The Development Of Early Social Environment, Emotional And Social Behavior Of The Mandarin Vole And Mechanism Study

The development of animals is a various and changeable process. The plasticity of gene and behavior is higher in early of development. During this period, social experiences have particularly profound effects. In mammals, mother-infant interactions, parental care and hormonal environment in neonatal period can induce long-term neuroanatomical and neuroendocrine changes and make long-lasting effects on behaviors. Most of the above studies which used nonsocial animal model were limited for exploring the development of social behaviors. Further, the effects of early social environment on social behaviors are less investigated. Previous research found that pups of high licking and grooming mothers have higher levels of oxytocin (OT). OT plays an important role in regulation of social organization and mating system in voles. OT can also influence various social behaviors, such as social cognition, reproductive behavior, parental care, partner preference, etc. But, whether OT plays a role in early social environment affecting emotional and social behaviors and whether estrogen receptor alpha (ERα) has effects on it are unknow. Based on the above reports, the present research used mandarin vole, which is a socially monogamous rodent , as animal model to answer the following questions: 1) Whether mandarin voles from various early social environments gain different amout of parental investment; 2) whether different parental investment induces different long-lasting effects on emotional and social behaviors in offspring; 3) whether early social environment influences expression of OT in the paraventricular hythalamic nucleus (PVN) and the supraoptic nucleus (SON); 4) whether neonatal exposure to OT induces different long-term effects on emotional and social behaviors in offspring; 5) whether early social environment and neonatal exposure to OT influence ERαexpression. Thus, in this study, we used mandarin vole, which has complex social behaviors, as animal model and established three social environments in the present research, those are biparental care (PC), paternal deprivation (PD) and early social deprivation (ED). We study the developmental influences of different social environments on subsequent emotional and social behaviors, and try to explore the neural mechanism that how early social environments regulate the development of behavior. The main results include the following points: 1. No significant differences were observed between parental care of PC mothers and fathers in F1 generation mandarin voles. Males, as well as females, take an active role in parental care. This suggests that mandarin vole is a socially monogamous rodent. In addition, no significant differences of maternal behaviors were found between PC mothers and PD mothers. No maternal compensation towards pups was found for the absence of the paternal care. Therefore, it could be suggested that the parental care in the model of PD was similar as in polygamy, and the total level of parental investment in PC families was significant more than in PD families.2. We tested the open field and social interaction of all F2 generation groups which developed in different social environments. The results showed that PD and ED increase the level of anxiety and fear in novel environment and reduce the level of exploratory, locomotor activity and sociality.3. We tested the partner preference of all F2 generation groups which developed in different social environments. The results showed that after 24h cohabitation, all groups can not form pair bonds, but PD and ED mandarin voles spent more time on physical contact with strangers. It could be confer that PD and ED may prolong the latency of pair bond formation.4. We tested the parental behavior of all F2 generation groups which developed in different social environments. The results showed that PD and ED reduce parental care and sociality of F2 mandarin voles. With the development of pups, parental care was reduced. Those results suggest that early social environment could affect the level of parental care transmitting across generations.5. Immunohistochemistry was used to test the expression of OT- immunoreactive (OT-IR) in PVN and SON in the age of 21 of all F2 generation groups which developed in different social environments. The results showed that PD and ED inhibite the expression of endogenous OT.6. We have observed the open field and social interaction of F2 generation mandarin voles which were given a single subcutaneous injection of isotonic saline (SAL), OT or OT antagonist (OTA) within 24h of birth. The results indicated that OT reduces the level of anxiety and increases sociality in both male and female voles. OT also increases the level of exploratory and locomotor activity just in females. Both OT and OTA reduce the level of exploratory and locomotor activity in male voles.7. We have observed partner preference of F2 generation mandarin voles which were given a single subcutaneous injection of SAL, OT or OTA within 24h of birth. The results indicated that OT promotes pair bond formation in females while has no effects in males. OTA enhances female to aggress stranger while both OT and OTA have no effects on aggression preference.8. We have observed parental care of F2 generation mandarin voles which were given a single subcutaneous injection of SAL, OT or OTA within 24h of birth. The results indicated that OT improves parental care in females while has no effects in males. OTA has no effects on parental behavior.9. Within 24h of birth, F2 generation mandarin voles were randomly divided into six groups: PC, PD, ED, SAL, OT and OTA. Immunohistochemistry was used to test the ERαexpression in the bed nucleus of the stria terminalis (BNST), the medial preoptic area (MPOA), the ventromedial hypothalamic nucleus (VMH) and the arcuate hypothalamic nucleus (Arc) in adult. The results showed that the ERαexpression in the BNST, MPOA and VMH of PC females were significantly more while in Arc was significantly less than those of males. The sex difference of ERαexpression in SAL group was similar as that in PC group. PD, ED and OTA reduce ERαexpression in all tested brain regions. OT increases ERα-IR expresion in females while has no effects on males.From the above results, the present study concludes that early social environment has long-term effects on emotional and social behaviors. Mandarin voles developed from various early social environments gain different amount of parental investment which change the OT and ERαexpression. Finally, the development of emotional and social behaviors were co-regulated by both neuro- and incretory system.