Effect of Sciatic Nerve Transection on acetylcholinesterase activity in spinal cord and skeletal muscles of the bullfrog Lithobates catesbeianus

Abstract Sciatic nerve transection (SNT), a model for studying neuropathic pain, mimics the clinical symptoms of “phantom limb”, a pain condition that arises in humans after amputation or transverse spinal lesions. In some vertebrate tissues, this condition decreases acetylcholinesterase (AChE) activity, the enzyme responsible for fast hydrolysis of released acetylcholine in cholinergic synapses. In spinal cord of frog Rana pipiens, this enzyme’s activity was not significantly changed in the first days following ventral root transection, another model for studying neuropathic pain. An answerable question is whether SNT decreases AChE activity in spinal cord of frog Lithobates catesbeianus, a species that has been used as a model for studying SNT-induced neuropathic pain. Since each animal model has been created with a specific methodology, and the findings tend to vary widely with slight changes in the method used to induce pain, our study assessed AChE activity 3 and 10 days after complete SNT in lumbosacral spinal cord of adult male bullfrog Lithobates catesbeianus. Because there are time scale differences of motor endplate maturation in rat skeletal muscles, our study also measured the AChE activity in bullfrog tibial posticus (a postural muscle) and gastrocnemius (a typical skeletal muscle that is frequently used to study the motor system) muscles. AChE activity did not show significant changes 3 and 10 days following SNT in spinal cord. Also, no significant change occurred in AChE activity in tibial posticus and gastrocnemius muscles at day 3. However, a significant decrease was found at day 10, with reductions of 18% and 20% in tibial posticus and gastrocnemius, respectively. At present we cannot explain this change in AChE activity. While temporally different, the direction of the change was similar to that described for rats. This similarity indicates that bullfrog is a valid model for investigating AChE activity following SNT.

摘要 坐骨神经横断术（Sciatic nerve transection, SNT）是研究神经病理性疼痛的经典模型，可模拟人类截肢或脊髓横断损伤后引发的幻肢痛临床症状。在部分脊椎动物组织中，该造模方式会降低乙酰胆碱酯酶（acetylcholinesterase, AChE）活性——该酶负责快速水解胆碱能突触中释放的乙酰胆碱。在豹蛙（Rana pipiens）的脊髓组织中，腹根横断术（ventral root transection，另一种神经病理性疼痛研究模型）造模后的最初几日，该酶的活性并未出现显著变化。由此产生一个可验证的科学问题：坐骨神经横断术是否会降低美洲牛蛙（Lithobates catesbeianus）脊髓中的乙酰胆碱酯酶活性？该物种已被用于构建坐骨神经横断术诱导的神经病理性疼痛研究模型。由于每种动物模型的构建均采用特定方法，且疼痛诱导方式的细微差异往往会导致研究结果出现显著分歧，本研究检测了成年雄性美洲牛蛙腰骶段脊髓在完全坐骨神经横断术后3天和10天的乙酰胆碱酯酶活性。鉴于大鼠骨骼肌运动终板成熟的时间尺度存在差异，本研究同时检测了美洲牛蛙胫骨后肌（一种姿势肌）和腓肠肌（一种常用于运动系统研究的典型骨骼肌）中的乙酰胆碱酯酶活性。实验结果显示：坐骨神经横断术后3天和10天，脊髓中的乙酰胆碱酯酶活性均未出现显著变化；术后3天，胫骨后肌与腓肠肌的乙酰胆碱酯酶活性同样无明显改变。但在术后10天，两种肌肉的酶活性均出现显著下降：胫骨后肌与腓肠肌的酶活性分别降低了18%和20%。目前我们尚无法解释这一乙酰胆碱酯酶活性的变化现象。尽管变化的时间尺度存在差异，但其变化方向与大鼠中的相关研究报道一致。这一相似性表明，美洲牛蛙可作为研究坐骨神经横断术后乙酰胆碱酯酶活性变化的有效动物模型。