Behavioural and physiological characterization of male mice under chronic psychosocial stress

Social stress is a major factor in the etiology of several psychopathologies, with individuals greatly differing in vulnerability. The development of appropriate animal models of social stress is, thus, a major challenge of modern bio-medical research. Adult male mice were subjected to a new model of chronic psychosocial stress in which resident/intruder dyads live chronically in sensory contact and physically interact on a daily basis. Four behavioral categories were identified: Resident Dominants (RD), Resident Subordinates (RS), Intruder Dominants (InD), Intruder Subordinates (InS). Here we investigated: behavior during aggressive interactions; gross physiological components of mice metabolism; organ physiology; response to dexamethasone suppression test (DST). RD and InD mice showed persistently high levels of aggression. All four categories of mice showed robust lack of suppression of corticosterone level when challenged with the DST. Although food intake was not altered under chronic stress, body weight decreased in RD and InD mice while increased in InS and, even more so, in RS mice, suggesting an alteration of their metabolic functions. In conclusion, social status and territory ownership were factors determining individual vulnerability to stress exposure. Our model could, thus, be regarded as a valid model to investigate the biological basis of the individual differences in the response to stressful events.