Beamline simulations using monochromators with high d-spacing crystals.

Monochromators for synchrotron radiation beamlines typically use perfect crystals for the hard X-ray regime and gratings for soft X-rays. There is an intermediate range, typically 1-3 keV (tender X-rays), which common perfect crystals have difficulties covering and gratings have low efficiency, although some less common crystals with high d-spacing could be suitable. To evaluate the suitability of these crystals for a particular beamline, it is useful to evaluate the crystals' performance using tools such as ray-tracing. However, simulations for double-crystal monochromators are only available for the most used crystals such as Si, Ge or diamond. Here, an upgrade of the SHADOW ray-tracing code and complementary tools in the OASYS suite are presented to simulate high d-spacing crystals with arbitrary, and sometimes complex, structures such as beryl, YB66, muscovite, etc. Isotropic and anisotropic temperature factors are also considered. The YB66 crystal with 1936 atomic sites in the unit cell is simulated, and its applicability for tender X-ray monochromators is discussed in the context of new low-emittance storage rings.

Evaluation of the concomitant use of oral preventive treatments and onabotulinumtoxinA in chronic migraine: the PREVENBOX study.

BACKGROUND AND PURPOSE: OnabotulinumtoxinA is an effective preventive treatment for chronic migraine (CM). In CM, in addition to a reduction in headache frequency, a decreased reliance on oral prophylactics is also indicative of treatment effectiveness. This study aimed to quantify the change in the use of oral prophylactics after treatment with onabotulinumtoxinA in patients with CM. METHODS: This was a retrospective, multicentric, cross-sectional study. Patients with CM (International Classification of Headache Disorders-3beta) that had been treated with onabotulinumtoxinA were enrolled consecutively. We collected parameters related to each patient's pre-treatment situation, as well as their current situation, focusing on frequency and intensity of migraine, number of oral prophylactics and the respective cycle of onabotulinumtoxinA. Univariate and logistic regression analyses were performed. RESULTS: We included 542 patients, 90.0% of whom were taking oral preventive treatments. During treatment with onabotulinumtoxinA, 47.8% withdrew at least one prophylactic and 41.6% stopped using oral prophylactics altogether. Factors associated with a reduction or cessation of oral prophylactics were >50% improvement in frequency and intensity, remission to episodic migraine, use of topiramate as an initial treatment, increased number of infiltrations and shorter chronification period (P < 0.05). The multivariate analysis showed that a chronification period <20 months, more than five cycles of onabotulinumtoxinA, >50% improvement in pain intensity and topiramate as an initial treatment were predictors of a reduction in oral prophylactics (area under the curve, 70.3%; P < 0.001). CONCLUSIONS: Our study demonstrated the efficacy and safety of onabotulinumtoxinA. This treatment reduced the use of oral prophylactics. Withdrawal of oral prophylactics was most likely to occur after five cycles of treatment.

Calcitonin gene-related peptide in migraine: from pathophysiology to treatment.

INTRODUCTION: It has been observed in recent years that levels of such molecules as calcitonin gene-related peptide (CGRP) and, to a lesser extent, the pituitary adenylate cyclase-activating peptide are elevated during migraine attacks and in chronic migraine, both in the cerebrospinal fluid and in the serum. Pharmacological reduction of these proteins is clinically significant, with an improvement in patients' migraines. It therefore seems logical that one of the main lines of migraine research should be based on the role of CGRP in the pathophysiology of this entity. DEVELOPMENT: The Spanish Society of Neurology's Headache Study Group decided to draft this document in order to address the evidence on such important issues as the role of CGRP in the pathophysiology of migraine and the mechanism of action of monoclonal antibodies and gepants; and to critically analyse the results of different studies and the profile of patients eligible for treatment with monoclonal antibodies, and the impact in terms of pharmacoeconomics. CONCLUSIONS: The clinical development of gepants, which are CGRP antagonists, for the acute treatment of migraine attacks, and CGRP ligand and receptor monoclonal antibodies offer promising results for these patients.

Neurophysiological tests and neuroimaging procedures in non-acute headache (2nd edition).

BACKGROUND AND PURPOSE: A large number of instrumental investigations are used in patients with non-acute headache in both research and clinical fields. Although the literature has shown that most of these tools contributed greatly to increasing understanding of the pathogenesis of primary headache, they are of little or no value in the clinical setting. METHODS: This paper provides an update of the 2004 EFNS guidelines and recommendations for the use of neurophysiological tools and neuroimaging procedures in non-acute headache (first edition). Even though the period since the publication of the first edition has seen an increase in the number of published papers dealing with this topic, the updated guidelines contain only minimal changes in the levels of evidence and grades of recommendation. RESULTS: (i) Interictal EEG is not routinely indicated in the diagnostic evaluation of patients with headache. Interictal EEG is, however, indicated if the clinical history suggests a possible diagnosis of epilepsy (differential diagnosis). Ictal EEG could be useful in certain patients suffering from hemiplegic or basilar migraine. (ii) Recording evoked potentials is not recommended for the diagnosis of headache disorders. (iii) There is no evidence warranting recommendation of reflex responses or autonomic tests for the routine clinical examination of patients with headache. (iv) Manual palpation of pericranial muscles, with standardized palpation pressure, can be recommended for subdividing patient groups but not for diagnosis. Pain threshold measurements and EMG are not recommended as clinical diagnostic tests. (v) In adult and pediatric patients with migraine, with no recent change in attack pattern, no history of seizures, and no other focal neurological symptoms or signs, the routine use of neuroimaging is not warranted. In patients with trigeminal autonomic cephalalgia, neuroimaging should be carefully considered and may necessitate additional scanning of intracranial/cervical vasculature and/or the sellar/orbital/(para)nasal region. In patients with atypical headache patterns, a history of seizures and/or focal neurological symptoms or signs, MRI may be indicated. (vi) If attacks can be fully accounted for by the standard headache classification (IHS), a PET or SPECT scan will normally be of no further diagnostic value. Nuclear medical examinations of the cerebral circulation and metabolism can be carried out in subgroups of patients with headache for the diagnosis and evaluation of complications, when patients experience unusually severe attacks or when the quality or severity of attacks has changed. (vii) Transcranial Doppler examination is not helpful in headache diagnosis. CONCLUSION: Although many of the examinations described in the present guidelines are of little or no value in the clinical setting, most of the tools, including thermal pain thresholds and transcranial magnetic stimulation, have considerable potential for differential diagnostic evaluation as well as for the further exploration of headache pathophysiology and the effects of pharmacological treatment.

Document of revision and updating of medication overuse headache (MOH). / Documento de revisión y actualización de la cefalea por uso excesivo de medicación (CUEM).

INTRODUCTION: Medication overuse headache is a secondary headache in which the regular or frequent use of analgesics can increase the frequency of the episodes, causing the transition from episodic to chronic headache. The prevalence of medication overuse headache is approximately 1-2%, with higher rates among women aged 30-50 years and with comorbid psychiatric disorders such as depression or anxiety, or other chronic pain disorders. It is important to be familiar with the management of this disease. To this end, the Spanish Society of Neurology's Headache Study Group has prepared a consensus document addressing this disorder. DEVELOPMENT: These guidelines were prepared by a group of neurologists specialising in headache after a systematic literature review and provides consensus recommendations on the proper management and treatment of medication overuse headache. The treatment of medication overuse headache is often complex, and is based on 4 fundamental pillars: education and information about the condition, preventive treatment, discontinuation of the drug being overused, and treatment for withdrawal symptoms. Follow-up of patients at risk of recurrence is important. CONCLUSIONS: We hope that this document will be useful in daily clinical practice and that it will update and improve understanding of medication overuse headache management.

1st Post-European Headache Federation Meeting: a review of the latest developments presented at the 2020 European Headache Federation Congress. / I Reunión Post-European Headache Federation: revisión de las novedades presentadas en el Congreso de la European Headache Federation de 2020.

INTRODUCTION: After the European Headache Federation (EHF) Congress, renowned Spanish neurologists specialised in migraine presented the most significant latest developments in research in this field at the Post-EHF Meeting. DEVELOPMENT: The main data presented concerning the treatment of chronic and episodic migraine were addressed, with attention paid more specifically to those related to preventive treatments and real-life experience in the management of the disease. An important review was carried out of the new therapeutic targets and the possibilities they offer in terms of understanding the pathophysiology of migraine and its treatment. An update was also presented of the latest developments in the treatment of migraine with fremanezumab, a monoclonal antibody recently authorised by the European Medicines Agency. Participants were also given an update on the latest developments in basic research on the pathology, as well as an overview of the symptoms of migraine and COVID-19. Finally, the repercussions of migraine in terms of its burden on the care and economic resources of the health system were addressed, along with its impact on society. CONCLUSIONS: The meeting summarised the content presented at the 14th EHF Congress, which took place in late June/early July 2020.

TITLE: I Reunión Post-European Headache Federation: revisión de las novedades presentadas en el Congreso de la European Headache Federation de 2020.Introducción. Tras la celebración del congreso de la European Headache Federation (EHF), reconocidos neurólogos españoles expertos en el tratamiento de la migraña expusieron en la Reunión Post-EHF las principales novedades presentadas en el congreso y relacionadas con ese ámbito. Desarrollo. Se abordan los principales datos presentados relacionados con el tratamiento de la migraña crónica y episódica; concretamente, los relacionados con los tratamientos preventivos y la experiencia en vida real en el manejo de la enfermedad. Se hizo una importante revisión de las nuevas dianas terapéuticas y las posibilidades que ofrecen en cuanto al conocimiento de la fisiopatología de la migraña y su tratamiento. Asimismo, se hizo una actualización de las novedades presentadas en el tratamiento de la migraña con fremanezumab, anticuerpo monoclonal recientemente autorizado por la Agencia Europea de Medicamentos. Se hizo una actualización de las novedades en investigación básica en la patología, así como una relación de los síntomas de migraña y COVID-19. Finalmente, se abordaron las implicaciones de la migraña en la carga sanitaria asistencial y económica, y su impacto en la sociedad. Conclusiones. En la reunión se hizo un resumen del contenido presentado en el 14 Congreso de la EHF, que tuvo lugar a finales de junio y principios de julio de 2020.

Migraines with and without aura and their response to preventive therapy with topiramate.

Data from the Prolonged Migraine Prevention (PROMPT) with Topiramate trial were evaluated post hoc to determine whether topiramate could prevent migraine auras, and whether its efficacy in preventing migraine headaches was similar in patients with (MA; n = 269) and without (MoA; n = 542) aura. Migraines and auras were recorded during prospective baseline, 6-month open-label (OL) topiramate and 6-month double-blind (DB), placebo-controlled phases. In the last 28 OL days, migraines without aura and migraine auras decreased by 43.1% and 54.1%, respectively, in MA patients. MoA patients experienced a 44.3% reduction in migraines. In the DB phase, increases in migraines with placebo vs. topiramate were similar to the full study, but were generally not statistically significant, probably due to lack of power in the subgroup analysis. Similarly, there were no statistically significant changes in number of auras between groups. Thus, topiramate appears to reduce migraine auras in parallel with headache reductions, which are similar in patients with and without aura.

Evidence of and experience with the use of onabotulinumtoxinA in trigeminal neuralgia and primary headaches other than chronic migraine. / Evidencia y experiencia del uso de onabotulinumtoxinA en neuralgia del trigémino y cefaleas primarias distintas de la migraña crónica.

INTRODUCTION: In the field of headaches, onabotulinumtoxinA (onabotA) is well established as a treatment for chronic migraine (CM). In recent years, it has been used increasingly to treat other primary headaches (high-frequency episodic migraine, trigeminal-autonomic cephalalgias, nummular headache) and trigeminal neuralgia. As this treatment will progressively be incorporated in the management of these patients, we consider it necessary to reflect, with a fundamentally practical approach, on the possible indications of onabotA, beyond CM, as well as its administration protocol, which will differ according to the type of headache and/or neuralgia. DEVELOPMENT: This consensus document was drafted based on a thorough review and analysis of the existing literature and our own clinical experience. The aim of the document is to serve as guidelines for professionals administering onabotA treatment. The first part will address onabotA's mechanism of action, and reasons for its use in other types of headache, from a physiopathological and clinical perspective. In the second part, we will review the available evidence and studies published in recent years. We will add an "expert recommendation" based on our own clinical experience, showing the best patient profile for this treatment and the most adequate dose and administration protocol. CONCLUSION: Treatment with onabotA should always be individualised and considered in selected patients who have not responded to conventional therapy.

Evidence and experience with onabotulinumtoxinA in chronic migraine: Recommendations for daily clinical practice. / Evidencia y experiencia de bótox en migraña crónica: Recomendaciones para la práctica clínica diaria.

OnabotulinumtoxinA has been demonstrated to be effective as a preventive treatment in patients with chronic migraine (CM). Five years after the approval of onabotulinumtoxinA in Spain, the Headache Study Group of the Spanish Society of Neurology considered it worthwhile to gather a group of experts in treating patients with CM in order to draw up, based on current evidence and our own experience, a series of guidelines aimed at facilitating the use of the drug in daily clinical practice. For this purpose, we posed 12 questions that we ask ourselves as doctors, and which we are also asked by our patients. Each author responded to one question, and the document was then reviewed by everyone. We hope that this review will constitute a practical tool to help neurologists treating patients with CM.

Calcitonin gene-related peptide in migraine: from pathophysiology to treatment. / CGRP en migraña: de la fisiopatología a la terapéutica.

INTRODUCTION: It has been observed in recent years that levels of such molecules as calcitonin gene-related peptide (CGRP) and, to a lesser extent, the pituitary adenylate cyclase-activating peptide are elevated during migraine attacks and in chronic migraine, both in the cerebrospinal fluid and in the serum. Pharmacological reduction of these proteins is clinically significant, with an improvement in patients' migraines. It therefore seems logical that one of the main lines of migraine research should be based on the role of CGRP in the pathophysiology of this entity. DEVELOPMENT: The Spanish Society of Neurology's Headache Study Group decided to draft this document in order to address the evidence on such important issues as the role of CGRP in the pathophysiology of migraine and the mechanism of action of monoclonal antibodies and gepants; and to critically analyse the results of different studies and the profile of patients eligible for treatment with monoclonal antibodies, and the impact in terms of pharmacoeconomics. CONCLUSIONS: The clinical development of gepants, which are CGRP antagonists, for the acute treatment of migraine attacks, and CGRP ligand and receptor monoclonal antibodies offer promising results for these patients.

Evaluation and proposal for optimization of neurophysiological tests in migraine: part 2--neuroimaging and the nitroglycerin test.

Neuroimaging methods have been widely used in headache and migraine research. They have provided invaluable information on brain perfusion, metabolism and structure during and outside of migraine attacks, contributing to an improved understanding of the pathophysiology of the disorder. Human models of migraine attacks are indispensable tools in pathophysiological and therapeutic research. This review of neuroimaging methods and the attack-provoking nitroglycerin test is part an initiative by a task force within the EUROHEAD project (EU Strep LSHM-CT-2004-5044837-Workpackage 9) with the objective of critically evaluating neurophysiological tests used in migraine. The first part, presented in a companion paper, is devoted to electrophysiological methods, this second part to neuroimaging methods such as functional magnetic resonance imaging, positron emission tomography and voxel-based morphometry, as well as the nitroglycerin test. For each of these methods, we summarize the results, analyse the methodological limitations and propose recommendations for improved methodology and standardization of research protocols.

[Functional magnetic resonance imaging of the visual cortex: relation between stimulus intensity and bold response]. / Resonancia magnética funcional de la corteza visual: estudio de las relaciones entre la intensidad del estímulo y la respuesta BOLD.

INTRODUCTION: Visual system is a high interest topic in neuroscience research. The new neuroimaging techniques, such as functional magnetic resonance imaging (fMRI), allow us to quickly improve our knowledge on the visual system using non-invasive methods. This work examines the effect of small changes in the intensity of a visual stimulus over the BOLD response in the visual cortex. AIMS: To perform a detailed analysis of the visual cortex reaction to different intensities of a light source and to verify the ties between the intensity of the visual stimulus and the cortical response. SUBJECTS AND METHODS: Using fMRI (3 T), we registered BOLD response (area and intensity of the signal change) in 20 photophobic patients and 20 controls while viewing different stimulus intensities from a light source. RESULTS: We found a direct relation between stimulus intensity and occipital response. We show that cortical reactivity is higher in patients with photophobia than normal controls, specially for the lower and medium intensities. CONCLUSIONS: fMRI is a valid and robust technique to register consistent and reproducible responses in different groups of subjects. It is useful for the study of normal cortex functioning as well as for clinical use.

Dose distribution from x-ray microbeam arrays applied to radiation therapy: an EGS4 Monte Carlo study.

We present EGS4 Monte Carlo calculations of the spatial distribution of the dose deposited by a single x-ray pencil beam, a planar microbeam, and an array of parallel planar microbeams as used in radiation therapy research. The profiles of the absorbed dose distribution in a phantom, including the peak-to-valley ratio of the dose distribution from microbeam arrays, were calculated at micrometer resolution. We determined the dependence of the findings on the main parameters of photon and electron transport. The results illustrate the dependence of the electron range and the deposited in-beam dose on the cut-off energy, of the electron transport, as well as the effects on the dose profiles of the beam energy, the array size, and the beam spacing. The effect of beam polarization also was studied for a single pencil beam and for an array of parallel planar microbeams. The results show that although the polarization effect on the dose distribution from a 3 cm x 3 cm microbeam array inside a water phantom is large enough to be measured at the outer side of the array (16% difference of the deposited dose for x-ray beams of 200 keV), it is not detectable at the array's center, thus being irrelevant for the radiation therapy purposes. Finally we show that to properly compare the dose profiles determined with a metal oxide semiconductor field emission transistor detector with the computational method predictions, it is important to simulate adequately the size and the material of the device's Si active element.

Functional neuroimaging: enhanced understanding of migraine pathophysiology.

Research into migraine pathophysiology has been hampered by the episodic nature and unpredictable onset of migraine attacks. Recently, newer imaging techniques have been providing noninvasive methods of studying metabolism and hemodynamics in the brains of migraineurs during and between acute attacks. 133Xe blood flow techniques, transcranial Doppler, and SPECT have all been employed to investigate hemodynamic changes during migraine aura. PET has been useful in the study of migraine without aura, with findings of increased blood flow related to pain in cortical areas and in the medial brainstem. Currently, three functional MRI imaging techniques are being used in migraine research. Diffusion-weighted imaging has shown normal findings in measures of the ability of neurons to maintain osmotic gradients. Studies using perfusion-weighted imaging have shown alterations in relative cerebral blood flow (CBF), relative cerebral blood volume, and mean transit time during migraine visual aura. The blood oxygen level-dependent technique can supply information related to neuronal activation during acute migraine aura. MRS has been used with mixed success to look for evidence of abnormal energy metabolism in the brains of migraineurs. Magnetoencephalography studies support the presence of a spreading depression-like phenomenon in migraine with aura. Two groups have used transcranial magnetic stimulation to assess whether neurons in the occipital cortex are hyperexcitable, predisposing patients to develop aura symptoms. Despite conflicting findings, migraine with visual aura appears to be generally associated with transient decreases in regional CBF.

Numular headache: a coin-shaped cephalgia.

Numular headache is a chronic, mild to moderate, pressurelike pain in a circumscribed cranial area of approximately 2 to 6 cm in diameter. Pain usually is limited to the parietal region, although it may appear in any cranial site. It is a benign process of usually unknown origin.

The NMDA receptor antagonist MK-801 reduces capsaicin-induced c-fos expression within rat trigeminal nucleus caudalis.

The effect of the N-methyl-D-aspartate (NMDA) receptor antagonist (5R, 10S)-(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclo-hepten-5,10-i mine hydrogen maleate (MK-801) was examined on c-fos-like immunoreactivity (c-fos-LI) in urethane-anesthetized Sprague-Dawley rats using a polyclonal antibody. C-fos, an indicator of neuronal activation, was assessed within the trigeminal nucleus caudalis (TNC), area postrema. lateral reticular and solitary tract nuclei 2 h after intracisternal injection of capsaicin. C-fos-positive cells were counted at three representative levels corresponding to obex, -2.05 mm and -6.45 mm in 18 tissue sections (50 microm). A weighted average was obtained reflecting total brainstem expression within lamina I, II of TNC using a recently validated method. Capsaicin (0.1, 1, 5, 10 and 15 nmol) caused a dose-dependent labeling of cells in lamina I, II at obex similar to that previously reported after intracisternal blood or carrageenin administration in rats and guinea pigs. MK-801 (0.3, 1 and 3 mg/kg) administered i.p. 30 min before capsaicin (5 nmol in 100 microl artificial CSF) reduced significantly and dose-dependently (12%, 36% and 47%, respectively) the c-fos-LI cells in TNC at each level from rostral to caudal but not in solitary tract, area postrema and lateral reticular nuclei, and for unexplained reasons, increased c-fos-LI within the inferior olive. These results suggest that NMDA receptors provide a potential therapeutic target for cephalic pain (e.g. migraine) due to trigeminovascular activation from meningeal afferents.

Non-NMDA glutamate receptors modulate capsaicin induced c-fos expression within trigeminal nucleus caudalis.

1. We examined the effects of the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)/kainate receptor antagonists 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) and 1,2,3,4-tetrahydro-6-nitro-2,3-dioxo-benzol[f]quinoxaline-7-sulpho namide (NBQX), the kainate receptor antagonists gamma-(R-)-glutamylaminomethanesulphonic acid (GAMS) and 6,7,8,9-tetrahydro-5-nitro-1H-benz[g]indole-2,3-dione-3-oxime (NS-102), and the group III metabotropic glutamate receptor (mGluR) agonist 2-amino-4-phosphono-S-butanoic acid (L-AP4) on c-fos-like immunoreactivity (c-fos LI) in trigeminal caudalis (Sp5C), lateral reticular (LRt), medullary reticular (Md) and solitary tract (Sol) nuclei, after intracisternal injection of capsaicin in urethane anaesthetized Sprague-Dawley rats. 2. Few c-fos labelled cells were observed within Sp5C in capsaicin-vehicle treated animals. The number of positive c-fos cells increased by 17 fold after intracisternal capsaicin (5 nmol) administration. 3. Pretreatment with CNQX (0.02, 0.1, 0.6, 3 and 15 mg kg-1) or NBQX (0.01, 0.1 and 1 mg kg-1), administered intraperitoneally 15 min before capsaicin, significantly reduced labelled cells within Sp5C by a maximum of 45 and 34%, respectively. The number of c-fox LI cells within LRt, Md and Sol was not affected. Pretreatment with L-AP4 (1, 3 and 10 mg kg-1) decreased the number of Sp5C c-fos LI cells by a maximum of 30%, whereas GAMS (1 and 10 mg kg-1) and NS-102 (1 and 5 mg kg-1) did not show any significant effect. 4. These results suggest that blockade of AMPA receptors, but not kainate receptors, or the activation of group III mGluRs, decrease the response of Sp5C neurons to trigeminovascular activation. Thus, in addition to NMDA receptors, mGluRs and AMPA receptors may modulate cephalic pain and may provide a potential therapeutic target for antimigraine drugs.

Both 5-HT1B and 5-HT1F receptors modulate c-fos expression within rat trigeminal nucleus caudalis.

A possible mechanism of action of antimigraine drugs such as sumatriptan is inhibition of the trigeminovascular pathway. Sumatriptan's effects might be mediated by 5-HT1B, 5-HT1D or 5-HT1F receptors. To establish the relative importance of these subtypes, we compared the effects of sumatriptan with those of a selective 5-HT1F receptor agonist (LY 344864) on c-fos protein expression in the trigeminal nucleus caudalis. c-fos expression was induced in urethane-anaesthetized rats by intracisternal capsaicin administration. Sumatriptan and LY 344864 decreased the number of capsaicin-induced c-fos-like immunoreactive cells within trigeminal nucleus caudalis (ID50 = 0.04 and 0.6 mg kg(-1)). The effect of sumatriptan, but not of LY 344864, was prevented by pretreatment with the antagonist SDZ 21-009, which displays high affinity for rat 5-HT1B receptors. LY 344864 appears to attenuate c-fos-like immunoreactivity via 5-HT1F receptors, while sumatriptan acts via 5-HT1B receptors. The fact that activation of 5-HT1F receptors is sufficient to modulate the activity of the trigeminal system suggests that this receptor may be a target for antimigraine drugs with improved safety profile.

High altitude headache. Lessons from headaches at sea level.

There is little known about high altitude headache, except that it is an important and serious problem that often heralds the onset of acute mountain sickness. We do know that the brain itself is an insensate organ except for its meninges which contain sensory axons projecting from the trigeminal nerve. These nerve fibers travel in proximity to meningeal blood vessels and constitute an important component of the trigeminovascular system. Signals generated at high altitude which may activate the trigeminovascular system can arise from brain, blood or the blood vessel wall, include protons, neurotransmitters and other potential noxious agents which can discharge or sensitize small unmyelinated fibers. Brain edema and raised intracranial pressure may cause headache by compressing brain structures leading to displacement and stretching of the pain-sensitive intracranial structures. Small hemorrhage may irritate and discharge these fibers chemically. Furthermore, high altitude seems capable of decreasing the threshold of response to sensory stimulation. Therefore, headache can be attributed to activation of a common pathway, the trigeminovascular system by both chemical or mechanical stimulation.