title: Autonomic control of post-air-breathing tachycardia in Clarias gariepinus (Teleostei: Clariidae).
abstract: The African catfish (Clarias gariepinus) is a teleost with bimodal respiration that utilizes a paired suprabranchial chamber located in the gill cavity as an air-breathing organ. Like all air-breathing fishes studied to date, the African catfish exhibits pronounced changes in heart rate (f H) that are associated with air-breathing events. We acquired f H, gill-breathing frequency (f G) and air-breathing frequency (f AB) in situations that require or do not require air breathing (during normoxia and hypoxia), and we assessed the autonomic control of post-air-breathing tachycardia using an infusion of the β-adrenergic antagonist propranolol and the muscarinic cholinergic antagonist atropine. During normoxia, C. gariepinus presented low f AB (1.85 ± 0.73 AB h(-1)) and a constant f G (43.16 ± 1.74 breaths min(-1)). During non-critical hypoxia (PO2 = 60 mmHg), f AB in the African catfish increased to 5.42 ± 1.19 AB h(-1) and f G decreased to 39.12 ± 1.58 breaths min(-1). During critical hypoxia (PO2 = 20 mmHg), f AB increased to 7.4 ± 1.39 AB h(-1) and f G decreased to 34.97 ± 1.78 breaths min(-1). These results were expected for a facultative air breather. Each air breath (AB) was followed by a brief but significant tachycardia, which in the critical hypoxia trials, reached a maximum of 143 % of the pre-AB f H values of untreated animals. Pharmacological blockade allowed the calculation of cardiac autonomic tones, which showed that post-AB tachycardia is predominantly regulated by the parasympathetic subdivision of the autonomic nervous system.
authors.affiliation: Department of Zoology and Botany, São Paulo State University (UNESP), Cristóvão Colombo Street, 2265, São José Do Rio Preto, SP, 15054-000, Brazil.
authors.forename: Mariana Teodoro
authors.initials: MT
authors.lastname: Teixeira
authors.forename: Vinicius Araújo
authors.initials: VA
authors.lastname: Armelin
authors.forename: Augusto Shinya
authors.initials: AS
authors.lastname: Abe
authors.forename: Francisco Tadeu
authors.initials: FT
authors.lastname: Rantin
authors.forename: Luiz Henrique
authors.initials: LH
authors.lastname: Florindo
mesh_terms: D000319:Adrenergic beta-Antagonists / Q000494:pharmacology; D000388:Air; D000818:Animals; D001285:Atropine; D002397:Catfishes / Q000502:physiology*; D004562:Electrocardiography; D005260:Female; D005880:Gills / Q000502:physiology; D006339:Heart Rate / Q000187:drug effects; D000860:Hypoxia; D008297:Male; D018727:Muscarinic Antagonists / Q000494:pharmacology; D011433:Propranolol; D012119:Respiration / Q000187:drug effects; D013610:Tachycardia / Q000503:physiopathology*
chemical_list: D000319:Adrenergic beta-Antagonists; D018727:Muscarinic Antagonists; D001285:Atropine; D011433:Propranolol