Ethanol-maintained behavior in a foraging context: effects of search and procurement cost.

In a simulated foraging procedure, the effects of manipulating search and procurement costs of access to ethanol, food, and water on ethanol self-administration were determined in rats. Completion of a response ratio on one lever (search) resulted in the opportunity to complete a high- or low-cost response ratio on one of three other levers (procurement). Each procurement lever was exclusively associated with access to ethanol, food, or water, and the six procurement opportunities occurred in random order. Any procurement opportunity could be rejected, and a new search subsequently initiated. Percent acceptance of high-cost opportunities varied directly with increases in search cost and inversely with increases in high procurement cost. When search cost was increased, daily water and food consumption decreased, whereas daily ethanol consumption was unaffected. Regardless of these manipulations, rats consumed 1.0-2.0 g/kg ethanol daily. Ethanol consumption also was unaffected by increases in low or high food procurement cost values. These results indicate that ethanol self-administration can be analyzed within a foraging environment in which the animal initiates and determines the length and size of all drinking bouts and meals. Within this environment, patterns of ethanol self-administration were orderly and distinguishable from patterns of food- and water-maintained behavior.