HTR3A and irritable bowel syndrome: These two 5-HTRs are gradually accepted as attractive therapeutic targets for diarrhea,19,40 and several antagonists are currently developed as efficient drugs for IBS diarrhea, such as 5-HT3R antagonist alosetron.23,41 Besides, the clinical efficacy of other 5-HT3R pharmaceutical agents, such as ondansetron and ramosetron, are also substantiated.41,42 Likewise, as a selective antagonist for 5-HT4R, GR113808 could inhibit intestinal motility,43 which indicate its potential in treating diarrhea.