Differences in Neuropathology between Nitroglycerin-Induced Mouse Models of Episodic and Chronic Migraine

Multiple animal models of migraine have been used to develop new therapies. Understanding the transition from episodic (EM) to chronic migraine (CM) is crucial. We established models mimicking EM and CM pain and assessed neuropathological differences. EM and CM models were induced with single NTG or multiple injections over 9 days. Mechanical hypersensitivity was assessed. Immunofluorescence utilized c-Fos, NeuN, and Iba1. Proinflammatory and anti-inflammatory markers were analyzed. Neuropeptides (CGRP, VIP, PACAP, and substance P) were assessed. Mechanical thresholds were similar. Notable neuropathological distinctions were observed in Sp5C and ACC. ACC showed increased c-Fos and NeuN expression in CM (p < 0.001) and unchanged in EM. Sp5C had higher c-Fos and NeuN expression in EM (p < 0.001). Iba1 was upregulated in Sp5C of EM and ACC of CM (p < 0.001). Proinflammatory markers were strongly expressed in Sp5C of EM and ACC of CM. CGRP expression was elevated in both regions and was higher in CM. VIP exhibited higher levels in the Sp5C of EM and ACC of CM, whereas PACAP and substance P were expressed in the Sp5C in both models. Despite similar thresholds, distinctive neuropathological differences in Sp5C and ACC between EM and CM models suggest a role in the EM to CM transformation.

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.

Differential actions of indomethacin: clinical relevance in headache

ABSTRACT

Nonsteroidal anti-inflammatory drugs, cyclooxygenase inhibitors, are used routinely in the treatment of primary headache disorders. Indomethacin is unique in its use in the diagnosis and treatment of hemicrania continua and paroxysmal hemicrania. The mechanism of this specific action is not fully understood, although an interaction with nitric oxide (NO) signaling pathways has been suggested. Trigeminovascular neurons were activated by dural electrical stimulation, systemic administration of an NO donor, or local microiontophoresis of L-glutamate. Using electrophysiological techniques, we subsequently recorded the activation of trigeminovascular neurons and their responses to intravenous indomethacin, naproxen, and ibuprofen. Administration of indomethacin (5 mg·kg-1), ibuprofen (30 mg·kg-1), or naproxen (30 mg·kg-1) inhibited dural-evoked firing within the trigeminocervical complex with different temporal profiles. Similarly, both indomethacin and naproxen inhibited L-glutamate-evoked cell firing suggesting a common action. By contrast, only indomethacin was able to inhibit NO-induced firing. The differences in profile of effect of indomethacin may be fundamental to its ability to treat paroxysmal hemicrania and hemicrania continua. The data implicate NO-related signaling as a potential therapeutic approach to these disorders.

PD-L1 and PD-1 expressed in trigeminal ganglia may inhibit pain in an acute migraine model

BACKGROUND

Neurogenic inflammation, mediated by the activation of primary neurons, is thought to be an important factor in migraine pathophysiology. Programmed cell death ligand-1 (PD-L1) can suppress the immune response through the Programmed cell death-1 receptor. However, the role of PD-L1/PD-1 in migraine remains unclear. In this study we evaluated the expression and role of PD-L1/PD-1 in the trigeminal ganglia in an animal model of acute migraine.

METHODS

Acute nitroglycerin induces acute mechanical hyperalgesia that can be used as a readout of migraine-like pain. We investigated the expression of PD-L1 and PD-1 in the trigeminal ganglia in a mouse model by means of immunofluorescence labeling, quantitative reverse transcription-polymerase chain reaction and western blotting. We explored the effects of PD-1 in a migraine model by the von Frey test and by analyzing the expression of calcitonin gene-related peptide, interleukin-1β (IL-1β), interleukin-18 (IL-18), Tumor Necrosis Factor-α (TNF-α), interleukin-6 (IL-6) and transient receptor potential vanilloid (TRPV4) after the intravenous injection of a PD-1 inhibitor.

RESULTS

PD-L1 and PD-1 immunoreactivity were present in healthy trigeminal ganglia neurons. The mRNA levels of PD-L1 and PD-1 were significantly elevated 2 h, 4 h and 6 h after acute nitroglycerin treatment (p < 0.05). The protein levels of PD-L1 were significantly increased 2 h, 4 h and 6 h after treatment, and PD-1 was significantly increased at 2 h and 6 h. The blockade of PD-1 increased acute nitroglycerin-induced hyperalgesia, and this effect was accompanied by a more significant increase in calcitonin gene-related peptide, IL-1β, TNF-α, IL-6 and IL-18 in the trigeminal ganglia.

CONCLUSION

These findings suggest that PD-L1 and PD-1 might inhibit migraine-like pain by downregulating CGRP and inflammatory factors in the trigeminal ganglia. The use of PD-L1 and PD-1 as analgesics should be further studied.

Abnormal cardiovascular response to nitroglycerin in migraine

Introduction

Migraine and vasovagal syncope are comorbid conditions that may share part of their pathophysiology through autonomic control of the systemic circulation. Nitroglycerin can trigger both syncope and migraine attacks, suggesting enhanced systemic sensitivity in migraine. We aimed to determine the cardiovascular responses to nitroglycerin in migraine.

Methods

In 16 women with migraine without aura and 10 age- and gender-matched controls without headache, intravenous nitroglycerin (0.5 µg·kg⁻¹·min⁻¹) was administered. Finger photoplethysmography continuously assessed cardiovascular parameters (mean arterial pressure, heart rate, cardiac output, stroke volume and total peripheral resistance) before, during and after nitroglycerin infusion.

Results

Nitroglycerin provoked a migraine-like attack in 13/16 (81.2%) migraineurs but not in controls (p = .0001). No syncope was provoked. Migraineurs who later developed a migraine-like attack showed different responses in all parameters vs. controls (all p < .001): The decreases in cardiac output and stroke volume were more rapid and longer lasting, heart rate increased, mean arterial pressure and total peripheral resistance were higher and decreased steeply after an initial increase.

Discussion

Migraineurs who developed a migraine-like attack in response to nitroglycerin showed stronger systemic cardiovascular responses compared to non-headache controls. The stronger systemic cardiovascular responses in migraine suggest increased systemic sensitivity to vasodilators, possibly due to insufficient autonomic compensatory mechanisms.

Amplification of glyceryl trinitrate-induced headache features by noxious craniofacial stimuli in pain-free healthy humans

AIM

Glyceryl trinitrate (GTN) provokes an immediate migraine-like headache, followed by a delayed migraine attack in migraineurs. In healthy volunteers, only an immediate, less severe and shorter headache occurs. The presence of an already sensitized nervous system in migraineurs may underlie the more intense and prolonged GTN-evoked headaches. We tested if in healthy humans, application of noxious cutaneous and/or mechanical stimulation within craniofacial region would enhance or prolong GTN-evoked headache.

MATERIALS & METHODS

Noxious stimuli with a capsaicin patch on forehead, a mechanical headband, or both were applied prior to sublingual GTN (0.5 mg) in 20 healthy volunteers. GTN-induced headache characteristics and sensory responsiveness were recorded.

RESULTS

A more intense GTN-evoked headache was produced following application of headband.

CONCLUSION

Noxious mechanical stimulation prior to GTN resulted in a more intense GTN-evoked headache.

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.

Pathophysiology of Migraine: A Disorder of Sensory Processing

Plaguing humans for more than two millennia, manifest on every continent studied, and with more than one billion patients having an attack in any year, migraine stands as the sixth most common cause of disability on the planet. The pathophysiology of migraine has emerged from a historical consideration of the "humors" through mid-20th century distraction of the now defunct Vascular Theory to a clear place as a neurological disorder. It could be said there are three questions: why, how, and when? Why: migraine is largely accepted to be an inherited tendency for the brain to lose control of its inputs. How: the now classical trigeminal durovascular afferent pathway has been explored in laboratory and clinic; interrogated with immunohistochemistry to functional brain imaging to offer a roadmap of the attack. When: migraine attacks emerge due to a disorder of brain sensory processing that itself likely cycles, influenced by genetics and the environment. In the first, premonitory, phase that precedes headache, brain stem and diencephalic systems modulating afferent signals, light-photophobia or sound-phonophobia, begin to dysfunction and eventually to evolve to the pain phase and with time the resolution or postdromal phase. Understanding the biology of migraine through careful bench-based research has led to major classes of therapeutics being identified: triptans, serotonin 5-HT1B/1D receptor agonists; gepants, calcitonin gene-related peptide (CGRP) receptor antagonists; ditans, 5-HT1F receptor agonists, CGRP mechanisms monoclonal antibodies; and glurants, mGlu5 modulators; with the promise of more to come. Investment in understanding migraine has been very successful and leaves us at a new dawn, able to transform its impact on a global scale, as well as understand fundamental aspects of human biology.

Pathophysiology of hypnic headache

Background

Hypnic headache (HH) is a rare primary headache disorder that is characterized by strictly sleep related headache attacks.

Purpose

The underlying pathophysiology of HH is mainly enigmatic but some clinical characteristics such as circadian rhythmicity and caffeine responsiveness may point toward possible underlying mechanisms.

Method

Current studies that deal with the pathophysiology of HH are summarized. Data on cerebral imaging, sleep, electrophysiology studies, effectiveness of drugs, and symptomatic headache types are discussed to illuminate underlying pathophysiologic mechanisms.

Conclusion

HH can be clearly differentiated by its clinical presentation as well as imaging and electrophysiological study results from other primary headaches such as migraine or cluster headache. The underlying pathophysiology is still enigmatic but a hypothalamic involvement seems to be likely.

Characterization of a novel model of chronic migraine

Chronic migraine is a disabling condition that affects hundreds of millions of individuals worldwide. The development of novel migraine treatments has been slow, in part as a result of a lack of predicative animal models. We have developed a new model of chronic migraine involving the use of nitroglycerin (NTG), a known migraine trigger in humans. Chronic intermittent administration of NTG to mice resulted in acute mechanical hyperalgesia with each exposure as well as a progressive and sustained basal hyperalgesia. This chronic basal hyperalgesia occurred in a dose-dependent fashion and persisted for days after cessation of NTG administration. NTG-evoked hyperalgesia was exacerbated by the phosphodiesterase 5 inhibitor sildenafil, also a human migraine trigger, consistent with nitric oxide as a primary mediator of this hyperalgesia. The acute but not the chronic basal hyperalgesia was significantly reduced by the acute migraine therapy sumatriptan, whereas both the acute and chronic hyperalgesia was significantly attenuated by the migraine preventive therapy topiramate. Chronic NTG-induced hyperalgesia is a mouse model that may be useful for the study of mechanisms underlying progression of migraine from an episodic to a chronic disorder, and for the identification and characterization of novel acute and preventive migraine therapies.

Lack of efficacy of the selective iNOS inhibitor GW274150 in prophylaxis of migraine headache

Introduction: This study investigated the efficacy and tolerability of the highly selective iNOS inhibitor GW274150 in prophylaxis of migraine headache.

Subjects and methods: The study was conducted in two parts, each comprising a 4-week baseline period, a 12-week, double-blind, parallel-group treatment period, and a 4-week follow-up period. The study had an adaptive design in that findings of Part 1 of the study were used to inform the conduct of Part 2. Following an interim analysis at the end of Part 1, the trial could be stopped for futility or continued in Part 2 to study the full-dose response or to increase sample size in case initial assumptions had been violated. The primary end-point in both parts of the study was the probability of the occurrence of a migraine headache day during the baseline period and the treatment period.

Results: In Part 1, adult male and female patients with migraine received GW274150 60 mg ( n = 37), 120 mg ( n = 37), or placebo ( n = 38) once daily for 12 weeks. In Part 2, female patients with migraine received GW274150 60 mg ( n = 160) or placebo ( n = 154) once daily for 12 weeks. GW274150 was no more effective than placebo for the primary efficacy end-point or any secondary efficacy end-point in Part 1 or Part 2. GW274150 was generally well tolerated.

Conclusions: GW274150 at doses predicted to inhibit iNOS >80% did not differ from placebo in the prophylaxis of migraine. The results do not support a role of iNOS inhibition in migraine prevention.

Rapid absorption of sumatriptan powder and effects on glyceryl trinitrate model of headache following intranasal delivery using a novel bi-directional device

Objectives

The aim was to investigate the pharmacokinetics of intranasal sumatriptan (administered using a novel bi-directional powder delivery device) and study its effects on quantitative electroencephalography in patients with migraine. The safety profiles of the two formulations were also compared.

Methods

The pharmacokinetics of intranasal sumatriptan (10 mg and 20 mg) administered using a novel breath-actuated bi-directional powder delivery device were compared with subcutaneous sumatriptan (6 mg), along with an investigation of their effects on the electroencephalogram (EEG) following glyceryl trinitrate (GTN) challenge in 12 patients with migraine using a randomized, three-way cross-over design.

Key findings

Following intranasal delivery, median tmax was 20 min with both doses compared with 10 min after the subcutaneous dose. Mean ± SD values for Cmax were 96 ± 25, 11 ± 7 and 16 ± 6 ng/ml for subcutaneous, intranasal 10 mg and intranasal 20 mg formulations, respectively. Values for area under the curve were also lower with the intranasal doses. Intranasal and subcutaneous sumatriptan induced similar EEG changes characterized by reduced theta-power and increased beta-power. The majority of study participants were free of pain according to the headache severity score with all treatments from 15 min through to 8 h post-dose. All treatments were well tolerated and there were no reports of bitter aftertaste after intranasal delivery. Sumatriptan was rapidly absorbed after intranasal administration using the new device. Using the GTN challenge, sumatriptan powder delivered intranasally at a dose of 20 mg by the new device had effects similar to those of subcutaneous sumatriptan on EEG and reported headache pain, despite much lower systemic exposure.

Conclusions

Administration of sumatriptan intranasally at doses of 10 mg and 20 mg by the breath actuated bi-directional powder delivery device results in rapid absorption. Delivery to target sites beyond the nasal valve induced a similar EEG profile to subcutaneous sumatriptan 6 mg and prevented migraine attacks in patients following GTN challenge. Intranasal administration of sumatriptan powder with the breath actuated bi-directional powder delivery device was well tolerated.

Nitric oxide-induced changes in endothelial expression of phosphodiesterases 2, 3, and 5

OBJECTIVE

To investigate nitric oxide (NO)-mediated changes in expression of cyclic nucleotide degrading phosphodiesterases 2A (PDE2A), PDE3B, and PDE5A in human endothelial cells.

BACKGROUND

Nitric oxide induces production of cyclic guanosine monophosphate (cGMP), which along with cyclic adenosine monophosphate (cAMP) is degraded by PDEs. NO donors and selective inhibitors of PDE3 and PDE5 induce migraine-like headache and play a role in endothelial dysfunction during stroke. The current study investigates possible NO modulation of cGMP-related PDEs relevant to headache induction in a cell line containing such PDEs.

METHODS

Real time polymerase chain reaction and Western blots were used to show expression of PDE2A, PDE3B, and PDE5A in a stable cell line of human brain microvascular endothelial cells. Effects of NO on PDE expression were analyzed at specific time intervals after continued DETA NONOate administration.

RESULTS

This study shows the expression of PDE2A, PDE3B, and PDE5A mRNA and PDE3B and PDE5A protein in human cerebral endothelial cells. Long-term DETA NONOate administration induced an immediate mRNA up-regulation of PDE5A (1.9-fold, 0.5 hour), an early peak of PDE2A (1.4-fold, 1 and 2 hours) and later up-regulation of both PDE3B (1.6-fold, 4 hours) and PDE2A (1.7-fold, 8 hours and 1.2-fold after 24 hours). Such changes were, however, not translated into significant changes in protein expression indicating few, if any, functional effects.

CONCLUSIONS

Long-term NO stimulation modulated PDE3 and PDE5 mRNA expression in endothelial cells. However, PDE3 and PDE5 protein levels were unaffected by NO. The presence of PDE3 or PDE5 in endothelial cells indicates that selective inhibitors may have functional effects in such cells. A complex interaction of cGMP and cAMP in response to NO administration may take place if the mRNA translates into active protein. Whether or not this plays a role in the headache mechanisms remains to be investigated.

A human experimental capsaicin model for trigeminal sensitization. Gender-specific differences

Migraine is much more common in women (18%) than in men (6%). Menstrual migraine in female migraineurs also varies from 7 to 19%. The main goals of the present study were (1) to investigate gender specific differences in an experimental capsaicin model of trigeminal sensitization (a proposed mechanism of migraine) and (2) to explore the influence of menstrual cycle phases. Twenty-eight healthy female and male volunteers were studied. Capsaicin (100 microg/0.1 ml) was injected intradermally to the forehead. Pain intensity and distribution together with the visual flare and allodynic area (central sensitization) were assessed for females (during their menstrual and luteal phases) and for males. Pain area significantly changed across the menstrual cycle with 19.2+/-2.0 cm x min at menstrual and 16.4+/-0.9 cm x min at luteal phase (P<0.001). The area was significantly larger in both phases for females compared to males (14.2+/-1.3 cm x min, P<0.0001). Flare area at menstrual phase (69.2+/-4.2 cm(2)) was significantly (P<0.0001) larger than luteal phase (58.6+/-2.1 cm(2)). Females, in both phases, showed larger flare area compared to males (44.9+/-3.6 cm(2), P<0.0001). Area of brush-evoked allodynia was also larger at the menstrual phase compared to the luteal phase (P<0.0001) and males (P<0.0001). A significant difference was found in the capsaicin-evoked pain distribution with a greater response in menstrual phase compared to the luteal phase (P<0.01) and men (P<0.0001). Capsaicin induced trigeminal sensitization and evoked gender specific sensory and vaso-motor responses, with menstruating females generally showing the strongest manifestations. The model may be further applied to explore mechanisms of human trigeminal sensitization.

Glyceryl trinitrate triggers premonitory symptoms in migraineurs

Studying attacks of migraine is considerably hampered by its fundamentally episodic nature. Developing approaches to triggering migraine reliably is important for advancing understanding of the disorder by facilitating its study. Based on the work of the Copenhagen Group we administered an intravenous infusion of 0.5 microg/kg/min glyceryl trinitrate (GTN) to 44 migraineurs, 23 migraine without aura, 21 migraine with aura, and to 12 healthy controls. We sought to characterise the GTN-induced migraine in terms of the clinical features of the attacks and reproducibility of triggering, and included a non-migraine control group for the purpose of comparing any effects to exclude an ordering effect. Of the 44 patients administered GTN, 33 had a migraine attack fulfilling International Headache Society criteria. Thirty-two attacks were of migraine without aura and one of migraine with aura. Twelve patients described typical premonitory symptoms, which have not been previously documented with GTN-induced migraine. A repeat attack was triggered in all subjects but one. In one case a visual aura was also triggered both times. Our study shows that GTN-induced triggering is common in our patients, and remarkably reproducible. The data will facilitate the use of the GTN model in studies requiring extensive planning, such as brain imaging, or where preventive questions are at issue. We also report the first patient with a reproducible GTN-triggered migraine with aura.

Nitric oxide pathway and response to nitroglycerin in cluster headache patients: plasma nitrite and citrulline levels

Nitric oxide (NO) may participate in the mechanisms underlying vascular headaches, such as migraine and cluster headache (CH), by triggering neurogenic inflammation and activation of fibres conveying nociceptive inputs to the trigeminal ganglion. Similarly to migraine, the administration of the NO donor glyceryltrinitrate (GTN) to CH patients is a known model of inducing spontaneous-like attacks. We carried out a GTN test (0.9 mg, sublingually) in 18 patients with episodic CH in active phase and 12 controls. The plasma levels of NO metabolite nitrites (NO2-), after conversion of nitrates to NO2-, were measured spectrophotometrically at baseline, at the maximum intensity of the induced response (or 45 min after GTN in controls), and 120 min after GTN administration. The basal plasma levels of L-citrulline were also assayed in patients and controls using high-performance liquid chromatography. Basal NO2- levels, similar in GTN-responsive patients and controls (48.3 +/- 10.6 and 44.6 +/- 9.5 micromol/l, respectively) were found to be increased significantly at pain peak in patients (76.1 +/- 10.2 micromol/l) and after 45 min in controls (78.2 +/- 9.6 micromol/l) (P < 0.01 vs. respective baseline values), but not after 120 min, without differences between groups. L-citrulline levels in basal conditions showed no differences between groups (patients 64.8 +/- 11.7, controls 67.3 +/- 10.8 micromol/l). These data do not support the presence of a basal hyperactivity of the L-arginine-NO pathway in CH patients. Increased NO production may be of importance in the mechanisms leading to CH attacks, but other factors are likely to render CH patients hyperresponsive to NO, and ultimately to cause the occurrence of pain and associated features.

Somatostatin infusion withdrawal: a study of patients with migraine, cluster headache and healthy volunteers

Migraine and cluster headache are the most common disabling primary headache syndromes and are typically episodic. A reliable method of triggering such headache attacks facilitates the study and treatment of these disorders. There is sufficient clinical and laboratory evidence to suggest that somatostatin withdrawal may be a useful way of triggering headache. We studied 15 subjects, eight migraineurs, four cluster headache sufferers and three healthy controls. Each subject had a standard somatostatin infusion, 250 microg/h for 3.5h. Subjects were followed for 24h post-infusion. Growth hormone was suppressed in each subject demonstrating a biologically active infusion of somatostatin. None of the non-headache sufferers had pain. Seven of eight migraine sufferers had no immediate headache and no delayed headache. One migraineur experienced short lasting headache with no migrainous features. Three of four patients with cluster headache had no significant pain with the infusion, while one had pain after 1h. The results suggest that somatostatin infusion is not a reliable way to produce headache in experimental settings in either migraine or cluster headache. The data do not exclude a role for somatostatinergic mechanisms in primary headache.