University of Groningen. Modelling trigeminovascular pain in the unrestrained rat Kemper, Richard Hendrikus Antonius

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1 University of Groningen Modelling trigeminovascular pain in the unrestrained rat Kemper, Richard Hendrikus Antonius IMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite from it. Please check the document version below. Document Version Publisher's PDF, also known as Version of record Publication date: 2000 Link to publication in University of Groningen/UMCG research database Citation for published version (APA): Kemper, R. H. A. (2000). Modelling trigeminovascular pain in the unrestrained rat: an approach to a better understanding of migraine headache s.n. Copyright Other than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons). Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. Downloaded from the University of Groningen/UMCG research database (Pure): For technical reasons the number of authors shown on this cover page is limited to 10 maximum. Download date:

2 Introduction

3 Migraine history Migraine has been known about for a long time already. From the days that man could write, descriptions are present that hint of migraine. Alvarez 5 discovered a description written, in a poem in Sumeria in Mesopotamia 3,000 years before Christ, where the poet says: The sick eyed says not 'l am sick eyed', The sick-headed (says) not 'I am sick-headed. Another poet from ancient Mesopotamia wrote (see 5 ): "The head throbs, When pain smites the eyes And vision is dimmed." Nowadays, a general practitioner would immediately think of a migraine if a patient were to complain of disturbed vision in combination with a throbbing headache behind the eyes. Somewhat later, 3,500 years ago, the oldest known complete medical book, the Ebers papyrus found in the Tomb of Thebes, Egypt, mentions a sickness of half of the head referring to the unilateral nature of migraine. The typical aura and the observation that the headache commences after the aura stops, was first described by Hippocrates (400 AD):... He seemed to see something shining before him like a light, usually in part of the right eye; at the end of a moment, a violent pain supervened in the right temple, then in all the head and neck..., who also observed that the headache could be relieved by vomiting. Better descriptions of migraine characteristics were found later on. Celsus (25 BC to AD 50) was the first to indicate that migraine was a life-long non-fatal disorder, that there were trigger factors and also emphasized that the headache could be localized or generalized: A long weakness of the head, but neither severe nor dangerous, through the whole life. Sometimes the pain is more violent, but short, yet not fatal; which is contracted either by drinking wine, or crudity, or cold, or heat of a fire, or the sun... Sometimes they afflict the whole head, at other times a part of it (see 359 ). Soranus of Ephesus (AD ) and Aretaeus of Cappadocia (AD 30-90) both recognize the combination of a unilateral headache ( the pain... remains in the half of the head ) with nausea and vomiting. Aretaeus of Cappadocia also noted photo and phonophobia ( For they flee the light; the darkness soothes their disease; nor can they bear readily to look upon or hear anything disagreeable ). He also introduced the earliest known comprehensive classification of primary headaches, and separated migraine ( heterocrania unilateral, blackness before eyes, nausea, photophobia) from cephalalgia (not very severe, short-lasting) and cephalea (instense, chronic, frequent) (see 165,359 ). Concerning heterocrania, he said that if they begin at dusk, they end by midday on the next day, and if they begin at midday, they end by nightfall. "It is rare for the attack to last longer." About the same time, Galen (AD ) introduced the term "hemicrania", which was later 10

4 Introduction modified gradually from hemigrania, emigrania, migrania, megrim, to its present form, migraine (see 359 ). In his Practice of Physick which was published posthumous in 1684, Thomas Willis ( ) hypothesized that intracranial vasodilatation caused the headache of migraine. Latham (1872), later argued that visual auras are caused by contraction of the cerebral arteries (see 94 ) Levine s On Megrim, Sick-Headache, and Some Allied Disorders was published in Herein Levine describes many individual migraine patients, he recognizes the enormous variety of migraine forms and especially put forward the theory that migraine is part of a continuum of paroxysmal disorders that is characterized by nerve storms. 239 BC AD ±3000 ±1500 ±400 ± 10 Sumeria, Mesopotamia. First descriptions that hint of migraine Thomb of Thebes, Egypt. Ebers Papyrus mentions 'sickness of half of the head' Hippocrates: Describes unilateral visual aura and the commencing of a unilateral headache (in same half of aura) after end of aura Celsus: Migraine is life-long, non-fatal, has trigger factors and can be localized or generalized ±80 Aretaeus of Cappadocia: Introduced term 'Heterocrania' which is unilateral, associated with nausea/vomiting and photo/phono phobia, and determines a timespan of several hours to a day ±170 Galen: Introduced term 'Hemicrania' Posthumous publication of 'Practice of Physick' from Thomas Willis; Hypothized that vasodilation causes headache of migraine Latham: Hypothized that visual aura is caused by cerebral arterial contraction' Publication of 'On Megrim, Sick-Headache and Some Allied Disorders' from Levine, puts migraine on continuum of paroxysmal disorders A. Tzanc: Ergotamine tatrate is effective for treating migraine Wolff: Amyl Nitrite alleviates aura in doses that cause vasodilation, identifies the dura and extracerebral bloodvessels as painful structures that may be related to migraine NIH develops diagnostic criteria for migraine Figure 1.1. Overview of some historical events that (partially) determine the present view of migraine. The first description of effective pharmacological treatment of migraine with ergotamine tartrate, which is still used by many migraineurs today, was reported in A great contribution to the discovery of the pathophysiological mechanisms causing migraine was made by Wolff and colleagues. They observed that amyl nitrite in doses that 11

5 caused vasodilatation alleviated the aura 258,380 and they identified the intracranial structures (dura and extracerebral bloodvessels) that may be involved in migraine pathophysiology. 81,354 In 1962 the Ad hoc committee on the classification of headache of the National Insitute of Health developed diagnostic criteria for migraine and identified classical (with aura) and common forms (without aura), 2 which were gradually modified to the presently used criteria of the International Headache Society (IHS). 145 Migraine present time IHS criteria The most common form of migraine is migraine without aura (MO) and according to the IHS, 145 migraine without aura is described as an idiopathic, recurring headache disorder manifesting in attacks lasting 4-72 hours. Typical characteristics of headache are unilateral location, pulsating quality, moderate or severe intensity, aggravation by routine physical activity, and association with nausea, photo- and phonophobia. The following diagnostic criteria are used: A. At least 5 attacks fulfilling B-D. B. Headache attacks lasting 4-72 hours C. Headache has at least two of the following characteristics: 1. Unilateral location 2. Pulsating quality 3. Moderate or severe intensity (inhibits or prohibits daily activities) 4. Aggravation by walking stairs or similar routine physical activity D. During headache at least one of the following: 1. Nausea and/or vomiting 2. Photophobia and phonophobia E. At least one of the following: 1. History, physical- and neurological examinations do not suggest one of the following disorders: Headache associated with head trauma, vascular disorders, nonvascular intercranial disorder, substances or their withdrawal, non-cephalic infection, metabolic disorder, disorder of cranium, neck, eyes, ears, nose, sinuses, teeth, mouth or other facial or cranial structures 2. History and/or physical- and/or neurological examinations do suggest such disorder, but it is ruled out by appropriate investigations 3. Such disorder is present, but migraine attacks do not occur for the first time in close temporal relation to the disorder. The second most common form of migraine is migraine with aura (MA), which is described as an idiopathic, recurring disorder, manifesting with attacks of neurological 12

6 absent. 145 The diagnostic criteria of the IHS are widely used nowadays in the research Introduction symptoms unequivocally localizable to cerebral cortex or brain stem, usually gradually developed over 5-20 minutes and usually lasting less than 60 minutes. Headache, nausea and/or photophobia usually follow neurological aura symptoms directly or after a free interval of less than an hour. The headache usually lasts 4-72 hours, but may be completely community and ensure that various studies done using migraineurs are comparable to a certain extent. Epidemiology Using IHS criteria, the prevalence of migraine is 6% among men and 15-17% among women (reviewed in 418 ). In both groups, prevalence really starts to rise in the early twenties and is highest around the age of fourty after which it declines again. 418 The prevalence of migraine without aura is generally 1.5 to 2 times higher than the prevalence of migraine with aura. 353,363 The median attack frequency in active migraineurs ranges from and to attacks per month and the median duration varies from 9 to 24 hours when using IHS criteria (reviewed in 417 ). In comparison to other headaches, migraine is more disabling and has a higher intensity compared to other headaches 417 ; 43% of employed migraineurs suffer from work loss. 352 Generally speaking, headache is a disorder which is an enormous burden on society. Not only in view of the economic costs, but also considering the psychosocial costs. 228 Up to 70 % of the interpersonal relationships are impaired by migraine. 95 It is remarkable that despite this burden, only 64 % of migraine patients search medical attention and that most migraine sufferers take over-the-counter drugs. 95 Migraine pathophysiology Migraine has received enhanced attention from the research community over the past 33 years. The number of scientific medical publications in a National Library of Medicine (NLM-) Medline database (Pubmed, using the term migraine in title, abstract or keywords has increased steadily from 99 publications per year in 1966 to 578 publications per year in The percentage of articles in comparison to the total number of scientific medical publications in the NLM Medline database has increased from 0.057% in 1966 to 0.133% in 1998 (figure 1.2), implying that the attention from the research-community in migraine pathophysiology increased continuously over the past 33 years. 13

7 Despite this increasing attention, little is still known about the pathophysiological mechanisms that underlie a migraine attack. Research has, however, advanced several theories concerning the pathophysiology of migraine in general, or the individual aspects of Total number of publications (x1000) Number of publications using term 'migraine' Number of publications Year Figure 1.2 Number of total scientific medical publications (filled squares, x1000) and those using the term migraine in title, abstract or keywords (open rounds) in a NLM Medline database (Pubmed, over time. a migraine attack. These will be discussed shortly. Neurogenic inflammation theory The complex of trigeminal sensory afferents that innervate the dura mater and the larger blood vessels of the brain is called the trigeminovascular system. Animal studies have shown that upon stimulation of these trigeminal afferents, neuropeptides such as substance P (SP) and calcitonin gene related peptide (CGRP) are released at the afferent terminal site, causing neurogenic inflammation (NI) in the perivascular space of bloodvessels of the meninges. 311 Part of the neurogenic inflammatory process is plasma protein extravasation (PPE) and vasodilation. Using animal models it has been shown that the classic ergot alkaloids, 365 sumatriptan 45 and also the new generation, centrally active triptans 64 inhibit dural PPE which is induced by trigeminal afferent stimulation. Also, non-steroidal-antiinflammatory-drugs inhibit dural PPE 48 and have been reported to be effective in the treatment of migraine 327,342. This argues for the relevance of NI in migraine. CGRP levels 14

8 Introduction present in plasma samples taken from the jugular vein from migraine patients are indeed elevated during a migraine attack. 128 These patients did not show an elevation of plasma SP levels 128, which argues against the occurrence of NI in migraine. Also, inflammation of the meninges has never been detected in migraineurs. Most anti-migraine drugs not only ameliorate PPE but also induce vasoconstriction. Bosentan, which blocks PPE without having vasoconstrictive effects, was ineffective in alleviating migraine attacks when given during the headache phase, 277 which implies that NI is not involved in migraine. However, it cannot be excluded that NI precedes the headache phase of migraine. Therefore, treatment with drugs such as Bosentan before the actual headache phase would be necessary to definitely prove the irrelevance of NI in migraine. The vascular theory The often-pulsating quality of a migraine headache implies that vasodilated vessels induce the pain felt during a migraine headache. Most anti-migraine drugs have, besides PPE inhibiting effects in animal models, vasoconstrictive properties. The vasoconstrictive properties of anti-migraine drugs have been examined using animal models. This has elucidated that the arteriovenous anastomoses are the primary target of vasoconstriction by anti-migraine drug. 83,409 These shunts between the arterial blood supply to the brain and the venous blood drainage are able to regulate the blood supply of oxygen and nutrients to the brain. Dilation in the shunts normally causes a decrease in the arterial blood supply whereas constriction causes an increased blood supply to the brain. As anti-migraine drugs have been shown to constrict the shunts, it is tempting to speculate that the headache phase of migraine is caused by deficient arterial oxygen supply to the brain, which is restored by shunt constriction induced by anti-migraine drugs. Studies that have examined the regional oxygen extraction in the brain could, however, not find it altered in cortical areas that showed decreased cerebral blood flow. 8,26 The constriction of shunts may attribute to resolving migraine in other ways. As mentioned earlier, the vascular theory which states that vasodilation of large intracranial extracerebral vessels causes the headache of migraine was advanced by Willis (1684). Latham put forward that cerebral vasoconstriction causes the aura phase. 94 Olesen and colleagues found that there is indeed a decrease of regional cerebral blood flow (rcbf) during the aura phase, supporting the local vasoconstriction theory of aura. 328 They also showed that the decrease of rcbf in the posterior hemisphere continued throughout the headache phase, 328 which was confirmed by others. 8,26 This argues against the theory that a change from regional vasoconstriction to vasodilation causes the headache. Several reports examined whether large cerebral vessels are dilated during a migraine attack, and although some were able to show this for the middle cerebral artery at the headache site, 106 these results remain controversial. 86, If extracerebral bloodvessel dilation is the cause of the 15

9 headache in migraine, then the trigeminal nociceptive afferents that innervate these vessels in the dura and subarachnoid space are the most likely candidate for processing the nociceptive information to the brain, where pain sensation is experienced. Cortical spreading depression theory The neurological symptoms and the reported local decrease of rcbf in cortical areas during the aura phase may be caused by cortical spreading depression (CSD, a shortlasting depolarization wave that moves across the cortex with a brief phase of neuronal excitation that is immediately followed by prolonged nerve cell depression and a reduction in regional cerebral bloodflow). 207,223,224,479 It has been shown in animals that CSD is able to activate the trigeminovascular system 312 but these findings are criticized. 164 Whereas there is little doubt that vasoconstriction occurs in cerebral cortex during aura, the actual prolonged decrease of neuronal activity has not been shown. Also, whereas CSD can be easily initiated in animals experimentally, similar actions have failed to elicit CSD in human subjects. 122 The relevance of CSD in migraine pathophysiology, therefore, still needs to be determined. Deficient habituation theory of migraine Extensive research from Schoenen and colleagues have shown that migraineurs (outside of the attack) show deficient cortical information processing (lack of habituation, hypo/hyperexcitability) to repetitive stimulation with a variety of sensory stimuli. 210,379,473,474 The lack of habituation to repeated sensory information may underlie the reason that migraineurs develop migraine from stimuli such as flickering lights and warm or crowded places. Schoenen argues that deficient processing of sensory information, will lead to a disruption of metabolic homeostasis, which through biochemical shifts will eventually result in stimulation of the trigeminovascular system. 379 Genetic theory of migraine Particularly the past few years, a completely new field of research in migraine pathophysiology was opened by the discovery of altered genes in a special, dominant hereditary form of migraine: familial hemiplegic migraine (FHM). The gene that codes for the calcium P/Q type channel was found to be altered in persons suffering from FHM by Ophoff and colleagues 330,331,439 and later, this group also reported of evidence that the same gene is involved in migraine with (MA) and without aura (MO). 438 Other genes may also be involved in the more common forms of migraine. The allelic distribution of the human serotonin transporter gene was found to be altered in MO and MA compared to controls and was altered in-between patients with MO or MA as well. 325 Also, a subgroup of MO patients that show dopaminergic hypersensitivity has different allelic distribution at the locus of the dopamine D2 receptor. 82 Different dopamine D2 receptor 16

10 Introduction allelic distribution has also been shown in MA patients that have anxiety disorders and/or major depression. 340 Finally, the increased prevalence of migraine in females may be related to a migraine susceptibility locus on the X chromosome. 323 How these altered allelic distributions in various groups of migraineurs are exactly involved in migraine pathophysiology is still speculative but they do suggest that multiple pathophysiological mechanisms may lead to one similar kind of disorder, migraine, whether or not this is associated with hemiplegia, dopamine hypersensitivity, aura or anxiety / depression. Nitric oxide theory of migraine Nitric oxide (NO) is a gas that easily diffuses into tissue and has acute vasodilatory properties. The role of NO in migraine is examined predominantly by the group of Olesen, Thomsen, Iversen and Lassen from the Department of Neurology, Glostrup Hospital Copenhagen. Several arguments exist for relating NO to migraine pathophysiology. These have been reviewed 442 and will be discussed shortly. First of all, the NO donor nitroglycerin can induce a migraine attack in migraineurs and headache in non-migraineurs. 167,169,329,442 Second, histamine can trigger migraine in migraineurs through NO-dependent mechanisms. 221 Third, nitroglycerin-induced headache can be antagonized by the anti-migraine drug sumatriptan. 168 Fourth, NO may cause the release of CGRP from perivascular nerve endings 477 a neuropeptide that is found elevated in the jugular vein of migraineurs. 128 Fifth, the vascular reactivity to NO in migraineurs is enhanced as the dilation of the middle cerebral artery caused by NO is increased in patients suffering from migraine 441 and finally, the NOS inhibitor 546C88 has been tested successfully in migraineurs. 217,218 All these findings, and more, 442 imply an import role of NO in migraine pathophysiology, at least as one of the key mediators. Cerebral theory Migraineurs may suffer from premonitory symptoms (fatique, yawning, hungry, higher irritability, shivering), which are different from aura symptoms, up to 48 hours prior to the actual attack. The number of migraineurs that suffer from such pro-dromal symptoms varies from 14% 353 to 88% 468 but this implies that the actual start of a migraine attack (at least in some migraineurs) is long before the start of the aura or headache phase. The nature of these symptoms implies that the brain itself is involved. The hypothalamus is involved in the control of yawning, 14 hunger 436,443 and shivering, 501 implicating the involvement of the hypothalamus early in the migraine attack. Other cerebral areas that may be involved in initiating migraine are the locus coeruleus (LC) and dorsal raphe (DR). Weiller and colleagues examined the cerebral activity patterns of humans suffering from a spontaneous migraine attack using regional cerebral 17

11 bloodflow (rcbf) measurement with positron emission tomography (PET). 478 The study showed that several cortical areas and brainstem regions were activated during a migraine attack. The activation of certain regions in the brainstem, that coincide with the location of the DR and LC, persisted after abolition of the migraine attack with sumatriptan. This finding led the authors to conclude that these regions may be involved in the initiation of the migraine attack. 478 The LC has been noted to play a role in migraine before. Lance and colleagues argued that the LC, due to its control on both cerebral circulation and pain transmission at the level of spinal and trigeminal medulla, may play an essential role in migraine. Enhanced activity of the LC may cause vascular changes in migraine, followed by decreased activity of the LC causing attenuated inhibition on pain transmission at the level of the spinal/trigeminal medulla. 215 Summary Some theories for the pathophysiology of (aspects of) migraine have been put forward. They do not exclude each other. It is possible, based on the various forms of migraine and the diverse ways it manifests itself in migraineurs, that different pathophysiological mechanisms underlie migraine. The various theories generally agree about one thing: the trigeminovascular system becomes activated during the most disabling phase of a migraine attack: the headache phase. 103,125,221,311,312,373,379 Many animal models of the headache phase of migraine are therefore based on stimulation of the trigeminovascular system. 18

12 Introduction Intermezzo Fos as a marker of neural activity after nociception in conscious animals Fos is the protein product of the proto-oncogene c-fos. It can regulate the expression of other genes in cells. To do this, it has to form a dimer with a protein member of the Jun family after which the dimmer complex can bind to the activator-protein-1 (AP-1) site in DNA gene expression promotor regions. The transcription of genes with an AP-1 site (for example the neuropeptides enkephalin and substance P) can be modulated by Fos-Jun dimers. 407 The value of Fos as an anatomical marker of neuronal activity after several types of stimuli, including nociception, has been discussed extensively elsewhere. 43,144,304,305 The general consensus is that the presence of Fos in neurons following a painful stimulus does reflect enhanced neuronal activity, 43,144,162 but that the absence of Fos in neurons does not necessarily mean that neurons were not activated. There are few areas in the brain that do not express Fos after painful stimulation of which activation could be expected based on electrophysiological and neuroanatomical studies. 43,144 The use of Fos as marker of neural activity has the great advantage that it can be analysed a few hours after the experiments (expression peaks approximately 2 hrs. after stimulation), so no invasive techniques have to be used during the experiments. This allows the study of neural activity in conscious, unrestrained animals. Interpretation of Fos expression results in brain sections obtained from conscious animals demands carefully controlled experiments that enable linkage of cerebral Fos patterns to the stimulus. Neural activation revealed by Fos may relate directly to the nociceptive stimulus but may also relate to the behavioural and physiological adaptations induced by the nociceptive stimulus. Animal models of migraine headache There is no animal model of migraine. We do not know whether animals do experience migraine, but most likely, they do not. At best, animal models mimic aspects of a migraine attack. As the term model implies, modelling an aspect of migraine pathophysiology in animals, implies that one has to acknowledge that it only mimics the situation in human migraineurs. A model, however, has the advantage that complex mechanisms that underlie a migraine attack can be studied in controlled conditions. Most animal models published thus far have modelled the headache phase of migraine, not only because this is the most disabling feature of a migraine attack but also because there is little doubt that the trigeminovascular system is involved. Animal models of trigeminovascular stimulation The trigeminovascular system consists of the intracranial, but extracerebral vasculature in the dura mater and the subarachnoid space that are innervated by afferents of the trigeminal system. Anatomical studies have shown that the meningeal vasculature is innervated by small unmyelinated sensory fibers which originate in the trigeminal ganglion. 238,280,281,452,454 Animal models of trigeminovascular stimulation are based on electrical, mechanical or chemical stimulation of the trigeminovascular system. Upon activation, trigeminal afferents transmit impulses orthodromically to synaptic nerve endings within layer I and II of the trigeminal nucleus caudalis (TNC I,II). 286 This is the primary relay 19

13 station of the brain for nociceptive information of the trigeminovascular system. From the TNC I,II, the signal is transduced to the cortical areas where the pain is sensed. After nociceptive stimulation of trigeminal afferents, not only orthodromic conduction occurs but also antidromic conduction. This will lead to the release of neuropeptides, such as SP and CGRP at the perivascular trigeminal nerve terminals. These neuropeptides will cause NI and PPE. It has to be noted that this antidromic conduction is not a mechanism specific for the trigeminal system but a more general primary defence mechanism of sensory nerves against possible tissue damage. In the mid and late eighties, a variety of animal models have been introduced using trigeminovascular stimulation to mimic various types of headache. Basically, they can be characterised by 1) the type of stimulation (e.g. chemical, electrical or mechanical), 2) the place of stimulation (e.g. trigeminal nerve, trigeminal ganglion or trigeminal afferent terminals) and 3) the markers used to measure activity in the trigeminovascular system (figure 1.3). The latter can be divided in parameters that assess orthodromic or antidromic activity in the trigeminovascular system. Most frequently used are Fos expression / electrical recordings in the TNC and PPE in the dura mater respectively. Electrical stimulation of the trigeminal ganglion combined with the measurement of PPE in the dura mater is the most extensively used paradigm. Electrical stimulation of the trigeminal ganglion and nerve, as 20 Intermezzo Capsaicin in the trigeminovascular system Capsaicin was isolated as the pungent ingredient of hot chilli peppers more than a century ago ( 444 cited in 430 ). In 1967, an international journal reported that capsaicin not only activated sensory fibers but could also block them at sufficiently high doses. 173 The primary target of action of capsaicin are the rat unmyelinated C-polymodal nociceptors (mechanoheat, chemonociceptive, warmth) and thinly myelinated A-delta afferents (mechanoheat). 429,430 This subpopulation of capsaicin sensitive primary afferent neurons (CSPANs) has the capability to release neurotransmitters from both their central and peripheral nerve endings enabling dual afferent orthodromic and efferent antidromic conduction. 156,250 The neurotransmitters that are frequently associated with CSPANs are the neuropeptides SP and CGRP 156,250,251 but other transmitters such as somatostatin, glutamate, aspartate, vasoactive intestinal polypeptide and adenosine have also been related to CSPANs (reviewed in 249 ). The result of antidromically CSPAN activation is an increase in vascular permeability, plasma protein extravasation (PPE), vasodilatation and the formation of oedema, together called neurogenic inflammation (NI). SP is involved in mediating PPE 38,52,56,170,194,203,371,490 whereas CGRP is a potent dilator substance 27,37,39,110,115,336 and potentiates the PPE caused by SP. 115 Intracranially, capsaicin induces dilatation of cerebral vessels through the release of CGRP. 174 CGRP is increased in the blood of migraineurs during the attack 128 pleading for the use of capsaicin in animal models that should mimic migraine-like headache. Many anti-migraine drugs reduce dural PPE in animal models, 45,46,48,64,201,227,266,274,275,365,385,386,485 a process mediated by CSPANs. Also, antimigraine drugs were effective in reducing the activity in the TNC I,II caused by intracranial afferent stimulation with capsaicin. These observations imply the occurrence of NI, and involvement of CSPANs in migraine and the use of capsaicin as a stimulating noxious substance in animal models of trigeminovascular headache.

14 Introduction model for the vascular changes during migraine was initiated in 1984 by Lambert and colleagues. 209 The measurement of dural PPE was coupled to trigeminal ganglion stimulation a few years later by Markowitz and colleagues. 261 Up until now, besides vascular effects 96,123,126,132,337,385 and dural PPE, 23,24,40,46,64,119,178,227,266,283,337,381,385,410,470,497 Fos expression in the TNC, 61,201,292,344 c-fos mrna in the TNC, 386 electrical recordings in the TNC 211,420 and the neuropeptide release in the jugular vein 125,127 have been used to study the anti and orthodromic activity in the trigeminovascular system after electrical trigeminal ganglion stimulation. Many anti-migraine drugs have been tested in these models and reduced the activity in the trigeminal system after electrical trigeminal ganglion/nerve stimulation, 45,46,48,64,201,227,266,274,275,365,385,386,485 which implicates that it is a valuable model for the pathophysiological mechanisms that occur during the headache phase of migraine. The sagittal sinus is one of the larger blood vessels in the dura mater, innervated by trigeminal nerves, and electrical and mechanical stimulation of this vessel has been used to mimic migraineous headache, especially by the group of Lambert, Goadsby, Zagami and others. 132,211,499,500 The majority of these experiments were performed in cats and TNC I,II Fos expression and TNC electrical recordings were used to assess the orthodromic conduction characteristics of trigeminovascular afferents. Also using these models, antimigraine drugs effectively inhibited trigeminovascular nociception. 129,130,157,158,185,186,419 The dura mater is innervated by trigeminal afferents and electrical and mechanical stimulation of the dura has therefore been used by some to activate the trigeminovascular system. 44,73,183,291,422,484,485,488 The final type of trigeminovascular stimulation employs noxious chemical compounds. Inflammatory soup has been applied to the dura mater, 44,488 bradykinin has been applied on extracerebral vessels, 202 nitroglycerin was injected systemically 433,434 and blood, carrageenin 321,322 and capsaicin have all been used intracisternally. 75,78,79,296,297 Intracisternal capsaicin infusions, to stimulate intracranial nociceptive fibers, was started in Intracisternal application of irritants as model of trigeminovascular nociception was initiated by the group of Moskowitz and co-workers, who started with the intracisternal application of autologous blood and carrageenin 321,322 in 1992 but later they switched to capsaicin application. 75,78,79,296,297 In the majority of experiment, Fos expression in the TNC I,II was determined in order to assess activity of the trigeminovascular system. Anti-migraine drugs also were studied successfully in this model. 77,297,322 All described models of trigeminovascular stimulation, except for the experiments of Tassorelli and colleagues, 433,434 are conducted on anaesthetized animals. Anaesthesia has the advantage, besides ethical considerations, that the reproducibility of the experimental design is high. Whereas anaesthetics prevent pain sensation and the study of cerebral processing of the pain signal, they most likely do not hinder the nociceptive processes that generate the pain signal in the meninges or the effects that are antidromically mediated. Orthodromic conduction of the trigeminovascular system, however, as often 21

15 measured by the activity of neurons in the TNC I,II, may be affected by anaesthetics as they block the signal somewhere between the TNC and the cortex. It is not surprising 1 Electrical Chemical Mechanical Plasma protein extravasation Neuropeptides in jugular vein Vascular alterations CGRP-ir afferent quality in dura mater 4 BLOODVESSEL IN MENINGES SP CGRP Trigeminal 2 Afferent terminals Ganglion Nerve Pain sensation Antidromic conduction 3 TNC Orthodromic conduction 3 Fos expression c-fos mrna expression Glucose utilization Electrical recordings CGRP-ir afferent quality 4 SP release therefore that activity downstream from the TNC has been measured only sporadically in trigeminovascular animal models. 434,500 To our knowledge, behavioural responses initiated by trigeminovascular activation have never been investigated nor quantified in animals. Availability of a validated conscious animal model of trigeminovascular activation, may not only enable us to study the cerebral and behavioural activity associated with trigeminovascular headache, but may be especially relevant for the treatment of migraineous headache, as more and more attention is paid to the development of antimigraine drugs with a central site of action. We chose to modify an existing model of chemical trigeminovascular stimulation in anaesthetized animals so it could be applied in conscious animals. Anti-migraine drugs like ergot alkaloids, sumatriptan, and NSAIDs were already tested in anaesthetized models of 22 Figure 1.3 Schematic representation of the various animal models of trigeminovascular activation. Stimulation (1) of various parts of the trigeminovascular system (2) causes orthodromic and antidromic conduction to the trigeminal nucleus caudalis (TNC) and the perivascular afferent terminal respectively (3). As result of antidromic activation SP (substance P) and CGRP (calcitonin gene related peptide) are released at the afferent terminal. To assess the orthodromic and antidromic activity of trigeminovascular afferents, various parameters are measured (4)

16 Introduction trigeminovascular nociception. 77,158,185,186,297,322 Therefore, potential anti-migraine drugs with a possible central site of action were studied in this thesis. Also, the relationship between the immunesystem and trigeminovascular nociception will be examined. Aim and outline of this thesis. Aim of this thesis is to study physiological and pharmacological modulation of trigeminovascular headache in a modified animal model of trigeminovascular stimulation in the unrestrained rat. Section 2, titled: Characterization of an animal model of trigeminovascular headache in the conscious rat, identifies the behavioural and cerebral Fos patterns associated with various doses of intracisternally applied capsaicin in the conscious rat (see also preface on page 26) Section 3, titled: Immunesystem modulation of trigeminovascular headache, reviews the literature on immunesytem dysfunction in migraine and studies the modulation of trigeminovascular nociception by infections (see also preface on page 54) Section 4, titled: Central pharmacological modulation of trigeminovascular headache, describes the modulation of trigeminovascular stimulation by the somatostatin analogue octreotide and the neuronal NOS inhibitor 7-NitroIndazole (see preface on page 94) 23

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