I. INTRODUCTION 1 II. METHODS AND MATERIALS 4 III. RESULTS 12 3.1. Antidepressant-like effect of Lactobacillus reuteri ATG-F4 in CUS-induced depressive-like behaviors 12 3.2. Modulation of caecal microbiota by F4 13 3.3. Effect of F4 on 5-HT and 5-HIAA expression levels in serum and the brain 14 3.4. Effect of F4 on 5-HT receptor mRNA expression in the mPFC 14 IV. DISCUSSION 16 V. REFERENCES 38 요 약 문 45