Effects Of Group Housing On Stress Induced Emotional And Neuroendocrine Alterations

Chronic 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. The absence of positive social interactions and social support can contribute to alterations in behavior and physiology, including both negative mood states and cardiovascular dysfunction. For instance, in humans perceived loneliness is associated with symptoms of depression and increased cardiovascular reactivity during exposure to a mental stressor. However, whether group living exerts effects on development of depression and anxiety induced by chronic restraint treatments and its detailed neuroendocrine mechanism remain unclear. The present study attempted to test a possible buffer effect of group housing as a social support after on anxiety and depression-like behavior induced by chronic restrict stress. Mice were assigned to one of the following four groups:Restrict/one individual housing (RI), Restrict/group-housing (RG). Non-restrict/one individual housing (NI), and Non-restrict/group-housing (NG). Following repeated restraint, the anxiety and depression-like behaviors of single and group housing mice were examined using the elevated plus-maze, open filed 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. The main results include the following points:1. In the open-field testWe found the percentage of time spent in the centre of the OF was significantly affected by treatment(F(3.34)=9.761.p<0.05).RI spent time in the centre of the OF has no significantly difference across NI(mean diff=0.7363. P=0.863).And so dose the NG and RG (mean diff=4.7152. P=0.817).RI spent significantly less time in the centre of the OF than the RG(mean diff=18.0625. P=0.01). The total distance traveled in the OF (F(3.34)=16.712. p<0.05) and total number of visiting in the centre of the OF (F(3.34)=18.718. p<0.05)for group were significantly different across treatment groups. RI moved distances has no significantly different across NI (mean diff =12.2763,P=0.908)and moved significantly shorter distances than RG(mean diff=545.5771. P=0.000). RG moved distances has no significantly different across NG(mean diff=25.7445, P=0.827).the visiting in the centre of the OF of RI has no significantly different across NI (mean diff=4.125,P=0.63)and significantly less than RG(mean diff=545.5771. P=0.000). There were no significant different between NG and RG(mean diff=0.4286, P=0.964).2. In the elevated plus-mazeTreatment type significantly affected the percentage of time spent in the open arms (F(3,34)=3.036, p<0.05), The total distance traveled (F(3,34)=4.152, p<0.05) and the number of visiting in the open arms(F(3,34)=4.808, p<0.01) RI spent significantly less time in the open arms than the NI (mean diff=4.5833, P=0.049) and RG (mean diff=7.2619, P=0.04), There were no statistically significant differences between NG and RG(mean diff=0.6006,P=0.964).The tests showed that RI showing a significant decrease of the total distance in the open arm entries compared to NI (mean diff=35.4487, P=0.021)and RG (mean diff=45.2186, P=0.005). There were no significant differences between NG and RG(mean diff=0.6006, P=0.964). Compared to RI, NI(mean diff=4.5833. P=0.049) and RG(mean diff=7.2619, P=0.004) spent much more times visite the open arms. No significant effects between NG and RG (mean diff=0.1714, P=0.933).3. In the forced swimming testThe mean percentage of time spent immobile,RI spent significantly greater percentage of time immobile during the forced swiming test than NI (mean diff=58770, P=0.035) and RG (mean diff=90521.2, P=0.002). There were no significant differences between the NG and RG (mean diff=6926.222.2. P=0.765).4. The OT-immunohistochemistryWe found significant differences in the number of OT-immunoreactive neurons in the PVN (F(3.34)=28.739. p<0.05).RG displayed significantly more OT-immunoreactive neurons than RI in the PVN (mean diff.=14.2519. P=0.000). There are no significantly differences between RG and NG(mean diff.=1.8750. P=0.548).5. The GR-immunohistochemistryThe number of GR-IR neurons varied across experimental group (F(3.31)=12.234, P <0.01) RG displayed significantly more number of GR-immunoreactive neurons compared with RI(mean diff=l23.0471.P=0.035). There are no significantly differences between RG and NG(mean diff.=20.0275. P=0.62).6. Corticosterone levels in serumWe found differences in Concentrations of Cortisol in Serum (F(3.36)=4.215. P<0.05); Within the populations post hoc tests showed that no significant difference was found in baseline corticosterone levels or in response to stress between RG and NG mice (mean diff.=18.7751,P=0.626). RI displayed significantly higher level of Cortisol in Serum than RG(mean diff.=63.5809,P=0.04)and measures also revealed that RI displayed higher lever of Cortisol in Serum than NI(mean diff.=42.8449,P=0.039).7. From the data of OT levels in serumThere were no significant difference was found among four group (F(3.36)=1.658, P>0.05).Our results show that chronic restraint significantly decreased time in open arm of elevated plus maze test and increased immobility time in forced swimming test in single housing mice. However, chronic restraint exerted no effects on these aspects in group living mice. Accompanying the changes of behaviors, chronic restraint up-regulated levels of serum CORT and reduced the hippocampus GR in single living animals, but did not change these measures in group living mice. Taken together, these results provide substantial evidence that group-housing can reduce levels of anxiety and depression induced by chronic restrict stress in mice. The elevation of central GR and decrease of circulating CORT may possibly be involved in these buffering effects.