The role of drug-paired stimuli in extinction and reinstatement of ethanol-seeking behaviour in the rat

Male Wistar rats were trained to respond for ethanol (30 min/day) in an oral self-administration procedure. A single lever press resulted in presentation of 0.1 ml of 8% ethanol from a liquid dipper. When responding for ethanol stabilised, reinstatement sessions started. In the 30-min reinstatement session, lever pressing was first extinguished for 20 min by switching the dipper off. Then, different kinds of stimuli were non-contingently delivered and reinstatement of lever pressing was assessed. Fifteen random (random time=15 s) presentations of the dipper containing 8% ethanol potently reinstated ethanol-seeking. The reinstatement of lever pressing was immediate and most responses were emitted during the time needed for the first five presentations to occur. Presentations of the empty dipper or delivery of a non-specific stimulus (high-amplitude tone) did not produce any reinstatement. These results indicate that non-contingent presentations of the ethanol-associated stimulus complex may reinstate operant behaviour previously reinforced with ethanol.