Effects of minimum-interreinforcer interval on ethanol-maintained performance of rats

Dipper cups filled with an 8% (w/v) ethanol solution were presented to Long-Evans hooded rats according to either a multiple Extinction chi sec Fixed-Ratio 1 or a chain Differential-Reinforcement-of-Other-Behavior chi sec Fixed-Ratio 1 schedule or reinforcement. The scheduled value of the extinction and differential-reinforcement-of-other-behavior components was varied to manipulate minimum-interreinforcer interval. Minimum-interreinforcer intervals from 0 sec (baseline condition of continuous reinforcement) to 480 sec were tested in an ascending series followed by a descending, retest series. Increasing the minimum-interreinforcer interval reduced the number of ethanol presentations obtained under both reinforcement schedules. These reductions were not due to ceiling effects imposed by the maximum number of possible deliveries obtainable within a session. The number of ethanol presentations obtained was always less than the maximum number of possible deliveries obtainable within a session. The number of ethanol presentations obtained was always less than the maximum number permitted by the value of the minimum-interreinforcer interval. Thus, imposing minimum-interreinforcer intervals between drinking opportunities reduces the level of ethanol self-administration relative to continuous-access baseline conditions.