Effect Of Acute Heat Stress On The Expression Patterns Of NPY/NPY5R/CCK In Muscovy And Laying Ducks

In most areas of China, especially in the south, high temperature almost lasts the whole summer, which leads a serious heat stress to laying ducks. Heat stress induces laying rates and other production performances, further causes great economic loss, affecting the duck production in China.Laying ducks(LD) endured more cold than heat, whose most suitable production temperature was15～25℃. In summer, when the temperature was above32℃, the breath frequency and metabolic heat production might increase, and the laying ducks were under heat stress. Heat stress also affected the digestion, metabolism, blood circulation, blood biochemical indicator, endocrine, immunization and so on. In contrast, the Muscovy ducks(MD) originated from tropics of South America endured heat and were less sensitive than laying duck. In this study, we used Shaoxing Duck as laying ducks while Yuyao Muscovy Duck as Muscovy ducks.Heat stress mostly affected food intake in poultry production. Hypothalamus played a critical role on food intake and energy balance. Neuropeptide Y (NPY) was one of the earliest recognized and most potent orexigenic neuropeptides acting in the hypothalamus,which regulated short-termed food intake and long-termed energy balance. NPY bound preferentially at the Yl, Y2, and Y5receptor, respictively, whose activation was an integral component underlying the role of NPY in feeding and body weight regulation. Cholecystokinin (CCK) was another important anorexigenic gut-brain peptide involved in food intake. CCK distributed widely throughout the gastrointestinal tract and the central nervous system, with a number of physiological effects. Central NPY and CCK were involved in stress regulation, particularly NPY. In this study,we compared the change of NPY, NPY5R and CCK mRNA expression after acute heat stress in MD and LD.We put the ducks in four incubation boxes for2hours’adaptation. Then the temperature was rapidly risen to40℃in heat stress groups and maintained room temperature in control groups for3hours. After that, ducks were sacrificed and the tissues were stored in nitrogen canister. Real-time fluorescence quantitative PCR was used to measure the mRNA expression of NPY，NPY5R and CCK.The results showed that acute heat stress induced NPY expression increasing in hypothalamus, adrenal, glandular stomach, lung, intestine and crureus, while decreasing in pituitary, muscular stomach, ovary and heart of MD. On the other hand, heat stress increased NPY expression in pituitary, heart and lung, and decreased NPY expression in hypothalamus, adrenal, muscular stomach and crureus of LD. We also compared the expression of NPY in MD and LD:hypothalamus NPY expression was higher in LD than MD in control groups, while lower in LD than MD in heat stress groups; Adrenal NPY expression was lower in LD than MD both in control groups and heat stress groups; pituitary, muscular stomach, heart, lung and crureus NPY expression was higher in LD than MD both in control groups and heat stress groups. Hypothalamus expression of NPY5R and CCK was higher in heat stress group of MD, while lower in heat stress group of LD. NPY5R and CCK expression was higher in LD control group than MD, while lower in LD heat stress group than MD.Our results demonstrated that acute heat stress induced central expression of NPY, NPY5R and CCK increasing in MD,which was identical to the preceding research on the rodents, might be related to the activation of HPA axis, HPT axis and sympathetic nervous system. On the contrary, the results in LD were decreased, connecting with the variability of the three genes on MD and LD. Additionally, different adaptability of the two species may cause various expression of NPY, NPY5R and CCK.