The cholecystokinin (CCK) concentration in individual brain stem nuclei of rat was determined using the Palkovits punch method19 and the CCK RIA3, CCK has a unique distribution in the brain stem, unlike other neuropeptides and biogenic amines8,19. In general, the CCK levels in the brain stem are 5-20% of rat cerebral cortex. The colliculi, midbrain central gray, nucleus of the solitary tract, and the interpeduncular nucleus had the highest CCK content (2.7-1 ng CCK mg protein).