Establishing preference for oral cocaine without an associative history with a reinforcer.

Using schedule-induced polydipsia (SIP), a stable, oral, preference for cocaine solution to water presented concurrently can be established by first presenting cocaine in a preferred vehicle, and subsequently fading the vehicle to water. The present study showed that rats exposed to a history of choosing 0.48 mg/ml cocaine in preference to concentrated lidocaine (2 mg/ml) under SIP conditions subsequently maintained this preference when the lidocaine concentration was progressively decreased to zero (water). Preference for lidocaine was tested by fixing it at 0.38 mg/ml (equimolar with 0.48 mg/ml cocaine) while subsequently increasing cocaine from 0.48 mg/ml to 2.5 mg/ml. Lidocaine preference did not occur, rather, preference for concentrated cocaine persisted. The results suggest that the avoidance of lidocaine solution may force the discrimination of the relation between high oral cocaine intake and its reinforcing effects, thereby instituting a stable preference for cocaine.