Electrophysiological properties of laryngeal motoneurones in rats submitted to chronic intermittent hypoxia

Abstract

Key points: The respiratory control of the glottis by laryngeal motoneurones is characterized by inspiratory abduction and post-inspiratory adduction causing decreases and increases in upper airway resistance, respectively. Chronic intermittent hypoxia (CIH), an important component of obstructive sleep apnoea, exaggerated glottal abduction (before inspiration), associated with active expiration and decreased glottal adduction during post-inspiration. CIH increased the inspiratory and decreased the post-inspiratory laryngeal motoneurone activities, which is not associated to changes in their intrinsic electrophysiological properties. We conclude that the changes in the respiratory network after CIH seem to be an adaptive process required for an appropriated pulmonary ventilation and control of upper airway resistance under intermittent episodes of hypoxia. To keep an appropriate airflow to and from the lungs under physiological conditions a precise neural co-ordination of the upper airway resistance by laryngeal motoneurones in the nucleus ambiguus is essential. Chronic intermittent hypoxia (CIH), an important component of obstructive sleep apnoea, may alter these fine mechanisms. Here, using nerve and whole cell patch clamp recordings in in situ preparations of rats we investigated the effects of CIH on the respiratory control of the upper airway resistance, on the electrophysiological properties of laryngeal motoneurones in the nucleus ambiguus, and the role of carotid body (CB) afferents to the brainstem on the underlying mechanisms of these effects. CIH rats exhibited longer pre-inspiratory and lower post-inspiratory superior laryngeal nerve activities than control rats. These changes produced exaggerated glottal abduction (before inspiration) and decreased glottal adduction during post-inspiration, indicating a reduction of upper airway resistance during these respiratory phases after CIH. CB denervation abolished these changes produced by CIH. Regarding choline acetyltransferase positive-laryngeal motoneurones, CIH increased the firing frequency of inspiratory and decreased the firing frequency of post-inspiratory laryngeal motoneurones, without changes in their intrinsic electrophysiological properties. These data show that the effects of CIH on the upper airway resistance and laryngeal motoneurones activities are driven by the integrity of CB, which afferents induce changes in the central respiratory generators in the brainstem. These neural changes in the respiratory network seem to be an adaptive process required for an appropriated pulmonary ventilation and control of upper airway resistance under intermittent episodes of hypoxia.