Clocklab data acquisition system

Young male Sprague Dawley rats (N = 108, 150–175 g on arrival) were housed in standard polypropylene cages with passive infrared motion sensors mounted over the cages, in cabinets with a 12∶12 LD cycle (∼30 lux during the light phase: <1 lux red, during the dark phase). Motion sensors were monitored continuously with the Clocklab data acquisition system (Actimetrics, Wilmette, IL, USA). The rats were allowed 12 days to entrain to the LD cycle, during which time standard rat chow (Bio-Serve, Frenchtown, NJ, USA) was provided ad libitum and average daily intake was recorded. All protocols were approved by the Animal Care Committee at Simon Fraser University (protocol 935p-09).

Operant chambers (N = 7, model ENV-008, Med-Associates, NY) were housed within individual ventilated sound-attenuation cubicles (model ENV-018MD) equipped with white lights (~ 60 lx) and an exhaust fan. The front panels of the operant chambers were outfitted with a retractable lever and a food trough. Food troughs were modified by use of a photobeam to allow for detection of food bin inspections (‘nose-pokes’). Pellets were provided via a 20 mg pellet dispenser positioned outside the chamber and attached to the food trough. Operant chambers were modified to allow for insertion of water bottles and plastic tops were replaced with wire mesh to allow for recording of locomotor activity using overhead infrared motion sensors. Operant responses (lever presses or nose-pokes) and reinforcements were summed and stored in 1-min intervals. Lever operation, reinforcement delivery, and data collection were controlled by a Pentium PC running Med-PC for Windows software (version 4.24; Med-Associates). Activity counts measured by overhead motion sensors were summed and stored in 1-min intervals using the ClockLab data acquisition system (Actimetrics, IL, US).