Nicotine vs. Ethanol Discrimination: Extinction and Spontaneous Recovery of Responding

Studies regarding extinction and spontaneous recovery of the discriminative stimulus effects of drugs are limited. Eight rats were initially trained to discriminate nicotine (0.4 mg/kg) vs. ethanol (800 mg/kg). For four rats, itraperitaneal (IP) administrations of nicotine fifteen minutes prior to fifteen-minute training sessions served as a discriminative stimulus (SD) for predicting food-reinforced lever pressing (VI-1 min). On other sessions ethanol functioned in predicting nonreinforcement (SA). The stimulus roles of the drugs were counterbalanced for the remaining four rats. SA and SD sessions alternated quasi-randomly with two daily sessions at 1000 and 1400 hours. Discriminative control was not disrupted following ten extinction sessions under a non-drug/saline condition, but was disrupted following extinction sessions under the original training drugs. Instances of spontaneous recovery (SR) occurred throughout extinction under the drug condtions. There was no evidence for SR two weeks following extinction, but partial recovery four weeks following the final extinction phase. Contextual status (context renewal) had neither a restorative or disruptive impact on extinguished or discriminated responding, respectively. These results support and extend the limited number of other studies by demonstrating extinction and spontaneous recovery of responding discriminated by two distinct drugs. Some theoretical interpretations regarding history effects and training in the context of drug discrimination are entertained.