Reinstatement and spontaneous recovery of cocaine-seeking following extinction and different durations of withdrawal.

Stimuli paired with drug use can acquire powerful motivational properties that are believed to induce relapse to drug-seeking in abstinent humans. Behavioural interventions for drug addiction, that have attempted to reduce the probability of relapse by extinguishing the motivational impact of drug-associated conditioned stimuli (CS), have had limited success. One explanation for the ready propensity to relapse to drug-seeking even following extinction of these stimuli may be that abstinence by humans can increase the ability of conditioned stimuli and drug primes to reinstate responding. In the present study, we sought to determine the effects on cocaine-seeking of imposing different periods of drug unavailability on rats, with or without extinction of the drug-seeking response and non-reinforced exposure to drug-associated stimuli. Rats were trained to self-administer cocaine under a second-order schedule of reinforcement, under which high response rates are maintained by drug-paired conditioned reinforcers, prior to extinction of the operant response alone or in combination with contingent presentation of the CS. Comparison of cocaine-seeking behaviour during a test session conducted either 1 day or 21 days after a 7-day period of extinction revealed that responding was significantly decreased the day after extinction, but spontaneously recovered following a further imposed period of 21 days during which cocaine and cocaine cues were not available. Self-administered cocaine further potentiated reinstated responding following all withdrawal periods. These findings are discussed with reference to interactions between drug unavailability, conditioned stimuli and cocaine self-administration, on the reinstatement of drug-seeking and the potential utility of extinction therapies for drug addiction.