title: Mice lacking cytosolic copper/zinc superoxide dismutase display a distinctive motor axonopathy.
abstract: OBJECTIVE
  To characterize the motor neuron dysfunction in two models by performing physiologic and morphometric studies.
  
  
  BACKGROUND
  Mutations in the gene encoding cytosolic superoxide dismutase 1 (SOD1) account for 25% of familial ALS (FALS). Transgenes with these mutations produce a pattern of lower motor neuron degeneration similar to that seen in patients with FALS. In contrast, mice lacking SOD1 develop subtle motor symptoms by approximately 6 months of age.
  
  
  METHODS
  Physiologic measurements, including motor conduction and motor unit estimation, were analyzed in normal mice, mice bearing the human transgene for FALS (mFALS mice), and knockout mice deficient in SOD1 (SOD1-KO). In addition, morphometric analysis was performed on the spinal cords of SOD1-KO and normal mice.
  
  
  RESULTS
  In mFALS mice, the motor unit number in the distal hind limb declined before behavioral abnormalities appeared, and motor unit size increased. Compound motor action potential amplitude and distal motor latency remained normal until later in the disease. In SOD1-KO mice, motor unit numbers were reduced early but declined slowly with age. In contrast with the mFALS mice, SOD1-KO mice demonstrated only a modest increase in motor unit size. Morphometric analysis of the spinal cords from normal and SOD1-KO mice showed no significant differences in the number and size of motor neurons.
  
  
  CONCLUSIONS
  The physiologic abnormalities in mFALS mice resemble those in human ALS. SOD1-deficient mice exhibit a qualitatively different pattern of motor unit remodeling that suggests that axonal sprouting and reinnervation of denervated muscle fibers are functionally impaired in the absence of SOD1.
authors.affiliation: Department of Neurology, State University of New York Health Science Center at Syracuse, 13210, USA. Shefnerj@Vax.cs.hscsyr.edu
authors.forename: J M
authors.initials: JM
authors.lastname: Shefner
authors.forename: A G
authors.initials: AG
authors.lastname: Reaume
authors.forename: D G
authors.initials: DG
authors.lastname: Flood
authors.forename: R W
authors.initials: RW
authors.lastname: Scott
authors.forename: N W
authors.initials: NW
authors.lastname: Kowall
authors.forename: R J
authors.initials: RJ
authors.lastname: Ferrante
authors.forename: D F
authors.initials: DF
authors.lastname: Siwek
authors.forename: M
authors.initials: M
authors.lastname: Upton-Rice
authors.forename: R H
authors.initials: RH
authors.lastname: Brown
mesh_terms: D000200:Action Potentials / Q000502:physiology; D000818:Animals; D001369:Axons / Q000502:physiology*; D004558:Electric Stimulation; D051379:Mice; D018345:Mice, Knockout; D016472:Motor Neuron Disease / Q000503:physiopathology*; D009046:Motor Neurons / Q000502:physiology*; D013482:Superoxide Dismutase / Q000172:deficiency*; D013997:Time Factors
chemical_list: D013482:Superoxide Dismutase