The Role of 5-Hydroxytryptamine in the Pathophysiology of Migraine and its Relevance to the Design of Novel Treatments.

BACKGROUND: Migraine is a highly prevalent neurovascular disorder. OBJECTIVE: Of the many factors that have been implicated over the years, 5-hydroxytryptamine (5-HT; serotonin) has long been involved in the pathophysiology of migraine. Certainly, some lines of evidence suggest: (i) a 5-HT depletion from blood platelets resulting in cranial extracerebral vasodilatation; and (ii) the effectiveness of an intravenous (i.v.) infusion of 5-HT to abort migraine in some patients. More direct evidence comes from some drugs that influence 5-HT release and/or interact (as agonists or antagonists) with 5-HT receptors to treat this disorder. Indeed, the development of sumatriptan and second generation triptans in the 1990's led to discover that these drugs produce selective cranial extracerebral vasoconstriction (via 5-HT1B receptors) and inhibition of the trigeminovascular system responses implicated in migraine (via 5-HT1D/5-HT1F receptors). Although the triptans represent the current mainstay of acute antimigraine treatment, a number of patients do not respond well to the triptans and are contraindicated in patients with cardiovascular pathologies. CONCLUSION: This mini-review outlines further developments in the design of novel (non-vasoconstrictor) antimigraine treatments acting via 5-HT receptors, including selective agonists at 5-HT1D and 5-HT1F receptors, agonists at 5-HT1B/1D receptors combined with other properties as well as antagonists at 5-HT2B/2C, 5-HT3 and 5-HT7 receptors. It also touches upon the recent development of antagonists and antibodies at calcitonin gene-related peptide (CGRP) and its receptors, which produce a direct blockade of the CGRPergic vasodilator mechanisms involved in migraine. These alternative pharmacological approaches will hopefully lead to less side-effects.

Antinociceptive effect of 7-hydroxy-3,4-dihydrocadalin isolated from Heterotheca inuloides: role of peripheral 5-HT1 serotonergic receptors.

The purpose of this study was to investigate the possible antinociceptive effect of Heterotheca inuloides in inflammatory pain and to identify the main compounds involved in this effect. Dose-response curves were obtained for hexane, dichlorometane, ethyl acetate and methanol extracts from Heterotheca inuloides inflorescences in the formalin test. Hexane extract was more potent and effective than other extracts. Bio-guided fractionation was performed to determine the main antinociceptive compounds of the plant. Gas chromatography-mass spectrometry technique demonstrated the composition of the most active fraction from hexane extract revealing the presence of caryophyllene oxide, cedrene, 7-hydroxy-3,4-dihydrocadalin, 7-hydroxycadalene and a compound not identified. The isolated compounds were individually evaluated in the formalin test in a preliminary dose of 100 µg/paw and only 7-hydroxy-3,4-dihydrocadalin showed a significant antinociceptive effect. Dose-response curves were then obtained for 7-hydroxy-3,4-dihydrocadalin and diclofenac, a prototypical analgesic drug. Both drugs were equieffective and equipotent in the second phase of the formalin test, but 7-hydroxy-3,4-dihydrocadalin was more effective and potent in the first phase than diclofenac. In addition, 7-hydroxy-3,4-dihydrocadalin reduced carrageenan-induced mechanical hyperalgesia and inflammation in a dose-dependent manner. Finally, in mechanistic studies, the antinociceptive effect of 7-hydroxy-3,4-dihydrocadalin in the formalin test was prevented by methiothepin, WAY100635, SB224289 and BRL15572 but not by naltrexone. Results support the use of H. inuloides inflorescences as analgesic in the Mexican traditional medicine. Moreover, data indicate that 7-hydroxy-3,4-dihydrocadalin is partly responsible of this pharmacological activity, and suggest that 5-HT(1A), 5-HT(1B), and 5-HT(1D) serotonergic, but not opioid, receptors participate in the antinociceptive effect of this drug.