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Evolution of Air-Breathing and Central CO2/H+ Respiratory Chemosensitivity: New Insights From an Old Fish?

2000; The Company of Biologists; Volume: 203; Issue: 22 Linguagem: Inglês

10.1242/jeb.203.22.3505

1477-9145

Richard J. A. Wilson, Michael B. Harris, John E. Remmers, Steven F. Perry,

Zebrafish Biomedical Research Applications

ABSTRACT While little is known of the origin of air-breathing in vertebrates, primitive air breathers can be found among extant lobe-finned (Sarcopterygii) and ray-finned (Actinopterygii) fish. The descendents of Sarcopterygii, the tetrapods, generate lung ventilation using a central pattern generator, the activity of which is modulated by central and peripheral CO2/H+ chemoreception. Air-breathing in Actinopterygii, in contrast, has been considered a ‘reflexive’ behaviour with little evidence for central CO2/H+ respiratory chemoreceptors. Here, we describe experiments using an in vitro brainstem preparation of a primitive air-breathing actinopterygian, the longnose gar Lepisosteus osseus. Our data suggest (i) that gill and air-breathing motor patterns can be produced autonomously by the isolated brainstem, and (ii) that the frequency of the air-breathing motor pattern is increased by hypercarbia. These results are the first evidence consistent with the presence of an air-breathing central pattern generator with central CO2/H+ respiratory chemosensitivity in any primitive actinopterygian fish. We speculate that the origin of the central neuronal controller for air-breathing preceded the divergence of the sarcopterygian and actinopterygian lineages and dates back to a common air-breathing ancestor.