Figure 3.

Percentage of animals selecting the morphine lever (emitting a total of 10 responses first on the morphine-appropriate lever prior to emitting 10 on the saline-appropriate lever) at each morphine test dose as a function of prefeeding versus no prefeeding. In this study, rats were trained to discriminate 5 mg/kg pentobarbital from saline when maintained at 80% of free-feeding weights and were tested when prefed 0%, 25%, or 50% of the amount of food required to produce satiation. This figure is based on data reported by Gaiardi et al. (1987, Figure 2).