GFAP and Fos immunoreactivity in lumbosacral spinal cord and medulla oblongata in rats with chronic colonic inflammation

Objective: To investigate the responses of astrocytes and neurons in rat lumbosacral spinal cord and medulla oblongata induced by chronic colonic inflammation, and the relationship between activated astrocytes and neurons. Methods: Thirty-three male Sprague-Dawley rats were randomly divided into two groups. In treated group(n = 17), colonic inflammation was induced by intraluminal administration of trinitrobenzenesulfonic acid (TNBS) in rats; In non-treated group (n = 16), saline was intraluminally administered. The lumbosacral spinal cord and medulla oblongata were removed 3, 7, 14 and 28 days after intraluminal administration and processed for anti-GFAP, Fos and GFAP/Fos immunohistochemistry. Results: Most activated GFAP positive astrocytes were distributed in the superficial laminae (I-II), intermediolateral nucleus (lamina V), posterior commissural nucleus(laminae X) and anterolateral nucleus(laminae IX) in lumbosacral spinal cord. Fos positive neurons were mainly expressed in the deeper laminae of the spinal cord(III-IV, V-VI). In the medulla oblongata, both GFAP-IR astrocytes and Fos-IR neurons were mainly distributed in medullary visceral zone(MVZ), which is composed of the nucleus of solitary tract (NTS), ventrolateral medulla(VLM) and intermediat reticular(IRt). The density of GFAP positive astrocytes in the spinal cord in treated rats 3, 7 and 14 days after TNBS administration was significantly higher than that in non-treated rats (P < 0.05). The density of GFAP positive astrocytes in MVZ was significantly higher in treated rats 3 days after TNBS administration than that in the non-treated rats(P < 0.05). The density of GFAP positive astrocytes in lumbosacral spinal cord and MVZ in treated rats 28 days after TNBS administration decreased and became comparable to that in non-treated rats(P > 0.05). Conclusions: The ast rocytes in lumbosacral spinal cord and medulla oblongata can be activated by colonic inflammation. The response of astrocytes decreased with the recovery of the colonic inflammation. Activated astrocytes are closely related to activated neurons in MVZ.