Absence of selective brain cooling in free-ranging zebras in their natural habitat.
Abstract: We used implanted miniature data loggers to measure brain and arterial blood temperatures in three free-ranging zebras (Equus burchelli) in their natural habitat, every 5 min for 9 days. The animals experienced globe temperatures exceeding 40 C, and radiant heat load of about 1000 W m-2. Arterial blood exhibited a moderate amplitude (1.7 C) nychthemeral rhythm, with an acrophase at 19.00 h and a nadir late in the morning, at 10.00 h. Brain temperature consistently exceeded blood temperature, on average by 0.2-0.4 C, and changes in brain temperature closely tracked changes in blood temperature. There was no evidence of selective brain cooling, even during the hyperthermia which followed surgery or that associated with intense, short-duration exercise. The relationship between brain and arterial blood temperatures in free-ranging zebras was unlike that reported for horses in the laboratory. Our results do not support the view that mammals lacking a carotid rete can achieve selective brain cooling.
Publication Date: 2001-02-07 PubMed ID: 10751518
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- Journal Article
- Research Support
- Non-U.S. Gov't
Summary
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This study explores brain cooling in zebras, using implanted data loggers to monitor brain and blood temperatures over nine days. Contrary to certain previous studies, it was found that the zebra’s brain temperature consistently exceeded blood temperature and there was no evidence of selective brain cooling despite testing in high-temperature conditions.
Research Methodology
- The research was conducted by implanting miniature data loggers in three free-ranging zebras (Equus burchelli) living in their natural habitat.
- The data loggers were programmed to record the brain and arterial blood temperatures of the zebras every 5 minutes for a total period of 9 days.
- The zebras were exposed to global temperatures surpassing 40 C and radiant heat load of approximately 1000 W m-2 during the study period.
Results and Findings
- The arterial blood of the zebras showcased a moderate amplitude (1.7 C) nychthemeral rhythm, peaking at 19.00 h and hitting a low point late in the morning at 10.00 h.
- Contrary to expectations, brain temperature was consistently found to be higher than blood temperature, on average by 0.2-0.4 C.
- Changes in brain temperature were found to closely align with changes in blood temperature in the zebras.
- No evidence of selective brain cooling was found, even during hyperthermia following surgery or after short, intense bouts of exercise.
- This lack of selective brain cooling in the zebras, even when exposed to extremely high temperatures, contradicted previous studies conducted on horses in a laboratory setting.
Implications
- The major implication of this study is that it challenges the notion that mammals lacking a carotid rete (a network of arteries and veins in the neck) can perform selective brain cooling.
- The significant difference between the relationship of brain and arterial blood temperatures observed in free-ranging zebras, as compared to horses in laboratory studies, hints at the possibility that environmental factors or the zebras’ response to natural conditions could influence this phenomenon.
Cite This Article
APA
Fuller A, Maloney SK, Kamerman PR, Mitchell G, Mitchell D.
(2001).
Absence of selective brain cooling in free-ranging zebras in their natural habitat.
Exp Physiol, 85(2), 209-217.
Publication
Researcher Affiliations
- Department of Physiology, University of the Witwatersrand Medical School, 7 York Road, Parktown 2193, South Africa. 127andy@chiron.wits.ac.za
MeSH Terms
- Animals
- Arteries
- Blood Physiological Phenomena
- Body Temperature / physiology
- Brain / physiology
- Circadian Rhythm
- Environment
- Equidae / physiology
- Fever / physiopathology
- Heat Stress Disorders / physiopathology
- Motor Activity / physiology
- Temperature
Citations
This article has been cited 7 times.- Riek A, Stölzl A, Marquina Bernedo R, Ruf T, Arnold W, Hambly C, Speakman JR, Gerken M. Energy expenditure and body temperature variations in llamas living in the High Andes of Peru.. Sci Rep 2019 Mar 11;9(1):4037.
- Strauss WM, Hetem RS, Mitchell D, Maloney SK, O'Brien HD, Meyer LCR, Fuller A. Body water conservation through selective brain cooling by the carotid rete: a physiological feature for surviving climate change?. Conserv Physiol 2017;5(1):cow078.
- Hetem RS, Strauss WM, Fick LG, Maloney SK, Meyer LC, Shobrak M, Fuller A, Mitchell D. Variation in the daily rhythm of body temperature of free-living Arabian oryx (Oryx leucoryx): does water limitation drive heterothermy?. J Comp Physiol B 2010 Oct;180(7):1111-9.
- Wilson WA, O'Riain MJ, Hetem RS, Fuller A, Fick LG. Winter body temperature patterns in free-ranging Cape ground squirrel, Xerus inauris: no evidence for torpor.. J Comp Physiol B 2010 Oct;180(7):1099-110.
- Maloney SK, Fuller A, Meyer LC, Kamerman PR, Mitchell G, Mitchell D. Brain thermal inertia, but no evidence for selective brain cooling, in free-ranging western grey kangaroos (Macropus fuliginosus).. J Comp Physiol B 2009 Apr;179(3):241-51.
- Mitchell G, Lust A. The carotid rete and artiodactyl success.. Biol Lett 2008 Aug 23;4(4):415-8.
- Mitchell G, Fuller A, Maloney SK, Rump N, Mitchell D. Guttural pouches, brain temperature and exercise in horses.. Biol Lett 2006 Sep 22;2(3):475-7.
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