China Rana (rana Chensinensis) Postembryonic Development Of The Digestive Tract And The 5-ht And Gas Cells,

During the anurans metamorphosis development, there are changes of both morphological structure and physiological function in the respiration system, motion system, alimentary system and circulation system. The development and perfection of alimentary system is a structure foundation of nutrition intake and growth. The digestive tract of animal was not only the important digestive organ but also the biggest endocrine organ which, with a great number of endocrine cells, played an important role in eating, digestion and other physiological activities, and might have regulation effect on the development and differentiation of digestive system of animals.In this study, the tadpoles of Rana chensiensis were used as experimental animals, making anatomical and histological observation on digestive tract of different stage during the postembryonic development. The morphology and distribution of 5-HT and GAS endocrine cells in the digestive tract of tadpoles were studied by immunohistochemical method. Some conclusions were drawn as follows:1 .Morphological characteristics in digestive tract of R.chensinensis during the postembryonic development: At stage 23, the digestive tract was only a thick and shot tubular structure.The length of digestive tract increased gradually from 37.0 mm at stage 28 to 95.3 mm at stage 39, and dropped suddenly to 22.0 mm in the metamorphosis process. The stomach swelled at stage 42 and the location and shape were similar to adult frog at stage 46.2.Histological characteristics in digestive tract of R. chensinensis during the postembryonic development: The epithelial layer developed completely, the submucosa and muscular layer of digestive canal appeared gradually and become thick subsequently. The gastrointestinal glands and goblet cells appeared in stages 42～43 .The wall of stomach and duodenum differentiated earlier than small intestine and rectum. The four layers(mucosa, submucosa, muscular propria (layer) and serosa)were identified clearly in duodenum at stage 38. They could not be identified in small intestine and rectum until stage 41, and the muscular propria (layer) was not well-developed.3.Ontogeny of 5-HT endocrine cells in digestive tract of Rana chensinensis during the postembryonic development: 5-HT-IR cells were extensively distributed, they could be found in stomach, duodenum, small intestine and rectum. Before the metamorphosis(stage28～41), there was no significant change. 5-HT-IR cells were first detected in duodenum at stage36. During the metomorphosis(stage42～45), the quantities of 5-HT-IR were increased in each part of the digestive tract The metamorphosis of R.chensinensis tadpole was a period contained two aspects : the living enviroment transition (from aquatic environment to terrestrial environment) and great changes in the body. During this period, the water of diet decreased in the terrestrial environment, which needed 5-HT to stimulate gastrointestinal tract mucus secretion for lubrication and protection. At stage46, the quantities of 5-HT-IR cells had a dramatic increase in the duodenum and rectum(P<0.01). It could be concluded that was an adaptation to amphibian lifestyle.By the study of 5-HT cells in the gastrointestinal tract of R. chensinensis tadpole, the results showed that the quantities of 5-HT-IR cells had a significant change in metamorphosis. It might be related to enhancement of 5-HT regulate ability and living environment change.4. Ontogeny of GAS endocrine cells in digestive tract of R.chensinensis during the postembryonic development: GAS-IR cells were primarily distributed in the stomach and duodenum. Before the metamorphosis(stage28～41),GAS immunoreactivity was not detected, except in the duodenum at stage33, where GAS-IR cells were first detected. During the metamorphosis(stage42~ 45), the quantities of GAS-IR cells were increased in stomach and much less in duodenum. It maybe related to continuous maturation of gastric mucosa. At stage46, the GAS-IR cells had a zonal distribution in the gastric mucosa, which was attributable to protein content increase in the diet. During the whole postembryonic development, GAS-IR cells were not detected in small intestine and rectum.The quantities of GAS-IR cells in the gastrointestinal tract of R. chensinensis tadpole had a significant change in metamorphosis. It is suggested that may related to feeding habits change from herbivorous to omnivorous, and the functional change of gastrointestinal digestion and absorption.