Postnatal maturation of vagal respiratory reflexes in preterm and full-term lambs

Abstract

The postnatal development of ventilatory reflexes originating from bronchopulmonary receptors was assessed in preterm vs. full-term lambs. Ventilation and arterial pressure were repeatedly measured in 10 preterm (gestational age, 132 days) and 7 full-term lambs without sedation from day 1 to day 42. The Hering-Breuer inhibitory reflex (slowly adapting stretch receptors) was assessed by the increase in expiratory time during end-inspiratory occlusion. The pulmonary chemoreflex (C-fiber endings) was assessed by the initial apnea + bradycardia + systemic hypotension and the secondary tachypnea after capsaicin intravenous injection. Results show the following. 1) Premature birth did not modify the maturation of the Hering-Breuer reflex. 2) Whereas a classic pulmonary chemoreflex was observed in the very first hours of life in preterm lambs, the tachypneic component of this reflex was weaker than in full-term lambs on day 1. 3) Premature birth led to a reversed postnatal maturation of this tachypneic response (tendency to increase with postnatal age). Our findings suggest that premature birth in lambs modifies postnatal maturation of the pulmonary chemoreflex.

Pontine Mechanisms of Respiratory Control

“…Beyond doubt, neonates are immediately able to process afferent inputs and many important afferent control mechanisms are fully functional at birth. However, several studies demonstrate changes in reflex responses during ontogeny (13, 97, 99, 141, 285, 377, 379, 381, 398) indicating the postnatal maturation of synaptic pathways integrating respiratory reflexes. Most of these reflex pathways involve the KF-area.…”

Electric Field Stimulation of Precision-Cut Lung Slices.

“…Therefore, the effects of capsaicin, a potent TRPV1 agonist That capsaicin failed to evoke clear bronchoconstriction in PCLS from marmosets is in line with data presented for marmoset trachea and bronchus, which weakly contracted by (2.3 ± 2.8)% and (8.0 ± 6.6)% of maximal contraction by 10 -4 M methacholine, respectively, after application of 100 µM capsaicin (158). In conflict to capsaicin responses in ovine PCLS, sheep lambs exerted a reduction in tidal volume from 91 mL to 36 mL when capsaicin (5 µg/kg) was injected intravenously (10). This opposing finding may be explained either by regional differences along the tracheobronchial tree (trachea/bronchus vs. peripheral airways in PCLS) (8) or by reflex arcs in vivo (79), which are destroyed in the PCLS preparation.…”

Bifurcation of the respiratory response to lung inflation in anesthetized dogs

“…Maturation of respiratory function including braking of expiratory airflow requires vagal activity in the newborn (Lalani et al ., 2001, Arsenault et al ., 2003). Expiratory braking is mediated by multiple mechanisms including the recruitment of ‘inspiratory’ motor activity during mid- and late- expiration (Noble et al ., 1987), which corresponds with the timing of TE bifurcation observed in our experiments.…”