Cholecystokinin (CCK) is a peptide hormone linked to the gastrointestinal (GI) system. The receptors are expressed in the central nervous system specifically in the hippocampus, cerebral cortex, and striatum . It is present in the nucleus of tractus solitarius and area postrema of the lower portion of the brain stem. CCK is tissue-specific and developmentally regulated. The expression of CCK-endocrine producing cells is biphasic, declines just before birth and increases immediately after birth. Levels of CCK-producing neurons in the brain are low at birth but steadily increase into adulthood. Low levels of CCK are clear in the thyroid C cells, adrenal medulla, bronchial mucosa, pituitary corticotrophs, and spermatogenic cells. CCK-1 and 2 are part of class 1 G-protein-coupled receptor family. CCK1R are found in the gallbladder smooth muscles, chief and D cells of gastric mucosa, pancreatic acinar cells, and selected areas of central and peripheral nervous systems while CCK2R/GR are identified in the stomach (in the parietal, chief, and ECL cell of gastric mucosa), human pancreas and central nervous system (CNS).