Autoradiographic Localization of Cholecystokinin A and B Receptors in Rat Brain Using [125I]D‐Tyr25 (NIe28,31)‐CCK 25‐33S

Abstract

The distribution of receptors for the sulphated octapeptide cholecystokinin 26–33 (CCK‐8S) in rat brain was investigated by radioligand binding in conjunction with autoradiography using the novel iodinable, non‐oxidizable, amino‐ and thiolendopeptidase‐resistant CCK analogue, d‐Tyr25(Nle28,31)‐CCK 25–33S. Labelling of the peptide was achieved by synthesis utilizing Na125l and Chloramine‐T. [125l]D‐Tyr25(Nle26,31)‐CCK 25–33S (100 pM) bound rapidly and reversibly to a single population of sites on slide‐mounted coronal sections of rat forebrain with a dissociation constant of 34 pM. Specific binding was fully inhibited by CCK‐8S, CCK‐8, CCK‐4, L‐365,260 and L‐364,718, with inhibition constants..