Effects Of Different Social Environment On Behaviors And Immunity In Male Mice

Backgrounds:Social pressure increases the morbidity of mental diseases such as anxiety,depression,post-traumatic stress disorder with the development of science and technology.The emergence of mental diseases not only seriously affects the learning ability and life quality of patients,but also brings a heavy burden to the family and affects social harmony.The occurrence and development of mental diseases is closely related to the surrounding environment.For example,children which lack of parental care are easy to produce autism and depression.Living alone is easy to lead to anxiety,depression and so on.Stress disorder can also be caused by serious injuries such as war,natural disasters,accident,etc.There is still unknown in the occurrence,development and treatment of mental disorders.The immunity and living surroundings are co-evolved.Therefore,this study discussed the effects of different social environment on behaviors and immunity of mice.Methods:1.Establishment of social isolation model:The day the pups born was assigned as postnatal day 0（P0）.The mice in social isolation group were separated for 6 hours a day（10 a.m.to 4 p.m.）,and the mother and pups were separated by the middle partition in the cage.Control animals were not treated.The time lasted from P0 to P21for 21 days.The behaviors of the pups were tested in adulthood.2.Establishment of isolated model:Each of isolated mice was put into a cage after it was weaned and raised for a month.Four of group housed mice were placed into a cage.Behavioral tests were performed in adult mice.3.Establishment of social stress model:social stress model was established by Resident-intruder mode.Kunming mice（35±5g）were Resident whereas C57B/L mice or CX3CR1⁺/GFP/GFP mice were Intruder.C57B/L mice or CX3CR1⁺/GFP/GFP mice were attacked by Kunming mice once they were put into the cage of Kunming mice.After10min,they were separated by transparent porous plastic partition to maintain visual and odor contact.After 6 hours,the partition was removed,then Kunming mice attacked C57B/L mice or CX3CR1⁺/GFP/GFP mice for another 10 minutes.The animals in the control group were not treated.4.IFN-γ^-/-mouse:IFN-γ^-/-mice were purchased from the Jackson Laboratory,genotypes were identified and the third generations homozygous adult male mice were selected for the experiment.5.Behavioral tests:the spontaneous activity of mice was evaluated by open field test,the anxiety-like behavior of mice was detected by sucrose preference test and lantency of uptaking experiment in novel environments,and the depression-like behavior was detected by tail suspension test.The three-box experiment was used to evaluate the social cognitive function.The social dominance was detected by tube test,and the motor function of mice was detected by rotarod test.6.Tissue preparation and assay:under anesthesia,blood was collected from the eyeball,and 20μl was quickly dropped into 1.5ml micro-tubes.The number of white cells,neutrophils and lymphocytes were detected by Hematology System for Multi-species.The lymphocytes of spleen,meninges and choroid plexus were extracted.The distribution of T lymphocytes in the lymphocytes of spleen,meninges and choroid plexus were detected by flow cytometry.7.Real-time PCR:total RNA was extracted from meninges,choroid plexuses,blood lymphocytes,spleen lymphocytes,prefrontal cortex,hippocampus and hypothalamus,respectively.Total mRNA was reverse-transcribed into cDNA.The mRNA levels of CREB,BDNF,IGF₂,Oxytocin and CRH were examined by using real-time PCR in different brain regions.Results:1.Effects of mother-child separation on behavior and immune function of adult male offspring:Social isolation increased the anxiety-like and aggressive behaviors but did not affect Spontaneous exploratory behavior.Social time were shortened and social recognition were weakened in social isolation group.Additionally,the number of immune cells in peripheral blood circulation were obviously reduced and the immunoreactivity was suppressed in social isolation group.Social isolation affected the molecular levels associated with synaptic plasticity in the hippocampus.However,the expression level of OXT in hypothalamus were increased.2.Changes in isolated housed model:Anxiety-like and aggressive behavior were enhanced,the number of immune cells in peripheral blood circulation,spleen,meninges and choroid plexuses were obviously reduced and the immunoreactivity was suppressed.In addition,the expression level of CREB in prefrontal cortex and the expression of IGF₂ in hippocampus were reduced.However,the expression levels of OXT and CRH in hypothalamus were increased.3.Changes in acute social stress model:Acute social stress led to social dysfunction in mice,manifested as social phobia and social withdrawal.The level of IFN-γin peripheral blood circulation was increased,and the expression level of IFN-γin the spleen lymphocytes,peripheral blood lymphocytes and choroid plexus were increased.The sensitivity of mice to social defeat were decreased and anxiety-like response were inhibited,accompanied by a decrease in the transcription level of IFN-γin peripheral blood and above-mentioned tissues in the splenectomy mice.Social stress led to a decrease in OXT levels,but splenectomy could inhibit this effect.Social stress led to a decrease in the levels of BDNF and IGF₂ in the hippocampus,but an increase in the prefrontal cortex,and spleen resection increased the level of BDNF in the hippocampus.4.Changes in IFN-γknockout mice:Social time were shortened and social recognition were weakened in IFN-γknockout mice.The number of immune cells in spleen,meninges and choroid plexuses were obviously reduced and the immunoreactivity was suppressed.The expression level of CREB was increased and the level of BDNF was reduced in prefrontal cortex.The levels of BDNF and IGF2 in hippocampus were reduced.The expression levels of OXT and CRH in hypothalamus were decreased.Meanwhile,the number of OXT positive neurons decreased in the PVN of hypothalamus,but theβ-gal positive cells were increased.Conclusion:1.Changes in social environment during juvenile period and acute social stress caused to the social deficit in mice,accompanied by anxiety and depression-like phenotype,which associated with the synaptic plasticity in prefrontal cortex,hippocampus and hypothalamus2.The early changes of social environment affected the immune function of mice,which was mainly manifested by the decrease of immune function.Acute social stress led to increased immune response in mice.3.IFN-γacts as a bridge between social behavior and immunomodulation.IFN-γknockout leads to social withdrawal in mice.