1 Department of Psychology, Center for Studies in Behavioral Neurobiology, Concordia University, Montreal, Quebec, Canada.
2 Department of Psychology, Center for Studies in Behavioral Neurobiology, Concordia University, Montreal, Quebec, Canada. uri.shalev@concordia.ca.

Rational: Stress is a major trigger for drug relapse in humans and animal models, even after prolonged abstinence. However, animal models for stress-induced relapse were criticized for the lack of predictive and face validity.

Objectives: Here we investigated the effect of acute food deprivation stress in a novel stress-induced relapse model using voluntary, punishment-imposed abstinence from heroin. We also performed a detailed characterization of the development of punishment-imposed abstinence.

Methods: Male rats were trained to self-administered heroin (0.1 mg/kg/infusion) for 2 weeks, using the seeking-taking chained schedule. Pressing the 'seeking' lever led to the insertion of the 'taking' lever and pressing the take lever resulted in heroin infusion. Following self-administration training, rats were exposed to 8 or 21 days of heroin-seeking punishment. During punishment, 30% of the completed seek links resulted in a mild escalating footshock instead of take lever presentation. Next, rats were tested for heroin seeking under extinction conditions after 24 h of food deprivation and sated conditions.

Results: Probabilistic punishment of seeking lever responses resulted in gradual suppression of heroin seeking and taking. Exposure to food-deprivation stress induced a robust relapse to heroin seeking after short and long punishment-imposed abstinence periods, without significant effects of time, i.e., no incubation of heroin seeking. Individual differences were observed in the development of punishment-induced abstinence and stress-induced relapse.

Conclusions: These results suggest that stress is a reliable trigger to relapse even after a prolonged period of punishment-induced, voluntary abstinence.