Dopamine D1 or D2 antagonists enhance inhibition of consummatory ingestive behavior by CCK-8.

A dopamine D1 (SKF-38393, 1 mg)- or D2 (LY-171555, 0.1 mg)-receptor agonist inhibited intake of an intraorally infused solution of sucrose by male rats, a test of consummatory ingestive behavior. Treatment with a D1 (SCH-39166, 0.1 mg) or D2 (raclopride, 0.6 mg) antagonist reversed inhibition by the respective agonist but enhanced the inhibitory effect of cholecystokinin octapeptide (CCK-8; 1.8 micrograms). It was not possible to demonstrate specific effects of D1 and D2 agonists on intake of pellets, a test that does not discriminate consummatory ingestive behavior from appetitive ingestive behavior, i.e., behavior used to obtain food. The results demonstrate specific involvement of dopamine D1 and D2 receptors in inhibition of consummatory ingestive behavior.