Background The 5-hydroxytryptamine7 receptor(5-HT7 receptor,5-HT7R) plays an important role in the regulation of smooth muscle relaxation and visceral sensation and might be involved in the pathogenesis of the gastrointestinal dyskinesia,abdominal pain and visceral paresthesia in irritable bowel syndrome(IBS).The aim of this study was to investigate the role of the 5-HT7 receptor in the pathogenesis of lBS.Methods A rat model of irritable bowel syndrome with diarrhea(IBS-D) was established by colonic instillation of acetic acid and restraint stress.A rat model with irritable bowel syndrome with constipation(IBS-C) was established by stomach irrigated with 0-4℃ Cool Water daily for 14 days.The content and distribution of 5-HT in the brain and gut were examined by immunohistochemistry and the mRNA expression of the 5-HT7 receptor was determined by fluorescent quantitative reverse transcription polymerase chain reaction.The accumulation of cyclic adenosine monophosphate (cAMP) in all the same tissues was measured by radioimmunity.Results The models of IBS were reliable by identification.The immunohistochemistry results showed that there were significantly more 5-HT positive cells in the IBS-D group than in the control group in the hippocampus,hypothalamus,jejunum,ileum,proximate colon and distal colon(P