PHARMACOLOGY BIOCHEMISTRY & BEHAVIOR

摘要: METHODSubjects were experimentally naive, male Wistar rats obtained from Charles River Breeding Farms (St. Constant, Quebec). Rats weighed between 275-300 g upon arrival at our laboratory. They were individually housed and provided with free access to both food and water. The colony room was maintained on a 12 L: 12 D cycle. All procedures were conducted during the light phase of the cycle.Apparatus and Drugs Pain sensitivity was assessed by the hot-plate test. The hotplate apparatus consisted of a 20 x 20 x 38-cm clear Plexiglas chamber mounted on a 0.6-cm thick, 27 x 31-cm piece of sheet metal. A hinged, wire mesh lid mounted on the top of the chamber prevented animals from escaping. The plate temperature was controlled by immersing the sheet metal in a water bath heated by an Haake (Berlin, Germany) E2 Immersion/Open Bath Circulator. The apparatus was located in a test room illuminated by two 25-W, red light bulbs and maintained at a constant 22 C temperature. Animals were isolated in the test room in separate 30× 20× 15-cm wooden boxes, which were lined with Beta-Chip and covered by steel grid tops. Drugs used were: naloxone HCl (Dupont de Nemours & Co., Wilmington, DE); baclofen HCl, muscimol HBr, and bicuculline (Research Biochemicals, Inc., Natick, MA); and diazepam (Sabex International, Montreal, Quebec). Naloxone, baclofen, and muscimol were dissolved in physiological saline. Diazepam was dissolved in a vehicle of 50% propylene glycol and 50% saline. Bicuculline was dissolved in a few drops of 1 N hydrochloric acid, diluted with distilled water, and then the pH was adjusted to 5.5 by the …