The Research Of Lactobacillus Rhamnosus GG Supernatant Regulating The Serotonin Transporter Expression In Post-infectious Irritable Bowel Syndrome Rats

Objects:Post-infectious Irritable Bowel Syndrome（PI-IBS）often exhibits characteristics of diarrhea,which has a history of acute gastrointestinal infection.It is characterized by sustained low inflammation,visceral hypersensitivity and intestinal dynamic disorder.The probiotics are approved to be used to relieve IBS,which can effectively alleviate abdominal symptoms such as abdominal pain and diarrhea,relieve anxiety and depression and other psychiatric symptoms,improving the quality of life of patients.Lactobacillus rhamnosus GG（LGG）is the best studied member of lactic acid bacteria play a supportive therapeutic efficacy in IBS.However,the mechanism is still remains a significant challenge to researchers.In this study,Campylobacter-jejuni（C.jejuni）was used to build the model of PI-IBS and then the expression levels of SERT（serotonin transporter）mRNA and SERT-protein to evaluate the affection of Lactobacillus rhamnosus GG supernatant（LGG-s）in the PI-IBS rats.Methods:The rats were then divided into two groups.The frst group of rats were designate as the control group（n=25）,which was given PBS（2 mL/d per rat）,and another group as the model group of PI-IBS（n=85）,which was given C.jejuni(10¹⁰CFU/mL,2 mL/d per rat)through an intra-gastric needle.The gavage continued for 7d.Then,the stool culture,body weight of the rats,and relative content of stool water were tested to evaluate the phase of infection.Aftert the test of abdominal withdrawal reflex（AWR）,intestinal motility and levels of SERT expression,the rats were regrouped;the control group was designated as M（n=20）and given PBS,and the PI-IBS model group was divided into four groups and given PBS,undiluted LGG-s,double diluted LGG-s,and triple diluted LGG-s,respectively（A,B,C and D,respectively,n=20）through a gavage needle.PBS or LGG-s was administered at 2mL/d/per rat,and the treatments were maintained for 1.0,2.0,3.0 or 4.0 wk during the experiment.Five rats of each group were sacrifced;the colons and brains were removed and SERT would be test by RT-PCR and Western blotting to evaluate the affection of LGG-s.Statistical analyses were carried out using SPSS 22.0.Quantitative data are expressed as mean±standard deviation.One-way analysis of variance（ANOVA）and post hoc tests（LSD and Dunnett’s T3）were used to compare the values of quantitative RT-PCR.For all analyses,P<0.05 was defned as statistical signifcance.Results:The rat weight in the model group was significantly lower and the relative content of water in the fresh stool was significantly higher than that of the control group.At the 70th day,tests were done to evaluate the PI-IBS.The intestinal transit was higher in the model group,the rats were visceral hypersensitivity and the level of SERT-protein was significantly lower than control.With the gavage of LGG-s,the levels of SERT-mRNA and SERT-protein were higher than those in PI-IBS gavaged with PBS-group in intestines of rats during the whole study.Undiluted-LGG-s up-regulated SERT-mRNA levels by 2.67-times the control-group by second week and continued increasing.Double-diluted LGG-s was similar to undiluted-LGG-s,maintaining a high-level of SERT-mRNA.Triple-diluted LGG-s up-regulated SERT-mRNA expression levels by 6.9-times the control-group,but decreased rapidly at the end of second week.SERT-P levels were basically flat for undiluted-LGG-s,double-diluted LGG-s and triple-diluted LGG-s,higher than control-group and PI-IBS PBS group.It was basically flat for B,C and D by the second and third week in the intestines of rats.SERT-mRNA and SERT-P levels in the brain of the rats had no statistical significance in the groups during the experiment.Conclusions:C.jejuni could be used in the establishment of PI-IBS model.LGG-s could up-regulate SERT mRNA and SERT-P levels in rat intestinal tissues and has no influence in rat brain tissues.