Changes in breathing pattern mediated by intrapulmonary CO2 receptors in chickens.

Area of Science:

• Respiratory Physiology
• Neuroscience
• Animal Models

Background:

• Ventilation control is crucial for maintaining homeostasis.
• The role of intrapulmonary CO2 receptors in respiratory reflexes was previously suggested but not fully elucidated.
• Arterial chemoreceptors are known to influence ventilation.

Purpose of the Study:

• To investigate the role of intrapulmonary CO2 receptors in controlling breathing patterns.
• To determine if arterial chemoreceptors are involved in the observed ventilatory responses to CO2.
• To identify the specific mechanisms by which intrapulmonary CO2 receptors affect respiratory timing.

Main Methods:

• Whole-body plethysmography was used to measure ventilation in unanesthetized, tracheostomized chickens.
• Inspired CO2 fractions were manipulated to deliver pulses of fresh air.
• A novel method for denervating carotid bodies was developed and employed to eliminate arterial chemoreflexes.

Main Results:

• Inspiration and expiration durations were dependent on the timing of fresh air pulses.
• Carotid body denervation abolished responses to intravenous NaCN and nitrogen breaths, confirming the removal of arterial chemoreflexes.
• Even after carotid body denervation, the ventilatory response to CO2 pulses persisted, with inspiration and expiration durations still influenced by pulse timing.

Conclusions:

• Intrapulmonary CO2 receptors (IPC) are the primary mediators of the studied respiratory reflexes.
• IPC directly influence the phase-switching mechanisms of breathing on a breath-by-breath basis.
• These findings provide strong evidence for the role of IPC in respiratory control, independent of arterial chemoreceptors.