Ten operant conditioning chambers (model ENV-008CT; Med Associates, St. Albans, VT, USA) were used for the four behavioral tasks and each was outfitted with two retractable levers, two white stimulus lights, a house light, a speaker, a pellet dispenser, and a syringe pump that were arranged as previously described (Szalay et al. 2013 (link)). Six of the chambers also were outfitted with a standalone aversive stimulator/scrambler module (model ENV-414S; Med Associates, St. Albans, VT, USA) that were used during the punished drug self-administration and operant avoidance procedures. Each chamber was enclosed in a sound attenuating cubicle with an exhaust fan.