Chronic social stress does not affect behavioural habituation in male CD1 mice

Various protocols to induce chronic stress in rodents are being used to determine the effects and underlying
mechanisms of prolonged stress experience. Recently, a novel chronic social stress (CSS) protocol
has been developed for mice where social instability in adolescence and early adulthood is induced. This
protocol has been shown to cause an increase in HPA-axis activity and acute avoidance behaviour in the
elevated plus maze. The aim of the present study was to investigate the effect of this CSS protocol on
habituation to an initially novel environment in CD1 mice, since it has been shown that initially high
avoidance behaviour in mice can still be followed by rapid habituation, pointing towards an adaptive
response. One group of male mice, the CSS group, was exposed to the CSS protocol for 7 weeks and we
compared their behavioural and physiological responses with male mice that were housed in a stable
social group, the SH group. The results reveal a decrease in body weight gain and fur condition, changes in
adrenal weight and decreased GR mRNA expression in the CA1 and the dentate gyrus of the hippocampus
in chronically stressed CD1 animals. Irrespective of such evidence for a significantly stressful effect of the
protocol, CD 1 mice, after termination of the stress procedure, revealed habituation profiles that matched
those of control animals. We conclude that the physiological and central-nervous effects caused by a CSS
procedure as used in this experiment fall within the coping capacities of CD1 mice at the behavioural
level.