Abstract: Objective To investigate the response of the capillaries and astrocytes in the spinal cord dorsal horn of rats after the spared nerve injury (SNI). Methods Male SD rats were randomly divided into two groups and used for light microscopy(n=30) or electromicroscopy(n=10) study respectively. The rats for light microscopy study were divided into control, sham-SNI and SNI subgroups. Ten rats were performed SNI operation and survived for 20d respectively. Five of them were injected Evans blue into caudal vein, 30min before perfusion, the L4 segment of spinal cord was removed and cut into 30 μm frontal sections on a cryostat. The section was detected under Olympus BX51 fluorescent microscope. Other five of them were perfused, the sections were performed anti-rat IgG and glial fibrillary acidic protein (GFAP, a marker for astrocyte) immunohistochemical staining (ABC method). Rats used for immunoelectromicroscopy were divided into control and SNI 20 days subgroups, the spinal cord sections were performed anti-rat IgG immuno-electromocroscopic staining. Results 1. On 20 days after SNI, many clear red effusion spots of Evans blue were observed in the dorsal horn. 2. SNI induced astrocytes became active type and the number were increased; IgG positive granules on the capillary wall and perivascular space were increased markedly.3. Immunoelectromicroscopy showed that at 20 days after SNI, IgG positive granules were increased, the following changes of the endothelial cells were found: (1)Many microprocesses extended from the endothelial cells were observed, some of them contained IgG positive granules. (2)Many “endocytosis concave” on the luminal side, vesicles in cytoplasm and “exocytosis steps” on aluminal side of endothelial cells containing IgG positive granules were observed respectively. （3）The tight junction of endothelial cells revealed gap and containing IgG positive granules.(4) Many “vesicles” revealed within the cytoplasm, some of them contained IgG positive granules and some did not. Conclusion After SNI the

Key words: Astrocyte, Evans blue, Spared nerve injury, Endothelial cell, Immunoelectromicroscopy, Rat