The Influence Of Social Defeat On The Formation Of Male Mandarin Vole Mate Relationship And Its Neuroendocrinological Mechanism

The continuous development and progress of society has brought convenience to human life,but at the same time,the adverse consequences caused by social pressure have also deeply affected human life and survival.The high incidence of mental and psychological diseases among people has become a non-negligible factor hindering the progress and development of modern society.Social pressure is not only one of the important factors leading to the occurrence of mental illness,but also has a negative impact on prosocial behavior.Prosocial behavior is a kind of positive social behavior which is beneficial to social stability and sustainable development.Stable pair bonding between adult males and females is an important aspect of human prosocial behavior.Studies have shown that individuals with stable marital relationships live longer,and the degree of intimacy between partners is positively correlated with individuals' positive mental state,and negatively correlated with immune function and the incidence of cardiovascular disease.In addition,stable marital relationships are very important to the physical and mental health of offspring as well as social harmony and stability.Chronic social defeat stress(CSDS),as a social stress source,is considered to be similar to the social stress suffered by human beings,because stressful life events is a major factor leading to mental and social disorders.Chronic social defeat stress will cause individuals to show emotional abnormalities and social behavior disorders,and the changes of these emotions and behaviors are inseparable with neuroendocrine changes,such as the hyperactivity of the hypothalamus-pituitary-adrenal(HPA)axis,the changes of the dopamine system,the oxytocin system and the vasopressin system.These systems are closely related to the formation and maintenance of marital relationship.Therefore,it is a scientific proposition worth exploring whether chronic social defeat stress can cause changes in marital relationship.In recent years,the model of chronic social defeat stress has been widely used in anxiety,depression and post-traumatic stress disorder(PTSD).However,due to the limitations of traditional experimental animals such as low sociality and non-monogamy,researches on prosocial behaviors such as marital relationship are still not common,especially on individual marital relationship after exposure to chronic social defeat stress.Mandarin voles has the characteristics of high sociality and monogamy,which makes it an ideal animal model to study prosocial behavior.This study will apreliminary exploration on the pair bonding of adult male mandarin voles exposed to chronic social defeat stress.The experiment is divided into behavior test and related molecular measure.In the behavioral experiment,the approach and avoidance experiment and social interaction experiment were used to explore the sociality of adult male mandarin voles exposed to chronic social defeat stress;We used the partener preference experiment to explore the formation time and stability of pair bonding in adult male mandarin voles exposed to chronic social defeat stress.Western Blot was used to detect the content changes of dopamine Dl-like receptor(DIR),dopamine D2-like receptor(D2R),oxytocin receptor(OT),vasopressin 1a receptor(V1aR)and arginine vasopressin(AVP)in nucleus accumbens(NAcc),lateral septum(LS),paraventricular nucleus(PVN)and ventral tegmental area(VTA),as well as the content changes of tyrosine hydroxylase(TH)in NAcc.Immunofluorescence was used to detect the OT and TH immunoreactive neurons in PVN and VTA.According to the results of behavior and molecular mechanism exploration,bilateral microinjection of DIR agonist in the NAcc using brain stereotactic technology was conducted to test the effect of the treatment of dopamine D1-like receptor agonist on the pair bonding of adult male mandarin voles exposed to chronic social defeat stress.The main results are as follows:1 Research results of Behavioral test1.1 The approach avoidance experimentThe approach avoidance experiment was used to detect the approach and avoidance behaviors of adult male mandarin voles to the same individuals.Results showed that adult male mandarin voles in the control group spent significantly more time in the interaction zone in the second stage(Target)than that in the first stage(No Target).Adult male mandarin voles in the chronic social defeat stress group spent significantly less time in the interaction area in the second stage(Target)than that in the first stage(No Target).These results suggested that adult male mandarin voles exposed to chronic social defeat stress exhibit avoidance behavior toward individuals of the same species.1.2 Social interaction experimentThe social interaction experiment was used to evaluate the behavior of adult male mandarin voles in social interaction.The experimental results showed that adult male mandarin voles exposed to chronic social defeat stress showed significantly decrease in aggressive behavior,significantly increase in defensive behavior,significantly increase in avoidance behavior,significantly decrease in intimate behavior,significantly decrease in exploratory behavior,significantly decrease in sniffing behavior,significantly increase in immobile behavior compared with the control group,and no significant change in self-grooming behavior and walking were found.These results suggested that adult male mandarin voles exposed to chronic social defeat stress reduced their interaction with strangers of the same species,and reduced their exploratory behavior and social behavior towards the environment and strangers.1.3 Partner preference experimentThe partner preference experiment was used to evaluate the partner preference formation and maintenance of adult male mandarin voles.The experimental results showed that adult male mandarin voles in the control group spent more time in the partner's chamber than the chronic social defeat stress group at 1,3,5,7,9 and 11 days of cohabitation time.Adult male mandarin voles in the control group spent significantly or very significantly more time in side-by-side contact with the partner than the chronic social defeat stress group at 1,3,5,7,9 and 11 days of cohabitation time.Adult male mandarin voles in the control group spent significantly or very significantly more time in the partner's chamber than in the stranger's chamber at 1,3,5,7,9 and 11 days of cohabitation time.Adult male mandarin voles in the control group spent significantly or very significantly more time in side-by-side contact with the partner versus the stranger at 1,3,5,7,9 and 11 days of cohabitation time.The attack time to the stranger was higher than that to the partner,and the attack time to the stranger showed an increasing trend with the extension of the cohabitation time.Adult male mandarin voles in the chronic social defeat stress group spent more time in the partner's chamber than in the stranger's chamber,with significant or extremely significant differences after cohabitation for 3,7,9 and 11 days.Adult male mandarin voles in the chronic social defeat stress group spent significantly more time in side-by-side contact with the partner versus the stranger at 1,3,9 and 11 days of cohabitation time,however,there was no significant difference at 5 days and 7 days of cohabitation time.The attack time to the stranger was higher than that to the partner,however,the attack time did not change regularly with the increase of cohabitation time.In addition,adult male mandarin voles in the control group spent significantly more time to rescuing their partner than they did to strangers at cohabitation time.Adult male mandarin voles in the chronic social defeat stress group spent more time to rescuing their partner than they did to strangers at 7 days of cohabitation time after.These results suggested that adult male mandarin voles in the control groups and the chronic social defeat stress groups can form partner preference after one day of cohabitation time.But the chronic social defeat stress can lead to the instability of the pair bond between adult male mandarin voles and their partner.And the chronic social defeat stress may affect the empathic behavior of adult male mandarin voles to their partner.2 Research results of molecular mechanism2.1 Western BlotThe content of D2R in NAcc increased significantly in adult male mandarin voles exposed to chronic social defeat stress,but there was no significant change in LS,PVN and VTA.The content of DIR in NAcc decreased significantly,while there was no significant change in D1R in LS,PVN and VTA.The content of OTR in PVN decreased significantly,and there was no significant change in OTR in NAcc,LS and PVN.There was no significant difference in the content of AVP and V1aR in NAcc,LS,PVN and VTA.There was no significant difference in TH content in NAcc.The above results showed that the chronic social defeat stress exposured will increased the content of D2R in NAcc of adult male mandarin voles,and decreased the content of DIR in NAcc and OTR in PVN.2.2 ImmunofluorescenceThere was no significant difference in OT immunoreactive neurons in PVN of adult male mandarin voles exposed to chronic social defeat stress compared with the control group.The TH immunoreactive neurons in the VTA of adult male mandarin voles exposed to chronic social defeat stress were significantly lower than those in the control group.The above results showed that chronic social defeat stress down-regulated the content of TH immunoreactive neurons in VTA.2.3 Stereotaxic cannulation and microinjectionAdult male mandarin voles injected with saline spent significantly more time in side-by-side contact with the partner versus the stranger at 1,3,5,7,9 and 11 days of cohabitation time.Adult male mandarin voles exposed to chronic social defeat stress treated with the saline spent significantly more time in side-by-side contact with the partner versus the stranger at land 9 days of cohabitation time.Adult male mandarin voles exposed to chronic social defeat stress were treated with the drug(D1R receptor agonist SKF38393)spent significantly more time in side-by-side contact with the partner versus the stranger at 1,3,5,7,9 and 11 days of cohabitation time.These results suggest that the treatment of DIR receptor agonist SKF38393 ameliorates the phenomenon of pair bond instability that exposed to social defeat stress.To sum up,this experiment proved that chronic social defeat stress affected the sociality of adult male mandarin voles,and chronic social defeat stress also led to the change of the stability of adult male mandarin voles' marital relationships.The change of stable marital relationships may be related to the reduced density of DIR receptor in NAcc of adult male mandarin voles exposed to chronic social defeat stress,and this change can be reversed by the use of DIR agonist SKF38393.In addition,this experiment also proved that chronic social defeat stress caused an increase in the density of D2R receptors in NAcc,a decrease in the density of OTR in PVN,and a decrease in the content of TH immunoreactive neurons in VTA.