Neural Mechanisms Of Aggressive Behavior In Brandt’s Voles (Lasiopodomys Brandtii) Affected By Density

The dynamic regulation of animal population is one of the important problems in ecology. The population density affects the aggressive behavior of individuals among the populations, aggressive behavior, in turn, has important influence on the regulation of the population of small mammals. And it is regulated by many hormones and neurotransmitters. Brandt’s voles are main rodent in Inner Mongolia, their population dynamics is involved in the ecological balance of grassland. In order to investigate the endocrine and neural mechanism of density on the aggressive behavior of Brandt’s voles and to provide basic theory for revealling the mechanism of internal regulation of population and for intergrated management of grassland rodents,35d old Brandt’s voles, feeding in 48 × 35 × 20cm cage indoors, were divided into 3 animals/cage,5 animals/cage and 8 animals/cage, respectively. Their behavior was recorded each 7 days and the duration of their attack behavior in different periods was campared among groups of different density.70 days later, the changes of serum corticosterone and sex hormone were measured by ELISA. The expression of the receptors of 5-HT (5-HT1A and 5-HT1B) and the key enzyme of synthesis of 5-HT (tryptophan hydroxylase 2, TPH2) in related brain regions were determined by RT-PCR. The results were as follows.At first, high density influenced the development of Brandt’s voles.70 days after exposure to different density, the body weight of the female or male Brandt’s voles in the 8 animals/cage groups were significantly lower than that of the 3 animals/cage groups, which indicated that density inhibited the growth of voles. There was no significant difference between the uterus and ovary index in female Brandt’s voles, but the testis and epididymis index of 5 animals/cage and 8 animals/cage groups were significantly lower than those of 3 animals/cage groups, which showed that the density also inhibited the development of sexual glands of male Brandt’s voles. The spleen index of 8 animals/cage groups of female Brandt’s voles was significantly higher than that of 3 animals/cage groups, which showed that the density had certain effect on the immune status of female Brandt’s voles, but no effect on the spleen index of male Brandt’s voles;Then, in all the observation time, the duration of aggressive behavior of 8 animals/cage groups were significantly longer than that of the groups of 3 animals/cage, which showed that the intensity of aggressive behavior of Brandt’s voles increased significantly with the increase of the density; Besides, with the increase of feeding time, that is, with the growth of the animals, the duration of aggressive behavior of each density group had a significant increase trend, which meant that the aggressive behavior of Brandt’s voles enhanced with their development.There was no significant difference in the serum corticosterone levels among females in different density groups, but the serum corticosterone level of 8 animals/cage groups of male Brandt’s voles was significantly higher than those groups of 3 animals/cage, which showed that the density had a certain stress function on the male individuals; The serum estradiol levels of 5 animals/cage groups of female Brandt’s voles were significantly higher than those of 3 animals/cage groups, and the serum testosterone levels of 8 animals/cage groups of male Brandt’s voles were significantly higher than those of 3 animals/cage groups, which indicated that the sex hormone level increased with the increase of density.Finally, the results showed that the increase of density significantly affected the synthesis of 5-HT and the number of their receptors in the central nervous system of Brandt’s voles. The most significant and consistent changes appeared in the 5 animals/cage groups. Compared to voles in 3 animals/cage groups, the expression of TPH2,5-HT1A and 5-HT1B in 5 animals/cage groups decreased in dorsal raphe nucleus, amygdala and prefrontal cortex. But there was sexual differentiation in groups of 8 animals/cage groups, because the expression of TPH2 and 5-HT1B of males in 8 animals/cage groups increased in the amygdala and prefrontal cortex, but the expression of 5-HT1A and 5-HT1B in amygdala and prefrontal cortex were down regulated in female 8 animals/cage groups.In summary, it was suggested that the population density regulate the aggressive behavior of Brandt’s voles by influence the functional of central 5-HT system. But there was no completely corresponding relationship between the strength of aggressive behavior of Brandt’s voles and the increase and/or decrease of their 5-HT1A and 5-HT1B receptors. The regulation of 5-HT system on the aggressive behavior of Brandt’s voles was accompanied by other neurotransmitters and endocrine system.