The Relationship Between AVP,OT And Social Behaviors Of Mandarin Voles Microtus Mandarinus

Social behavior plays important role in animal life and is one of the most important study focuses in animal behavioral study and hot topics in Ecology. Mating system and social organization of animals are the most important studying field in Animal Behavioral Ecology and have been studied profoundly for gaining the insight of life history strategies and maximal reproductive success varying with the mating system.More recently, the roles of the neuropeptides OT and AVP in modulating reproductive and social behaviors have begun to be elucidated. Comparative studies focusing on these hormones suggest that the specific behavioral roles of these neuropeptides may be quite species specific. Both peptides could affect many social behaviors, such as social recognition, partner preference and parental behavior. Also, distributions of oxytocin and vasopressin receptors were significantly different between monogamous vole and polygamous vole. These brain areas with different distribution were considered to play an important role in social behaviors which were associated with mating system.The microtine rodents show profound differences in reproductive biology and social organization in spite of their taxonomic relationship. They are an ideal group of rodents for comparative studies. So voles are informative for studies on the neurobiological basis of social behaviors.In order to probe evolution mechanism and adaptation function of microtine species, we used monogamous mandarin voles (Microtus mandarinus) and reed voles (microtus fortis) with promiscuous reproductive characteristics as two study objects. Our results were the following:1. The statistic in present experiment showed that s.c. injection of vasopressin significantly increased the number of Fos-IR cells in the suprachiasmatic, supraoptic and paraventricular nuclei of the hypothalamus, septum, cingulated gyrus, amygdaloid nucleus and ventromedial hypothalamic nucleus of mature male mandarin voles. These results suggested that the vasopressin might exert its central action by activating a cellular immediate early gene in specific brain regions. Thesebrain regions were closely related with mating behavior of rodent. So the relationship between AVP and mating system may be confirmed.2. On the day of birth, madarin vole pups received an intraperitoneal injection of OT, or saline (vehicle contral), while an additional control group was handled but not injected. One hour after treatment brains were collected and Fos-IR neurons in brain were marked. There were significant differences between males and females. Females handled only displayed significantly higher levels of c-Fos IR in the MD than males, while handled males had higher c-Fos IR in the PAN of the hypothalamus than females. Intraperitoneal injection of OT caused significant increase of c-fos expression in the SON and PAN in males. This inferred that exogenous OT stimulated neuronal activity in the SON and PAN in males. The results indicate that neuronal activity and responses to OT are sexually dimorphic in newborn mandarin voles. In males, changes in FOS expression were stimulated by treatment with OT, suggesting that exogenous OT affects cellular activity while females are sensitive to endogenous OT.3. Adult female mandarin voles received an i.c.v. injection of OT, or saline, while an additional group was only handled but not injected. Two hours after treatment brains were collected and Fos-IR neurons in brain were marked. Compared with injection saline, there were significant increase in the number of Fos-IR cells in the CPU, CE, ME, PE, VMH after injection of OT. CPU, ME and VMH could affect social behaviors, especially sexual behaviors. These results suggested that exogenous OT potentially induced neural activity of mandarin vole, CPU, CE, ME, PE, VMH may be the effective brain regiones of OT, and the correlative relationship between OT and mating system was confirmed.4. By using vasopressin V1a receptor antibody, specific binding to brain vasopressin V1a receptor was observed in both the monogamous mandarin vole and the polygamous reed vole. In the mandarin vole, vasopressin V1a receptor neurons densities were higher in the limbic system and hypothalamus, BST, MD, ME and LA. These brain areas showed low densities of V1a receptor neurons in the reed vole, in which V1a receptor neurons were localized in the LSD, VMH, and MFB. We suggest that variable expressions of the V1a receptor in brain regions in two species may be an important mechanism in evolution of species-typical differences in social bonding and affiliated behaviors.5. By using oxytocin receptor antibody, specific binding to brain oxytocin receptor neurons was observed in both the monogamous mandain vole and the polygamous reed vole. In the mandarin vole, oxytocin receptor neurons densities were higher in the limbic system and hyperthalamous neurons, such as LSD, BST, MD, VMH, PAN, ME and LA. These brain regions showed low densities of OT receptors neurons in the reed vole. LSD played an important role of social recognition, while BST, VMH, LA and ME were the center of social behaviors, especially sexual behaviors. Our results were similar with that of prairie voles and montan voles. These results confirmed that mandarin vole was monogamous from neuron biology aspect. It is suggest that different distribution of the oxytocin receptor neurons in brain regions may be an important mechanism in evolution of species-typical differences in social bonding and affiliated behavior.6. We examined AVP V1a and oxytocin receptors expression in the brain, while the mandarin voles were exposed to their partner or another strange voles. We found elevated levels of V1a receptor positive immunoreactivity in the LSD, BST, ME, VMH, AR and LA in mandarin voles encountering their mates as compared to voles exposed to strangers. While densities of oxytocin receptor expression neurons were higher in LSD, BST, ME, VMH, LD and MD in mandarin voles exposed mate. LSD played an important role of social recognition, while BST, ME, VMH and AR could modulate sexual and mating behavior. But MD and LD were important brain regions of rewards and punishment system. These results suggest that AVP V1a and oxytocin receptor may be important in the formation of association recognition, pair bond formations, and MD and LD might be involved in the modulation of social behaviors in monogamous mammals.7. We examined FOS expression in mandarin voles' brain, while the mandarin voles were exposed to their partner or another strange voles. We found elevated levels of fos immunoreactivity in the LSD, BST, VMH, AR, MD, LD, ME and LA of voles encountering mate as compared to voles were exposured to strange individuals. We hypothesized that the increase of the fos protein positive neurons after a period of time for vole to encounter its mate may indicate specific brain areas that are especially important in recognition mate, pare bond formation and affinity behavior. We suggest that brain regions of mandarin voles that showed significant increase of fos expression neurons after encountering mate may be important in the formation...