PACAP (1-38) free acid is an endogenous neuropeptide. PACAP (1-38) free acid potently stimulates antral motility and somatostatin secretion, inhibits the secretion of gastrin and stimulates the release of vasoactive intestinal polypeptide, gastrin releasing peptide and substance P. PACAP (1-38) free acid also enhances N-methyl-D-aspartate receptor function and expression of brain-derived neurotrophic factor through RACK1.