Effects of group housing on stress induced emotional and neuroendocrine alterations.

Chronic restraint stress can induce depressive and anxiety-like behavior and neurophysiological disturbances. The social living shows the health-promoting and stress-protective effects on both human and animal. However, whether group housing exerts effects on development of depression and anxiety induced by chronic restraint treatments and its detailed neuroendocrine mechanism remain unclear. Following repeated restraint, the anxiety and depression-like behaviors of single and group housing mice were examined using the elevated plus-maze, open field test and forced swimming test. The levels of central oxytocin (OT) expression in the paraventricular nucleus (PVN), glucocorticoid receptors (GR) in the hippocampus and serum OT and corticosterone (CORT) were also measured using immunohistochemistry and ELISA methods. Our results show that chronic restraint significantly decreased time in open arm of elevated plus maze and increased immobility time in forced swimming test in single-housed mice. However, chronic restraint exerted no effects on these aspects in group-housed mice. Accompanying the changes of behaviors, chronic restraint up-regulated levels of serum CORT and reduced the hippocampus GR in single-housed animals, but did not change these measures in group-housed mice. Furthermore, repeated restraint had no effect on OT levels in these two housing conditions although group-housing significantly increased the PVN OT levels. Taken together, these results provide substantial evidence that group housing can reduce levels of anxiety and depression induced by chronic restraint stress in mice. The elevation of central GR and OT, and decrease of circulating CORT may possibly be involved in these buffering effects.