Effects of group and individual rearing conditions on behavioral and autonomic thermoregulation during cold in mice

Issei Kato a, Kei Nagashima b
a) JSPS Postdoctoral Research Fellow, Waseda University
b) Body Temperature and Fluid Laboratory, Faculty of Human Sciences, Waseda University

Abstract:

[Background] Mice show huddling behavior when living in groups, which is considered both social and thermoregulatory behavior. The present study aimed to estimate that such huddling behavior affects behavioral and autonomic responses when the mice were individually exposed to heat and cold. [Methods] C57BL6/J mice (n=47, 8 w old, male) were divided into two groups that were reared individually and in groups (I Group and G Group, respectively). In addition, they were reared at an ambient temperature (Ta) of 27°C or 22°C. First, their deep body temperature (Tb) and huddling behavior (only G group) were assessed. Second, cold-escape/warm-seeking behavior in both groups was evaluated with a behavior system in which mice were placed on cold plates but could find a warmer plate. Third, mice were exposed to 18°C cold and Tb, and the expression of UCP1 mRNA in the interscapular brown fat was evaluated. [Results] The huddling behavior in the daytime was not different between Ta of 27°C and 22°C. However, the huddling behavior in the nighttime was greater at Ta at 22°C than at 27°C. The heat-escape/cold-seeking behavior was decreased in G Group reared at Ta of 22°C than I Group reared at Ta of 27°C and 22°C and G Group reared at Ta of 27°C. The expression of UCP1 mRNA in the brown fat was greater in I Group reared at Ta of 22°C. [Discussion] Huddling behavior in the nighttime (i.e., active phase) increased in a cooler environment, suggesting an involvement of the behavior in thermoregulation. However, other cold-escape/warm-seeking behavior may be suppressed in the mice reared in group and cold. In addition, heat production in cold activated in the brown fat may also be suppressed in the mice.