The Role Of Leptin In Energy Metabolism And Seasonal Reproduction In Black - Line Hamster

In recent years, the interrelation between seasonal breeding and energy metabolism level in small mammals has been a hot topic among the field of biology. In the natural environment, how wild mammals regulate the rhythm of seasonal breeding? And how the energy metabolism acts on the rhythm of seasonal breeding? These problems are still unsolved.Leptin, as the set point signal of energy metabolism balance, can linked the fat content in various body organs and tissues. Through the leptin receptors in hypothalamus, leptin coordinated the energy consumption and metabolism of various organs. Gonadotropin-releasing hormone(GnRH) is an important factor affect the seasonal breeding. Secrete and release in the hypothalamus. GnRH regulates reproduction through the hypothalamus-adenohypophysis-gonadal axis. There still exist some questions. Does leptin effect to the expression of GnRH in hypothalamus? Whether the expression patterns of leptin and GnRH were related? Does leptin involved in the regulation of seasonal breeding rhythm of small mammals?To explore these questions, We choose wild striped hamsters(Cricetulus barabensis) population in Shandong Province as the animals for research, studied the striped hamsters’ physiological diversity, tested the protein expression of leptin, leptin receptor, GnRH, GnRH receptor and the mRNA expression of seasonal patterns, explored the body mass index which would more scientific evaluate small mammals energy metabolism and reproduction conditions. Some methods were used in these studies, such as morphological measurements, measuring resting metabolic rate(RMR), histology, immunohistochemistry and real-time fluorescent quantitative PCR method. Experiment content involves the striped hamsters’ physiological diversity of gender, age and season, the optimization of body mass index, the immunohistochemical localization and relative quantitative of leptin and its receptor protein, GnRH and its receptor protein in the brain and the hypothalamus, the seasonal dynamics of leptin mRNA relative expression in peripheral adipose tissue, etc.The results show that: ①GnRH-positive cells in the hypothalamus of striped hamsters(both male and female) showed a significant seasonal variation. The high breeding season(spring and autumn) was usually significantly higher than the low breeding season(summer and winter). However the GnRH receptor-positive cells are opposite. These results suggest that the hypothalamic GnRH main regulate breeding function, while GnRH receptors in the hypothalamus may be mainly involved in the negative feedback regulation of GnRH. ②Leptin-positive cells in the hypothalamus of striped hamsters(both male and female) showed a significant seasonal variation. Variations of male and female are not the same. For males, leptin-positive cells were minimum in spring & autumn, and maximum in winter. For females, while minimum in autumn and maximum in winter. Leptin-receptor-positive cells were also significantly different between seasons. Male and female have similar change pattern, that showed leptin-receptor-positive cells were significantly less in high breeding season(spring & fall) and more in low breeding season(summer & winter). Leptin gene(OB) mRNA in peripheral adipose tissue were significantly differences between seasons, male and female are similar expression patterns, namely relatively expression was low in high breeding season(spring & fall) an high in low breeding season(summer & winter). The results suggest that leptin may serve as a permissive factor in the central nervous system to start reproduction other than an initiation factor, and to inhibit the reproduction rhythm in some extent. The high leptin receptor expression in the low breeding season can mediate leptin action, further inhibiting the body’s energy expenditure, while increasing energy storage. ③RMR of striped hamsters shows significant differences in gender, age and seasonal, in which the male was significantly lower than the female, and show a decreased trend with the increase of the age and air temperature. In terms of body mass index, fatness K value and carcass weights are not significant differences between genders. Ratio of weight and length(KWL values) existed significant differences between the genders, and characterized by increases with the increase of age. KWL values are also characterized by significant difference between the seasons. These results suggest that, as a body mass index, ratio of heavy and length is more convenient and scientific when evaluating small mammals’ physical condition.As the dominant rodents in farmland of Northern of China, striped hamsters have a high fertility and population density. This is a main reason for their serious harm. Therefore, comprehensive prevention and control of the hamsters will have a long way to go. The results will help to understand leptin’s impact on energy metabolism and reproduction at the molecular level, explain the relationship between seasonal breeding and the energy metabolism, meanwhile help to more accurately evaluate the small physical condition of mammals, and provide reference for revealing the molecular mechanism of striped hamsters’ outbreaks and seasonal fluctuations.