limited to) acute stressors such as foot-shock or social defeat stress. In many cases, it appears that social stress can potentiate drug reinstatement just as strongly as exposure to the drug itself Apparatus Animal self-administration experiments are typically performed in standard operant conditioning chambers adapted for the catheters used to deliver a drug intravenously. The catheter is secured to the animal by a harness or backplate and is tethered to a protective leash that extends upward through a hole in the top of a chamber, where it attaches to a rotating swivel on a mechanical arm that allows the subject to move around freely. The chamber houses two levers: one whose depression results in the delivery of a drug, the other whose depression does nothing. Activity on these levers can be used to measure drug administration (via activity at the drug-inducing lever) as well as changes in nonspecific behavior that reflect short- and long-term effects of the drug (via activity at the non-inducing lever). The sterile intravenous catheter used to deliver the drug into the bloodstream of the subject is typically composed of flexible plastic, silastic tubing, and nylon mesh placed subcutaneously. It is attached to a mechanical pump that can be calibrated to deliver a specific amount of drug upon depression of one of the levers in the chamber. Other chamber modifications are required if the drug is to be delivered orally or via inhalation, such as liquid containers or an aerosol distribution mechanism. Significant findings Self-administration studies have long been considered the “standard” in addiction research using both animal and human models. Conducting self-administration studies in animal models provides a much greater level of experimental flexibility than in humans because investigating the effects of novel pharmacological drug treatments poses significantly fewer ethical and practical barriers. In 1999, Pilla and colleagues published in Nature a study documenting the efficacy of a partial D3-agonist (BP-897) in reducing environmental cue-induced cocaine craving and vulnerability to relapse. An interesting aspect of this study was the use of second-order reinforcement schedules to identify a dissociation in the effects of BP-897 in that the drug inhibits cue-induced cocaine-seeking but has no primary reinforcement effect. This latter condition is important for any pharmacological agent to be used in the treatment of addiction—drugs used to treat addiction should be less reinforcing than the drug whose addiction they treat and optimally have no reinforcing effects. A 2010