PACAP and migraine headache: immunomodulation of neural circuits in autonomic ganglia and brain parenchyma

Hallmarks of primary headache: part 1 - migraine

BACKGROUND AND AIM

Migraine is a common disabling conditions which, globally, affects 15.2% of the population. It is the second cause of health loss in terms of years lived with disability, the first among women. Despite being so common, it is poorly recognised and too often undertreated. Specialty centres and neurologists with specific expertise on headache disorders have the knowledge to provide specific care: however, those who do not regularly treat patients with migraine will benefit from a synopsis on the most relevant and updated information about this condition. This paper presents a comprehensive view on the hallmarks of migraine, from genetics and diagnostic markers, up to treatments and societal impact, and reports the elements that identify migraine specific features.

MAIN RESULTS

The most relevant hallmark of migraine is that it has common and individual features together. Besides the known clinical manifestations, migraine presentation is heterogeneous with regard to frequency of attacks, presence of aura, response to therapy, associated comorbidities or other symptoms, which likely reflect migraine heterogeneous genetic and molecular basis. The amount of therapies for acute and for prophylactic treatment is really wide, and one of the difficulties is with finding the best treatment for the single patient. In addition to this, patients carry out different daily life activities, and might show lifestyle habits which are not entirely adequate to manage migraine day by day. Education will be more and more important as a strategy of brain health promotion, because this will enable reducing the amount of subjects needing specialty care, thus leaving it to those who require it in reason of refractory condition or presence of comorbidities.

CONCLUSIONS

Recognizing the hallmarks of migraine and the features of single patients enables prescribing specific pharmacological and non-pharmacological treatments. Medical research on headaches today particularly suffers from the syndrome of single-disease approach, but it is important to have a cross-sectional and joint vision with other close specialties, in order to treat our patients with a comprehensive approach that a heterogeneous condition like migraine requires.

Exploring the Role of Pituitary Adenylate Cyclase-Activating Polypeptide (PACAP) and Kynurenine Pathway Dysregulation in Migraine Pathophysiology Among Women With Polycystic Ovary Syndrome (PCOS)

A narrative review was undertaken to explore the current understanding of the relationship between polycystic ovary syndrome and migraine headaches, with a focus on the potential roles of pituitary adenylate cyclase-activating polypeptide and the kynurenine pathway in the shared pathophysiology of these conditions. Emerging evidence suggests that pituitary adenylate cyclase-activating polypeptide may be a key player in the development of migraine headaches, with potential implications for the higher incidence of migraine observed in women with polycystic ovary syndrome. Additionally, dysregulation of the kynurenine pathway and altered levels of kynurenine metabolites have been linked to both migraine and polycystic ovary syndrome, indicating a complex interplay between hormonal, metabolic, and neurological factors in the comorbid presentation of these disorders. Further research is needed to elucidate the specific mechanisms underlying these associations and to develop targeted therapeutic approaches for managing migraine in the context of polycystic ovary syndrome.

Pharmacological investigation of genistein for its therapeutic potential against nitroglycerin-induced migraine headache

OBJECTIVES

Migraine, typically occurs on one side of the head, lasts for hours to days. Trigemino-vascular system (TVS) plays a vital role in pain generation, with neurogenic inflammation and oxidative stress playing key roles in its pathophysiology.

METHODS

This study aimed to investigate genistein's potential as anti-inflammatory and anti-oxidant agent in mitigating migraine pain. Genistein (20 and 50 mg/kg) was administered intraperitoneally (IP) to nitroglycerin (NTG; 10 mg/kg)-induced migraine model in rats. Behavioral analysis, antioxidant assay, immunohistochemistry (IHC), histopathological examination, ELISA, and RT-PCR were conducted to evaluate the antimigraine potential of genistein.

KEY FINDINGS

In-silico analysis showed genestien's ACE values of -4.8 to -9.2 Kcal/mol against selected protein targets. Genistein significantly reversed mechanical and thermal nociception, light phobicity, and head scratching; increased the intensities of GST, GSH, catalase; and down regulated lipid peroxidase (LPO) in cortex and trigeminal nucleus caudalis (TNC). It also reduced Nrf2, NF-kB, and IL6 expression, analyzed through IHC, improved histopathological features, and increased COX-2 and decreased PPAR-γ expressions, while RT-PCR analysis revealed increased PPAR-γ expressions in genistein-treated rats.

CONCLUSION

Genistein exhibited potent antioxidant and anti-inflammatory properties in migraine treatment, acting through multifactorial mechanisms by modulating the expression of numerous proteins in the region cortex and TNC.

The Brain, the Eating Plate, and the Gut Microbiome: Partners in Migraine Pathogenesis

This review summarizes the relationship between diet, the gut microbiome, and migraine. Key findings reveal that certain dietary factors, such as caffeine and alcohol, can trigger migraine, while nutrients like magnesium and riboflavin may help alleviate migraine symptoms. The gut microbiome, through its influence on neuroinflammation (e.g., vagus nerve and cytokines), gut-brain signaling (e.g., gamma-aminobutyric acid), and metabolic function (e.g., short-chain fatty acids), plays a crucial role in migraine susceptibility. Migraine can also alter eating behaviors, leading to poor nutritional choices and further exacerbating the condition. Individual variability in diet and microbiome composition highlights the need for personalized dietary and prebiotic interventions. Epidemiological and clinical data support the effectiveness of tailored nutritional approaches, such as elimination diets and the inclusion of beneficial nutrients, in managing migraine. More work is needed to confirm the role of prebiotics, probiotics, and potentially fecal microbiome translation in the management of migraine. Future research should focus on large-scale studies to elucidate the underlying mechanisms of bidirectional interaction between diet and migraine and develop evidence-based clinical guidelines. Integrating dietary management, gut health optimization, and lifestyle modifications can potentially offer a holistic approach to reducing migraine frequency and severity, ultimately improving patient outcomes and quality of life.

Targeting the PACAP-38 pathway is an emerging therapeutic strategy for migraine prevention

INTRODUCTION

The pituitary adenylate cyclase-activating polypeptide-38 (PACAP-38) has emerged as a key mediator of migraine pathogenesis. PACAP-38 and its receptors are predominantly distributed in arteries, sensory and parasympathetic neurons of the trigeminovascular system. Phase 2 trials have tested human monoclonal antibodies designed to bind and inhibit PACAP-38 and the pituitary adenylate cyclase-activating polypeptide type I (PAC1) receptor for migraine prevention.

AREAS COVERED

This review focuses on the significance of the PACAP-38 pathway as a target in migraine prevention. English peer-reviewed articles were searched in PubMed, Scopus and ClinicalTrials.gov electronic databases.

EXPERT OPINION

A PAC1 receptor monoclonal antibody was not effective for preventing migraine in a proof-of-concept trial, paving the way for alternative strategies to be considered. Lu AG09222 is a humanized monoclonal antibody targeting PACAP-38 that was effective in preventing physiological responses of PACAP38 and reducing monthly migraine days in individuals with migraine. Further studies are necessary to elucidate the clinical utility, long-term safety and cost-effectiveness of therapies targeting the PACAP pathway.

From CGRP to PACAP, VIP, and Beyond: Unraveling the Next Chapters in Migraine Treatment

Migraine is a neurovascular disorder that can be debilitating for individuals and society. Current research focuses on finding effective analgesics and management strategies for migraines by targeting specific receptors and neuropeptides. Nonetheless, newly approved calcitonin gene-related peptide (CGRP) monoclonal antibodies (mAbs) have a 50% responder rate ranging from 27 to 71.0%, whereas CGRP receptor inhibitors have a 50% responder rate ranging from 56 to 71%. To address the need for novel therapeutic targets, researchers are exploring the potential of another secretin family peptide, pituitary adenylate cyclase-activating polypeptide (PACAP), as a ground-breaking treatment avenue for migraine. Preclinical models have revealed how PACAP affects the trigeminal system, which is implicated in headache disorders. Clinical studies have demonstrated the significance of PACAP in migraine pathophysiology; however, a few clinical trials remain inconclusive: the pituitary adenylate cyclase-activating peptide 1 receptor mAb, AMG 301 showed no benefit for migraine prevention, while the PACAP ligand mAb, Lu AG09222 significantly reduced the number of monthly migraine days over placebo in a phase 2 clinical trial. Meanwhile, another secretin family peptide vasoactive intestinal peptide (VIP) is gaining interest as a potential new target. In light of recent advances in PACAP research, we emphasize the potential of PACAP as a promising target for migraine treatment, highlighting the significance of exploring PACAP as a member of the antimigraine armamentarium, especially for patients who do not respond to or contraindicated to anti-CGRP therapies. By updating our knowledge of PACAP and its unique contribution to migraine pathophysiology, we can pave the way for reinforcing PACAP and other secretin peptides, including VIP, as a novel treatment option for migraines.

Multimodal Migraine Management and the Pursuit of Migraine Freedom: A Narrative Review

Migraine is a neurologic disease with a complex pathophysiology that can be controlled with current treatment options but not cured. Therefore, treatment expectations are highly variable. The concept of migraine freedom was recently introduced and can mean different things, with some, for example, expecting complete freedom from headache and associated symptoms and others accepting the occasional migraine attack if it does not impact functioning. Therefore, migraine management should be optimized so that patients can have the best opportunity to achieve their optimal treatment goals. With migraine freedom as a goal and, given the complex pathophysiology of migraine and the high incidence of comorbidities among individuals with migraine, treatment with a single modality may be insufficient, as it may not achieve migraine freedom in those with more frequent or disabling attacks. In this clinical perspective article, we have identified four key, partially overlapping principles of multimodal migraine treatment: (1) manage common comorbidities; (2) control modifiable risk factors for progression by addressing medication and caffeine overuse; (3) diagnose and treat secondary causes of headache, if present; and (4) individualize acute and preventive treatments to minimize pain, functional disability, and allodynia. There are many barriers to pursuing migraine freedom, and strategies to overcome them should be optimized. Migraine freedom should be an aspirational goal both at the individual attack level and for the disease overall. We believe that a comprehensive and multimodal approach that addresses all barriers people with migraine face could move patients closer to migraine freedom.

Central generators of migraine and autonomic cephalalgias as targets for personalized pain management: Translational links

BACKGROUND AND OBJECTIVE

Migraine oscillates between different states in association with internal homeostatic functions and biological rhythms that become more easily dysregulated in genetically susceptible individuals. Clinical and pre-clinical data on migraine pathophysiology support a primary role of the central nervous system (CNS) through 'dysexcitability' of certain brain networks, and a critical contribution of the peripheral sensory and autonomic signalling from the intracranial meningeal innervation. This review focuses on the most relevant back and forward translational studies devoted to the assessment of CNS dysfunctions involved in primary headaches and discusses the role they play in rendering the brain susceptible to headache states.

METHODS AND RESULTS

We collected a body of scientific literature from human and animal investigations that provide a compelling perspective on the anatomical and functional underpinnings of the CNS in migraine and trigeminal autonomic cephalalgias. We focus on medullary, hypothalamic and corticofugal modulation mechanisms that represent strategic neural substrates for elucidating the links between trigeminovascular maladaptive states, migraine triggering and the temporal phenotype of the disease.

CONCLUSION

It is argued that a better understanding of homeostatic dysfunctional states appears fundamental and may benefit the development of personalized therapeutic approaches for improving clinical outcomes in primary headache disorders.

SIGNIFICANCE

This review focuses on the most relevant back and forward translational studies showing the crucial role of top-down brain modulation in triggering and maintaining primary headache states and how these central dysfunctions may interact with personalized pain management strategies.

Mitochondrial metabolism related markers GDF-15, FGF-21, and HIF-1α are elevated in pediatric migraine attacks

OBJECTIVE

The purpose of this study was to investigate the serum levels of mitochondrial metabolism/reactive oxygen species (ROS)-related peptides (hypoxia inducible factor-1α [HIF-1α], fibroblast growth factor-21 [FGF-21], growth differentiation factor-15 [GDF-15]) and key migraine-related neuropeptides (calcitonin gene-related peptide [CGRP], pituitary adenylate cyclase-activating peptide-38 [PACAP-38], substance P [SP], and vasoactive intestinal peptide [VIP]) during migraine attacks and to evaluate their diagnostic value in pediatric migraine.

BACKGROUND

There is increasing evidence for the important role of impairment in oxidative mitochondrial metabolism in the pathophysiology of migraine. Potential biomarkers that may reflect the relationship between migraine and mitochondrial dysfunction are unclear.

METHODS

A total of 68 female pediatric migraine patients without aura and 20 female healthy controls aged 8-18 years, admitted to the hospital, were enrolled in this cross-sectional study. Serum concentrations of these molecules were determined by enzyme-linked immunosorbent assays, and clinical features and their possible diagnostic value were analyzed.

RESULTS

Serum levels of HIF-1α (252.4 ± 51.9 [mean ± standard deviation]) pg/mL), GDF-15 (233.7 ± 24.7 pg/mL), FGF-21 (96.1 ± 13.1 pg/mL), CGRP (44.5 ± 11.3), and PACAP-38 (504.7 ± 128.9) were significantly higher in migraine patients compared to healthy controls (199.8 ± 26.8, 192.8 ± 20.7, 79.3 ± 4.1, 34.1 ± 3.5 and 361.2 ± 86.3 pg/mL, respectively). The serum levels of these peptides were also higher in patients with chronic migraine than in patients with episodic migraine, and higher in the ictal period than in the interictal period. A positive correlation was found between attack frequency and both HIF-1α and FGF-21 levels in migraine patients. Serum levels of VIP and SP were not different between the migraine patients and healthy controls.

CONCLUSION

Migraine attacks are accompanied by elevated HIF-1α, FGF-21, GDF-15, CGRP, and PACAP-38 in medication-naive pediatric patients with migraine. Elevated circulating mitochondrial metabolism/ROS-related peptides suggest a mitochondrial stress in pediatric migraine attacks and may have potential diagnostic value in monitoring disease progression and treatment response in children. Novel approaches intervening with mitochondrial metabolism need to be investigated.

Molecular and Cellular Neurobiology of Circadian and Circannual Rhythms in Migraine: A Narrative Review

Migraine-a primary headache-has circadian and circannual rhythms in the onset of attacks. The circadian and circannual rhythms involve the hypothalamus, which is strongly associated with pain processing in migraines. Moreover, the role of melatonin in circadian rhythms has been implied in the pathophysiology of migraines. However, the prophylactic effect of melatonin in migraines is controversial. Calcitonin gene-related peptide (CGRP) has recently attracted attention in the pathophysiology and treatment of migraines. Pituitary adenylate cyclase-activating peptide (PACAP)-a neuropeptide identical to CGRP-is a potential therapeutic target after CGRP. PACAP is involved in the regulation of circadian entrainment to light. This review provides an overview of circadian and circannual rhythms in the hypothalamus and describes the relationship between migraines and the molecular and cellular neurobiology of circadian and circannual rhythms. Furthermore, the potential clinical applications of PACAP are presented.

Glia Signaling and Brain Microenvironment in Migraine

Migraine is a complicated neurological disorder affecting 6% of men and 18% of women worldwide. Various mechanisms, including neuroinflammation, oxidative stress, altered mitochondrial function, neurotransmitter disturbances, cortical hyperexcitability, genetic factors, and endocrine system problems, are responsible for migraine. However, these mechanisms have not completely delineated the pathophysiology behind migraine, and they should be further studied. The brain microenvironment comprises neurons, glial cells, and vascular structures with complex interactions. Disruption of the brain microenvironment is the main culprit behind various neurological disorders. Neuron-glia crosstalk contributes to hyperalgesia in migraine. In the brain, microenvironment and related peripheral regulatory circuits, microglia, astrocytes, and satellite cells are necessary for proper function. These are the most important cells that could induce migraine headaches by disturbing the balance of the neurotransmitters in the nervous system. Neuroinflammation and oxidative stress are the prominent reactions glial cells drive during migraine. Understanding the role of cellular and molecular components of the brain microenvironment on the major neurotransmitters engaged in migraine pathophysiology facilitates the development of new therapeutic approaches with higher effectiveness for migraine headaches. Investigating the role of the brain microenvironment and neuroinflammation in migraine may help decipher its pathophysiology and provide an opportunity to develop novel therapeutic approaches for its management. This review aims to discuss the neuron-glia interactions in the brain microenvironment during migraine and their potential role as a therapeutic target for the treatment of migraine.

The putative role of neuroinflammation in the complex pathophysiology of migraine: From bench to bedside

The implications of neurogenic inflammation and neuroinflammation in the pathophysiology of migraine have been clearly demonstrated in preclinical migraine models involving several sites relevant in the trigemino-vascular system, including dural vessels and trigeminal endings, the trigeminal ganglion, the trigeminal nucleus caudalis as well as central trigeminal pain processing structures. In this context, a relevant role has been attributed over the years to some sensory and parasympathetic neuropeptides, in particular calcitonin gene neuropeptide, vasoactive intestinal peptide and pituitary adenylate cyclase-activating polypeptide. Several preclinical and clinical lines of evidence also support the implication of the potent vasodilator and messenger molecule nitric oxide in migraine pathophysiology. All these molecules are involved in vasodilation of the intracranial vasculature, as well as in the peripheral and central sensitization of the trigeminal system. At meningeal level, the engagement of some immune cells of innate immunity, including mast-cells and dendritic cells, and their mediators, has been observed in preclinical migraine models of neurogenic inflammation in response to sensory neuropeptides release due to trigemino-vascular system activation. In the context of neuroinflammatory events implicated in migraine pathogenesis, also activated glial cells in the peripheral and central structures processing trigeminal nociceptive signals seem to play a relevant role. Finally, cortical spreading depression, the pathophysiological substrate of migraine aura, has been reported to be associated with inflammatory mechanisms such as pro-inflammatory cytokine upregulation and intracellular signalling. Reactive astrocytosis consequent to cortical spreading depression is linked to an upregulation of these inflammatory markers. The present review summarizes current findings on the roles of immune cells and inflammatory responses in the pathophysiology of migraine and their possible exploitation in the view of innovative disease-modifying strategies.

Clinical evaluation of super-responders vs. non-responders to CGRP(-receptor) monoclonal antibodies: a real-world experience

BACKGROUND

Clinical trials and real-world studies revealed a spectrum of response to CGRP(-receptor) monoclonal antibodies (mAbs) in migraine prophylaxis, ranging from no effect at all to total migraine freedom. In this study, we aimed to compare clinical characteristics between super-responders (SR) and non-responders (NR) to CGRP(-receptor) mAbs.

METHODS

We performed a retrospective cohort study at the Headache Center, Charité - Universitätsmedizin Berlin. The definition of super-response was a ≥ 75% reduction in monthly headache days (MHD) in the third month after treatment initiation compared to the month prior to treatment begin (baseline). Non-response was defined as ≤ 25% reduction in MHD after three months of treatment with a CGRP-receptor mAb and subsequent three months of treatment with CGRP mAb, or vice versa. We collected demographic data, migraine disease characteristics, migraine symptoms during the attacks in both study groups (SR/NR) as well as the general medical history. SR and NR were compared using Chi-square test for categorical variables, and t-test for continuous variables.

RESULTS

Between November 2018 and June 2022, n = 260 patients with migraine received preventive treatment with CGRP(-receptor) mAbs and provided complete headache documentation for the baseline phase and the third treatment month. Among those, we identified n = 29 SR (11%) and n = 26 NR (10%). SR reported more often especially vomiting (SR n = 12/25, 48% vs. NR n = 4/22, 18%; p = 0.031) and typical migraine characteristics such as unilateral localization, pulsating character, photophobia and nausea. A subjective good response to triptans was significantly higher in SR (n = 26/29, 90%) than in NR (n = 15/25, 60%, p = 0.010). NR suffered more frequently from chronic migraine (NR n = 24/26, 92% vs. SR n = 15/29, 52%; p = 0.001), medication overuse headache (NR n = 14/24, 58% versus SR n = 8/29, 28%; p = 0.024), and concomitant depression (NR n = 17/26, 65% vs. SR n = 8/29, 28%; p = 0.005).

CONCLUSION

Several clinical parameters differ between SR and NR to prophylactic CGRP(-R) mAbs. A thorough clinical evaluation prior to treatment initiation might help to achieve a more personalized management in patients with migraine.

Exploration of phytochemicals and probing potential effects of Priva cordifolia active extract on PACAP 38 and its nociceptor in the human trigeminovascular system

Several tribal medicinal systems assert anti-migraine and common headache-remedying properties in all parts of Priva cordifolia (L.f.) Druce. Therefore, there are no clear scientific references to the validated traditional use of this plant. The present study provides a scientific basis for the ethnobotanical utility of P. cordifolia whose whole-plant extracts were evaluated against target proteins (PACAP 38 and PAC1-R) that cause migraine. Understanding the polarity-based distribution and oxidative stress scavenging ability was reported higher in ethyl acetate extracts due to the moderate distribution of secondary metabolites. Based on the preliminary analysis anti-migraine activity in the wet and dry lab experiments was compared with a commercial drug Sumatriptan. The GC-MS analysis revealed that two lead volatile compounds Bicyclo(3.2.1)oct-3-en-2-one,3,8-Dihydroxy-1-methoxy-7-(7-methoxy-1,3- and -Hexyl-2-nitrocyclohexane, present in the ethyl acetate extract showed favourable in silico anti-migraine efficiency. Notably, the ex-vivo results also showed considerable downregulation of the extract-induced mRNA expression of PACAP38. The conclusion of our study justifies that P. cordifolia has valuable plant metabolites that portray it as an efficient anti-oxidant and anti-migraine source.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-023-03462-w.

Pharmacological evaluation of carvacrol anti-migraine potential

Migraine is a devitalizing neurovascular disorder that affects millions of people worldwide. This study was directed against the determination of the effectiveness of carvacrol against migraine. In silico results revealed that carvacrol possesses specific scoring values of - 4.4 to - 6 against selected targets. In vivo studies showed that carvacrol (25-50 mg/Kg) decreased migraine pain by reversing thermal allodynia, mechanical allodynia, number of head-scratching, and light phobicity in rats. Levels of glutathione, glutathione-s-transferase, and catalase enhanced in the cortex and trigeminal nucleus caudalis of the animal's brain tissues, i.e., cortex and trigeminal nucleus caudalis with the use of carvacrol, while a significant decrease in lipid peroxide level was seen. Histopathological evaluation showed improvement in cellular architecture and a decrease in expression of certain inflammatory markers such as tumor necrosis factor-alpha, nuclear factor kappa B, interleukin-18, and prostaglandin E2 validated by enzyme-linked immune sorbent assay, immunohistochemistry, and western blot analysis. This study indicates that carvacrol exhibits binding affinities against different targets involved in migraine pathology and possesses anti-migraine action, mediated through anti-inflammatory and anti-oxidant pathways.

PACAP-PAC1 receptor inhibition is effective in opioid induced hyperalgesia and medication overuse headache models

Opioids prescribed for pain and migraine can produce opioid-induced hyperalgesia (OIH) or medication overuse headache (MOH). We previously demonstrated that pituitary adenylate cyclase activating polypeptide (PACAP) is upregulated in OIH and chronic migraine models. Here we determined if PACAP acts as a bridge between opioids and pain chronification. We tested PACAP-PAC1 receptor inhibition in novel models of opioid-exacerbated trigeminovascular pain. The PAC1 antagonist, M65, reversed chronic allodynia in a model which combines morphine with the migraine trigger, nitroglycerin. Chronic opioids also exacerbated cortical spreading depression, a correlate of migraine aura; and M65 inhibited this augmentation. In situ hybridization showed MOR and PACAP co-expression in trigeminal ganglia, and near complete overlap between MOR and PAC1 in the trigeminal nucleus caudalis and periaqueductal gray. PACAPergic mechanisms appear to facilitate the transition to chronic headache following opioid use, and strategies targeting this system may be particularly beneficial for OIH and MOH.

Role of PACAP in migraine: An alternative to CGRP?

Migraine is a widespread and debilitating neurological condition affecting more than a billion people worldwide. Thus, more effective migraine therapies are highly needed. In the last decade, two endogenous neuropeptides, calcitonin gene-related peptide (CGRP) and pituitary adenylate cyclase-activating peptide (PACAP), were identified to be implicated in migraine. Recently, introduction of monoclonal antibodies (mAbs) blocking the CGRP is the most important advance in migraine therapy for decades. However, 40% of patients are unresponsive to these new drugs. We believe that PACAP may be involved in these patients. Like CGRP, PACAP is located to sensory nerve fibers, it dilates cranial arteries, it causes migraine when infused into patients and it is a peptide that lends itself to antibody therapy. Also, recent studies suggest that the PACAP pathway is independent of the CGRP pathway. Understanding the signaling pathways of PACAP may therefore lead to identification of novel therapeutic targets of particular interest in patients unresponsive to anti-CGRP therapy. Accordingly, neutralizing mAb to PACAP is currently in clinical phase II development. The aim of the present review is, therefore, to give a thorough account of the existing data on PACAP, its receptors and its relation to migraine.

Hypoxia-related mechanisms inducing acute mountain sickness and migraine

Experimental models of human diseases are vital for pathophysiological and therapeutic research. To investigate the initiation, maintenance, pathophysiology and even termination of a migraine/headache attack these models are urgently needed. Results from different studies promote the profound involvement of hypoxia in migraine and other primary/secondary headaches. The possible mechanisms that drive the induction of headaches through hypoxia are still unknown, but several modes of action, such as increased blood flow, dilation of cerebral arteries, the release of nitroglycerin, calcitonin gene-related peptide and adenosine or increased oxygen extraction are discussed intensively. In studies exposing healthy volunteers and people with a history of migraine to controlled normobaric hypoxia, our research group could demonstrate normobaric hypoxia to be an effective trigger of migraine headaches. Furthermore, a longitudinal measurement of calcitonin gene-related peptide (CGRP), during a hypoxic challenge in migraine patients, revealed increasing CGRP levels with prolonged hypoxic challenge. Since GRP has been linked to migraine and other headache disorders, hypoxia could be regarded as initiator for headaches on a neurotransmitter basis. Furthermore, it has been known for more than 2 decades from studies in vitro and in vivo that hypoxia can induce cortical spreading depression, a phenomenon believed to represent aura. Considering the increased prevalence of migraine in altitude populations and the solid pathophysiological changes on cellular and neurotransmitter level–the role of hypoxia should be investigated in greater detail by the headache community.

Anatomy and Physiology of Headache

Headache disorders can produce recurrent, incapacitating pain. Migraine and cluster headache are notable for their ability to produce significant disability. The anatomy and physiology of headache disorders is fundamental to evolving treatment approaches and research priorities. Key concepts in headache mechanisms include activation and sensitization of trigeminovascular, brainstem, thalamic, and hypothalamic neurons; modulation of cortical brain regions; and activation of descending pain circuits. This review will examine the relevant anatomy of the trigeminal, brainstem, subcortical, and cortical brain regions and concepts related to the pathophysiology of migraine and cluster headache disorders.

Brazilian descriptive study of 104 consecutive real-world migraine patients treated with monoclonal antibodies

BACKGROUND

Migraine is a highly disabling and prevalent neurological disorder. A peptide, calcitonin gene-related peptide, was identified as involved in migraine pathophysiology and monoclonal anti-CGRP antibodies have been developed.

AIM

To describe the clinical characteristics and therapeutic response of migraine patients treated with monoclonal antibodies.

METHOD

An observational, prospective, uncontrolled and descriptive study was carried out with a sample of 112 consecutive patients with episodic or chronic migraine treated with monoclonal antibodies. Eight patients did not return for the following medical consultation. They were excluded from the study.

RESULTS

A total of 104 patients were described. There was a predominance of episodic migraine. Before treatment, the average frequency of headache was 15.3±8.5 days per month, during the previous three months. Monoclonal antibodies were prescribed at the following frequency: erenumab (49%), galcanezumab (45.2%), and fremanezumab (5.8%). After the third month, the reduction in headache attacks was greater than 50% in 57.7% of patients. Adverse events were referred by 18.3% of patients, in this order of frequency: constipation (7.7%), insomnia (2.9%), vertigo (1.9%), erythema at the injection site (1.9%), arthralgia (1%), nasopharyngitis (1%), facial and hand edema (1%), irritation at the injection site (1%), and paresthesia at the injection site (1%).

CONCLUSIONS

This described analysis of migraine patients who used monoclonal antibodies presented one of the first Brazilian experiences with real-world patients. Our results may enlighten clinicians on the outcomes and ways of prescribing anti-CGRP antibodies.

Parenchymal neuroinflammatory signaling and dural neurogenic inflammation in migraine

Background

Pain is generally concomitant with an inflammatory reaction at the site where the nociceptive fibers are activated. Rodent studies suggest that a sterile meningeal inflammatory signaling cascade may play a role in migraine headache as well. Experimental studies also suggest that a parenchymal inflammatory signaling cascade may report the non-homeostatic conditions in brain to the meninges to induce headache. However, how these signaling mechanisms function in patients is unclear and debated. Our aim is to discuss the role of inflammatory signaling in migraine pathophysiology in light of recent developments.

Body

Rodent studies suggest that a sterile meningeal inflammatory reaction can be initiated by release of peptides from active trigeminocervical C-fibers and stimulation of resident macrophages and dendritic/mast cells. This inflammatory reaction might be needed for sustained stimulation and sensitization of meningeal nociceptors after initial activation along with ganglionic and central mechanisms. Most migraines likely have cerebral origin as suggested by prodromal neurologic symptoms. Based on rodent studies, a parenchymal inflammatory signaling cascade has been proposed as a potential mechanism linking cortical spreading depolarization (CSD) to meningeal nociception. A recent PET/MRI study using a sensitive inflammation marker showed the presence of meningeal inflammatory activity in migraine with aura patients over the occipital cortex generating the visual aura. These studies also suggest the presence of a parenchymal inflammatory activity, supporting the experimental findings. In rodents, parenchymal inflammatory signaling has also been shown to be activated by migraine triggers such as sleep deprivation without requiring a CSD because of the resultant transcriptional changes, predisposing to inadequate synaptic energy supply during intense excitatory transmission. Thus, it may be hypothesized that neuronal stress created by either CSD or synaptic activity-energy mismatch could both initiate a parenchymal inflammatory signaling cascade, propagating to the meninges, where it is converted to a lasting headache with or without aura.

Conclusion

Experimental studies in animals and emerging imaging findings from patients warrant further research to gain deeper insight to the complex role of inflammatory signaling in headache generation in migraine.

A critical review of the neurovascular nature of migraine and the main mechanisms of action of prophylactic antimigraine medications

INTRODUCTION

Migraine involves neurovascular, functional, and anatomical alterations. Migraineurs experience an intense unilateral and pulsatile headache frequently accompanied with vomiting, nausea, photophobia, etc. Although there is no ideal preventive medication, frequency in migraine days may be partially decreased by some prophylactics, including antihypertensives, antidepressants, antiepileptics, and CGRPergic inhibitors. However, the mechanisms of action involved in antimigraine prophylaxis remain elusive.

AREAS COVERED

This review recaps some of the main neurovascular phenomena related to migraine and currently available preventive medications. Moreover, it discusses the major mechanisms of action of the recommended prophylactic medications.

EXPERT OPINION

In the last three years, migraine prophylaxis has evolved from nonspecific to specific antimigraine treatments. Overall, nonspecific treatments  mainly involve neural actions, whereas specific pharmacotherapy (represented by CGRP receptor antagonists and CGRPergic monoclonal antibodies) is predominantly mediated by neurovascular mechanisms that may include, among others: (i) reduction in the cortical spreading depression (CSD)-associated events; (ii) inhibition of pain sensitization; (iii) blockade of neurogenic inflammation; and/or (iv) increase in cranial vascular tone. Accordingly, the novel antimigraine prophylaxis promises to be more effective, devoid of significant adverse effects (unlike nonspecific treatments), and more beneficial for the quality of life of migraineurs.

Updated review on the link between cortical spreading depression and headache disorders

INTRODUCTION

Experimental animal studies have revealed mechanisms that link cortical spreading depression (CSD) to the trigeminal activation mediating lateralized headache. However, conventional CSD as seen in lissencephalic brain is insufficient to explain some clinical features of aura and migraine headache.

AREAS COVERED

The importance of CSD in headache development including dysfunction of the thalamocortical network, neuroinflammation, calcitonin gene-related peptide, transgenic models, and the role of CSD in migraine triggers, treatment options, neuromodulation and future directions are reviewed.

EXPERT OPINION

The conventional understanding of CSD marching across the hemisphere is invalid in gyrencephalic brains. Thalamocortical dysfunction and interruption of functional cortical network systems by CSD, may provide alternative explanations for clinical manifestations of migraine phases including aura. Not all drugs showing CSD blocking properties in lissencephalic brains, have efficacy in migraine headache and monoclonal antibodies against CGRP ligand/receptors which are effective in migraine treatment, have no impact on aura in humans or CSD properties in rodents. Functional networks and molecular mechanisms mediating and amplifying the effects of limited CSD in migraine brain remain to be investigated to define new targets.

Brain glycogen metabolism: A possible link between sleep disturbances, headache and depression

The functions of sleep and its links with neuropsychiatric diseases have long been questioned. Among the numerous hypotheses on sleep function, early studies proposed that sleep helps to replenish glycogen stores consumed during waking. Later studies found increased brain glycogen after sleep deprivation, leading to "glycogenetic" hypothesis, which states that there is a parallel increase in synthesis and utilization of glycogen during wakefulness, whereas decrease in the excitatory transmission creates an imbalance causing accumulation of glycogen during sleep. Glycogen is a vital energy reservoir to match the synaptic demand particularly for re-uptake of potassium and glutamate during intense glutamatergic transmission. Therefore, sleep deprivation-induced transcriptional changes may trigger migraine by reducing glycogen availability, which slows clearance of extracellular potassium and glutamate, hence, creates susceptibility to cortical spreading depolarization, the electrophysiological correlate of migraine aura. Interestingly, chronic stress accompanied by increased glucocorticoid levels and locus coeruleus activity and leading to mood disorders in which sleep disturbances are prevalent, also affects brain glycogen turnover via glucocorticoids, noradrenaline, serotonin and adenosine. These observations altogether suggest that inadequate astrocytic glycogen turnover may be one of the mechanisms linking migraine, mood disorders and sleep.

Drug profile: galcanezumab for prevention of cluster headache

Introduction: Cluster headache [CH] is a severely disabling trigeminal autonomic cephalalgia [TAC]. Approximately 1 in 1,000 adults are affected by CH. Calcitonin gene-related peptide [CGRP] is an important mediator in the pathophysiology of CH. Galcanezumab is a monoclonal antibody with an affinity for the CGRP peptide, FDA approved for the prevention of episodic CH. Areas covered: Search words queried were 'cluster headache,' 'cluster headache, and CGRP,' 'cluster headache, and galcanezumab.' Over 99 articles in Pubmed and prescribing information for galcanezumab were reviewed. Some of the data pertaining to CH trials with fremanezumab were reviewed using clinical trials.org. Expert opinion: Galcanezumab has shown benefit in decreasing the weekly frequency of CH attacks across week 1 through week 3 in patients with CH; 8.7 attacks in the galcanezumab group, as compared with 5.2 in the placebo group (95% confidence interval, 0.2 to 6.7; P = 0.04). It has a favorable risk-benefit ratio. The prevention of CH with CGRP inhibition represents a novel advance for a condition with a significant unmet need. The negative trial results of galcanezumab for chronic cluster headache [CCH] may be due to the refractory nature and sheds light on the critical need to investigate the underlying biology and therapeutic options.

Serum CGRP, VIP, and PACAP usefulness in migraine: a case-control study in chronic migraine patients in real clinical practice

Calcitonin gene-related peptide (CGRP), vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase activating polypetide-38 (PACAP-38) have relevant roles in migraine pathophysiology. Their serum levels have been proposed as biomarkers for migraine. Our aim was to assess their diagnostic value in real clinical practice in a cohort of chronic migraine (CM), episodic migraine (EM) and healthy controls (HC). We recruited subjects with CM, EM and HC at two medical centers. Blood samples were drawn under fasting conditions in the interictal period, immediately centrifuged and stored at - 80 ºC. Serum levels were determined by ELISA. Neuropeptide levels, the effect of preventatives, correlations with clinical and demographic variables, and their diagnostic value were studied among clinical categories. 296 age- and sex-matched subjects (101 CM, 98 EM and 97 HC) were included. All three neuropeptide serum levels were higher in CM [median and IQ for CGRP = 18.023 pg/ml (14.4-24.7); VIP = 121.732 pg/ml (48.72-186.72) and PACAP = 204.931 pg/ml (101.08-597.64)] vs EM [CGRP = 14.659 pg/ml (10.29-17.45); VIP = 75.603 pg/ml (28.722-107.10); and PACAP = 94.992 pg/ml (65.77-128.48)] and vs HC [CGRP = 13.988 pg/ml (10.095-17.87); VIP = 84.685 pg/ml (35.32-99.79), and PACAP = 103.142 pg/ml (59.42-123.97)]. Using multinomial modeling, only VIP (OR 1.011, 95% CI  1.003-1.018, p = 0.005) and PACAP (OR 1.003, 95% CI 1.001-1.005, p = 0.002) increased the risk for CM, but not for EM. CGRP did not predict CM or EM. This model could correctly classify only 62/101 (61.38%) of CM, 75/98 (76.53%) of EM, and 5/97 (4.12%) of HC [globally 147/296 (49.8%)]. Individually, PACAP performed the best for classifying clinical categories [global accuracy 150/296 (50.67%)]. In CM, neuropeptide levels were higher in those OnaBT-treated than in no-treated patients. Although interictal serum CGRP and VIP were higher in CM than both EM or HC, their utility to discriminate migraine categories was low. Contrary to other studies, PACAP serum levels were also higher in CM than in EM or HC and had more discriminative capability to distinguish CM from EM and HC. Further investigation is needed for determination technique standardization.

Multidisciplinary Management of the Adverse Effects of Apremilast

We present a series of general and specific recommendations based on pathophysiologic considerations for managing the most common adverse effects of apremilast that lead to treatment discontinuation: diarrhea, nausea, and headache. The recommendations are based on a review of the literature and the experience of a multidisciplinary team of 14 experts including dermatologists, rheumatologists, neurologists, gastroenterologists, pharmacists, and nurses. We propose a series of simple algorithms that include clinical actions and suggestions for pharmacologic treatment. The adverse effects of apremilast can be managed from a multidisciplinary approach. The purpose of optimizing management is to bring clinical benefits to patients.

Plasma levels of vasoactive neuropeptides in pediatric patients with migraine during attack and attack-free periods

BACKGROUND

Increasing evidence suggests that vasoactive neuropeptides such as pituitary adenylate cyclase-activating polypeptide-38 (PACAP-38), substance P, calcitonin gene-related peptide, and vasoactive intestinal peptide are involved in the pathophysiology of migraine in adults, but their role in pediatric migraineurs remains unclear. We prospectively investigated plasma levels of these vasoactive neuropeptides in pediatric migraine patients without aura and compared the results with those of age-matched healthy controls.

METHODS

Thirty-eight children aged 6-18 years with migraine without aura and 20 age-matched control subjects were included in the study. Neuropeptides in plasma samples from the controls, and in either the ictal or interictal periods in pediatric migraine without aura, were measured using ELISA.

RESULTS

PACAP-38 and vasoactive intestinal peptide levels in both ictal and interictal plasma were higher in the patients with pediatric migraine without aura than in the controls (p < 0.001), although calcitonin gene-related peptide and substance P levels remained unchanged. Otherwise, no significant difference was determined between ictal and interictal periods in terms of all neuropeptide levels.

CONCLUSIONS

This study demonstrates increased plasma PACAP-38 and vasoactive intestinal peptide levels, but not calcitonin gene-related peptide and substance P levels, in pediatric patients with migraine during both attack and attack-free periods. The study findings suggest that PACAP-38 and vasoactive intestinal peptide may be implicated in the pathophysiology of migraine, particularly in pediatric migraineurs.

Emerging Treatment Targets for Migraine and Other Headaches

Migraine is a complex disorder that is characterized by an assortment of neurological and systemic effects. While headache is the most prominent feature of migraine, a host of symptoms affecting many physiological functions are also observed before, during, and after an attack. Furthermore, migraineurs are heterogeneous and have a wide range of responses to migraine therapies. The recent approval of calcitonin gene-related-peptide based therapies has opened up the treatment of migraine and generated a renewed interest in migraine research and discovery. Ongoing advances in migraine research have identified a number of other promising therapeutic targets for this disorder. In this review, we highlight emergent treatments within the following biological systems: pituitary adenylate cyclase activating peptdie, 2 non-mu opioid receptors that have low abuse liability - the delta and kappa opioid receptors, orexin, and nitric oxide-based therapies. Multiple mechanisms have been identified in the induction and maintenance of migraine symptoms; and this divergent set of targets have highly distinct biological effects. Increasing the mechanistic diversity of the migraine tool box will lead to more treatment options and better patient care.

Differences in pituitary adenylate cyclase-activating peptide and calcitonin gene-related peptide release in the trigeminovascular system

Background

Several neurotransmitters are expressed in the neurons of the trigeminal ganglion. One such signalling molecule is the pituitary adenylate cyclase-activating peptide (PACAP). PACAP signalling has been suggested to have a possible role in the pathophysiology of primary headaches.

Objective

The present study was designed to investigate the relationship between PACAP and calcitonin gene-related peptide, currently the two most relevant migraine peptides.

Methods

In the current study, we used ELISA to investigate PACAP and calcitonin gene-related peptide release in response to 60 mM K+ or capsaicin using a rat hemi-skull model. We combined this analysis with qPCR and immunohistochemistry to study the expression of PACAP and calcitonin gene-related peptide receptors and ligands.

Results

Calcitonin gene-related peptide (CGRP) is released from the trigeminal ganglion and dura mater. In contrast, PACAP is only released from the trigeminal ganglion. We observed a weak correlation between the stimulated release of the two neuropeptides. PACAP-38 immunoreactivity was expressed alone and in a subpopulation of neurons in the trigeminal ganglion that also store calcitonin gene-related peptide. The receptor subtype PAC1 was mainly expressed in the satellite glial cells (SGCs), which envelop the neurons in the trigeminal ganglion, in some neuronal processes, inside the Aδ-fibres and in the outermost layer of the myelin sheath that envelopes the Aδ-fibres.

Conclusion

Unlike CGRP, PACAP is only released within the trigeminal ganglion. This raises the question of whether a migraine therapy aimed at preventing peripheral PACAP signalling would be as successful as the CGRP signalling targeted treatments.

Cryo-EM structures of PAC1 receptor reveal ligand binding mechanism

The pituitary adenylate cyclase-activating polypeptide type I receptor (PAC1R) belongs to the secretin receptor family and is widely distributed in the central neural system and peripheral organs. Abnormal activation of the receptor mediates trigeminovascular activation and sensitization, which is highly related to migraine, making PAC1R a potential therapeutic target. Elucidation of PAC1R activation mechanism would benefit discovery of therapeutic drugs for neuronal disorders. PAC1R activity is governed by pituitary adenylate cyclase-activating polypeptide (PACAP), known as a major vasodilator neuropeptide, and maxadilan, a native peptide from the sand fly, which is also capable of activating the receptor with similar potency. These peptide ligands have divergent sequences yet initiate convergent PAC1R activity. It is of interest to understand the mechanism of PAC1R ligand recognition and receptor activity regulation through structural biology. Here we report two near-atomic resolution cryo-EM structures of PAC1R activated by PACAP38 or maxadilan, providing structural insights into two distinct ligand binding modes. The structures illustrate flexibility of the extracellular domain (ECD) for ligands with distinct conformations, where ECD accommodates ligands in different orientations while extracellular loop 1 (ECL1) protrudes to further anchor the ligand bound in the orthosteric site. By structure-guided molecular modeling and mutagenesis, we tested residues in the ligand-binding pockets and identified clusters of residues that are critical for receptor activity. The structures reported here for the first time elucidate the mechanism of specificity and flexibility of ligand recognition and binding for PAC1R, and provide insights toward the design of therapeutic molecules targeting PAC1R.

[Recent advances in the elucidation of migraine pathophysiology]

Three hypotheses have been proposed so far regarding the pathophysiology of migraine: one is the "vascular theory", which posits cerebral vascular dysfunction as the etiological factor. The second is the "neuronal theory", which suggests that migraine is triggered by cortical spreading depression. The third is the "trigemino-vascular theory", which postulates that migraine is triggered by inflammation of trigeminal nerves and vessels around trigeminal ganglion cells. Nowadays, the "trigemino-vascular theory" is widely accepted. However, recent advances in imaging analysis indicate that the origin of migraine lies in a premonitory phase which precedes the aura phase. Modern imaging techniques such as functional MRI and PET reveal high activity of the hypothalamic area during the premonitory phase of migraine. These findings suggest that hypothalamic activation might be a generator of a migraine attack. On the other hand, current analyses show that the photosensitivity of migraine (photophobia) could be caused by dysfunction of the newly discovered intrinsically photosensitive retinal ganglion cells (ipRGCs). In the absence of visual signaling from rods and cones, light activation of ipRGCs expressing melanopsin photopigment is sufficient to produce photophobia during migraine. The ipRGCs project to the hypothalamus; their activation might be the trigger for migraine attacks. Significant advances in molecular biology and imaging in recent years have clarified the previous hypotheses of migraine pathophysiology.

PACAP and Other Neuropeptide Targets Link Chronic Migraine and Opioid-induced Hyperalgesia in Mouse Models

Chronic use of opioids can produce opioid-induced hyperalgesia (OIH), and when used to treat migraine, these drugs can result in increased pain and headache chronicity. We hypothesized that overlapping mechanisms between OIH and chronic migraine occur through neuropeptide dysregulation. Using label-free, non-biased liquid chromatography-mass spectrometry to identify and measure changes in more than 1500 neuropeptides under these two conditions, we observed only 16 neuropeptides that were altered between the two conditions. The known pro-migraine molecule, calcitonin-gene related peptide, was among seven peptides associated with chronic migraine, with several pain-processing neuropeptides among the nine other peptides affected in OIH. Further, composite peptide complements Pituitary adenylate cyclase-activating polypeptide (PACAP), Vasoactive intestinal peptide (VIP) and Secretogranin (SCG) showed significant changes in both chronic migraine and OIH. In a follow-up pharmacological study, we confirmed the role of PACAP in models of these two disorders, validating the effectiveness of our peptidomic approach, and identifying PACAP as a mechanistic link between chronic migraine and OIH. Data are available via ProteomeXchange with identifier PXD013362.

PACAP38 improves airway epithelial barrier destruction induced by house dust mites allergen

PURPOSE

This study aimed to investigate the mechanism of PACAP38 on house dust mite (HDM)-induced asthmatic airway epithelial barrier destruction.

METHODS

The HDM-induced asthma mice model and 16HBE cell model was established respectively. The enzyme linked immunosorbent assay (ELSIA), cell count and immunohistochemical assay were performed on mice in control group, HDM group and PACAP38 + HDM group.The cAMP/PKA activity, p-CREB and total CREB expression, TEER and the FITC-DX were investigated on cells in control-16HBE group, HDM-16HBE group and PACAP38 + HDM-16HBE group.

RESULTS

The levels of IL-4 and IL-5 in the HDM group were significantly higher than those in the control group (P < 0.05), while the above indexes in the PACAP38 + HDM group were lower than those in the HDM group (P < 0.05). E-cadherin, β-catenin, ZO-1 and occludin in the control group were highly immunoreactive in airway epithelial cells, whereas connexin staining was attenuated after HDM induction. The TEER level, cAMP levels and PKA activity were decreased, while FITC-DX transmittance was increased in HDM-16HBE group (P < 0.05) compared with the control-16HBE group.

CONCLUSION

PACAP38 could reduce the airway inflammation, weaken the AJC protein heterotopia and activate cAMP/PKA signaling pathway in HDM-induced asthma, which indicate that PACAP38 may be an important contributor in HDM-induced asthma.

Volume of Hypothalamus as a Diagnostic Biomarker of Chronic Migraine

It is believed than hypothalamus (HTH) might be involved in generation of migraine, and evidence from high resolution fMRI reported that the more anterior part of HTH seemed to play an important role in migraine chronification. The current study was aimed to identify the alteration of morphology and resting-state functional connectivity (FC) of the hypothalamus (HTH) in interictal episodic migraine (EM) and chronic migraine (CM). High-resolution structural and resting-state functional magnetic resonance images were acquired in 18 EM patients, 16 CM patients, and 21 normal controls (NC). The volume of HTH was calculated and voxel-based morphometry (VBM) was performed over the whole HTH. Receiver operating characteristics (ROC) curve analysis was applied to evaluate the diagnostic efficacy of HTH volume. Correlation analyses with clinical variables were performed and FC maps were generated for positive HTH regions according to VBM comparison. The volume of the HTH significantly decreased in both EM and CM patients compared with NC. The cut-off volume of HTH as 1.429 ml had a good diagnostic accuracy for CM with sensitivity of 81.25% and specificity of 100%. VBM analyses identified volume reduction of posterior HTH in EM vs. NC which was negatively correlated with headache frequency. The posterior HTH presented decreased FC with the left inferior temporal gyrus (Brodmann area 20) in EM. Decreased volume of anterior HTH was identified in CM vs. NC and CM vs. EM which was positively correlated with headache frequency in CM. The anterior HTH presented increased FC with the right anterior orbital gyrus (AOrG) (Brodmann area 11) in CM compared with NC and increased FC with the right medial orbital gyrus (MOrG) (Brodmann area 11) in CM compared with EM. Our study provided evidence of structural plasticity and FC changes of HTH in the pathogensis of migraine generation and chronification, supporting potential therapeutic target toward the HTH and its peptide.

Update on the pathophysiology of cluster headache: imaging and neuropeptide studies

OBJECTIVE

Cluster headache (CH) is the most severe primary headache condition. Its pathophysiology is multifaceted and incompletely understood. This review brings together the latest neuroimaging and neuropeptide evidence on the pathophysiology of CH.

METHODS

A review of the literature was conducted by searching PubMed and Web of Science. The search was conducted using the following keywords: imaging studies, voxel-based morphometry, diffusion-tensor imaging, diffusion magnetic resonance imaging, tractography, connectivity, cerebral networks, neuromodulation, central modulation, deep brain stimulation, orexin-A, orexin-B, tract-based spatial statistics, single-photon emission computer tomography studies, positron-emission tomography, functional magnetic resonance imaging, magnetic resonance spectroscopy, trigeminovascular system, neuropeptides, calcitonin gene-related peptide, neurokinin A, substance P, nitric oxide synthase, pituitary adenylate cyclase-activating peptide, vasoactive intestinal peptide, neuropeptide Y, acetylcholine, noradrenaline, and ATP. "Cluster headache" was combined with each keyword for more relevant results. All irrelevant and duplicated records were excluded. Search dates were from October 1976 to May 2018.

RESULTS

Neuroimaging studies support the role of the hypothalamus in CH, as well as other brain areas involved in the pain matrix. Activation of the trigeminovascular system and the release of neuropeptides play an important role in CH pathophysiology. Among neuropeptides, calcitonin gene-related peptide, vasoactive intestinal peptide, and pituitary adenylate cyclase-activating peptide have been reported to be reliable biomarkers for CH attacks, though not specific for CH. Several other neuropeptides are involved in trigeminovascular activation, but the current evidence does not qualify them as reliable biomarkers in CH.

CONCLUSION

CH has a complex pathophysiology and the pain mechanism is not completely understood. Recent neuroimaging studies have provided insight into the functional and structural network bases of CH pathophysiology. Although there has been important progress in neuropeptide studies, a specific biomarker for CH is yet to be found.

Emerging Treatments in Episodic Migraine

PURPOSE OF REVIEW

The purpose of this review is to evaluate and describe recent and emerging treatment options for episodic migraine.

RECENT FINDINGS

Recent advances have been made in better understanding the pathophysiology of migraine, which has led to further investigation of potential new pharmacologic and non-pharmacologic treatment options. A number of new medications are emerging for the acute and preventive treatment of migraine, including CGRP monoclonal antibodies, CGRP receptor antagonists, serotonin 5-HT_1F agonists, and PACAP receptor monoclonal antibodies. Additionally, newer studies on existing non-invasive neuromodulation devices including transcranial magnetic stimulation, supraorbital transcutaneous nerve stimulation, and transcutaneous vagus nerve stimulation have recently received FDA approval for use in migraine. Neuromodulation devices including percutaneous mastoid electrical stimulation, non-painful remote electrical stimulation, and caloric vestibular stimulation are undergoing further investigation and have shown promising results thus far. These new developments are expected to contribute to better treatment and decreased disability in migraine.

Review on PACAP-Induced Transcriptomic and Proteomic Changes in Neuronal Development and Repair

Pituitary adenylate cyclase activating polypeptide (PACAP) is a neuropeptide with widespread occurrence and diverse biological effects. Among its several different effects, of special importance is the action of PACAP on neuronal proliferation, differentiation and migration, and neuroprotection. The neuroprotective mechanism of PACAP is both direct and indirect, via neuronal and non-neuronal cells. Several research groups have performed transcriptomic and proteomic analysis on PACAP-mediated genes and proteins. Hundreds of proteins have been described as being involved in the PACAP-mediated neuroprotection. In the present review we summarize the few currently available transcriptomic data potentially leading to the proteomic changes in neuronal development and protection. Proteomic studies focusing on the neuroprotective role of PACAP are also reviewed and discussed in light of the most intriguing and promising effect of this neuropeptide, which may possibly have future therapeutic potential.