Early changes of neuromuscular transmission in the SOD1(G93A) mice model of ALS start long before motor symptoms onset

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amyotrophic Lateral Sclerosis / genetics
  • Amyotrophic Lateral Sclerosis / pathology
  • Amyotrophic Lateral Sclerosis / physiopathology*
  • Animals
  • Diaphragm / innervation
  • Diaphragm / metabolism
  • Disease Models, Animal*
  • Female
  • Humans
  • Male
  • Mice
  • Mice, Transgenic
  • Motor Activity / genetics
  • Motor Activity / physiology
  • Muscle, Skeletal / innervation
  • Muscle, Skeletal / metabolism
  • Neuromuscular Junction / metabolism
  • Neuromuscular Junction / physiology*
  • Superoxide Dismutase / genetics
  • Superoxide Dismutase / metabolism*
  • Synaptic Potentials / genetics
  • Synaptic Potentials / physiology
  • Synaptic Transmission / genetics
  • Synaptic Transmission / physiology*
  • Time Factors


  • SOD1 G93A protein
  • Superoxide Dismutase

Grant support

This work was supported by Fundação do Ministério da Ciência e Tecnologia de Portugal [Grant PTCD/SAU-NEU/101752/2008] and European Union [Grant NEREPLAS, COST B30]. P.A.P. received a fellowship from Fundação do Ministério de Ciência e Tecnologia de Portugal [Grant SFRH/BD/28073/2006]. M.C.R. was a research fellow from Fundação do Ministério de Ciência e Tecnologia de Portugal [Grant PTCD/SAU-NEU/101752/2008]. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.