Abstract: Objective： To explore the effect of inherent depression on chronic visceral hypersensitivity. The differences of visceral sensitivity, colitis, and brain activation between Fawn-Hooded (FH/Wjd) and Sprague-Dawley(SD) rats were identified after neonatal colon acetate stimulation. Methods: The specific pathogen free Fawn-Hooded (FH/Wjd) and Sprague-Dawley(SD) rats were used to establish irritable bowel syndrome (IBS) model. The visceral sensitivity was measured by colorectal distension (CRD). The expression of 5-hydroxytryptamine (5-HT), mast cell (MC), indoleamine 2,3-dioxygenase (IDO) in colon and IDO in specific cerebral regions were detected through immunohistochemistry. Results: Abdominal withdrawal reflex (AWR) scores showed that visceral sensitivity of acetate-enema groups was significantly higher than that of saline-enema groups (FH/Wjd:2.44±0.04 vs.1.96±0.07, P<0.05; SD: 1.75±0.13 vs.1.32±0.05, P<0.05). Furthermore, FH/Wjd rats of IBS group scored significantly higher than SD rats of IBS group (2.44± 0.04 vs.1.75 ± 0.13, P<0.05). The MC amounts of both SD and FH/Wjd IBS group rats were significantly more than those of their control groups (FH/Wjd:43.24 ± 1.72 vs. 24.92 ± 1.38, P < 0.01. SD: 23.80 ± 1.28 vs. 14.24 ± 0.92, P < 0.01). Besides, the MC amounts of control and IBS group of FH/Wjd rats were significantly more than that of SD IBS group rats (P<0.01). The IDO and 5-HT positive cells in colonic mucosa of IBS group of both SD and FH/Wjd rats were significantly more than those of their control groups, respectively(P <0.01). The IDO, 5-HT positive cells in colonic mucosa of both control and IBS group of FH/Wjd rats were significantly more than those of both control and IBS group of SD rats (control:IDO,24.64 ± 2.22 vs. 15.52 ± 1.39;5HT,21.32± 1.26 vs. 12.72±1.12. IBS: IDO，44.92±2.31 vs. 20.85±1.72; 5-HT, 31.84±1.57 vs. 19.65±1.09.P <0.01). The expression of IDO in prelimbic cortex (PrL) areas of FH/Wjd IBS rats was significantly higher than that of IBS group of SD rats (49.60 ± 4.31 vs. 35.60 ± 2.42, P <0.01), and the expression of IDO in rostral anterior cingulate cortex (rACC) areas of FH/Wjd IBS rats was significantly more than that of FH/Wjd control rats (45.44±1.16 vs. 34.08±2.76, P <0.01). Conclusion: Inherent depressive FH/Wjd rats were more sensitive to neonatal colon acetate stimulation, presenting as visceral hypersensitivity which maybe associated with increased MC amounts and over-expression of 5HT and IDO in colon, suggesting that depression disorder may aggravate functional disturbance of gastrointestinal tract by regulating the response to inflammatory stimulation.

Key words: Depression, Irritable bowel syndrome, Serotonin, Indoleamine-pyrrole 2,3-dioxygenase