Reward-dependent suppression or facilitation of consummatory behaviour by raclopride

Rats were presented for 1 h with 0.7%, 7% or 34% sucrose solutions, either separately with water as an alternative (two-bottle test), or with all three concentrations concurrently available (three-bottle test). In trained animals, 7% sucrose produced the highest intakes in the two-bottle test, but 34% sucrose was preferred in the three-bottle test. In both tests the dopamine D-2 antagonist raclopride (100-400 micrograms/kg) reduced intake of 0.7% sucrose solution, but increased intake of 34% sucrose; both effects were apparent during the first 5 min of testing. In the two-bottle test, intake of the intermediate 7% concentration showed both effects: an immediate decrease and a later increase. In the three-bottle test, sucrose-naive animals showed a gradual onset of preference for 34% sucrose, and enhancements of intake by raclopride were not at first immediate; immediate enhancements required three sessions of exposure. Raclopride did not alter the consumption of a 0.001% solution of quinine. We consider the implications of these results for theories of neuroleptic drug action.