title: 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.
authors.affiliation: Department of Physiology, University of the Witwatersrand Medical School, 7 York Road, Parktown 2193, South Africa. 127andy@chiron.wits.ac.za
authors.forename: A
authors.initials: A
authors.lastname: Fuller
authors.forename: S K
authors.initials: SK
authors.lastname: Maloney
authors.forename: P R
authors.initials: PR
authors.lastname: Kamerman
authors.forename: G
authors.initials: G
authors.lastname: Mitchell
authors.forename: D
authors.initials: D
authors.lastname: Mitchell
mesh_terms: D000818:Animals; D001158:Arteries; D001790:Blood Physiological Phenomena; D001831:Body Temperature / Q000502:physiology*; D001921:Brain / Q000502:physiology*; D002940:Circadian Rhythm; D004777:Environment; D018397:Equidae / Q000502:physiology*; D005334:Fever / Q000503:physiopathology; D018882:Heat Stress Disorders / Q000503:physiopathology; D009043:Motor Activity / Q000502:physiology; D013696:Temperature