Tph1 and Tph2 gene expression in colonic mucosa was higher in the IBS group than in the Control group (P < 0.01 and P < 0.05, respectively, Figure 3C), whereas TXYF treatment down-regulated Tph1 and Tph2 gene expression compared with the IBS group (P < 0.05 for both genes, Figure 3C). Here, TPH1 is linked to irritable bowel syndrome.