Reinforcer interactions under concurrent schedules of food, water, and intravenous cocaine

Rats housed in three-lever, operant-conditioning chambers were trained under a concurrent, chained fixed-ratio 1, fixed-ratio 9 schedule (conc chain FR1 FR9) of food and water deliveries. After stable patterns of food and water intake were observed, the rats were prepared with intravenous catheters and a drug self-administration option was added to the schedule. Cocaine infusions (0.33 mg/infusion) were available for only 6 h (09.00 h-15.00 h), while access to food and water was available for 24 h. Addition of the cocaine option produced a minimal decrease in food and water intake and a considerable disruption ruption of food and water intake patterns. Changes in the cocaine dose (0.08-0.84 mg/infusion) did not alter responding on the levers resulting in either food or water deliveries. Cocaine self-administration, however, showed an inverted "U" shaped function as the dose of cocaine was increased. Drug extinction probes resulted in a significant increase in responding on the levers resulting in food and water deliveries and substantial decreases on the lever previously resulting in cocaine infusions. Twenty-four hour food extinction probes decreased responding on the levers resulting in food and water deliveries and produced a modest decrease in the self-administration of cocaine.