title: Firing rate of the lower motoneuron and contractile properties of its muscle fibers after upper motoneuron lesion in man.
abstract: We studied motor unit (MU) firing rate and contractile properties and myosin isoform composition of single muscle fibers after upper motoneuron lesion. Single-MUs and surface electromyogram (EMG) were recorded during voluntary contractions and locomotion in the paretic (P) and nonparetic (NP) tibialis anterior (TA) of 15 hemiparetics. P TA low-threshold MUs fired within the lower end of their normal range. High-threshold MUs fired below their normal range or were not recruited. Surface EMG was abnormally low and high in the P TA and NP TA, respectively. On muscle cross sections stained with histochemical methods, type I fibers represented 99.4%, 74.3% and 66.6% of NP, P, and control TA, respectively. P TA fibers expressing type I myosin heavy chain (MyHC) were smaller, weaker, and slower. In conclusion, low MU firing rate and activity in the P TA was associated with slower type I MyHC fibers, while increased activity in NP TA resulted in homogenous expression of type I MyHC.
authors.affiliation: Department of Clinical Neurophysiology, Karolinska Hospital, Stockholm, Sweden.
authors.forename: W R
authors.initials: WR
authors.lastname: Frontera
authors.forename: L
authors.initials: L
authors.lastname: Grimby
authors.forename: L
authors.initials: L
authors.lastname: Larsson
mesh_terms: D000328:Adult; D000368:Aged; D001706:Biopsy; D004576:Electromyography; D006429:Hemiplegia / Q000378:metabolism / Q000503:physiopathology; D006801:Humans; D008124:Locomotion / Q000502:physiology; D008875:Middle Aged; D009046:Motor Neurons / Q000502:physiology*; D009119:Muscle Contraction / Q000502:physiology*; D018485:Muscle Fibers, Skeletal / Q000201:enzymology* / Q000473:pathology; D018908:Muscle Weakness / Q000378:metabolism / Q000503:physiopathology; D018995:Myosin Heavy Chains / Q000032:analysis / Q000378:metabolism; D018994:Myosin Light Chains / Q000032:analysis / Q000378:metabolism; D009218:Myosins / Q000378:metabolism; D014836:Volition / Q000502:physiology
chemical_list: D018994:Myosin Light Chains; D018995:Myosin Heavy Chains; D009218:Myosins