Changes in the number of synapses and neurons in spinal dorsal horn in a rat model of phantom limb pain

Abstract

Objective To investigate the changes in the number of synapses and neurons in the spinal dorsal horn in a rat model of phantom limb pain. Methods Eleven healthy adult SD rats of both sexes weighing 209-300 g were randomly divided into 2 groups： sham operation group （group S, n = 5） and phantom limb pain group （group P, n = 6）. Phantom limb pain was induced by resection of a 0.5 cm segment of unilateral sciatic nerve in group P. In group S unilateral sciatic nerve was exposed but not transected. The animals were observed for autotomy and scored （0 = no autotomy, 13 = the worst autotomy） after operation and were sacrificed on the 28th day after operation. The L3-6 segment of the spinal cord was removed for determination of the number of neurons （by Nissl＇s staining） and synapses （by synaptophysin immuno-histochemistry）.Results In group S no animal developed autotomy. In group P autotomy started from the 2nd day after operation and the score reached 9-11. The number of the neurons in the spinal dorsal horn in all 4 segments and the number of synapses in L3 and 16 segments were comparable between the two sides and the 2 groups. The number of synapses in the spinal dorsal horn of L4and L5 segment was significantly larger in the operated side than in the contralateral side in group P. Conclusion The number of synapses in the spinal dorsal horn significantly increases in animals with plantom limb pain which induces no increase in the number of neurons in the spinal dorsal horn. Key words: Acrodynia; Posterior horn cells; Synapses; Spinal cord