Effect of pre-amputation pain block on the spinal and anterior cingulated cortex NMDA receptor activation in amputated rats

Abstract

To investigate the effect of pre-amputation pain block on the N-methyl-D-aspartate receptor activation in the central nervous system of amputated rats, and the association between pre-amputation pain block and chronic amputation-related pain. Thirty-six adult male SD rats were randomly assigned to an NA group (n=12), a PA group (n=12) and a PAB group (n=12). Group NA was intraplantarly injected saline l00 μL while group PA and group PAB were intraplantarly injected complete Freund adjuvant (CFA) 100 μL. The sciatic nerve of group NA and group PA were freed from surrounding tissue, and that of group PAB was blocked by bupivacaine under pentobarbital sodium anesthesia 5 days after the injection. Thermal withdrawal latency (TWL) was measured before and after the injection. All rats were amputated at the scheduled survival time. The expression of N-methyl-D-aspartate receptor (NR2B) was measured by immunohistochemistry in L4-6 of the spinal cord and the anterior cingulated cortex 7 days after the amputation procedure. The TWL after intraplantar administration of CFA in group PA and group PAB decreased significantly compared with the baseline value (P<0.05), while the saline treated control group remained unchanged. Besides the basic value, the TWL of group PA was shorter than that of group NA at the above-mentioned time-points (P<0.05). Compared with the basic value and group NA, the TWL of group PAB after the block increased significantly (P<0.05). Compared with group NA and group PAB, group PA had a remarkably high expression of NR2B (P<0.05), while there was no difference between group PA and group PAB. Pre-amputation pain may activate N-methyl-D-aspartate receptor of the central nervous system, which may lead acute postoperative pain to chronic pain. It is necessary to treat pre-amputation pain.