Social status in mice: behavioral, endocrine and immune changes are context dependent.

The aim of the present study was to investigate the effect of social status on the endocrine, immune and behavior response of male mice. We found that in mice reared in a group of siblings since weaning, no difference exists between dominants and subordinates in basal corticosterone level, in behavior in the open-field test (OFT) and in a series of immune parameters. These results suggest that living with siblings is not a stressful condition for either dominant or subordinate mice. Therefore, group-housed siblings can be regarded as a valid control group in social stress studies. When mice were subjected to chronic psychosocial stress for 21 days, four types of social outcome occurred: residents becoming dominants, intruders becoming subordinates, residents becoming subordinates and intruders becoming dominants. Interestingly, the behavioral profile in the OFT revealed a status-dependent effect, with resident dominants (RD) and intruder dominants (InD) showing the highest locomotor and exploratory activity, whereas the corticosterone level was higher than control for all four categories. In addition, a context-dependent effect emerged at the immune level: resident subordinates (RS) had a reduced splenocyte proliferation and IL-4 and IL-10 production. Mice in all the other three social ranks showed no immune alterations. Therefore, the loss of an individual's social rank position seems a promising field of study to investigate the psychological impact of stressful events.