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Ultradian oscillations in brain temperature in sheep: implications for thermoregulatory control?

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Abstract

We compared body temperature patterns and selective brain cooling (SBC) in eight adult female sheep in an indoor (22–25 °C) and outdoor (mean ~ 21 °C) environment, by measuring brain, carotid arterial, and jugular venous blood temperatures at 5-min intervals using implanted data loggers. To investigate whether ultradian oscillations in brain temperature had thermoregulatory consequences for the sheep, we determined the cranial arterio-venous (AV) temperature difference as an indicator of respiratory evaporative heat loss (REHL). The 24-h pattern of SBC was similar in both environments, despite carotid blood temperature fluctuating 0.4 °C more outdoors compared to indoors. The sheep employed SBC more often during the night than during the day, but SBC was abolished at intervals of 1–3 h throughout the 24-h period. The suppression of SBC appeared to be associated with events that increased sympathetic nervous system activity, including shifts between stages of sleep. Short-term changes (over 5-min) in brain temperature were positively correlated with changes in the AV temperature difference 5 min later, and negatively correlated with changes in carotid temperature 10 min later. These data support the idea that increases in brain temperature modulate thermoregulation by increasing REHL, which leads to a decrease in carotid blood temperature. Ultradian oscillations in core temperature of sheep, therefore, appear to arise as a consequence of frequent brain temperature changes invoked by non-thermal inputs, in animals housed both in indoor and outdoor environments.

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Data will be made available upon request to the corresponding author to any researcher wishing to use them for non-commercial purposes.

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Acknowledgements

We thank the staff of the Central Animal Service at the University of the Witwatersrand for their care of the animals, and Brenda de Witt, Linda Fick, Peter Kamerman and Lennox Nqobo for help with experiments.

Funding

This work was funded by the National Research Foundation, South Africa, the Iris Ellen Hodges Trust, and the Friedel Sellschop to A Fuller award from the University of the Witwatersrand.

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Authors and Affiliations

  1. Brain Function Research Group, School of Physiology, Faculty of Health Sciences, University of the Witwatersrand Medical School, 7 York Road, Parktown, Johannesburg, 2193, South Africa

    Andrea Fuller, Robyn S. Hetem, Leith C. R. Meyer, Duncan Mitchell & Shane K. Maloney

  2. School of Animal, Plant and Environmental Sciences, University of the Witwatersrand, Jan Smuts Avenue, Johannesburg, South Africa

    Robyn S. Hetem

  3. Centre for Veterinary Wildlife Studies and Department of Paraclinical Sciences, Faculty of Veterinary Science, University of Pretoria, Soutpan Road, Pretoria, South Africa

    Leith C. R. Meyer

  4. School of Human Sciences, University of Western Australia, Crawley, Perth, 6009, Australia

    Duncan Mitchell & Shane K. Maloney

Authors
  1. Andrea Fuller
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  2. Robyn S. Hetem
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  3. Leith C. R. Meyer
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  4. Duncan Mitchell
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  5. Shane K. Maloney
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Contributions

AF and SKM: conception and design of research. AF, RSH, LCRM, DM and SKM: performed experiments. AF: analyzed data. AF, RSH, LCRM, DM and SKM: interpreted results of experiments. AF: drafted manuscript. RSH, LCRM, DM and SKM: edited and revised manuscript. AF, RSH, LCRM, DM and SKM: approved final version of manuscript.

Corresponding author

Correspondence to Andrea Fuller.

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Conflict of interest

No conflicts of interest, financial or otherwise, are declared by the authors.

Ethical approval

All applicable international, national, and/or institutional guidelines for the care and use of animals were followed. All procedures performed in this study involving animals were in accordance with the ethical standards of the institution or practice at which the studies were conducted (Animal Research Ethics Committee, University of the Witwatersrand, number 2004/94/5).

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Communicated by G. Heldmaier.

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Fuller, A., Hetem, R.S., Meyer, L.C.R. et al. Ultradian oscillations in brain temperature in sheep: implications for thermoregulatory control?. J Comp Physiol B 190, 125–138 (2020). https://doi.org/10.1007/s00360-019-01248-2

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  • DOI: https://doi.org/10.1007/s00360-019-01248-2

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