Emotional fever after habituation to the temperature-recording procedure

To examine whether habituation to having temperatures taken might reduce the emotional fever induced by other stressors, 20 rats were habituated by having three colonic temperatures taken within 6 min twice a week for 8 weeks. Two novel stressors were added during Week 9; rats were given an intraperitoneal saline injection before taking their temperatures on Day 1, and on a second day, they were housed with a group of unfamiliar animals for 5 min before taking their temperatures. Temperatures during Weeks 10-11 were taken as during Weeks 1-8. Results showed that, overall, the third daily temperature averaged 1 degrees C higher than the first, indicating that taking temperatures was stressful. Between weeks, temperatures rose between Weeks 1 and 2, suggesting a conditioned fever. Temperatures fell 1.5 degrees C from Weeks 2-8, indicating habituation. During Week 9, temperatures after the intraperitoneal injection were no higher than during Week 8; however, 5 min of group housing raised temperatures 1.5 degrees C for males and 2.5 degrees C for females. Temperatures during Weeks 10 and 11 were below those of Week 8, suggesting that the fever induced by group housing in Week 9 was situation specific. These results indicate that rats habituated to having their temperatures taken exhibit emotional fever only to selected new stimuli. Body temperatures do not rise after an intraperitoneal injection given by a familiar handler, but briefly placing rats with unfamiliar animals induces a substantial febrile response.