Defensive behavioral strategies and enhanced state anxiety during chronic subordinate colony housing are accompanied by reduced hypothalamic vasopressin, but not oxytocin, expression.

Chronic subordinate colony (CSC) housing has recently been shown to be a clinically relevant model of chronic psychosocial stress for male mice and to cause an increase in the animals' anxiety-related behavior on the plus-maze. Here, we investigated (1) the detailed subordinate/dominant behavior during CSC housing, (2) the anxiety-related behavior of CSC and control mice in two independent tests, and (3) whether CSC exposure also influences the hypothalamic expression of oxytocin (OXT) and/or arginine vasopressin (AVP), specifically within the paraventricular nucleus. Both neuropeptides are known to be involved in the regulation of anxiety and stress responses. Behavioral observation revealed that all male CSC mice that were co-housed with a slightly larger male mouse obtained a subordinate status within their colonies over 19 consecutive days. Furthermore, CSC exposure resulted in diminished body weight gain and increased anxiety-related behavior as quantified both on the elevated plus-maze and in the light-dark box. Hypothalamic mRNA levels of OXT remained unchanged, whereas AVP mRNA was found to be decreased on day 20 of CSC exposure. In conclusion, exposure to CSC enhances anxiety, an effect that seems to be independent of the hypothalamic expression of the neuropeptides OXT and AVP.