Conditioned and unconditioned influences on body temperature and ethanol hypothermia in laboratory rats.

Both a naive group and a group of chronically handled rats were observed to develop hyperthermia when their cages (rats in situ) were removed from their usual positions on cage rack shelving and placed upon the laboratory bench for a period of 60 minutes. That procedure apparently functioned as a stressful unconditioned stimulus for the naive group. The extent of hyperthermia was more pronounced in the chronic group, presumably owing to the classical conditioning of environmental cues to the stressful events that had repeatedly been associated in the past with placement of the cage onto the benchtop. Doses of naloxone (10 mg/kg) and of ethanol (1 g/kg) that normally produced negligible effects on body temperature were found to significantly reduce the hyperthermia that developed when cages were placed onto the benchtop. The hypothermic response to 2 g/kg of ethanol was lessened in both groups by placement of the cages onto the benchtop.