Effect of preamputation pain on the behavioral changes and spinal astrocytic activation in amputated rats

Abstract

To determine the effect of preamputation pain on the behavioral response and astrocytic activation in the spinal cord of amputated rats, and to assess the association between preamputation pain and chronic amputation-related pain. A total of 84 adult male SD rats were randomly distributed into an NA group (n=42) and a PA group (n=42). The NA group was intraplantarly injected with saline 100 μL, while the PA group was intraplantarly injected with complete Freund's adjuvant (CFA) 100 μL in both cases at 7 d before the amputation. Thermal withdrawal latency (TWL) was measured before the injection and at 1, 3, 5, and 7 d after the injection. All rats were amputated on the 7th day. The TWL, diet and water intake were measured on 1, 3, 5, 7, 10, 14, 17, 21, and 28 d after the amputation. Expression of glial fibrillary acidic protein (GFAP) in the L4-6 of spinal cord was measured by immunohistochemistry before the saline/ CFA injection, 7 d after the injection and 1, 3, 5, 7, 10 d after the amputation.. The TWL significantly decreased on 1, 3, 5, and 7 d after the intraplantar administration of CFA compared with the basic value in the PA group (P<0.05), while there was no difference between 1, 3, 5, and 7 d after the intraplantar administration of saline and the basic value in the NA group (P>0.05). In addtions to the basic value, the TWL of the PA group was shorter than that of the NA group at the above-mentioned time-points (P<0.05). Compared with the preoperative level, the diet and water intake decreased significantly after the amputation in both groups, but recovered to the preoperative levels, by 3 d after the amputation in the NA group, and by 5 d after the amputation in the PA group. Compared with the TWL of the residual limb on the day of amputation, the TWL of the residual limb increased significantly 3 d after the amputation and remained elevated until 28 d after the amputation in the NA group (P<0.05), while there was no difference between each time point after the amputation and the day of the amputation in the PA group. Compared with the basic value, there was an obviously high expression of GFAP in the NA group beginning on the day of amputation and in the PA group 7 d after the CFA injection (P<0.05). After the amputation, the expression of GFAP was significantly higher in the PA group (P<0.05). Preamputation pain delays the recovery and activates the spinal astrocytes which may turn the acute postoperative pain into a chronic one.