A comparison of the reinforcing efficacy of alcohol in alcohol-preferring (P) and alcohol-nonpreferring (NP) rats

A key feature of the selective breeding program that produced alcohol-preferring (P) and alcohol-nonpreferring (NP) rats is that the alcohol was mixed with water. However, humans typically drink sweetened or palatably flavored alcohol. The experiments in this study tested whether the differences in P and NP rats generalize to sweetened alcohol. In Experiment 1, P rats drank more alcohol than NP rats when the vehicle was water, but NP rats drank about as much alcohol as P rats (1.1 to 1.3 g/kg/30 min) when the vehicle was a saccharin solution. Experiment 2 tested whether P rats were more susceptible to the rewarding properties of sweetened alcohol than were NP rats. The criterion for reward strength was the degree to which alcohol-reinforced lever pressing persisted, despite increases in the schedule requirements for the alcohol reward. In baseline, lever presses were reinforced with sweetened alcohol and an isocaloric Polycose solution according to two, concurrent, variable-interval 5-s schedules. In subsequent conditions, the interval schedule for alcohol was increased, and then, after a return to baseline, the interval schedule for Polycose was increased. By the criterion of resistance to change, alcohol was a stronger reinforcer than was Polycose, and alcohol was a stronger reinforcer in NP rats than in P rats.