The Biological Basis Research Of Sweet Perception In Oral Cavity And Intestine Of Mice After Preference Sweetness Exposure

In recent years, obesity, diabetes and some other metabolic diseases which affect human health have become a global problem and now are becoming more and more serious. The excessive energy intake and metabolic imbalance are the main reasons which lead to such metabolic disease. Sweet food generally riches in nutrient and is the body’s major source of energy, excessive intake of sweet substance is closely related with the health of the body. Oral cavity is the most important human taste perception organ, and the taste perception system in the oral cavity plays a very important role in taste preference of the body which determines whether the body would ingest a kind of food and the amount of food to ingest, so the taste perception system in the oral cavity is essential to the body’s energy intake. Some studies demonstrated that, in addition to the oral cavity, taste perception is also found in the intestinal tract, which plays an extremely important role in the glucose metabolism in the gut. Therefore, in this thesis, ICR male adult mice of postnatal32days were used as experiment models and exposed to sucrose and4kinds of non-energy sweeteners (aspartame, cyclamate, sucralose and AK) in the form of separation and combination for32days. During exposure procedure, the behavioral indices of mice such as body weight, food intake and solution consumption were measured. After the stimulation was completed, the influence of chronic sweet exposure on oral taste biology of the mice was studied by using the methods of whole-mount preparation of tongue epithelium, nuclear staining, Q-PCR and laser confocal scanning microscope technology. In addition, the impact of chronic sweet exposure on the intestinal taste system and the intestinal glucose homeostasis of mice were researched by using the methods of glucose determination, ELISA, stereomicroscope and Q-PCR. Results achieved from the study were as follows:(1) The influence of chronic sweet exposure on such physiological characteristics as body weight, solution consumption and food intake of miceAfter long-term sweet exposure, except the bodyweight gain of aspartame group mice was significantly lower than the control mice, the body weight change of the other sweet exposure group mice did not differ obviously from the control group. During the whole exposure period, because of the post-ingestive effect, the mice showed obvious sugar addition phenomenon to sucrose which was both sweet and rich in energy, i.e. the solution consumptions of mice exposed to sweet solutions containing sucrose were remarkably higher than the control mice. In addition, the intake of sweet substances may affect the appetite and food intake of mice by stimulating them to produce cephalic phase response. Sweet substances could stimulate the oral cavity to make the body produce cephalic phase response to increase the body’s energy needs. Because sucrose itself has energy, while aspartame and cyclamate can not cause sweet feeling to mice, so only when the mice were stimulated alone by sucralose and AK which was sweet to mice but was free of energy, the mean food intake of the mice was significantly higher than the control mice.(2) The influence of chronic sweet exposure to oral taste biologyChronic sweet exposure increased the number of fungiform taste buds but not very strikingly, what’s more, it increased the cross-section area of fungifrom taste buds, the number of taste cells in fungiform taste bud and the expression of T1R2and T1R3in tongue epithelium at mRNA level. The above results showed that postnatal feeding experience could really remold the taste system, but because that the experimental subjects were adult mice whose taste system had fully developed, so this effect was not very obvious. Studies have found that the fungiform taste buds in tongue epithelium were innervated by chorda tympani and that chorda tympani nerve transaction could lead to the degradation of fungiform taste buds, so we speculated that sweet exposure may have effect on chorda tympani nerve, which could lead to the changes of the size of fungiform taste buds and the number of taste cells in the taste buds. Sweet taste receptors express on the membrane of taste cells, so the increase in the number of taste cells would inevitably lead to the increase of the expression of sweet taste receptor. The series of changes may eventually affect the sensitivity of mice to sweet substances, which may affect the preferred solution concentration and the preferred ratio of the mice to sweet substances.(3) The influence of chronic sweet exposure to intestinal sweet perception system and intestinal glucose homeostasisAfter chronic sweet exposure, the glucose tolerance of mice enhanced. In the whole detection procedure, before and after intraperitoneal injection of glucose, the blood glucose concentration of sweet exposed mice was always lower than the control mice, especially at the peak value, the blood glucose concentration of the sweet exposed mice was more lower than the control mice. Chronic sweet exposure increased the ratio of villus and crypt of mice and the expression of intestinal sweet receptor and glucose transporter. As sweet receptors and glucose transporters mainly expressed in endocrine cells and brush cells which are located at the top and middle part of intestinal villi, the increase of the ratio of intestinal villus and crypt formed the basis of the increase of the expression of sweet receptors and glucose transporters. Because the incretin GLP-1and GIP could promote the secretion of insulin, which is the only hormone that could directly lower blood glucose, in the thesis the effect of sweet exposure on the secretion of insulin, GLP-1and GIP were also measured. However, because that too much operation processes were involved in the plasma collection and that the detected hormones were instability and easily degradable, which led to large errors of the results, it was necessary to repeat the experiments or explore new methods to re-measure the impact of sweet exposure on the release of insulin, GLP-1and GIP.In summary, the mice exerted sugar addition phenomenon during the long-term sweet exposure period, that is to say, the mice showed special preference for sucrose solution or sucrose-containing solutions compared with the other solutions. Chronic sweet exposure changed the biological basis of mice oral cavity taste system, this structural changes may affect the preference of mice to sweet substances and the food intake of mice. In addition, long-term sweet exposure changed the intestinal peripheral sweet taste system of mice and the intestinal glucose metabolic balance system, in other words, sweet exposure could affect intestinal glucose absorption metabolism and the sweet taste pathway in intestine. The conclusions obtained above provided theoretical basis for the research of oral and intestinal taste system, provided theoretical basis for the development of composite sweetners and opened up new ideas for prevention and treatment for obesity, diabetes and other disease.