Comparison of five diarrhea-predominant irritable bowel syndrome (IBS-D) rat models in the brain-gut-microbiota axis

The brain-gut-microbiota (BGM) axis is known to be essential for diarrhea-predominant irritable bowel syndrome (IBS-D). In order to evaluate the effects of IBS-D rat models (the central sensitization model, the peripheral sensitization model and the compound model) on the BGM axis, five models were induced in Wistar rats with 4% acetic acid (AD, dissolved 0.4 ml of AD in 9.6 ml of ultrapure water) + wrap restrain stress (WRS), 4% AD, colorectal distention (CRD), WRS, and neonatal maternal separation (NMS). Abdominal withdrawal reflex (AWR) scale scores and the moisture content of feces (MCF) were evaluated on the day of completing modeling. Body weight was measured every 7 days during modeling. Brain gut peptides, cytokine levels, the activity of spinal cord neurons, intestinal mucosal barrier function, and gut microbiota were determined after induction of IBS-D. We found intervention with 4% AD + WRS, 4% AD, CRD, WRS, and NMS induced a similar course of effects on the BGM axis. Among the five models, AWR scores (60 mmHg, 80 mmHg) were all increased. The levels of 5-hydroxytryptamine, corticotropin-releasing factor, substance P, and calcitonin gene-related protein in serum rapidly increased, whereas that of neuropeptide Y decreased. C-fos in the spinal cord showed increased neuronal activity. The intestinal permeability was increased and the composition and structure of gut microbiota were changed. In conclusion, the five models could cause changes in BGM axis, but the 4% AD + WRS model was closer to the changes BGM axis of post-inflammatory models of IBS-D.