Effect Of Tannic Acid On The Taste Receptors And Appetite-Related Brain-gut Peptides In Brandt's Voles(Lasiopodomys Brandtii)

The co-evolution between plants and herbivorous animals,based on the plants second metabolites(PSMs),is one of the attractive points of biological research.Plants secrete the PSMs to hinder animals' feeding,and animals adapt to the PSMs in food with various mechanisms.Tannic acid(TA)is one of important PSMs with bitter and astingency,few about the influence of TA on animal's taste sensing system and the brain-gut axis,which regulates the appetite and feeding behavior of animal.The subjects of this study were Brandt's voles,which were captured from Inner Mongolia grassland,matched and bred indoor until fully grown up.They were given 500 ?L tannic acid solution on the surface of their tongues with different concentrations(0 mg mL-1,30 mg·mL-1 and 60 mg·mL-1 as control,low dose and high dose group,respectively)for different times(1 d,5 d,10 d and 20 d).The change of body weight and the feeding intake of animals was assayed during the treatment.Meantime,the change of 6 types of serum brain-gut peptides(Five of them inhibit the appetite,they are pancreatic polypeptide,peptide YY,oxyntomodulin,glucagon-like peptide-1 and cholecystokinin,only ghrelin enhances appetite)was detected by Elisa.Then the real-time quantitative PCR(RT-qPCR)was used to assay the mRNA expression of taste receptors T2R38,T2R106 and Gnat3 of the tongue.In addition,the immunohistochemistry(IHC)was used to measure the protein contents of T2R38,T2R106 and GNAT3 in anterior,central,and posterior part of the tongue.So,the influence of TA on the taste receptors and appetite-related brain-gut peptides of Brandt's Voles could be determined,the way that animals' taste system sensing TA could be explored.These results would be helpful to discuss the neural mechanisms of the effect of TA on the feeding behavior of herbivores and would provide new theoretical basis for the co-evolution between animals and plants.The results were as follows:1.Brandt's voles were given different concentration of TA solution for 20 d,their body weight were recorded every other day(total for 11 times).As a result,no significant difference of body weight was found among them,no matter how much they were treated with TA for how long time(P>0.05).So,it was indicated that oral infusion of certain dose of TA solution could not influence the body weight of Brandt's voles.2.TA inhibited the Brandt's voles' food intake after they were oral administrated different concentration of TA solution for 5 d and 10 d(P<0.05).However,after treated with TA for 20 d,the food intake of Brandt's voles in low and high dose group was not significantly different from that of control group(P>0.05).3.After treated with different concentration of TA for 5 d,10 d,15 d and 20 d,compared with the control group,the serum levels of hormones that inhibit the appetite,such as pancreatic polypeptide,peptide YY,oxyntomodulin,glucagon-like peptide-1 and cholecystokinin,were significantly higher in both low and high dose groups(P<0.05).The level of serum ghrelin,which stimulate the appetite,was reduced significantly by TA when animals treated with low or high doses for 1,5 or 10 d(P<0.05),but not changed in groups treated for 20 d(P>0.05).4.The mRNA levels of T2R38,T2R106 and Gnat3 in the tongue of Brandt's voles in low or high dose groups were significantly higher than that in control group when they were given TA for different times(P<0.05),and animals in high-dose group expressed more than animals in low dose group(P<0.05).5.The result of the IHC showed that T2R38 and T2R106 were not expressed in the anterior and central part of the tongue tissue,but expressed in the posterior part of the tongue in Brandt's voles.While GNAT3 was expressed in all three regions of the tongue.Both of low and high doses of TA made Brandt's voles have more T2R38 and T2R106 in the posterior part of the tongue and GNAT3 in all three regions of the tongue(P<0.05).And the amount of three proteins increased with doses of TA(P<0.05).All of these above suggested that consecutive administration of TA only inhibit the feeding of Brandt's voles within a short time,and with the prolongation of treatment,no significant difference of body weight was found in control,low and high dose group.Two kinds of taste receptors and a-gustducin in the tongue of Brandt's vole were involved in this animal's taste sense of TA.TA could increase the secretion of appetite suppressor hormone in the Brandt's vole and reduced the secretion of appetite stimulating hormone.Maybe these changes would influence the feeding behavior of Brandt's voles by modulating their feeding center.