Effects of rat visual, olfactory, or combined stimuli during cohousing on stress-related physiology and behavior in C57BL/6NCrl mice

The Guide for the Care and Use of Laboratory Animals recommends housing rats and mice separately to reduce the potential for environmental stress to mice. The literature presents equivocal support for this practice, and housing practices vary widely. According to the existing literature, it is unclear whether visual, olfactory, or combined stimuli are responsible for stress-related changes in mouse physiology and behavior. To determine the extent to which exposure to visual, olfactory, or combined stimuli produce stress-related changes, measures of physiologic and behavioral stress were evaluated in mice after cohousing them in a room with rats. Adult, male C57BL/6NCrl mice (n = 8 per group) were randomly assigned to control, isolator cage, visual stimuli, olfactory stimuli, or visual+olfactory stimuli groups. After 15 d of exposure, body, and adrenal weights did not differ between groups. None of the groups of mice experienced significant increases in corticosterone or stress-related behavior in the open-field test after exposure to rat stimuli. These results suggest that the stress-related effects of cohousing with rats are negligible in mice and have implications for housing rats and mice in shared rooms, thereby allowing efficient use of research resources.