5-HT1 receptors in migraine pathophysiology and treatment.

Migraine is a frequent paroxysmal headache disorder of unknown aetiology. Genetic factors may control attack frequency and possibly attack severity. Serotonin1D (5-HT1Dβ ) receptors have a prominent position within the final common pathway of the mechanisms involved in the headache and associated symptoms. Stimulation of these receptors by selective 5-HT1Dβ receptor agonists such as sumatriptan and newer compounds including MK-462 and 311C90, rapidly and fully blocks the symptoms of the headache phase. The efficacy depends on factors such as timing of administration during or before the headache, speed of initial rise of drug plasma levels, and possibly degree of brain penetration. All agonists at S-HT1Dβ receptors share a short duration of action resulting in recurrence of the headache symptoms within 24 h in about one-third of attacks in clinical trials. The risk for headache recurrence seems patient dependent: about 10% of patients treating multiple attacks experience headache recurrence in every treated attack, whereas 40% never experience recurrence. These differences are not related to simple pharmacokinetic differences between patients or drugs. Increasing plasma half-life of the drug will most likely not reduce the risk of recurrence. "Breakthrough of peripheral suppressive effect" with an ongoing "central migraine generator", rather than the occurrence of a new attack, seems to be the most likely underlying mechanism for headache recurrence. In a minority of, possibly predisposed, patients, use of sumatriptan may induce increase of attack frequency. Four mechanisms have been suggested for the antimigraine action of 5-HT1Dβ receptor agonists: (1) vasoconstriction of cranial, most likely meningeal and dural blood vessels; (2) inhibition of release of vasoactive neuropeptides from perivascular trigeminal nerve terminals within dura mater and meninges; (3) blockade of trigeminal nerve terminal depolarization; and (4) central inhibition within the trigeminal nucleus caudatus in the brainstem. Which of these mechanisms is the most important, and whether or not vasoconstrictor action is necessary for antimigraine efficacy, is currently under extensive investigation. At this point all drugs with proven antimigraine efficacy share the ability to contract blood vessels and thus all feature also the potential risk of causing vasoconstriction of coronary vessels. In relation herewith, major efforts are put into the search for "the antimigraine receptor" and which receptor subtype mediates which action of sumatriptan-like drugs. At this point, the 5-HT1Dβ receptor subtype is thought to mediate vasoconstriction. Some investigators feel that the 5-HT1Dα receptor subtype mediates the neuronal effects of sumatriptan, while others are much less convinced about the physiological role of this subtype of receptor. Further research into receptor subtype specificity and affinity of compounds may promote the development of even better antimigraine drugs.