The nitric oxide hypothesis of migraine and other vascular headaches

Investigations into the role of nitric oxide and the large intracranial arteries in migraine headache

Previous studies suggest that nitric oxide (NO) is involved in headaches induced by i.v. infusion of the vasodilator and NO donor glyceryl trinitrate (GTN) in healthy subjects. Extending these studies to sufferers of migraine without aura, it was found that migraineurs experienced a stronger headache than non-migraineurs. In addition, most migraineurs experienced a delayed migraine attack at variable times (mean 5.5 h) after GTN provocation. This biphasic headache response in migraineurs may be linked to hypersensitivity in the NO-cGMP pathway. Thus, compared to controls, migraineurs were found to be more sensitive to GTN-induced intracranial arterial dilatation, which is known to be mediated via liberation of NO and subsequent synthesis of cGMP Furthermore, histamine infusions in migraineurs induced headache responses and intracranial arterial responses resembling those induced by GTN in migraineurs. Histamine is known to liberate NO from the endothelium via stimulation of the H1 receptor, which is present in the large intracranial arteries in man. Because both immediate histamine-induced headache and intracranial arterial dilatation and delayed histamine-induced migraine are blocked by H1-receptor blockade, a likely common pathway for GTN and histamine-induced headaches/migraines and intracranial arterial responses may be via activation of the NO-cGMP pathway. The delay in the development of these experimental migraines may reflect activation of multiple physiological processes. The intracranial arteries of migraineurs were found supersensitive to the vasodilating effect of GTN (exogenous NO). This relates to clinical findings suggesting dilatation of the large intracranial arteries on the headache side during spontaneous migraine attacks. The function of arterial regulatory mechanisms involving NO in migraine was therefore studied. In peripheral arteries, no endothelial dysfunction of NO was found and cardiovascular and intracranial arterial sympathetic function was normal. A mild parasympathetic dysfunction may be involved and may, via denervation supersensitivity, be responsible for the observed supersensitivity to NO. Another possibility is that NO initiates a perivascular neurogenic inflammation with liberation of vasoactive peptides. NO also mediates a variety of other physiological phenomena. One of these, the pain-modulating effect observed in animals, was evaluated in a human study using GTN infusion and measurements of pain thresholds. No definite effects of GTN were demonstrated. The precise mechanisms involved in NO-triggered migraines and which part of the NO-activated cascade that is involved remain to be determined. The possibilities for pharmacological stimulation and/or inhibition of several steps of the NO-activated cascade increase rapidly and soon may be available for human studies.

Role of nitric oxide in the physiopathology of pain

Many painful disorders, including joint dysfunctions such as rheumatoid arthritis (RA) or temporomandibular joint disorders (TMD), are associated with hyperthermia of the overlying skin. The same is true of certain intractable chronic pain conditions, such as chronic orofacial pain, which may be associated with TMD. We suggest that this skin hyperthermia, caused by regional vasodilation, is induced by extravascular nitric oxide (NO). Extravascular NO can be produced in the affected joint by osteoblasts, chondrocytes, and macrophages, by mechanical stimulation of endothelial cells, or by stimulated neurons. In view of a strong correlation between pain and skin hyperthermia in these disorders, and the evidence that NO enhances the sensitivity of peripheral nociceptors, we also suggest that at least this kind of pain is associated with excessive local level of NO. This hypothesis can be verified by dynamic area telethermometry, assessing the effect of NO on the sympathetic nervous function. This mechanism, which is in line with the general role of NO as a mediator between different organ systems, also may be relevant to any pain associated with enhanced immune response. Clinical implications of the proposed mechanism are discussed.

Prophylactic treatment of migraine with bisoprolol: a placebo-controlled study

The objective of the present study was to assess the efficacy of bisoprolol in migraine prophylaxis. A double-blind placebo-controlled study was conducted in 226 patients with migraine with or without aura, a migraine history of at least 2 years at least 3 documented attacks during the 28 days run-in period. The duration of treatment was 12 weeks following an initial 28 days' run-in period. Patients reported the number of attacks and their severity in a diary. Treatment with bisoprolol 5 mg resulted in a significant reduction in the frequency of migraine attacks (39% vs 22%) compared to placebo treatment (p < 0.05). Treatment had no effect on the duration and severity of the attacks. Bisoprolol was well tolerated.

On the pathogenesis of headache following TIA

Twelve out of 49 patients with single or multiple transient ischemic attacks (TIAs) had TIA-related headaches, mostly in close temporal relation to the ischemic onset. Headache predominated in patients taking vasodilators when TIA occurred or with orthostatic hypotension at the first clinical examination, but atrial hypertension or a personal history of migraine were not more frequent in patients with headache. The site of the pain did not correlate with the presumed territory of cerebral ischemia. Pain during TIA is conceivably due to an interaction between cerebral vessels and the surrounding nervous system. Blood vessels have a sturdy physiological role concerning blood flow regulation, with receptors and signaling molecules potentially involved with pain production. Reflex mechanisms should justify pain in other areas.

Nitric oxide synthase inhibition in the histamine headache model

Histamine has been widely used experimentally to induce headache in healthy subjects and migraine in migraineurs. There is evidence that the vascular effects of histamine are at least partially mediated by nitric oxide (NO). Hence we hypothesized that subjective symptoms and hemodynamic effects of histamine could be reduced by systemic NO-synthase inhibition. We therefore studied the effect of pretreatment with N-monomethyl-L-arginine (L-NMMA), a competitive inhibitor of NO-synthase, or placebo on headache, flush and discomfort scores during histamine infusion. Additionally, blood flow velocities in the middle cerebral and the ophthalmic artery and ocular fundus pulsations were measured. Whereas L-NMMA blunted the effect of histamine in the ophthalmic artery and the ocular circulation, NO-synthase inhibition did not mitigate subjective symptoms. Histamine did not affect mean blood flow velocities in the middle cerebral artery. Hence, we conclude that NO-synthase inhibition reduces the histamine-induced vascular effects in the ocular circulation, but is not sufficient to attenuate or abort the subjective symptoms provoked by histamine infusion.

Headache induced by serotonergic agonists--a key to the interpretation of migraine pathogenesis?

Serotonergic agonists such as m-chlorophenylpiperazine (m-CPP) and fenfluramine may induce migraine attacks. This has led to opposing theories concerning the role of 5-hydroxytryptamine (5HT) in triggering migraine attacks; is there hyperfunction or hypofunction of the central serotonergic system. Our review of the literature strongly suggests that m-CPP and fenfluramine provoke migraine attacks by stimulating, directly or indirectly, the 5HT2C/5HT2B receptors, although there is no total agreement with this interpretation. Central 5HT hypersensitivity in migraine patients, probably due to 5HT neuronal depletion, is proposed on the basis of review of electrophysiological tests and neuroendocrine challenge paradigms.

Recognizing exercise-related headache

Active patients may suffer not only from the common headache syndromes that plague the general population, but also from headache brought on by exercise. Valsalva-type maneuvers can bring on exertional headache; maximal or submaximal aerobic activity can precipitate effort headache. Trauma to the head and neck can lead to posttraumatic headache. Other headache syndromes in athletes include cervicogenic headache, goggle headache, diver's headache, and altitude headache.

Histamine inhalation is a specific but insensitive laboratory test for migraine

Migraine is a subjective complaint and no laboratory test has until now been of value. The aim of the present study is to evaluate whether histamine inhalation may be used as a diagnostic test for migraine. In a double-blind study design, 15 migraineurs and 15 control subjects scored headache intensity and characteristics before, during, and in the subsequent 12 h after inhalation of increasing doses of histamine (0, 2, 4, 8, 16, 32 and 64 mg/ml). During the histamine inhalations, headaches increased dose-dependently in both groups. Eleven of the migraineurs and eight of the healthy controls experienced headaches after the inhalations. These headaches fulfilled the IHS criteria for migraine without aura in six of the migraineurs, but in none of the control subjects. Using this as a test parameter, the specificity of the test was 1, but the sensitivity was only 0.4. Our results indicate that histamine inhalation is a specific but insensitive laboratory test for migraine. Migraineurs should be informed about the risk of a migraine attack being provoked before histamine inhalation in pulmonary laboratories.

The autonomic nervous system and the regulation of arterial tone in migraine

Abnormal regulation of the large cranial arteries seems to play a significant role in the mechanisms of migraine pain. Thus, vasodilatation of extra- and intracranial conductance arteries has been described both during spontaneous migraine attacks and during experimentally provoked vascular headaches. The regulation of the diameter of these arteries is complex and involves autonomic, trigeminovascular, endothelial and humoral mechanisms. Studies concerned with the function of the autonomic nervous system in migraine suggest that a mild parasympathetic dysfunction may be present. Cerebral arteries in migraineurs are hypersensitive to nitric oxide, which may induce migraine attacks. As the enzyme responsible for nitric oxide synthesis is present in parasympathetic nerve endings around cerebral arteries, this supports a role for the parasympathetic nervous system in migraine. In addition, vasoactive transmitters released from perivascular trigeminal nerve endings may be implicated. Several of these aspects are closely linked to the presumed mechanisms of action of modern migraine therapeutics.