Mice with null mutation in the α5 nAChR subunit gene and their wildtype littermates, or male Wistar rats (Charles River Laboratories, Raleigh, NC), were surgically prepared with silastic catheters in the jugular vein and trained to respond on an “active” lever for food pellets under a fixed ratio 5 time-out 20 sec (FR5TO20) schedule of reinforcement. Mice and rats then responded for nicotine infusions on the FR5TO20 sec reinforcement schedule during 1 h daily testing sessions. Nicotine hydrogen tartrate salt was dissolved in sterile saline solution (0.9% w/v). Each nicotine reward earned resulted in the delivery of a nicotine infusion (0.033 ml injection volume delivered over 3-sec in mice; 0.1 ml delivered over 1-sec in rats) and initiated a 20-sec time-out period signaled by a light cue located above the active lever during which responding on the lever was without consequence.