Developments in 5-hydroxytryptamine receptor pharmacology in migraine

Because a satisfactory animal model for migraine does not exist, attempts to determine a common mechanism of action for effective antimigraine agents may be of benefit in elucidating the pathogenesis of this neurologic syndrome. The present review demonstrates that the clinical data that has developed over the past 30 years may allow for the elucidation of the role of specific 5-HT receptor subtypes in the pathophysiology of migraine. A large number of both acute and prophylactic antimigraine agents share an ability to interact with 5-HT receptor subtypes in human brain. As summarized in Table 3, acute antimigraine drugs (e.g., ergots, sumatriptan) share high affinity for 5-HTID receptors and somewhat lower affinity for 5-HT1A receptors. These receptors are present in certain intracranial blood vessels. 5-HT1D receptors are also located on nerve terminals where they act to inhibit the release of 5-HT and other neurotransmitters. Theoretically, 5-HTID receptor agonists may acutely inhibit the release of vasoactive or pain-inducing substances in the perivascular space. Conceivably, drugs acting at this receptor would stop the progression of this perivascular process. In addition, a number of prophylactic antimigraine drugs display a relatively high affinity for both 5-HT2 and 5-HT1C receptors in human brain. Although these receptors are also found in certain blood vessels, they are present throughout the nervous system. The receptors appear to mediate neuronal depolarizations at the cellular level. Moreover, the 5-HT2 receptor appears to play a key role in the development of inflammation in certain smooth muscle systems. Theoretically, the ability of 5-HT2 antagonists to protect perivascular inflammation may account for their efficacy in the prophylactic treatment of migraine. These data offer a novel approach to the analysis of antimigraine agents. Drugs could be selected for use in clinical migraine studies based on their selectivity for a specific 5-HT receptor subtype. For example, an agent that displays both high affinity and selectivity for 5-HT1D receptors could be clinically evaluated. Its effectiveness, or lack thereof, would indicate the importance of this specific 5-HT receptor site in the pathogenesis of migraine. Future attempts to determine a common mechanism of action for effective antimigraine agents should facilitate the elucidation of the pathogenesis of this neurologic syndrome.