Episodic breathing in frogs: Sonverging hypotheses on neural control of respiration in air breathing vertebrates

Abstract

SYNOPSIS. The episodic, or intermittent, breathing of frogs and many ectothermic vertebrates results in important fluctuations of arterial blood gases. This pattern of breathing differs from the rhythmic and continuous alternation of inspiration observed in most homeotherms, which maintain O2 and CO2 levels within narrow ranges. These differences in pattern of breathing indicate that the respiratory control systems of ectotherms and homeotherms differ substantially. The results of recent studies using in vitro brainstemspinal cord preparations of adult frogs and premetamorphic tadpoles (Rana catesbeiana and Rana pipiens) demonstrate, however, that the mechanisms for rhythm generation and pattern formation described previously for mammals are also key features of the respiratory control system of frogs. These findings therefore support the hypothesis that the respiratory control system is highly conserved amongst air breathing vertebrates, whether they breathe continuously or episodically.