The Construction Of Caffeine Adaptation Model In Mice And The Primary Study On Mechanism In Peripheral Gustatory System

The expression of certain genes can be modified by early taste experience, whichcontributes to the individual difference in gustatory sensation. That is to say, tastepreference is largely plastic. The main study on the plasticity of taste preference wasfocused on the sweet taste for the moment, while the article about the bitter tastepreference was rarely reported. Some bitter tasting food or beverages, such as coffee,tea and bitter gourd, are attracted by more and more people, but we don’t know muchabout the mechanism underlie the attraction. In our study, we try to use a conventionalbitter tastant-caffeine to establish a bitter adaptation model based on ICR mice andprimarily explore the mechanism in the peripheral gustatory system based on this model.Specifically, we analyses the behavioral response to caffeine solution of ICR mice indifferent gender intersecting with different age by two bottle preference test, therebyconstruct a caffeine bitter adaptation model and then apply immunofluorescenthistochemical method and western blotting to study the physiological change inperipheral gustatory system including the morphology of fungiform taste bud and theexpression of α-gustducin and TRPM5. The results are conducive to understand therelationship between caffeine adaptation behavior and the plasticity of peripheral tastesystem, and will help us extensively to investigate the mechanism of bitter tastepreference depending on this model.Our study suggested that the gender, age and the concentration of caffeine duringexposure period can affect the behavioral responses of adult ICR mice to caffeine withtwo bottle preference test. After exposing the male mice at3rd week to200、500and750mg/l caffeine solution for3weeks respectively, the preference pattern of the mice tocaffeine solution with a ascending concentration was changed to“indifference-preference-indifference-avoidance”, compared to the“indifference-avoidance” pattern of the mice with no caffeine experience before TBP test. Meanwhile, comparing with the control group, the avoidant thresholds wereimproved. However, the weights of the mice exposed to500、750mg/l caffeine weresignificantly declined, we suspected that these relatively high concentrations impactedthe health of mice, therefore, we exclude these concentrations during constructing themodel. Then, when the male mice at P32or P49were exposed to200mg/l caffeine for3weeks, the result indicated that this experience had no effect on the preference pattern ofthe mice. Similarly, we applied the200mg/l caffeine exposure to the female mice atP21, and found that the change in preference pattern was the same as that in male miceexcept that the preferred concentration was0.2mmol/l and the avoidant threshold wasput off from7.5mmol/l in control group to10mmol/l. These results suggest that thefemale mice are more sensitive for the low concentration of caffeine and have highertolerance to concentrated caffeine solution. This study provides a behavioral basal forthe further exploration on the mechanism of bitter preference depending on the mice.The full-mount technology and immunofluorescent histochemical method wereused to study the fungiform taste buds on the tongue of the male mice which areexposed to200mg/l caffeine for3weeks from postnatal21days. The results verify thatthe cross sectional areas of the fungiform taste bud of the mice in experimental groupswere significantly reduced, but the number of the taste cells in a single taste bud wasinvariant compared with that of the mice in control groups. We assumed that the volumeof a single taste cell became smaller. Meanwhile the number of the α-gustducin positivecells in taste buds of the mice with caffeine experience was significantly smaller thanthat of the control.We investigated the expression of key proteins of the taste signal transduction bywestern blotting. The expression of α-gustducin in the lingual epithelium of both maleand female mice that were exposed to200mg/l caffeine, was dramatically lower thanthat of mice with no caffeine experience. However, there was no change in theexpression of TRPM5. These results demonstrate that the early caffeine experience ofthe mice partly modifies the taste signal conduction in the peripheral taste system, andthis may be the foundation of the caffeine bitter adaption from taste cells level in mice.Our study successfully established a model of caffeine bitter adaption based on theICR mice, and explored the mechanism in peripheral taste system. However, tastesensation is a complex process. We don’t know much about how the brain response to the lasting and diversity taste experience and integrate this message to form or changethe taste preference, further investigation are awaited to unfold mystery.