Jooby John1, E Fiona Bailey, Ralph F Fregosi. 1. Department of Physiology, Gittings Building, College of Medicine, University of Arizona, Tucson, Arizona 85721, USA.
Abstract
RATIONALE: Little is known about the respiratory-related discharge properties of motor units driving any of the eight muscles that control the movement, shape, and stiffness of the mammalian tongue. OBJECTIVES: To characterize the respiratory-related discharge of genioglossus motor units as synaptic drive to the hypoglossal motoneuron pool is increased with hypercapnia. MEASUREMENTS: We recorded airflow, genioglossus muscle EMG activity, and the respiratory-related discharge of 30 genioglossus muscle motor units in spontaneously breathing, urethane-anesthetized rats under control conditions and in hypercapnia (inspired CO2: 3, 6, 9, and 12%, 3-5 min at each level). MAIN RESULTS: All motor units were active throughout all or most of inspiration. Nine of 30 units showed "preinspiratory" activity (discharge onset within the last 20% of expiration), with continued discharge into inspiration. Six inspiratory units transitioned to a preinspiratory pattern when inspired CO2 exceeded 6%. For the majority of units (23/30), discharge rate increased with hypercapnia, with the maximum increase averaging about 50%. The average variability of interspike intervals within a spike train increased from 33% under baseline conditions to 50% with maximal hypercapnia. CONCLUSIONS: (1) The discharge pattern of genioglossus muscle motor units can be altered by hypercapnia; (2) most, but not all, genioglossus motor units receive synaptic input from CO2-sensitive chemoreceptors; (3) individual motor units have a wide range of CO2 sensitivities; and (4) hypercapnia significantly increases the variability of motor unit discharge, which may enhance muscle force output.
RATIONALE: Little is known about the respiratory-related discharge properties of motor units driving any of the eight muscles that control the movement, shape, and stiffness of the mammalian tongue. OBJECTIVES: To characterize the respiratory-related discharge of genioglossus motor units as synaptic drive to the hypoglossal motoneuron pool is increased with hypercapnia. MEASUREMENTS: We recorded airflow, genioglossus muscle EMG activity, and the respiratory-related discharge of 30 genioglossus muscle motor units in spontaneously breathing, urethane-anesthetized rats under control conditions and in hypercapnia (inspired CO2: 3, 6, 9, and 12%, 3-5 min at each level). MAIN RESULTS: All motor units were active throughout all or most of inspiration. Nine of 30 units showed "preinspiratory" activity (discharge onset within the last 20% of expiration), with continued discharge into inspiration. Six inspiratory units transitioned to a preinspiratory pattern when inspired CO2 exceeded 6%. For the majority of units (23/30), discharge rate increased with hypercapnia, with the maximum increase averaging about 50%. The average variability of interspike intervals within a spike train increased from 33% under baseline conditions to 50% with maximal hypercapnia. CONCLUSIONS: (1) The discharge pattern of genioglossus muscle motor units can be altered by hypercapnia; (2) most, but not all, genioglossus motor units receive synaptic input from CO2-sensitive chemoreceptors; (3) individual motor units have a wide range of CO2 sensitivities; and (4) hypercapnia significantly increases the variability of motor unit discharge, which may enhance muscle force output.
Authors: Mai K ElMallah; David A Stanley; Kun-Ze Lee; Sara M F Turner; Kristi A Streeter; David M Baekey; David D Fuller Journal: J Neurophysiol Date: 2015-12-16 Impact factor: 2.714
Authors: Vanessa Wilkinson; Atul Malhotra; Christian L Nicholas; Christopher Worsnop; Amy S Jordan; Jane E Butler; Julian P Saboisky; Simon C Gandevia; David P White; John Trinder Journal: Sleep Date: 2008-04 Impact factor: 5.849