title: Intrinsic excitability differs between murine hypoglossal and spinal motoneurons.
abstract: Motoneurons differ in the behaviors they control and their vulnerability to disease and aging. For example, brain stem motoneurons such as hypoglossal motoneurons (HMs) are involved in licking, suckling, swallowing, respiration, and vocalization. In contrast, spinal motoneurons (SMs) innervating the limbs are involved in postural and locomotor tasks requiring higher loads and lower movement velocities. Surprisingly, the properties of these two motoneuron pools have not been directly compared, even though studies on HMs predominate in the literature compared with SMs, especially for adult animals. Here we used whole cell patch-clamp recording to compare the electrophysiological properties of HMs and SMs in age-matched neonatal mice (P7-P10). Passive membrane properties were remarkably similar in HMs and SMs, and afterhyperpolarization properties did not differ markedly between the two populations. HMs had narrower action potentials (APs) and a faster upstroke on their APs compared with SMs. Furthermore, HMs discharged APs at higher frequencies in response to both step and ramp current injection than SMs. Therefore, while HMs and SMs have similar passive properties, they differ in their response to similar levels of depolarizing current. This suggests that each population possesses differing suites of ion channels that allow them to discharge at rates matched to the different mechanical properties of the muscle fibers that drive their distinct motor functions.
authors.affiliation: School of Biomedical Sciences and Pharmacy, Faculty of Health and Hunter Medical Research Institute, The University of Newcastle, Callaghan, New South Wales, Australia; and.
authors.forename: M A
authors.initials: MA
authors.lastname: Tadros
authors.affiliation: Department of Physiology, College of Medicine, University of Arizona, Tucson, Arizona.
authors.forename: A J
authors.initials: AJ
authors.lastname: Fuglevand
authors.affiliation: School of Biomedical Sciences and Pharmacy, Faculty of Health and Hunter Medical Research Institute, The University of Newcastle, Callaghan, New South Wales, Australia; and.
authors.forename: A M
authors.initials: AM
authors.lastname: Brichta
authors.affiliation: School of Biomedical Sciences and Pharmacy, Faculty of Health and Hunter Medical Research Institute, The University of Newcastle, Callaghan, New South Wales, Australia; and robert.callister@newcastle.edu.au.
authors.forename: R J
authors.initials: RJ
authors.lastname: Callister
mesh_terms: D000200:Action Potentials; D000818:Animals; D005260:Female; D007002:Hypoglossal Nerve / Q000166:cytology / Q000502:physiology*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D009046:Motor Neurons / Q000502:physiology*; D009068:Movement; D013116:Spinal Cord / Q000166:cytology / Q000502:physiology*
keywords: action potential; excitability; motoneuron