Acetylsalicylic acid activates antinociceptive brain-stem reflex activity in headache patients and in healthy subjects

Exteroceptive Suppression of Masseter Muscle Activity in Juvenile Migraineurs

The second exteroceptive suppression period (ES2) of masseter or temporalis muscle activity may be reduced in adults with chronic tension-type headache. In adults with migraine, ES2 was found normal or tended to be protracted. To date, no studies on exteroceptive suppression in children and adolescents with headaches have been published. We investigated the exteroceptive suppression of masseter muscle activity in 14 migraineurs and 19 controls between 6 and 18 years of age. It was elicited by electrical stimulation at the labial commissure. No differences were found regarding the first suppression period, but ES2 was significantly longer in the migraine group than in controls. The results of the migraine group suggest overactivity of the interneurons of the reflex loop due to impaired inhibitory control from superior antinociceptive systems already at the beginning of this headache disorder.

Central effects of acetylsalicylic acid on trigeminal-nociceptive stimuli

BACKGROUND

Acetylsalicylic acid is one of the most used analgesics to treat an acute migraine attack. Next to the inhibitory effects on peripheral prostaglandin synthesis, central mechanisms of action have also been discussed.

METHODS

Using a standardized model for trigeminal-nociceptive stimulation during fMRI scanning, we investigated the effect of acetylsalicylic acid on acute pain compared to saline in 22 healthy volunteers in a double-blind within-subject design. Painful stimulation was applied using gaseous ammonia and presented in a pseudo-randomized order with several control stimuli. All participants were instructed to rate the intensity and unpleasantness of every stimulus on a VAS scale. Based on previous results, we hypothesized to find an effect of ASA on central pain processing structures like the ACC, SI and SII as well as the trigeminal nuclei and the hypothalamus.

RESULTS

Even though we did not find any differences in pain ratings between saline and ASA, we observed decreased BOLD signal changes in response to trigemino-nociceptive stimulation in the ACC and SII after administration of ASA compared to saline. This finding is in line with earlier imaging results investigating the effect of ASA on acute pain. Contrary to earlier findings from animal studies, we could not find an effect of ASA on the trigeminal nuclei in the brainstem or within the hypothalamic area.

CONCLUSION

Taken together our study replicates earlier findings of an attenuating effect of ASA on pain processing structures, which adds further evidence to a possibly central mechanism of action of ASA.

The science of migraine

The cardinal symptom of migraine is headache pain. In this paper we review the neurobiology of this pain as it is currently understood. In recent years, we discovered that the network of neurons that sense pain signals from the dura changes rapidly during the course of a single migraine attack and that the treatment of an attack is a moving target. We found that if the pain is not stopped within 10-20 minutes after it starts, the first set of neurons in the network, those located in the trigeminal ganglion, undergo molecular changes that make them hypersensitive to the changing pressure inside the head, which explains why migraine headache throbs and is worsened by bending over and sneezing. We found that if the pain is not stopped within 60-120 minutes, the second group of neurons in the network, those located in the spinal trigeminal nucleus, undergoes molecular changes that convert them from being dependent on sensory signals they receive from the dura by the first set of neurons, into an independent state in which they themselves become the pain generator of the headache. When this happens, patients notice that brushing their hair, taking a shower, touching their periorbital skin, shaving, wearing earrings, etc become painful, a condition called cutaneous allodynia. Based on this scenario, we showed recently that the success rate of rendering migraine patients pain-free increased dramatically if medication was given before the establishment of cutaneous allodynia and central sensitization. The molecular shift from activity-dependent to activity-independent central sensitization together with our recent conclusion that triptans have the ability to disrupt communications between peripheral and central trigeminovascular neurons (rather than inhibiting directly peripheral or central neurons) explain their clinical effects. Both our clinical and pre-clinical findings of the last five years point to possible short- and long-term advantages in using an early-treatment approach in the treatment of acute migraine attacks.

Acetylsalicylic acid inhibits α,β-meATP-induced facilitation of neck muscle nociception in mice--implications for acute treatment of tension-type headache

Infusion of α,β-methylene ATP (α,β-meATP) into murine neck muscle facilitates brainstem nociception. This animal experimental model is suggested to be appropriate for investigating pathophysiological mechanisms in tension-type headache. It was hypothesized that d-lysine acetylsalicylic acid (ASA, aspirin®) reverses this α,β-meATP effect. Facilitation of neck muscle nociceptive processing was induced via bilateral infusion of α,β-meATP into semispinal neck muscles (100 nM, 20 μl each) in 42 anesthetized mice. Brainstem nociception was monitored by the jaw-opening reflex elicited via electrical tongue stimulation. The hypothesis was addressed by subsequent (15, 30, 60 mg/kg) and preceding (60 mg/kg) intraperitoneal ASA injection. Saline served as control to ASA solution. Subsequent ASA dose-dependently reversed α,β-meATP-induced reflex facilitation and was the most prominent with 60 mg/kg. Preceding 60 mg/kg ASA prevented reflex facilitation. Cyclooxygenases are involved in nociceptive transmission. Former experiments showed that unspecific inhibition of cyclooxygenases does not alter the α,β-meATP effect. This suggests a specific mode of action of ASA. The concept is accepted that neck muscle nociception is involved in the pathophysiology of tension-type headache. Thus, objective proof of ASA effects in this experimental model may emphasize its major role in pharmacological treatment of tension-type headache attacks.

NSAIDs in the Acute Treatment of Migraine: A Review of Clinical and Experimental Data

Migraine is a common disabling neurological disorder with a serious socio-economical burden. By blocking cyclooxygenase nonsteroidal anti-inflammatory drugs (NSAIDs) decrease the synthesis of prostaglandins, which are involved in the pathophysiology of migraine headaches. Despite the introduction more than a decade ago of a new class of migraine-specific drugs with superior efficacy, the triptans, NSAIDs remain the most commonly used therapies for the migraine attack. This is in part due to their wide availability as over-the-counter drugs and their pharmaco-economic advantages, but also to a favorable efficacy/side effect profile at least in attacks of mild and moderate intensity. We summarize here both the experimental data showing that NSAIDs are able to influence several pathophysiological facets of the migraine headache and the clinical studies providing evidence for the therapeutic efficacy of various subclasses of NSAIDs in migraine therapy. Taken together these data indicate that there are several targets for NSAIDs in migraine pathophysiology and that on the spectrum of clinical potency acetaminophen is at the lower end while ibuprofen is among the most effective drugs. Acetaminophen and aspirin excluded, comparative trials between the other NSAIDs are missing. Since evidence-based criteria are scarce, the selection of an NSAID should take into account proof and degree of efficacy, rapid GI absorption, gastric ulcer risk and previous experience of each individual patient. If selected and prescribed wisely, NSAIDs are precious, safe and cost-efficient drugs for the treatment of migraine attacks.

Managing migraine associated with sensitization

The majority of migraineurs seeking secondary or tertiary medical care experience throbbing pain and cutaneous allodynia during the course of migraine. Underlying the origin of these symptoms are peripheral and central trigeminovascular neurons, whose cell bodies are located in the trigeminal ganglion and the spinal dorsal horn, respectively. The development of throbbing in the initial phase of migraine is mediated by sensitization of peripheral trigeminovascular neurons, whereas the development of cutaneous allodynia later in the attack is propelled by sensitization of central trigeminovascular neurons which, unfortunately, are not equipped to respond to triptans directly. Triptans appear to act presynaptically in the dorsal horn, such as to inhibit signal transmission from peripheral to central trigeminovascular neurons. Reining in the central neurons using triptan treatment is possible as long as their excitability remains driven by incoming signals from the meninges, but not after they develop autonomous activity. Accordingly, attacks with allodynia can be effectively terminated, provided that the patient vigilantly resorts to triptan therapy before or soon after the onset of allodynia, but not after allodynia has become firmly established. On the other hand, allodynic patients who missed the critical window for effective triptan therapy can still be rendered pain-free using an intravenous infusion of non-steroidal anti-inflammatory drugs.

Rofecoxib versus ibuprofen for acute treatment of migraine: a randomised placebo controlled trial

BACKGROUND

Rofecoxib is a potent cyclo-oxygenase-2 inhibitor with a long duration of action. Its role in migraine has not been systematically evaluated.

AIM

To study the efficacy of rofecoxib in migraine.

METHOD

In a randomised placebo controlled trial rofecoxib 25 mg, ibuprofen 400 mg, and placebo were compared regarding their efficacy in relieving acute migraine attack. Migraine patients with 2-6 attacks per month were recruited. Headache severity, functional disability, and severity of associated symptoms were graded on a 0-3 scale. The primary endpoint was pain relief at two hours. Relief of associated symptoms and sustained pain relief for 24 hours were also noted.

RESULT

One hundred and twenty four patients were randomised into rofecoxib (42), ibuprofen (40), and placebo (42) groups. One hundred and one patients were followed up: 33 on rofecoxib, 35 ibuprofen, and 33 placebo. Patients' ages ranged from 16-62 (mean 31.4) years, and 83 were females. Pain relief at two hours was noted in 45.5% on rofecoxib, 55.6% on ibuprofen, and 9.1% in the placebo group. The associated symptoms at two hours were reduced in 39.4% on rofecoxib, 50% on ibuprofen, and 9.1% in the placebo group. Sustained 24 hour pain relief was noted in 36.4% on rofecoxib, 41% on ibuprofen, and 6.1% in the placebo group. In the ibuprofen group, five patients had abdominal pain but there were no side effects in those on rofecoxib or in the control group. Both rofecoxib and ibuprofen were significantly effective in relieving pain, associated symptoms at two hours, and in sustained pain relief. There was no significant difference between rofecoxib and ibuprofen in aborting acute migraine attacks.

CONCLUSIONS

Both ibuprofen and rofecoxib were superior to placebo in aborting an acute migraine attack, and there was no significant difference in their efficacy in an acute migraine attack.

Central sensitization in tension-type headache--possible pathophysiological mechanisms

The aim of the present thesis was to investigate the pathophysiology of chronic tension-type headache with special reference to central mechanisms. Increased tenderness to palpation of pericranial myofascial tissues is the most apparent abnormality in patients with tension-type headache. A new piece of equipment, a so-called palpometer, that makes it possible to control the pressure intensity exerted during palpation, was developed. Thereafter, it was demonstrated that the measurement of tenderness could be compared between two observers if the palpation pressure was controlled, and that the Total Tenderness Scoring system was well suited for the scoring of tenderness during manual palpation. Subsequently, it was found that pressure pain detection and tolerance thresholds were significantly decreased in the finger and tended to be decreased in the temporal region in chronic tension-type headache patients compared with controls. In addition, the electrical pain threshold in the cephalic region was significantly decreased in patients. It was concluded that the central pain sensitivity was increased in the patients probably due to sensitization of supraspinal neurones. The stimulus-response function for palpation pressure vs. pain was found to be qualitatively altered in chronic tension-type headache patients compared with controls. The abnormality was related to the degree of tenderness and not to the diagnosis of tension-type headache. In support of this, the stimulus-response function was found to be qualitatively altered also in patients with fibromyalgia. It was concluded that the qualitatively altered nociception was probably due to central sensitization at the level of the spinal dorsal horn/trigeminal nucleus. Thereafter, the prophylactic effect of amitriptyline, a non-selective serotonin (5-HT) reuptake inhibitor, and of citalopram, a highly selective 5-HT reuptake inhibitor, was examined in patients with chronic tension-type headache. Amitriptyline reduced headache significantly more than placebo, while citalopram had only a slight and insignificant effect. It was concluded that the blockade of 5-HT reuptake could only partly explain the efficacy of amitriptyline in tension-type headache, and that also other actions of amitriptyline, e.g. reduction of central sensitization, were involved. Finally, the plasma 5-HT level, the platelet 5-HT level and the number of platelet 5-HT transporters were found to be normal in chronic tension-type headache. On the basis of the present and previous studies, a pathophysiological model for tension-type headache is presented. According to the model, the main problem in chronic tension-type headache is central sensitization at the level of the spinal dorsal horn/trigeminal nucleus due to prolonged nociceptive inputs from pericranial myofascial tissues. The increased nociceptive input to supraspinal structures may in turn result in supraspinal sensitization. The central neuroplastic changes may affect the regulation of peripheral mechanisms and thereby lead to, for example, increased pericranial muscle activity or release of neurotransmitters in the myofascial tissues. By such mechanisms the central sensitization may be maintained even after the initial eliciting factors have been normalized, resulting in the conversion of episodic into chronic tension-type headache. Future basic and clinical research should aim at identifying the source of peripheral nociception in order to prevent the development of central sensitization and at ways of reducing established sensitization. This may lead to a much needed improvement in the treatment of chronic tension-type headache and other chronic myofascial pain conditions.

Relation between perceived stimulus intensity and exteroceptive reflex responses in the human masseter muscles

OBJECTIVES

Two periods of exteroceptive suppression are elicited in human masseter muscle following perioral electrical stimulation: ES 1 and ES2. Furthermore, in the masseter EMG, two periods of apparent excitation can be distinguished from the background activity: intersuppression period (ISP) and post-suppression period (PSP). In the present study, the relationship between nociception and ES1, ISP and PSP was investigated.

METHODS

The reflex responses were electrically elicited in 15 volunteers. A novel computer algorithm was used to detect and quantitate ES1, ES2, ISP and PSP.

RESULTS

(a) ES1 and ES2 were more susceptible to changes in magnitude of suppression and excitation, respectively, than ISP and PSP; (b) the on-set latencies were almost unaffected; (c) both ES1 and ES2 occurred at stimulus intensities well below pain threshold; (d) magnitude of ES1 and ES2 suppression increased with increasing stimulus intensity, but supra pain threshold stimulation did not result in further suppression; and (e) no correlation was found between perceived stimulus intensity and ES1, ISP or PSP.

CONCLUSIONS

The increase in ES1 and ES2 suppression seen in our study at increasing stimulus intensity is suggested to be mediated by activity in both nociceptive and non-nociceptive fibres converging onto central interneurones in the reflex circuits. We suggest that neither ISP nor PSP are reflex responses. It is unlikely that ES1, ES2, ISP and PSP evoked by electrical stimuli are directly linked to noxious activity.

Exteroceptive suppression of temporalis and masseter muscle activity is enhanced in offspring of hypertensives

Exteroceptive suppression of temporalis and masseter muscle activity was examined in young men with and without a parental history of hypertension. Recent clinical studies suggest that the second exteroceptive suppression period is attenuated in several chronic pain disorders and that this brainstem reflex may serve as a noninvasive index of endogenous pain control. In the present study, offspring of hypertensives exhibited a significant protraction of the late exteroceptive suppression period for both muscle sites, suggesting that the decreased pain sensitivity previously observed in individuals at risk for hypertension may be related to enhanced central pain modulation.

Influence of aspirin on the contingent negative wave in healthy subjects

A study was made of the alterations of the parameters of the slow brain potential, the contingent negative wave, under the influence of aspirin in healthy individuals, using the double blind method. The early and late wave of the CNW were investigated. A statistically significant decrease in the early CN wave was obtained after the ingestion of aspirin, and an increase in the late wave after the ingestion of aspirin and placebo. A central effect of aspirin, affecting the noradrenergic and dopaminergic brain systems, is hypothesized to explain the changes described.

Exteroceptive suppression of temporal muscle activity is normal in chronic tension-type headache and not related to actual headache state

The aim of the present study was to compare the late exteroceptive suppression period (ES2) of temporalis muscle activity between patients with chronic tension-type headache and healthy controls, and to investigate the influence, if any, of actual headache on ES2. ES2 was recorded in 55 patients and in 55 controls with a previously evaluated methodology and analysed by a blinded observer. The first 20 patients were randomly studied on 2 additional days, 1 day with and 1 day without headache. The duration of ES2 did not differ between patients and controls and did not differ on days with headache compared with days without headache. ES2 duration was not related to the frequency of headache, headache intensity, age, pericranial muscle tenderness or electrical pain threshold. Our results strongly indicate that ES2 is normal in chronic tension-type headache and therefore may not be related to the pathophysiology of this disorder.

Central and peripheral mechanisms in chronic tension-type headache

The second exteroceptive suppression of masseter muscle activity (ES2) and tenderness in pericranial muscles were evaluated in 112 young adults who met IHS criteria in the following diagnostic classifications: 31 chronic tension headache, 31 episodic tension headache, 33 migraine without aura and 17 migraine with aura. An additional 31 subjects served as controls. Pericranial muscle tenderness better distinguished diagnostic subgroups and better distinguished recurrent headache sufferers from controls than did masseter ES2. Chronic tension headache sufferers exhibited the highest pericranial muscle tenderness, and controls exhibited the lowest tenderness (P < 0.01). All chronic tension headache sufferers exhibited muscle tenderness in at least one of the pericranial muscles evaluated, while tenderness was exhibited by 52% of controls. The association between pericranial muscle tenderness and chronic tension headache was independent of the intensity, frequency, or chronicity of headaches. Our findings raise the possibility that pericranial muscle tenderness is present early in the development of tension headache, while ES2 suppression only emerges later in the evolution of the disorder.

The effects of aspirin on the CNV in healthy individuals

The effects of aspirin on the contingent negative variation (CNV) of 16 healthy, right-handed volunteers were studied in accordance with a placebo-controlled double-blind crossover design. Early and late CNV factors were measured. Aspirin caused a statistically significant decrease of the early wave and an increase of mean amplitude of the late wave. A central action of aspirin, affecting noradrenergic and dopaminergic structures, may be responsible for the CNV changes.

Combined oral lysine acetylsalicylate and metoclopramide in the acute treatment of migraine: a multicentre double-blind placebo-controlled study

This multicentre, double-blind, randomized, placebo-controlled, parallel study was designed to evaluate the efficacy of combined oral lysine acetylsalicylate and metoclopramide (LAS-MCP) in the acute treatment of migraine attacks. A total of 266 patients, 18-65 years old, with two to six attacks of migraine with or without aura (IHS criteria) per month were included. The patients had to treat two migraine attacks with LAS-MCP (1620 mg lysine acetylsalicylate--the equivalent of 900 mg aspirin--combined with 10 mg metoclopramide) or placebo. The main outcome measure was headache relief (reduction in headache severity from grade 3 or 2--severe or moderate--to grade 1 or 0--mild or none) 2 h after treatment. LAS-MCP was superior to placebo for headache relief (56% vs 28%) and for the following secondary outcome measures: complete headache relief (18% vs 7%; p < 0.001), nausea (28% vs 44%; p < 0.001), vomiting (3% vs 11%; p = 0.001), use of rescue medication (47% vs 68%; p < 0.001), global efficacy judged as good or excellent (32% vs 14%; p < 0.001). The tolerability was considered as good in 94% of treated attacks in both groups. Combined oral lysine acetylsalicylate and metoclopramide is an effective and well-tolerated acute treatment of migraine attacks.

Exteroceptive suppression of temporalis muscle activity during migraine attack and migraine interval before and after treatment with sumatriptan

We compared the early (ES1) and late (ES2) exteroceptive suppression (ES) periods of temporalis muscle activity in 18 migraine patients during both the migraine interval and migraine attack and investigated the effect of sumatriptan and placebo on ES parameters. The measurements were performed in a balanced sequence at four different times on each patient, twice during the migraine interval and once in each of two migraine attacks. First ES1 and ES2 were measured (stimulus intensity 20 mA, stimulus duration 0.2 ms, stimulation frequency 2 Hz, averaging of 10 responses), then the medication was given on a double-blind basis with an autoinjector using either 6 mg sumatriptan or a placebo solution. Thirty minutes after application the measurements were repeated. No significant differences were found in early and late exteroceptive suppression latencies and durations between baseline measurements. Treatment did not affect the latencies of ES1 and ES2. While sumatriptan caused a significant increase in ES1 duration (p < or = 0.05) both during the migraine interval and during the migraine attack, placebo showed no significant effect on ES1 duration. Treatment with sumatriptan during the migraine attack was accompanied by a significant increase in the duration of ES2 (p < or = 0.05), but no significant changes in the durations of the late suppression periods were observed under any other conditions. The results do not support the assumption that under the experimental conditions chosen migraine attacks are accompanied by a paroxysmal change in the brain-stem mechanisms involved in the modulation of the ES parameters.(ABSTRACT TRUNCATED AT 250 WORDS)

Exteroceptive suppression periods in jaw-closing muscles. Variability and relation to experimental pain and sustained muscle contraction

The duration of the late exteroceptive suppression period (ES2) of temporal muscle EMG activity has been reported to be reduced in patients suffering from chronic tension-type headache. Methods of recording and analysing ES2 have varied between centers and reproducibility of results within subjects, although insufficiently studied, has generally been poor. ES2 was investigated in 30 healthy subjects, using a computerized technique of recording, rectifying and averaging the EMG signals. Hour to hour and week to week variations of ES2 durations were calculated, and the influence of pain during a cold pressor test and of sustained muscle contraction on ES2 durations was investigated. The intra-individual variation of ES2 durations was 16.0% from hour to hour and 20.7% from week to week. The inter-individual variation was 36.7%. The present method for analysis of ES2 periods proved to be reliable, as the intra-observer variation was 4.2% and the inter-observer variation 4.6%. ES2 periods were significantly shorter on the first compared to the second day of examination (p = 0.006) and during experimental pain (p = 0.0005). We recommend the use of the computerized average technique in future studies and caution against the dependence of results upon factors such as conditioning and pain.

Exteroceptive suppression of temporalis muscle activity: findings in headache

Exteroceptive suppression of temporalis muscle activity was proposed by Schoenen and co-workers in 1987 as a tool in headache diagnosis and research. Their finding of a decreased or abolished second silent period (ES2) in chronic tension-type headache sufferers has been confirmed by several independent laboratories during the last five years. Temporalis silent periods have also been studied in various other types of headaches. Their modulation by neuropsychological factors and pharmacological agents has also been investigated as well as their retest reliability. The pathophysiological concept of muscle contraction in tension-type headache has been challenged by studies using temporalis silent periods. The exteroceptive suppression of temporalis muscle activity points unequivocally towards a central pathogenetic mechanism, although it remains unclear whether the abnormalities of temporalis ES2 represent the primary dysfunction or a secondary phenomenon in chronic tension-type headache.

Exteroceptive suppression of temporalis muscle activity: methodological and physiological aspects

In recent years studies of the suppression of EMG activity in temporalis muscle induced by stimulation in the trigeminal territory have opened new perspectives in headache research. The various methods that have been used in different laboratories are reviewed and some of the physiological modulations of temporalis exteroceptive suppression are described. Among different methods of recording, averaging 10 full-wave rectified EMG responses produces results with acceptable variability and discomfort. In order to obtain maximal responses the intensity of the stimulation should reach at least 20 mA. To avoid habituation of the second temporalis exteroceptive suppression period (ES2), the stimulation frequency has to be at 0.1 Hz or below. The level of voluntary contraction is not a critical variable as long as it reaches 50% of maximum. Some physiological variations of temporalis suppression are well documented. In females, ES2 is shorter during menstruation than at mid-cycle and correlated with the estradiol/progesterone ratio in plasma. Conditioning temporalis ES2 by a preceding peripheral stimulus markedly reduces its duration, which is partly reversible by naloxone. Various pharmacological agents are able to modify temporalis ES2: its duration is increased by 5-HT1 antagonists, but decreased by 5-HT uptake blockers; contradictory results have been obtained with acetylsalicylic acid. These results suggest that inhibitory brain-stem interneurons mediating temporalis ES2 are inhibited by serotonergic afferents, probably from the raphe magnus nucleus, and that the latter receives an excitatory input from the periaqueductal gray matter and other limbic structures, in part via opioid receptors.

Exteroceptive suppression of temporalis muscle activity: perspectives in headache and pain research

The paper describes possible future applications of the exteroceptive suppression (ES) of temporalis muscle activity in headache and pain research. ES is examined as a method for investigating the pathophysiology of pain mechanisms, for assisting clinical diagnosis, and for evaluating therapeutic effects. ES is one of the newest methods in headache research which permits an objective analysis of head pain as well as pain mechanisms and accordingly has an important future in headache research.