Env 018

We used 10 conditioning chambers (30.5×24.1×21.0 cm; LxWxH; ENV-018, MedAssociates, Georgia, VT, USA) enclosed in sound- and light-attenuating cubicles. Chamber front and back walls and ceiling were transparent polycarbonate, and sidewalls and floor were aluminum. Chambers had two retractable levers on the right wall with a single cue light directly above each lever, and a house light on the opposite wall. An emitter-detector unit to measure locomotor activity was located 5.5 cm from the lever-containing sidewall and 6 cm from the grid floor. A precision pump with nicotine syringe provided deliveries of IV nicotine via PE50 tygon tubing attached to a swivel then threaded through metal tether within the chamber. MedAssociates interface and software-controlled stimulus outputs and recorded inputs.

Daily experimental sessions were conducted in operant conditioning chambers (modified ENV 007, Med Associates, Inc. St. Albans, VT) housed within sound-attenuating cubicles (ENV-018, Med Associates, Inc.). The chambers contained two levers mounted 5.1 cm above the floor and equidistant from the center of the front wall of the chamber. Pairs of light-emitting diodes (LEDs) were mounted above each lever, and a 28 v d.c. lamp was mounted at the top of the front panel for ambient illumination. A 45-mg food-pellet (Bio-Serv, Inc., Frenchtown, NJ) dispenser (ENV-203, Med Associates, Inc.) was mounted behind the front panel and connected via plastic tubing to a trough contained within a ~5×5 cm opening that was centered between the two levers and accessible to the subject. White noise masked extraneous sounds. A relay mounted behind the front panel produced a click for each response, providing auditory feedback for responses.