Higher heart rate of laboratory mice housed individually vs in pairs (2003)

Spani, D., Arras, M., Koenig, B. et al.

Abstract

Many studies have shown that housing mice individually over a long period significantly alters their physiology, but in most cases measurement has required human interference and restraint for sampling. Using a radio-telemetry system with implantable transmitters, we recorded heart rate (HR), motor activity (ACT) and body temperature (BT) of freely moving male mice (NMRI) housed either individually or in pairs with an ovarectomized female. .. Even after severalweeks of habituation to the social conditions, HR was increased in mice housed individually compared with mice housed in pairs, although their measured ACT did not differ. .. Furthermore, individually-housed mice had more, but shorter, resting bouts, indicating disruption of the normal circadian sleep pattern. Enhanced HR in individually-housed mice does not necessarily indicate stress, but might be an important physiological indicator of discomfort. The fact that individual housing alters basic physiological parameters in laboratory mice highlights the need to control for housing-dependent variation, especially in experiments that are sensitive to changes in these parameters. The observed instability of ultradian rhythms in individually-housed mice may thus indicate that the elevated HR levels reflect a chronic impairment of animals welfare. Anxiety and aggressiveness increase in isolated mice, whereas the duration of sleep periods decreases. In mice, HR responds promptly to almost all kinds of disturbances. If the experimenter simply enters the animal room without touching the cage there are immediately strong elevations in HR (data not shown).