VIP and migraine disorder: PACAP, a multi-functional peptide, shares receptors with other peptides, such as the vasoactive intestinal peptide (VIP), which shares 68% sequence homology with PACAP [8] The three main PACAP receptors (VPAC1, VPAC2 and PAC1) are all found in the migraine-relevant trigeminovascular system e.g. the trigeminal ganglia, sphenopalatine ganglia, and cranial arteries [9] VPAC1 and VPAC2 receptors have equal affinity for PACAP38 and VIP, while the PAC1 receptor has a much higher affinity for PACAP38 than for VIP [10].