Brain thermal inertia, but no evidence for selective brain cooling, in free-ranging western grey kangaroos (Macropus fuliginosus)

Marsupials reportedly can implement selective brain cooling despite lacking a carotid rete. We measured brain (hypothalamic) and carotid arterial blood temperatures every 5 min for 5, 17, and 63 days in spring in three free-living western grey kangaroos. Body temperature was highest during the night...

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Bibliographic Details
Published in:Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology Biochemical, systemic, and environmental physiology, 2009-04, Vol.179 (3), p.241-251
Main Authors: Maloney, Shane K, Fuller, Andrea, Meyer, Leith C. R, Kamerman, Peter R, Mitchell, Graham, Mitchell, Duncan
Format: Article
Language:English
Subjects:
Animal Physiology
Animals
Biochemistry
Biomedical and Life Sciences
Biomedicine
Blood
Body Temperature
Body Temperature Regulation - physiology
Brain
Brain - anatomy & histology
Brain - physiology
Carotid arteries
Cooling
Female
Heat
Human Physiology
Life Sciences
Macropodidae - physiology
Male
Marsupials
Original Paper
Physiology
Sinuses
Time Factors
Weather
Western Australia
Zoology
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Summary:Marsupials reportedly can implement selective brain cooling despite lacking a carotid rete. We measured brain (hypothalamic) and carotid arterial blood temperatures every 5 min for 5, 17, and 63 days in spring in three free-living western grey kangaroos. Body temperature was highest during the night, and decreased rapidly early in the morning, reaching a nadir at 10:00. The highest body temperatures recorded occurred sporadically in the afternoon, presumably associated with exercise. Hypothalamic temperature consistently exceeded arterial blood temperature, by an average 0.3°C, except during these afternoon events when hypothalamic temperature lagged behind, and was occasionally lower than, the simultaneous arterial blood temperature. The reversal in temperatures resulted from the thermal inertia of the brain; changes in the brain to arterial blood temperature difference were related to the rate of change of arterial blood temperature on both heating and cooling (P < 0.001 for all three kangaroos). We conclude that these data are not evidence for active selective brain cooling in kangaroos. The effect of thermal inertia on brain temperature is larger than might be expected in the grey kangaroo, a discrepancy that we speculate derives from the unique vascular anatomy of the marsupial brain.
ISSN:0174-1578
1432-136X
DOI:10.1007/s00360-008-0308-2