Investigation of the pathophysiological mechanisms of migraine attacks induced by pituitary adenylate cyclase-activating polypeptide-38.

Pituitary adenylate cyclase-activating polypeptide-38 (PACAP38) and vasoactive intestinal polypeptide are structurally and functionally closely related but show differences in migraine-inducing properties. Mechanisms responsible for the difference in migraine induction are unknown. Here, for the first time, we present a head-to-head comparison study of the immediate and long-lasting observations of the migraine-inducing, arterial, physiological and biochemical responses comparing PACAP38 and vasoactive intestinal polypeptide. In a double-blind crossover study 24 female migraine patients without aura were randomly allocated to intravenous infusion of PACAP38 (10 pmol/kg/min) or vasoactive intestinal polypeptide (8 pmol/kg/min) over 20 min. We recorded incidence of migraine during and after infusion (0-24 h). Magnetic resonance angiography of selected extra- and intracranial arteries, blood samples (plasma PACAP38 and vasoactive intestinal polypeptide and serum tryptase), and vital signs (blood pressure, heart rate, respiratory frequency, and end-tidal pressure of CO2) was recorded before and up to 5 h after infusion. Twenty-two patients [mean age 24 years (range 19-36)] completed the study on both days. Sixteen patients (73%) reported migraine-like attacks after PACAP38 and four after vasoactive intestinal polypeptide (18%) infusion (P = 0.002). Three of four patients, who reported migraine-like attacks after vasoactive intestinal polypeptide, also reported attacks after PACAP38. Both peptides induced marked dilatation of the extracranial (P < 0.05), but not intracranial arteries (P > 0.05). PACAP38-induced vasodilatation was longer lasting (>2 h), whereas vasoactive intestinal polypeptide-induced dilatation was normalized after 2 h. We recorded elevated plasma PACAP38 at 1 h after the start of PACAP38 infusion only in those patients who later reported migraine attacks. Blood levels of vasoactive intestinal polypeptide and tryptase were unchanged after PACAP38 infusion. In conclusion, PACAP38-induced migraine was associated with sustained dilatation of extracranial arteries and elevated plasma PACAP38 before onset of migraine-like attacks. PACAP38 has a much higher affinity for the PAC1 receptor and we therefore suggest that migraine induction by PACAP38 may be because of activation of the PAC1 receptor, which may be a future anti-migraine drug target.

Evidence for a vascular factor in migraine.

OBJECTIVE: It has been suggested that migraine is caused by neural dysfunction without involvement of vasodilatation. Because dismissal of vascular mechanisms seemed premature, we examined diameter of extra- and intracranial vessels in migraine without aura patients. METHODS: A novel high-resolution direct magnetic resonance angiography imaging technique was used to measure arterial circumference of the extracranial middle meningeal artery (MMA) and the intracranial middle cerebral artery (MCA). Data were obtained at baseline, during migraine attack, and after treatment with the migraine abortive drug sumatriptan (a 5-hydroxytryptamine agonist). RESULTS: We found dilatation of both MMA and MCA during migraine attack (p = 0.001). Sumatriptan administration caused amelioration of headache (p < 0.001) and contraction of MMA (p < 0.001), but MCA remained unchanged (p = 0.16). Exploratory analysis revealed that in migraine attacks with half-sided headache, there was only dilatation on the headache side of MMA of 12.49% (95% confidence interval [CI], 4.16-20.83%) and of MCA of 12.88% (95% CI, 3.49-22.27%) and no dilatation on the non headache side of MMA (95% CI, -4.27 to 11.53%) and MCA (95% CI, -6.7 to 14.28%). In double-sided headache we found bilateral vasodilatation of both MMA and MCA (p < 0.001). INTERPRETATION: These data show that migraine without aura is associated with dilatation of extra- and intracerebral arteries and that the headache location is associated with the location of the vasodilatation. Furthermore, contraction of extracerebral and not intracerebral arteries is associated with amelioration of headache. Collectively, these data suggest that vasodilatation and perivascular release of vasoactive substances is an integral mechanism of migraine pathophysiology.

Effect of CGRP and sumatriptan on the BOLD response in visual cortex.

To test the hypothesis that calcitonin gene-related peptide (CGRP) modulates brain activity, we investigated the effect of intravenous CGRP on brain activity in response to a visual stimulus. In addition, we examined if possible alteration in brain activity was reversed by the anti-migraine drug sumatriptan. Eighteen healthy volunteers were randomly allocated to receive CGRP infusion (1.5 µg/min for 20 min) or placebo. In vivo activity in the visual cortex was recorded before, during and after infusion and after 6 mg subcutaneous sumatriptan by functional magnetic resonance imaging (3 T). 77% of the participants reported headache after CGRP. We found no changes in brain activity after CGRP (P = 0.12) or after placebo (P = 0.41). Sumatriptan did not affect brain activity after CGRP (P = 0.71) or after placebo (P = 0.98). Systemic CGRP or sumatriptan has no direct effects on the BOLD activity in visual cortex. This suggests that in healthy volunteers both CGRP and sumatriptan may exert their actions outside of the blood-brain barrier.

Pharmacological modulation of the BOLD response: a study of acetazolamide and glyceryl trinitrate in humans.

PURPOSE: To examine the effect of acetazolamide, known to increase cerebral blood flow (CBF) and glyceryl trinitrate (GTN), known to increase cerebral blood volume (CBV) on the blood oxygenation level-dependent (BOLD) response in humans using 3 T magnetic resonance imaging (MRI), and to evaluate how pharmacological agents may modulate cerebral hemodynamic and thereby possibly the BOLD signal. MATERIALS AND METHODS: Six subjects were randomly allocated to receive acetazolamide, GTN, or placebo in a double-blind three-way crossover controlled study. Before, during, and after drug administration we recorded the BOLD response during visual stimulation with reversing checkerboard. RESULTS: We found that acetazolamide caused significant depression of the BOLD response (P = 0.0066). The maximum decrease occurred at 5 minutes after infusion and was 51.9% (95% confidence interval [CI], 22.03-81.76). GTN did not influence the BOLD response (P = 0.55). CONCLUSION: The BOLD response is decreased during increased CBF by acetazolamide, suggesting an inverse relationship between global CBF and the BOLD response. GTN does not change the BOLD response. This indicates that GTN exerts an effect on the large vessels only and that CBV changes in the microvascular system are necessary to alter the BOLD response.

The association between areas of secondary hyperalgesia and volumes of the caudate nuclei and other pain relevant brain structures-A 3-tesla MRI study of healthy men.

INTRODUCTION: Central sensitization plays a pivotal role in maintenance of pain and is believed to be intricately involved in several chronic pain conditions. One clinical manifestation of central sensitization is secondary hyperalgesia. The degree of secondary hyperalgesia presumably reflects individual levels of central sensitization. The objective of this study was to investigate the association between areas of secondary hyperalgesia and volumes of the caudate nuclei and other brain structures involved in pain processing. MATERIALS AND METHODS: We recruited 121 healthy male participants; 118 were included in the final analysis. All participants underwent whole brain magnetic resonance imaging (MRI). Prior to MRI, all participants underwent pain testing. Secondary hyperalgesia was induced by brief thermal sensitization. Additionally, we recorded heat pain detection thresholds (HPDT), pain during one minute thermal stimulation (p-TS) and results of the Pain Catastrophizing Scale (PCS) and Hospital Anxiety and Depression score (HADS). RESULTS: We found no significant associations between the size of the area of secondary hyperalgesia and the volume of the caudate nuclei or of the following structures: primary somatosensory cortex, anterior and mid cingulate cortex, putamen, nucleus accumbens, globus pallidus, insula and the cerebellum. Likewise, we found no significant associations between the volume of the caudate nuclei and HPDTs, p-TS, PCS and HADS. CONCLUSIONS: Our findings indicate that the size of the secondary hyperalgesia area is not associated with the volume of brain structures relevant for pain processing, suggesting that the propensity to develop central sensitization, assessed as secondary hyperalgesia, is not correlated to brain structure volume.