Persistence of ethanol self-administration as a function of interreinforcer interval and concentration.

Dipper cups filled with an ethanol solution were presented to Long-Evans hooded rats according to multiple extinction x s fixed-ratio 1 (mult EXT x s FR1) schedules of reinforcement. The scheduled duration of the EXT component was varied to manipulate minimum interreinforcer interval. Increasing the minimum interreinforcer interval by increasing the EXT component was used to challenge responding maintained by ethanol for purposes of evaluating the persistence of ethanol-maintained responding. EXT durations of 0 s (baseline conditions of continuous reinforcement) to 480 s were examined across ethanol concentrations of 0 (water, vehicle), 2, 4, 8, 16, and 32% (w/v). Increasing the EXT component duration resulted in reductions in the number of dipper presentations obtained at each concentration. Reductions in dipper presentations were less, relative to 0-s baseline conditions, the higher the concentration of the ethanol solution available. It was concluded that increasing the ethanol concentration that is self-administered increases the strength of responding that is subsequently maintained in that drug-maintained behavior becomes more resistant to modulation by a procedure (scheduling minimum interreinforcer intervals) which generally reduces numbers of drug deliveries.