5-HT7 receptor-mediated meningeal dilatation induced by 5-carboxamidotryptamine in rats is not altered by 5-HT depletion and chronic corticosterone treatment.

Low brain serotonin levels and high circulating levels of corticosterone are features of migraine. The 5-HT7 receptor was shown to mediate dilator responses to the 5-HT1B/1D and 5-HT7 receptor agonist, 5-carboxamidotryptamine in the middle meningeal artery of rats. Here we analyzed the effect of serotonin depletion and chronic corticosterone treatment on 5-HT7 receptor-mediated dilatation induced by 5-carboxamidotryptamine in the middle meningeal artery of anesthetized rats. Two weeks before experiments, male Wistar rats received i.c.v. injections of vehicle or the neurotoxin, 5,7-dihydroxytryptamine; upon recovery, animals received a chronic s.c. treatment (2 weeks) with vehicle (1 ml/kg/day) or corticosterone (20 mg/kg/day). At the end of treatments, animals were anesthetized and prepared for recording of blood pressure and blood flow in the middle meningeal artery, and i.v. drug administration. All animals received the 5-HT1B/1D receptor antagonist GR-127935 (1 mg/kg, i.v.) alone or combined with the 5-HT7 receptor antagonist, SB-269970 (1 mg/kg, i.v.). Topical 5-carboxamidotryptamine (0.01-1000 microM) to the exposed dura mater encephala produced decreases in diastolic blood pressure, variable changes in meningeal blood flow and increases in conductance (i.e. dilatation) in the middle meningeal artery. Meningeal dilator responses to 5-carboxamidotryptamine did not differ among treatment groups. In all cases, the combined treatment with GR-127935 + SB-269970 inhibited hypotensive and meningeal dilator responses to 5- carboxamidotryptamine. Together, these data do not support the notion that 5-HT7 receptors mediating dilatation in the middle meningeal artery are regulated by low brain serotonin levels and/or chronically high circulating levels of corticosterone. Further studies are required to elucidate the potential impact of these conditions and the role of 5-HT7 receptors in migraine.