Effects of Nogo-neutralizing antibody and neurotrophin-3 on axonal regeneration following spinal cord injury in rats

BACKGROUND: Recent studies have suggested that regeneration of the central nerve fiber following spinal cord injury occurs under specific conditions.OBJECTIVE: To study the effects of Nogo-neutralizing antibody (IN-l), in combination with neurotrophin-3 (NT-3), on axonal regeneration and motor function following spinal cord injury in the rat.DESIGN, TIME AND SETTING: A randomized, controlled, animal study combining immunohistochemistry was performed at the Laboratory of Neuroanatomy of Xiangya Medical College, and Central Laboratory of Xiangya the Third Hospital, Central South University from January 2006 to December 2007.MATERIALS: Eighteen healthy, Sprague Dawley rats were randomly divided into three groups, with six rats per group: control, IN-1, and IN-1/NT-3. Hemisectioned spinal cord injury models were established by cutting the posterior 2/3 of spinal cord, which is equivalent to the T8 level.METHODS: A polyethylene tubing was inserted through into subarachnoid cavity, equivalent to the superior margin at the Ts level. Saline, IN-1, and IN-1/NT-3 were respectively injected into control, IN-1, and IN-1/NT-3 groups, three times/day for seven consecutive days.MAIN OUTCOME MEASURES: At 2 weeks post-surgery, biotin dextran amine (10%) was injected into the fight sensorimotor cortex area. At day 28 post-surgery, spinal cord tissue was prepared for frozen sections.Positive astrocytic expression was observed with glial fibrillary acidic protein (GFAP) immunohistochemical staining whose proliferation level was represented by gray value, i.e. the higher the gray value was, the less the positive cells were, and growth of positive fibers was observed with a biotin dextran amine histological reaction. Motor function was measured according to BBB scores pre-operatively, as well as at days 1, 7, 14,21. and 28 post-operatively.RESULTS: Three rats died during experimentation. By random supplement, a total of 18 rats were included.GFAP-positive astrocytes were observed in all the three groups. In the control group, astrocytes were characterized according to active function, hyperplasia, proliferation, hypertrophy, and increasing processes as compared to IN-1 group and IN-1/IN-3 group. Astrocyte hyperplasia represented by gray value in the IN-1 group was less than the control group. Gray value of GFAP-positive products in the IN-1/IN-3 group was higher than other two groups (P < 0.05). Biotin dextran amine tracing demonstrated no corticospinal tract fiber outgrowth following spinal cord injury; the fibers were incapable of passing through the glial scar in the control group. Several fibers were distributed in the proximal scar tissue region in the IN-1 group, and the regenerated fibers were disarranged. Many nerve fibers were distributed throughout the scar tissue, and even several biotin dextran amine-positive fibers were observed at the distal end of the injured segment.Post-operative Basso, Beattie, Bresnahan scores were greater than pre-operative ones, while Basso, Beattie,Bresnahan scores in the IN-1/NT-3 group were significantly greater than the other two groups at days 14, 21,and 28 post-surgery (P < 0.05).CONCLUSION: IN-1, in combination with NT-3, promoted axonal regeneration following spinal cord injury, inhibited the colloidal effect, and enhanced the correlation between proximal and distal processes to recover motor function. The recovery effect of IN-1/NT-3 on motor function was superior that of to IN-1 alone.