Proceedings of The Physiological Society
University of Cambridge (2004) J Physiol 555P, C83
Investigating the control of heart rate variability in fishes using power spectral analysis
H.A. Campbell, E.W. Taylor*, W. Davison and S. Egginton
Department of Physiology and * School of Biological Sciences, University of Birmingham, UK and Department of Zoology, University of Canterbury, New Zealand
The intrinsic heart rate (fH) in fish, like all higher vertebrates, is modified on a beat-to-beat basis by the level of vagal activity. Power Spectral Analysis (PSA) is used clinically to explore this regulation of cardiac performance noninvasively (Sands et al. 1989), and we have adapted this application for use with fishes using a similar approach to that described previously (Altimiras et al. 1995).
ECG electrodes were implanted under MS222 anaesthesia (0.5g/l). Anaesthesia was maintained during surgery, then animals allowed to recover. Animals were humanely killed after the experiments. PSA applied to recordings of instantaneous heart rate from resting fish (Myoxocephalus scorpius) displayed dual spectral peaks (0.02 Hz and 0.05 Hz). The effects of minor surgery or vagotomy decreased the mean R-R interval from 2946 ± 232 ms to 1912 ± 87 ms (mean ± S.E.M., n = 5). The variability in beat to beat (R-R) interval, and both frequency peaks were also abolished temporarily by disturbance and permanently by bilateral cardiac vagotomy, suggesting that much of the regulation of heart rate was under parasympathetic, cholinergic control. Interestingly, the mean and standard deviation of R-R interval (SDRR) determined by cholinergic tonus showed a close correlation with oxygen consumption (MO2), indicating a high degree of cardio-respiratory coupling. This was further explored in 7 species of Antarctic fish, as the closely related Notothenioid group allows the physiological consequences of ecological differences between species to be evaluated without the difficulties posed by comparing fish with different phylogenetic backgrounds. Comparison between species showed that whilst mean fH and MO2 rates were significantly different (ANCOVA, P < 0.05), linear correlation between relative fH and MO2 were not. Furthermore, PSA analysis showed two underlying oscillations in the instantaneous heart rate, a higher frequency peak at 0.03-0.08 Hz that was fH dependent being similar in period between species, and a lower frequency peak at 0.02 Hz that was independent of fH. Thus the degree of cholinergic control on fH and heart rate variability was similar across the Antarctic species, but different from the closely related sub-Antarctic Paranotothenia angustata or the temperate Myoxocephalus scorpius which has a similar benthic habitat.
We conclude that cholinergic tonus on the fish heart shows retention of ancestral characteristics, with a degree of phenotypic plasticity that appears to be associated with species ecology.
This work was supported by NERC
Where applicable, experiments conform with Society ethical requirements