Pharmacological characterization of MK-0974 [N-[(3R, 6S)-6(2,3-difluorophenyl)-2-oxo-1-(2,2,2-trifluoroethyl)azepan-3-yl]-4-(2-oxo-2,3-dihydro-1H-imidazo[4,5-b] pyridin-1-yl)piperidine-1-carboxamide], a potent and orally Active calcitonin gene-related peptide receptor antagonist for the treatment of migraine