Ethanol reinforced responding in the rat: a concurrent analysis using sucrose as the alternate choice.

Rats were trained on a two lever concurrent schedule of reinforcement (Fixed Ratio 8 Fixed Ratio 8) with ethanol (5% v/v) and water as the two available fluids. After establishing baseline responding patterns, various concentrations of sucrose (0.05% to 5.0% w/v) were substituted for the water in an ascending series. When water was the alternative fluid, ethanol responding predominated. With increasing sucrose concentration, percent ethanol responding decreased. At sucrose concentrations between 1.00% and 1.25% approximately half of the total responses per session were for each substance. This change in relative responding for the two fluids occurred as a result of increased total responding and not as a result of decreased ethanol responses. When ethanol was paired with either a 3% or 5% sucrose concentration, ethanol responding decreased, with increased sucrose responding. However, when the number of responses required to obtain these sucrose solutions was greatly increased (Fixed Ratio 64), ethanol responding increased to levels of up to twice that of the water ethanol condition. This increased ethanol responding was found to remain in the following ethanol water session after the sucrose schedule manipulation.