Spinal Cord Injury in the Rat: Treatment with Bacterial Lipopolysaccharide and Indomethacin Enhances Cellular Repair and Locomotor Function

Abstract

Trauma to the rat's spinal cord results in a lesion characterized by ingrowth of glial cells, accumulation of macrophages, and the progressive development of necrosis and cavitation. Since, when appropriately activated, both astrocytes and macrophages secrete growth-promoting cytokines, we examined whether treatment with drugs that stimulate the secretory activities of these cells might promote tissue repair and reduce necrosis in the traumatized spinal cord. The spinal cord of rats was crushed extradurally at T8 and the rats were injected intraperitoneally with (i) a lipopolysaccharide (LPS) or ImuVert to activate cytokine secretion, (ii) Indomethacin to reduce necrosis by inhibiting prostaglandin synthesis, (iii) a combination of LPS+ Indomethacin, or (iv) vehicle. After 28 days the lesion site was examined quantitatively by light microscopical image analysis. The lesion of vehicle-treated control animals showed large cavities, extensive infiltration by debris-engorged macrophages, and relatively few axons. Treatment with LPS or ImuVert significantly reduced the degree of cavitation and increased the number of cells and axons in the lesion. Treatment with LPS+Indomethacin was significantly more effective than treatment with LPS alone, while treatment with Indomethacin alone was ineffective. To test whether the histopathological differences between treated and control rats might be reflected in functional improvement, rats were subjected to a contusion (weight-drop) injury and their walking ability was quantified by the Tarlov scale for 28 days postoperatively. Treatment with LPS+Indomethacin significantly improved locomotor function of animals subjected to a moderate (1.25 g × 20 cm) injury. We conclude that tissue repair and functional recovery after spinal cord injury are enhanced by combined treatment with agents that promote the secretory activities of the nonneuronal cells and that inhibit prostaglandin synthesis. These results indicate that the search for more effective treatments should include studies on combinations of drugs having different pharmacological specificities.