BACKGROUND/AIMS: Although studies using conventional animal models have shown that specific stressors cause irritable bowel syndrome (IBS), it is unclear whether depression itself causes IBS. Our aim was to establish a rat model to determine if depression itself promotes the onset of IBS and to elucidate the role of gut microbiota in brain-gut axis pathogenesis during coincident depression and IBS. METHODS: Rat models of depression were induced using our shuttle box method of learned helplessness. Visceral hypersensitivity was evaluated by colorectal distension (CRD) to diagnose IBS. Gut microbiota compositions were analyzed using high-throughput sequencing. In the subanalysis of rats without depression-like symptoms, rats with posttraumatic stress disorder (PTSD) were also examined. RESULTS: The threshold value of CRD in depressed rats was significantly lower than that in control rats. Microbial community analysis of cecal microbiota showed that the relative abundance of Clostridiales incertae sedis, the most prevalent microbe, was significantly lower in depressed rats than in control rats. The distribution pattern of the microbiota clearly differed between depressed rats and control rats. Neither visceral hypersensitivity nor the composition of gut microbiota was altered in rats with PTSD-like phenotypes. CONCLUSIONS: Our rat model of depression is useful for clarifying the effect of depression on IBS and suggests that depression itself, rather than specific stressors, promotes the onset of IBS. Further, we provided evidence that various psychiatric diseases, viz., depression and PTSD, are associated with unique gut microbiota profiles, which could differentially affect the onset and progression of coincident IBS.
Animals ; Clostridiales ; Depression ; Dysbiosis ; Gastrointestinal Microbiome ; Helplessness, Learned ; Hypersensitivity ; Irritable Bowel Syndrome ; Methods ; Microbiota ; Models, Animal ; Phenotype ; Rats ; Stress Disorders, Post-Traumatic

A man in his 70s was transported to our hospital for acute exacerbation of chronic kidney disease. After arrival, he began having visual hallucinations, which were attributed to cognitive decline. We subsequently found that he had been taking amantadine 100 mg/day prescribed by another hospital. We thought that the visual hallucinations were caused by overdose of amantadine and discontinued the drug. Since abrupt discontinuation of antiparkinsonian drugs has a risk of neuroleptic malignant syndrome, tapering the dosage is desirable in most cases. However, the half-life of amantadine in patients with severe renal dysfunction is estimated to be 7-10 days, and thus the blood concentration of amantadine can be inferred to decrease slowly. Therefore, we chose to discontinue amantadine without tapering in the expectation of rapid improvement of the visual hallucinations, considering that the risk of neuroleptic malignant syndrome would be lower than that in patients with normal renal function who discontinued amantadine immediately. After the discontinuation of amantadine, no increase in creatine kinase level or muscle rigidity was observed, and the visual hallucinations improved on day 7 after discontinuation.

Background/Aims: Recent studies indicate that probiotics, which have attracted attention as a treatment for irritable bowel syndrome, affect intestinal homeostasis. In this study, we investigated whether Zygosaccharomyces sapae (strain I-6), a probiotic yeast isolated from miso (a traditional Japanese fermented food), could improve irritable bowel syndrome symptoms. Methods: Male Wistar rats were exposed to water avoidance stress (WAS). The number of defecations during WAS and the visceral hypersensitivity before and after WAS were evaluated using colorectal distension. Tight junction changes were assessed by Western blotting. Some rats were fed with strain I-6 or β-glucan from strain I-6. Changes in the intestinal microbiota were analyzed.The effect of fecal microbiota transplantation after WAS was evaluated similarly. Caco-2 cells were stimulated with interleukin-1β and tight junction changes were investigated after coculture with strain I-6. Results: The increased number of stool pellets and visceral hypersensitivity induced by WAS were suppressed by administering strain I-6. The decrease in tight junction protein occludin by WAS was reversed by the administration of strain I-6. β-Glucan from strain I-6 also suppressed those changes induced by WAS. In the rat intestinal microbiota, treatment with strain I-6 altered the β-diversity and induced changes in bacterial occupancy. Upon fecal microbiota transplantation, some symptoms caused by WAS were ameliorated. Conclusions These results suggest that traditional fermented foods such as miso in Japan are valuable sources of probiotic yeast candidates, which may be useful for preventing and treating stress-induced visceral hypersensitivity.