肉鸡腹泻型肠易激综合征模型的肠道形态和功能改变与5-羟色胺的相关性研究

Irritable bowel syndrome (IBS) is a functional gastrointestinal disorder with a high incidence in mammals. The pathophysiology, etiology and pathogenesis of IBS are poorly understood and stress is reported to be a risk factor involved in this process. Stress related intestinal dysfunction is commonly observed in poultry industry and is associated with intestinal bacteria colonization, intestinal barrier breakdown, pathogen invasion, and led to huge economic loss if not be rectified or appropriatelytreated.The characteristics of IBS have been observed in chicken and the growth performance, animal welfare, the onset of infectious diseases, and meat quality are influenced. However, as far as we know, there is very few data on the IBS in chicken.It is of importance to explore the effect of IBS on poultry industry and underlying mechanisms. Diverse factors, including psychological stress, intestinal infection, intestinal immune disruption and/or inflammation, changes in the intestinal microbiota or bacterial have been found to contribute to the development of IBS. However, recent studies highlight that disturbance of the bidirectional brain-gut axis in which the enteric, autonomic and/or central nervous systems are implicated and associated with IBS pathophysiology. Stress response is an adaptation to endogenous or exogenous stimuli and leads to over-activity or under-activity alongthe hypothalamic-pituitary-adrenal (HPA) axis and the autonomic nervous (ANS), it can alter brain-gut interactions, ultimately affecting different physiological functions of the gastrointestinal tract. The tryptophan derivative 5-hydroxytryptophan (5-HT), a neurotransmitterreleased in response to stresses, from mast cells, EC cells, plays an important role in regulating gut function. In this scenario, we hypothesized that 5-HT implicates in and contributes to the development of IBS in response to stress. In this study, broilers will be subjected to chronic stress, acute stress or the acute and chronic stress, to establish an animal model. The characteristic of IBS for example the food intakes, the diarrhea score, the intestinal morphology, and biochemical analysis will be examined to validate the success of the model. To investigate the functional role of 5-HT, the antagonistic or agonist of 5-HT, or SERT antagonistic will be applied and intestinal permeability, the expression of tight junction protein, 5-HT receptor, and stress related hormone will be determined. The result of this study will elucidate the potential role of 5-HT in the development of IBS in chicken and provide nutritional strategy to attenuate the economic loss caused by stress related IBS in poultry industry.

在人和哺乳动物的研究中，将应激引起的胃肠功能异常称为肠易激综合征(Irritable bowel syndrome, IBS)，是临床最常见的胃肠功能失调性症候群。家禽生产中往往忽略应激因素引起的胃肠功能改变,多将其归因于传染性因素。由应激引起的家禽肠道形态和功能改变，如果没能及时恢复会使肠道菌群组成及区系发生改变，继发感染的球虫与有害病菌和病毒相互协同，加强了致病性，影响家禽养殖的经济效益。但据国内外文献，关于家禽IBS方面的研究依然是空白，然而IBS在家禽实际生产中的确存在，并且对动物福利、家离生产性能、肉品质以及传染性疾病的发生都产生一定的影响。根据5-HT在哺乳动物IBS发生过程中的参与机制，本项目通过建立肉鸡腹泻型IBS模型，研究5-HT在IBS发病过程中引起肠道形态学和生理功能改变中的作用，找到其参与IBS的信号通路，确定其关键作用靶点，以及相关营养调控措施的预防效果。

家禽饲养过程中，往往是多种应激源并存共同影响家禽生产，而单一应激源处理的研究很难反映家禽生产中的真实状况，对家禽生产的指导意义不大。色氨酸作为抗应激的氨基酸，其机制目前尚不清楚。因此，本研究中将家禽饲养过程中所能遇到的应激源叠加模拟哺乳动物CUMS模型来检测慢性应激对家禽肠道屏障功能的影响以及在日粮中添加L-色氨酸来研究其与其中间产物5-羟色胺缓解应激的机制。.实验在基础日粮中分别添加L-色氨酸使色氨酸水平分别达到0.42%（0~21日龄）及0.36%（22~42日龄），并分为正常饲养和应激条件饲养，试验期为6周。研究结果发现：CUMS处理促进了肠道炎症反应的发生，破坏了肠道紧密连接功能，增加了肠道通透性，而色氨酸降低了炎症细胞因子mRNA表达，提高了紧密连接蛋白表达，促进肠道屏障功能修复，抑制了应激的发生。进一步研究其机制发现CUMS处理显著提高了5-羟色胺再摄取蛋白SERT的基因表达，SERT促进5-HT再吸收入5-HT池，因而加剧了游离5-HT的减少，添加色氨酸后，降低了该基因的表达，进而减轻了CUMS诱导的5-HT的快速耗竭，增加了5-HT的水平，从而缓解了应激反应，同时发现慢性不可预知温和应激模型下的肉鸡IBS与5-羟色胺再摄取转运蛋白SERT基因多态性无关。.家禽生产中往往忽略应激因素引起的胃肠功能改变，研究多集中在应激后传染性因素引起的腹泻和胃肠功能异常，造成的经济损失可窥一斑。本项目通过研究5-羟色胺在肉鸡腹泻型肠易激综合征模型的肠道形态和功能改变中所起的作用，发现部分可以调控应激激发胃肠功能改变的信号靶点，除从管理和养殖方式上减小应激外，还能通过营养调控的方式预防并减小一些不可避免的应激对禽群的影响，改善家禽生产的福利状况，进而提高生产性能和禽产品品质。研究结果具有较普遍的科学意义，应用到实际生产中可以在一定程度上减小肉鸡应激过度发生造成的经济损失。

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