CHOLINERGIC BRADYCARDIA TEMPERATURE INDUCED IN ANTARCTIC FISHES NOTOTHENIA NEGLECTA AND CHAENOCEPHALUS ACERATUS (19th Symposium on Polar Biology)

• Main Authors: Wilma Pereira BASTOS-RAMOS, Neuza Maria Ferraz de Mello GONCALVES, Metry BACILA
• Format: Report
• Language: English
• Published: Proceeding 1998
• Subjects: Antarctic fish; cholinergic bradycardia; fish cardiac arrest; Notothenia neglecta; Chaenocephalus aceratus; Antarctic; The Antarctic; Antarc*; Polar Biology; Proceedings of the NIPR Symposium on Polar Biology
• Online Access: https://nipr.repo.nii.ac.jp/?action=repository_uri&item_id=5363; http://id.nii.ac.jp/1291/00005363/; https://nipr.repo.nii.ac.jp/?action=repository_action_common_download&item_id=5363&item_no=1&attribute_id=18&file_no=1

The cardiac responses of the Antarctic fishes Notothema neglecta and Chaenocephalus aceratus to acute changes of temperature were studied. The fishes were surgically prepared for electrocardiogram (ECG) recording and placed in a three hour experiment in an experimental chamber containing aerated marine water. The temperature was controlled from +2℃ to -1.8℃. Presence of nitrites in the fish bath was monitored. Atropine and epinephrine were administered into the abdominal cavity through a surgically inserted cannula. Blood samples were taken at initial +2.0℃ and final -1.8℃ for cholmesterase assay. Results showed that: 1. A temperature decrease from +2.0°C to～-1.8℃ significantly depressed cardiac rate, from 26.9±27 to 5.2±1.4 beats min^<-1> in N neglecta and from 19.0 to 3.0 beats min^<-1> in C aceratus. In one specimen of N. neglecta, a reversible cardiac arrest of 3.0mm was observed. ECG waves did not change during the experiments, except the QRS to QRS or the Q-T intervals at lower temperatures. Respiratory rate was not significantly influenced by temperature, 2. Return of temperature to +1.5/2.0℃ immediately ceased bradycardia, 3. Administration of atropme reversed bradycardia within 5 min; 4. Serum cholmesterase activity decreased at the lowest temperature; 5. Epinephrine neither influenced the cardiac rate at any temperature nor altered cardiac waves. Results demonstrate that severe bradycardia at subzero temperatures is not only an intrinsic cardiac response to cold, but an active one, due to the higher cholinergic tone, that was not observed in the resting state at +2.0℃. No adrenergic influence on heart chronotropism has been found.