Zolmitriptan reverses blink reflex changes induced during the migraine attack in humans

Preventive treatment with CGRP monoclonal antibodies restores brain stem habituation deficits and excitability to painful stimuli in migraine: results from a prospective case-control study

Background & Objectives

Calcitonin gene-related peptide ligand/receptor (CGRP) antibodies effectively reduce headache frequency in migraine. It is understood that they act peripherally, which raises the question whether treatment merely interferes with the last stage of headache generation or, alternatively, causes secondary adaptations in the central nervous system and might thus possess disease modifying potential. This study addresses this question by investigating the nociceptive blink reflex (nBR), which is closely tied to central disease activity, before and after treatment with CGRP antibodies.

Methods

We enrolled 22 patients suffering episodic migraine (21 female, 46.2 ± 13.8 years of age) and 22 age-/gender-matched controls. Patients received assessments of the nBR (R2 component, 10 trials, 6 stimuli/trial) before (V0) and three months (V3) after treatment with CGRP antibodies started, controls were assessed once. The R2 area (R2a) and habituation (R2h; gradient of R2a against stimulus order) of the stimulated/non-stimulated side (_s/_ns) following repeated supraorbital stimulation provide a direct readout of brainstem excitability and habituation as key mechanisms in migraine.

Results

All patients showed a substantial reduction of headache days/month (V0: 12.4±3.3, V3: 6.6 ± 4.9). R2a_s (F_global=5.86, p<0.001; block 1: R2a_s: -28%, p<0.001) and R2a_ns (F_global=8.22, p<0.001, block 1: R2a_ns: -22%, p=0.003) were significantly decreased, and R2h_ns was significantly enhanced (F_global=3.07, p<0.001; block 6: R2h_ns: r=-1.36, p=0.007) from V0 to V3. The global test for changes of R2h_s was non-significant (F_global=1.46, p=0.095). Changes of R2h significantly correlated with improvement of headache frequency (R2h_s, r=0.56, p=0.010; R2h_ns: r=0.45, p=0.045). None of the nBR parameters assessed at baseline predicted treatment response.

Discussion

We provide evidence that three months of treatment with CGRP antibodies restores brain stem responses to painful stimuli and thus might be considered disease modifying. The nociceptive blink reflex may provide a biomarker to monitor central disease activity. Future studies should evaluate the blink reflex as a clinical biomarker to predict treatment response at baseline and to establish the risk of relapse after treatment discontinuation.

Trial registration

This trial was prospectively registered at clinicaltrials.gov (ID: NCT04019496, date of registration: July 15, 2019).

Defensive reflexes in people with pain – a biomarker of the need to protect? A meta-analytical systematic review

Upregulation of defensive reflexes such as the nociceptive flexion reflex (NFR) has been attributed to sensitisation of peripheral and spinal nociceptors and is often considered biomarkers of pain. Experimental modulation of defensive reflexes raises the possibility that they might be better conceptualised as markers of descending cognitive control. Despite strongly held views on both sides and several narrative reviews, there has been no attempt to evaluate the evidence in a systematic manner. We undertook a meta-analytical systematic review of the extant English-language literature from inception. Thirty-six studies satisfied our a priori criteria. Seventeen were included in the meta-analysis. Reflexive threshold was lower in people with clinical pain than it was in pain-free controls, but reflex size, latency, and duration were unaffected. The pattern of difference was not consistent with sensitisation of nociceptive neurones, as these changes were not isolated to the affected body part but was more consistent with top-down cognitive control reflective of heightened protection of body tissue. The pattern of modulation is dependent on potentially complex evaluative mechanisms. We offer recommendations for future investigations and suggest that defensive reflex threshold may reflect a biomarker of a broader psychological construct related to bodily protection, rather than sensitisation of primary nociceptors, spinal nociceptors, or pain.

Pharmacology of reflex blinks in the rat: a novel model for headache research

Background

Migraineurs are highly sensitive to the nitric oxide donor glyceryl trinitrate which triggers attacks in many sufferers. In animal studies, glyceryl trinitrate increases neuronal activity in the trigeminovascular pathway and elevates neurotransmitter levels in the brainstem. Many migraineurs also display alterations in blink reflexes, known to involve brainstem circuits. We investigated the effect of GTN on evoked blinks in the anaesthetised rat to determine whether such reflexes may prove useful as the basis for a novel animal model to evaluate potential anti-migraine therapeutic agents.

Method

In anaesthetised rats the electromyogram associated with the reflex blink evoked by corneal airpuff was recorded. Rats were infused with glyceryl trinitrate, sumatriptan plus glyceryl trinitrate or vehicle control. Changes in the magnitude of the reflex blink-associated electromyogram following these treatments were measured.

Results

Glyceryl trinitrate potentiated the evoked reflex blink-associated EMG response from 2 h after infusion. That effect was abolished by simultaneous infusion of sumatriptan with glyceryl trinitrate.

Conclusions

These results show that simple skin surface measurements of evoked electromyographic activity in the rat can reliably detect the evoked blink reflex that can be potentiated by nitric oxide donors. This novel model may be an effective tool for evaluating putative anti-migraine therapeutic agents.

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.

Trigeminal somatosensorial evoked potentials suggest increased excitability during interictal period in patients with long disease duration in migraine

INTRODUCTION

Migraine pathogenesis is suggested to involve many structures in cerebral cortex, brainstem and trigeminovascular system. Electrophysiological studies revealed loss of habituation, decreased cortical preactivation, segmental hypersensitivity and reduction in control of inhibitory descending pathways. Given these information, we aimed to evaluate the excitability changes of the trigeminal pathway in the cortex and brainstem in migraine using trigeminal nerve somatosensory evoked potentials (TSEP).

PATIENTS AND METHOD

Fifty-one women with migraine without aura and 32 age-matched healthy women were included. TSEPs were recorded in migraine patients during interictal period and in healthy subjects. Sensory thresholds, stimulation intensities, latencies of N1, P1, N2 and P2 waves as well as N1/P1 and N2/P1 amplitudes were measured.

RESULTS

Comparisons of ipsilateral latencies with N1-P1 and N2-P1 amplitudes between migraine and control groups showed no difference. Sensory thresholds were also similar. Stimulation thresholds decreased as the attack frequency increased and ipsilateral N1/P1 amplitude increased with prolonged disease duration (p=0.043).

CONCLUSION

Our study did not show significant difference between migraine patients and healthy subjects during interictal period. However, migraine with long duration affects the excitability of the cortical and brainstem trigeminal pathways even during interictal periods.

Nociception-specific blink reflex: pharmacology in healthy volunteers

BACKGROUND

The physiology and pharmacology of activation or perception of activation of pain-coding trigeminovascular afferents in humans is fundamental to understanding the biology of headache and developing new treatments.

METHODS

The blink reflex was elicited using a concentric electrode and recorded in four separate sessions, at baseline and two minutes after administration of ramped doses of diazepam (final dose 0.07 mg/kg), fentanyl (final dose 1.11 μg/kg), ketamine (final dose 0.084 mg/kg) and 0.9 % saline solution. The AUC (area under the curve, μV*ms) and the latency (ms) of the ipsi- and contralateral R2 component of the blink reflex were calculated by PC-based offline analysis. Immediately after each block of blink reflex recordings certain psychometric parameters were assessed.

RESULTS

There was an effect due to DRUG on the ipsilateral (F 3,60 = 7.3, P < 0.001) AUC as well as on the contralateral (F 3,60 = 6.02, P < 0.001) AUC across the study. A significant decrement in comparison to placebo was observed only for diazepam, affecting the ipsilateral AUC. The scores of alertness, calmness, contentedness, reaction time and precision were not affected by the DRUG across the sessions.

CONCLUSION

Previous studies suggest central, rather than peripheral changes in nociceptive trigeminal transmission in migraine. This study demonstrates a robust effect of benzodiazepine receptor modulation of the nociception specific blink reflex (nBR) without any μ-opiate or glutamate NMDA receptor component. The nociception specific blink reflex offers a reproducible, quantifiable method of assessment of trigeminal nociceptive system in humans that can be used to dissect pharmacology relevant to primary headache disorders.

Effects of subthalamic deep brain stimulation on blink abnormalities of 6-OHDA lesioned rats

Parkinson's disease (PD) patients and the 6-hydroxydopamine (6-OHDA) lesioned rat model share blink abnormalities. In view of the evolutionarily conserved organization of blinking, characterization of blink reflex circuits in rodents may elucidate the neural mechanisms of PD reflex abnormalities. We examine the extent of this shared pattern of blink abnormalities by measuring blink reflex excitability, blink reflex plasticity, and spontaneous blinking in 6-OHDA lesioned rats. We also investigate whether 130-Hz subthalamic nucleus deep brain stimulation (STN DBS) affects blink abnormalities, as it does in PD patients. Like PD patients, 6-OHDA-lesioned rats exhibit reflex blink hyperexcitability, impaired blink plasticity, and a reduced spontaneous blink rate. At 130 Hz, but not 16 Hz, STN DBS eliminates reflex blink hyperexcitability and restores both short- and long-term blink plasticity. Replicating its lack of effect in PD patients, 130-Hz STN DBS does not reinstate a normal temporal pattern or rate to spontaneous blinking in 6-OHDA lesioned rats. These data show that the 6-OHDA lesioned rat is an ideal model system for investigating the neural bases of reflex abnormalities in PD and highlight the complexity of PD's effects on motor control, by showing that dopamine depletion does not affect all blink systems via the same neural mechanisms.

Variability of the blink reflex in patients with migraine

BACKGROUND AND PURPOSE

Sensitization of brainstem trigeminal nuclei and activation of the trigeminovascular system are thought to play an important role in migraine. The blink reflex has become a valuable tool for investigating trigeminal nerve function. The aim of the study was to assess the differences in electrophysiological examinations of the trigeminal nerve (blink reflex) in a group of patients with migraine in comparison with a healthy control group.

MATERIAL AND METHODS

The examination was conducted among 58 patients. Patients were diagnosed in the Polyclinic or hospitalized in the Department of Neurology of Warsaw Medical University in Bielański Hospital. The study group included 29 patients suffering from migraine (diagnosed according to the International Classification of Headache Disorders, 2nd edition) and 29 patients without headaches served as controls. All patients underwent neurological examination and magnetic resonance imaging to identify organic disorders. The blink reflex was tested among all patients in accordance with electrophysiological laboratory standards.

RESULTS

The latency of the R1 response was significantly shorter among patients with migraine. The latency of R2 and R2' responses was similar in patients and controls. A significant inverse correlation was observed between latency of R2 and R2' responses and frequency of migraine attacks.

CONCLUSIONS

The inverse correlation between the frequency of attacks and the latency of R2 and R2' responses of the blink reflex confirms the abnormal eaxcitability induced by the high frequency of migraine attacks.

Inhibition of the PKCγ-ε pathway relieves from meningeal nociception in an animal model: an innovative perspective for migraine therapy?

There is convincing evidence that nitric oxide (NO) may be a causative factor in the pathogenesis of migraine. We investigated the consequences of NO donors' administration on meningeal processes related to the development of migraine pain in an animal model of meningeal nociception. The administration in mice of the NO donors nitroglycerin (GTN) and sodium nitroprusside (SNP) produced a delayed meningeal upregulation of interleukin-1ß and inducible NO synthase. A thermal allodynia and hyperalgesia devoid of side effects was produced 1 to 4 h after administration. To clarify the cellular pathways modulated by GTN and SNP, we examined the expression of cellular factors involved in pain modulation, such as protein kinase C (PKC) and its downstream effectors. Western blotting experiments showed an upregulation and increased phosphorylation of PKCγ and PKCε within dura mater after NO donors' administration. A dramatic PKC-dependent increase of the phosphorylation of cyclic AMP response element binding protein (CREB) and signal transducer and activator of transcription (STAT)-1 was observed, along with an activation of the nuclear factor-κB (NF-κB) pathway, as reflected by a reduction of the inhibitory protein-κ-Bα (IκBα). Furthermore, the PKC blocker, Calphostin C, prevented the GTN and SNP-induced pain hypersensitivity. These results suggest the relevance of the PKC-mediated pathway in the induction of meningeal nociception and might help clarify the etiopathology of migraines. We can suggest PKC as a new target for migraine pain.

Where does a migraine attack originate? In the brainstem

Migraine is a common, paroxysmal, highly disabling primary headache disorder. The origin of migraine attacks is enigmatic. Numerous clinical and experimental results suggest that the activation of distinct brainstem nuclei is crucial in its pathogenesis, but the primary cause of this activation is not fully understood. We conclude that the initialization of a migraine attack can be explained as an altered function of the neuronal elements of the brainstem nuclei. In light of our findings and the literature data, we can assume that migraine is a subcortical disorder of a specific brainstem area.

Oral nitric-oxide donor glyceryl-trinitrate induces sensitization in spinal cord pain processing in migraineurs: a double-blind, placebo-controlled, cross-over study

Nitric-oxide donor glyceryl-trinitrate (GTN) modulates cerebral and spinal regions that are involved in migraine and pain processing. We hypothesized that in migraineurs, the susceptibility to develop a migraine attack after GTN administration should parallel with an high sensitivity to GTN-induced change in the pain processing at spinal level. We used the temporal summation threshold (TST) of the lower limb nociceptive withdrawal reflex (NWR) and the related pain sensation to study in parallel the time-course of the effect of the GTN administration on the pain processing at spinal level in migraine and healthy subjects. Twenty-eight (21 F; 7M; mean age 34.2 ± 8.2) migraine and 15 (11 F; 4M; mean age 35.9 ± 8.9) healthy subjects were recruited in a double-blind, placebo-controlled, cross-over trial. Neurophysiological examinations were carried out before (baseline) and 30', 60', 120', 180' and 240' after GTN (0.9 mg sublingual) or placebo administration during two different sessions. In migraineurs, GTN administration was associated to a significant facilitation in temporal summation of pain (reduced TST and increased painful sensation) 60', 120' and 180' after drug intake when compared to baseline, to placebo condition and to controls after GTN intake. Furthermore, in migraineurs who developed migraine after GTN, a significant facilitation in temporal summation of pain was detected 60', 120' and 180' after drug intake when compared to patients without clinical response. In migraineurs the susceptibility to develop migraine attack after GTN administration seems to be a specific trait of a subgroup of patients linked to a supersensitivity of the pain system to GTN.

Sumatriptan and corneal reflexes in headache-free migraine patients: a randomized and placebo-controlled crossover study

A temporary sensitization of central trigeminal neurones in migraine patients during acute attacks has been described in previous studies using the electrically evoked nociceptive blink reflex. The cornea is innervated by small myelinated A-delta and unmyelinated C-fibres only. Stimulation with air puffs activates peripheral nociceptors and allows the investigation of peripheral trigeminal nerve structures. Our objective was to investigate whether corneal reflex examinations with air puff stimulation detect abnormalities in migraineurs during their pain-free interval and if the corneal reflex may be modulated by the administration of an oral triptan. After validation of the nociceptive air puff technique by investigating the corneal reflexes before and after a local anaesthesia of the cornea, we recorded corneal reflexes in 25 migraineurs during their pain-free period and 25 healthy controls before and after the oral administration of 100 mg sumatriptan in a randomized, placebo-controlled, crossover study. Baseline response areas under the curve (AUCs) and latencies of the R2 components of the corneal reflexes did not show any significant differences between patients and controls. Patients did not show any significant differences regarding their headache and non-headache side. The use of an oral triptan had no significant influence on latencies or AUCs in both patients and controls. Our data suggest that there is no facilitation of the trigeminal system in the headache-free interval among patients with migraine. The stable corneal reflexes after the oral administration of 100 mg sumatriptan suggest that there was no inhibition of the trigeminal system, both in patients during their headache-free period and in healthy controls.

Blink reflex R2 amplitudes in cervicogenic headache, chronic tension-type headache and migraine

Blink reflex R2 amplitude was investigated in seven patients with cervicogenic headache (CEH), 12 patients with chronic tension-type headache, 23 patients with migraine (10 with aura) and 17 headache-free controls. Standard electrical stimulation of the supraorbital nerve was applied and the response was recorded from the ipsilateral and the contralateral orbicularis oculi muscles. Low R2 amplitude was found in CEH patients compared with control subjects. Headache is unilateral in CEH and the ipsilateral and contralateral responses after stimulation on the painful side were most depressed. R2 amplitude was not significantly affected in migraine and tension headache patients. The results suggest that lower brainstem excitability is reduced in CEH. A state of hypoactivity may be present in caudal trigeminal nucleus neurons on the symptomatic side.

Change of Excitability in Brainstem and Cortical Visual Processing in Migraine Exhibiting Allodynia

BACKGROUND

Clinical and neurophysiological manifestations of information processing associated with central sensitization are little known. Allodynic migraine (AM) can be caused by the sensitization of trigeminal neuron, but no study has reported on AM between attacks using blink reflex (BR) and pattern-reversal visual evoked potentials (PVEPs).

OBJECTIVE

We explored the characteristics of AM between attacks associated with central sensitization using BR and PVEP.

METHODS

We recruited 13 patients with interictal AM and 15 patients with nonallodynic migraine (NA), and 30 healthy subjects (HS). BRs were obtained using paired pulses delivered at the interstimulus interval (ISI) of 150, 300, and 500 ms. The ratio of the area in the R2 of the second to R2 of the first shock was measured for each ISI. PVEP were recorded with 2 spatial frequencies (0.5 and 4.0 cpd) and 2 low and high contrasts (29% and 98%, respectively). Amplitudes of P100 were measured.

RESULTS

For BR, there were no significant differences in the ratio of the area of the R2 between the sides of stimulation, and the sides of headache. AM patients had less suppression of the R2 at the ISI of 150 and 300 ms when compared with the NA patients and HS. For PVEP, at 0.5, there were significant differences of amplitude between AM patients and HS, and between NA patients and HS in low and high contrast. At 4.0 cpd, there were significant differences of amplitude between AM patients and HS in low contrast, and between AM patients and HS, and NA patients and HS in high contrast. In AM patients, there was a significant difference of amplitude ratio between 0.5 and 4.0 cpd. Conclusions.-Our BR and PVEP study showed that migraine patients exhibiting allodynia may show central sensitization of brainstem trigeminal neuron and have contrast modulating dysfunction during the cortical visual processing of striate and extrastriate on visual cortex in-between attacks.

Nociceptive Blink Reflex and Visual Evoked Potential Habituations Are Correlated in Migraine

BACKGROUND

Lack of habituation, as reported in migraine patients between attacks for evoked cortical responses, was also recently found for the nociceptive blink reflex (nBR) mediated by brainstem neurons. It is not known if both brain stem and cortical habituation deficits are correlated in the same patient, which would favor a common underlying mechanism.

OBJECTIVE

To search for intraindividual correlations between habituation of pattern reversal-visual evoked potentials and that of the nociception-specific blink reflex in migraineurs and in healthy volunteers (HV).

METHODS

We recorded 15 HV and 15 migraine without aura patients between attacks. Habituation for visual evoked potentials was measured by comparing the N1-P1 amplitude change (%) between the first and sixth block of 100 sequential averaged responses. Habituation for the nBR was defined as the percentage change of the R2 response area between the 1st and 10th block of five averaged EMG responses, elicited by stimulating the right side every 2 minutes for 32 minutes. We also calculated the slope of N1-P1 amplitude and R2 response area changes from the first to the last response and the correlation with attack frequency.

RESULTS

A significant habituation deficit in both cortical and brain stem evoked activity characterized on average the group of migraineurs compared to controls. In migraine patients, but not in HV, we found a significant positive correlation between habituation of pattern reversal-visual evoked potentials and that of the nociception-specific blink reflex both for the degree of habituation between first and last blocks of averagings (r = 0.703; P = .003) and for the habituation slope (r = 0.751; P = .001). Moreover, nBR habituation was positively correlated with attack frequency (r = 0.548; P = .034).

CONCLUSION

The positive correlation between visual evoked potential and nBR habituations is consistent with the idea that in migraine the same neurobiological dysfunction might be responsible for the habituation deficit both in cortex and brain stem. As nBR habituation increases with attack frequency, its interictal deficit is unlikely to be due to trigeminal sensitization.

Effects of symptomatic treatments on cutaneous hyperalgesia and laser evoked potentials during migraine attack

Previously an amplitude enhancement of laser evoked potentials (LEPs) was detected during migraine attack: we further examined pain threshold to CO2 laser stimuli and LEPs during attacks, evaluating the effect of almotriptan, lysine-acetylsalicylate and placebo treatment on cutaneous hyperalgesia to thermal stimuli delivered by CO2 laser and on LEP components. Eighteen patients suffering from migraine without aura were analysed. They were divided into three groups of six patients each, randomly assigned to lysine acetyl-salicylate, almotriptan or placebo treatments. The supraorbital zones and the dorsum of the hand were stimulated on both the symptomatic and not symptomatic side in all patients. The LEPs were recorded by 25 scalp electrodes. During attacks, the P2 wave was significantly enhanced; the amplitude of the P2 component obtained by the stimulation of the supraorbital zone during the attack on the side of the headache was significantly correlated with the intensity of pain and the frequency of headache. Both almotriptan and lysine acetyl-salicylate significantly reduced the P2 amplitude but they showed no effects on hyperalgesia to laser stimulation; headache relief following therapy was correlated with the reduction of the P2 amplitude. The cortical elaboration of laser-induced experimental pain seemed increased during migraine attack, and the severity of headache was mainly related to the increase of the later LEPs components expressing the attentive and emotive compounds of suffering. Reversion of this process appeared to be primarily responsible for the efficacy of drugs in treating migraine, though both almotriptan and lysine-acetil salicilate seemed to have no effect in reducing sensitization at second and third order nociceptive neurons.

Topographic and dipolar analysis of laser-evoked potentials during migraine attack

OBJECTIVE

The aim of this study was to perform further evaluation of laser-evoked potentials (LEPs) during migraine attacks using multichannel recording and topographic analysis. Specifically, this study aimed to confirm the pattern previously observed in acute migraine, while also defining the components of LEPs that are mainly modified during headache, as well as the correlation between features of LEPs and clinical variables. In addition, we aimed to conduct a dipolar source analysis of the main LEP waves in migraine patients to check the variability in the source location of LEPs during acute migraine.

BACKGROUND

An amplitude enhancement of LEPs was previously detected during migraine attack using a single scalp derivation on the vertex; hyperalgesia to heat stimuli was also detected for both the face and hand.

METHODS

Eighteen patients suffering from migraine without aura were analyzed. The supraorbital zones and the dorsum of the hand were stimulated on both the symptomatic and nonsymptomatic sides in all patients. The LEPs were recorded via 25 scalp electrodes. Dipolar source analysis of the P2 components was performed using a spherical model in all patients and using a realistic Magnetic Resonance model in four patients.

RESULTS

During attacks, the later waves, and particularly the P2 component, were significantly enhanced; the amplitude of the P2 component obtained during the attack by stimulation of the supraorbital zone on the side of the headache was significantly correlated with the intensity of pain and the frequency of headache. In our patients, the P2 wave was generated in the anterior cingulate cortex, with a shift toward its rostrocaudal portion, and was mainly devoted to elaboration of the emotive compound of pain during migraine attack.

CONCLUSIONS

Cortical activation by laser stimuli during migraine attack was confirmed. This effect was more pronounced in patients with a higher frequency of migraine attacks. This may be due to a lack of inhibitory control over the transmission of pain to the cortex. The increased activation of cortical areas devoted to attention and emotion may be linked to headache.

Trigeminofacial reflexes in primary headaches

Nociceptive processing in trigeminal system is likely to undergo to significant changes in chronic pain disorders such as in primary headache. The electrophysiological testing of brainstem reflexes seems to offer a valuable adjunct to the clinical evaluation, providing direct evidence for central dysmodulation of sensory and pain neurotransmission, i.e. dishabituation pattern and reduced pain threshold. We review the contribution of trigeminofacial reflex studies in the light of those recent data supporting the view of a dysfunctional sensory processing in primary headache.

Effect of the adenosine A1 receptor agonist GR79236 on trigeminal nociception with blink reflex recordings in healthy human subjects

GR79236 is a highly potent and selective adenosine A1 receptor agonist that has analgesic and anti-inflammatory actions in humans and animals. In animal models it inhibits trigeminal nerve firing and calcitonin gene-related peptide release which play a pivotal role in migraine pathophysiology. Thus GR79236 may have therapeutic potential in migraine. Although there are no validated human models of migraine, the trigeminal nociceptive pathways may be studied with a novel electrode to elicit nociception-specific blink reflex responses. Twelve healthy female volunteers were randomized in a double-blind, placebo-controlled, cross-over trial to investigate the effect of GR79236 on trigeminal nociceptive pathways, as measured by the blink reflex. A secondary objective was to compare the use of two types of electrode, the standard (SE) and nociception-specific electrodes (NE), to investigate human trigeminal pharmacology. Blink reflexes were elicited with SE and NE before and 30 min after GR79236 (10 microg/kg i.v.) or placebo. The median area under the curve of repeated sweeps of the R2 component of the blink reflex was analysed using analysis of covariance with baseline as covariate. Using NE, GR79236 produced a non-significant reduction of the ipsilateral R2 compared with placebo (P = 0.097) and a significant reduction contralaterally (P = 0.008). No significant changes were observed using SE. There were no significant adverse events. The results suggest that NE is more sensitive than SE to detect pharmacological effects in the trigeminal nociceptive system. Furthermore, the adenosine A1 receptor agonist GR79236 inhibits trigeminal nociception in humans. These results support a possible therapeutic role for GR79236 in primary headache disorders.

Nociceptive-specific blink reflex and glyceryl trinitrate infusion in healthy volunteers

Glyceryl trinitrate (GTN) is known to induce early headache in healthy humans after intravenous infusion. Moreover, in animal models subcutaneous administration produces an increase in Fos expression in brainstem areas that are involved in trigeminal pain processing. In a double-blind crossover study, we tested the blink reflex before, during and immediately after GTN and placebo intravenous infusion in eight healthy volunteers using a new stimulation electrode that preferentially activates A-delta nociceptive afferent fibres. The initial hypothesis that GTN could induce an increase in the magnitude of the nociceptive blink reflex R2 component by stimulating activity of trigeminal nucleus caudalis wide dynamic range interneurones was not confirmed. Although mild headache was induced in six subjects, there was no significant change between the R2 area under the curve before and after drug vs. placebo.

The electrophysiology of migraine

Migraine is currently regarded as a neurovascular disorder of trigeminal sensory processing, generated centrally, probably at the level of the brainstem. In the past, electrophysiological techniques have drawn no definite conclusions on either interictal or ictal changes in migraineurs compared with controls, largely because of methodological differences. Recently, two findings have been shown consistently: an interictal increasing lack of habituation of evoked potentials with a normalization at the start of the attack and strong intensity dependence of auditory evoked potentials. These findings substantiate migraine sufferers as having an abnormal trait interictally, with the attack characterized by a change in the state of central processing. Exploitation of these differences may be a useful tool to study the mechanism of action of drugs used for the treatment of migraine.

Modulation of trigeminal reflex excitability in migraine: effects of attention and habituation on the blink reflex

The modulation of trigeminal reflex excitability in migraine patients was evaluated during the asymptomatic phase by studying the effects of attention, habituation and preconditioning stimulus on the R2 and R3 components of the blink reflex (BR). Fifty patients suffering from migraine without aura, 20 affected by migraine with aura and 35 sex- and age-matched controls were selected. In subgroups of migraine with-aura and without-aura patients, and normal controls, the blink reflex was elicited during different cognitive situations: (a) spontaneous mental activity; (b) stimulus anticipation; (c) recognition of target numbers. In the remaining subjects, R2 and R3 habituation was evaluated by repetitive stimulation at 1, 5, 10, 15, 20, 25 and 30 s intervals. The R2 and R3 recovery curves were also computed. A reduced R3 threshold with a normal pain threshold was found in migraine with-aura and without-aura patients; the R3 component was not significantly correlated with the pain thresholds in patients and controls. The R2 and R3 components were less influenced by the warning of the stimulus in migraine without-aura and migraine with-aura patients, in comparison with the control group. A slight increase of both R2 and R3 recovery after preconditioning stimulus was also observed in migraine patients, probably caused by a phenomenon of trigeminal hyperexcitability persisting after the last attack. The abnormal BR modulation by alerting expresses in migraine a dysfunction of adaptation capacity to environmental conditions, probably predisposing to migraine.

Acute migraine headache: possible sensitization of neurons in the spinal trigeminal nucleus?

OBJECTIVE

To investigate trigeminal sensory processing in patients with migraine using a novel "nociception-specific" blink reflex.

METHODS

Seventeen patients with unilateral migraine headache were studied within 6 hours of onset. Blink reflexes were elicited with a standard stimulating electrode (standard blink reflex) and concentric stimulating electrode (nociception-specific blink reflex) during the acute migraine attack, after treatment with IV lysine acetylsalicylate (1,000 mg) or oral zolmitriptan (5 mg) and interictally.

RESULTS

After standard stimulation, no differences were detected for the R1 and R2 onset latencies and areas under the curve (AUC) between the different time points and the headache and nonheadache side. Nociception-specific stimulation revealed a shortening of R2 onset latencies (44.3 +/- 5.4 ms for headache side vs 48.9 +/- 5.8 ms for nonheadache side) during the acute migraine attack compared with the headache-free interval (49.8 +/- 5.3 vs 49.8 +/- 4.5 ms). The AUC of the R2 increased on the headache side by 680% and on the nonheadache side by 230% compared with the headache-free interval. Drug treatment parallel to pain relief increased the onset latencies (zolmitriptan: 48.0 +/- 8.2 ms for headache side vs 52.3 +/- 7.6 ms for nonheadache side; lysine acetylsalicylate: 48.0 +/- 5.0 ms for headache side vs 51.2 +/- 5.6 ms for nonheadache side) and reduced the AUC of R2 (zolmitriptan by 45% and lysine acetylsalicylate by 48%).

CONCLUSION

The data suggest temporary sensitization of central trigeminal neurons during acute migraine attacks.