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The origin of air breathing in vertebrates: turn (on) your head and cough
Author(s) -
Hoffman Megan,
Taylor Barbara E.,
Harris Michael B.
Publication year - 2013
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.27.1_supplement.1137.20
Subject(s) - hypercapnia , ventilation (architecture) , breathing , rhythm , chemoreceptor , central pattern generator , biology , lamprey , respiratory system , lung , basal (medicine) , anatomy , medicine , endocrinology , mechanical engineering , biochemistry , receptor , fishery , insulin , engineering
Air breathing in tetrapods involves a centrally generated rhythmic activation of respiratory muscles to ventilate a lung, and modulation of this rhythm by central CO 2 ‐sensitive chemoreceptors that match ventilation to metabolic demands. The tetrapod lung arose in primitive air‐breathing fish. The origins of the central rhythm generator and chemoreceptor(s) are unknown. We propose that these critical elements were present in basal vertebrates and were exapted for air breathing with the evolution of the lung. Lamprey represent the basal vertebrate form and as larvae (ammocoetes) are aquatic burrow dwelling filter feeders. We propose that a behavior characterized as “cough” in lamprey is the basis for subsequent evolution of air breathing, and test the hypothesis that the centrally generated cough is stimulated by CO 2 . Ammocetes in vivo and isolated brainstems in vitro were exposed to hypercapnia. Ammocetes responded with a dose dependant increase in the frequency of spontaneous cough. Brainstems in vitro also produced the cough motor pattern, illustrating that cough results from a centrally CO 2 ‐sensitive rhythm generator. We conclude that a central CO 2 ‐sensitive chemoreceptor and central rhythm generator were present in basal vertebrates. We propose that, with the evolution of the lung, CO 2 ‐sensitive cough is exapted to form the basis for air breathing common to air‐breathing tetrapods. Supported by NSFIOS‐1022442