Postnatal ontogeny of cholecystokinin receptors in rat brain

The postnatal ontogeny of cholecystokinin receptors and cholecystokinin was determined in rat brain. The binding of cholecystokinin (CCK) to rat forebrain receptors was very low at 1-2 days of age, rose to a maximum at 12 days (Bmax = 31 fmol/mg protein, Kd = 1.47 nM), and declined to adult levels by 26 days (Bmax = 17 fmol/mg protein, Kd = 1.39 nM). In contrast, forebrain concentrations of CCK measured by radioimmunoassay rose monotonically through day 27. Possible implications of the transient developmental peak of CCK receptors are discussed.