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AIM: To investigate the mechanisms of tegaserod, a partial 5-HT4 agonist, in reducing visceral sensitivity by observing Fos, substance P (SP) and calcitonin gene-related peptide (CGRP) expression in the lumbarsacral spinal cord inducedby colonic inflammation in rats.METHODS: Twenty-four male rats with colonic inflammation induced by intraluminal instillation of trinitrobenzenesulfonic acid (TNBS) were divided into 3 groups. Treatment group Treatment group 2: intra-gastric administration of tegaserod,saline, 2.0 mL/d. After 7 d of intra-gastric administration,lumbarsacral spinal cord was removed and processed for Fos, SP and CGRP immunohistochemistry.RESULTS: In rats of the control group, the majority of Fos labeled neurons was localized in deeper laminae of the lumbarsacral spinal cord (L5-S1). SP and CGRP were primarily expressed in the superficial laminae of the spinal cord after TNBS injection. Intra-gastric administration of tegaserod neurons (22.0±7.7) and SP density (12.5±1.4) in the dorsal h in the lumbarsacral spinal cord compared to those of the control group (62.2±18.9, 35.9±8.9, P＜0.05). However,CGRP content in dorsal h did not significantly reduce in rats of treatment group 1 (1.2±1.1) compared to that of the control group (2.8±2.4, P＞0.05). Neither Fos expression nor SP or CGRP density in the dorsal h significantly declined in rats of treatment group 2 compared to those of the control group (P＞0.05).CONCLUSION: Tegaserod can significantly reduce Fos labeled neurons in the lumbarsacral spinal cord induced by colonic inflammation. Tegaserod may reduce visceral sensitivity by inhibiting SP expression in the dorsal h of spinal cord.