Experimental study on the control effect of interleukin-10 for secondary damage after acute spinal cord injury *
Numerous factors are involved in the spread of secondary damage in the spinal cord after traumatic injury, including ischemia, edema, increased excitatory amino acids, inflammatory response, NO, and oxidative damage to the tissue from reactive oxygen species. Activated macrophages and microglia can produce neurotoxic cytokines, such as IL-lp\ TNF-a, and inducible NO synthase and thus may contribute to the spread of damage to levels of the rostral and caudal cord after spinal cord injury (SCI). We hypothesized that attenuation of an inflammatory response and reduction of NO from macrophages/microglia suppresses the spread of secondary damage in the spinal cord. In this study, a laminectomy was performed in male Sprague-Dawley rats (380-420 g) at the T7 level under general anesthesia, and the spinal cord was injured using a weight drop technique (30g weight, 10mm height). We divided the rats into two groups. The IL-10group was administered IL-10 ( 2 /j.g/ml) and the control group was given saline ( 1ml) from the femoral vein at 30 minutes after SCI. This study examined the morphology of microglia, the rostral-caudal distribution of macrophages/microglia, serous NO2" and NO3" (NOx) , and behavior using a modified Tarlov's score at 24 and 72 h after SCI. Macrophages/microglia were visualized with antibodies against OX-42 and ED1. OX-42 staining revealed activated microglia with blunt processes, called the ameboid type. At 24 h after SCI, activated microglia were observed in all level in the control group. Though activated microglia were observed at 2 mm rostral and caudal to the lesion, OX-42 staining revealed microglia with the resting morphology, with numerous fine processes, called ramified type at 4 mm and 6 mm rostral and caudal to the lesion in the IL-10 group. At 72 h after SCI, the majority of OX-42 positive cells at 2 mm from the lesion showed the phagocytic morphology, and at 4 mm and 6 mm from the lesion showed the activated morphology in the control group. The activated microglia and the round phagocytic cells were observed at 2 mm from the lesion, and the resting microglia were observed at 4 mm and 6 mm from the lesion in the IL-10 group. From these results, activation of microglia was suppressed by administration of IL-10. Numerous cells with the phagocytic morphology were present at 72 h in both groups. These cells tended to locate within gray matter and dorsal white matter near the lesion and were limited to the necrotic area of dorsal white matter at levels distant to the lesion. The total number of EDl-positive cells gradually declined through 6 mm rostral and caudal to the lesion, particularly in the IL-10 group. Furthermore, EDl-positive cells with a phagocytic morphology stained antigen iNOS. Plasma NOx levels increased at 30 minutes after injury and gradually decreased. So there were no significant differences at 30 minutes and 24 h after injury. However significant difference in plasma NOx levels was observed between the control group and IL-10 group at 72 h after injury. The behavior score significantly improved at 72 h in both groups, as compared with the score at 24 h. However there were no significant differences at 72 h in either group. Suppression of the activation of macrophages/microglia broke the vicious circle of an acute inflammatory response, and it is thought that this may play some role in controlling the spread of secondary damage. (Accepted on October 14, 2003)
