Ethanol-reinforced responding by AA and ANA rats following the sucrose-substitution initiation procedure

Ethanol-reinforced responding was initiated in male AA and ANA rats using the sucrose-substitution procedure. Before the initiation procedure, a homecage, two-bottle preference test was conducted. The rats were then trained to respond on an Fixed-Ratio 1 schedule with sucrose reinforcement. Over sessions, ethanol was added gradually to the sucrose solution as the concentration of sucrose was reduced until 10% ethanol (v/v) alone functioned as the reinforcer for lever pressing. The schedule of reinforcement was then increased to Fixed-Ratio 4. Next, the ethanol concentration presented as the reinforcer was increased over weeks to 15%, 20%, 30%, and then returned to 10%. A second homecage test was then performed. The results showed that the AA and ANA lines differed significantly on preference and intake (g/kg) during the homecage preference tests. There was a significant increase in preference during the second homecage test. During sucrose substitution, initial large differences in responding were observed between the lines. When the ethanol concentration was increased, intake (grams per kilogram) increased for the AA line but not for the ANA line. These effects were a function of no change in responding by the AA rats as concentration was increased and a decrease in responding by the ANA rats at the higher concentrations (20% and 30%). Taken together, data indicate that ethanol can function as a positive reinforcer for the behavior of AA and ANA rats. Even though 10% ethanol functioned as a reinforcer similarly for the two lines, ethanol intake in the AA line was significantly greater at the higher concentrations of ethanol, suggesting that ethanol functioned as a qualitatively different reinforcer for the AA rats, compared with the ANA rats.