A concurrently available nondrug reinforcer prevents the acquisition or decreases the maintenance of cocaine-reinforced behavior

Lever-Pressing responses of 55 rats were reinforced with IV-delivered cocaine (0.2 mg/kg) or saline under conditions of continuous access for 15 24-h sessions. The rats also responded on tongue-operated drinking devices for deliveries of a 3% (w/v) glucose +0.125% (w/v) sacharin (G+S) solution or water. The effects of removing these substances on behavior maintained by G+S, water, cocaine, or saline were compared in 11 groups. Terminating cocaine access produced a decrease in G+S drinking and an increase in food and water intake. In contrast, a group of rats that did not initially self-administer G+S showed increases in G+S drinking when cocaine was removed, and G+S-maintained responding persisted when cocaine was reinstated. Substitution of water for G+S produced a nearly two-fold increase in cocaine-reinforced behavior but no change in IV-delivered saline self-administration in a control group. A group that did not initially self-administer cocaine increased its infusion rate to over 400 infusions per day as soon as G+S was replaced with water. The effect of presenting cocaine to a group that responded for G+S alone was to decrease G+S intake, but there was only a a transient decrease in water intake in the control group. Likewise, presentation of G+S to a group of rats self-administering cocaine resulted in a decrease in infusions, but saline infusions did not change in a control group. Generally, there was an increase in food and water intake during cocaine removal, but food and water intake did not vary systematically with the removal or presentation of G+S. The results suggest that behavior reinforced by IV-delivered cocaine can be substantially altered by the discontinuation or presentation of G+S, an orally self-administered nondrug reinforcer.