Induction of Migraine-Like Photophobic Behavior in Mice by Both Peripheral and Central CGRP Mechanisms

Migraine neuroscience: from experimental models to target therapy

Migraine sciences have witnessed tremendous advances in recent years. Pre-clinical and clinical experimental models have contributed significantly to provide useful insights into the brain structures that mediate migraine attacks. These models have contributed to elucidate the role of neurotransmission pathways and to identify the role of important molecules within the complex network involved in migraine pathogenesis. The contribution and efforts of several research groups from all over the world has ultimately lead to the generation of novel therapeutic approaches, specifically targeted for the prevention of migraine attacks, the monoclonal antibodies directed against calcitonin gene-related peptide or its receptor. These drugs have been validated in randomized placebo-controlled trials and are now ready to improve the lives of a large multitude of migraine sufferers. Others are in the pipeline and will soon be available.

9-Methylfascaplysin exerts anti-ischemic stroke neuroprotective effects via the inhibition of neuroinflammation and oxidative stress in rats

OBJECTIVES

This study was aimed to investigate the neuroprotective effects of 9-methylfascaplysin, a novel marine derivative derived from sponge, against middle cerebral artery occlusion/reperfusion (MCAO)-induced motor impairments, neuroinflammation and oxidative stress in rats.

METHODS

Neurological and behavioral tests were used to evaluate behavioral changes. The 2, 3, 5-triphenyltetrazolium chloride staining was used to determine infarct size and edema extent. Activated microglia/macrophage was analyzed by immunohistochemical staining of Iba-1. RT-PCR and ELISA were used to measure the expression of inducible nitric oxide synthase, tumor necrosis factor-α, interleukin-1β, CD16 and CD206. Western blotting analysis was performed to explore the activation of nuclear factor-κB (NF-κB) and NLRP3. The levels of oxidative stress were studied by evaluating the activities of superoxide dismutase, catalase and glutathione peroxidase.

RESULTS

Post-occlusion intracerebroventricular injection of 9-methylfascaplysin significantly attenuated motor impairments and infarct size in MCAO rats. Moreover, 9-methylfascaplysin reduced the activation of microglia/macrophage in ischemic penumbra as evidenced by the decreased Iba-1-positive area and the reduced expression of pro-inflammatory factors. Furthermore, 9-methylfascaplysin inhibited MCAO-induced oxidative stress and activation of NF-κB and NLRP3 inflammasome.

CONCLUSION

All the results suggested that 9-methylfascaplysin might produce neuroprotective effects against MCAO via the reduction of oxidative stress and neuroinflammation, simultaneously, possibly via the inhibition of NF-κB and NLRP3 inflammasome.

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

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

Exploring the Link Between Dry Eye and Migraine: From Eye to Brain

Dry eye and migraine are common diseases with large societal and economic burdens that have recently been associated in the literature. This review outlines the link between dry eye and migraine, which may have implications for reducing their respective burdens. We highlight possible shared pathophysiology, including peripheral and central sensitization, as the potential link between dry eye and migraine. Finally, therapies targeting similar pathophysiological mechanisms between dry eye and migraine are discussed.

An underrepresented majority: A systematic review utilizing allodynic criteria to examine the present scarcity of discrete animal models for episodic migraine

BACKGROUND

Despite increasing evidence differentiating episodic and chronic migraine, little work has determined how currently utilized animal models of migraine best represent each distinct disease state.

AIM

In this review, we seek to characterize accepted preclinical models of migraine-like headache by their ability to recapitulate the clinical allodynic features of either episodic or chronic migraine.

METHODS

From a search of the Pu bMed database for "animal models of migraine", "headache models" and "preclinical migraine", we identified approximately 80 recent (within the past 20 years) publications that utilized one of 10 different models for migraine research. Models reviewed fit into one of the following categories: Dural KCl application, direct electrical stimulation, nitroglycerin administration, inflammatory soup injection, CGRP injection, medication overuse, monogenic animals, post-traumatic headache, specific channel activation, and hormone manipulation. Recapitulation of clinical features including cephalic and extracephalic hypersensitivity were evaluated for each and compared.

DISCUSSION

Episodic migraineurs comprise over half of the migraine population, yet the vast majority of current animal models of migraine appear to best represent chronic migraine states. While some of these models can be modified to reflect episodic migraine, there remains a need for non-invasive, validated models of episodic migraine to enhance the clinical translation of migraine research.

Vascular actions of peripheral CGRP in migraine-like photophobia in mice

BACKGROUND

Calcitonin gene-related peptide is recognized as a key player in migraine, yet the mechanisms and sites of calcitonin gene-related peptide action remain unknown. The efficacy of calcitonin gene-related peptide-blocking antibodies as preventative migraine drugs supports a peripheral site of action, such as the trigeminovasculature. Given the apparent disconnect between the importance of vasodilatory peptides in migraine and the prevailing opinion that vasodilation is an epiphenomenon, the goal of this study was to test whether vasodilation plays a role in calcitonin gene-related peptide-induced light aversive behavior in mice.

METHODS

Systemic mean arterial pressure and light aversive behavior were measured after intraperitoneal administration of calcitonin gene-related peptide and vasoactive intestinal peptide in wild-type CD1 mice. The functional significance of vasodilation was tested by co-administration of a vasoconstrictor (phenylephrine, endothelin-1, or caffeine) with calcitonin gene-related peptide to normalize blood pressure during the light aversion assay.

RESULTS

Both calcitonin gene-related peptide and vasoactive intestinal peptide induced light aversion that was associated with their effect on mean arterial pressure. Notably, vasoactive intestinal peptide caused relatively transient vasodilation and light aversion. Calcitonin gene-related peptide-induced light aversion was still observed even with normalized blood pressure. However, two of the agents, endothelin-1 and caffeine, did reduce the magnitude of light aversion.

CONCLUSION

We propose that perivascular calcitonin gene-related peptide causes light-aversive behavior in mice by both vasomotor and non-vasomotor mechanisms.

Stimulation of Posterior Thalamic Nuclei Induces Photophobic Behavior in Mice

OBJECTIVE

A hallmark of migraine is photophobia. In mice, photophobia-like behavior is induced by calcitonin gene-related peptide (CGRP), a neuropeptide known to be a key player in migraine. In this study, we sought to identify sites within the brain from which CGRP could induce photophobia.

DESIGN

We focused on the posterior thalamic region, which contains neurons responsive to both light and dural stimulation and has CGRP binding sites. We probed this area with both optogenetic stimulation and acute CGRP injections in wild-type mice. Since the light/dark assay has historically been used to investigate anxiety-like responses in animals, we measured anxiety in a light-independent open field assay and asked if stimulation of a brain region, the periaqueductal gray, that induces anxiety would yield similar results to posterior thalamic stimulation. The hippocampus was used as an anatomical control to ensure that light-aversive behaviors could not be induced by the stimulation of any brain region.

RESULTS

Optogenetic activation of neuronal cell bodies in the posterior thalamic nuclei elicited light aversion in both bright and dim light without an anxiety-like response in an open field assay. Injection of CGRP into the posterior thalamic region triggered similar light-aversive behavior without anxiety. In contrast to the posterior thalamic nuclei, optogenetic stimulation of dorsal periaqueductal gray cell bodies caused both light aversion and an anxiety-like response, while CGRP injection had no effect. In the dorsal hippocampus, neither optical stimulation nor CGRP injection affected light aversion or open field behaviors.

CONCLUSION

Stimulation of posterior thalamic nuclei is able to initiate light-aversive signals in mice that may be modulated by CGRP to cause photophobia in migraine.

Biochemical Modulation and Pathophysiology of Migraine

BACKGROUND

Migraine is a common disabling neurological disorder where attacks have been recognized to consist of more than headache. The premonitory, headache, and postdromal phases are the various phases of the migraine cycle, where aura can occur before, during, or after the onset of pain. Migraine is also associated with photosensitivity and cranial autonomic symptoms, which includes lacrimation, conjunctival injection, periorbital edema, ptosis, nasal congestion, and rhinorrhoea. This review will present the current understanding of migraine pathophysiology and the relationship to the observed symptoms.

EVIDENCE ACQUISITION

The literature was reviewed with specific focus on clinical, neurophysiological, functional imaging, and preclinical studies in migraine including the studies on the role of calcitonin gene-related peptide (CGRP) and pituitary adenylate cyclase activating polypeptide (PACAP).

RESULTS

The phases of the migraine cycle have been delineated by several studies. The observations of clinical symptoms help develop hypotheses of the key structures involved and the biochemical and neuronal pathways through which the effects are mediated. Preclinical studies and functional imaging studies have provided evidence for the role of multiple cortical areas, the diencephalon, especially the hypothalamus, and certain brainstem nuclei in the modulation of nociceptive processing, symptoms of the premonitory phase, aura, and photophobia. CGRP and PACAP have been found to be involved in nociceptive modulation and through exploration of CGRP mechanisms, new successful treatments have been developed.

CONCLUSIONS

Migraine is a complex neural disorder and is important to understand when seeing patients who present to neuro-ophthalmology, especially with the successful translation from preclinical and clinical research leading to successful advances in migraine management.

Cortical spreading depolarisation-induced facial hyperalgesia, photophobia and hypomotility are ameliorated by sumatriptan and olcegepant

Cortical spreading depolarisation (CSD), the neural mechanism underlying migraine aura, may cause headache by sensitising the trigeminal system. Photophobia, the most bothersome accompanying symptom during migraine attacks, is more prevalent in migraine with aura than in migraine without aura. Whether CSD plays a role in developing photophobia remains unknown. Moreover, migraine-induced physical hypoactivity contributes to loss of productivity. We aimed to investigate the development of trigeminal sensitisation, photophobia and locomotive abnormality after KCl-induced CSD using 86 male C57BL/6 mice. Sham-operated mice were used as controls. We confirmed the presence of trigeminal sensitisation and photophobia at 24 h after CSD. CSD-subjected mice also exhibited significantly reduced locomotive activity in both light and dark zones. Hence, the CSD-induced hypomobility was likely to be independent of photophobia. The 5-HT1B/1D agonist, sumatriptan, corrected all these CSD-induced abnormalities. Moreover, dose dependency was demonstrated in the ameliorating effect of the calcitonin gene-related peptide (CGRP) receptor antagonist, olcegepant, on these abnormalities. Sumatriptan and olcegepant improved mouse locomotion with therapeutic lags ranging from 20 to 30 min. Collectively, CSD caused trigeminal sensitisation, photophobia and hypomobility that persisted for at least 24 h by a mechanism involving the 5-HT1B/1D and CGRP activity.

A novel immunocompetent model of metastatic prostate cancer-induced bone pain

BACKGROUND

Over 70% to 85% of men with advanced prostate cancer (PCa) develop bone metastases characterized by severe bone pain and increased likelihood of bone fracture. These clinical features result in decreased quality of life and act as a predictor of higher mortality. Mechanistically, the skeletal pathologies such as osteolytic lesions and abnormal osteoblastic activity drive these symptoms. The role of immune cells in bone cancer pain remains understudied, here we sought to recapitulate this symptomology in a murine model.

METHODS

The prostate cancer bone metastasis-induced pain model (CIBP) was established by transplanting a mouse prostate cancer cell line into the femur of immunocompetent mice. Pain development, gait dynamics, and the changes in emotional activities like depression and anxiety were evaluated. Animal tissues including femurs, dorsal root ganglion (DRG), and spinal cord were collected at killing and microcomputed tomography (μCT), histology/immunohistochemistry, and quantitative immunofluorescent analysis were performed.

RESULTS

Mice receiving prostate cancer cells showed a significantly lower threshold for paw withdrawal responses induced by mechanical stimulation compared with their control counterparts. Zero maze and DigiGait analyses indicated reduced and aberrant movement associated emotional activity compared with sham control at 8-weeks postinjection. The μCT analysis showed osteolytic and osteoblastic changes and a 50% reduction of the trabecular volumes within the prostate cancer group. Neurologically we demonstrated, increased calcitonin gene-related peptide (CGRP) and neuronal p75NTR immune-reactivities in both the projected terminals of the superficial dorsal horn and partial afferent neurons in DRG at L2 to L4 level in tumor-bearing mice. Furthermore, our data show elevated nerve growth factor (NGF) and TrkA immunoreactivities in the same segment of the superficial dorsal horn that were, however, not colocalized with CGRP and p75NTR .

CONCLUSIONS

This study describes a novel immunocompetent model of CIBP and demonstrates the contribution of NGF and p75NTR to chronic pain in bone metastasis.

Increased severity of closed head injury or repetitive subconcussive head impacts enhances post-traumatic headache-like behaviors in a rat model

INTRODUCTION

Posttraumatic headache is one of the most common, debilitating, and difficult symptoms to manage after a traumatic head injury. The development of novel therapeutic approaches is nevertheless hampered by the paucity of preclinical models and poor understanding of the mechanisms underlying posttraumatic headache. To address these shortcomings, we previously characterized the development of posttraumatic headache-like pain behaviors in rats subjected to a single mild closed head injury using a 250 g weight drop. Here, we conducted a follow-up study to further extend the preclinical research toolbox for studying posttraumatic headache by exploring the development of headache-like pain behaviors in male rats subjected to a single, but more severe head trauma (450 g) as well as following repetitive, subconcussive head impacts (150 g). In addition, we tested whether these behaviors involve peripheral calcitonin gene-related peptide signaling by testing the effect of systemic treatment with an anti-calcitonin gene-related peptide monoclonal antibody (anti-calcitonin gene-related peptide mAb).

METHODS

Adult male Sprague Dawley rats (total n = 138) were subjected to diffuse closed head injury using a weight-drop device, or a sham procedure. Three injury paradigms were employed: A single hit, using 450 g or 150 g weight drop, and three successive 150 g weight drop events conducted 72 hours apart. Changes in open field activity and development of cephalic and extracephalic tactile pain hypersensitivity were assessed up to 42 days post head trauma. Systemic administration of the anti-calcitonin gene-related peptide mAb or its control IgG (30 mg/kg) began immediately after the 450 g injury or the third 150 g weight drop with additional doses given every 6 days subsequently.

RESULTS

Rats subjected to 450 g closed head injury displayed an acute decrease in rearing and increased thigmotaxis, together with cephalic tactile pain hypersensitivity that resolved by 6 weeks post-injury. Injured animals also displayed delayed and prolonged extracephalic tactile pain hypersensitivity that remained present at 6 weeks post-injury. Repetitive subconcussive head impacts using the 150 g weight drop, but not a single event, led to decreased vertical rearing as well as cephalic and extracephalic tactile pain hypersensitivity that resolved by 6 weeks post-injury. Early and prolonged anti-calcitonin gene-related peptide mAb treatment inhibited the development of the cephalic tactile pain hypersensitivity in both the severe and repetitive subconcussive head impact models.

CONCLUSIONS

Severe head injury gives rise to a prolonged state of cephalic and extracephalic tactile pain hypersensitivity. These pain behaviors also develop following repetitive, subconcussive head impacts. Extended cephalic tactile pain hypersensitivity following severe and repetitive mild closed head injury are ameliorated by early and prolonged anti-calcitonin gene-related peptide mAb treatment, suggesting a mechanism linked to calcitonin gene-related peptide signaling, potentially of trigeminal origin.

NOP receptor agonist attenuates nitroglycerin-induced migraine-like symptoms in mice

Migraine is an extraordinarily prevalent and disabling headache disorder that affects one billion people worldwide. Throbbing pain is one of several migraine symptoms including sensitivity to light (photophobia), sometimes to sounds, smell and touch. The basic mechanisms underlying migraine remain inadequately understood, and current treatments (with triptans being the primary standard of care) are not well tolerated by some patients. NOP (Nociceptin OPioid) receptors, the fourth member of the opioid receptor family, are expressed in the brain and periphery with particularly high expression known to be in trigeminal ganglia (TG). The aim of our study was to further explore the involvement of the NOP receptor system in migraine. To this end, we used immunohistochemistry to examine NOP receptor distribution in TG and trigeminal nucleus caudalus (TNC) in mice, including colocalization with specific cellular markers, and used nitroglycerin (NTG) models of migraine to assess the influence of the selective NOP receptor agonist, Ro 64-6198, on NTG-induced pain (sensitivity of paw and head using von Frey filaments) and photophobia in mice. Our immunohistochemical studies with NOP-eGFP knock-in mice indicate that NOP receptors are on the majority of neurons in the TG and are also very highly expressed in the TNC. In addition, Ro 64-6198 can dose dependently block NTG-induced paw and head allodynia, an effect that is blocked by the NOP antagonist, SB-612111. Moreover, Ro 64-6198, can decrease NTG-induced light sensitivity in mice. These results suggest that NOP receptor agonists should be futher explored as treatment for migraine symptoms. This article is part of the special issue on Neuropeptides.

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.

Enhanced post-traumatic headache-like behaviors and diminished contribution of peripheral CGRP in female rats following a mild closed head injury

INTRODUCTION

Females are thought to have increased risk of developing post-traumatic headache following a traumatic head injury or concussion. However, the processes underlying this susceptibility remain unclear. We previously demonstrated the development of post-traumatic headache-like pain behaviors in a male rat model of mild closed head injury, along with the ability of sumatriptan and an anti-calcitonin-gene-related peptide monoclonal antibody to ameliorate these behaviors. Here, we conducted a follow-up study to explore the development of post-traumatic headache-like behaviors and the effectiveness of these headache therapies in females subjected to the same head trauma protocol.

METHODS

Adult female Sprague Dawley rats were subjected to a mild closed head injury using a weight-drop device (n = 126), or to a sham procedure (n = 28). Characterization of headache and pain related behaviors included assessment of changes in cutaneous cephalic and extracephalic tactile pain sensitivity, using von Frey monofilaments. Sensitivity to headache/migraine triggers was tested by examining the effect of intraperitoneal administration of a low dose of glyceryl trinitrate (100 µg/kg). Treatments included acute systemic administration of sumatriptan (1 mg/kg) and repeated systemic administration of a mouse anti-calcitonin gene-related peptide monoclonal antibody (30 mg/kg). Serum levels of calcitonin gene-related peptide were measured at baseline and at various time points post head injury in new cohorts of females (n = 38) and males (n = 36).

RESULTS

Female rats subjected to a mild closed head injury developed cutaneous mechanical hyperalgesia, which was limited to the cephalic region and was resolved 4 weeks later. Cephalic pain hypersensitivity was ameliorated by treatment with sumatriptan but was resistant to an early and prolonged treatment with the anti-calcitonin gene-related peptide monoclonal antibody. Following the resolution of the head injury-evoked cephalic hypersensitivity, administration of glyceryl trinitrate produced a renewed and pronounced cephalic and extracephalic pain hypersensitivity that was inhibited by sumatriptan, but only partially by the anti-calcitonin gene-related peptide treatment. Calcitonin gene-related peptide serum levels were elevated in females but not in males at 7 days post head injury.

CONCLUSIONS

Development of post-traumatic headache-like pain behaviors following a mild closed head injury, and responsiveness to treatment in rats is sexually dimorphic. When compared to the data obtained from male rats in the previous study, female rats display a prolonged state of cephalic hyperalgesia, increased responsiveness to a headache trigger, and a poorer effectiveness of an early and prolonged anti-calcitonin gene-related peptide treatment. The increased risk of females to develop post-traumatic headache may be linked to enhanced responsiveness of peripheral and/or central pain pathways and a mechanism independent of peripheral calcitonin gene-related peptide signaling.

Calcitonin gene-related peptide (CGRP): role in migraine pathophysiology and therapeutic targeting

Introduction: The neuropeptide calcitonin gene-related peptide (CGRP) is recognized as a critical player in migraine pathophysiology. Excitement has grown regarding CGRP because of the development and clinical testing of drugs targeting CGRP or its receptor. While these drugs alleviate migraine symptoms in half of the patients, the remaining unresponsive half of this population creates an impetus to address unanswered questions that exist in this field.Areas covered: We describe the role of CGRP in migraine pathophysiology and CGRP-targeted therapeutics currently under development and in use. We also discuss how a second CGRP receptor may provide a new therapeutic target.Expert opinion: CGRP-targeting drugs have shown a remarkable safety profile. We speculate that this may reflect the redundancy of peptides within the CGRP family and a second CGRP receptor that may compensate for reduced CGRP activity. Furthermore, we propose that an inherent safety feature of peptide-blocking antibodies is attributed to the fundamental nature of peptide release, which occurs as a large bolus in short bursts of volume transmission. These facts support the development of more refined CGRP therapeutic drugs, as well as drugs that target other neuropeptides. We believe that the future of migraine research is bright with exciting advances on the horizon.

Insulin-like growth factor-1 inhibits spreading depression-induced trigeminal calcitonin gene related peptide, oxidative stress & neuronal activation in rat

Migraineurs can show brain hyperexcitability and oxidative stress that may promote headache. Since hyperexcitability can enhance oxidative stress which promotes hyperexcitability, ending this feed-back loop may reduce migraine. Neocortical spreading depression, an animal model of migraine begins with hyperexcitability and triggers oxidative stress in the neocortical area involved and in the trigeminal system, which is important to pain pathway nociceptive activation in migraine. Additionally, oxidative stress causes increased trigeminal ganglion calcitonin gene-related peptide release and oxidative stress can reduce spreading depression threshold. Insulin-like growth factor-1 significantly protects against spreading depression in vitro by reducing oxidative stress and it is effective against spreading depression after intranasal delivery to animals. Here, we used adult male rats and extend this work to study the trigeminal system where insulin-like growth factor-1 receptors are highly expressed. Recurrent neocortical spreading depression significantly increased surrogate markers of trigeminal activation - immunostaining for trigeminal ganglion oxidative stress, calcitonin gene related peptide levels and c-fos in the trigeminocervical complex versus sham. These effects were significantly reduced by intranasal delivery of insulin-like growth factor-1 a day before recurrent neocortical spreading depression. Furthermore, intranasal treatment with insulin-like growth factor-1 significantly reduced naïve levels of trigeminal ganglion calcitonin gene related peptide versus sham with no impact on blood glucose levels. Intranasal delivery of insulin-like growth factor-1 not only mitigates neocortical spreading depression, a cause of migraine hyperexcitability modeled in animals, but also when neocortical spreading depression is triggered by supra-threshold stimuli, insulin-like growth factor-1 effectively reduces nociceptive activation in the trigeminal system.

Contribution of intraganglionic CGRP to migraine-like responses in male and female rats

Objective

To evaluate whether intraganglionic calcitonin gene-related peptide induced differential migraine-like responses in male and female rats.

Methods

Calcitonin gene-related peptide was injected in the trigeminal ganglion of male and female rats followed by assessment of periorbital mechanical allodynia with von Frey hairs. The influence of systemic treatment with sumatriptan or intraganglionic treatment with minocycline and propentofylline was determined on the calcitonin gene-related peptide-induced mechanical allodynia in male and female rats. One additional group was exposed to an aversive light 24 h after calcitonin gene-related peptide priming, followed by evaluation of periorbital mechanical threshold, and another group was tested in the elevated-plus maze.

Results

Intraganglionar calcitonin gene-related peptide-induced periorbital mechanical allodynia in female (0.5 to 6 h) and male rats (0.5 to 4 h). Systemic sumatriptan briefly attenuated the mechanical allodynia, but intraganglionar minocycline or propentofylline injection was effective only in male rats. Calcitonin gene-related peptide induced photic sensitivity in female and male rats (lasting 4 h and 1 h, respectively), as well as anxiety-like behavior.

Conclusions

Intraganglionar calcitonin gene-related peptide may play a major role in migraine-like responses, including periorbital mechanical allodynia, light sensitivity and anxiety like-behavior. Female rats are likely to be more susceptible to calcitonin gene-related peptide effects and a better understanding of the sexual dimorphism in calcitonin gene-related peptide signaling may help to improve migraine therapy.

Fluorescently-labeled fremanezumab is distributed to sensory and autonomic ganglia and the dura but not to the brain of rats with uncompromised blood brain barrier

Background

The presence of calcitonin gene-related peptide and its receptors in multiple brain areas and peripheral tissues previously implicated in migraine initiation and its many associated symptoms raises the possibility that humanized monoclonal anti-calcitonin gene-related peptide antibodies (CGRP-mAbs) can prevent migraine by modulating neuronal behavior inside and outside the brain. Critical to our ability to conduct a fair discussion over the mechanisms of action of CGRP-mAbs in migraine prevention is data generation that determines which of the many possible peripheral and central sites are accessible to these antibodies – a question raised frequently due to their large size.

Material and methods

Rats with uncompromised and compromised blood-brain barrier (BBB) were injected with Alexa Fluor 594-conjugated fremanezumab (Frema594), sacrificed 4 h or 7 d later, and relevant tissues were examined for the presence of Frema594.

Results

In rats with uncompromised BBB, Frema594 was similarly observed at 4 h and 7 d in the dura, dural blood vessels, trigeminal ganglion, C2 dorsal root ganglion, the parasympathetic sphenopalatine ganglion and the sympathetic superior cervical ganglion but not in the spinal trigeminal nucleus, thalamus, hypothalamus or cortex. In rats with compromised BBB, Frema594 was detected in the cortex (100 µm surrounding the compromised BBB site) 4 h but not 7 d after injections.

Discussion

Our inability to detect fluorescent (CGRP-mAbs) in the brain supports the conclusion that CGRP-mAbs prevent the headache phase of migraine by acting mostly, if not exclusively, outside the brain as the amount of CGRP-mAbs that enters the brain (if any) is too small to be physiologically meaningful.

Effects of fremanezumab on the use of acute headache medication and associated symptoms of migraine in patients with episodic migraine

BACKGROUND

Fremanezumab, a fully humanized monoclonal antibody targeting calcitonin gene-related peptide, has demonstrated efficacy for the preventive treatment of migraine in adults.

OBJECTIVE

To evaluate the effect of fremanezumab treatment on acute headache medication use and migraine-associated symptoms in patients with episodic migraine.

METHODS

In the Phase 3 HALO trial, patients with episodic migraine were randomized to receive subcutaneous fremanezumab monthly (225 mg at baseline, weeks 4 and 8), fremanezumab quarterly (675 mg at baseline, placebo at weeks 4 and 8), or placebo over a 12-week period. The secondary endpoint was change from baseline in the monthly number of days with use of any acute headache mediation or migraine-specific acute headache medication; exploratory endpoints were change from baseline in the monthly number of days with nausea or vomiting, photophobia, or phonophobia.

RESULTS

Of 875 patients randomized, 865 were included in the analysis (monthly, n = 287; quarterly, n = 288; placebo, n = 290). Baseline mean ± standard deviation days with: Any acute headache medication use (monthly: 7.7 ± 3.4; quarterly: 7.8 ± 3.7; placebo: 7.7 ± 3.6), migraine-specific acute headache medication use (6.1 ± 3.1; 6.6 ± 3.1; 7.1 ± 3.0), nausea or vomiting (4.5 ± 3.6; 4.9 ± 3.7; 4.5 ± 3.3) and photophobia and phonophobia (5.5 ± 4.1; 6.3 ± 4.1; 6.0 ± 3.9) were similar among treatment arms. Fremanezumab reduced the number of days of acute headache medication use ([least-squares mean change vs. placebo] monthly: -1.4 [95% confidence interval: -1.84, -0.89], p < 0.001; quarterly: -1.3 [-1.76, -0.82], p < 0.001) and migraine-specific acute headache medication use (monthly: -2.2 [-2.80, -1.56], p < 0.001; quarterly: -2.2 [-2.81, -1.58], p < 0.001) compared with placebo. Fremanezumab also reduced nausea or vomiting, photophobia, and phonophobia compared with placebo.

CONCLUSIONS

Fremanezumab reduced the need for acute headache medications, including migraine-specific medications, while treating migraine-associated symptoms in patients with episodic migraine.

TRIAL REGISTRATION

Clinicaltrials.gov NCT02629861.

Current understanding of photophobia, visual networks and headaches

OBJECTIVE

To review clinical and pre-clinical evidence supporting the role of visual pathways, from the eye to the cortex, in the development of photophobia in headache disorders.

BACKGROUND

Photophobia is a poorly understood light-induced phenomenon that emerges in a variety of neurological and ophthalmological conditions. Over the years, multiple mechanisms have been proposed to explain its causes; however, scarce research and lack of systematic assessment of photophobia in patients has made the search for answers quite challenging. In the field of headaches, significant progress has been made recently on how specific visual networks contribute to photophobia features such as light-induced intensification of headache, increased perception of brightness and visual discomfort, which are frequently experienced by migraineurs. Such progress improved our understanding of the phenomenon and points to abnormal processing of light by both cone/rod-mediated image-forming and melanopsin-mediated non-image-forming visual pathways, and the consequential transfer of photic signals to multiple brain regions involved in sensory, autonomic and emotional regulation.

CONCLUSION

Photophobia phenotype is diverse, and the relative contribution of visual, trigeminal and autonomic systems may depend on the disease it emerges from. In migraine, photophobia could result from photic activation of retina-driven pathways involved in the regulation of homeostasis, making its association with headache more complex than previously thought.

New discoveries in migraine mechanisms and therapeutic targets

Migraine is among the most common and most disabling disorders worldwide, yet its underlying pathophysiology is among the most poorly understood. New information continues to emerge on mechanisms within the central and peripheral nervous systems that may contribute to migraine attacks. Additionally, new therapeutics have recently become available and along with much needed relief for many patients, these drugs provide insight into the disorder based on their mechanism of action. This review will cover new findings within the last several years that add to the understanding of migraine pathophysiology, including those related to the vasculature, calcitonin gene-related peptide (CGRP), and mechanisms within the cortex and meninges that may contribute to attacks. Discussion will also cover recent findings on novel therapeutic targets, several of which continue to show promise in new preclinical studies, including acid-sensing ion channels (ASICs) and the delta-opioid receptor (DOR).

CGRP in Animal Models of Migraine

With the approval of calcitonin gene-related peptide (CGRP) and CGRP receptor monoclonal antibodies by the Federal Drug Administration, a new era in the treatment of migraine patients is beginning. However, there are still many unknowns in terms of CGRP mechanisms of action that need to be elucidated to allow new advances in migraine therapies. CGRP has been studied both clinically and preclinically since its discovery. Here we review some of the preclinical data regarding CGRP in animal models of migraine.

Animal models of migraine and experimental techniques used to examine trigeminal sensory processing

Background

Migraine is a common debilitating condition whose main attributes are severe recurrent headaches with accompanying sensitivity to light and sound, nausea and vomiting. Migraine-related pain is a major cause of its accompanying disability and can encumber almost every aspect of daily life.

Main body

Advancements in our understanding of the neurobiology of migraine headache have come in large from basic science research utilizing small animal models of migraine-related pain. In this current review, we aim to describe several commonly utilized preclinical models of migraine. We will discuss the diverse array of methodologies for triggering and measuring migraine-related pain phenotypes and highlight briefly specific advantages and limitations therein. Finally, we will address potential future challenges/opportunities to refine existing and develop novel preclinical models of migraine that move beyond migraine-related pain and expand into alternate migraine-related phenotypes.

Conclusion

Several well validated animal models of pain relevant for headache exist, the researcher should consider the advantages and limitations of each model before selecting the most appropriate to answer the specific research question. Further, we should continually strive to refine existing and generate new animal and non-animal models that have the ability to advance our understanding of head pain as well as non-pain symptoms of primary headache disorders.

Calcitonin gene-related peptide potentiated the excitatory transmission and network propagation in the anterior cingulate cortex of adult mice

The neuropeptide of calcitonin gene-related peptide (CGRP) plays critical roles in chronic pain, especially in migraine. Immunohistochemistry and in situ hybridization studies have shown that CGRP and its receptors are expressed in cortical areas including pain perception-related prefrontal anterior cingulate cortex. However, less information is available for the functional roles of CGRP in cortical regions such as the anterior cingulate cortex (ACC). Recent studies have consistently demonstrated that long-term potentiation is a key cellular mechanism for chronic pain in the ACC. In the present study, we used 64-electrode array field recording system to investigate the effect of CGRP on excitatory transmission in the ACC. We found that CGRP induced potentiation of synaptic transmission in a dose-dependently manner (1, 10, 50, and 100 nM). CGRP also recruited inactive circuit in the ACC. An application of the calcitonin receptor-like receptor antagonist CGRP_8-37 blocked CGRP-induced chemical long-term potentiation and the recruitment of inactive channels. CGRP-induced long-term potentiation was also blocked by N-methyl-D-aspartate (NMDA) receptor antagonist AP-5. Consistently, the application of CGRP increased NMDA receptor-mediated excitatory postsynaptic currents. Finally, we found that CGRP-induced long-term potentiation required the activation of calcium-stimulated adenylyl cyclase subtype 1 (AC1) and protein kinase A. Genetic deletion of AC1 using AC1^−/− mice, an AC1 inhibitor NB001 or a protein kinase A inhibitor KT5720, all reduced or blocked CGRP-induced potentiation. Our results provide direct evidence that CGRP may contribute to synaptic potentiation in important physiological and pathological conditions in the ACC, an AC1 inhibitor NB001 may be beneficial for the treatment of chronic headache.

CGRP and the Trigeminal System in Migraine

OBJECTIVE

The goal of this narrative review is to provide an overview of migraine pathophysiology, with an emphasis on the role of calcitonin gene-related peptide (CGRP) within the context of the trigeminovascular system.

BACKGROUND

Migraine is a prevalent and disabling neurological disease that is characterized in part by intense, throbbing, and unilateral headaches. Despite recent advances in understanding its pathophysiology, migraine still represents an unmet medical need, as it is often underrecognized and undertreated. Although CGRP has been known to play a pivotal role in migraine for the last 2 decades, this has now received more interest spurred by the early clinical successes of drugs that block CGRP signaling in the trigeminovascular system.

DESIGN

This narrative review presents an update on the role of CGRP within the trigeminovascular system. PubMed searches were used to find recent (ie, 2016 to November 2018) published articles presenting new study results. Review articles are also included not as primary references but to bring these to the attention of the reader. Original research is referenced in describing the core of the narrative, and review articles are used to support ancillary points.

RESULTS

The trigeminal ganglion neurons provide the connection between the periphery, stemming from the interface between the primary afferent fibers of the trigeminal ganglion and the meningeal vasculature and the central terminals in the trigeminal nucleus caudalis. The neuropeptide CGRP is abundant in trigeminal ganglion neurons, and is released from the peripheral nerve and central nerve terminals as well as being secreted within the trigeminal ganglion. Release of CGRP from the peripheral terminals initiates a cascade of events that include increased synthesis of nitric oxide and sensitization of the trigeminal nerves. Secreted CGRP in the trigeminal ganglion interacts with adjacent neurons and satellite glial cells to perpetuate peripheral sensitization, and can drive central sensitization of the second-order neurons. A shift in central sensitization from activity-dependent to activity-independent central sensitization may indicate a mechanism driving the progression of episodic migraine to chronic migraine. The pathophysiology of cluster headache is much more obscure than that of migraine, but emerging evidence suggests that it may also involve hypersensitivity of the trigeminovascular system. Ongoing clinical studies with therapies targeted at CGRP will provide additional, valuable insights into the pathophysiology of this disorder.

CONCLUSIONS

CGRP plays an essential role in the pathophysiology of migraine. Treatments that interfere with the functioning of CGRP in the peripheral trigeminal system are effective against migraine. Blocking sensitization of the trigeminal nerve by attenuating CGRP activity in the periphery may be sufficient to block a migraine attack. Additionally, the potential exists that this therapeutic strategy may also alleviate cluster headache as well.

Dural Calcitonin Gene-Related Peptide Produces Female-Specific Responses in Rodent Migraine Models

Migraine is the second leading cause for disability worldwide and the most common neurological disorder. It is also three times more common in women; reasons for this sex difference are not known. Using preclinical behavioral models of migraine, we show that application of calcitonin gene-related peptide (CGRP) to the rat dura mater produces cutaneous periorbital hypersensitivity. Surprisingly, this response was observed only in females; dural CGRP at doses from 1 pg to 3.8 μg produce no responses in males. In females, dural CGRP causes priming to a pH 7.0 solution after animals recover from the initial CGRP-induced allodynia. Dural application of interleukin-6 causes acute responses in males and females but only causes priming to subthreshold dural CGRP (0.1 pg) in females. Intracisternal application of BDNF also causes similar acute hypersensitivity responses in males and females but only priming to subthreshold dural CGRP (0.1 pg) in females. Females were additionally primed to a subthreshold dose of the NO-donor sodium nitroprusside (0.1 mg/kg) following dural CGRP. Finally, the sexually dimorphic responses to dural CGRP were not specific to rats as similar female-specific hypersensitivity responses were seen in mice, where increased grimace responses were also observed. These data are the first to demonstrate that CGRP-induced headache-like behavioral responses at doses up to 3.8 μg are female-specific both acutely and following central and peripheral priming. These data further implicate dural CGRP signaling in the pathophysiology of migraine and propose a model where dural CGRP-based mechanisms contribute to the sexual disparity of this female-biased disorder.SIGNIFICANCE STATEMENT Calcitonin gene-related peptide (CGRP) has long been implicated in the pathophysiology of migraine, and CGRP-based therapeutics are efficacious for the treatment of migraine in humans. However, the location of action for CGRP in migraine remains unclear. We show here that application of CGRP to the cranial meninges causes behavioral responses consistent with headache in preclinical rodent models. Surprisingly, however, these responses are only observed in females. Acute responses to meningeal CGRP are female-specific and sensitization to CGRP after two distinct stimuli are also female-specific. These data implicate the dura mater as a primary location of action for CGRP in migraine and suggest that female-specific mechanisms downstream of CGRP receptor activation contribute to the higher prevalence of migraine in women.

Increased receptor activity-modifying protein 1 in the nervous system is sufficient to protect against autonomic dysregulation and hypertension

Calcitonin gene-related peptide (CGRP) can cause migraines, yet it is also a potent vasodilator that protects against hypertension. Given the emerging role of CGRP-targeted antibodies for migraine prevention, an important question is whether the protective actions of CGRP are mediated by vascular or neural CGRP receptors. To address this, we have characterized the cardiovascular phenotype of transgenic nestin/hRAMP1 mice that have selective elevation of a CGRP receptor subunit in the nervous system, human receptor activity-modifying protein 1 (hRAMP1). Nestin/hRAMP1 mice had relatively little hRAMP1 RNA in blood vessels and intravenous injection of CGRP caused a similar blood pressure decrease in transgenic and control mice. At baseline, nestin/hRAMP1 mice exhibited similar mean arterial pressure, heart rate, baroreflex sensitivity, and sympathetic vasomotor tone as control mice. We previously reported that expression of hRAMP1 in all tissues favorably improved autonomic regulation and attenuated hypertension induced by angiotensin II (Ang II). Similarly, in nestin/hRAMP1 mice, hypertension caused by Ang II or phenylephrine was greatly attenuated, and associated autonomic dysregulation and increased sympathetic vasomotor tone were diminished or abolished. We conclude that increased expression of neuronal CGRP receptors is sufficient to induce a protective change in cardiovascular autonomic regulation with implications for migraine therapy.

Calcitonin-gene-related peptide pathway mAbs and migraine prevention

PURPOSE OF REVIEW

Monoclonal antibodies (mAbs) targeting the calcitonin-gene-related peptide (CGRP) pathway have been developed for episodic and chronic migraine prevention, either through binding the CGRP ligand (eptinezumab, fremanezumab, galcanezumab) or the CGRP receptor (erenumab). We provide an update on published Phase 2 and Phase 3 trials, safety/tolerability data, pharmacokinetics and mechanism of action of these biologicals.

RECENT FINDINGS

The efficacy data from Phase 2 trials are corroborated by those from published Phase 3 trials, with a multitude of publications expected in 2018. Review of safety data concluded there was no difference in total adverse events or main adverse events (including upper respiratory tract infection, nasopharyngitis, nausea, injection-site pain and back pain) between the mAbs and placebo injections except apparently for dizziness. The site of action of these mAbs is not fully elucidated but current insight is that their effect resides in the periphery; a contribution of central effect(s) can however not be excluded at present.

SUMMARY

Although efficacy of all four drugs is modest over placebo in episodic and chronic migraine prevention and overall comparable with available oral preventive treatments, current tolerability and (short-term) safety data of this new treatment approach certainly promise a major step forward for migraine patients.

CGRP-based Migraine Therapeutics: How Might They Work, Why So Safe, and What Next?

Migraine is a debilitating neurological condition that involves the neuropeptide calcitonin gene-related peptide (CGRP). An exciting development is the recent FDA approval of the first in an emerging class of CGRP-targeted drugs designed to prevent migraine. Yet despite this efficacy, there are some fundamental unanswered questions, such as where and how CGRP works in migraine. Preclinical data suggest that CGRP acts via both peripheral and central mechanisms. The relevance of peripheral sites is highlighted by the clinical efficacy of CGRP-blocking antibodies, even though they do not appreciably cross the blood-brain barrier. The most likely sites of action are within the dura and trigeminal ganglia. Furthermore, it would be foolish to ignore perivascular actions in the dura since CGRP is the most potent vasodilatory peptide. Ultimately, the consequence of blocking CGRP or its receptor is reduced peripheral neural sensitization. Underlying their efficacy is the question of why the antibodies have such an excellent safety profile so far. This may be due to the presence of a second CGRP receptor and vesicular release of a large bolus of peptides. Finally, despite the promise of these drugs, there are unmet gaps because they do not work for all patients; so what next? We can expect advances on several fronts, including CGRP receptor structures that may help development of centrally-acting antagonists, combinatorial treatments that integrate other therapies, and development of drugs that target other neuropeptides. This is truly an exciting time for CGRP and the migraine field with many more discoveries on the horizon.

Behavioral and cognitive animal models in headache research

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

Peripherally administered calcitonin gene-related peptide induces spontaneous pain in mice: implications for migraine

Migraine is the third most common disease in the world (behind dental caries and tension-type headache) with an estimated global prevalence of 15%, yet its etiology remains poorly understood. Recent clinical trials have heralded the potential of therapeutic antibodies that block the actions of the neuropeptide calcitonin gene-related peptide (CGRP) or its receptor to prevent migraine. Calcitonin gene-related peptide is believed to contribute to trigeminal nerve hypersensitivity and photosensitivity in migraine, but a direct role in pain associated with migraine has not been established. In this study, we report that peripherally administered CGRP can act in a light-independent manner to produce spontaneous pain in mice that is manifested as a facial grimace. As an objective validation of the orbital tightening action unit of the grimace response, we developed a squint assay using a video-based measurement of the eyelid fissure, which confirmed a significant squint response after CGRP injection, both in complete darkness and very bright light. These indicators of discomfort were completely blocked by preadministration of a monoclonal anti-CGRP-blocking antibody. However, the nonsteroidal anti-inflammatory drug meloxicam failed to block the effect of CGRP. Interestingly, an apparent sex-specific response to treatment was observed with the antimigraine drug sumatriptan partially blocking the CGRP response in male, but not female mice. These results demonstrate that CGRP can induce spontaneous pain, even in the absence of light, and that the squint response provides an objective biomarker for CGRP-induced pain that is translatable to humans.

The DH31/CGRP enteroendocrine peptide triggers intestinal contractions favoring the elimination of opportunistic bacteria

The digestive tract is the first organ affected by the ingestion of foodborne bacteria. While commensal bacteria become resident, opportunistic or virulent bacteria are eliminated from the gut by the local innate immune system. Here we characterize a new mechanism of defense, independent of the immune system, in Drosophila melanogaster. We observed strong contractions of longitudinal visceral muscle fibers for the first 2 hours following bacterial ingestion. We showed that these visceral muscle contractions are induced by immune reactive oxygen species (ROS) that accumulate in the lumen and depend on the ROS-sensing TRPA1 receptor. We then demonstrate that both ROS and TRPA1 are required in a subset of anterior enteroendocrine cells for the release of the DH31 neuropeptide which activates its receptor in the neighboring visceral muscles. The resulting contractions of the visceral muscles favors quick expulsion of the bacteria, limiting their presence in the gut. Our results unveil a precocious mechanism of defense against ingested opportunistic bacteria, whether they are Gram-positive like Bacillus thuringiensis or Gram-negative like Erwinia carotovora carotovora. Finally, we found that the human homolog of DH31, CGRP, has a conserved function in Drosophila.

The intestine is the first barrier to fight non-commensal bacteria ingested along with the food. The innate immune system is the main mean mounted by the gut lining in response to ill-causing bacteria to avoid detrimental impact. Intestinal cells produce chlorine bleach and antimicrobial peptides that destroy exogenous bacteria. Here, we identified and characterized a new mechanism of gut defense that occurs rapidly after ingestion of exogenous bacteria. We found that the enteroendocrine cells perceive the presence of chlorine bleach in the lumen thanks to a sensor. This sensor promotes a calcium flux within enteroendocrine cells that allows the release of a hormone. This hormone acts locally on the visceral muscle surrounding the intestine by provoking its strong contractions (or spasms). We show that these strong but brief visceral contractions are helping to the quick expulsion of the ingested bacteria thus limiting their potential detrimental impact on the intestine. Markedly, the bleach-sensor is well known to be involved in pain. Therefore we have deciphered in this study a biological mechanism that has so far been described only empirically by medicine, potentially explaining intestinal pain and visceral spasms upon food poisoning.

Vascular Contributions to Migraine: Time to Revisit?

Migraine is one of the most prevalent and disabling neurovascular disorders worldwide. However, despite the increase in awareness and research, the understanding of migraine pathophysiology and treatment options remain limited. For centuries, migraine was considered to be a vascular disorder. In fact, the throbbing, pulsating quality of the headache is thought to be caused by mechanical changes in vessels. Moreover, the most successful migraine treatments act on the vasculature and induction of migraine can be accomplished with vasoactive agents. However, over the past 20 years, the emphasis has shifted to the neural imbalances associated with migraine, and vascular changes have generally been viewed as an epiphenomenon that is neither sufficient nor necessary to induce migraine. With the clinical success of peripherally-acting antibodies that target calcitonin gene-related peptide (CGRP) and its receptor for preventing migraine, this neurocentric view warrants a critical re-evaluation. This review will highlight the likely importance of the vasculature in migraine.

Strides Toward Better Understanding of Post-Traumatic Headache Pathophysiology Using Animal Models

PURPOSE OF REVIEW

In recent years, the awareness of the detrimental impact of concussion and mild traumatic brain injuries (mTBI) is becoming more apparent. Concussive head trauma results in a constellation of cognitive and somatic symptoms of which post-traumatic headache is the most common. Our understanding of post-traumatic headache is limited by the paucity of well validated, characterized, and clinically relevant animal models with strong predictive validity. In this review, we aim to summarize and discuss current animal models of concussion/mTBI and related data that start to shed light on the pathophysiology of post-traumatic headache.

RECENT FINDINGS

Each of the models will be discussed in terms of their face, construct, and predictive validity as well as overall translational relevance to concussion, mTBI, and post-traumatic headache. Significant contributions to the pathophysiology of PTH garnered from these models are discussed as well as potential contributors to the development of chronic post-traumatic headache. Although post-traumatic headache is one of the most common symptoms following mild head trauma, there remains a disconnect between the study of mild traumatic brain injury and headache in the pre-clinical literature. A greater understanding of the relationship between these phenomena is currently needed to provide more insight into the increasing frequency of this debilitating condition in both military and civilian populations.

Drosophila CaV2 channels harboring human migraine mutations cause synapse hyperexcitability that can be suppressed by inhibition of a Ca2+ store release pathway

Gain-of-function mutations in the human CaV2.1 gene CACNA1A cause familial hemiplegic migraine type 1 (FHM1). To characterize cellular problems potentially triggered by CaV2.1 gains of function, we engineered mutations encoding FHM1 amino-acid substitutions S218L (SL) and R192Q (RQ) into transgenes of Drosophila melanogaster CaV2/cacophony. We expressed the transgenes pan-neuronally. Phenotypes were mild for RQ-expressing animals. By contrast, single mutant SL- and complex allele RQ,SL-expressing animals showed overt phenotypes, including sharply decreased viability. By electrophysiology, SL- and RQ,SL-expressing neuromuscular junctions (NMJs) exhibited enhanced evoked discharges, supernumerary discharges, and an increase in the amplitudes and frequencies of spontaneous events. Some spontaneous events were gigantic (10-40 mV), multi-quantal events. Gigantic spontaneous events were eliminated by application of TTX-or by lowered or chelated Ca2+-suggesting that gigantic events were elicited by spontaneous nerve firing. A follow-up genetic approach revealed that some neuronal hyperexcitability phenotypes were reversed after knockdown or mutation of Drosophila homologs of phospholipase Cβ (PLCβ), IP3 receptor, or ryanodine receptor (RyR)-all factors known to mediate Ca2+ release from intracellular stores. Pharmacological inhibitors of intracellular Ca2+ store release produced similar effects. Interestingly, however, the decreased viability phenotype was not reversed by genetic impairment of intracellular Ca2+ release factors. On a cellular level, our data suggest inhibition of signaling that triggers intracellular Ca2+ release could counteract hyperexcitability induced by gains of CaV2.1 function.

Pulmonary neuroendocrine cells amplify allergic asthma responses

Pulmonary neuroendocrine cells (PNECs) are rare airway epithelial cells whose function is poorly understood. Here we show that Ascl1-mutant mice that have no PNECs exhibit severely blunted mucosal type 2 response in models of allergic asthma. PNECs reside in close proximity to group 2 innate lymphoid cells (ILC2s) near airway branch points. PNECs act through calcitonin gene-related peptide (CGRP) to stimulate ILC2s and elicit downstream immune responses. In addition, PNECs act through the neurotransmitter γ-aminobutyric acid (GABA) to induce goblet cell hyperplasia. The instillation of a mixture of CGRP and GABA in Ascl1-mutant airways restores both immune and goblet cell responses. In accordance, lungs from human asthmatics show increased PNECs. These findings demonstrate that the PNEC-ILC2 neuroimmunological modules function at airway branch points to amplify allergic asthma responses.

AMPA receptor GluA1 Ser831 phosphorylation is critical for nitroglycerin-induced migraine-like pain

Migraine is the third most common disease worldwide; however, the mechanisms underlying migraine headache are still not fully understood. Previous studies have demonstrated that α-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid (AMPA) receptor phosphorylation plays an important role in central sensitization of pain transmission. In the present study, we observed that AMPA receptor GluA1 Ser831 phosphorylation was enhanced in the spinal trigeminal nucleus caudalis (Sp5C) after intraperitoneal injection of nitroglycerin (NTG). The NTG injection induced acute migraine-like pain including photophobia and mechanical hypersensitivity as reported previously. Interestingly, targeted mutation of GluA1 Ser831 site to prevent phosphorylation significantly inhibited NTG-induced migraine-like pain. Moreover, NTG incubation caused a robust Ca2+ influx in cultured brainstem neurons, which was dramatically inhibited by GluA1 S831A (serine at the 831 site of GluA1 is mutated to alanine) phospho-deficient mutation, and treatment with 1-naphthyl acetyl spermine (NASPM), a selective Ca2+-permeable AMPA receptor channel blocker, dose-dependently blocked the NTG-evoked increase of Ca2+ influx in the cultured neurons. We further found that intra-Sp5C injection of NASPM significantly inhibited NTG-produced mechanical hypersensitivity. These results suggest that AMPA receptor phosphorylation at the Ser831 site in the Sp5C is critical for NTG-induced migraine-like pain.

A Systems Neuroscience Approach to Migraine

Migraine is an extremely common but poorly understood nervous system disorder. We conceptualize migraine as a disorder of sensory network gain and plasticity, and we propose that this framing makes it amenable to the tools of current systems neuroscience.

Update on the pharmacology of calcitonin/CGRP family of peptides: IUPHAR Review 25

The calcitonin/CGRP family of peptides includes calcitonin, α and β CGRP, amylin, adrenomedullin (AM) and adrenomedullin 2/intermedin (AM2/IMD). Their receptors consist of one of two GPCRs, the calcitonin receptor (CTR) or the calcitonin receptor-like receptor (CLR). Further diversity arises from heterodimerization of these GPCRs with one of three receptor activity-modifying proteins (RAMPs). This gives the CGRP receptor (CLR/RAMP1), the AM₁ and AM₂ receptors (CLR/RAMP2 or RAMP3) and the AMY_1, AMY₂ and AMY₃ receptors (CTR/RAMPs1-3 complexes, respectively). Apart from the CGRP receptor, there are only peptide antagonists widely available for these receptors, and these have limited selectivity, thus defining the function of each receptor in vivo remains challenging. Further challenges arise from the probable co-expression of CTR with the CTR/RAMP complexes and species-dependent splice variants of the CTR (CT_(a) and CT_(b) ). Furthermore, the AMY_1(a) receptor is activated equally well by both amylin and CGRP, and the preferred receptor for AM2/IMD has been unclear. However, there are clear therapeutic rationales for developing agents against the various receptors for these peptides. For example, many agents targeting the CGRP system are in clinical trials, and pramlintide, an amylin analogue, is an approved therapy for insulin-requiring diabetes. This review provides an update on the pharmacology of the calcitonin family of peptides by members of the corresponding subcommittee of the International Union of Basic and Clinical Pharmacology and colleagues.

Soluble guanylyl cyclase is a critical regulator of migraine-associated pain

Background Nitric oxide (NO) has been heavily implicated in migraine. Nitroglycerin is a prototypic NO-donor, and triggers migraine in humans. However, nitroglycerin also induces oxidative/nitrosative stress and is a source of peroxynitrite - factors previously linked with migraine etiology. Soluble guanylyl cyclase (sGC) is the high affinity NO receptor in the body, and the aim of this study was to identify the precise role of sGC in acute and chronic migraine. Methods We developed a novel brain-bioavailable sGC stimulator (VL-102), and tested its hyperalgesic properties in mice. We also determined the effect of VL-102 on c-fos and calcitonin gene related peptide (CGRP) immunoreactivity within the trigeminovascular complex. In addition, we also tested the known sGC inhibitor, ODQ, within the chronic nitroglycerin migraine model. Results VL-102-evoked acute and chronic mechanical cephalic and hind-paw allodynia in a dose-dependent manner, which was blocked by the migraine medications sumatriptan, propranolol, and topiramate. In addition, VL-102 also increased c-fos and CGRP expressing cells within the trigeminovascular complex. Importantly, ODQ completely inhibited acute and chronic hyperalgesia induced by nitroglycerin. ODQ also blocked hyperalgesia already established by chronic nitroglycerin, implicating this pathway in migraine chronicity. Conclusions These results indicate that nitroglycerin causes migraine-related pain through stimulation of the sGC pathway, and that super-activation of this receptor may be an important component for the maintenance of chronic migraine. This work opens the possibility for negative sGC modulators as novel migraine therapies.