Respiratory Rhythms in the amphibian brainstem

A unique respiratory situation arises where two respiratory rhythms transiently co-exist in the tadpole as it metamorphoses from water to air breathing animal . These two rhythms, the gill and lung rhythms are preserved in the isolated intact tadpole brainstem and can be recorded from cranial (CN: V, VII, IX, X) and spinal nerves (SN: II). Throughout development, low amplitude rhythmic bursts from CN VII describe gill rhythms, whereas high amplitude rhythmic bursts observed from both CN VII and SN II describe lung rhythms. These network changes make the isolated intact brainstem of the bullfrog tadpole, Rana catesbeiana , an elegant model for studying the complex developmental interaction between the two oscillatory networks.

Despite being well documented that the isolated intact tadpole brainstem spontaneously generates both gill and lung rhythms in vitro , little is known about the: (i) anatomical, (ii) electrophysiological, (iii) neurochemical make-up of these two circuits, or (iv) has the relationship of the gill and lung rhythm in amphibians to eupnea and gasping in mammals been well established.

This study is important as it addresses three key issues: (a) the location, (b) the interaction, and (c) the mechanisms of generation of gill and lung rhythms. Analysis of these three issues will broaden our knowledge regarding the interaction between distinct neural circuits providing insight into the mechanism underlying more complex patterns of behavior. These data will aid in understanding how the amphibian gill and lung rhythm is evolutionarily related to eupnea and gasping in mammals.