Brainstem activation specific to migraine headache

CADASIL and migraine: A narrative review

Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is caused by mutations in the NOTCH3 gene and is clinically characterized by recurrent stroke, cognitive decline, psychiatric disturbances and migraine. The prevalence of migraine in CADASIL is slightly higher than in the general population, and the proportion of migraine with aura is much higher. The pathophysiological mechanism that leads to increased aura prevalence in CADASIL is unknown. Possible mechanisms of the excess of migraine with aura are an increased susceptibility to cortical spreading depression (CSD) or a different expression of CSD. It is also possible that the brainstem migraine area is involved in CADASIL. Last, it is possible that the NOTCH3 mutation acts as a migraine aura susceptibility gene by itself.

In this narrative review we summarize the literature about migraine in CADASIL, with a special focus on what CADASIL might teach us about the pathophysiology of migraine.

Animal models of headache: from bedside to bench and back to bedside

In recent years bench-based studies have greatly enhanced our understanding of headache pathophysiology, while facilitating the development of new headache medicines. At present, established animal models of headache utilize activation of pain-producing cranial structures, which for a complex syndrome, such as migraine, leaves many dimensions of the syndrome unstudied. The focus on modeling the central nociceptive mechanisms and the complexity of sensory phenomena that accompany migraine may offer new approaches for the development of new therapeutics. Given the complexity of the primary headaches, multiple approaches and techniques need to be employed. As an example, recently a model for trigeminal autonomic cephalalgias has been tested successfully, while by contrast, a satisfactory model of tension-type headache has been elusive. Moreover, although useful in many regards, migraine models are yet to provide a more complete picture of the disorder.

Sumatriptan alleviates nitroglycerin-induced mechanical and thermal allodynia in mice

The association between the clinical use of nitroglycerin (NTG) and headache has led to the examination of NTG as a model trigger for migraine and related headache disorders, both in humans and laboratory animals. In this study in mice, we hypothesized that NTG could trigger behavioural and physiological responses that resemble a common manifestation of migraine in humans. We report that animals exhibit a dose-dependent and prolonged NTG-induced thermal and mechanical allodynia, starting 30-60 min after intraperitoneal injection of NTG at 5-10 mg/kg. NTG administration also induced Fos expression, an anatomical marker of neuronal activity in neurons of the trigeminal nucleus caudalis and cervical spinal cord dorsal horn, suggesting that enhanced nociceptive processing within the spinal cord contributes to the increased nociceptive behaviour. Moreover, sumatriptan, a drug with relative specificity for migraine, alleviated the NTG-induced allodynia. We also tested whether NTG reduces the threshold for cortical spreading depression (CSD), an event considered to be the physiological substrate of the migraine aura. We found that the threshold of CSD was unaffected by NTG, suggesting that NTG stimulates migraine mechanisms that are independent of the regulation of cortical excitability.

The neurobiology of migraine

The understanding of migraine has moved well beyond its traditional characterization as a "vascular headache." In considering the basic neurobiology of migraine, it is important to begin with the concept of migraine as not merely a headache, but rather a heterogeneous array of episodic symptoms. Among the array of phenomena experienced by migraine patients are visual disturbances, nausea, cognitive dysfunction, fatigue, and sensitivity to light, sound, smell, and touch. These symptoms may occur independently or in any combination, and in some patients occur even in the absence of headache. The diversity and variability of symptoms experienced by migraine patients belies a complex neurobiology, involving multiple cellular, neurochemical, and neurophysiological processes occurring at multiple neuroanatomical sites. Migraine is a multifaceted neurobiological phenomenon that involves activation of diverse neurochemical and cellular signaling pathways in multiple regions of the brain. Propagated waves of cellular activity in the cortex, possibly involving distinct glial and vascular signaling mechanisms, can occur along with activation of brainstem centers and nociceptive pathways. Whether different brain regions become involved in a linear sequence, or as parallel processes, is uncertain. The modulation of brain signaling by genetic factors, and by sex and sex hormones, provides important clues regarding the fundamental mechanisms by which migraine is initiated and sustained. Each of these mechanisms may represent distinct therapeutic targets for this complex and commonly disabling disorder.

Headache endocrinological aspects

In this chapter we review the current understanding of how hormones, neurohormones, and neurotransmitters participate in the pain modulation of primary headaches. Stressful conditions and hormones intimately implicated in headache neurobiology are also discussed. With the recent progress in neuroimaging techniques and the development of animal models to study headache mechanisms, the physiopathology of several of the primary headaches is starting to be better understood. Various clinical characteristics of the primary headaches, such as pain, autonomic disturbances, and behavioral changes, are linked to hypothalamic brainstem activation and hormonal influence. Headache is greatly influenced by the circadian circle. Over the millennia the nervous system has evolved to meet changing environmental conditions, including the light-dark cycle, in order to ensure survival and reproduction. The main elements for synchronization between internal biological events and the external environment are the pineal gland and its main secretory product, melatonin. Melatonin is believed to be a significant element in migraine and in other headache disorders, which has implications for treatment. A potential therapeutic use of melatonin has been considered in several headache syndromes. In short, primary headaches are strongly influenced by physiological hormonal fluctuations, when nociceptive and non-nociceptive pathways are differentially activated to modulate the perception of pain.

Neuroimaging in headache

The neurobiology of migraine is complex, but considerable progress has been made during recent decades with the aid of functional neuroimaging. Imaging studies have provided evidence of both abnormal brain functioning and structural changes. In migraine aura, the blood flow changes initially occur in V3A, an area also showing morphometric abnormalities. Pontine activation is also associated with increased volumetric changes. Similar findings are observed in the hypothalamic region in cluster headache. Other paroxysmal headache disorders, such as short-lasting unilateral neuralgiform headache attacks with conjunctival injection and tearing (SUNCT), hemicrania paroxistica and hemicrania continua, share this similar pattern of activation as cluster headache, pointing to a common pathogenic mechanism. Further studies are required in order to determine whether these changes are the cause or the consequence of the disease, as well as the possible role they may play in the progression into a chronic disorder.

The primary headaches as a reflection of genetic darwinian adaptive behavioral responses

OBJECTIVE

The objective of this study is to present a view of the primary headaches as genetically determined behavioral responses consistent with sickness behavior and defense reaction, respectively.

BACKGROUND AND DESIGN

A review of the literature bearing on the behavioral, humoral, and functional imaging aspects of the primary headaches shows that migraine and cluster headache (CH) are pain conditions characterized by different behaviors during the attacks. Here it is postulated that the behavioral responses to migraine and CH are evolutionary conserved reactions consistent with sickness behavior and defense reaction.

RESULTS

The sickness behavior observed during migraine attacks is a pan-mammalian adaptive response to internal and external stressors, characterized by withdrawal and motor quiescence, sympatho-inhibition and lethargy, in which visceral pain signals a homeostatic imbalance of the body and/or brain. In contrast, the defense reaction in CH consists of a fight-or-flight reaction, with motor restlessness and agitation, in which pain is exteroceptive in kind.

CONCLUSION

These different behavioral responses are thus specific to different kinds of pain, distinguished by the behavioral significance of the pain (visceral pain in migraine vs exteroceptive pain in CH), and imply brain matrices involving different networks in the brainstem, hypothalamus, and forebrain regions that engender evolutionarily conserved adaptive genetic responses. Cytokines play an important role in their development. Predictions and limitations of the hypothesis are discussed together with implications for genetic studies on headaches.

The Prevalence of Premonitory Symptoms in Paediatric Migraine: A Questionnaire Study in 103 Children and Adolescents

The prevalence and characterization of premonitory symptoms have not been rigorously studied in children and adolescents. Using a questionnaire, we retrospectively studied the prevalence of 15 predefined premonitory symptoms in a clinic-based population. In 103 children and adolescents fulfilling the International Classification of Headache Disorders, 2nd edn criteria for paediatric migraine, at least one premonitory symptom was reported by 69 (67%). The most frequently reported premonitory symptoms were face changes, fatigue and irritability. The mean number of premonitory symptoms reported per subject was 1.8 (median 2.2). Age, migraine subtype (with or without aura) and mean attack frequency per month had no effect on the mean number of premonitory symptoms reported per subject. In conclusion, premonitory symptoms are frequently reported by children and adolescents with migraine. Face changes seem to be a premonitory symptom peculiar to paediatric migraine.

Therapeutic potential of novel glutamate receptor antagonists in migraine

BACKGROUND

Migraine is a common and disabling neurological disorder. Although the pharmacotherapy of migraine has advanced in parallel with our understanding of the pathophysiology of the disease, there is still a considerable unmet need to find more effective treatments. Migraine pathophysiology involves activation or the perception of activation of the trigeminovascular system. Glutamate, the major excitatory neurotransmitter in the CNS, is implicated in elements of the pathophysiology of the disorder, including trigeminovascular activation, central sensitization and cortical spreading depression.

OBJECTIVE

The aim of this article is to review the potential use of glutamate receptor antagonists as innovative neuronally targeted treatments of migraine.

METHODS

A systematic search of peer-reviewed publications was performed in PubMed on glutamate and migraine/trigeminovascular activation, and important references providing an insight into migraine pathophysiology are included. The results of unpublished trials were obtained from presentations at national and international meetings.

RESULTS/CONCLUSIONS

The preclinical and clinical data argue strongly for a role of glutamatergic receptor activation in migraine. The pharmacology of glutamatergic trigeminovascular responses in brain areas involved in migraine pathophysiology is relevant to the development of new therapies for this disabling condition. Glutamate receptors represent a promising target for a valuable, non-vasoconstrictor, and perhaps more importantly neuronal-specific therapeutic approach to the treatment of migraine.

Activation of the Brainstem but not of the Hypothalamus in Hemicrania Continua without Autonomic Symptoms

A 64-year-old woman presented with a 6-month history of right-sided continuous headache, without autonomic symptoms and complete response to indomethacin. Clinical examination and structural brain imaging were normal. A diagnosis of hemicrania continua (HC) was made. We sought to determine the brain structures active during the pain in a patient who met all of the diagnostic criteria for HC with the exception of autonomic symptoms. A brain positron emission tomography study was performed during pain, and completely pain-free after indomethacin administration. Comparing the pain with pain-free states, the region of the dorsal pons was significantly activated. There was no activation in the hypothalamus, as previously reported in HC with autonomic symptoms. Although definitive conclusions can not be drawn from a single observation, the lack of autonomic symptoms along with the absence of hypothalamic activation suggests that the clinical presentation may predict the pattern of brain activation in primary headache syndromes.

Interictal quantitative EEG in migraine: a blinded controlled study

Abnormal electroencephalography (EEG) in migraineurs has been reported in several studies. However, few have evaluated EEG findings in migraineurs during a time period when neither the last attack nor the next attack may interact with the results. We, therefore, compared interictal EEG in migraineurs and headache-free subjects with a design controlled for interference by pre-ictal changes. Pre-ictal EEG findings in the painful cranial side during the next attack after registration were also investigated. Correlations between clinical variables and EEG are reported as well. Interictal EEGs from 33 migraineurs (6 with and 27 without aura) and 31 controls were compared. Absolute power, asymmetry and relative power were studied for delta, theta and alpha frequency bands in parieto-occipital, temporal and fronto-central areas. EEG variables were correlated to attack frequency, headache duration, attack duration, pain intensity, photo- and phonophobia. Compared with controls, migraineurs had increased relative theta power in all cortical regions and increased delta activity in the painful fronto-central region. Absolute power and asymmetry were similar among groups. In age-adjusted analyses, headache intensity correlated with increased delta activity. In this blinded controlled study, we found globally increased relative theta activity in migraineurs. A slight interictal brain dysfunction is probably present between attacks.

Origin of pain in migraine: evidence for peripheral sensitisation

Migraine is the most common neurological disorder, and much has been learned about its mechanisms in recent years. However, the origin of painful impulses in the trigeminal nerve is still uncertain. Despite the attention paid recently to the role of central sensitisation in migraine pathophysiology, in our view, neuronal hyperexcitability depends on activation of peripheral nociceptors. Although the onset of a migraine attack might take place in deep-brain structures, some evidence indicates that the headache phase depends on nociceptive input from perivascular sensory nerve terminals. The input from arteries is probably more important than the input from veins. Several studies provide evidence for input from extracranial, dural, and pial arteries but, likewise, there is also evidence against all three of these locations. On balance, afferents are most probably excited in all three territories or the importance of individual territories varies from patient to patient. We suggest that migraine can be explained to patients as a disorder of the brain, and that the headache originates in the sensory fibres that convey pain signals from intracranial and extracranial blood vessels.

Visual paired-pulse stimulation reveals enhanced visual cortex excitability in migraineurs

Migraine is a common ictal disorder with an interindividual heterogeneous characteristic, whose underlying mechanisms remain elusive. On the one hand migraine is associated with abnormal cortical hyperexcitability. On the other hand, studies reported lower amplitudes of visual-evoked potentials (VEPs) and concluded that low preactivation levels imply decreased excitability. Here we measured visual cortex excitability and paired-pulse suppression in subjects suffering from migraine without aura and in a group of aged- and gender-matched healthy subjects to address the relation between activation levels and excitability. To that aim, we analysed amplitudes of VEPs and paired-pulse suppression evoked by a paired-pulse stimulation paradigm using stimulus onset asynchronies (SOAs) between 80 and 133 ms. We found that in migraineurs in the interictal state the amplitudes of the first VEP were reduced as compared with healthy subjects by approximately 20%. In the case of paired-pulse suppression comparable to healthy controls, the second response amplitude should be reduced as well, which was not the case. Instead, the ratio between the first and second VEP was higher than in healthy controls and did not depend on SOA in the range tested, which demonstrates reduced paired-pulse suppression and therefore implicates increased cortical excitability. Our data show that in migraineurs VEPs were reduced presumably due to reduced activation levels. However, paired-pulse suppression using short SOAs in the range of 100 ms or less was even higher than in normal subjects. Thus, our data show that signatures of both hyper- and hypoexcitability can be found depending on stimulation condition.

Migraine and the Hypothalamus

Migraine is a complex brain disorder where several neuronal pathways and neurotransmitters are involved in the pathophysiology. To search for a specific anatomical or physiological defect in migraine may be futile, but the hypothalamus, with its widespread connections with other parts of the central nervous system and its paramount control of the hypophysis and the autonomic nervous system, is a suspected locus in quo. Several lines of evidence support involvement of this small brain structure in migraine. However, whether it plays a major or minor role is unclear. The most convincing support for a pivotal role so far is the activation of the hypothalamus shown by positron emission tomography (PET) scanning during spontaneous migraine attacks. A well-known theory is that the joint effect of several triggers may cause temporary hypothalamic dysfunction, resulting in a migraine attack. If PET scanning had consistently confirmed hypothalamic activation prior to migraine headache, this hypothesis would have been supported. However, such evidence has not been provided, and the role of the hypothalamus in migraine remains puzzling. This review summarizes and discusses some of the clues.

Sensitisation of spinal cord pain processing in medication overuse headache involves supraspinal pain control

Medication overuse could interfere with the activity of critical brain regions involved in the supraspinal control of pain signals at the trigeminal and spinal level, leading to a sensitisation phenomenon responsible for chronic pain. We hypothesised that medication-overuse headache (MOH) patients might display abnormal processing of pain stimuli at the spinal level and defective functioning of the diffuse noxious inhibitory controls. We tested 31 MOH patients before (bWT) and after (aWT) standard inpatient withdrawal treatment, 28 episodic migraine (EM) patients and 23 healthy control subjects. We measured the threshold, the area and the temporal summation threshold (TST) of the nociceptive withdrawal reflex before, during and after activation of the diffuse noxious inhibitory controls by means of the cold pressor test. A significantly lower TST was found in both the MOH (bWT and aWT) and the EM patients compared with the controls, and in the MOH patients bWT compared with both the MOH patients aWT and the EM patients. In the MOH bWT patients the cold pressor test induced a TST increase significantly lower than that found in the MOH aWT, EM and control groups. Abnormal spinal cord pain processing and a decrease of the antinociceptive activity of the supraspinal structures in MOH patients can be hypothesised. These abnormalities could, in part, be related to the medication overuse, given that the withdrawal treatment was related to an improvement in the neurophysiological findings.

Neurostimulation approaches to primary headache disorders

PURPOSE OF REVIEW

Conventional management options in medically intractable chronic-headache syndromes, such as chronic migraine, chronic cluster headache and hemicrania continua, are often limited. This review summarizes the current concepts, approaches and outcome data of invasive device-based neurostimulation approaches using occipital-nerve stimulation and deep-brain stimulation.

RECENT FINDINGS

Recently, there has been considerable progress in neurostimulation approaches to medically intractable chronic-headache syndromes. Previous studies have analysed the safety and efficacy of suboccipital neurostimulation in drug-resistant chronic-headache syndromes such as in chronic migraine, chronic cluster headache and hemicrania continua. The studies suggest suboccipital neurostimulation can have an effect even decades after onset of headaches, thus representing a possible therapeutic option inpatients that do not respond to any medication. Similarly, to date over 50 patients with cluster headaches underwent hypothalamic deep-brain stimulation. From these, an average of 50-70% did show a significant positive response.

SUMMARY

These findings will help to further elucidate the clinical potential of neurostimulation in chronic headache.

Migraine: an endemic disease inside the blood–brain barrier

Migraine is a complex neurological disorder that in recent years has received more and more attention. Knowledge regarding this primary headache has increased substantially, both with respect to its pathogenesis and how to effectively treat its symptoms. Over the years, the proposed location of the onset of migraine has moved from the periphery of the nervous system toward deeper parts of the brain. Migraine can be viewed as an inherited failure of trigeminal sensory processing with abnormal neuronal excitability in the trigeminal nucleus caudalis, which, in turn, causes central sensitization and amplification of the pain. Increased activation of the trigeminal nerve during a migraine attack causes release of the calcitonin gene-related peptide (CGRP) inside and outside the BBB. Within the CNS, CGRP promotes trigeminal sensory input and facilitates central sensitization. The future introduction of CGRP antagonists in clinical practice could represent significant progress for acute migraine therapy.

Migraine and cardiovascular disease: possible mechanisms of interaction

Migraine, especially migraine with aura (MA), is an established risk factor for ischemic lesions of the brain. Recent evidence has also linked migraine to a broader range of ischemic vascular disorders including angina, myocardial infarction, coronary revascularization, claudication, and cardiovascular mortality. The mechanisms which link migraine to ischemic vascular disease remain uncertain and are likely to be complex. Cortical spreading depression, the presumed substrate of aura, may directly predispose to brain lesions and that would explain why MA is consistently demonstrated as a risk factor for cerebral ischemia, while for migraine without aura (MO), the evidence is less consistent. Additionally, individuals with migraine have a higher prevalence of risk factors known to be associated with cardiovascular disease (CVD), including hypertension, diabetes, and hyperlipidemia. The increased prevalence of CVD risk factors is also higher for MA than for MO. Since the evidence linking migraine and CVD is getting robust, neurologists should be aware of this association. Individuals with MO seem to be at little increased risk of CVD. MA is associated with an increased risk of ischemic stroke and likely also for other ischemic CVD events. Accordingly, heightened vigilance is recommended for modifiable cardiovascular risk factors in migraineurs, especially with MA. Ultimately, it will be important to determine whether MA is a modifiable risk factor for CVD and if preventive medications for migraine or antiplatelet therapy might reduce the risk of CVD in patients with MA.

Advanced neuroimaging of migraine

Advanced neuroimaging has helped to increase our knowledge about migraine pathophysiology. Our perception of migraine has transformed from a vascular, to a neurovascular, and most recently, to a CNS disorder. Functional imaging has confirmed the importance of cortical spreading depression (CSD) as the pathophysiological mechanism of migraine aura in human beings, whereas novel animal studies are unravelling the mechanistic underpinnings of CSD. Altered cerebral blood flow and neurotransmitter systems have been identified during and between headaches in migraine with and without aura. Advanced neuroimaging has identified mechanisms involved in the transformation of migraine from an episodic disorder to one with near continuous symptomatology. Questions regarding the secondary effects of migraine on brain structure and function, possibly related to attack frequency and duration of illness, have been raised. New imaging techniques could lead to novel diagnostic and therapeutic interventions that will help to improve the lives of millions of patients with migraine. In this Review, we summarise the most important findings from current imaging studies of migraine.

Migraine pain: reflections against vasodilatation

The original Wolff’s vascular theory of migraine was supported by the discovery of a class of drugs, the triptans, developed as a selective cephalic vasoconstrictor agents. Even in the neurovascular hypothesis of Moskowitz, that is the neurogenic inflammation of meningeal vessels provoked by peptides released from trigeminal sensory neurons, the vasodilatation provoked by calcitonin gene-related peptide (CGRP) is considered today much more important than oedema. The role of cephalic vasodilatation as a cause of migraine pain was recently sustained by studies showing the therapeutic effect of CGRP receptor antagonists. We discuss the evidence against vasodilatation as migraine pain generator and some findings which we suggest in support of a central (brain) origin of pain.

Migraine in the triptan era: progresses achieved, lessons learned and future developments

Triptans, serotonin 5-HT1B/1D receptor agonists, more than revolutionizing the treatment of migraine, stimulated also ground breaking research that provided insights into the anatomy, physiology, and molecular pharmacology of migraine. This knowledge, in turn, is stimulating research on new mechanisms of action for the treatment of migraine. Accordingly, it is opportune to critically review the main advances in migraine science that happened in the triptan era. Herein we first review and conceptualize some of the progresses achieved in migraine science during the triptan era. We then review the class of the triptans - mechanism of action and clinical evidence. We close by briefly discussing the class of CGRP receptor antagonists, which is currently being developed for the acute treatment of migraine.

Transient burning pain in the ipsilateral orbit as an initial manifestation of dorsal pontine hemorrhage: case report

A 45-year-old man with a past history of hypertension and hyperlipidemia presented with right dorsal pontine hemorrhage manifesting as transient burning pain in the right orbital region, followed by numbness and mild weakness of the left side of the body. Magnetic resonance imaging showed a hyperintense lesion in the right dorsal pons on T(1)-weighted and T(2)-weighted images, but no other abnormalities suggesting vascular lesions in the midbrain, medulla, cerebellum, or cerebrum. These findings were consistent with the subacute stage of small pontine hemorrhage. He was treated to decrease his blood pressure. The symptoms gradually improved and he has suffered neither recurrence of the orbital pain nor migraine for several months after the first episode of headache. The trigeminal nociceptive system in the dorsal lateral pons may be linked to this characteristic pain, as suggested by reports of secondary migraine caused by cavernous hemangioma and arteriovenous malformation, and activation of the dorsal lateral pons during migraine attacks on positron emission tomography.

Migraine in the triptan era: lessons from epidemiology, pathophysiology, and clinical science

The triptan era has been a time of remarkable progress for migraine diagnosis and treatment. In this paper, we review some of the advances achieved in migraine science during this era focusing on 3 themes: lessons from clinical practice, lessons from epidemiology and lessons from pathophysiology. Science has shown that migraine is a disorder of the brain, and that the key events happen in the the trigeminal neuronal pathways, not on blood vessels. Clinical science has led to the observation that migraine sometimes progresses or remits. This in turn led to longitudinal epidemiologic studies focusing on factors that determine migraine prognosis. In addition, these studies raised questions about the mechanisms of migraine progression, including the role of allodynia, obesity, inflammation, and medications as determinants of progression. This in turn opens a new set of scientific questions about the neurobiologic determinants of migraine, as well as of its clinical course, and exciting opportunities to develop new therapies for this highly disabling brain disorder.

Iron accumulation in deep brain nuclei in migraine: a population-based magnetic resonance imaging study

A small magnetic resonance imaging (MRI) study showed increased iron depositions in the periaqueductal grey matter in migraineurs, suggestive of a disturbed central antinociceptive neuronal network. With 1.5-T MRI, we assessed iron concentrations in seven deep brain nuclei in a large population-based cohort. We compared T2 values between migraineurs (n = 138) and controls (n = 75), with multivariate regression analysis. Analyses were conducted in age strata (< 50, n = 112; > or = 50) because iron measures are increasingly influenced by non-iron-related factors in the older group. Overall, migraineurs and controls did not differ, nor did migraineurs with vs. without aura. In the younger migraineurs compared with controls, T2 values were lower in the putamen (P = 0.02), globus pallidus (P = 0.03) and red nucleus (P = 0.03). Similarly, in these younger migraineurs, controlling for age, those with longer migraine history had lower T2 values in the putamen (P = 0.01), caudate (P = 0.04) and red nucleus (P = 0.001). Repeated migraine attacks are associated with increased iron concentration/accumulation in multiple deep nuclei that are involved in central pain processing and migraine pathophysiology. It remains unclear whether iron accumulation in the antinociceptive network has a causative role in the development of (chronic) migraine headache.

Brainstem and thalamic projections from a craniovascular sensory nervous centre in the rostral cervical spinal dorsal horn of rats

To examine the ascending projections from the headache-related trigeminocervical complex in rats, biotinylated dextran amine (BDA) was injected into the ventrolateral dorsal horn of segments C1 and C2, a region previously demonstrated to receive input from sensory nerves in cranial blood vessels. Following injections into laminae I-II, BDA-labelled terminations were found bilaterally in several nuclei in the pons and the midbrain, including the pontine reticular nucleus, the parabrachial nuclei, the cuneiform nucleus and the periaqueductal grey. In the diencephalon, terminations were confined to the contralateral side and evident foremost in the posterior nuclear group, especially its triangular part, and in the ventral posteromedial nucleus. Following injections extending through laminae I-IV, anterograde labelling was more extensive. Some of the above regions are likely to be involved in the central processing of noxious signals of craniovascular origin and therefore putatively involved in mechanisms associated with primary headaches.

Refractory migraine and chronic migraine: pathophysiological mechanisms

Despite increased understanding of primary headaches and their treatment, the underlying causes of refractory migraine remain unknown. This note considers potential genetic, structural, functional and pharmacological factors that could contribute to this relatively intractable condition. Further understanding of refractory migraine will require the use of medical imaging technologies, clinical experimental medicine studies on novel pharmacological agents and astute observations in clinical practice to direct potential novel therapeutic approaches.

Abnormal cerebral glucose metabolism in alternating hemiplegia of childhood

Alternating hemiplegia of childhood (AHC) is a rare and intractable disorder of unknown cause. To determine cerebral neuronal function in five patients with AHC (two adults and three children), we analyzed brain glucose metabolism by positron emission tomography (PET) using 2-deoxy-2 [(18)F] fluoro-d-glucose (FDG), performed between hemiplegic attacks. Interictal FDG-PET revealed abnormal cerebral glucose metabolism; all patients showed low glucose metabolism in the frontal lobes with some laterality, and three had low glucose metabolism in the ipsilateral putamen. The adult patients also showed low glucose metabolism and mild atrophy in the cerebellum. Glucose metabolism in the brainstem was virtually normal for all patients. The areas of low glucose metabolism indicated local or regional neuronal damage, possible reflecting progressive neurological symptoms. AHC might therefore result from focal abnormal glucose metabolism in the brain occurring progressively or permanently, particularly in the frontal lobes and the cerebellum.

[Cortical spreading depression (CSD): a neurophysiological correlate of migraine aura]

Cortical spreading depression (CSD) is a transient (60-120 s) and at 3-5 mm/min propagating depolarization wave of cortical neurons and glial cells and is characterized by a DC shift of 20-35 mV. It is accompanied by massive redistribution of ions between extracellular and intracellular compartments and by a water influx into the cells. Extracellular potassium ion concentration increases up to 60 mM/l. Potassium ions and the excitatory neurotransmitter glutamate essentially contribute to the initiation and propagation of CSD. Both depolarization and disturbance of brain ion homeostasis regenerate within a few minutes while enhancing energy metabolism, but do not cause damage to normally perfused brain tissue. The similar propagation velocity of CSD and visual scotoma during migraine aura led to the assumption that CSD could be the underlying mechanism of migraine aura. The observation of CSD waves in migraine aura patients with the magnet encephalogram (MEG) technique confirmed this theory. Although many data support the relationship between CSD and aura phase in migraine, the role of CSD in migraine headache is still disputed.

Antiepileptic Drugs on Calcium Currents Recorded from Cortical and PAG Neurons: Therapeutic Implications for Migraine

Cortex and periaqueductal grey (PAG) play a major role in the pathophysiology of migraine. Some antiepileptic drugs (AEDs) influence the activity of these structures by modulating high-voltage-activated (HVA) Ca2+ channels and are effective in migraine prevention. The aim of the present study was to investigate the expression of total HVA Ca2+ channels in cortical and PAG neurons and to study the differential action of AEDs on these channels. Isolated neurons were visually identified based on morphological criteria. HVA currents were recorded by whole-cell patch-clamp technique. The distribution ratio of L-, N-, P-, Q- and R-type HVA Ca2+ channels was different between cortical and PAG neurons. In particular, we found that P- and Q-type HVA Ca2+ channels were more expressed in PAG neurons than in cortical cells, whereas L- and R-type HVA Ca2+ channels showed an opposite distribution. Interestingly, N-type HVA Ca2+ channels were equally distributed in these two neuronal populations. A differential sensitivity to AEDs of HVA Ca2+ channels located on cortical and PAG neurons was observed for topiramate (TPM), but not for lamotrigine (LTG) or levetiracetam (LEV). In fact, whereas both LTG and LEV were equally effective and potent in inhibiting HVA Ca2+ currents in the two neuronal populations, TPM showed a much higher potency and efficacy in blocking these currents in PAG neurons than in cortical pyramidal cells. TPM, in fact, inhibited N-, P- and L-type channels in PAG neurons, whereas in cortical neurons this AED modulated only P- and L-type channels. Unlike the other AEDs investigated, valproic acid did not affect HVA Ca2+ currents in cortical and PAG neurons. The negative modulation of specific subtypes of HVA Ca2+ channels by various AEDs can restore normal electrical activity in target brain areas such as cortex and PAG, providing interesting therapeutic approaches in migraine prevention.

Interictal dysfunction of a brainstem descending modulatory center in migraine patients

BACKGROUND

The brainstem contains descending circuitry that can modulate nociceptive processing (neural signals associated with pain) in the dorsal horn of the spinal cord and the medullary dorsal horn. In migraineurs, abnormal brainstem function during attacks suggest that dysfunction of descending modulation may facilitate migraine attacks, either by reducing descending inhibition or increasing facilitation. To determine whether a brainstem dysfunction could play a role in facilitating migraine attacks, we measured brainstem function in migraineurs when they were not having an attack (i.e. the interictal phase).

METHODS AND FINDINGS

Using fMRI (functional magnetic resonance imaging), we mapped brainstem activity to heat stimuli in 12 episodic migraine patients during the interictal phase. Separate scans were collected to measure responses to 41 degrees C and noxious heat (pain threshold+1 degrees C). Stimuli were either applied to the forehead on the affected side (as reported during an attack) or the dorsum of the hand. This was repeated in 12 age-gender-matched control subjects, and the side tested corresponded to that in the matched migraine patients. Nucleus cuneiformis (NCF), a component of brainstem pain modulatory circuits, appears to be hypofunctional in migraineurs. 3 out of the 4 thermal stimulus conditions showed significantly greater NCF activation in control subjects than the migraine patients.

CONCLUSIONS

Altered descending modulation has been postulated to contribute to migraine, leading to loss of inhibition or enhanced facilitation resulting in hyperexcitability of trigeminovascular neurons. NCF function could potentially serve as a diagnostic measure in migraine patients, even when not experiencing an attack. This has important implications for the evaluation of therapies for migraine.