Sweetness-dependent facilitation of sucrose drinking by raclopride is unrelated to calorie content.

Previous studies have reported that dopamine receptor antagonists increase the intake of solid or liquid diets containing high concentrations of sucrose. In Experiment 1, different groups of rats were trained in two-bottle tests (sweet solution vs. water), using three concentrations of either sucrose (0.7, 7 or 34%) or saccharin (0.02, 0.2 or 0.8%). Both sweeteners showed an inverted-U-shaped concentration-intake function. Raclopride increased intake of 34% sucrose, but not of 0.8% saccharin. In Experiment 2, raclopride had similar effects in three-bottle tests (all 3 concentrations available concurrently). However, whereas 34% was the most preferred sucrose solution, 0.2% saccharin was preferred to 0.8%. Thus, 0.8% saccharin differs from 34% sucrose in two ways, being not only noncaloric, but also aversive. In Experiment 3, 34% sucrose was rendered aversive by the addition of 0.08% quinine. Intake of this cocktail was not increased by raclopride. These results suggest that the difference between sucrose and saccharin in the effects of raclopride is related to the aversive properties of a concentrated solution of saccharin, rather than to its lack of calories.