Afferent signal oscillations and the control of breathing in Bufo marinus

While we often think of breathing as a regular and rhythmic motor pattern, even a casual examination reveals that intermittent or episodic breathing is the rule rather than the exception in air breathing fishes, amphibians, reptiles and a number of primitive mammals. Pathological conditions in humans can also produce episodic breathing patterns, the most common being sleep apneas, which can also occur in healthy individuals. Episodic breathing can be generated by constant afferent input, but it has long been hypothesized that oscillations in afferent activity from peripheral chemoreceptors contain information that adaptively modifies breathing.;In this study, the role of sensory oscillations (as opposed to average levels) in modulating the breathing pattern and mechanics was investigated in Bufo marinus, the marine toad. The resting ventilatory behavior of Bufo was described and discussed to highlight its ability to generate afferent signal variability, which was the main object of this study as it investigated its relationship to the control of breathing. The main source of oscillations in chemoreceptor information are long apneas, which are a common feature of Bufo's natural ventilatory behavior. The oscillations in blood gases generated by long apneas were quantified. Unidirectional ventilation was used as a tool to remove oscillations from respiratory-relevant afferent sources.;The results show that afferent signal oscillations are relevant for the control of breathing in toads, and their main effects are on the variability of the ventilatory output. The artificial reintroduction of oscillations in blood oxygen levels leads to recovery of part of the ventilatory variability lost with the unidirectional ventilation.