title: Motor unit firing pattern: evidence for motoneuronal or axonal discharge origin?
abstract: In neuromuscular diseases, a fasciculation origin is disputed. In some reports, it was suggested that motor unit firing pattern alone is evidence for motoneuronal or axonal fasciculations; namely interspike intervals of approximately 5 ms (doublet intervals) provide evidence for the axonal firing. To clarify the reliability of the suggestion, we compared doublet intervals originated in motoneurons and their axons in healthy humans. For this aim, the H-reflex and M-response of single motor units were elicited during gentle voluntary muscle contractions. Peri-stimulus time histograms allowed reliable judgment about a doublet origin: motoneuronal (at the H-reflex latency) or axonal (at the M-response latency). Significant difference between motoneuronal and axonal doublet intervals was absent. It was concluded that doublet interval alone cannot be the reliable criterion for an axonal firing origin; additional evidences are needed for this conclusion, for example, the appearance of the F-wave. The approach may be used as an additional estimation of mechanisms underlying motor unit diseases.
authors.affiliation: Institute for Information Transmission Problems (Kharkevich Institute), Russian Academy of Sciences, 19, Bol'shoi Karetnyi pereulok, GSP-4, 127994, Moscow, Russia. kudina@iitp.ru.
authors.forename: Lydia P
authors.initials: LP
authors.lastname: Kudina
authors.affiliation: Institute for Information Transmission Problems (Kharkevich Institute), Russian Academy of Sciences, 19, Bol'shoi Karetnyi pereulok, GSP-4, 127994, Moscow, Russia.
authors.forename: Regina E
authors.initials: RE
authors.lastname: Andreeva
mesh_terms: D000200:Action Potentials / Q000502:physiology*; D000328:Adult; D001369:Axons / Q000502:physiology*; D004558:Electric Stimulation; D004576:Electromyography; D006801:Humans; D008875:Middle Aged; D009043:Motor Activity / Q000502:physiology; D009046:Motor Neurons / Q000502:physiology*; D009119:Muscle Contraction / Q000502:physiology; D012018:Reflex / Q000502:physiology; D014836:Volition / Q000502:physiology
keywords: Axonal and motoneuronal double discharges; Fasciculation potentials; Human firing motor units; Interspike interval analysis