Behaviour in the elevated plus-maze predicts coping after subchronic mild stress in mice.

This study was aimed at investigating the coping style of mice subjected to a subchronic unpredictable mild stress procedure and its relationship to initial emotional reactivity. Two inbred strains of mice, the BALB/c ByJ and the C57BL/6 J, known to exhibit distinct emotionality, have been used. They were first observed in the elevated plus-maze and the free exploratory paradigm, each provides a separation of the population in high and low emotional mice. Half of the mice of each strain were then confronted to a 2-week subchronic unpredictable mild stress and tested for their responses in different behavioural situations (consumption of a palatable food, physical state, grooming behaviours and reactivity to a conflict situation). Mice were also tested in the light/dark procedure to assess the effect of the subchronic stress on emotional reactivity. First, a relationship between initial emotional reactivity in the elevated plus-maze and behavioural coping style in response to stress was found, high emotional mice (i.e., BALB mice) displaying inhibited behaviours and less emotional mice (i.e., BL/6 mice) exhibiting few behavioural changes. Furthermore, emotional reactivity was increased in stressed mice compared with nonstressed ones.