Stereological study of the numbers of microglia and astrocytes in the spinal dorsal horn of neuropathic pain rats

Objective To determine whether neuropathic pain(NNP) induced by chronic constriction injury(CCI) is associated with changes in the number of microglia and astrocytes in the spinal dorsal horn of rats and the effects of COX-2 inhibitor on NNP.Methods Twelve class II adult SD rats were randomly divided into two groups: the CCI group(7 rats) was subjected to unilateral loose ligation of the sciatic nerve;and the parecoxib group(5 rats) was treated as CCI group and then intraperitoneally injected with parecoxib 3 mg/kg twice a day on postoperative days 1-3.The paw withdraw threshold(PWT) was measured on preoperative day 1,and postoperative days 4,7,14 and 28.The rats were sacrificed 28 days after operation,and the L5 segment of spinal cord was removed and paraffin-embedded serial sections were prepared and stained with GFAP immunohistochemical staining to show astrocytes.The areas of capillary lumens and the number of microglia,astrocytes and endothelial cells in the spinal dorsal horn were estimated using stereological techniques.Results At 4 to 28 days after CCI,the PWT on the operated side was significantly decreased in both groups,compared with that on the non-operated side.PWT in the parecoxib group was significantly higher than that in the CCI group.In the CCI group and parecoxib group,28 days post operation,the area of capillary lumens and the number of microglia,astrocytes and endothelial cells in the spinal dorsal horn were not significantly different,compared with those on the non-operated side,and no inflammatory cell infiltration was found.Conclusions In the subacute phase of neuropathic pain,there are no significant inflammatory response and changes in the numbers of microglia and astrocytes in the rat spinal dorsal horn.