Raclopride decreases sucrose intake of rat pups in independent ingestion tests.

To investigate the role of dopaminergic activity at D2 receptors in the mediation of the positive reinforcing effect of sucrose on ingestion in preweanling rats, we tested the effects of the D2 antagonist, raclopride, on the intake of 10% sucrose of rats on postnatal days (PN) 7, 14, and 21. Intake was measured during independent ingestion tests in which pups licked sucrose from the floor of a beaker and during oral catheter tests in which sucrose was continuously infused through an anterior, sublingual, oral catheter. Rats were tested once to eliminate the possibility that repeated test experience would affect the response to raclopride. Pretreatment with raclopride resulted in decreased intake in independent ingestion (II) tests, but not in oral catheter (OC) tests on PN 7, 14, and 21. The inhibition of intake was not due to a generalized motor deficit because raclopride did not affect latency to eat, time-sampled activity scores, or latency to withdraw the hindlimb from a raised position. These results demonstrate that dopaminergic activity at D2 receptors is necessary for the positive reinforcing effect of sucrose that maintains ingestion in the II test but not in the OC test.