Intracerebroventricular administration of cholecystokinin inhibits the activity of the dopaminergic and serotoninergic systems of the brain.

The behavioral and biochemical effects of intracerebroventricular administration of cholecystokinin were investigated in experiments on male Wistar rats. Cholecystokinin induced specific dose-dependent changes in the behavior of the animals. At low doses the inhibiting influence on behavior predominated; at high doses stereo-typed behavior, shaking of the head and increased reactivity to pain stimuli were observed. Cholecystokinin appreciably inhibited the circulation of serotonin and dopamine in the brain structures in comparison with physiological saline solution. Administration of cholecystokinin against a background of phenamine and 5-hydroxy-tryptophan briefly entirely inhibited the behavioral effects induced by these substances. On the basis of the data obtained it can be assumed that cholecystokinin is an endogenous modulator of the activity of the monoaminergic systems of the brain.