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First published online June 29, 2007
Journal of Experimental Biology 210, 2472-2480 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.003822

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The vagus nerve mediates cardio-respiratory coupling that changes with metabolic demand in a temperate nototheniod fish

Hamish A. Campbell^1,2 and Stuart Egginton^1,*

¹ Department of Physiology, University of Birmingham, PO Box 363, Edgbaston, Birmingham, B15 2TT, UK
² Portobello Marine Laboratory, University of Otago, Dunedin, New Zealand

^* Author for correspondence (e-mail: s.egginton{at}bham.ac.uk)

Accepted 25 April 2007

The extent and efficiency of cardio-respiratory coupling (CRC) in teleost fishes is unclear. We simultaneously monitored heart rate (f_H) and ventilation rate (f_V) in Paranotothenia angustata, and applied modern power spectral analysis (PSA) mathematics to examine the rate association under varying levels of oxygen consumption (_O2). At low _O2 (0.94 mmol O₂ kg^–1 h^–1) there was a correspondingly low f_H and f_V (25.5±2.4 min^–1 and 29.2±2.6 min^–1, respectively). Heart rate variability (HRV) consisted of oscillatory components caused by periodic vagal inhibition of the heart beat. Cross-spectral analysis showed that f_H and f_V were coupled, with the response lag in heart beat being approximately one seventh of each ventilation cycle. Ingestion of food elevated _O2 (1.99±0.02 mmol O₂ kg^–1 h^–1) and increased both f_H and f_V (45±2.3 min^–1 and 52±2 min^–1, respectively, P<0.05), but CRC was maintained despite a reduction in HRV. The elevated stress caused by handling and placement of fish into respirometry chambers raised f_H and f_V to a similar rate as observed after feeding, although high-frequency (>0.2 Hz) oscillations in f_H were lacking and _O2 was lower (1.82±0.03 mmol O₂ kg^–1 h^–1, P<0.05). Subsequent cardiac vagotomy elevated f_H and f_V (55.5±0.8 min^–1 and 48.2±0.7 min^–1, respectively; P<0.05) but abolished all HRV and CRC, although _O2 was significantly less for a given f_H and f_V compared to intact fish. Thus, P. angustata exhibits vagally mediated CRC, and the association between f_H and f_V varies according to oxygen demand.

Key words: power spectral analysis, heart rate variability, ventilation rate variability, ECG

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