFEM, and CM were assessed in each of the 4 migraine phases (HFEM and LFEM: interictal, preictal, ictal, and postictal; CM: interictal and ictal) and compared vs. each other's (matched for the phase) and controls.

RESULTS

A total of 56 controls, 105 LFEM, 74 HFEM, and 32 CM were included. No differences in QST parameters were observed between LFEM, HFEM, and CM in any of the phases. During the interictal phase and when comparing with controls the following were found: 1) LFEM had lower trigeminal PPT (p = 0.001) and 2) lower cervical PPT (p = 0.001). No differences were observed between HFEM or CM and healthy controls. During the ictal phase and when comparing with controls the following were found: HFEM and CM had 1) lower trigeminal PPTs (HFEM p = 0.001; CM = p < 0.001), 2) lower cervical PPT s (HFEM p = 0.007; CM p < 0.001), and 3) higher trigeminal WUR (HFEM p = 0.001, CM p = 0.006). No differences were observed between LFEM and healthy controls. During the preictal phase and when comparing with controls the following were found: 1) LFEM had lower cervical PPT (p = 0.007), 2) HFEM had lower trigeminal (p = 0.013) and 3) HFEM had lower cervical (p = .006) PPTs. During the postictal phase and when comparing with controls the following were found: 1) LFEM had lower cervical PPT (p = 0.003), 2) HFEM had lower trigeminal PPT (p = 0.005), and 3) and HFEM had lower cervical (p = 0.007) PPTs.

CONCLUSION

This study suggested that HFEM patients have a sensory profile matching CM better than LFEM. When assessing pain sensitivity in migraine populations, the phase with respects to headache attacks is of utmost importance and can explain the inconsistency in pain sensitivity data reported in the literature.

Insights into migraine attacks from neuroimaging

Migraine is one of the most common neurological diseases and it has a huge social and personal impact. Although head pain is the core symptom, individuals with migraine can have a plethora of non-headache symptoms that precede, accompany, or follow the pain. Neuroimaging studies have shown that the involvement of specific brain areas can explain many of the symptoms reported during the different phases of migraine. Recruitment of the hypothalamus, pons, spinal trigeminal nucleus, thalamus, and visual and pain-processing cortical areas starts during the premonitory phase and persists through the headache phase, contributing to the onset of pain and associated symptoms. Once the pain stops, the involvement of most brain areas ends, although the pons, hypothalamus, and visual cortex remain active after acute treatment intake and resolution of migraine symptoms. A better understanding of the correlations between imaging findings and migraine symptomatology can provide new insight into migraine pathophysiology and the mechanisms of novel migraine-specific treatments.

Neuroimaging in the pre-ictal or premonitory phase of migraine: a narrative review

BACKGROUND

The premonitory phase, or prodrome, of migraine, provides valuable opportunities to study attack initiation and for treating the attack before headache starts. Much that has been learned about this phase in recent times has come from the outcomes of functional imaging studies. This review will summarise these studies to date and use their results to provide some feasible insights into migraine neurobiology.

MAIN BODY

The ability to scan repeatedly a patient without radiation and with non-invasive imaging modalities, as well as the recognition that human experimental migraine provocation compounds, such as nitroglycerin (NTG) and pituitary adenylate cyclase activating polypeptide (PACAP), can trigger typical premonitory symptoms (PS) and migraine-like headache in patients with migraine, have allowed feasible and reproducible imaging of the premonitory phase using NTG. Some studies have used serial scanning of patients with migraine to image the migraine cycle, including the 'pre-ictal' phase, defined by timing to headache onset rather than symptom phenotype. Direct observation and functional neuroimaging of triggered PS have also revealed compatible neural substrates for PS in the absence of headache. Various imaging methods including resting state functional MRI (rsfMRI), arterial spin labelling (ASL), positron emission tomography (PET) and diffusion tensor imaging (DTI) have been used. The results of imaging the spontaneous and triggered premonitory phase have been largely consistent and support a theory of central migraine attack initiation involving brain areas such as the hypothalamus, midbrain and limbic system. Early dysfunctional pain, sensory, limbic and homeostatic processing via monoaminergic and peptidergic neurotransmission likely manifests in the heterogeneous PS phenotype.

CONCLUSION

Advances in human migraine research, including the use of functional imaging techniques lacking radiation or radio-isotope exposure, have led to an exciting opportunity to study the premonitory phase using repeated measures imaging designs. These studies have provided novel insights into attack initiation, migraine neurochemistry and therapeutic targets. Emerging migraine-specific therapies, such as those targeting calcitonin gene-related peptide (CGRP), are showing promise acutely when taken during premonitory phase to reduce symptoms and prevent subsequent headache. Therapeutic research in this area using PS for headache onset prediction and early treatment is likely to grow in the future.

Regional cerebral perfusion during the premonitory phase of triggered migraine: A double-blind randomized placebo-controlled functional imaging study using pseudo-continuous arterial spin labeling

OBJECTIVE

To identify changes in regional cerebral blood flow (CBF) associated with premonitory symptoms (PS) of nitroglycerin (NTG)-triggered migraine attacks.

BACKGROUND

PS could provide insights into attack initiation and alterations in neuronal function prior to headache onset.

METHODS

We undertook a functional imaging study using a double-blind placebo-controlled randomized approach in patients with migraine who spontaneously experienced PS, and in whom PS and migraine-like headache could be induced by administration of NTG. All study visits took place in a dedicated clinical research facility housing a monitoring area with clinical beds next to a 3Tesla magnetic resonance imaging scanner. Fifty-three patients with migraine were enrolled; imaging on at least one triggered visit was obtained from 25 patients, with 21 patients completing the entire imaging protocol including a placebo visit. Whole brain CBF maps were acquired using 3D pseudo-continuous arterial spin labeling (3D pCASL).

RESULTS

The primary outcome was that patients with migraine not taking preventive treatment (n = 12) displayed significant increases in CBF in anterior cingulate cortex, caudate, midbrain, lentiform, amygdala and hippocampus (p < 0.05 family-wise error-corrected) during NTG-induced PS. A separate region of interest analysis revealed significant CBF increases in the region of the hypothalamus (p = 0.006, effect size 0.77). Post hoc analyses revealed significant reductions in CBF over the occipital cortices in participants with a history of migraine with underlying aura (n = 14).

CONCLUSIONS

We identified significant regional CBF changes associated with NTG-induced PS, consistent with other investigations and with novel findings, withstanding statistical comparison against placebo. These findings were not present in patients who continually took preventive medication. Additional findings were identified only in participants who experience migraine with aura. Understanding this biological and treatment-related heterogeneity is vital to evaluating functional imaging outcomes in migraine research.

Functional connectivity of the language area in migraine: a preliminary classification model

BACKGROUND

Migraine is a complex disorder characterized by debilitating headaches. Despite its prevalence, its pathophysiology remains unknown, with subsequent gaps in diagnosis and treatment. We combined machine learning with connectivity analysis and applied a whole-brain network approach to identify potential targets for migraine diagnosis and treatment.

METHODS

Baseline anatomical T1 magnetic resonance imaging (MRI), resting-state functional MRI(rfMRI), and diffusion weighted scans were obtained from 31 patients with migraine, and 17 controls. A recently developed machine learning technique, Hollow Tree Super (HoTS) was used to classify subjects into diagnostic groups based on functional connectivity (FC) and derive networks and parcels contributing to the model. PageRank centrality analysis was also performed on the structural connectome to identify changes in hubness.

RESULTS

Our model attained an area under the receiver operating characteristic curve (AUC-ROC) of 0.68, which rose to 0.86 following hyperparameter tuning. FC of the language network was most predictive of the model's classification, though patients with migraine also demonstrated differences in the accessory language, visual and medial temporal regions. Several analogous regions in the right hemisphere demonstrated changes in PageRank centrality, suggesting possible compensation.

CONCLUSIONS

Although our small sample size demands caution, our preliminary findings demonstrate the utility of our method in providing a network-based perspective to diagnosis and treatment of migraine.

Functional magnetic resonance imaging in migraine: A systematic review

BACKGROUND

Migraine is a highly prevalent primary headache disorder. Despite a high burden of disease, key disease mechanisms are not entirely understood. Functional magnetic resonance imaging is an imaging method using the blood-oxygen-level-dependent signal, which has been increasingly used in migraine research over recent years. This systematic review summarizes recent findings employing functional magnetic resonance imaging for the investigation of migraine.

METHODS

We conducted a systematic search and selection of functional magnetic resonance imaging applications in migraine from April 2014 to December 2021 (PubMed and references of identified articles according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines). Methodological details and main findings were extracted and synthesized.

RESULTS

Out of 224 articles identified, 114 were included after selection. Repeatedly emerging structures of interest included the insula, brainstem, limbic system, hypothalamus, thalamus, and functional networks. Assessment of functional brain changes in response to treatment is emerging, and machine learning has been used to investigate potential functional magnetic resonance imaging-based markers of migraine.

CONCLUSIONS

A wide variety of functional magnetic resonance imaging-based metrics were found altered across the brain for heterogeneous migraine cohorts, partially correlating with clinical parameters and supporting the concept to conceive migraine as a brain state. However, a majority of findings from previous studies have not been replicated, and studies varied considerably regarding image acquisition and analyses techniques. Thus, while functional magnetic resonance imaging appears to have the potential to advance our understanding of migraine pathophysiology, replication of findings in large representative datasets and precise, standardized reporting of clinical data would likely benefit the field and further increase the value of observations.

What imaging has revealed about migraine and chronic migraine

Although migraine pathophysiology is not yet entirely understood, it is now established that migraine should be viewed as a complex neurological disease, which involves the interplay of different brain networks and the release of signaling molecules, instead of a pure vascular disorder. The field of migraine research has also progressed significantly due to the advancement of brain imaging techniques. Numerous studies have investigated the relation between migraine pathophysiology and cerebral hemodynamic changes, showing that vascular changes are neither necessary nor sufficient to cause the migraine pain. Abnormal function and structure of key cortical, subcortical, and brainstem regions involved in multisensory, including pain, processing have been shown to occur in migraine patients during both an acute attack and the interictal phase. Whether brain imaging alterations represent a predisposing trait or are the consequence of the recurrence of headache attacks is still a matter of debate. It is highly likely that brain functional and structural alterations observed in migraine patients derive from the interaction between predisposing brain traits and experience-dependent responses. Neuroimaging studies have also enriched our knowledge of the mechanisms responsible for migraine chronification and have shed light on the mechanisms of actions of acute and preventive migraine treatments.

The anatomy of head pain

Pain-sensitive structures in the head and neck, including the scalp, periosteum, meninges, and blood vessels, are innervated predominantly by the trigeminal and upper cervical nerves. The trigeminal nerve supplies most of the sensation to the head and face, with the ophthalmic division (V1) providing innervation to much of the supratentorial dura mater and vessels. This creates referral patterns for pain that may be misleading to clinicians and patients, as described by studies involving awake craniotomies and stimulation with electrical and mechanical stimuli. Most brain parenchyma and supratentorial vessels refer pain to the ipsilateral V1 territory, and less commonly the V2 or V3 region. The upper cervical nerves provide innervation to the posterior scalp, while the periauricular region and posterior fossa are territories with shared innervation. Afferent fibers that innervate the head and neck send nociceptive input to the trigeminocervical complex, which then projects to additional pain processing areas in the brainstem, thalamus, hypothalamus, and cortex. This chapter discusses the pain-sensitive structures in the head and neck, including pain referral patterns for many of these structures. It also provides an overview of peripheral and central nervous system structures responsible for transmitting and interpreting these nociceptive signals.

Longitudinal changes in functional connectivity and pain-induced brain activations in patients with migraine: a functional MRI study pre- and post- treatment with Erenumab

Abstract

Background

Migraine involves central and peripheral nervous system mechanisms. Erenumab, an anti-calcitonin gene-related peptide (CGRP) receptor monoclonal antibody with little central nervous system penetrance, is effective for migraine prevention. The objective of this study was to determine if response to erenumab is associated with alterations in brain functional connectivity and pain-induced brain activations.

Methods

Adults with 6–25 migraine days per month during a 4-week headache diary run-in phase underwent pre-treatment brain functional MRI (fMRI) that included resting-state functional connectivity and BOLD measurements in response to moderately painful heat stimulation to the forearm. This was followed by two treatments with 140 mg erenumab, at baseline and 4 weeks later. Post-treatment fMRI was performed 2 weeks and 8 weeks following the first erenumab treatment. A longitudinal Sandwich estimator analysis was used to identify pre- to post-treatment changes in resting-state functional connectivity and brain activations in response to thermal pain. fMRI findings were compared between erenumab treatment-responders vs. erenumab non-responders.

Results

Pre- and post-treatment longitudinal imaging data were available from 32 participants. Average age was 40.3 (+/− 13) years and 29 were female. Pre-treatment average migraine day frequency was 13.8 (+/− 4.7) / 28 days and average headache day frequency was 15.8 (+/− 4.4) / 28 days. Eighteen of 32 (56%) were erenumab responders. Compared to erenumab non-responders, erenumab responders had post-treatment differences in 1) network functional connectivity amongst pain-processing regions, including higher global efficiency, clustering coefficient, node degree, regional efficiency, and modularity, 2) region-to-region functional connectivity between several regions including temporal pole, supramarginal gyrus, and hypothalamus, and 3) pain-induced activations in the middle cingulate, posterior cingulate, and periaqueductal gray matter.

Conclusions

Reductions in migraine day frequency accompanying erenumab treatment are associated with changes in resting state functional connectivity and central processing of extracranial painful stimuli that differ from erenumab non-responders.

Trial registration

clinicaltrials.gov (NCT03773562).

The premonitory phase of migraine is due to hypothalamic dysfunction: revisiting the evidence

OBJECTIVE

To critically appraise the evidence for and against premonitory symptoms in migraine being due to hypothalamic dysfunction.

DISCUSSION

Some premonitory symptoms (e.g. fatigue, mood changes, yawning, and food craving) are associated with the physiologic effects of neurotransmitters such as orexins, neuropeptide Y, and dopamine; all of which are expressed in hypothalamic neurons. In rodents, electrophysiologic recordings have shown that these neurotransmitters modulate nociceptive transmission at the level of second-order neurons in the trigeminocervical complex (TCC). Additional insights have been gained from neuroimaging studies that report hypothalamic activation during the premonitory phase of migraine. However, the available evidence is limited by methodologic issues, inconsistent reporting, and a lack of adherence to ICHD definitions of premonitory symptoms (or prodromes) in human experimental studies.

CONCLUSIONS

The current trend to accept that premonitory symptoms are due to hypothalamic dysfunction might be premature. More rigorously designed studies are needed to ascertain whether the neurobiologic basis of premonitory symptoms is due to hypothalamic dysfunction or rather reflects modulatory input to the trigeminovascular system from several cortical and subcortical areas. On a final note, the available epidemiologic data raises questions as to whether the existence of premonitory symptoms and even more so a distinct premonitory phase is a true migraine phenomenon. Video recording of the debate held at the 1st International Conference on Advances in Migraine Sciences (ICAMS 2022, Copenhagen, Denmark) is available at: https://www.youtube.com/watch?v=d4Y2x0Hr4Q8 .

Predicting response to tVNS in patients with migraine using functional MRI: A voxels-based machine learning analysis

Background

Migraine is a common disorder, affecting many patients. However, for one thing, lacking objective biomarkers, misdiagnosis, and missed diagnosis happen occasionally. For another, though transcutaneous vagus nerve stimulation (tVNS) could alleviate migraine symptoms, the individual difference of tVNS efficacy in migraineurs hamper the clinical application of tVNS. Therefore, it is necessary to identify biomarkers to discriminate migraineurs as well as select patients suitable for tVNS treatment.

Methods

A total of 70 patients diagnosed with migraine without aura (MWoA) and 70 matched healthy controls were recruited to complete fMRI scanning. In study 1, the fractional amplitude of low-frequency fluctuation (fALFF) of each voxel was calculated, and the differences between healthy controls and MWoA were compared. Meaningful voxels were extracted as features for discriminating model construction by a support vector machine. The performance of the discriminating model was assessed by accuracy, sensitivity, and specificity. In addition, a mask of these significant brain regions was generated for further analysis. Then, in study 2, 33 of the 70 patients with MWoA in study 1 receiving real tVNS were included to construct the predicting model in the generated mask. Discriminative features of the discriminating model in study 1 were used to predict the reduction of attack frequency after a 4-week tVNS treatment by support vector regression. A correlation coefficient between predicted value and actual value of the reduction of migraine attack frequency was conducted in 33 patients to assess the performance of predicting model after tVNS treatment. We vislized the distribution of the predictive voxels as well as investigated the association between fALFF change (post-per treatment) of predict weight brain regions and clinical outcomes (frequency of migraine attack) in the real group.

Results

A biomarker containing 3,650 features was identified with an accuracy of 79.3%, sensitivity of 78.6%, and specificity of 80.0% (p &lt; 0.002). The discriminative features were found in the trigeminal cervical complex/rostral ventromedial medulla (TCC/RVM), thalamus, medial prefrontal cortex (mPFC), and temporal gyrus. Then, 70 of 3,650 discriminative features were identified to predict the reduction of attack frequency after tVNS treatment with a correlation coefficient of 0.36 (p = 0.03). The 70 predictive features were involved in TCC/RVM, mPFC, temporal gyrus, middle cingulate cortex (MCC), and insula. The reduction of migraine attack frequency had a positive correlation with right TCC/RVM (r = 0.433, p = 0.021), left MCC (r = 0.451, p = 0.016), and bilateral mPFC (r = 0.416, p = 0.028), and negative with left insula (r = −0.473, p = 0.011) and right superior temporal gyrus/middle temporal gyrus (r = −0.684, p &lt; 0.001), respectively.

Conclusions

By machine learning, the study proposed two potential biomarkers that could discriminate patients with MWoA and predict the efficacy of tVNS in reducing migraine attack frequency. The pivotal features were mainly located in the TCC/RVM, thalamus, mPFC, and temporal gyrus.

Alterations in brain structure associated with trigeminal nerve anatomy in episodic migraine

The pathophysiology of migraine remains to be elucidated. We have recently shown that interictal migraineurs exhibit reduced fractional anisotropy (FA) in the root entry zone of the trigeminal nerve when compared to controls, but it is not known if this altered nerve anatomy is associated with changes within the brainstem or higher cortical brain regions. Diffusion tensor imaging of the brain was used to calculate regional measures of structure, including mean diffusivity (MD), axial diffusivity (AX) and radial diffusivity (RD) in addition to voxel-based morphometry of T1-weighted anatomical images. Linear relationships between trigeminal nerve anatomy (FA) and MD throughout the brainstem and/or higher cortical regions were determined in both controls (n = 31, brainstem; n = 38, wholebrain) and interictal migraineurs (n = 32, brainstem; n = 38, wholebrain). Additionally, within the same brain areas, relationships of AX and RD with nerve FA were determined. We found that in both interictal migraine and control participants, decreasing trigeminal nerve FA was associated with significantly increased MD in brainstem regions including the spinal trigeminal nucleus and midbrain periaqueductal gray matter (PAG), and in higher brain regions such as the hypothalamus, insula, posterior cingulate, primary somatosensory and primary visual (V1) cortices. Whereas, both control and migraineur groups individually displayed significant inverse correlations between nerve FA and MD, in migraineurs this pattern was disrupted in the areas of the PAG and V1, with only the control group displaying a significant linear relationship (PAG controls r = –0.58, p = 0.003; migraineurs r = –0.25, p = 0.17 and V1 controls r = −0.52, p = 0.002; migraineurs r = –0.10, p = 0.55). Contrastingly, we found no gray matter volume changes in brainstem or wholebrain areas. These data show that overall, trigeminal nerve anatomy is significantly related to regional brain structure in both controls and migraineurs. Importantly, the PAG showed a disruption of this relationship in migraineurs suggesting that the anatomy and possibly the function of the PAG is uniquely altered in episodic migraine, which may contribute to altered orofacial pain processing in migraine.

Cycling multisensory changes in migraine: more than a headache

PURPOSE OF REVIEW

Research on migraine usually focuses on the headache; however, accumulating evidence suggests that migraine not only changes the somatosensory system for nociception (pain), but also the other modalities of perception, such as visual, auditory or tactile sense. More importantly, the multisensory changes exist beyond the headache (ictal) phase of migraine and show cyclic changes, suggesting a central generator driving the multiple sensory changes across different migraine phases. This review summarizes the latest studies that explored the cyclic sensory changes of migraine.

RECENT FINDINGS

Considerable evidence from recent neurophysiological and functional imaging studies suggests that alterations in brain activation start at least 48 h before the migraine headache and outlast the pain itself for 24 h. Several sensory modalities are involved with cyclic changes in sensitivity that peak during the ictal phase.

SUMMARY

In many ways, migraine represents more than just vascular-mediated headaches. Migraine alters the propagation of sensory information long before the headache attack starts.

The pain conductor: brainstem modulation in acute and chronic pain

PURPOSE OF REVIEW

It is well established in experimental settings that brainstem circuits powerfully modulate the multidimensional experience of pain. This review summarizes current understanding of the roles of brainstem nuclei in modulating the intensity of pain, and how these circuits might be recruited therapeutically for pain relief in chronic and palliative settings.

RECENT FINDINGS

The development of ultra-high field magnetic resonance imaging and more robust statistical analyses has led to a more integrated understanding of brainstem function during pain. It is clear that a number of brainstem nuclei and their overlapping pathways are recruited to either enhance or inhibit incoming nociceptive signals. This review reflects on early preclinical research, which identified in detail brainstem analgesic function, putting into context contemporary investigations in humans that have identified the role of specific brainstem circuits in modulating pain, their contribution to pain chronicity, and even the alleviation of palliative comorbidities.

SUMMARY

The brainstem is an integral component of the circuitry underpinning pain perception. Enhanced understanding of its circuitry in experimental studies in humans has, in recent years, increased the possibility for better optimized pain-relief strategies and the identification of vulnerabilities to postsurgical pain problems. When integrated into the clinical landscape, these experimental findings of brainstem modulation of pain signalling have the potential to contribute to the optimization of pain management and patient care from acute, to chronic, to palliative states.

Role of Estrogens in Menstrual Migraine

Migraine is a major neurological disorder affecting one in nine adults worldwide with a significant impact on health care and socioeconomic systems. Migraine is more prevalent in women than in men, with 17% of all women meeting the diagnostic criteria for migraine. In women, the frequency of migraine attacks shows variations over the menstrual cycle and pregnancy, and the use of combined hormonal contraception (CHC) or hormone replacement therapy (HRT) can unveil or modify migraine disease. In the general population, 18–25% of female migraineurs display a menstrual association of their headache. Here we present an overview on the evidence supporting the role of reproductive hormones, in particular estrogens, in the pathophysiology of migraine. We also analyze the efficacy and safety of prescribing exogenous estrogens as a potential treatment for menstrual-related migraine. Finally, we point to controversial issues and future research areas in the field of reproductive hormones and migraine.

New Insights on Metabolic and Genetic Basis of Migraine: Novel Impact on Management and Therapeutical Approach

Migraine is a hereditary disease, usually one-sided, sometimes bilateral. It is characterized by moderate to severe pain, which worsens with physical activity and may be associated with nausea and vomiting, may be accompanied by photophobia and phonophobia. The disorder can occur at any time of the day and can last from 4 to 72 h, with and without aura. The pathogenic mechanism is unclear, but extensive preclinical and clinical studies are ongoing. According to electrophysiology and imaging studies, many brain areas are involved, such as cerebral cortex, thalamus, hypothalamus, and brainstem. The activation of the trigeminovascular system has a key role in the headache phase. There also appears to be a genetic basis behind the development of migraine. Numerous alterations have been identified, and in addition to the genetic cause, there is also a close association with the surrounding environment, as if on the one hand, the genetic alterations may be responsible for the onset of migraine, on the other, the environmental factors seem to be more strongly associated with exacerbations. This review is an analysis of neurophysiological mechanisms, neuropeptide activity, and genetic alterations that play a fundamental role in choosing the best therapeutic strategy. To date, the goal is to create a therapy that is as personalized as possible, and for this reason, steps forward have been made in the pharmacological field in order to identify new therapeutic strategies for both acute treatment and prophylaxis.

Dynamic brainstem and somatosensory cortical excitability during migraine cycles

Abstract

Background

Migraine has complex pathophysiological characteristics and episodic attacks. To decipher the cyclic neurophysiological features of migraine attacks, in this study, we compared neuronal excitability in the brainstem and primary somatosensory (S1) region between migraine phases for 30 consecutive days in two patients with episodic migraine.

Methods

Both patients underwent EEG recording of event-related potentials with the somatosensory and paired-pulse paradigms for 30 consecutive days. The migraine cycle was divided into the following phases: 24–48 h before headache onset (Pre2), within 24 h before headache onset (Pre1), during the migraine attack (Ictal), within 24 h after headache offset (Post1), and the interval of ˃48 h between the last and next headache phase (Interictal). The normalised current intensity in the brainstem and S1 and gating ratio in the S1 were recorded and examined.

Results

Six migraine cycles (three for each patient) were analysed. In both patients, the somatosensory excitability in the brainstem (peaking at 12–14 ms after stimulation) and S1 (peaking at 18–19 ms after stimulation) peaked in the Pre1 phase. The S1 inhibitory capability was higher in the Ictal phase than in the Pre1 phase.

Conclusion

This study demonstrates that migraine is a cyclic excitatory disorder and that the neural substrates involved include the somatosensory system, starting in the brainstem and spanning subsequently to the S1 before the migraine occurs. Further investigations with larger sample sizes are warranted.

Real-World Analysis of Remote Electrical Neuromodulation (REN) for the Acute Treatment of Migraine

Introduction: Migraine is a chronic neurological disease that is the primary cause of years lived with disability in people under the age of 50. Remote electrical neuromodulation (REN) is a novel drug-free acute treatment of migraine, that is FDA cleared for episodic and chronic migraine. As a prescribed digital therapeutic, REN enables large-scale post-marketing research, thus providing real-world information on the use of the intervention in a wide range of populations, environments, and situations.

Methods: The REN device (®Nerivio) includes a secured, personal migraine diary, which patients can use to record their symptoms before treatment and 2 h post-treatment. Real-world data on REN treatments were collected via the app from patients across the United States who used Nerivio between October 1st, 2019, and May 24th, 2021. Data analysis focused on four metrics: 1. Per-treatment patterns of REN use as a standalone treatment vs. in combination with medications. 2. Per-user intra-individual efficacy across multiple treatments. 3. Distribution of treatment intensity among users (the electroceutical equivalent to treatment dose). 4. Prevalence and severity of adverse events.

Results: 1. Out of 23,151 treatments, in 66.5% of treatments REN was used as a standalone treatment, in 12.9% it was followed by over-the-counter medications, and in 20.6% followed by prescription medications. 2. Out of 2,514 patients, response in at least 50% of treatments was achieved in 66.5% of cases for pain relief, and in 22.6% for pain freedom. 3. Out of 117,583 treatments, in 80% of cases intensity levels were between 18 and 55% of the stimulator's range. The mean intensity was 34.3% of the stimulator's output (±16.6%). 4. Out of 12,368 users (121,947 treatments), there were 59 users (0.48%) who reported device related adverse events, 56 (0.45%) of which were mild, three (0.03%) were moderate, and none were severe.

Conclusions: The current analysis of real-world clinical data indicates that REN provides an efficacious, stable, and safe treatment option for acute treatment of migraine in real-world settings, both as a standalone replacement of pharmaceuticals, as well as an adjunct to medications.

Alterations in pain processing circuitries in episodic migraine

Background

The precise underlying mechanisms of migraine remain unknown. Although we have previously shown acute orofacial pain evoked changes within the brainstem of individuals with migraine, we do not know if these brainstem alterations are driven by changes in higher cortical regions. The aim of this investigation is to extend our previous investigation to determine if higher brain centers display altered activation patterns and connectivity in migraineurs during acute orofacial noxious stimuli.

Methods

Functional magnetic resonance imaging was performed in 29 healthy controls and 25 migraineurs during the interictal and immediately (within 24-h) prior to migraine phases. We assessed activation of higher cortical areas during noxious orofacial heat stimulation using a thermode device and assessed whole scan and pain-related changes in connectivity.

Results

Despite similar overall pain intensity ratings between all three groups, migraineurs in the group immediately prior to migraine displayed greater activation of the ipsilateral nucleus accumbens, the contralateral ventrolateral prefrontal cortex and two clusters in the dorsolateral prefrontal cortex (dlPFC). Reduced whole scan dlPFC [Z + 44] connectivity with cortical/subcortical and brainstem regions involved in pain modulation such as the putamen and primary motor cortex was demonstrated in migraineurs. Pain-related changes in connectivity of the dlPFC and the hypothalamus immediately prior to migraine was also found to be reduced with brainstem pain modulatory areas such as the rostral ventromedial medulla and dorsolateral pons.

Conclusions

These data reveal that the modulation of brainstem pain modulatory areas by higher cortical regions may be aberrant during pain and these alterations in this descending pain modulatory pathway manifests exclusively prior to the development of a migraine attack.

Exploring alterations in sensory pathways in migraine

Background

Migraine is a neurological disorder characterized by intense, debilitating headaches, often coupled with nausea, vomiting and sensitivity to light and sound. Whilst changes in sensory processes during a migraine attack have been well-described, there is growing evidence that even between migraine attacks, sensory abilities are disrupted in migraine. Brain imaging studies have investigated altered coupling between areas of the descending pain modulatory pathway but coupling between somatosensory processing regions between migraine attacks has not been properly studied. The aim of this study was to determine if ongoing functional connectivity between visual, auditory, olfactory, gustatory and somatosensory cortices are altered during the interictal phase of migraine.

Methods

To explore the neural mechanisms underpinning interictal changes in sensory processing, we used functional magnetic resonance imaging to compare resting brain activity patterns and connectivity in migraineurs between migraine attacks (n = 32) and in healthy controls (n = 71). Significant differences between groups were determined using two-sample random effects procedures (p < 0.05, corrected for multiple comparisons, minimum cluster size 10 contiguous voxels, age and gender included as nuisance variables).

Results

In the migraine group, increases in infra-slow oscillatory activity were detected in the right primary visual cortex (V1), secondary visual cortex (V2) and third visual complex (V3), and left V3. In addition, resting connectivity analysis revealed that migraineurs displayed significantly enhanced connectivity between V1 and V2 with other sensory cortices including the auditory, gustatory, motor and somatosensory cortices.

Conclusions

These data provide evidence for a dysfunctional sensory network in pain-free migraine patients which may be underlying altered sensory processing between migraine attacks.

Inter-individual differences in pain anticipation and pain perception in migraine: Neural correlates of migraine frequency and cortisol-to-dehydroepiandrosterone sulfate (DHEA-S) ratio

Previous studies targeting inter-individual differences in pain processing in migraine mainly focused on the perception of pain. Our main aim was to disentangle pain anticipation and perception using a classical fear conditioning task, and investigate how migraine frequency and pre-scan cortisol-to-dehydroepiandrosterone sulfate (DHEA-S) ratio as an index of neurobiological stress response would relate to neural activation in these two phases. Functional Magnetic Resonance Imaging (fMRI) data of 23 participants (18 females; mean age: 27.61± 5.36) with episodic migraine without aura were analysed. We found that migraine frequency was significantly associated with pain anticipation in brain regions comprising the midcingulate and caudate, whereas pre-scan cortisol-to DHEA-S ratio was related to pain perception in the pre-supplementary motor area (pre-SMA). Both results suggest exaggerated preparatory responses to pain or more general to stressors, which may contribute to the allostatic load caused by stressors and migraine attacks on the brain.

A Narrative Review of Neuroimaging Studies in Acupuncture for Migraine

Acupuncture has been widely used as an alternative and complementary therapy for migraine. With the development of neuroimaging techniques, the central mechanism of acupuncture for migraine has gained increasing attention. This review aimed to analyze the study design and main findings of neuroimaging studies of acupuncture for migraine to provide the reference for future research. The original studies were collected and screened in three English databases (PubMed, Embase, and Cochrane Library) and four Chinese databases (Chinese National Knowledge Infrastructure, Chinese Biomedical Literature database, the Chongqing VIP database, and Wanfang database). As a result, a total of 28 articles were included. Functional magnetic resonance imaging was the most used neuroimaging technique to explore the cerebral activities of acupuncture for migraine. This review manifested that acupuncture could elicit cerebral responses on patients with migraine, different from sham acupuncture. The results indicated that the pain systems, including the medial pain pathway, lateral pain pathway, and descending pain modulatory system, participated in the modulation of the cerebral activities of migraine by acupuncture.

Regional homogeneity alterations in multi-frequency bands in tension-type headache: a resting-state fMRI study

OBJECTIVES

In this study, we aimed to investigate the spontaneous neural activity in the conventional frequency band (0.01-0.08 Hz) and two sub-frequency bands (slow-4: 0.027-0.073 Hz, and slow-5: 0.01-0.027 Hz) in tension-type headache (TTH) patients with regional homogeneity (ReHo) analyses.

METHODS

Thirty-eight TTH patients and thirty-eight healthy controls (HCs) underwent resting-state functional magnetic resonance imaging (RS-fMRI) scanning to investigate abnormal spontaneous neural activity using ReHo analysis in conventional frequency band (0.01-0.08 Hz) and two sub-frequency bands (slow-4: 0.027-0.073 Hz and slow-5: 0.01-0.027 Hz).

RESULTS

In comparison with the HC group, patients with TTH exhibited ReHo increases in the right medial superior frontal gyrus in the conventional frequency band (0.01-0.08 Hz). The between group differences in the slow-5 band (0.01-0.027 Hz) highly resembled the differences in the conventional frequency band (0.01-0.08 Hz); even the voxels with increased ReHo were spatially more extensive, including the right medial superior frontal gyrus and the middle frontal gyrus. In contrast, no region showed significant between-group differences in the slow-4 band (0.027-0.073 Hz). The correlation analyses showed no correlation between the ReHo values in TTH patients and VAS scores, course of disease and number of seizures per month in conventional band (0.01-0.08 Hz), slow-4 band (0.027-0.073 Hz), as well as in slow-5 band (0.01-0.027 Hz).

CONCLUSIONS

The results showed that the superior frontal gyrus and middle frontal gyrus were involved in the integration and processing of pain signals. In addition, the abnormal spontaneous neural activity in TTH patients was frequency-specific. Namely, slow-5 band (0.01-0.027 Hz) might contain additional useful information in comparison to slow-4 band (0.027-0.073 Hz). This preliminary exploration might provide an objective imaging basis for the understanding of the pathophysiological mechanism of TTH.

The association between pain-induced autonomic reactivity and descending pain control is mediated by the periaqueductal grey

There is a strict interaction between the autonomic nervous system (ANS) and pain, which might involve descending pain modulatory mechanisms. The periaqueductal grey (PAG) is involved both in descending pain modulation and ANS, but its role in mediating this relationship has not yet been explored. Here, we sought to determine brain regions mediating ANS and descending pain control associations. Thirty participants underwent conditioned pain modulation (CPM) assessments, in which they rated painful pressure stimuli applied to their thumbnail, either alone or with a painful cold contralateral stimulation. Differences in pain ratings between 'pressure-only' and 'pressure + cold' stimuli provided a measure of descending pain control. In 18 of the 30 participants, structural scans and two functional MRI assessments, one pain-free and one during cold-pain were acquired. Heart rate variability (HRV) was simultaneously recorded. Normalised low-frequency HRV (LF-HRVnu) and the CPM score were negatively correlated; individuals with higher LF-HRVnu during pain reported reductions in pain during CPM. PAG-ventro-medial prefrontal cortex (vmPFC) and PAG-rostral ventromedial medulla (RVM) functional connectivity correlated negatively with the CPM. Importantly, PAG-vmPFC functional connectivity mediated the strength of the LF-HRVnu-CPM association. CPM response magnitude was also negatively correlated with vmPFC GM volume. Our multi-modal approach, using behavioural, physiological and MRI measures, provides important new evidence of interactions between ANS and descending pain mechanisms. ANS dysregulation and dysfunctional descending pain modulation are characteristics of chronic pain. We suggest that further investigation of body-brain interactions in chronic pain patients may catalyse the development of new treatments. KEY POINTS: Heart rate variability (HRV) is associated with descending pain modulation as measured by the conditioned pain modulation protocol (CPM). There is an association between CPM scores and the functional connectivity between the periaqueductal grey (PAG) and ventro-medial prefrontal cortex (vmPFC). CPM scores are also associated with vmPFC grey matter volume. The strength of functional connectivity between the PAG and vmPFC mediates the association between HRV and CPM. Our data provide new evidence of interactions between the autonomic nervous system and descending pain mechanisms.

Hormonal influences in migraine - interactions of oestrogen, oxytocin and CGRP

Migraine is ranked as the second highest cause of disability worldwide and the first among women aged 15-49 years. Overall, the incidence of migraine is threefold higher among women than men, though the frequency and severity of attacks varies during puberty, the menstrual cycle, pregnancy, the postpartum period and menopause. Reproductive hormones are clearly a key influence in the susceptibility of women to migraine. A fall in plasma oestrogen levels can trigger attacks of migraine without aura, whereas higher oestrogen levels seem to be protective. The basis of these effects is unknown. In this Review, we discuss what is known about sex hormones and their receptors in migraine-related areas in the CNS and the peripheral trigeminovascular pathway. We consider the actions of oestrogen via its multiple receptor subtypes and the involvement of oxytocin, which has been shown to prevent migraine attacks. We also discuss possible interactions of these hormones with the calcitonin gene-related peptide (CGRP) system in light of the success of anti-CGRP treatments. We propose a simple model to explain the hormone withdrawal trigger in menstrual migraine, which could provide a foundation for improved management and therapy for hormone-related migraine in women.

Chronic Migraine Pathophysiology and Treatment: A Review of Current Perspectives

Chronic migraine is a disabling neurological disorder that imposes a considerable burden on individual and socioeconomic outcomes. Chronic migraine is defined as headaches occurring on at least 15 days per month with at least eight of these fulfilling the criteria for migraine. Chronic migraine typically evolves from episodic migraine as a result of increasing attack frequency and/or several other risk factors that have been implicated with migraine chronification. Despite this evolution, chronic migraine likely develops into its own distinct clinical entity, with unique features and pathophysiology separating it from episodic migraine. Furthermore, chronic migraine is characterized with higher disability and incidence of comorbidities in comparison to episodic migraine. While existing migraine studies primarily focus on episodic migraine, less is known about chronic migraine pathophysiology. Mounting evidence on aberrant alterations suggest that pronounced functional and structural brain changes, central sensitization and neuroinflammation may underlie chronic migraine mechanisms. Current treatment options for chronic migraine include risk factor modification, acute and prophylactic therapies, evidence-based treatments such as onabotulinumtoxinA, topiramate and newly approved calcitonin gene-related peptide or receptor targeted monoclonal antibodies. Unfortunately, treatments are still predominantly ineffective in aborting migraine attacks and decreasing intensity and frequency, and poor adherence and compliance with preventative medications remains a significant challenge. Novel emerging chronic migraine treatments such as neuromodulation offer promising therapeutic approaches that warrant further investigation. The aim of this narrative review is to provide an update of current knowledge and perspectives regarding chronic migraine background, pathophysiology, current and emerging treatment options with the intention of facilitating future research into this debilitating and largely indeterminant disorder.

Brainstem Pain-Modulation Circuitry and Its Plasticity in Neuropathic Pain: Insights From Human Brain Imaging Investigations

Acute pain serves as a protective mechanism that alerts us to potential tissue damage and drives a behavioural response that removes us from danger. The neural circuitry critical for mounting this behavioural response is situated within the brainstem and is also crucial for producing analgesic and hyperalgesic responses. In particular, the periaqueductal grey, rostral ventromedial medulla, locus coeruleus and subnucleus reticularis dorsalis are important structures that directly or indirectly modulate nociceptive transmission at the primary nociceptive synapse. Substantial evidence from experimental animal studies suggests that plasticity within this system contributes to the initiation and/or maintenance of chronic neuropathic pain, and may even predispose individuals to developing chronic pain. Indeed, overwhelming evidence indicates that plasticity within this circuitry favours pro-nociception at the primary synapse in neuropathic pain conditions, a process that ultimately contributes to a hyperalgesic state. Although experimental animal investigations have been crucial in our understanding of the anatomy and function of the brainstem pain-modulation circuitry, it is vital to understand this system in acute and chronic pain states in humans so that more effective treatments can be developed. Recent functional MRI studies have identified a key role of this system during various analgesic and hyperalgesic responses including placebo analgesia, offset analgesia, attentional analgesia, conditioned pain modulation, central sensitisation and temporal summation. Moreover, recent MRI investigations have begun to explore brainstem pain-modulation circuitry plasticity in chronic neuropathic pain conditions and have identified altered grey matter volumes and functioning throughout the circuitry. Considering the findings from animal investigations, it is likely that these changes reflect a shift towards pro-nociception that ultimately contributes to the maintenance of neuropathic pain. The purpose of this review is to provide an overview of the human brain imaging investigations that have improved our understanding of the pain-modulation system in acute pain states and in neuropathic conditions. Our interpretation of the findings from these studies is often guided by the existing body of experimental animal literature, in addition to evidence from psychophysical investigations. Overall, understanding the plasticity of this system in human neuropathic pain conditions alongside the existing experimental animal literature will ultimately improve treatment options.

White matter changes in the trigeminal spinal tract in chronic migraineurs: an ex vivo study combining ultra-high field diffusion tensor imaging and polarized light imaging microscopy

ABSTRACT

Chronic migraine (CM) is a disabling neurologic disorder that affects approximately 2% of the general population. Neuroimaging studies show functional involvement of trigeminal structures, such as the trigeminal spinal nucleus (Sp5) in migraine. However, structural changes in the Sp5 and the afferent trigeminal spinal tract (sp5) have never been found. The aim of this study was to test the hypothesis that white matter changes in the sp5 are a key feature of brain alterations in CM patients. We used diffusion Magnetic Resonance Imaging (dMRI) and polarized light imaging (PLI) of post mortem brainstem specimens from healthy controls (n = 5) and CM patients (n = 5) to study white matter alterations in the sp5. Within the sp5, dMRI metrics included fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD) and radial diffusivity (RD) values. PLI was used to assess myelin density by measure of the retardance values in the sp5. The present study provides histological evidence that structural alterations occur in the sp5 in CM patients as compared to healthy controls. Myelin-density, as assessed by retardance values, showed to be higher and a corresponding increase in FA-values was observed. In addition, accompanying decreases in MD-, AD- and RD-values were observed. This study shows that the sp5 undergoes neuroplastic changes, a feature which substantiates evidence for the hyperactivity of the Sp5 in migraine patients. More insights are needed to observe whether these changes only occur in CM patients.

Migraine Is More Than Just Headache: Is the Link to Chronic Fatigue and Mood Disorders Simply Due to Shared Biological Systems?

Migraine is a symptomatically heterogeneous condition, of which headache is just one manifestation. Migraine is a disorder of altered sensory thresholding, with hypersensitivity among sufferers to sensory input. Advances in functional neuroimaging have highlighted that several brain areas are involved even prior to pain onset. Clinically, patients can experience symptoms hours to days prior to migraine pain, which can warn of impending headache. These symptoms can include mood and cognitive change, fatigue, and neck discomfort. Some epidemiological studies have suggested that migraine is associated in a bidirectional fashion with other disorders, such as mood disorders and chronic fatigue, as well as with other pain conditions such as fibromyalgia. This review will focus on the literature surrounding alterations in fatigue, mood, and cognition in particular, in association with migraine, and the suggested links to disorders such as chronic fatigue syndrome and depression. We hypothesize that migraine should be considered a neural disorder of brain function, in which alterations in aminergic networks integrating the limbic system with the sensory and homeostatic systems occur early and persist after headache resolution and perhaps interictally. The associations with some of these other disorders may allude to the inherent sensory sensitivity of the migraine brain and shared neurobiology and neurotransmitter systems rather than true co-morbidity.

Are some patient-perceived migraine triggers simply early manifestations of the attack?

OBJECTIVE

To study the agreement between self-reported trigger factors and early premonitory symptoms amongst a group of migraineurs in both spontaneous and pharmacologically provoked attacks.

METHODS

Fifty-three subjects with migraine with and without aura, with ≤ 22 headache days/month, with spontaneous premonitory symptoms associated with migraine attacks were recruited nationally. A detailed history was taken by a study investigator to confirm diagnosis and extended phenotyping was performed to identify patient-reported triggers for migraine attacks, premonitory symptom phenotype and headache characteristics, using a standardised physician-administered questionnaire. The same subjects were exposed to a 0.5 mcg/kg/min nitroglycerin infusion over 20 min, to determine if similar migraine symptoms could be triggered. The triggered attacks were phenotyped in the same way as spontaneous ones. Percentage agreement and Cohen's kappa measure of agreement were used to identify concordance between patient-reported triggers and the corresponding spontaneous and triggered premonitory symptoms. Percentage agreement of > 60% and/or a kappa value > 0.3 with P < 0.05 were considered significant.

RESULTS

There was statistically significant agreement between perception of light as a migraine trigger and spontaneous premonitory photophobia; perception of sound as a trigger and triggered premonitory phonophobia; skipping meals as a trigger and spontaneous premonitory food cravings; and food triggers and spontaneous premonitory food cravings. There was good agreement between stress and premonitory triggered mood change.

CONCLUSIONS

At least some patient-reported triggers, such as light, sound, foods and skipping meals, may represent early brain manifestations of the premonitory phase of the migraine attack.

Brainstem functional oscillations across the migraine cycle: A longitudinal investigation

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Individual migraineurs’ brainstem function alters through the migraine cycle.

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Functional changes occurred in the 24-hour period immediately prior to a migraine.

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Greater resting activity variability was found in the SpV, pons and PAG.

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Increased infra-slow oscillations and regional homogeneity in the SpV and pons.

Although the mechanisms responsible for migraine initiation remain unknown, recent evidence shows that brain function is different immediately preceding a migraine. This is consistent with the idea that altered brain function, particularly in brainstem sites, may either trigger a migraine or facilitate a peripheral trigger that activates the brain, resulting in pain. The aim of this longitudinal study is therefore to expand on the above findings, and to determine if brainstem function oscillates over a migraine cycle in individual subjects. We performed resting state functional magnetic resonance imaging in three migraineurs and five controls each weekday for four weeks. We found that although resting activity variability was similar in controls and interictal migraineurs, brainstem variability increased dramatically during the 24-hour period preceding a migraine. This increase occurred in brainstem areas in which orofacial afferents terminate: the spinal trigeminal nucleus and dorsal pons. These increases were characterized by increased power at infra-slow frequencies, principally between 0.03 and 0.06 Hz. Furthermore, these power increases were associated with increased regional homogeneity, a measure of local signal coherence. The results show within-individual alterations in brain activity immediately preceding migraine onset and support the hypothesis that altered regional brainstem function before a migraine attack is involved in underlying migraine neurobiology.

Persistent Brainstem Dysfunction in Long-COVID: A Hypothesis

Long-COVID is a postviral illness that can affect survivors of COVID-19, regardless of initial disease severity or age. Symptoms of long-COVID include fatigue, dyspnea, gastrointestinal and cardiac problems, cognitive impairments, myalgia, and others. While the possible causes of long-COVID include long-term tissue damage, viral persistence, and chronic inflammation, the review proposes, perhaps for the first time, that persistent brainstem dysfunction may also be involved. This hypothesis can be split into two parts. The first is the brainstem tropism and damage in COVID-19. As the brainstem has a relatively high expression of ACE2 receptor compared with other brain regions, SARS-CoV-2 may exhibit tropism therein. Evidence also exists that neuropilin-1, a co-receptor of SARS-CoV-2, may be expressed in the brainstem. Indeed, autopsy studies have found SARS-CoV-2 RNA and proteins in the brainstem. The brainstem is also highly prone to damage from pathological immune or vascular activation, which has also been observed in autopsy of COVID-19 cases. The second part concerns functions of the brainstem that overlap with symptoms of long-COVID. The brainstem contains numerous distinct nuclei and subparts that regulate the respiratory, cardiovascular, gastrointestinal, and neurological processes, which can be linked to long-COVID. As neurons do not readily regenerate, brainstem dysfunction may be long-lasting and, thus, is long-COVID. Indeed, brainstem dysfunction has been implicated in other similar disorders, such as chronic pain and migraine and myalgic encephalomyelitis or chronic fatigue syndrome.

A potential role for two brainstem nuclei in craniovascular nociception and the triggering of migraine headache

AIM

To use an animal model of migraine to test whether migraine headache might arise from a brainstem-trigeminal nucleus pathway.

METHODS

We measured evoked and spontaneous activity of second-order trigeminovascular neurons in rats to test whether the activity of these neurons increased following the induction of cortical spreading depression or the imposition of light flash - two potential migraine triggers, or headache provokers. We then tested whether drugs that could activate, or inactivate, neurons of the nucleus raphe magnus or the periaqueductal gray matter, would affect any such increases selectively for the dura mater.

RESULTS

Injection of sodium glutamate (a neuronal excitant) into these two nuclei selectively inhibited the responses of trigeminovascular second-order neurons to dura mater, but not to facial skin, stimulation. Injection of lignocaine (a local anaesthetic) into these nuclei selectively potentiated the responses of these neurons to dura, but not to facial skin, stimulation. Furthermore, injections into either nucleus of glutamate inhibited the increase in the ongoing discharge rate of these neurons produced by cortical spreading depression and light flash.

CONCLUSIONS

These results provide indirect evidence that trigeminovascular nociception may be tightly controlled by these two nuclei, whereas cutaneous trigeminal sensation may be less so. These nuclei may be relays of one possible brainstem-trigeminal pathway that could mediate migraine headache. Modification of neuronal activity in these two nuclei produced by migraine (headache) triggers may lie behind the pain of a migraine attack, at least in some cases.

Microstructural changes in the trigeminal nerve of patients with episodic migraine assessed using magnetic resonance imaging

BACKGROUND

There is histological evidence of microstructural changes in the zygomaticotemporal branch of the trigeminal nerve in migraineurs. This raises the possibility that altered trigeminal nerve properties contribute to migraine pathophysiology. Whilst it is not possible to explore the anatomy of small trigeminal nerve branches it is possible to explore the anatomy of the trigeminal root entry zone using magnetic resonance imaging in humans. The aim of this investigation is to assess the microstructure of the trigeminal nerve in vivo to determine if nerve alterations occur in individuals with episodic migraine.

METHODS

In 39 migraineurs and 39 matched controls, T1-weighted anatomical images were used to calculate the volume (mm³) and maximal cross-sectional area of the trigeminal nerve root entry zone; diffusion tensor images were used to calculate fractional anisotropy, mean diffusion, axial diffusion and radial diffusion.

RESULTS

There were significant differences between the left and right nerve of controls and migraineurs with respect to volume and not cross-sectional area. Migraineurs displayed reduced axial diffusion in the right nerve compared to the left nerve, and reduced fractional anisotropy in the left nerve compared to left controls. Furthermore, although there were no differences in mean diffusion or radial diffusion, regional analysis of the nerve revealed significantly greater radial diffusion in the middle and rostral portion of the left trigeminal nerve in migraineurs compared with controls.

CONCLUSIONS

Migraine pathophysiology is associated with microstructural abnormalities within the trigeminal nerve that are consistent with histological evidence of altered myelin and/or organization. These peripheral nerve changes may provide further insight into migraine pathophysiology and enable a greater understanding for targeted treatments of pain alleviation.

An Update: Pathophysiology of Migraine

Migraine is the most common disabling primary headache globally. Attacks typically present with unilateral throbbing headache and associated symptoms including, nausea, multisensory hypersensitivity, and marked fatigue. In this article, the authors address the underlying neuroanatomical basis for migraine-related headache, associated symptomatology, and discuss key clinical and preclinical findings that indicate that migraine likely results from dysfunctional homeostatic mechanisms. Whereby, abnormal central nervous system responses to extrinsic and intrinsic cues may lead to increased attack susceptibility.

Ethenzamide Exerts Analgesic Effect at the Spinal Cord via Multiple Mechanisms of Action Including the 5HT2B Receptor Blockade in the Rat Formalin Test

Ethenzamide (ETZ), an antipyretic analgesic categorized as a non-steroidal anti-inflammatory drug (NSAID), is widely used as an OTC drug in combination with other NSAIDs. However, its site of action and mechanism underlying its analgesic action have not yet been fully elucidated. In this study, we performed in vitro pharmacological assays to identify the mechanism underlying the analgesic action of ETZ, and also conducted the rat formalin test to investigate its analgesic effect and site of action. Of the 85 receptors, ion channels, transporters and enzymes tested, we found that ETZ binds to the 5-hydroxytryptamine (5HT)_2B receptor in concentration-dependent manner with modest inhibitory effects on monoamine oxidase-A and transient potential vanilloid 1 channel. The 5HT_2B receptor antagonist activity of ETZ was also confirmed in a cellular functional assay. Furthermore, the drug exerted no inhibitory effects on cycrooxygenase-1 and -2. In the rat formalin test, oral administration of ETZ significantly reduced the nociceptive responses of the second phase and also the number of c-Fos-expressing cells in the spinal dorsal horn, in a dose-dependent manner. Moreover, intrathecal administration of ETZ significantly reduced the nociceptive responses. These results suggest that the analgesic effect of ETZ is exerted at least in the spinal cord, and the effect would be attributed to multiple mechanisms of action including 5HT_2B receptor blockade.

Tracking the Migraine Cycle Using Visual Tasks

There are a number of reports that perceptual, electrophysiological and imaging measures can track migraine periodicity. As the electrophysiological and imaging research requires specialist equipment, it has few practical applications. This study sought to track changes in performance on four visual tasks over the migraine cycle. Coherence thresholds were measured for two motion and two orientation tasks. The first part of the study confirmed that the data obtained from an online study produced comparable results to those obtained under controlled laboratory conditions. Thirteen migraine with aura, 12 without aura, and 12 healthy controls participated. The second part of the study showed that thresholds for discriminating vertical coherent motion varied with the migraine cycle for a majority of the participants who tested themselves multiple times (four with aura, seven without). Performance improved two days prior to a migraine attack and remained improved for two days afterwards. This outcome is as expected from an extrapolation of earlier electrophysiological research. This research points to the possibility of developing sensitive visual tests that patients can use at home to predict an impending migraine attack and so take steps to try to abort it or, if it is inevitable, to plan their lives around it.

No central action of CGRP antagonising drugs in the GTN mouse model of migraine

Introduction

Clinically, calcitonin gene-related peptide antagonising drugs are recognized as effective in migraine treatment, but their site of action is debated. Only a small fraction of these compounds pass the blood-brain barrier and accesses the central nervous system. Regardless, it has been argued that the central nervous system is the site of action. Here, we test this hypothesis by bypassing the blood-brain barrier through intracerebroventricular injection of calcitonin gene-related peptide antagonising drugs.

Methods

We used the glyceryl trinitrate (GTN) mouse model, which is well validated by its response to specific migraine drugs. The calcitonin gene-related peptide receptor antagonist olcegepant and the calcitonin gene-related peptide monoclonal antibody ALD405 were administered either intraperitoneally or intracerebroventricularly. The outcome measure was cutaneous mechanical allodynia.

Results

Mice given olcegepant intraperitoneally + GTN on day 1 had a mean 50% withdrawal threshold of 1.2 g in contrast to mice receiving placebo + GTN, which had a threshold of 0.3 g ( p < 0.001). Similarly, in the ALD405 + GTN group, mice had thresholds of 1.2 g versus 0.2 g in the placebo + GTN group ( p < 0.001). However, both drugs were ineffective when delivered intracerebroventricularly, as control and active groups had identical mechanical sensitivity thresholds, 0.2 g versus 0.1 g and 0.1 g versus 0.1 g for olcegepant and ALD405, respectively ( p > 0.99 in both cases).

Discussion

The site of action of olcegepant and of the monoclonal antibody ALD405 is outside the blood-brain barrier in this mouse model of migraine. It is likely that these results can be generalised to all gepants and all antibodies and that the results are relevant for human migraine.

Imaging the Premonitory Phase of Migraine

Migraine is a common and disabling brain disorder with a broad and heterogeneous phenotype, involving both pain and painless symptoms. Over recent years, more clinical and research attention has been focused toward the premonitory phase of the migraine attack, which can start up to days before the onset of head pain. This early phase can involve symptomatology, such as cognitive and mood change, yawning, thirst and urinary frequency and sensory sensitivities, such as photophobia and phonophobia. In some patients, these symptoms can warn of an impending headache and therefore offer novel neurobiological insights and therapeutic potential. As well as characterization of the phenotype of this phase, recent studies have attempted to image this early phase using functional neuroimaging and tried to understand how the symptoms are mediated, how a migraine attack may be initiated, and how nociception may follow thereafter. This review will summarize the recent and evolving findings in this field and hypothesize a mechanism of subcortical and diencephalic brain activation during the start of the attack, including that of basal ganglia, hypothalamus, and thalamus prior to headache, which causes a top-down effect on brainstem structures involved in trigeminovascular nociception, leading ultimately to headache.

Altered regional cerebral blood flow and hypothalamic connectivity immediately prior to a migraine headache

BACKGROUND

There is evidence of altered resting hypothalamic activity patterns and connectivity prior to a migraine, however it remains unknown if these changes are driven by changes in overall hypothalamic activity levels. If they are, it would corroborate the idea that changes in hypothalamic function result in alteration in brainstem pain processing sensitivity, which either triggers a migraine headache itself or allows an external trigger to initiate a migraine headache. We hypothesise that hypothalamic activity increases immediately prior to a migraine headache and this is accompanied by altered functional connectivity to pain processing sites in the brainstem.

METHODS

In 34 migraineurs and 26 healthy controls, we collected a series comprising 108 pseudo-continuous arterial spin labelling images and 180 gradient-echo echo planar resting-state functional magnetic resonance volumes to measure resting regional cerebral blood flow and functional connectivity respectively. Images were pre-processed and analysed using custom SPM12 and Matlab software.

RESULTS

Our results reflect that immediately prior to a migraine headache, resting regional cerebral blood flow decreases in the lateral hypothalamus. In addition, resting functional connectivity strength decreased between the lateral hypothalamus and important regions of the pain processing pathway, such as the midbrain periaqueductal gray, dorsal pons, rostral ventromedial medulla and cingulate cortex, only during this critical period before a migraine headache.

CONCLUSION

These data suggest altered hypothalamic function and connectivity in the period immediately prior to a migraine headache and supports the hypothesis that the hypothalamus is involved in migraine initiation.

Composite Pain Biomarker Signatures for Objective Assessment and Effective Treatment

Pain is a subjective sensory experience that can, mostly, be reported but cannot be directly measured or quantified. Nevertheless, a suite of biomarkers related to mechanisms, neural activity, and susceptibility offer the possibility-especially when used in combination-to produce objective pain-related indicators with the specificity and sensitivity required for diagnosis and for evaluation of risk of developing pain and of analgesic efficacy. Such composite biomarkers will also provide improved understanding of pain pathophysiology.