Spontaneous Recovery During, But not Following, Extinction of the Discriminative Stimulus Effects of Nicotine in Rats: Reinstatement of Stimulus Control

Abstract

Extinction of the discriminative stimulus effects of drugs has received little research attention. Using a one-lever food-reinforcement (VI-1 min) operant procedure with rats (N = 16), the studies reported here assessed extinction, spontaneous recovery, and reinstatement of responding to the discriminative stimulus effects of nicotine. Experiment 1 found evidence for retention of differential responding to IP administrations of nicotine after a 3-month (87 days) delay following acquisition. Experiment 2 compared spontaneous recovery of discriminative control 2 and 4 weeks following extinction. Additionally, the impact of noncontingent reinforcement on discriminative control was evaluated (reinstatement). During extinction training, nicotine (.4 mg/kg) or saline was administered 15 min prior to each 15-min session, as they were during training, but responding was not reinforced under either stimulus condition. Spontaneous recovery (SR) of responding under the SD condition occurred during a session (11th) preceded by two consecutive SΔ sessions. Matched by response rate, 8 rats were randomly assigned to either a 2-week delay group or a 4-week delay group. There was no evidence for SR of discriminated responding to the drugs 2 or 4 weeks following the final extinction session. Between-group comparisons further revealed that SR did not vary as a function of delay following extinction. Reinstatement of stimulus control was observed following 2 brief sessions of noncontingent food delivery (levers retracted and conducted in the absence of the drug cues). These results suggest that the maintenance and extinction of the discriminative stimulus effects of nicotine are temporally stable. Theoretical ideas regarding drug self-administration, craving, and therapy are entertained.