Env 203

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.

Operant-conditioning chambers (modified ENV-008CT; Med Associates, St. Albans, VT) that measured 25.5 cm × 32.0 cm × 25.0 cm were enclosed within sound-attenuating cubicles equipped with a fan for ventilation and white noise to mask extraneous sounds. Within the chamber, on the front wall, were two response levers, 5.0 cm from the midline and 4.0 cm above the grid floor. A downward displacement of either lever with a force approximating 20 g (0.20 N) produced an audible “feedback” click of a relay mounted behind the front wall of the chamber and defined a response. Three light-emitting diodes (LEDs) were located in a row above each lever. A pellet dispenser (ENV-203; Med Associates) delivered 20-mg sucrose food pellets (Bio-Serv, Flemington, NJ) to a receptacle mounted behind accessible from a 5.0 × 5.0 cm opening in the front wall midway between the two levers and 2.0 cm above the floor.
A syringe driver (model 22; Harvard Apparatus, Holliston, MA) placed above each chamber delivered injections of specified volumes and durations from a 10-ml syringe. The syringe was connected by Tygon tubing to a single-channel fluid swivel (375 Series Single Channel Swivels; Instech Laboratories, Inc., Plymouth Meeting, PA) which was mounted on a balance arm above the chamber. Tygon tubing from the swivel connecting the subject’s catheter was protected by a surrounding metal spring.

Experimental sessions were conducted with animals placed in operant-conditioning chambers (modified ENV-203; MED Associates, St. Albans, VT) that measured 25.5 × 32.05 × 25.5 cm and were enclosed within sound-attenuating cubicles equipped with a fan for ventilation and white noise to mask extraneous sounds. On the front wall of each chamber were two response levers, 5.0 cm from the midline and 4.0 cm above the floor. A downward displacement of the lever with a force equivalent to approximately 20 g defined a response, which always activated a relay mounted behind the front wall of the chamber, producing an audible feedback click. Three light-emitting diodes (LEDs) were located above each lever. A syringe infusion pump (model 22; Harvard Apparatus, Holliston, MA) placed above each chamber delivered injections of specified volumes and durations from a 10 mL syringe. The syringe was connected by Tygon tubing to a single-channel fluid swivel (375 Series Single Channel Swivels; Instech Laboratories, Inc. Plymouth Meeting, PA) that was mounted on a balance arm above the chamber. Tubing from the swivel was connected to the subject’s catheter using a tether provided by Envigo, equipped with a protective metal spring around the tubing.