Motilin, a Novel Orexigenic Factor, Involved in Feeding Regulation in Yangtze Sturgeon ().

Motilin is a gastrointestinal hormone that is mainly produced in the duodenum of mammals, and it is responsible for regulating appetite. However, the role and expression of motilin are poorly understood during starvation and the weaning stage, which is of great importance in the seeding cultivation of fish. In this study, the sequences of Yangtze sturgeon ( ()) motilin receptor () were cloned and characterized. The results of tissue expression showed that by contrast with mammals, mRNA was richly expressed in the brain, whereas was highly expressed in the stomach, duodenum, and brain. Weaning from a natural diet of to commercial feed significantly promoted the expression of in the brain during the period from day 1 to day 10, and after re-feeding with the change in expression of was partially reversed. Similarly, it was revealed that fasting increased the expression of in the brain (3 h, 6 h) and duodenum (3 h), and the expression of in the brain (1 h) in a time-dependent manner. Furthermore, it was observed that peripheral injection of motilin-NH increased food intake and the filling index of the digestive tract in the Yangtze sturgeon, which was accompanied by the changes of and appetite factors expression in the brain (, , , and ) and stomach (). These results indicate that motilin acts as an indicator of nutritional status, and also serves as a novel orexigenic factor that stimulates food intake in . This study lays a strong foundation for the application of as a biomarker in the estimation of hunger in juvenile during the weaning phase, and enhances the understanding of the role of motilin as a novel regulator of feeding in fish.