Identification of lung priming area in frog brainstem, adjacent to the lung oscillator, distinct from the buccal oscillator: homologous to RTN/pFRG?

Abstract

Data from mammals and frogs suggest tetrapods have an anatomically‐discrete inspiratory oscillator, necessary and sufficient for expression of the powerstroke phase of lung inflation (preBötzinger Complex in mammals; Lung Area in frogs). In mammals a second Pre‐Inspiratory / late‐phase expiratory oscillator has been hypothesized; this oscillator likely resides in the retrotrapezoid/parafacial respiratory group (RTN/pFRG) and is “conditional”, recruited during high respiratory demand. In isolated frog brainstems, lung bursts often have a powerstroke and priming phase. Though the priming phase is always observed with a subsequent powerstroke, the priming phase is “conditional”: powerstrokes can occur without a priming phase.Here we identify a region of the frog brainstem necessary and sufficient for the priming phase. This priming area is adjacent to the area that produces the powerstroke (between CNVII‐IX) and distinct from the buccal area (caudal of CN X). Using AMPA microinjections to locally excite the priming area, we demonstrate ectopic priming bursts uncoupled from powerstroke bursts. We propose the priming and powerstroke areas are homologous to the PreI and PreBötC, respectively. We further postulate that rhombomeric differences may be explained by a “gene cassette” for air breathing rhythmogenesis, turned on in different rhombomeres in different clades. Work funded by NSERC.