title: Axonal Dysfunction Precedes Motor Neuronal Death in Amyotrophic Lateral Sclerosis.
abstract: Wide-spread fasciculations are a characteristic feature in amyotrophic lateral sclerosis (ALS), suggesting motor axonal hyperexcitability. Previous excitability studies have shown increased nodal persistent sodium conductances and decreased potassium currents in motor axons of ALS patients, both of the changes inducing hyperexcitability. Altered axonal excitability potentially contributes to motor neuron death in ALS, but the relationship of the extent of motor neuronal death and abnormal excitability has not been fully elucidated. We performed multiple nerve excitability measurements in the median nerve at the wrist of 140 ALS patients and analyzed the relationship of compound muscle action potential (CMAP) amplitude (index of motor neuronal loss) and excitability indices, such as strength-duration time constant, threshold electrotonus, recovery cycle and current-threshold relationships. Compared to age-matched normal controls (n = 44), ALS patients (n = 140) had longer strength-duration time constant (SDTC: a measure of nodal persistent sodium current; p < 0.05), greater threshold changes in depolarizing threshold electrotonus (p < 0.05) and depolarizing current threshold relationship (i.e. less accommodation; (p < 0.05), greater superexcitability (a measure of fast potassium current; p < 0.05) and reduced late subexcitability (a measure of slow potassium current; p < 0.05), suggesting increased persistent sodium currents and decreased potassium currents. The reduced potassium currents were found even in the patient subgroups with normal CMAP (> 5mV). Regression analyses showed that SDTC (R = -0.22) and depolarizing threshold electrotonus (R = -0.22) increased with CMAP decline. These findings suggest that motor nerve hyperexcitability occurs in the early stage of the disease, and precedes motor neuronal loss in ALS. Modulation of altered ion channel function could be a treatment option for ALS.
authors.affiliation: Department of Neurology, Graduate School of Medicine, Chiba University, Chiba, Japan.
authors.forename: Yuta
authors.initials: Y
authors.lastname: Iwai
authors.affiliation: Department of Neurology, Graduate School of Medicine, Chiba University, Chiba, Japan.
authors.forename: Kazumoto
authors.initials: K
authors.lastname: Shibuya
authors.affiliation: Department of Neurology, Graduate School of Medicine, Chiba University, Chiba, Japan.
authors.forename: Sonoko
authors.initials: S
authors.lastname: Misawa
authors.affiliation: Department of Neurology, Graduate School of Medicine, Chiba University, Chiba, Japan.
authors.forename: Yukari
authors.initials: Y
authors.lastname: Sekiguchi
authors.affiliation: Department of Neurology, Graduate School of Medicine, Chiba University, Chiba, Japan.
authors.forename: Keisuke
authors.initials: K
authors.lastname: Watanabe
authors.affiliation: Department of Neurology, Graduate School of Medicine, Chiba University, Chiba, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Amino
authors.affiliation: Department of Neurology, Graduate School of Medicine, Chiba University, Chiba, Japan.
authors.forename: Satoshi
authors.initials: S
authors.lastname: Kuwabara
mesh_terms: D000200:Action Potentials / Q000502:physiology; D000368:Aged; D000369:Aged, 80 and over; D000690:Amyotrophic Lateral Sclerosis / Q000503:physiopathology*; D001369:Axons / Q000502:physiology*; D016923:Cell Death; D004558:Electric Stimulation; D005260:Female; D006801:Humans; D008297:Male; D008475:Median Nerve / Q000503:physiopathology*; D008875:Middle Aged; D009046:Motor Neurons / Q000502:physiology*; D009132:Muscles / Q000294:innervation; D015221:Potassium Channels / Q000378:metabolism; D015222:Sodium Channels / Q000378:metabolism; D013997:Time Factors; D014953:Wrist / Q000294:innervation
chemical_list: D015221:Potassium Channels; D015222:Sodium Channels