DIFFERENTIAL-EFFECTS OF CERULETIDE ON AMPHETAMINE-INDUCED BEHAVIORS AND REGIONAL DOPAMINE RELEASE IN THE RAT

This study concerned the effects of ceruletide, a cholecystokinin (CCK)-related peptide, on amphetamine-stimulated behaviors (hyperlocomotion and stereotypy) and amphetamine-induced dopamine (DA) release from the striatum and the nucleus accumbens of the rat. Also, behavioral alterations due to ceruletide administration were compared with the change in DA release from these areas. Ceruletide 160 mug/kg s.c., attenuated hyperlocomotion induced by amphetamine, 1 mg/kg and 3 mg/kg s.c., but had no effect on amphetamine-induced stereotypy. Results from in vivo microdialysis experiments showed that s.c. administration of ceruletide caused a significant inhibition of the amphetamine-induced increase in DA release in the nucleus accumbens but not in the striatum. These neurochemical inhibitory effects of ceruletide disappeared completely with bilateral subdiaphragmatic vagotomy. However, infusion of 1 muM of ceruletide into the nucleus accumbens through the dialysis probe had no effect on amphetamine-induced DA release. These results suggest that the inhibitory effect of peripheral administration of ceruletide on amphetamine-induced hyperlocomotion is closely related to the change in DA release from the nucleus accumbens. In the nucleus accumbens, systemically administered ceruletide acts initially on the peripheral organs and influences the activity of DA terminals via an unknown path related to the vagus. Ceruletide had different actions on the dopaminergic system in the striatum and that in the nucleus accumbens.