Resurgence of sucrose and cocaine seeking in free-feeding rats.

Resurgence is relapse of an extinguished operant response following the removal of alternative reinforcement. In animal models of resurgence to date, rats have been food deprived and food is used as the source of alternative reinforcement. Thus, when the alternative reinforcer is removed, the only remaining source of food during experimental sessions is no longer available. Acute food deprivation is known to produce reinstatement of drug seeking, thus such deprivation has been suggested a potential mechanism of resurgence. The present experiments examined whether resurgence of sucrose and cocaine seeking could be obtained with rats that were not food deprived. Free-feeding rats were trained to press a lever for either sucrose (Experiment 1) or cocaine infusions (Experiment 2). Next, lever pressing was extinguished and an alternative response (nose poking) was reinforced with sucrose. When nose poking was also placed on extinction, resurgence of both sucrose and cocaine seeking was observed. Thus, resurgence of both sucrose and cocaine seeking can be obtained in rats that are not food restricted and it appears unlikely that an acute hunger state is responsible for resurgence. In addition, the present procedures for studying resurgence in the absence of interpretive complexities introduced by the use of food-deprivation may prove useful for further investigations of the neurobiological mechanisms of resurgence.