Group housing and nest building only slightly ameliorate the cold stress of typical housing in female C57BL/6J mice

Huddling and nest building are two methods of behavioral thermoregulation used by mice under cold stress. In the laboratory, mice are typically housed at an ambient temperature (T-a) of 20 degrees C, well below the lower end of their thermoneutral zone. We tested the hypothesis that the thermoregulatory benefits of huddling and nest building at a Ta of 20 degrees C would ameliorate this cold stress compared with being singly housed at 20 degrees C as assessed by heart rate (HR), blood pressure (BP), triiodothyronine (T3), brown adipose (BAT) expression of Elovl3 mRNA, and BAT lipid content. A series of experiments using C57BL/6J female mice exposed to 20 degrees C in the presence or absence of nesting material and/or cage mates was used to test this hypothesis. Mice showed large differences in HR, BP, shivering, and core body temperature (T-b) when comparing singly housed mice at 20 degrees C and 30 degrees C, but only a modest reduction in HR with the inclusion of cage mates or bedding. However, group housing and/or nesting at 20 degrees C decreased T3 levels compared with singly housed mice at 20 degrees C. Singly housed mice at 20 degrees C had a 22-fold higher level of BAT Elovl3 mRNA expression and a significantly lower triacylglycerol (TAG) content of BAT compared with singly housed mice at 30 degrees C. Group housing at 20 degrees C led to blunted changes in both Elovl3 mRNA and TAG levels. These findings suggest that huddling and nest building have a limited effect to ameliorate the cold stress associated with housing at 20 degrees C.