Buffering Effect Of Group Housing On Acute Restraint Stress Induced Anxiety/Depression And Neuroendocrine Alterations In Mandarin Voles

Social animals live in groups and company with each other is beneficial to the survival and health. Living in social groups could increase the chance of survival, reduce predation risk and enhance reproduction rate of the group. In primates, a complex organization of social systems and multiple forms of social interactions evolved, which are not restricted to pure reproductive functions such as the search for a mate, mating, and care for the offspring. In fact, social company may promote social bonding and the social stability of the group. Rather, social interactions affect daily life in an overwhelming complexity and intensity. In the development of animals and human, there were various kinds of stress, such as social stress and physical stress, etc. Stress is a situation of threatened homeostasis during which a plenty variety of adaptive processes are activated to generated physiological and behavioral changes. Stress is a major risk factor to mental and physical health, alter autonomic and neuroendocrine, emotional and cognitive, such as anxiety, depression and so on. However, the social support shows the health-promoting and stress-protective effects on both human and animals. Social support is a complex. social behavior, including pair bonding, parental-offspring bonding, peer bonding, etc. Studies have examining such reciprocal interaction, especially mother-offspring bonding (which is a reproductive social connections) can improve the unhealthy emotions caused by stress. Studies on monogamous species such as the prairie vole demonstrated that pair bonding could drop the increased corticosterone level after the individuals were separated from their bonding partner in a novel environment. However, few studies have focused on the peer bonding, which is a non-reproductive social connections, and most of these studies are concentrate on the improve effects of social support, whether group housing exerts buffering effects of anxiety/depression, prevent the incidence of anxiety/depression and its detailed neuroendocrine mechanism remain unclear.So this study is the first time to use socially monogamous mandarin vole as model, utilize the behavior test, ELISA, immunohistochemistry methods to explore acute restraint stress-induced anxiety-/depression-like behavior in animals, discuss buffering effects of group housing on acute restraint stress-induced mental disorder and the changes of the related neurotransmitters or hormones. To reveal the neuroendocrine mechanisms of social support buffering effects on the stress-induced emotional disorder.According to housing condition (single/group housing), and restraint stress (exposing restraint stress/without restraint stress), we divided these adult voles into four groups:single housing+no-restraint (SN), group housing+no-restraint (GN), single housing+restraint (SS), group housing+restraint (GS). Utilize the behavior test to examine the anxiety/depression-like behaviors of the four group voles; make use of ELISA to detection the levels of serum CORT; though immunohistochemistry methods to measure the levels of PVN and SON OT and hippocampus CA1 GR expression.Our results show that:1. Behavior test1.1 In the OFT, LDB and EPMIn female voles, the visits in central area, the distance in central area in OFT; the visits into the light box and the distance traveled in the light box in LDB of SS were significantly reduction than that of SN. Compared with SS, the visits in central area, the distance in central area in OFT; the visits in light box, the percentage of time in light box in LDB of GS tend to increase. The results revealed that acute restraint stress could induce anxiety behavior in female voles, and the group housing as a social support was able to buffer this effect.In male voles, the acute restraint stress has no effects on the percentage of time spent in central area, the visits in central area, the distance in central area in OFT and the percentage of visits in open arms, the total enters into the open arms in EPM in both single housed and group housed groups. But, the visits in central area, the distance in central area in OFT of GS were significantly higher than that of SS, and the percentage of time spent in central area in OFT; the percentage of time in light box in LDB; the total enters into the open arms in EPM of GS tend to increase than that of SS. The results show that whether single housed or group housed, acute restraint stress could not induce anxiety behavior in male voles.1.2 In the FSTCompared with non-restraint female voles, the acute restraint stress has no effect on the immobility time in both single housed and group housed groups. But the immobility time of GS is much less compared to SS. The results show that whether single housed or group housed, acute restraint stress could not induce depression behavior in female voles.In male voles, whether it is single housed or group housed, the acute restraint stress groups spent significantly more time keeping immobility than non-restraint stress groups. Meanwhile, the group GS spent less time keeping immobility than the group SS. The results reveal that acute restraint stress can induce depression behavior in male voles, and the group housing was able to buffer this effect.2. ELISAThe level of serum corticosterone in both male and female voles was tested by ELISA method. The experimental results show that the serum CORT level did not have significant difference of the four groups in the same sex voles. But the CORT levels in serum of SS tend to increase compared to SN, shown that acute restraint stress could increase the serum CORT level in a certain extent. Meanwhile, compared with SS, the CORT levels in serum of GS tend to decrease, shown that group housing could buffer the activity of HPA aix response to stress in some extent.3. Immunohistochemistry3.1 The OT-immunohistochemistryIn female voles, whether single housed or group housed, the PVN OT expression of restraint group were significantly less than non-restraint group. Meanwhile, the group GS up-regulated the number of OT neurons in the PVN compared to SS.In male voles, whether single housed or group housed, the PVN OT expression of restraint group were less than non-restraint group. Meanwhile, compared with SS, the group GS up-regulated the number of OT neurons in the PVN. The results indicated that acute restraint stress could decrease the OT expression in mandarin voles, at the same time, group housing was able to buffer this effect.3.2 The GR-immunohistochemistryIn the same sex voles, compared with SN, group SS had significantly higher hippocampus GR expression. The results provided that acute restraint stress increased single housed animals GR expression. Meanwhile, group GS had significantly higher hippocampus GR expression than group SS in both female and male voles inferred that the buffer effect of group housing possibly due to higher levels of GR expression.In conclusion, acute restraint stress could induce anxiety and/or depression behavior in adult mandarin voles, and group housing as a kind of social support has buffered effect on the emotion disorder. Stress can change the serum CORT level, decrease the OT expression in PVN and SON, and increase the GR expression in hippocampus. It provides that group housing might through influence OT and GR system to buffer acute restraint stress-induced emotional disorder in animals. Further, our research is established to improve animal mood, and at the same time built a theoretical foundation on animal's feeding and management.