Individual housing of mice--impact on behaviour and stress responses.

The replicability of results derived from studies in rodents might be influenced by stress caused by inappropriate housing conditions. Here we compared the experimental behaviour and stress response (circulating corticosterone level and adrenal tyrosine hydroxylase activity) of individually-housed male and female inbred mice with that of animals housed in social groups. All mice were behaviourally tested in the modified hole board test (mHB). Male C57BL/6, BALB/c and A mice housed in groups of 3 were compared with individually-housed mice. In a subsequent experiment female C57BL/6 and BALB/c mice were housed under similar conditions. To exclude the possible effects of within-cage order of testing, only one individual per group was behaviourally tested. Neither male nor female mice housed individually showed stronger signs of stress than their socially-housed counterparts. However, we observed a within-cage order effect on the hormonal stress response (corticosterone) in socially-housed female C57BL/6 mice. No effects of individual housing on behaviour in the mHB were found.