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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
The vagus nerve mediates cardio-respiratory coupling that changes with metabolic demand in a temperate nototheniod fish
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
(fH) and ventilation rate
(fV) 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 kg1 h1) there was a
correspondingly low fH and fV
(25.5±2.4 min1 and 29.2±2.6
min1, respectively). Heart rate variability (HRV) consisted
of oscillatory components caused by periodic vagal inhibition of the heart
beat. Cross-spectral analysis showed that fH and
fV 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 kg1
h1) and increased both fH and
fV (45±2.3 min1 and 52±2
min1, 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 fH
and fV to a similar rate as observed after feeding,
although high-frequency (>0.2 Hz) oscillations in fH
were lacking and
O2 was lower
(1.82±0.03 mmol O2 kg1
h1, P<0.05). Subsequent cardiac vagotomy
elevated fH and fV (55.5±0.8
min1 and 48.2±0.7 min1,
respectively; P<0.05) but abolished all HRV and CRC, although
O2 was
significantly less for a given fH and
fV compared to intact fish. Thus, P. angustata
exhibits vagally mediated CRC, and the association between
fH and fV varies according to oxygen
demand.
Key words: power spectral analysis, heart rate variability, ventilation rate variability, ECG
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