Mechanisms contributing to the genesis of hypoglossal preinspiratory discharge

Abstract

Preinspiratory discharge manifests in the neuronal recordings of the pre-Bötzinger complex, parafacial respiratory group, retrotrapezoid nucleus, and Kölliker-Fuse nucleus, as well as the efferent neural discharge of respiratory-related nerves innervating upper airway musculature. This neural component of triphasic eupnea contemporaneously contributes to the genesis of native and originate respiratory rhythmic activity, as well as the preinspiratory component of efferent neural respiratory discharges. In the course of our investigations evaluating hypoglossal discharge in response to asphyxia, we noted a curious pattern of neural respiratory recovery following postasphyxia resuscitation in hypoglossal, vagal, and phrenic neurograms in unanesthetized decerebrate rats. Specifically, we observed a gradual return of a pseudobiphasic eupnea characterized by initial transition bursts followed by robust eupneic bursts with dynamics inclusive of a gradually and progressively increasing duration of the hypoglossal eupneic bursts and duration and amplitude of the preinspiratory component of these bursts, as well as progressively lengthening expiratory interval between these bursts in the phrenic nerve discharge. This was followed by conversion to regular triphasic eupnea. We discuss our extrapolations based on these findings regarding eupneic respiratory central pattern generation and mechanisms contributing to the genesis of preinspiratory activity in hypoglossal discharge.

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“…In the preinspiratory phase, the preBötC neurons send activating signals to the neurons of the hypoglossal nerve (CN XII) [19]. CN XII also receives impulses from other sites, such as the trigeminal nerve (CN V), the facial nerve (CN VII), the glossopharyngeal nerve (CN IX), and the vagus nerve (CN X) as the phases of the breath are also influenced by the orofacial region [19, 23]. Other areas involved in the action of respiration are connected efferently to CN XII: the raphe-pontomedullary network, the parabrachial/Kölliker-Fuse complex, the nucleus subcoeruleus, the medullary division of the lateral tegmental field and the nucleus tractus solitarii (NTS) [23-28].…”

“…Bötzinger’s neural bodies are stimulated by the parabrachial/Kölliker-Fuse complex, which are located in the pontine area [21]. The NTS, located in the dorsal neural group of the brain stem area, manages Bötzinger neurons and its connections; afferents come to NTS from chemoreceptors, baroreceptors and other receptors involved in the regulation of respiration, such as pulmonary receptors (slow-adapting stretch receptors; rapidly adapting irritation receptors; juxtacapillary or J receptors) and various receptors of the respiratory musculature [23]. The NTS also affects the behavior of the preBötC [23].…”

“…The postinspiratory complex influences the phrenic nerve and CN XII, prolonging the inspiratory period. The contraction of the adductor muscles of the larynx (and the vagus nerve) is stimulated in order to increase the resistance of the upper airways [19, 23]. Pulmonary deflation is thus delayed, and the gas exchange times of the alveoli are lengthened.…”