Establishing preference for lidocaine solution to water: comparison between a fading and an abrupt-removal procedure for withdrawing a compound vehicle.

Rats were exposed to daily, 3-h, fixed-time 1-min food-pellet delivery sessions, which is a procedure that produces overdrinking (schedule-induced polydipsia). In previous polydipsia studies, rats came to prefer solutions of drug or non-drug agents to concurrently presented water if the agents had first been offered in a glucose-saccharin vehicle that was slowly eliminated (faded), leaving a choice between a substance in water vehicle vs water. In the first experiment, a more rapid vehicle-fading procedure was used to produce a preference for 0.19mg/ml lidocaine to water. In the second experiment, the vehicle was abruptly changed to water, which also resulted in a strong preference for lidocaine solution, although the lidocaine solution volumes ingested for the final sessions were significantly less than in the first experiment. The results are consistent with a conditioned flavor/nutrient preference interpretation for the institution of the lidocaine preference in both experiments. Although flavor/nutrient conditioning can be a sufficient condition for generating a substance preference, a previous experiment showed that it was not a necessary condition.