Passive exposure to a contextual discriminative stimulus reinstates cocaine-seeking behavior in rats.

A significant problem in treating cocaine dependence is craving-induced relapse elicited by inadvertent (i.e., passive) exposure to cocaine-paired stimuli. Extinction/reinstatement of cocaine-seeking behavior in animals has been used to investigate this phenomenon. Most studies using this model have examined reinstatement by response-contingent exposure to discrete cocaine-paired stimuli. The present study expanded this research by examining passive (i.e., not contingent upon an operant response) exposure to a contextual cocaine-paired stimulus to better model craving elicited by inadvertent exposure to cocaine-associated environmental stimuli. Rats underwent daily cocaine and saline self-administration sessions that were identical to each other except for a discriminative stimulus (scented bedding) signaling cocaine availability (S+) or nonavailability (S-). Subsequently, they were placed into the self-administration chambers in the presence of neutral bedding. Reinforcement was not available and cocaine-seeking behavior (i.e., nonreinforced operant responses) was extinguished across days. Rats were then reintroduced to the S+ and S- stimuli. Presentation of the S+, but not the S-, elicited significant reinstatement of cocaine-seeking behavior. The results demonstrate that passive exposure to a contextual discriminative stimulus reinstates extinguished cocaine-seeking behavior. Furthermore, we suggest that reinstatement of cocaine-seeking behavior by passive exposure to cocaine-paired stimuli may provide a model of craving-induced relapse elicited by inadvertent exposure to a cocaine-associated environment.