Tracheal occlusions evoke respiratory load compensation and neural activation in anesthetized rats

Abstract

Airway obstruction in animals leads to compensation and avoidance behavior and elicits respiratory mechanosensation. The pattern of respiratory load compensation and neural activation in response to intrinsic, transient, tracheal occlusions (ITTO) via an inflatable tracheal cuff are unknown. We hypothesized that ITTO would cause increased diaphragm activity, decreased breathing frequency, and activation of neurons within the medullary and pontine respiratory centers without changing airway compliance. Obstructions were performed for 2-3 breaths followed by a minimum of 15 unobstructed breaths with an inflatable cuff sutured around the trachea in rats. The obstruction procedure was repeated for 10 min. The brains of obstructed and control animals were removed, fixed, sectioned, and stained for c-Fos. Respiratory pattern was measured from esophageal pressure (P(es)) and diaphragm electromyography (EMG(dia)). The obstructed breaths resulted in a prolonged inspiratory and expiratory time, an increase in EMG(dia) amplitude, and a more negative P(es) compared with control breaths. Neurons labeled with c-Fos were found in brain stem and suprapontine nuclei, with a significant increase in c-Fos expression for the occluded experimental group compared with the control groups in the nucleus ambiguus, nucleus of the solitary tract, lateral parabrachial nucleus, and periaqueductal gray matter. The results of this study demonstrate tracheal occlusion-elicited activation of neurons in brain stem respiratory nuclei and neural areas involved in stress responses and defensive behaviors, suggesting that these neurons mediate the load compensation breathing pattern response and may be part of the neural pathway for respiratory mechanosensation.