Thus, to explore the involvement of TLR4 signalling in the anti-colitic effects of melatonin in vivo, colitis was induced in 8-week-old wild type (WT) and TLR4 KO mice by administration of 2.5% dextran sulfate sodium (DSS) in drinking water and intraperitoneal (i.p.)treatment with melatonin (Mel) or vehicle (Veh). Here, TLR4 is linked to colitis.