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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

View larger version (6K): [in this window] [in a new window]   Fig. 1. Changes in O2 and associated fH (filled symbols) and fV (open symbols) measured simultaneously for 10 min three times daily in 12 N. angustata (mean ± s.e.m., n=12, N=36 observations), subjected to the following sequential measurements. Circles, recordings made for 120 h following initial anesthesia, surgery and placement in the respirometry chamber; squares, recordings taken for the subsequent 120 h after ingestion of a 5%b.m. food ration; triangles, daily recordings made in the same fish after it had returned to pre-fed values and had then undergone anaesthesia, bilateral section of the vagal nerve and placement back in the respirometry chamber.

View larger version (21K): [in this window] [in a new window]   Fig. 2. Scattergram plots of 256 consecutive heart beat intervals (R-R) and ventilation cycles (V-V) plotted against its preceding interval (n–1). All plots are from a single individual: (A) with a high O2 due to surgery and placement in the respirometer; (B) a low O2 after 120 h undisturbed starvation; (C) a high O2 due to ingestion of a 5%b.m. ration; (D) a high O2 due to bilateral vagotomy. Each graph is fitted with an ellipse and axis orientated with the line of identity. Long-term heart rate variability runs along the diagonal axis from the origin (OA), and beat-to-beat variations occur along the normal to the axis maxima (MA).

View larger version (43K): [in this window] [in a new window]   Fig. 3. Power spectra calculated using the discrete FT from raw ECG traces containing either 128 consecutive heart beats (black spectra) or ventilation cycles (grey spectra). All plots are from the same individual. (A) Spectra generated when O2 (1.8 mmol O2 kg–1 h–1), fH (49 min–1) and fV (47 min–1) were high due to surgery and placement in a respirometer; the peaks are very narrow, showing very little variability in either fH or fV. (B) After a period of no disturbance and starvation, O2 (0.91 mmol O2 kg–1 h–1), fH (25 min–1) and fV (28 min–1) were reduced dramatically and the fH spectral peaks were spread within the bandwidth. (C) Ingestion of a 5%b.m. ration resulted in a very high O2 (2.11 mmol O2 kg–1 h–1), fH (43 min–1) and fV (47 min–1); the spectral peaks reduced in amplitude but remained with a broad bandwidth. (D) Bilateral vagotomy resulted in a moderately high O2 (1.41 mmol O2 kg–1 h–1), fH (53 min–1) and fV (53 min–1), and the spectral peaks were very narrow, indicating little variability.

View larger version (18K): [in this window] [in a new window]   Fig. 4. Spectra from cross-spectral analysis, describing the coherence (solid lines) and phase relationship (broken lines) of frequency oscillations between fH and fV. All plots are from a single individual with: (A) a high O2 due to surgery and placement in a respirometer; (B) a low O2 after 120 h undisturbed starvation; (C) a high O2 due to ingestion of a 5%b.m. ration; (D) a high O2 due to bilateral vagotomy.