Institute of Pharmacology and Neurosciences, Faculty of Medicine, University of Lisbon, Lisbon, Portugal ; Unit of Neurosciences, Institute of Molecular Medicine, University of Lisbon, Lisbon, Portugal.
PLoS One. 2013 Sep 5;8(9):e73846. doi: 10.1371/journal.pone.0073846. eCollection 2013.
Amyotrophic lateral sclerosis is characterized by a progressive degeneration of the corticospinal tract motor neurons. Growing evidence suggests that degeneration may begin at the distal axon proceeding in a dying-back pattern. It seemed therefore of interest to investigate synaptic transmission at the neuromuscular junction (NMJ) in pre- and symptomatic phases of the disease. Endplate potentials (EPPs), miniatures endplate potentials (MEPPs) and giant MEPPs (GMEPPs) were recorded from innervated diaphragm muscle fibers from 4-6 and 12-15 weeks-old SOD1(G93A) mice and non-transgenic aged-matched littermates (WT). In the pre-symptomatic phase, SOD1(G93A) mice exhibited a significant increase in the mean amplitude of EPPs together with an increase in the mean quantal content of EPPs, suggesting that more acetylcholine is being released into the synaptic cleft. SOD1(G93A) mice presented a higher frequency of GMEPPs, suggestive of intracellular Ca(2+) deregulation in nerve terminals. The increase in the mean amplitude of MEPPs and the decreased mean rise-time of MEPPs in SOD1(G93A) mice point to post-synaptic related changes. In the symptomatic phase, electrophysiological data showed evidence for two NMJ groups in SOD1(G93A) mice: SOD1a and SOD1b. SOD1a group presented reduced mean amplitude of both EPPs and MEPPs. The mean rise-time of MEPPs was increased, when compared to WT and to SOD1b group, indicating impairments in the neuromuscular transmission. In contrast, the neuromuscular transmission of SOD1b group was not different from age-matched WT nor pre-symptomatic SOD1(G93A) mice, being somehow in between both groups. Altogether these results show that the neuromuscular transmission of SOD1(G93A) mice is enhanced in the pre-symptomatic phase. In the symptomatic phase our results are consistent with the hypothesis that the diaphragm of SOD1(G93A) mice is undergoing cycles of denervation/re-innervation supported by mixed neuromuscular junction populations. These early changes in the neuromuscular transmission of SOD1(G93A) mice suggest that the ALS associated events start long before symptoms onset.
肌萎缩侧索硬化症的特征是皮质脊髓束运动神经元的进行性退化。越来越多的证据表明，退化可能从远端轴突开始，呈退行性变。因此，研究疾病的预症状和症状期神经肌肉接点（NMJ）的突触传递似乎很有趣。从 4-6 周和 12-15 周龄的 SOD1（G93A）小鼠和非转基因年龄匹配的同窝仔鼠（WT）的神经支配膈肌纤维中记录到终板电位（EPPs）、微型终板电位（MEPPs）和巨大 MEPPs（GMEPPs）。在预症状期，SOD1（G93A）小鼠的 EPP 平均幅度显著增加，同时 EPP 的平均量子含量增加，表明更多的乙酰胆碱被释放到突触间隙。SOD1（G93A）小鼠的 GMEPPs 频率更高，提示神经末梢细胞内 Ca（2+）失调。SOD1（G93A）小鼠的 MEPP 平均幅度增加和 MEPP 平均上升时间减少表明突触后相关变化。在症状期，电生理数据显示 SOD1（G93A）小鼠的两个 NMJ 组存在证据：SOD1a 和 SOD1b。SOD1a 组的 EPP 和 MEPP 平均幅度均降低。与 WT 和 SOD1b 组相比，MEPP 的平均上升时间增加，表明神经肌肉传递受损。相比之下，SOD1b 组的神经肌肉传递与年龄匹配的 WT 或预症状 SOD1（G93A）小鼠没有差异，介于两组之间。总的来说，这些结果表明 SOD1（G93A）小鼠的神经肌肉传递在预症状期增强。在症状期，我们的结果与假设一致，即 SOD1（G93A）小鼠的膈肌正在经历由混合神经肌肉接点群体支持的去神经再支配循环。SOD1（G93A）小鼠的神经肌肉传递的这些早期变化表明，与 ALS 相关的事件早在症状出现之前就开始了。
