Activation of 5-HT1B/1D receptor in the periaqueductal gray inhibits nociception

Intervening in the Premonitory Phase to Prevent Migraine: Prospects for Pharmacotherapy

Migraine is a common brain condition characterised by disabling attacks of headache with sensory sensitivities. Despite increasing understanding of migraine neurobiology and the impacts of this on therapeutic developments, there remains a need for treatment options for patients underserved by currently available therapies. The first specific drugs developed to treat migraine acutely, the serotonin-5-hydroxytryptamine [5-HT1B/1D] receptor agonists (triptans), seem to require headache onset in order to have an effect, while early treatment during mild pain before headache escalation improves short-term and long-term outcomes. Some patients find treating in the early window once headache has started but not escalated difficult, and migraine can arise from sleep or in the early hours of the morning, making prompt treatment after pain onset challenging. Triptans may be deemed unsuitable for use in patients with vascular disease and in those of older age and may not be effective in a proportion of patients. Headache is also increasingly recognised as being just one of the many facets of the migraine attack, and for some patients it is not the most disabling symptom. In many patients, painless symptoms can start prior to headache onset and can reliably warn of impending headache. There is, therefore, a need to identify therapeutic targets and agents that may be used as early as possible in the course of the attack, to prevent headache onset before it starts, and to reduce both headache and non-headache related attack burden. Early small studies using domperidone, naratriptan and dihydroergotamine have suggested that this approach could be useful; these studies were methodologically less rigorous than modern day treatment studies, of small sample size, and have not since been replicated. The emergence of novel targeted migraine treatments more recently, specifically calcitonin gene-related peptide (CGRP) receptor antagonists (gepants), has reignited interest in this strategy, with encouraging results. This review summarises historical and emerging data in this area, supporting use of the premonitory phase as an opportunity to intervene as early as possible in migraine to prevent attack-related morbidity.

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

BACKGROUND

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

MAIN BODY

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

CONCLUSION

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

Pharmacological modulation of ventral tegmental area neurons elicits changes in trigeminovascular sensory processing and is accompanied by glycemic changes: Implications for migraine

BACKGROUND

Imaging migraine premonitory studies show increased midbrain activation consistent with the ventral tegmental area, an area involved in pain modulation and hedonic feeding. We investigated ventral tegmental area pharmacological modulation effects on trigeminovascular processing and consequent glycemic levels, which could be involved in appetite changes in susceptible migraine patients.

METHODS

Serotonin and pituitary adenylate cyclase-activating polypeptide receptors immunohistochemistry was performed in ventral tegmental area parabrachial pigmented nucleus of male Sprague Dawley rats. In vivo trigeminocervical complex neuronal responses to dura mater nociceptive electrical stimulation, and facial mechanical stimulation of the ophthalmic dermatome were recorded. Changes in trigeminocervical complex responses following ventral tegmental area parabrachial pigmented nucleus microinjection of glutamate, bicuculline, naratriptan, pituitary adenylate cyclase-activating polypeptide-38 and quinpirole were measured, and blood glucose levels assessed pre- and post-microinjection.

RESULTS

Glutamatergic stimulation of ventral tegmental area parabrachial pigmented nucleus neurons reduced nociceptive and spontaneous trigeminocervical complex neuronal firing. Naratriptan, pituitary adenylate cyclase-activating polypeptide-38 and quinpirole inhibited trigeminovascular spontaneous activity, and trigeminocervical complex neuronal responses to dural-evoked electrical and mechanical noxious stimulation. Trigeminovascular sensory processing through modulation of the ventral tegmental area parabrachial pigmented nucleus resulted in reduced circulating glucose levels.

CONCLUSION

Pharmacological modulation of ventral tegmental area parabrachial pigmented nucleus neurons elicits changes in trigeminovascular sensory processing. The interplay between ventral tegmental area parabrachial pigmented nucleus activity and the sensory processing by the trigeminovascular system may be relevant to understand associated sensory and homeostatic symptoms in susceptible migraine patients.

Sumatriptan prevents central sensitisation specifically in the trigeminal dermatome in humans

BACKGROUND

The exact mechanism and site of action of triptans in aborting migraine attacks remain under debate. We hypothesized that the clinical efficacy of triptans lies in aborting central sensitization and focused on the question of why triptans are headache-specific, i.e. highly effective in migraine and cluster headache and ineffective in extracephalic pain.

METHODS

Forty healthy participants were enrolled in this double-blinded, randomized, placebo-controlled study. The effect of sumatriptan (n=20) vs placebo (n=20) was investigated in a cephalic (V1) vs an extracephalic dermatome (forearm) using a topical capsaicin sensitization model. Capsaicin-induced primary and secondary hyperalgesia were evaluated using quantitative sensory testing.

RESULTS

After capsaicin application, primary hyperalgesia developed in both sumatriptan and placebo groups in both dermatomes. However, sumatriptan exclusively prevented secondary hyperalgesia in the V1 dermatome but not on the forearm. Placebo exerted no effects on secondary hyperalgesia in both trigeminal and extracephalic dermatomes. Additionally, sumatriptan reduced the flare size exclusively in the V1 dermatome.

CONCLUSIONS

Our data suggest that sumatriptan reduces central sensitization (secondary hyperalgesia) without modulating peripheral sensitization (primary hyperalgesia) in a human pain model of capsaicin-induced sensitization. Moreover, despite a systemic administration of sumatriptan, the modulatory effects are trigeminal-specific, echoing the clinical effect of triptans in aborting headaches, but not extracephalic pain.

KCl-induced repetitive cortical spreading depression inhibiting trigeminal neuronal firing is mediated by 5-HT1B/1D and opioid receptors

Background

We aimed to examine the effects of repetitive cortical spreading depression on the responses of nociceptive trigeminal neurons with dural afferents and characterize the role of 5-HT_1B/1D and opioid receptors.

Methods

Trigeminocervical complex neurons (n = 53) responsive to nociceptive activation of the dura mater were studied in rats using electrophysiological techniques.

Results

A sub-population (n = 32) showed an average inhibition of dural-evoked responses of 65 ± 14% from baseline with cortical spreading depression. This response was reversed by the selective 5-HT_1B/1D receptor antagonist, GR127935 (3 mg/kg; n = 6, iv), and a non-selective opioid receptor antagonist, naloxone (1.5 mg/kg; n = 6, iv), five minutes after injection. To determine the role of the nucleus raphe magnus in the trigeminocervical complex inhibitory effect, microinjection of lidocaine (2%, n = 6) or muscimol (100 mM, n = 5) into the nucleus raphe magnus was performed. There was no effect on cortical spreading depression-induced inhibition of neuronal firing in trigeminocervical complex by either.

Conclusion

The data demonstrate that repetitive cortical spreading depression inhibits a subpopulation of dural nociceptive trigeminocervical neurons, an effect mediated by serotonin and opioid receptors. This inhibition does not involve modulation of nucleus raphe magnus neurons.

Overexpression of BDNF in the ventrolateral periaqueductal gray regulates the behavior of epilepsy-migraine comorbid rats

OBJECTIVE

To investigate the effects of brain-derived neurotrophic factor (BDNF) overexpression in the ventrolateral periaqueductal gray (vlPAG) on behavioral changes in epilepsy-migraine comorbid rats.

METHOD

We used an adeno-associated virus (AAV)-mediated vector to supplement BDNF in the vlPAG area prior to the establishment of a pilocarpine-nitroglycerin (Pilo-NTG) combination-induced comorbid model of epilepsy and migraine. Seizure- and migraine-related behaviors were analyzed. Cell loss and apoptosis in vlPAG were detected through hematoxylin-eosin (HE) and TUNEL staining. Immunofluorescence staining analyses were employed to detect expressions of BDNF and its receptor, tyrosine kinase B (TrkB), in vlPAG. Immunohistochemical staining was conducted to detect expressions of c-Fos and calcitonin gene-related peptide (CGRP) in the trigeminal nucleus caudalis (TNC) and trigeminal ganglion (TG).

RESULTS

Comparing to control group, AAV-BDNF injected comorbid group showed lower pain sensitivity, scratching head, and spontaneous seizures accompanied by the downregulation of c-Fos labeling neurons and CGRP immunoreactivity in the TNC and TG. However, these changes were still significantly higher in the comorbid group than those in both epilepsy and migraine groups under the same intervention.

CONCLUSION

These data demonstrated that supplying BDNF to vlPAG may protect structural and functional abnormalities in vlPAG and provide an antiepileptic and analgesic therapy.

Evaluation of Brain Targeting Potential of Zolmitriptan Mucoadhesive Nanoparticles for Intranasal Drug Delivery

BACKGROUND

Hydrophilic drugs are poor applicants of brain targeting via oral route due to the presence of blood-brain barrier that allows only small lipophilic molecules to freely access the brain. Due to unique anatomical connections between the nasal cavity and the brain, intranasal administration can be explored for drug delivery to the brain directly that circumvents blood-brain barrier too.

OBJECTIVES

Zolmitriptan is a widely used antimigraine drug and its brain targeting by nasal route in form of mucoadhesive nanoparticles is more effective in migraine treatment as it provide fast relief and good bioavailability as compared to its oral drug delivery. In the present study zolmitriptan mucoadhesive nanoparticles were prepared to improve the bioavailability and brain targeting for the better management of Migraine attacks.

METHODS

The mucoadhesive polymeric nanoparticles of zolmitriptan were formulated by modified ionic gelation method using thiolated chitosan. The pharmacokinetic parameters were counted in male Wistar rats by intranasal and oral delivery of anti-migraine drug zolmitriptan and compared statistically. The concentration of zolmitriptan in the blood plasma and brain samples was determined by using liquid-liquid extraction method followed by a reversed- phase high performance liquid chromatography (RP-HPLC) analysis. The pharmacodynamic analysis was done in adult male Swiss albino mice by behavioral models, light/dark box model, and acetic acid- induced writhing (abdominal stretching or constriction). These tests were used to reproduce the important associated symptoms of migraine viz. hyperalgesia (nociceptive sensitization) and photophobia for the assessment of the therapeutic potential of intranasal delivery of nanoparticles for anti-migraine activity.

RESULTS

The absolute bioavailability accessed for Zolmitriptan nanoparticles by IN route was found to be very high (193%), suggested that the sufficient amount drug transported by nanoparticles and DTE ratio was calculated 2.8, revealed better nose to brain transport by zolmitriptan nanoparticles as compared to oral delivery in male Wistar rats. A Significant increase in tolerance capacity of animals to bright light and fall in the numbers of stretching in mice suggested that the better management of migraine-associated symptoms by the zolmitriptan nanoparticles.

CONCLUSION

Thus present study confers the significance of nasal drug delivery for brain targeting of zolmitriptan nanoparticles for the treatment of migraine.

Migraine

Migraine is a common, chronic, disorder that is typically characterized by recurrent disabling attacks of headache and accompanying symptoms, including aura. The aetiology is multifactorial with rare monogenic variants. Depression, epilepsy, stroke and myocardial infarction are comorbid diseases. Spreading depolarization probably causes aura and possibly also triggers trigeminal sensory activation, the underlying mechanism for the headache. Despite earlier beliefs, vasodilation is only a secondary phenomenon and vasoconstriction is not essential for antimigraine efficacy. Management includes analgesics or NSAIDs for mild attacks, and, for moderate or severe attacks, triptans or 5HT_1B/1D receptor agonists. Because of cardiovascular safety concerns, unreliable efficacy and tolerability issues, use of ergots to abort attacks has nearly vanished in most countries. CGRP receptor antagonists (gepants) and lasmiditan, a selective 5HT1_F receptor agonist, have emerged as effective acute treatments. Intramuscular onabotulinumtoxinA may be helpful in chronic migraine (migraine on ≥15 days per month) and monoclonal antibodies targeting CGRP or its receptor, as well as two gepants, have proven effective and well tolerated for the preventive treatment of migraine. Several neuromodulation modalities have been approved for acute and/or preventive migraine treatment. The emergence of new treatment targets and therapies illustrates the bright future for migraine management.

Vortioxetine as an analgesic in preclinical inflammatory pain models: Mechanism of action

Vortioxetine is a novel atypical antidepressant with multimodal activity that has recently demonstrated efficacy against neuropathic pain. There is no published data about its analgesic properties in models characterized by peripheral inflammation and consequent pain pathway sensitization, nor data on its mechanism of antinociceptive action. This study aimed to investigate vortioxetine's antinociceptive/antihyperalgesic effects in trigeminal, visceral, and somatic inflammatory pain models, and provide evidence on its mechanism of action in the modulation of trigeminal nociception. Vortioxetine's effects on the nociceptive behavior in orofacial formalin test (OFT) and acetic acid-writhing test in mice and on mechanical hyperalgesia in carrageenan-induced paw inflammation in rats were examined following peroral single administration. The involvement of serotonergic/adrenergic/cholinergic/cannabinoid/adenosine receptors was evaluated in OFT by intraperitoneally treating mice with an appropriate antagonist immediately after vortioxetine application. We used antagonists of 5-HT_1B/1D serotonergic (GR 127935), α₁ -adrenergic (prazosin), α₂ -adrenergic (yohimbine), β₁ -adrenergic (metoprolol), muscarinic (atropine), α₇ nicotinic (methyllycaconitine), CB₁ /CB₂ cannabinoid (AM251 and AM630), and adenosine A₁ (DPCPX) receptors. Vortioxetine dose-dependently reduced pain behavior in OFT and acetic acid writhing test, as well as inflammatory hyperalgesia in paw pressure test. All examined antagonists except prazosin dose-dependently inhibited vortioxetine's antinociceptive effects. In conclusion, vortioxetine exerted analgesic efficacy in trigeminal, visceral, and somatic inflammatory pain. The effect is at least in part mediated by 5-HT_1B/1D serotonergic, α₂ /β₁ -adrenergic, muscarinic and nicotinic cholinergic, CB₁ /CB₂ cannabinoid, and adenosine A₁ receptors. These findings contribute to better understanding of the analgesic effect of vortioxetine and suggest its potential usefulness for inflammatory pain treatment.

The neurobiology of cluster headache

Cluster headache is a primary headache form occurring in paroxysmal excruciatingly severe unilateral head pain attacks usually grouped in periods lasting 1-2months, the cluster periods. A genetic component is suggested by the familial occurrence of the disease but a genetic linkage is yet to be identified. Contemporary activation of trigeminal and cranial parasympathetic systems-the so-called trigemino-parasympathetic reflex-during the headache attacks seem to cause the pain and accompanying oculo-facial autonomic phenomena respectively. At peripheral level, the increased calcitonin gene related peptide (CGRP) plasma levels suggests trigeminal system activation during cluster headache attacks. The temporal pattern of the disease both in terms of circadian rhythmicity and seasonal recurrence has suggested involvement of the hypothalamic biological clock in the pathophysiology of cluster headache. The posterior hypothalamus was investigate as the cluster generator leading to activation of the trigemino-parasympathetic reflex, but the accumulated experience after 20 years of hypothalamic electrical stimulation to treat the condition indicate that this brain region rather acts as pain modulator. Efficacy of monoclonal antibodies to treat episodic cluster headache points to a key role of CGRP in the pathophysiology of the condition.

Cardamonin Modulates Neuropathic Pain through the Possible Involvement of Serotonergic 5-HT1A Receptor Pathway in CCI-Induced Neuropathic Pain Mice Model

Cardamonin, a naturally occurring chalcone isolated from Alpinia species has shown to possess strong anti-inflammatory and anti-nociceptive activities. Previous studies have demonstrated that cardamonin exerts antihyperalgesic and antiallodynic properties in chronic constriction injury (CCI)-induced neuropathic pain animal model. However, the mechanisms underlying cardamonin's effect have yet to be fully understood. The present study aims to investigate the involvement of the serotonergic system in cardamonin induced antihyperalgesic and antiallodynic effects in CCI-induced neuropathic pain mice model. The neuropathic pain symptoms in the CCI mice model were assessed using Hargreaves Plantar test and von-Frey filament test on day 14 post-surgery. Central depletion of serotonin along the descending serotonergic pathway was done using ρ-chlorophenylalanine (PCPA, 100 mg/kg, i.p.), an inhibitor of serotonin synthesis for four consecutive days before cardamonin treatment, and was found to reverse the antihyperalgesic and antiallodynic effect produced by cardamonin. Pretreatment of the mice with several 5-HT receptor subtypes antagonists: methiothepin (5-HT1/6/77 receptor antagonist, 0.1 mg/kg), WAY 100635 (5-HT1A receptor antagonist, 1 mg/kg), isamoltane (5-HT1B receptor antagonist, 2.5 mg/kg), ketanserin (5-HT2A receptor antagonist, 0.3 mg/kg), and ondansetron (5-HT3 receptor antagonist, 0.5 mg/kg) were shown to abolish the effect of cardamonin induced antihyperalgesic and antiallodynic effects. Further evaluation of the 5-HT1A receptor subtype protein expressions reveals that cardamonin significantly upregulated its expression in the brainstem and spinal cord. Our results suggest that the serotonergic pathway is essential for cardamonin to exert its antineuropathic effect in CCI mice through the involvement of the 5-HT1A receptor subtype in the central nervous system.

Evaluation of Patients with Insufficient Efficacy and/or Tolerability to Triptans for the Acute Treatment of Migraine: A Systematic Literature Review

INTRODUCTION

Use of triptans for acute treatment of migraine is associated with insufficient efficacy and/or tolerability in approximately 30-40% of people. We conducted a systematic literature review (SLR) to synthesize definitions, terminology, subsequent treatment outcomes, and characteristics associated with this subpopulation.

METHODS

A comprehensive SLR was conducted to identify studies, published from Jan 1995 to May 2019, which focused on insufficient efficacy and/or tolerability to triptans.

RESULTS

Thirty-five publications were identified, of which 22 described randomized controlled trials and open-label studies, and 13 described observational studies. Across studies, multiple objectives and a high amount of variability in methodologies and outcomes were noted. The most commonly applied measures of efficacy were headache pain freedom and pain relief at 2 h. Ten studies assessed efficacy of switching or optimizing treatment in patients with historical insufficient efficacy or tolerability to previous triptan treatment and demonstrated varying levels of success. Factors associated with increased risk of triptan insufficient efficacy included severe baseline headache severity, photophobia, phonophobia, nausea, and depression.

CONCLUSIONS

Irrespective of the methodology or definition used to identify people with insufficient efficacy and/or tolerability to triptans, study results support the assertion that a high unmet need remains for effective acute treatment of migraine.

A new era for migraine: The role of calcitonin gene-related peptide in the trigeminovascular system

There is a huge improvement in our understanding of migraine pathophysiology in the past decades. The activation of the trigeminovascular system has been proved to play a key role in migraine. Calcitonin gene-related peptide (CGRP) and CGRP receptors are widely distributed in the trigeminovascular system. The CGRP is expressed on the C-fibers, and the CGRP receptors are distributed on the A-δ fibers of the trigeminal ganglion and nerves. Further studies found elevated serum CGRP level during migraine attacks, and infusion of CGRP can trigger migraine-like attacks, provide more direct evidence of the link between CGRP and migraine attack. Based on these findings, several treatment options have been designed for migraine treatment, including CGRP receptor antagonists (gepants) and monoclonal antibodies targeting CGRP or CGRP receptors. The clinical trials show both gepants and monoclonal antibodies are effective for migraine treatment. In this section, we describe the roles of the trigeminovascular system in migraine, the discovery of CGRP, and the CGRP signaling pathway.

Lasmiditan mechanism of action - review of a selective 5-HT1F agonist

Migraine is a leading cause of disability worldwide, but it is still underdiagnosed and undertreated. Research on the pathophysiology of this neurological disease led to the discovery that calcitonin gene-related peptide (CGRP) is a key neuropeptide involved in pain signaling during a migraine attack. CGRP-mediated neuronal sensitization and glutamate-based second- and third-order neuronal signaling may be an important component involved in migraine pain. The activation of several serotonergic receptor subtypes can block the release of CGRP, other neuropeptides, and neurotransmitters, and can relieve the symptoms of migraine. Triptans were the first therapeutics developed for the treatment of migraine, working through serotonin 5-HT1B/1D receptors. The discovery that the serotonin 1F (5-HT1F) receptor was expressed in the human trigeminal ganglion suggested that this receptor subtype may have a role in the treatment of migraine. The 5-HT1F receptor is found on terminals and cell bodies of trigeminal ganglion neurons and can modulate the release of CGRP from these nerves. Unlike 5-HT1B receptors, the activation of 5-HT1F receptors does not cause vasoconstriction.The potency of different serotonergic agonists towards 5-HT1F was correlated in an animal model of migraine (dural plasma protein extravasation model) leading to the development of lasmiditan. Lasmiditan is a newly approved acute treatment for migraine in the United States and is a lipophilic, highly selective 5-HT1F agonist that can cross the blood-brain barrier and act at peripheral nervous system (PNS) and central nervous system (CNS) sites.Lasmiditan activation of CNS-located 5-HT1F receptors (e.g., in the trigeminal nucleus caudalis) could potentially block the release of CGRP and the neurotransmitter glutamate, thus preventing and possibly reversing the development of central sensitization. Activation of 5-HT1F receptors in the thalamus can block secondary central sensitization of this region, which is associated with progression of migraine and extracephalic cutaneous allodynia. The 5-HT1F receptors are also elements of descending pain modulation, presenting another site where lasmiditan may alleviate migraine. There is emerging evidence that mitochondrial dysfunction might be implicated in the pathophysiology of migraine, and that 5-HT1F receptors can promote mitochondrial biogenesis. While the exact mechanism is unknown, evidence suggests that lasmiditan can alleviate migraine through 5-HT1F agonist activity that leads to inhibition of neuropeptide and neurotransmitter release and inhibition of PNS trigeminovascular and CNS pain signaling pathways.

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.

Investigation of apomorphine during sleep in Parkinson's: Improvement in UPDRS Scores

Sleep is responsible for several functions required for homeostasis. REM sleep could be a rearrangement period where limits of certain functions can be moved to a new state of balance. This study proposes that dopaminergic deficit may be responsible for the circadian dysregulation that occur with neurodegeneration and therefore a restitution of REM sleep and an improvement in Parkinson disease’s symptoms can be achieved with the controlled use of dopamine agonists during the night. Twenty parkinsonian patients underwent to a onemonth study of subcutaneous nocturnal apomorphine treatment at the beginning of each REM stage. This therapeutic approach led to a significant benefit for patients in all of the 3 UPDRS scores. The mean change from baseline in the MDS-UPDRS Part I, II and III was significantly greater in the apomorphine vs. placebo group. In the UPDRS Part I total score was 0.8 (95% confidence interval [CI]: 1.612, -0.012) and 3.3 (95% CI: 4.732, 1.867) for the placebo and apomorphine groups, respectively (difference between groups: 2.5, 95% CI: 3.454, 1.545; P = 0.002). For UPDRS Part II total score, the mean change was 1.3 (95% CI: 2.692, - 0.09) and 4.6 (6.916, 2.28). Difference between groups: 3.3, 95% CI: 4.752, 1.847; P = 0.013. In UPDRS Part III was 1.1 (95% CI: 2.425, -0.225) and 5.5 (95% CI: 8.808, 2.191). Difference between groups: 4.4, (95% CI: 6.321, 2.478; P = 0.012). We can conclude that sleep alteration in PD can be improved by stimulation of D2 receptors. The symptomatic benefits obtained due to restoration of REM functions were significant.

Effects of Salmon Calcitonin on the Concentrations of Monoamines in Periaqueductal Gray in Formalin Test

Background:

The receptors of salmon calcitonin, located on certain areas of the brain such as the periaqueductal gray matter, are responsible for pain modulation.

Aims:

The effects of intracerebroventricular injection of salmon calcitonin on the behavioral response to pain and on the levels of monoamines in the periaqueductal gray were explored using a biphasic animal model of pain.

Study Design:

Animal experiment.

Methods:

A total of 45 male rats were divided into four groups (n=6). Salmon calcitonin was injected into the lateral ventricle of the brain (1.5 nmol, with a volume of 5 μL). After 20 min, 2.5% formalin was subcutaneously injected into the right leg claw, and pain behavior was recorded on a numerical basis. At the time of the formalin test, the periaqueductal gray area was microdialized. High-performance liquid chromatography method was used to gauge the levels of monoamines and their metabolites.

Results:

Intracerebroventricular injections of salmon calcitonin resulted in pain reduction in the formalin test (p<0.05). The dialysate concentrations of serotonin, dopamine, norepinephrine, 5-hydroxyindoleacetic acid, 3,4-dihydroxyphenylacetic, and 4-hydroxy-3-methoxyphenylglycol increased in the periaqueductal gray area in different phases of the formalin pain test (p<0.05).

Conclusion:

Salmon calcitonin reduced pain by increasing the concentrations of monoamines and the metabolites derived from them in the periaqueductal gray area.

Neurovascular mechanisms of migraine and cluster headache

Vascular theories of migraine and cluster headache have dominated for many years the pathobiological concept of these disorders. This view is supported by observations that trigeminal activation induces a vascular response and that several vasodilating molecules trigger acute attacks of migraine and cluster headache in susceptible individuals. Over the past 30 years, this rationale has been questioned as it became clear that the actions of some of these molecules, in particular, calcitonin gene-related peptide and pituitary adenylate cyclase-activating peptide, extend far beyond the vasoactive effects, as they possess the ability to modulate nociceptive neuronal activity in several key regions of the trigeminovascular system. These findings have shifted our understanding of these disorders to a primarily neuronal origin with the vascular manifestations being the consequence rather than the origin of trigeminal activation. Nevertheless, the neurovascular component, or coupling, seems to be far more complex than initially thought, being involved in several accompanying features. The review will discuss in detail the anatomical basis and the functional role of the neurovascular mechanisms relevant to migraine and cluster headache.

The influence of rapid eye movement sleep deprivation on nociceptive transmission and the duration of facial allodynia in rats: a behavioral and Fos immunohistochemical study

Background

Disrupted sleep is associated with a reciprocal influence on headaches and is one of the contributing factors in the process of chronicity. The goal of the present study was to investigate the influence of sleep on headaches using animal rapid eye movement (REM) sleep deprivation and supradural capsaicin infusion models.

Method

Sprague-Dawley rats underwent REM sleep deprivation (REMSD) for 96 h. The sensory threshold to mechanical stimuli, assessed by the von Frey monofilament test, was measured during the REMSD period. Additionally, the Fos protein expression level was measured in the trigeminocervical complex, periaqueductal gray, and hypothalamus. Following supradural infusion of capsaicin, we evaluated the duration of facial allodynia for 28 days after REMSD.

Results

After REMSD, the sensory threshold to mechanical stimuli was significantly decreased (p < 0.01) and Fos-positivity in the posterior (p = 0.010) and dorsomedial hypothalamus (p = 0.024), ventrolateral periaqueductal gray (p = 0.016), and superficial layer of the trigeminocervical complex (p = 0.019) were significantly increased. The duration of facial allodynia induced by supradural capsaicin infusion was significantly longer in the REM sleep deprivation and capsaicin infusion group (Day 10 PSD vs. Day 25 PSD).

Conclusion

The present study demonstrates that REM sleep deprivation increased nociceptive transmission from trigeminal nerve endings. Furthermore, it suggests that sleep deprivation may contribute to the chronicity of facial allodynia.

Periaqueductal gray and emotions: the complexity of the problem and the light at the end of the tunnel, the magnetic resonance imaging

The periaqueductal gray (PAG) is less referred in relationship with emotions than other parts of the brain (e.g. cortex, thalamus, amygdala), most probably because of the difficulty to reach and manipulate this small and deeply lying structure. After defining how to evaluate emotions, we have reviewed the literature and summarized data of the PAG contribution to the feeling of emotions focusing on the behavioral and neurochemical considerations. In humans, emotions can be characterized by three main domains: the physiological changes, the communicative expressions, and the subjective experiences. In animals, the physiological changes can mainly be studied. Indeed, early studies have considered the PAG as an important center of the emotions-related autonomic and motoric processes. However, in vivo imaging have changed our view by highlighting the PAG as a significant player in emotions-related cognitive processes. The PAG lies on the crossroad of networks important in the regulation of emotions and therefore it should not be neglected. In vivo imaging represents a good tool for studying this structure in living organism and may reveal new information about its role beyond its importance in the neurovegetative regulation.

Brain structure and function related to headache: Brainstem structure and function in headache

OBJECTIVE

To review and discuss the literature relevant to the role of brainstem structure and function in headache.

BACKGROUND

Primary headache disorders, such as migraine and cluster headache, are considered disorders of the brain. As well as head-related pain, these headache disorders are also associated with other neurological symptoms, such as those related to sensory, homeostatic, autonomic, cognitive and affective processing that can all occur before, during or even after headache has ceased. Many imaging studies demonstrate activation in brainstem areas that appear specifically associated with headache disorders, especially migraine, which may be related to the mechanisms of many of these symptoms. This is further supported by preclinical studies, which demonstrate that modulation of specific brainstem nuclei alters sensory processing relevant to these symptoms, including headache, cranial autonomic responses and homeostatic mechanisms.

REVIEW FOCUS

This review will specifically focus on the role of brainstem structures relevant to primary headaches, including medullary, pontine, and midbrain, and describe their functional role and how they relate to mechanisms of primary headaches, especially migraine.

Is selective 5-HT1F receptor agonism an entity apart from that of the triptans in antimigraine therapy?

Migraine is a neurovascular disorder that involves activation of the trigeminovascular system and cranial vasodilation mediated by release of calcitonin gene-related peptide (CGRP). The gold standard for acute migraine treatment are the triptans, 5-HT1B/1D/(1F) receptor agonists. Their actions are thought to be mediated through activation of: (i) 5-HT1B receptors in cranial blood vessels with subsequent cranial vasoconstriction; (ii) prejunctional 5-HT1D receptors on trigeminal fibers that inhibit trigeminal CGRP release; and (iii) 5-HT1B/1D/1F receptors in central nervous system involved in (anti)nociceptive modulation. Unfortunately, coronary arteries also express 5-HT1B receptors whose activation would produce coronary vasoconstriction; hence, triptans are contraindicated in patients with cardiovascular disease. In addition, since migraineurs have an increased cardiovascular risk, it is important to develop antimigraine drugs devoid of vascular (side) effects. Ditans, here defined as selective 5-HT1F receptor agonists, were developed on the basis that most of the triptans activate trigeminal 5-HT1F receptors, which may explain part of the triptans' antimigraine action. Amongst the ditans, lasmiditan: (i) fails to constrict human coronary arteries; and (ii) is effective for the acute treatment of migraine in preliminary Phase III clinical trials. Admittedly, the exact site of action is still unknown, but lasmiditan possess a high lipophilicity, which suggests a direct action on the central descending antinociceptive pathways. Furthermore, since 5-HT1F receptors are located on trigeminal fibers, they could modulate CGRP release. This review will be particularly focussed on the similarities and differences between the triptans and the ditans, their proposed sites of action, side effects and their cardiovascular risk profile.

Cluster headache

Cluster headache is an excruciating, strictly one-sided pain syndrome with attacks that last between 15 minutes and 180 minutes and that are accompanied by marked ipsilateral cranial autonomic symptoms, such as lacrimation and conjunctival injection. The pain is so severe that female patients describe each attack as worse than childbirth. The past decade has seen remarkable progress in the understanding of the pathophysiological background of cluster headache and has implicated the brain, particularly the hypothalamus, as the generator of both the pain and the autonomic symptoms. Anatomical connections between the hypothalamus and the trigeminovascular system, as well as the parasympathetic nervous system, have also been implicated in cluster headache pathophysiology. The diagnosis of cluster headache involves excluding other primary headaches and secondary headaches and is based primarily on the patient's symptoms. Remarkable progress has been achieved in developing effective treatment options for single cluster attacks and in developing preventive measures, which include pharmacological therapies and neuromodulation.

The role of the brainstem in migraine: Potential brainstem effects of CGRP and CGRP receptor activation in animal models

Background

Migraine is a severe debilitating disorder of the brain that is ranked as the sixth most disabling disorder globally, with respect to disability adjusted life years, and there remains a significant unmet demand for an improved understanding of its underlying mechanisms. In conjunction with perturbed sensory processing, migraine sufferers often present with diverse neurological manifestations (premonitory symptoms) that highlight potential brainstem involvement. Thus, as the field moves away from the view of migraine as a consequence of purely vasodilation to a greater understanding of migraine as a complex brain disorder, it is critical to consider the underlying physiology and pharmacology of key neural networks likely involved.

Discussion

The current review will therefore focus on the available evidence for the brainstem as a key regulator of migraine biology and associated symptoms. We will further discuss the potential role of CGRP in the brainstem and its modulation for migraine therapy, given the emergence of targeted CGRP small molecule and monoclonal antibody therapies.

Conclusion

The brainstem forms a functional unit with several hypothalamic nuclei that are capable of modulating diverse functions including migraine-relevant trigeminal pain processing, appetite and arousal regulatory networks. As such, the brainstem has emerged as a key regulator of migraine and is appropriately considered as a potential therapeutic target. While currently available CGRP targeted therapies have limited blood brain barrier penetrability, the expression of CGRP and its receptors in several key brainstem nuclei and the demonstration of brainstem effects of CGRP modulation highlight the significant potential for the development of CNS penetrant molecules.

Anti-migraine effect of ∆9-tetrahydrocannabinol in the female rat

Current anti-migraine treatments have limited efficacy and many side effects. Although anecdotal evidence suggests that marijuana is useful for migraine, this hypothesis has not been tested in a controlled experiment. Thus, the present study tested whether administration of ∆⁹-tetrahydrocannabinol (THC) produces anti-migraine effects in the female rat. Microinjection of the TRPA1 agonist allyl isothiocyanate (AITC) onto the dura mater produced migraine-like pain for 3h as measured by depression of home cage wheel running. Concurrent systemic administration of 0.32 but not 0.1mg/kg of THC prevented AITC-induced depression of wheel running. However, 0.32mg/kg was ineffective when administered 90min after AITC. Administration of a higher dose of THC (1.0mg/kg) depressed wheel running whether rats were injected with AITC or not. Administration of a CB₁, but not a CB₂, receptor antagonist attenuated the anti-migraine effect of THC. These data suggest that: 1) THC reduces migraine-like pain when administered at the right dose (0.32mg/kg) and time (immediately after AITC); 2) THC's anti-migraine effect is mediated by CB₁ receptors; and 3) Wheel running is an effective method to assess migraine treatments because only treatments producing antinociception without disruptive side effects will restore normal activity. These findings support anecdotal evidence for the use of cannabinoids as a treatment for migraine in humans and implicate the CB₁ receptor as a therapeutic target for migraine.

Facial presentations of primary headache disorders

Background

Many patients with mid-face or lower face craniofacial pain are diagnosed, based on accompanying signs and symptoms and features other than location, as either atypical migraines or atypical TACs. Distinguishing features of headache disorders as a cause of facial pain include the temporal pattern of pain, associated symptoms including light and sound sensitivity and nausea, cranial autonomic symptoms, and the lack of local triggering among others.

Results

An intraoral neurovascular pain has been observed, and was termed neurovascular orofacial pain (NVOP). Due to its location, and signs imitating dental pulpitis, it has great diagnostic and therapeutic importance for differentiating NVOP from dental pathology. The hypothesized mechanism is neurogenic inflammatory activation within the space confined by dentine around the dental pulp, expressed in strong paroxysmal pain and typical allodynia to cold foods.

Conclusion

Facial manifestations of headache disorders and primary facial pain disorders share common trigeminal nerve input, yet they are highly distinct disorders. Somatotopic segregation may occur at the level of the trigeminal nucleus, thalamus, and somatosensory cortex, and distinct ionic or neurochemical signaling pathways may be involved. Further investigation of facial presentations of headache disorders has the potential to provide new insight into the interface between headache and facial pain.

Current and novel insights into the neurophysiology of migraine and its implications for therapeutics

Migraine headache and its associated symptoms have plagued humans for two millennia. It is manifest throughout the world, and affects more than 1/6 of the global population. It is the most common brain disorder, and is characterized by moderate to severe unilateral headache that is accompanied by vomiting, nausea, photophobia, phonophobia, and other hypersensitive symptoms of the senses. While there is still a clear lack of understanding of its neurophysiology, it is beginning to be understood, and it seems to suggest migraine is a disorder of brain sensory processing, characterized by a generalized neuronal hyperexcitability. The complex symptomatology of migraine indicates that multiple neuronal systems are involved, including brainstem and diencephalic systems, which function abnormally, resulting in premonitory symptoms, ultimately evolving to affect the dural trigeminovascular system, and the pain phase of migraine. The migraineur also seems to be particularly sensitive to fluctuations in homeostasis, such as sleep, feeding and stress, reflecting the abnormality of functioning in these brainstem and diencephalic systems. Implications for therapeutic development have grown out of our understanding of migraine neurophysiology, leading to major drug classes, such as triptans, calcitonin gene-related peptide receptor antagonists, and 5-HT1F receptor agonists, as well as neuromodulatory approaches, with the promise of more to come. The present review will discuss the current understanding of the neurophysiology of migraine, particularly migraine headache, and novel insights into the complex neural networks responsible for associated neurological symptoms, and how interaction of these networks with migraine pain pathways has implications for the development of novel therapeutics.

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.

Multivariate Optimization of Rizatriptan Benzoate-Loaded Solid Lipid Nanoparticles for Brain Targeting and Migraine Management

The present investigation aimed at development of brain-targeted rizatriptan benzoate-loaded solid lipid nanoparticles (RB-SLNs) by design of experiment, for improvement of its anti-migraine potential. Several formulation variables affecting the fabrication of RB-SLNs were screened using the Plackett-Burman design (PBD). The PBD results demonstrated lipid (Precirol® ATO 5) concentration, co-surfactant (Phospholipon® 90 H) concentration and temperature of lipid melt to be the critical variables, having a significant effect on the achievement of minimum particle size, maximum entrapment efficiency coupled with sustained drug release. The interactions between these formulation parameters and the variability between the batches were further explored employing the Box-Behnken design (BBD). The BBD results were validated by fabricating the suggested optimized solution, which yielded 220.4 ± 2.3 nm particle size with a sufficiently high entrapment efficiency of 71.8 ± 1.9% and 45.9 ± 2.7% cumulative drug release in 8 h. The optimized formulation was, thereafter, characterized by FTIR spectroscopy, wide angle XRD, thermal analysis and TEM imaging technique. The in vivo studies revealed the brain uptake potential of optimized RB-SLNs to be 18.43-folds higher with respect to the pure drug in its free form, post 2 h of oral drug administration. The significant anti-migraine efficacy of RB-SLNs was corroborated through the pharmacodynamic studies on adult male Swiss albino mice. The results hence explicate that RB-SLNs have distinctly improved brain target ability and offer an apt approach for the efficient therapeutic management of migraine.

Advances in the understanding of cluster headache

INTRODUCTION

Cluster headache is the worst primary headache form; it occurs in paroxysmal excruciatingly severe unilateral head pain attacks usually grouped in cluster periods. The familial occurrence of the disease indicates a genetic component but a gene abnormality is yet to be disclosed. Activation of trigeminal afferents and cranial parasympathetic efferents, the so-called trigemino-parasympathetic reflex, can explain pain and accompanying oculo-facial autonomic phenomena. In particular, pain in cluster headache is attributed, at least in part, to the increased CGRP plasma levels released by activated trigeminal system. Posterior hypothalamus was hypothesized to be the cluster generator activating the trigemino-parasympathetic reflex. Efficacy of monoclonal antibodies against CRGP is under investigation in randomized clinical trials. Areas covered: This paper will focus on main findings contributing to consider cluster headache as a neurovascular disorder with an origin from within the brain. Expert commentary: Accumulated evidence with hypothalamic stimulation in cluster headache patients indicate that posterior hypothalamus terminates rather than triggers the attacks. More extensive studies on the genetics of cluster headache are necessary to disclose anomalies behind the increased familial risk of the disease. Results from ongoing clinical trials in cluster headache sufferers using monoclonal antibodies against CGRP will open soon a new era.

Serotonergic mechanisms in the migraine brain - a systematic review

Background Migraine is one of the most common and disabling of all medical conditions, affecting 16% of the general population, causing huge socioeconomic costs globally. Current available treatment options are inadequate. Serotonin is a key molecule in the neurobiology of migraine, but the exact role of brain serotonergic mechanisms remains a matter of controversy. Methods We systematically searched PubMed for studies investigating the serotonergic system in the migraine brain by either molecular neuroimaging or electrophysiological methods. Results The literature search resulted in 59 papers, of which 13 were eligible for review. The reviewed papers collectively support the notion that migraine patients have alterations in serotonergic neurotransmission. Most likely, migraine patients have a low cerebral serotonin level between attacks, which elevates during a migraine attack. Conclusion This review suggests that novel methods of investigating the serotonergic system in the migraine brain are warranted. Uncovering the serotonergic mechanisms in migraine pathophysiology could prove useful for the development of future migraine drugs.

Serotonin and Migraine: Biology and Clinical Implications

Migraine is the most frequent neurological disorder in the adult population worldwide, affecting up to 12% of the general population and more frequent in women (~25%). It has a high impact on our society due to its disabling nature and, therein, reduced quality of life and increased absenteeism from work. Headache is the primary clinical manifestation and it has been associated with ‘a hereditary or predisposed sensitivity of neurovascular reactions to certain stimuli or to cyclic changes in the central nervous system’ (1). Amongst the many neurotransmitters in the brain, the serotonergic (serotonin, 5-HT) system from the brainstem raphe nucleus has been most convincingly implicated in migraine pathophysiology. The documented changes in 5-HT metabolism and in the processing of central 5-HT-mediated responses during and in between migraine attacks have led to the suggestion that migraine is a consequence of a central neurochemical imbalance that involves a low serotonergic disposition. Although the exact cascade of events that link abnormal serotonergic neurotransmission to the manifestation of head pain and the accompanying symptoms has yet to be fully understood, recent evidence suggests that a low 5-HT state facilitates activation of the trigeminovascular nociceptive pathway, as induced by cortical spreading depression. In this short review, we present and discuss the original and most recent findings that support a role for altered serotonergic neurotransmission in the manifestation of migraine headache.

Migraine with brainstem aura presenting as recurrent hypersomnia (Kleine-Levin syndrome)

Recurrent hypersomnia, or Kleine-Levin syndrome, is rare and frequently causes substantial diagnostic anxiety and delay. Patients often undergo multiple investigations to rule out other causes of encephalopathy. The treatment options are unsatisfactory. Migraine with brainstem aura has not previously been widely considered in the medical literature as a differential diagnosis. We describe two patients referred to a tertiary sleep neurology service with a putative diagnosis of Kleine-Levin syndrome. Each described attacks of hypersomnia with elements of migraine with brainstem aura, in addition to having a history of migraine with aura. Simple acute migraine treatment clearly attenuated further attacks. These cases generate discussion as to the common features and potential mechanisms underlying both disorders. Furthermore, they highlight a hitherto underexplored alternative diagnosis of Kleine-Levin syndrome. This provides scope for offering established and effective migraine treatment options to patients who with a potential misdiagnosis of Kleine-Levin syndrome, providing scope for offering established and effective migraine treatment to some patients originally diagnosed with a rare condition for which there is no current consistently effective therapeutic options.

Ictal lack of binding to brain parenchyma suggests integrity of the blood-brain barrier for 11C-dihydroergotamine during glyceryl trinitrate-induced migraine

See Dreier (doi: 10.1093/aww112 ) for a scientific commentary on this article.

For many decades a breakdown of the blood–brain barrier has been postulated to occur in migraine. Hypothetically this would facilitate access of medications, such as dihydroergotamine or triptans, to the brain despite physical properties otherwise restricting their entry. We studied the permeability of the blood–brain barrier in six migraineurs and six control subjects at rest and during acute glyceryl trinitrate-induced migraine attacks using positron emission tomography with the novel radioligand ¹¹ C-dihydroergotamine, which is chemically identical to pharmacologically active dihydroergotamine. The influx rate constant K _i , average dynamic image and time activity curve were assessed using arterial blood sampling and served as measures for receptor binding and thus blood–brain barrier penetration. At rest, there was binding of ¹¹ C-dihydroergotamine in the choroid plexus, pituitary gland, and venous sinuses as expected from the pharmacology of dihydroergotamine. However, there was no binding to the brain parenchyma, including the hippocampus, the area with the highest density of the highest-affinity dihydroergotamine receptors, and the raphe nuclei, a postulated brainstem site of action during migraine, suggesting that dihydroergotamine is not able to cross the blood–brain barrier. This binding pattern was identical in migraineurs during glyceryl trinitrate-induced migraine attacks as well as in matched control subjects. We conclude that ¹¹ C-dihydroergotamine is unable to cross the blood–brain barrier interictally or ictally demonstrating that the blood–brain barrier remains tight for dihydroergotamine during acute glyceryl trinitrate-induced migraine attacks.

Mechanisms mediating nitroglycerin-induced delayed-onset hyperalgesia in the rat

Nitroglycerin (glycerol trinitrate, GTN) induces headache in migraineurs, an effect that has been used both diagnostically and in the study of the pathophysiology of this neurovascular pain syndrome. An important feature of this headache is a delay from the administration of GTN to headache onset that, because of GTN's very rapid metabolism, cannot be due to its pharmacokinetic profile. It has recently been suggested that activation of perivascular mast cells, which has been implicated in the pathophysiology of migraine, may contribute to this delay. We reported that hyperalgesia induced by intradermal GTN has a delay to onset of ∼ 30 min in male and ∼ 45 min in female rats. This hyperalgesia was greater in females, was prevented by pretreatment with the anti-migraine drug, sumatriptan, as well as by chronic pretreatment with the mast cell degranulator, compound 48/80. The acute administration of GTN and compound 48/80 both induced hyperalgesia that was prevented by pretreatment with octoxynol-9, which attenuates endothelial function, suggesting that GTN and mast cell-mediated hyperalgesia are endothelial cell-dependent. Furthermore, A-317491, a P2X3 antagonist, which inhibits endothelial cell-dependent hyperalgesia, also prevents GTN and mast cell-mediated hyperalgesia. We conclude that delayed-onset mechanical hyperalgesia induced by GTN is mediated by activation of mast cells, which in turn release mediators that stimulate endothelial cells to release ATP, to act on P2X3, a ligand-gated ion channel, in perivascular nociceptors. A role of the mast and endothelial cell in GTN-induced hyperalgesia suggests potential novel risk factors and targets for the treatment of migraine.

Primary Headache Disorders: Focus on Migraine

Migraine is the most common disabling headache disorder.Most patients with disabling tension-type headache are likely to have migraine and accordingly respond to treatments efficacious in migraine.Individuals are genetically predisposed to experiencing recurrent migraine.Evidence supports migraine to be a primarily neural and not vascular mediated disorder.1-2% of the population have chronic daily headache associated with acute-relief medication overuse; the majority are migraineurs.The presence of acute-relief medication overuse renders preventative medication less adequately efficacious.

Comprehensive Review of Medicinal Marijuana, Cannabinoids, and Therapeutic Implications in Medicine and Headache: What a Long Strange Trip It's Been …

BACKGROUND

The use of cannabis, or marijuana, for medicinal purposes is deeply rooted though history, dating back to ancient times. It once held a prominent position in the history of medicine, recommended by many eminent physicians for numerous diseases, particularly headache and migraine. Through the decades, this plant has taken a fascinating journey from a legal and frequently prescribed status to illegal, driven by political and social factors rather than by science. However, with an abundance of growing support for its multitude of medicinal uses, the misguided stigma of cannabis is fading, and there has been a dramatic push for legalizing medicinal cannabis and research. Almost half of the United States has now legalized medicinal cannabis, several states have legalized recreational use, and others have legalized cannabidiol-only use, which is one of many therapeutic cannabinoids extracted from cannabis. Physicians need to be educated on the history, pharmacology, clinical indications, and proper clinical use of cannabis, as patients will inevitably inquire about it for many diseases, including chronic pain and headache disorders for which there is some intriguing supportive evidence.

OBJECTIVE

To review the history of medicinal cannabis use, discuss the pharmacology and physiology of the endocannabinoid system and cannabis-derived cannabinoids, perform a comprehensive literature review of the clinical uses of medicinal cannabis and cannabinoids with a focus on migraine and other headache disorders, and outline general clinical practice guidelines.

CONCLUSION

The literature suggests that the medicinal use of cannabis may have a therapeutic role for a multitude of diseases, particularly chronic pain disorders including headache. Supporting literature suggests a role for medicinal cannabis and cannabinoids in several types of headache disorders including migraine and cluster headache, although it is primarily limited to case based, anecdotal, or laboratory-based scientific research. Cannabis contains an extensive number of pharmacological and biochemical compounds, of which only a minority are understood, so many potential therapeutic uses likely remain undiscovered. Cannabinoids appear to modulate and interact at many pathways inherent to migraine, triptan mechanisms ofaction, and opiate pathways, suggesting potential synergistic or similar benefits. Modulation of the endocannabinoid system through agonism or antagonism of its receptors, targeting its metabolic pathways, or combining cannabinoids with other analgesics for synergistic effects, may provide the foundation for many new classes of medications. Despite the limited evidence and research suggesting a role for cannabis and cannabinoids in some headache disorders, randomized clinical trials are lacking and necessary for confirmation and further evaluation.

Periaqueductal gray calcitonin gene-related peptide modulates trigeminovascular neurons

Background

Calcitonin gene-related peptide (CGRP) receptor antagonism is an approach to migraine therapy. The locus of action of antimigraine treatment is not resolved. The objective was to investigate CGRP receptors in the ventrolateral periaqueductal gray (vlPAG) involved in the modulation of trigeminovascular nociception by descending influences on neurotransmission.

Methods

The presence of calcitonin receptor-like receptor (CLR) and receptor activity modifying protein 1 (RAMP1), which form functional CGRP receptors, was investigated. CGRP and its receptor antagonists, olcegepant and CGRP ( 8 – 37 ), were microinjected into the vlPAG while changes of neural responses in the trigeminocervical complex (TCC) were monitored.

Results

Immunoreactivity indicated the presence of functional CGRP receptor components in the vlPAG and adjacent mesencephalic trigeminal nucleus. Inhibition of TCC responses to stimulation of dural afferents and ophthalmic cutaneous receptive fields after microinjection of bicuculline into vlPAG indicated a connection between the vlPAG and TCC neurons. CGRP facilitated these TCC responses, whereas olcegepant and CGRP ( 8 – 37 ) decreased them.

Conclusions

CGRP and its receptor antagonists act on neurons in the region of vlPAG to influence nociceptive transmission in the TCC. This suggests CGRP receptor antagonists may act at loci outside of the TCC and reinforces the concept of migraine as a disorder of the brain.

Inhibitory effect of chronic oral treatment with fluoxetine on capsaicin-induced external carotid vasodilatation in anaesthetised dogs

Background

During migraine, capsaicin-sensitive trigeminal sensory nerves release calcitonin gene-related peptide (CGRP), resulting in cranial vasodilatation and central nociception. Moreover, 5-HT is involved in the pathophysiology of migraine and depression. Interestingly, some limited lines of evidence suggest that fluoxetine may be effective in migraine prophylaxis, but the underlying mechanisms are uncertain. Hence, this study investigated the canine external carotid vasodilator responses to capsaicin, α-CGRP and acetylcholine before and after acute and chronic oral treatment with fluoxetine.

Methods

Forty-eight vagosympathectomised male mongrel dogs were prepared to measure blood pressure, heart rate and external carotid blood flow. The thyroid artery was cannulated for infusions of agonists. In 16 of these dogs, a spinal cannula was inserted (C1–C3) for infusions of 5-HT.

Results

The external carotid vasodilator responses to capsaicin, α-CGRP and acetylcholine remained unaffected after intracarotid or i.v. fluoxetine. In contrast, the vasodilator responses to capsaicin, but not those to α-CGRP or acetylcholine, were inhibited after chronic oral treatment with fluoxetine (300 µg/kg; for 90 days) or intrathecal 5-HT.

Conclusions

Chronic oral fluoxetine inhibited capsaicin-induced external carotid vasodilatation, and this inhibition could partly explain its potential prophylactic antimigraine action.