Disappearance of stress-induced hyperthermia following a low dose of X-irradiation: involvement of the vomeronasal system in the modulation of the radiation-induced effects.

Abstract

When the rectal temperatures of group-housed mice are measured sequentially, the temperature of the last mouse to be measured is higher than that of the first mouse. The hyperthermia effect observed in the last animal to be measured forms the basis of an experimental paradigm for studying the neurobiology of anticipatory anxiety. Stress-induced hyperthermia (SIH) was calculated as the difference (delta T) between the basal temperature (the averages of the first three mice) and the final temperature (the averages of the last three mice) when the temperatures of the 15 mice were measured sequentially, with a 2 min interval between each temperature measurement. The hyperthermia observed in the last animals measured was abolished by prior treatment with X-irradiation at the relatively low dose of 5-15 cGy. Prevention of the SIH response could be found when the irradiation was confined to the head region only, suggesting the importance of the brain in the radiation-induced effect. Relatively higher doses of 25 or 35 cGy failed to reduce the hyperthermia stress effect. Furthermore, the effect of X-irradiation was not observed following olfactory bulbectomy or resection of the vomeronasal tract. These results indicate that the disappearance of SIH response may only be found following irradiation at low dose levels. Furthermore, the results implicate the olfactory system in the radiation-induced anti-stress effect.