Abstract: Objective To study the developmental changes in distributional density, histological localization and morphology of five types of endocrine cells in the digestive tract of EM>Bufo gargarizans/EM> during metamorphosis with gut hormone antisera of 5-hydroxytryptamine (5-HT), gastrin (GAS), somatostatin (SS), glucagon (GLU) and pancreatic polypeptide (PP). Methods Six samples were used at every developmental stage. The endocrine cells of digestive tract were studied by immunohistochemical techniques of streptavidin peroxidase (SP) method. Results 5-HT cells were detected in the digestive tract at every stage of EM>Bufo gargarizans/EM> during metamorphosis, and they first occurred in the middle portion of the digestive tract at hatching stage. They were distributed in the whole digestive tract after prometamorphosis stage, and the density of these cells in the middle portion of the digestive tract increased significantly (EM>P/EM><0.05). The density of 5-HT cells significantly increased in the esophagus and cardia from metamorphosis climax stage to juvenile stage ( EM>P /EM><0.05); GAS cells first occurred at juvenile stage, and they were mainly distributed in the duodenum and occasionally detected in the pylorus; SS cells first appeared at metamorphosis climax stage and they were occasionally distributed in the fundus and duodenum. SS cells were distributed in every portion from the esophagus to the jejunum at juvenile stage, and the density of these cells significantly increased (P<0.05); GLU cells were detected in the digestive tract at every stage of Bufo gargarizans during metamorphosis and the distributional density of GLU cells in the middle portion of the digestive tract significantly increased (P<0.05) after prometamorphosis stage; PP cells were not detected at every stage of Bufo gargarizans during metamorphosis. At hatching stage，the endocrine cells were located in the lamina propria with round in shape; At premetamorphosis stage and prometamorphosis stage, they were located in the epithelium of the whole digestive tract with round, oval or shuttle in shape; At metamorphosis climax stage, they were located in the gastric gland or the basal portion of epithelium of mucosa of the digestive tract with oval or taper in shape and occasionally detected in the lamina propria; At juvenile stage, they were located in the gastric gland and the epithelium of mucosa of the digestive tract with round or oval in shape, and some cell had a long cytoplasmic process reaching into the digestive lumen. Conclusion Comparing with other amphibians, there are both common and specific features in the developmental changes of endocrine cells in the digestive tract of Bufo gargarizans during metamorphosis, and the developmental changes of endocrine cells are adaptive to the changes of the digestive physiological activities and the individual physiological functions.

Key words: Metamorphosis, Digestive tract, Endocrine cell, Immunohistochemistry, EM>Bufo gargarizan/EM>