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.