Objective To investigate Fos expression in rat lumbarsacral spinal cord and medulla oblongata induced by chronic colonic inflammation. Methods Thirty-three male Sprague-Dawley rats were randomly divided into two groups: experimental group: colonic inflammation was induced in seventeen rats by intraluminal administration of trinitrobenzenesulfonic acid (TNBS); control group: saline was administered intraluminally in sixteen rats; After 3, 7, 14 and 28 days of administration, lumbarsacral spinal cord and medulla oblongata were removed and processed for Fos immunohistochemistry. Results Fos-immunoreactive (Fos-IR) neurons induced by TNBS administration were primarily distributed in deep laminae (laminae Ⅲ-Ⅳ,Ⅴ-Ⅵ) in the spinal dorsal horn and in medullary visceral zone (MVZ) in the medulla oblongata. The number of Fos-IR cells in the spinal cord and MVZ in rats after 7 and 14 days of TNBS administration were significantly higher than that in the control rats (P<0.05). After 28 days of TNBS instillation, the number of Fos-IR neurons in MVZ decreased and became comparable to the control group. However, the number of Fos cells in the spinal cord in some rats were still significantly increased compared with the control rats (P<0.05). Conclusion Fos-IR neurons after colonic inflammation recovery may play an important role in the development of visceral hypersensitivity. Medulla oblongata was a less important structure than the spinal cord in inducing visceral hypersensitivity after chronic colonic inflammation. Objective To investigate Fos expression in rat lumbarsacral spinal cord and medulla oblongata induced by chronic colonic inflammation. Methods Thirty-three male Sprague-Dawley rats were divided into two groups: experimental group: colonic inflammation was induced in seventeen rats by intraluminal administration of trinitrobenzenesulfonic acid (TNBS); control group: saline was administered intraluminally in sixteen rats; After 3, 7, 14 and 28 days of administration, lumbarsacral spinal cord and medulla oblongata were removed and processed for Fos immunohistochemistry. Results Fos-immunoreactive (Fos-IR ) neurons induced by TNBS administration were primarily distributed in deep laminae (laminae III-IV, V-VI) in the spinal dorsal horn and in medullary visceral zone (MVZ) in the medulla oblongata. The number of Fos-IR cells in the spinal cord and MVZ in rats after 7 and 14 days of TNBS administration were significantly higher than that in the control rats (P <0.05). After 28 days Of the TNBS instillation, the number of Fos-IR neurons in MVZ decreased and became comparable to the control group. However, the number of Fos cells in the spinal cord in some rats were still significantly increased compared with the control rats (P <0.05) . Conclusion Fos-IR neurons after colonic inflammation recovery may play an important role in the development of visceral hypersensitivity. Medulla oblongata was a less important structure than the spinal cord in inducing visceral hypersensitivity after chronic colonic inflammation.