Published ahead of print on September 1, 2005, doi:10.1164/rccm.200505-790OC Am. J. Respir. Crit. Care Med., Volume 172, Number 10, November 2005, 1331-1337 A more recent version of this article appeared on November 15, 2005
Submitted on May 18, 2005 Respiratory Related Discharge of Genioglossus Muscle Motor UnitsJooby John1,1 Department of Physiology, University of Arizona, College of Medicine, Tucson, AZ, USA * To whom correspondence should be addressed. E-mail: fregosi{at}u.arizona.edu.
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 "pre-inspiratory" activity (discharge onset within the last 20% of expiration), with continued discharge into inspiration. Six inspiratory units transitioned to a pre- inspiratory 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; 4) hypercapnia significantly increases the variability of motor unit discharge, which may enhance muscle force output. Key words: electrophysiology, respiratory muscles, tongue
This article has been cited by other articles:
|
|
||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
