title: Uncoupling of upper airway motor activity from phrenic bursting by positive end-expired pressure in the rat.
abstract: Phasic bursting in the hypoglossal nerve can be uncoupled from phrenic bursting by application of positive end-expired pressure (PEEP). We wished to determine whether similar uncoupling can also be induced in other respiratory-modulated upper airway (UAW) motor outputs. Discharge of the facial, hypoglossal, superior laryngeal, recurrent laryngeal, and phrenic nerves was recorded in anesthetized, ventilated rats during stepwise changes in PEEP with a normocapnic, hyperoxic background. Application of 3- to 6-cmH(2)O PEEP caused the onset inspiratory (I) UAW nerve bursting to precede the phrenic burst but did not uncouple bursting. In contrast, application of 9- to 12-cmH(2)O PEEP uncoupled UAW neurograms such that rhythmic bursting occurred during periods of phrenic quiescence. Single-fiber recording experiments were conducted to determine whether a specific population of UAW motoneurons is recruited during uncoupled bursting. The data indicate that expiratory-inspiratory (EI) motoneurons remained active, while I motoneurons did not fire during uncoupled UAW bursting. Finally, we examined the relationship between motoneuron discharge rate and PEEP during coupled UAW and phrenic bursting. EI discharge rate was linearly related to PEEP during preinspiration, but showed no relationship to PEEP during inspiration. Our results demonstrate that multiple UAW motor outputs can be uncoupled from phrenic bursting, and this response is associated with bursting of EI nerve fibers. The relationship between PEEP and EI motoneuron discharge rate differs during preinspiratory and I periods; this may indicate that bursting during these phases of the respiratory cycle is controlled by distinct neuronal outputs.
authors.affiliation: Dept. of Life Science, National Taiwan Normal University, Taipei, Taiwan.
authors.forename: Kun-Ze
authors.initials: KZ
authors.lastname: Lee
authors.forename: David D
authors.initials: DD
authors.lastname: Fuller
authors.forename: Li-Chu
authors.initials: LC
authors.lastname: Tung
authors.forename: I-Jung
authors.initials: IJ
authors.lastname: Lu
authors.forename: Li-Chi
authors.initials: LC
authors.lastname: Ku
authors.forename: Ji-Chuu
authors.initials: JC
authors.lastname: Hwang
mesh_terms: D000818:Animals; D001794:Blood Pressure / Q000502:physiology; D045853:Exhalation / Q000502:physiology; D006339:Heart Rate / Q000502:physiology; D001239:Inhalation / Q000502:physiology; D008297:Male; D009043:Motor Activity / Q000502:physiology*; D009046:Motor Neurons / Q000502:physiology; D010791:Phrenic Nerve / Q000502:physiology*; D011175:Positive-Pressure Respiration; D051381:Rats; D017208:Rats, Wistar; D012143:Respiratory Physiological Phenomena; D012137:Respiratory System / Q000294:innervation*