Identification And Localization Of Brain-gut Peptides In The Gastroenteropancreatic Endocrine System And Central Nervous System Of Alligator Sinensis

The Chinese alligator(Alligator sinensis) belongs to alligatoridae family, crocodylia of reptilia, which is an endemic rare species in China with an important ecological and economic value. Brain-gut peptides are distributed both in gastroenteropancreatic endocrine system(GEPS) and central nervous system(CNS)(including 5-HT), which can regulate the food intake, digestion, cell proliferation, vessels activity and immune. The present study was to investigate the distribution of the brain-gut peptides in the GEPS and CNS of Alligator sinensis by using Streptavidin-Biotin-Peroxidase Complex(SABC) immunohistochemical method combining with biological statistically analysis. The aim of the study was to enhance our understanding of digestive function and neuroendocrine function of Alligator sinensis, and provide basic data for its artificial breeding and ecological protection, and enrich the knoeledge of comparative endocrinology and neuroendocrinology.The results indicated that 5-HT-IR cells were distributed throughout the entire digestive tract, which were most predominant in duodenum and jejunum. The density increased significantly in stomach and duodenum during hibernation. GAS-IR cells were limited in small stomach and small intestine. The density decreased significantly in small stomach during hibernation, while increased in duodenum. SS-IR cells were limited in stomach and small stomach. The density increased in stomach while decreased in small stomach during hibernation, meanwhile, fewer IR cells occurred in small intestine. VIP-IR cells occurred in stomach and small stomach. The density decreased in small stomach, while increased in stomach during hibernation. Five types of endocrine cells were detected in the pancreas of Alligator sinensis, they are SS-IR cells, GLU-IR cells, PP-IR-cells, 5-HT-IR cells and GHR-IR cells, while the INS-IR cells and GAS-IR cells were not detected. As the INS antiserum was come from the mammals, and the molecular structure of Insulin in the Alligator sinensis has a larger difference with that of mammals. The distribution of SS-IR cells mainly exsisted in the form of cell clusters, while the 5-HT-IR cells and PP-IR cells mainly in a single cell form. The distribution of GLU-IR cells and GHR-IR cells exsisted both in cell clusters and single cell form. Additionally, the distribution of GLU-IR cells was more homogeneous. During hibernation, the distribution and morphology of five types of endocrine cells had no obvious changes. While the distributed density of SS-IR cells in the middle pancreas was decreased significantly, no obvious changes in the other parts. In conclusion, the distributed density of endocrine cells in the GEP system of Alligator sinensis have similarities with other animals, and also have its certain specificity, and their changes during the hibernating period were adaptive response to hibernation.It was the first time to investigate the distribution of SS and 5-HT in the CNS of adult Alligator sinensis. The results showed that SS was widely distributed in the CNS except the olfactory bulb. The positive reaction was most intense in the hippocampus cortex, accessory olfactory bulb nuclear, hippocampus, lenticular nucleus, caudate nucleus, supraoptic nucleus, paraventricular nucleus hypothalamus, funnel, median eminence and the pituitary gland. The IR-fibers were abundant in numerous areas and nucleus. The fibers displayed pot-shaped and varicosity. The IR perikarya were mainly distributed in the specific nucleus, while its morphology had some difference. 5-HT was also widely distributed in the CNS, while the stronger positive reaction was distributed in the hippocampus, paraventricular nucleus of hypothalamus, paraventricular organ, rhombencephalon, spinal cord and blood vessel of brain. The distribution of SS and 5-HT in the CNS of Alligator sinensis suggested they were two neurotransmitters, and the present study can also lay a foundation for the further studies on their changes in different physiological status and the regulatory roles of food intake and other physiological activities.