Effects of the duration of individual or group housing on behavioural and adrenocortical reactivity in male mice

Abstract

Male ‘TO’ strain mice were individually or group-housed for different durations (7–196 days). Behavioural reactivity was assessed over 3 days in each category in a novel arena and an emergence test. Plasma samples were later collected after 5 min exposure to ether vapour, these generated stress corticosterone values. Basal corticosterone titres were obtained from similar untested and unanaesthetized categories of mice. Ether stress values were obtained from a limited number of mice subjected to ether anaesthesia but no behavioural testing. The basal adrenocortical activity of these two housing categories did not differ. With longer periods of isolation stress corticosterone values were higher than in comparable grouped animals. Individually-housed mice had significantly lower defaecation scores and exhibited higher levels of exploratory rearing in a novel arena than grouped mice. At about the time an isolated mouse became increasingly aggressive, it became less active in the open-field, and adrenal reactivity increased. Although the relationship is only correlational in nature, it is possible these measures have a common basis.