Cholecystokinin Octapeptide (CCK-8), labeled with 125I. Cholecystokinin is a neuropeptide that exists in several forms, identified by the number of amino acids in the peptide sequence. CCK8 contains 8 amino acids. The sulphated version of cholecystokinin can bind both Cholecystokinin A and Cholecystokinin B receptors. These receptors are involved in anxiety, feeding, and locomotion and are potential drug targets for depression and satiety.