Env 008ct

We used sixteen conditioning chambers (ENV-008CT; Med-Associates, Inc., St. Albans, VT; measuring 30.5 × 24.1 × 21.0 cm, L×W×H), enclosed in light- and sound-attenuating cubicles fitted with an exhaust fan. Sidewalls were aluminum; the ceiling and front and back walls were clear polycarbonate. One sidewall featured a dipper receptacle, occupying a 5.2 × 5.2 × 3.8 cm (LxWxH) recessed space, into which a dipper arm provided 0.1 ml of sucrose solution when raised. Retractable response levers were featured on either side of the dipper receptacle, approximately 5 cm above the rod floor. White 28V DC (100-mA) lamps were located 3 cm above each lever, hereafter termed lever lights. Two 28V DC (100-mA) houselights were also located above the conditioning chamber, but within the sound attenuating cubicle. An infrared emitter/detector unit, positioned 4 cm above the floor, bisected the chamber 14.5 cm from the sidewall featuring the dipper receptacle and functioned to monitor chamber activity. Data collection and presentation of experimental events were controlled via personal computer with Med Associates interface and software (MedPC for Windows, IV).

All sessions were conducted in a single testing room with ten conditioning chambers (ENV-008CT, Med Associates, Inc., St. Albans, VT, USA; 30.5 × 24.1 × 21.0 cm; l × w × h). Each chamber was housed separately inside a sound- and light-attenuating cubicle. The cubicle was equipped with a fan to increase air circulation and further decrease external noise. Each chamber had two aluminum side walls, polycarbonate ceiling, front and back walls, and metal rod flooring. Liquid trays containing 26% sucrose (w/v) solution were placed beneath an automated dipper arm on the right side-wall of the chamber. The arm was programmed to raise and lower a 0.1-ml cup that was accessible in the recessed port (5.2 × 5.2 × 3.8 cm; l × w × d). An emitter/detector beam fixed 1.2 cm within the recessed port and 3 cm above the metal rod floor recorded head entries.

For self-administration studies, rats were placed in operant chambers (ENV-008CT, Med Associates, St. Albans, VT)
inside sound-attenuating chambers (ENV-018CT, Med Associates). The operant boxes were outfitted with two nose poke devices
each containing a yellow light (ENV-114BM), which were located on either side of a pellet receptacle (ENV-200R7M. Med
Associates) attached to a dispenser (ENV-203-45, Med Associates) filled with 45 mg sucrose pellets. A white house light was on
the wall opposite the nose poke devices. Drug solutions were delivered via a variable infusion rate syringe pump (PHM-107, Med
Associates) connected by Tygon tubing to a single channel plastic swivel (375/22PS, Instech Laboratories, Plymouth Meeting,
PA) on a counter-balanced arm (PHM-110-SAI, Med Associates). The Tygon tubing inside the operant chamber was protected with a
stainless-steel spring. Data were collected using MED-PC Software (SOF-735, Med Associates).

The drug self-administration chambers (model ENV-008CT; Med Associates, St Albans, VT, USA) were configured and outfitted as previously described in detail [29 (link)]. Briefly, each chamber was enclosed in a ventilated sound-attenuating cubicle and was equipped with 2 levers, 2 cue lights, a house light, a single-channel fluid swivel, a spring leash and counterbalanced arm assembly, a syringe pump, an 8-ohn speaker, and a food trough and pellet dispenser. The environmental enrichment chambers also were as previously described in detail [11 (link)]. Briefly, each powder-coated wire cage (76 × 46 × 74 cm; Super Pet Inc., Walnut Creek, CA, USA) was equipped with two running wheels, three levels of ramps and platforms, movable tunnel structures, and numerous manipulable items and chew toys. Items were changed weekly to maintain novelty. Commercial pulp fiber bedding was used as nesting material on the cage bottom and pieces of sweetened cereal were hidden in various locations to encourage foraging.