Med syst 8

Temperature was measured by inserting a probe (RET-3) (Physitemp Instruments, Inc., Clifton, NJ) attached to a microcomputer thermometer (7001H) (Physitemp Instruments, Inc., Clifton, NJ) 2 cm into the rectum. For drug discrimination, mice were placed in ventilated, sound-attenuating mouse operant chambers (MedAssociates, St. Albans, VT) with a house light located in the ceiling. On one wall were three holes spaced 5.5 cm apart (2.2 cm diameter each); each hole contained a photo beam and a light, and the center of each hole was 1.6 cm from the floor. In the center of the opposite wall was a fourth hole (also 2.2 cm diameter, center 1.6 cm from the floor) containing a dipper containing 0.01 cm³ condensed milk. An interface (MED-SYST-8, MedAssociates) connected the operant chambers to a computer running Med-PC software (MedAssociates), which controlled and recorded all experimental events.

Operant conditioning chambers (ENV-307A-CT, MedAssociates, St. Albans, VT) were kept in ventilated, sound-attenuating boxes. Each chamber contained a house light, a recessed 2.2 cm-diameter hole for reinforcer presentation on one wall, and three identical holes horizontally arranged and spaced 5.5 cm apart on the opposite wall. The center of each hole was 1.6 cm from the floor. Only the center hole was illuminated in the current study. When the center hole was illuminated, disruption of a photobeam in the hole resulted in access to 0.01 cc of 50% v/v condensed milk/water through the hole on the opposite wall. The operant conditioning chambers were connected to a computer through an interface (MED-SYST-8, MedAssociates). Med-PC software (MedAssociates) controlled experimental events and provided a record of responses. Rectal temperature was measured with a digital thermometer (BAT7001H, Physitemp, Clifton, NJ) attached to a rectal probe designed for mice. The probe was 2 cm long and had a diameter 0.7112 mm along its entire length except for the tip, which was 1.651 mm in diameter (RET-2-ISO, Physitemp, Clifton, NJ). The probe was inserted 2 cm into the rectum.

Operant conditioning chambers (ENV-307A-CT, Med Associates Inc., St. Albans, VT) were stored in cubicles that attenuated external noise; each cubicle was equipped with an exhaust fan. External noise was masked further with a white-noise generator. Each chamber contained a stand-alone light on one wall, a 2.2 cm-diameter hole recessed on one wall for presentation of liquid food, and three identical nose-poking holes horizontally arranged and spaced 5.5 cm apart on the opposite wall. A stimulus light-emitting diode (LED) was installed in each nose-poking hole. The center of each hole was 1.6 cm above from the floor. When one or both the left and right holes were illuminated, disruption of a photobeam in one of the holes resulted in access to 0.01 cc of 50% v/v unsweetened condensed milk/water through the dispenser hole on the opposite wall. The operant conditioning chambers were connected through an interface (MED-SYST-8, Med Associates Inc.) to a PC. Med-PC software (Med Associates Inc.) was used to control experimental events and provide a record of responses.