title: Hypoxia switches episodic breathing to singlet breathing in red-eared slider turtles (Trachemys scripta) via a tropisetron-sensitive mechanism.
abstract: Hypoxia-induced changes in the chelonian breathing pattern are poorly understood. Thus, breathing was measured in freely swimming adult red-eared slider turtles breathing air prior to breathing nitrogen for 4h. Ventilation increased 10-fold within 10min due to increased breath frequency and tidal volume. Breaths/episode decreased by ∼50% within after 1h of hypoxia while the number of singlet breaths increased from 3.1±1.6singlets/h to a maximum of 66.1±23.5singlets/h. Expiratory and inspiratory duration increased during hypoxia. For doublet and triplet breaths, expiratory duration increased during the first breath only, while inspiratory duration increased for all breaths. Tropisetron (5-HT3 receptor antagonist, 5mg/kg) administration prior to hypoxia attenuated the hypoxia-induced increase in singlet breath frequency. Along with results from previous in vitro studies, this study suggests that 5-HT3 receptor activation may be required for the hypoxia-induced increase in singlet breathing pattern in red-eared slider turtles.
authors.affiliation: Department of Comparative Biosciences, School of Veterinary Medicine University of Wisconsin, Madison, WI 53706, USA. Electronic address: johnsons@svm.vetmed.wisc.edu.
authors.forename: Stephen M
authors.initials: SM
authors.lastname: Johnson
authors.affiliation: Department of Comparative Biosciences, School of Veterinary Medicine University of Wisconsin, Madison, WI 53706, USA.
authors.forename: Ashley R
authors.initials: AR
authors.lastname: Krisp
authors.affiliation: Department of Comparative Biosciences, School of Veterinary Medicine University of Wisconsin, Madison, WI 53706, USA.
authors.forename: Michelle E
authors.initials: ME
authors.lastname: Bartman
mesh_terms: D000818:Animals; D000889:Anti-Arrhythmia Agents / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D005260:Female; D000860:Hypoxia / Q000503:physiopathology*; D007211:Indoles / Q000494:pharmacology*; D008297:Male; D009584:Nitrogen / Q000494:pharmacology; D012123:Pulmonary Ventilation / Q000187:drug effects / Q000502:physiology*; D012119:Respiration / Q000187:drug effects*; D013997:Time Factors; D000077526:Tropisetron; D014426:Turtles / Q000502:physiology*
chemical_list: D000889:Anti-Arrhythmia Agents; D007211:Indoles; D000077526:Tropisetron; D009584:Nitrogen
keywords: 5-HT(3) receptors; Chelonian; Episodic breathing; Reptile; Respiratory motor control; Serotonin