Retracted: Control of hypoglossal pre‐inspiratory discharge
Authors: Ghali Michael George Zaki 
Published: June 2020

New Findings

What is the topic of this review?

This review explores the modulatory role of lung vagal afferents and intra‐neuraxial and carotid body chemoreceptors upon hypoglossal pre‐inspiratory activity.

What advances does it highlight?

Pre‐inspiratory activity manifesting in hypoglossal neural efferent discharge may be potentiated by mechanical interruption of vagal continuity and challenge with administration of a hypoxic and/or hypercapnic gas mixture and attenuated by static and/or dynamic pulmonary stretch. Differential excitability of, or premotoneuronal volleys exhibiting distinct spatiotemporal patterns of discharge arriving at, motoneurons residing within the hypoglossal motor nucleus may emergently generate phase‐spanning pre‐inspiratory inspiratory activity of hypoglossal neural efferent discharge manifest at the population level.

The hypoglossal nerve (XII) innervates muscles mediating excursive movements of the tongue. The population discharge of hypoglossalmotoneuronal axons constituting the hypoglossal nerve precedes and extends through the inspiratory epoch. The epoch subtended between the onsets of hypoglossal and phrenic neural discharge constitutes so‐called pre‐inspiration. Hypoglossal pre‐inspiratory neural discharge serendipitously displaces the tongue along a tensor reducing upper airway resistance anticipative of succeeding inspiratory efforts. Hypoglossal motoneurons exhibiting discharge onset during pre‐inspiration experience successive hyperpolarization of membrane voltage and attenuation of unitary spiking frequency, although a subset may, paradoxically and state‐dependently, exhibit depolarization of membrane voltage and augmentation of neuronal spiking frequency, by dynamic stretch placed upon the alveolar walls and interstitium. Marked static elevation of positive‐end expiratory pressure may induce hypoglossal bursting decoupled from phasic rhythmic phrenic discharge. Augmentation of the amplitude and/or duration of hypoglossal inspiratory discharge during successive pre‐inspiratory and inspiratory epochs by inhalation of a hypoxic and/or hypercapnic gas mixture remains restrained in the presence of intact vagal inputs and is potentiated by interruptions of vagal continuity. Unravelling the mechanisms underlying the genesis of pre‐inspiratory activity will inform our understanding of respiratory rhythm generation and pattern shaping. In the present work, I seek to explore the mechanisms underlying modulation of hypoglossal pre‐inspiratory discharge by hypercapnia, hypoxia and static and dynamic lung stretch placed upon hypoglossal pre‐inspiratory activity, the mechanisms underlying the generation of hypoglossal pre‐inspiratory activity, and the extent of microanatomical and functional overlap between propriobulbar interneuronal microcircuits generating hypoglossal pre‐inspiratory activity and propriobulbar interneuronal microcircuit oscillators generating pre‐inspiratory activity inaugurally inducing respiratory rhythmic activity and thus use experimental data from previous work and that developed by other investigators to explore the modulatory role of lung vagal afferents and intra‐neuraxial and carotid body chemoreceptors upon hypoglossal pre‐inspiratory activity.