Anandamide acts as a vasodilator of dural blood vessels in vivo by activating TRPV1 receptors

Migraine pathophysiology is believed to involve the release of neuropeptides via the activation of trigeminal afferents that innervate the cranial vasculature. Anandamide, the endogenous ligand to the cannabinoid receptor, is able to inhibit neurogenic dural vasodilatation, calcitonin gene‐related peptide (CGRP)‐induced and nitric oxide‐induced dural vessel dilation in the intravital microscopy model. In an in vitro setting anandamide is also able to activate the vanilloid type 1 (TRPV1) receptor and cause vasodilation, via the release of CGRP. In this study we used intravital microscopy to study whether anandamide behaves as a TRPV1 receptor agonist in the trigeminovascular system. We examined if anandamide‐induced dural vasodilation involves CGRP release that can be reversed by the CGRP receptor antagonist, CGRP8–37, and whether like capsaicin the anandamide effect could be reversed by the TRPV1 receptor antagonist, capsazepine. Anandamide 1 (19±9%, n=12), 3 (29±5%, n=37), 5 (74±7%, n=13) and 10 mg kg−1 (89±18%, n=6) was able to cause a dose‐dependent increase in dural vessel diameter. Capsazepine (3 mg kg−1, t5=6.2, P