(A) Mean water consumption during the habituation phase for all F344 and LEW animals prior to conditioning with various doses of (−)-U50,488H. LEW animals consumed more water than the F344 rats on all days during this phase, except for days 7, 9 and 11. (B) Mean saccharin consumption across conditioning trials for all F344 (left panel) and LEW (right panel) animals receiving different doses of (−)-U50,488H or vehicle. * indicates saccharin consumption of animals conditioned with vehicle, 0.28, and 0.90 mg/kg was significantly higher than that of animals conditioned with 1.60 mg/kg. (C) Percent saccharin consumption (left panel) and total fluid consumption (right panel) for all animals conditioned with varying doses of U50,488H or vehicle. * denotes significant difference from animals receiving vehicle. # denotes significantly less saccharin consumed compared to animals receiving 0.28 mg/kg. ^ denotes significantly less saccharin consumed compared to animals receiving 0.90 mg/kg