26.05 Role for 5-HT in Migraine

5-HT is thought to be intrinsically linked to migraine. Evidence shows a sharp increase in urinary 5-HIAA (the catabolic product of 5-HT) and a fall in blood 5-HT concentration during a migraine attack. Moreover, migraine sufferers display perturbed 5-HT metabolism and transmission. 5-HT_1B and 5-HT₂ receptors are found on extracerebral blood vessels. Stimulation of 5-HT₂ receptors indirectly causes vasodilation via release of nitric oxide, while activation of 5-HT_1B receptors leads to vasoconstriction. As highlighted in Figure 1, 5HT_{1B, 1D} and _1F receptors, located on trigeminal nerve fibres and the trigeminal nucleus caudalis, become important regulators of the trigeminocerebrovascular system, since their activation would have an inhibitory effect on neurotransmission.