The Effects Of Oxytocin And Testosterone Propionate On The Development Of Social Behaviors In Mandarin Voles(Microtus Mandarinus)

The development of animals is a various and changeable process. The survival and reproduction of every species or individuals relies on its short-term or long-term adaptation to environments. The behavior-neuroendocrine environment of the individual development can induce long-term anatomical and physiological changes and make profound effects on behaviors, so this system plays an important role in the development of behavioral and physiological characteristics. The social behaviors of rodents are regulated by neuroendocrine system, especially by neuropeptides and steroid hormones. Oxytocin and testosterone play an important role in social recognition, reproductive behavior, sex behavior, maternal behavior, parental behavior, partner preference behavior and so on. Thus, we can study the neuroendocrine mechanism of social behaviors and research the relationship between neuropeptides and mating system.Monogamous mandarin voles (Microtus mandarinus) were used to investigate intrasexual behavior, affiliative behavior and partner preference behavior of mature animals, which were manipulated by neonatal OT or testosterone propionate (TP) and discuss the development effects of OT or TP on behavior. We also used immunohistochemistry to test the variation of the number of Fos-IR cells or AR-IR cells after those behaviors following early exposure to OT and TP, then discuss the mechanism of behavior-neuroendocrine effects on the development of social behaviors. The study is divided into five parts:1. When manipulated by neonatal injection of OT or TP, animals were weight on 0d, 1d, 3d, 5d, 10d, 20d, 30d, 45d and 60d. The statistics in present experiment showed that neonatal exposure of OT or TP reduces livability and also affects their weight.2. We have observed intrasexual aggression of mandarin voles, which were given a single subcutaneous injection of OT within 24h of birth. The statistics showed that the effects of OT on intrasexual aggression could display obviously only after cohabitation with opposite sex. The effects on female are more significant than male. The brains of different groups were collected and Fos-IR cells neurons in brainregions were marked after behavior. Compared with injection saline on female, there were significant increases in the number of Fos-IR cells in the BST, LSD, MPO, PAN, MD, VMH, ME, CE after injection of OT. There were significant reduction in the number of Fos-IR cells in the MPO, PAN, SON, VMH and increase in the BST and CE after injection of OT on male.3. We have also observed partner preference behavior of individuals, which were given a single subcutaneous injection of OT within 24h of birth. The statistics showed that the effects on female are more significant than male. OT could increase the total duration and frequency of behaviors such as friendly behavior and investigating behavior and reduce aggression and defensive behavior to strange opposite sex individuals. Treated brains were collected and Fos-IR cells neurons in brains were marked after behavior. Compared with injection saline on female, there were significant reduction in the number of Fos-IR cells in the BST> LSD, MPO, PAN, SON, MD, VMH, LA, ME, CE and ar after injection of OT. There were significant reduction in the number of Fos-IR cells in the BST,PAN,MD and increase in the LSD,MPO and CE after injection of OT on male.4. We have observed affiliative behavior of mandarin voles, which were given repeated subcutaneous injection of TP from Od to 6d after birth. The statistics showed that TP could increase the total duration and frequency of behaviors such as friendly behavior and probe behavior to strange opposite sex individuals. The effects on female are more significant than male. Treated brains were collected and Fos-IR cells or AR-IR cells in brain were marked after behavior. Compared with injection saline on female, there were significant increase in the number of Fos-IR cells in the MPO, MD, LA, ME and AR-IRs in the BST, LSD, MPO, MD, VMH, LA and ME after injection of TP. There were significant increase in the number of Fos-IR cells in the BST, MPO and reduction in the number of AR-IR cells in the LSD, VMH, LA after injection of TP on male.5. We have observed partner preference behavior of mandarin voles, which were given repeated subcutaneous injection of TP from Od to 6d after birth. The statistic showed that TP could increase the total duration and frequency of behaviors such as friendly behavior and investigating behavior and reduce aggression and defensive behavior to strange opposite sex individuals. The effects on female are more significant than male. The brains of treated animals were collected and Fos-IR cells or AR-IR cellsin brains were marked after behavior. Compared with injection saline on female, there were significant reduction in the number of Fos-IR cells in the BST, LSD, MD, VMH, LA, ME and increase in the number of AR-IRs in the LSD, MPO, MD after injection of TP. There were significant reduction in the number of Fos-IR cells in the BST, LA, increase in the number of Fos-IR cells in the MPO, VMH and reduction in the number of AR-IR cells in the BST, MPO, LA, ME after injection of TP on male.All these results suggested the important roles of OT and TP in the development and expression of social behavior. Neonatal OT and TP could reduce livability and also affect their weight. Moreover, OT and TP on certain period can alter neuronantomy and physiology functions and then influence the number and sensitivity of their receptors. Hence, we have proved early exposure to OT or TP have long-term consequences on animals' social behaviors. Our researches are also useful for confirming the relationship between neuropeptides and mating system and play an important role in the study of evolution of mating system.