BEHAVIORAL ECONOMICS OF CONCURRENT ETHANOL-SUCROSE AND SUCROSE REINFORCEMENT IN THE RAT - EFFECTS OF ALTERING VARIABLE-RATIO REQUIREMENTS

These experiments examined the own-price and cross-price elasticities of a drug (ethanol mixed with 10% sucrose) and a nondrug (10% sucrose) reinforcer. Rats were presented with ethanol-sucrose and sucrose, bot h available on concurrent independent variable-ratio (VR) 8 schedules of reinforcement. In Experiment 1, the variable ratio for the ethanol mix was systematically raised to 10, 12, 14, 16, 20, and 30, while the variable ratio for sucrose remained at 8. Five of the 6 rats increase d ethanol-reinforced responding at some of the increments and defended baseline levels of ethanol intake. However, the rats eventually cease d ethanol-reinforced responding at the highest variable ratios. Sucros e-reinforced responding was not systematically affected by the changes in variable ratio for ethanol mix. In Experiment 2, the variable rati o for sucrose was systematically increased while the ethanol-sucrose r esponse requirement remained constant. The rats decreased sucrose-rein forced responding and increased ethanol-sucrose-reinforced responding, resulting in a two- to 10-fold increase in ethanol intake. Experiment 3 examined the substitutability of qualitatively identical reinforcer s: 10% sucrose versus 10% sucrose. Increases in variable-ratio require ments at the preferred lever resulted in a switch in lever preference. Experiment 4 examined whether 10% ethanol mix substituted for 5% etha nol mix, with increasing variable-ratio requirements of the 5% ethanol . All rats eventually responded predominantly for the 10% ethanol mix, but total amount of ethanol consumed per session did not systematical ly change. In Experiment 5, the variable-ratio requirements for both e thanol and sucrose were simultaneously raised to VR 120; 7 of 8 rats i ncreased ethanol-reinforced responding while decreasing sucrose-reinfo rced responding. These data suggest that, within this ethanol-inductio n procedure and within certain parameters, demand for ethanol-sucrose was relatively inelastic, and sucrose consumption was independent of e thanol-sucrose consumption. Demand for sucrose, on the other hand, was relatively elastic, and ethanol-sucrose readily substituted for it. T he results are discussed in terms of applying a behavioral economic ap proach to relationships between drug and nondrug reinforcers.