The pituitary adenylate cyclase-activating peptide (PACAP) (Ohkubo S et al, 1992) is a peptide hormone similar to vasoactive intestinal peptide (VIP). PACAP functions as a hypophysiotropic hormone, neurotransmitter and neuromodulator. Three active peptides are cleaved from the precursor protein; PACAP-related peptide, PACAP-27 and PACAP-38. The effects of the PACAP peptides are mediated by the PACAP receptor (Ogi K et al, 1993). This receptor is predominantly expressed in the CNS. The activity of the receptor is mediated by coupling with the G protein alpha s subunit, which stimulates adenylyl cyclase which increases intracellular cAMP levels (Ogi K et al, 1993).