Body temperature and nesting behavior following influenza challenge in mice: effects of age.

We studied the interaction of age and influenza on core body temperature (Tc) of mice. Following influenza challenge, 2-mo-old female BALB/c mice demonstrated a significant fall in Tc. Female BALB/c mice 24 mo of age had lower baseline Tc than young mice and a larger fall in Tc post influenza challenge. We noted there were marked differences in nesting behavior between the young and aged mice. A nesting score was devised, and we found that at baseline, aged mice had a much lower score than young mice (15.6 +/- 7.4 vs. 24.7 +/- 0.3, P < 0.0001). Following influenza challenge, nesting behavior of young mice dropped considerably, while no significant change occurred in the behavior of aged mice. When mice were housed without bedding, there were significant decreases in Tc of young, but not aged mice. There was a further fall in Tc with influenza challenge in young mice. These data imply that nesting is an important mechanism for maintaining Tc in young mice, but alternative mechanisms are used by aged mice. The lower body temperatures in the aged mice are similar to studies in aging humans.