Triptans are 5-HT1 receptor agonists used as anti-migraine drugs. They act primarily on meningeal blood vessels and on trigeminovascular afferents, but they may also exert central effects. We studied the regional effects of acute and chronic treatment with sumatriptan or zolmitriptan on the rate of serotonin (5-HT) synthesis in the rat brain, using the α-14C-methyl-L-tryptophan quantitative autoradiographic method. Sumatriptan at low (300 μg/kg, s.c.) and high (1 mg/kg) doses, as well as zolmitriptan (100 μg/kg), acutely decreased (15-40%, P < 0.05-0.001) 5-HT synthetic rate in many brain regions, including the dorsal raphe nucleus. Chronically, sumatriptan (21 days, approximately 300 μg/kg per day via osmotic minipumps) induced significant increases in the 5-HT synthesis rate in many projection areas but had no effect in the dorsal raphe nucleus. The acute effects on 5-HT synthesis rate would be compatible with activation of 5-HT1 autoreceptors that inhibit serotonin release. In contrast, the increased 5-HT synthesis rate observed after chronic sumatriptan might possibly result from a down-regulation/desensitization of 5-HT1 receptors and/or unmasking of excitatory triptan-sensitive 5-HT receptors. Overall, the present findings indicate that not only zolmitriptan but also sumatriptan affect brain serotonergic neurotransmission.
Effect of the CB1 receptor antagonists rimonabant and AM251 on the firing rate of dorsal raphe nucleus neurons in rat brain slices
