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Williams CL, Hindle AG. Field Physiology: Studying Organismal Function in the Natural Environment. Compr Physiol 2021; 11:1979-2015. [PMID: 34190338 DOI: 10.1002/cphy.c200005] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
Continuous physiological measurements collected in field settings are essential to understand baseline, free-ranging physiology, physiological range and variability, and the physiological responses of organisms to disturbances. This article presents a current summary of the available technologies to continuously measure the direct physiological parameters in the field at high-resolution/instantaneous timescales from freely behaving animals. There is a particular focus on advantages versus disadvantages of available methods as well as emerging technologies "on the horizon" that may have been validated in captive or laboratory-based scenarios but have yet to be applied in the wild. Systems to record physiological variables from free-ranging animals are reviewed, including radio (VHF/UFH) telemetry, acoustic telemetry, and dataloggers. Physiological parameters that have been continuously measured in the field are addressed in seven sections including heart rate and electrocardiography (ECG); electromyography (EMG); electroencephalography (EEG); body temperature; respiratory, blood, and muscle oxygen; gastric pH and motility; and blood pressure and flow. The primary focal sections are heart rate and temperature as these can be, and have been, extensively studied in free-ranging organisms. Predicted aspects of future innovation in physiological monitoring are also discussed. The article concludes with an overview of best practices and points to consider regarding experimental designs, cautions, and effects on animals. © 2021 American Physiological Society. Compr Physiol 11:1979-2015, 2021.
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Affiliation(s)
- Cassondra L Williams
- National Marine Mammal Foundation, San Diego, California, USA.,Department of Ecology and Evolutionary Biology, School of Biological Science, University of California Irvine, Irvine, California, USA
| | - Allyson G Hindle
- School of Life Sciences, University of Nevada Las Vegas, Las Vegas, Nevada, USA
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Botha A, Lease HM, Fuller A, Mitchell D, Hetem RS. Biologging subcutaneous temperatures to detect orientation to solar radiation remotely in savanna antelope. JOURNAL OF EXPERIMENTAL ZOOLOGY PART 2019; 331:267-279. [PMID: 31033258 DOI: 10.1002/jez.2267] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/22/2019] [Revised: 03/19/2019] [Accepted: 03/20/2019] [Indexed: 11/07/2022]
Abstract
Observations of animal thermoregulatory behavior are labor-intensive, and human presence may disturb the normal behavior of the animal. Therefore, we investigated whether a remote biologging technique could be used to detect orientation to solar radiation in savanna antelope. We predicted that when a mammal was orientated perpendicular to solar radiation, the subcutaneous temperature on the side of the body facing the sun would be greater than that on the opposite side, whereas when the mammal was orientated parallel to solar radiation, subcutaneous temperatures on both sides would be similar. A pilot study showed that the difference between left- and right-side temperatures under a pelt reflected orientation to solar radiation if a pelt-covered cylinder had been orientated for 15 min or longer. In addition, the rate of change in temperature difference could detect orientation that had changed within the previous 5 min. We implanted temperature-sensitive data loggers subcutaneously into the flanks of eight black (Connochaetes gnu) and eight blue (Connochaetes taurinus) wildebeest. By incorporating both the rate of change and subcutaneous temperature differences and excluding times when wildebeest were lying down, our predictions correctly matched behavioral observations of wildebeest orientation to solar radiation 71% of the time. Our technique tended to fail when wildebeest were lying down, wind speeds were high and the sun was overhead. But those are conditions in which the benefits of manipulating orientation to solar radiation is of diminishing importance to a free-living mammal. Therefore, subcutaneous temperatures provide physiologically relevant information on the importance of solar radiation to mammals.
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Affiliation(s)
- Arista Botha
- Brain Function Research Group, School of Physiology, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa
| | - Hilary M Lease
- Brain Function Research Group, School of Physiology, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa.,Department of Physiology, University of Arizona, Tucson, Arizona
| | - Andrea Fuller
- Brain Function Research Group, School of Physiology, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa
| | - Duncan Mitchell
- Brain Function Research Group, School of Physiology, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa.,School of Human Sciences, University of Western Australia, Perth, Australia
| | - Robyn S Hetem
- Brain Function Research Group, School of Physiology, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa.,School of Animal, Plant and Environmental Sciences, Faculty of Science, University of the Witwatersrand, Johannesburg, South Africa
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Chmura HE, Glass TW, Williams CT. Biologging Physiological and Ecological Responses to Climatic Variation: New Tools for the Climate Change Era. Front Ecol Evol 2018. [DOI: 10.3389/fevo.2018.00092] [Citation(s) in RCA: 34] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
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Mitchell D, Snelling EP, Hetem RS, Maloney SK, Strauss WM, Fuller A. Revisiting concepts of thermal physiology: Predicting responses of mammals to climate change. J Anim Ecol 2018; 87:956-973. [DOI: 10.1111/1365-2656.12818] [Citation(s) in RCA: 105] [Impact Index Per Article: 17.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2017] [Accepted: 01/17/2018] [Indexed: 11/29/2022]
Affiliation(s)
- Duncan Mitchell
- Brain Function Research Group; School of Physiology; Faculty of Health Sciences; University of the Witwatersrand; Johannesburg South Africa
- School of Human Sciences; University of Western Australia; Crawley WA Australia
| | - Edward P. Snelling
- Brain Function Research Group; School of Physiology; Faculty of Health Sciences; University of the Witwatersrand; Johannesburg South Africa
| | - Robyn S. Hetem
- Brain Function Research Group; School of Physiology; Faculty of Health Sciences; University of the Witwatersrand; Johannesburg South Africa
- School of Animal, Plant and Environmental Sciences; Faculty of Science; University of the Witwatersrand; Johannesburg South Africa
| | - Shane K. Maloney
- Brain Function Research Group; School of Physiology; Faculty of Health Sciences; University of the Witwatersrand; Johannesburg South Africa
- School of Human Sciences; University of Western Australia; Crawley WA Australia
| | - Willem Maartin Strauss
- Brain Function Research Group; School of Physiology; Faculty of Health Sciences; University of the Witwatersrand; Johannesburg South Africa
- Department of Environmental Science; University of South Africa; Johannesburg South Africa
| | - Andrea Fuller
- Brain Function Research Group; School of Physiology; Faculty of Health Sciences; University of the Witwatersrand; Johannesburg South Africa
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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? CONSERVATION PHYSIOLOGY 2017; 5:cow078. [PMID: 29383253 PMCID: PMC5778374 DOI: 10.1093/conphys/cow078] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 10/14/2016] [Revised: 12/16/2016] [Accepted: 01/03/2017] [Indexed: 06/07/2023]
Abstract
Some mammals have the ability to lower their hypothalamic temperature below that of carotid arterial blood temperature, a process termed selective brain cooling. Although the requisite anatomical structure that facilitates this physiological process, the carotid rete, is present in members of the Cetartiodactyla, Felidae and Canidae, the carotid rete is particularly well developed in the artiodactyls, e.g. antelopes, cattle, sheep and goats. First described in the domestic cat, the seemingly obvious function initially attributed to selective brain cooling was that of protecting the brain from thermal damage. However, hyperthermia is not a prerequisite for selective brain cooling, and selective brain cooling can be exhibited at all times of the day, even when carotid arterial blood temperature is relatively low. More recently, it has been shown that selective brain cooling functions primarily as a water-conservation mechanism, allowing artiodactyls to save more than half of their daily water requirements. Here, we argue that the evolutionary success of the artiodactyls may, in part, be attributed to the evolution of the carotid rete and the resulting ability to conserve body water during past environmental conditions, and we suggest that this group of mammals may therefore have a selective advantage in the hotter and drier conditions associated with current anthropogenic climate change. A better understanding of how selective brain cooling provides physiological plasticity to mammals in changing environments will improve our ability to predict their responses and to implement appropriate conservation measures.
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Affiliation(s)
- W. Maartin Strauss
- Brain Function Research Group, School of Physiology, Faculty of Heath Sciences, University of the Witwatersrand, Johannesburg, 2193, South Africa
- Department of Environmental Science, University of South Africa, Johannesburg, 1709, South Africa
| | - Robyn S. Hetem
- Brain Function Research Group, School of Physiology, Faculty of Heath Sciences, University of the Witwatersrand, Johannesburg, 2193, South Africa
- School of Animal, Plant and Environmental Sciences, Faculty of Science, University of the Witwatersrand, Johannesburg, 2050, South Africa
| | - Duncan Mitchell
- Brain Function Research Group, School of Physiology, Faculty of Heath Sciences, University of the Witwatersrand, Johannesburg, 2193, South Africa
- School of Anatomy, Physiology, and Human Biology, University of Western Australia, Perth, WA 6009, Australia
| | - Shane K. Maloney
- Brain Function Research Group, School of Physiology, Faculty of Heath Sciences, University of the Witwatersrand, Johannesburg, 2193, South Africa
- School of Anatomy, Physiology, and Human Biology, University of Western Australia, Perth, WA 6009, Australia
| | - Haley D. O'Brien
- Department of Anatomy and Cell Biology, Oklahoma State University Center for Health Sciences, Oklahoma, OK 74107, USA
| | - Leith C. R. Meyer
- Brain Function Research Group, School of Physiology, Faculty of Heath Sciences, University of the Witwatersrand, Johannesburg, 2193, South Africa
- Department of Paraclinical Sciences, Faculty of Veterinary Science, University of Pretoria, Pretoria, 0110, South Africa
| | - Andrea Fuller
- Brain Function Research Group, School of Physiology, Faculty of Heath Sciences, University of the Witwatersrand, Johannesburg, 2193, South Africa
- Department of Paraclinical Sciences, Faculty of Veterinary Science, University of Pretoria, Pretoria, 0110, South Africa
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Porter WR, Sedlmayr JC, Witmer LM. Vascular patterns in the heads of crocodilians: blood vessels and sites of thermal exchange. J Anat 2016; 229:800-824. [PMID: 27677246 DOI: 10.1111/joa.12539] [Citation(s) in RCA: 52] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 07/11/2016] [Indexed: 11/27/2022] Open
Abstract
Extant crocodilians are a highly apomorphic archosaur clade that is ectothermic, yet often achieve large body sizes that can be subject to higher heat loads. Therefore, the anatomical and physiological roles that blood vessels play in crocodilian thermoregulation need further investigation to better understand how crocodilians establish and maintain cephalic temperatures and regulate neurosensory tissue temperatures during basking and normal activities. The cephalic vascular anatomy of extant crocodilians, particularly American alligator (Alligator mississippiensis) was investigated using a differential-contrast, dual-vascular injection technique and high resolution X-ray micro-computed tomography (μCT). Blood vessels were digitally isolated to create representations of vascular pathways. The specimens were then dissected to confirm CT results. Sites of thermal exchange, consisting of the oral, nasal, and orbital regions, were given special attention due to their role in evaporative cooling and cephalic thermoregulation in other diapsids. Blood vessels to and from sites of thermal exchange were studied to detect conserved vascular patterns and to assess their ability to deliver cooled blood to neurosensory tissues. Within the orbital region, both the arteries and veins demonstrated consistent branching patterns, with the supraorbital, infraorbital, and ophthalmotemporal vessels supplying and draining the orbit. The venous drainage of the orbital region showed connections to the dural sinuses via the orbital veins and cavernous sinus. The palatal region demonstrated a vast plexus that comprised both arteries and veins. The most direct route of venous drainage of the palatal plexus was through the palatomaxillary veins, essentially bypassing neurosensory tissues. Anastomotic connections with the nasal region, however, may provide an alternative route for palatal venous blood to reach neurosensory tissues. The nasal region in crocodilians is probably the most prominent site of thermal exchange, as it offers a substantial surface area and is completely surrounded by blood vessels. The venous drainage routes from the nasal region offer routes directly to the dural venous sinuses and the orbit, offering evidence of the potential to directly affect neurosensory tissue temperatures. The evolutionary history of crocodilians is complex, with large-bodied, terrestrial, and possibly endothermic taxa that may have had to deal with thermal loads that likely provided the anatomical building-blocks for such an extensive vascularization of sites of thermal exchange. A clear understanding of the physiological abilities and the role of blood vessels in the thermoregulation of crocodilians neurosensory tissues is not available but vascular anatomical patterns of crocodilian sites of thermal exchange indicate possible physiological abilities that may be more sophisticated than in other extant diapsids.
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Affiliation(s)
- William Ruger Porter
- Department of Biomedical Sciences, Ohio University Heritage College of Osteopathic Medicine, Athens, OH, USA
| | - Jayc C Sedlmayr
- Department of Cell Biology and Anatomy, Louisiana State University Heath Sciences Center, New Orleans, LA, USA
| | - Lawrence M Witmer
- Department of Biomedical Sciences, Ohio University Heritage College of Osteopathic Medicine, Athens, OH, USA
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Sinclair BJ, Marshall KE, Sewell MA, Levesque DL, Willett CS, Slotsbo S, Dong Y, Harley CDG, Marshall DJ, Helmuth BS, Huey RB. Can we predict ectotherm responses to climate change using thermal performance curves and body temperatures? Ecol Lett 2016; 19:1372-1385. [DOI: 10.1111/ele.12686] [Citation(s) in RCA: 448] [Impact Index Per Article: 56.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2016] [Revised: 07/25/2016] [Accepted: 08/20/2016] [Indexed: 12/16/2022]
Affiliation(s)
- Brent J. Sinclair
- Department of Biology University of Western Ontario London ON Canada
| | - Katie E. Marshall
- Department of Zoology University of British Columbia Vancouver BC Canada
| | - Mary A. Sewell
- School of Biological Sciences University of Auckland Auckland New Zealand
| | - Danielle L. Levesque
- Institute of Biodiversity and Environmental Conservation Universiti Malaysia Sarawak Kota Samarahan Sarawak Malaysia
| | | | - Stine Slotsbo
- Department of Bioscience Aarhus University Aarhus Denmark
| | - Yunwei Dong
- State Key Laboratory of Marine Environmental Science Xiamen University Xiamen China
| | | | - David J. Marshall
- Faculty of Science Universiti Brunei Darussalam Gadong Brunei Darussalam
| | - Brian S. Helmuth
- Department of Marine and Environmental Sciences and School of Public Policy and Urban Affairs Northeastern University Marine Science Center Nahant MA USA
| | - Raymond B. Huey
- Department of Biology University of Washington Seattle WA USA
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Strauss WM, Hetem RS, Mitchell D, Maloney SK, Meyer LCR, Fuller A. Three African antelope species with varying water dependencies exhibit similar selective brain cooling. J Comp Physiol B 2016; 186:527-40. [DOI: 10.1007/s00360-016-0968-2] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2015] [Revised: 01/27/2016] [Accepted: 02/10/2016] [Indexed: 11/28/2022]
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Strauss WM, Hetem RS, Mitchell D, Maloney SK, Meyer LCR, Fuller A. Selective brain cooling reduces water turnover in dehydrated sheep. PLoS One 2015; 10:e0115514. [PMID: 25675092 PMCID: PMC4326457 DOI: 10.1371/journal.pone.0115514] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2014] [Accepted: 11/25/2014] [Indexed: 11/19/2022] Open
Abstract
In artiodactyls, arterial blood destined for the brain can be cooled through counter-current heat exchange within the cavernous sinus via a process called selective brain cooling. We test the hypothesis that selective brain cooling, which results in lowered hypothalamic temperature, contributes to water conservation in sheep. Nine Dorper sheep, instrumented to provide measurements of carotid blood and brain temperature, were dosed with deuterium oxide (D2O), exposed to heat for 8 days (40 ◦C for 6-h per day) and deprived of water for the last five days (days 3 to 8). Plasma osmolality increased and the body water fraction decreased over the five days of water deprivation, with the sheep losing 16.7% of their body mass. Following water deprivation, both the mean 24h carotid blood temperature and the mean 24h brain temperature increased, but carotid blood temperature increased more than did brain temperature resulting in increased selective brain cooling. There was considerable inter-individual variation in the degree to which individual sheep used selective brain cooling. In general, sheep spent more time using selective brain cooling, and it was of greater magnitude, when dehydrated compared to when they were euhydrated. We found a significant positive correlation between selective brain cooling magnitude and osmolality (an index of hydration state). Both the magnitude of selective brain cooling and the proportion of time that sheep spent selective brain cooling were negatively correlated with water turnover. Sheep that used selective brain cooling more frequently, and with greater magnitude, lost less water than did conspecifics using selective brain cooling less efficiently. Our results show that a 50 kg sheep can save 2.6L of water per day (~60% of daily water intake) when it employs selective brain cooling for 50% of the day during heat exposure. We conclude that selective brain cooling has a water conservation function in artiodactyls.
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Affiliation(s)
- W. Maartin Strauss
- Brain Function Research Group, School of Physiology, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa
- Department of Environmental Sciences, College of Agriculture and Environmental Sciences, University of South Africa, Johannesburg, South Africa
- * E-mail:
| | - Robyn S. Hetem
- Brain Function Research Group, School of Physiology, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa
| | - Duncan Mitchell
- Brain Function Research Group, School of Physiology, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa
| | - Shane K. Maloney
- Brain Function Research Group, School of Physiology, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa
- School of Anatomy, Physiology, and Human Biology, University of Western Australia, Crawley 6009, Australia
| | - Leith C. R. Meyer
- Brain Function Research Group, School of Physiology, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa
| | - Andrea Fuller
- Brain Function Research Group, School of Physiology, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa
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Fuller A, Hetem RS, Maloney SK, Mitchell D. Adaptation to Heat and Water Shortage in Large, Arid-Zone Mammals. Physiology (Bethesda) 2014; 29:159-67. [DOI: 10.1152/physiol.00049.2013] [Citation(s) in RCA: 51] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Although laboratory studies of large mammals have revealed valuable information on thermoregulation, such studies cannot predict accurately how animals respond in their natural habitats. Through insights obtained on thermoregulatory behavior, body temperature variability, and selective brain cooling in free-living mammals, we show here how we can better understand the physiological capacity of large mammals to cope with hotter and drier arid-zone habitats likely with climate change.
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Affiliation(s)
- Andrea Fuller
- Brain Function Research Group, School of Physiology, University of the Witwatersrand, Johannesburg, South Africa; and
| | - Robyn S. Hetem
- Brain Function Research Group, School of Physiology, University of the Witwatersrand, Johannesburg, South Africa; and
| | - Shane K. Maloney
- Brain Function Research Group, School of Physiology, University of the Witwatersrand, Johannesburg, South Africa; and
- School of Anatomy, Physiology, and Human Biology, University of Western Australia, Perth, Australia
| | - Duncan Mitchell
- Brain Function Research Group, School of Physiology, University of the Witwatersrand, Johannesburg, South Africa; and
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Hetem RS, Strauss WM, Fick LG, Maloney SK, Meyer LCR, Fuller A, Shobrak M, Mitchell D. Selective brain cooling in Arabian oryx (Oryx leucoryx): a physiological mechanism for coping with aridity? ACTA ACUST UNITED AC 2012; 215:3917-24. [PMID: 22899527 DOI: 10.1242/jeb.074666] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Selective brain cooling is a thermoregulatory effector proposed to conserve body water and, as such, may help artiodactyls cope with aridity. We measured brain and carotid blood temperature, using implanted data loggers, in five Arabian oryx (Oryx leucoryx) in the desert of Saudi Arabia. On average, brain temperature was 0.24±0.05°C lower than carotid blood temperature for four oryx in April. Selective brain cooling was enhanced in our Arabian oryx compared with another species from the same genus (gemsbok Oryx gazella gazella) exposed to similar ambient temperatures but less aridity. Arabian oryx displayed a lower threshold (37.8±0.1°C vs 39.8±0.4°C), a higher frequency (87±6% vs 15±15%) and a higher maximum magnitude (1.2±0.2°C vs 0.5±0.3°C) of selective brain cooling than did gemsbok. The dominant male oryx displayed less selective brain cooling than did any of the other oryx, but selective brain cooling was enhanced in this oryx as conditions became hotter and drier. Enhanced selective brain cooling in Arabian oryx supports the hypothesis that selective brain cooling would bestow survival advantages for artiodactyl species inhabiting hot hyper-arid environments.
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Affiliation(s)
- Robyn S Hetem
- Brain Function Research Group, School of Physiology, University of the Witwatersrand, 7 York Road, Parktown 2193, South Africa.
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Scharf B, Johnson J, Weaber R, Spiers D. Utilizing laboratory and field studies to determine physiological responses of cattle to multiple environmental stressors. J Therm Biol 2012. [DOI: 10.1016/j.jtherbio.2011.10.002] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/16/2022]
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Weissenböck NM, Arnold W, Ruf T. Taking the heat: thermoregulation in Asian elephants under different climatic conditions. J Comp Physiol B 2011; 182:311-9. [DOI: 10.1007/s00360-011-0609-8] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2011] [Revised: 08/09/2011] [Accepted: 08/11/2011] [Indexed: 11/24/2022]
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Bertolizio G, Mason L, Bissonnette B. Brain temperature: heat production, elimination and clinical relevance. Paediatr Anaesth 2011; 21:347-58. [PMID: 21371165 DOI: 10.1111/j.1460-9592.2011.03542.x] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Neurological insults are a leading cause of morbidity and mortality, both in adults and especially in children. Among possible therapeutic strategies to limit clinical cerebral damage and improve outcomes, hypothermia remains a promising and beneficial approach. However, its advantages are still debated after decades of use. Studies in adults have generated conflicting results, whereas in children recent data even suggest that hypothermia may be detrimental. Is it because brain temperature physiology is not well understood and/or not applied properly, that hypothermia fails to convince clinicians of its potential benefits? Or is it because hypothermia is not, as believed, the optimal strategy to improve outcome in patients affected with an acute neurological insult? This review article should help to explain the fundamental physiological principles of brain heat production, distribution and elimination under normal conditions and discuss why hypothermia cannot yet be recommended routinely in the management of children affected with various neurological insults.
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Hetem RS, Strauss WM, Fick LG, Maloney SK, Meyer LCR, 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; 180:1111-9. [PMID: 20502901 DOI: 10.1007/s00360-010-0480-z] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2010] [Revised: 04/28/2010] [Accepted: 05/03/2010] [Indexed: 11/24/2022]
Abstract
Heterothermy, a variability in body temperature beyond the limits of homeothermy, has been advanced as a key adaptation of Arabian oryx (Oryx leucoryx) to their arid-zone life. We measured body temperature using implanted data loggers, for a 1-year period, in five oryx free-living in the deserts of Saudi Arabia. As predicted for adaptive heterothermy, during hot months compared to cooler months, not only were maximum daily body temperatures higher (41.1 ± 0.3 vs. 39.7 ± 0.1°C, P = 0.0002) but minimum daily body temperatures also were lower (36.1 ± 0.3 vs. 36.8 ± 0.2°C, P = 0.04), resulting in a larger daily amplitude of the body temperature rhythm (5.0 ± 0.5 vs. 2.9 ± 0.2°C, P = 0.0007), while mean daily body temperature rose by only 0.4°C. The maximum daily amplitude of the body temperature rhythm reached 7.7°C for two of our oryx during the hot-dry period, the largest amplitude ever recorded for a large mammal. Body temperature variability was influenced not only by ambient temperature but also water availability, with oryx displaying larger daily amplitudes of the body temperature rhythm during warm-dry months compared to warm-wet months (3.6 ± 0.6 vs. 2.3 ± 0.3°C, P = 0.005), even though ambient temperatures were the same. Free-living Arabian oryx therefore employ heterothermy greater than that recorded in any other large mammal, but water limitation, rather than high ambient temperature, seems to be the primary driver of this heterothermy.
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Affiliation(s)
- Robyn Sheila Hetem
- Brain Function Research Group, School of Physiology, Medical School, University of the Witwatersrand, 7 York Road, Parktown, Johannesburg 2193, South Africa.
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Grzegorzewski WJ, Chłopek J, Tabecka-Łonczyńska A, Stefańczyk-Krzymowska S. The influence of steroids on vascular tension of isolated superficial veins of the nose and face during the estrous cycle of gilts. Theriogenology 2010; 73:215-24. [PMID: 19878982 DOI: 10.1016/j.theriogenology.2009.09.002] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2009] [Revised: 09/11/2009] [Accepted: 09/11/2009] [Indexed: 11/18/2022]
Abstract
The arrangement of the superficial facial veins enables blood flow from the nasal cavity into the peripheral circulation by two pathways: through the frontal vein into the cavernous sinus and through the facial vein into the external jugular vein. The current study was designed to determine whether estradiol and progesterone affect the vascular tone of the superficial veins of the nose and face in cycling gilts (Sus scrofa f. domestica) and to analyze the immunolocalization of progesterone receptors and estradiol receptors in these veins. The influence of hormones on vascular tension differed depending on the type of vessel and the phase of the estrous cycle. Estradiol decreased vascular tension in the nasal vein during the follicular phase (P<0.05) and increased tension in the frontal vein during the luteal phase (P<0.05). Progesterone increased the vascular tension of the frontal vein (P<0.05) and decreased the tension of the other veins (P<0.05) in both phases of the cycle. Expression of estradiol receptor beta but not of progesterone receptor was observed in the superficial veins of the nose and face. In conclusion, the effect of ovarian steroid hormones on the vascular tension of the superficial veins of the nose and face in female pigs as well as the reactivity of these veins to steroid boar pheromones can affect the blood supply from the nasal cavity to the venous cavernous sinus. We propose that the ovarian steroid hormones that modulate the vascular tension of the nasal and facial veins may also influence the action of boar pheromones absorbed into the nasal mucosa in gilts and may reach the brain via local destination transfer.
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Affiliation(s)
- W J Grzegorzewski
- Department of Local Physiological Regulation, Institute of Animal Reproduction and Food Research of the Polish Academy of Sciences, Olsztyn, Poland.
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Hayward MW, Slotow R. Temporal Partitioning of Activity in Large African Carnivores: Tests of Multiple Hypotheses. ACTA ACUST UNITED AC 2009. [DOI: 10.3957/056.039.0207] [Citation(s) in RCA: 196] [Impact Index Per Article: 13.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/01/2022]
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Hetem RS, de Witt BA, Fick LG, Fuller A, Kerley GI, Meyer LC, Mitchell D, Maloney SK. Body temperature, thermoregulatory behaviour and pelt characteristics of three colour morphs of springbok (Antidorcas marsupialis). Comp Biochem Physiol A Mol Integr Physiol 2009; 152:379-88. [DOI: 10.1016/j.cbpa.2008.11.011] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2008] [Revised: 11/10/2008] [Accepted: 11/11/2008] [Indexed: 11/16/2022]
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Maloney SK, Fuller A, Meyer LCR, 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 2008; 179:241-51. [DOI: 10.1007/s00360-008-0308-2] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2008] [Revised: 09/05/2008] [Accepted: 09/09/2008] [Indexed: 11/29/2022]
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20
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Hetem RS, Maloney SK, Fuller A, Meyer LCR, Mitchell D. Validation of a biotelemetric technique, using ambulatory miniature black globe thermometers, to quantify thermoregulatory behaviour in ungulates. ACTA ACUST UNITED AC 2007; 307:342-56. [PMID: 17480034 DOI: 10.1002/jez.389] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
Behavioural thermoregulation is an animal's primary defence against changes in the thermal environment. We aimed to validate a remote technique to quantify the thermal environment behaviourally selected by free-ranging ungulates. First, we demonstrated that the temperature of miniature, 30 mm diameter, black globes (miniglobes) could be converted to standard, 150 mm diameter, black globe temperatures. Miniglobe temperature sensors subsequently were fitted to collars on three free-ranging ungulates, namely blue wildebeest (Connochaetes taurinus), impala (Aepyceros melampus) and horse (Equus caballus). Behavioural observations were reflected in animal miniglobe temperatures which differed from those recorded by an identical miniglobe on a nearby exposed weather station. The wildebeest often selected sites protected from the wind, whereas the impala and the horse sheltered from the sun. Nested analysis of variances revealed that the impala and horse selected significantly less variable environments than those recorded at the weather station (P<0.001) over a 20-min time interval, whereas, the microclimates selected by wildebeest tended to be more variable (P=0.08). Correlation of animal miniglobe against weather station miniglobe temperature resulted in regression slopes significantly less than one (P<0.001) for all species studied, implying that, overall, the animals selected cooler microclimates at high environmental heat loads and/or warmer microclimates at low environmental heat loads. We, therefore, have developed an ambulatory device, which can be attached to free-ranging animals, to remotely quantify thermoregulatory behaviour and selected microclimates.
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Affiliation(s)
- Robyn S Hetem
- Brain Function Research Group, School of Physiology, University of the Witwatersrand, Medical School, 7 York Road, Parktown, South Africa.
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Robertshaw D. Mechanisms for the control of respiratory evaporative heat loss in panting animals. J Appl Physiol (1985) 2006; 101:664-8. [PMID: 16675613 DOI: 10.1152/japplphysiol.01380.2005] [Citation(s) in RCA: 96] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Panting is a controlled increase in respiratory frequency accompanied by a decrease in tidal volume, the purpose of which is to increase ventilation of the upper respiratory tract, preserve alveolar ventilation, and thereby elevate evaporative heat loss. The increased energy cost of panting is offset by reducing the metabolism of nonrespiratory muscles. The panting mechanism tends to be important in smaller mammalian species and in larger species is supplemented by sweating. At elevated respiratory frequencies and body temperatures alveolar hyperventilation begins to develop but is accompanied by a decline in the control of carbon dioxide partial pressure in arterial blood, probably through central chemoreceptors. Most heat exchange takes place at the nasal epithelial lining, and venous drainage can be directed to a special network of arteries at the base of the brain whereby countercurrent heat transfer can occur, which results in selective brain cooling. Such a phenomenon has also been suggested in nonpanting species, including humans, and although originally thought to be a mechanism for protecting the thermally vulnerable brain is now considered to be one of the thermoregulatory reflexes whereby respiratory evaporation can be closely controlled in the interests of thermal homeostasis.
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Affiliation(s)
- David Robertshaw
- Weill Cornell Medical College in Qatar, PO Box 24144, Doha, Qatar.
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Ostrowski S, Williams JB. Heterothermy of free-living Arabian sand gazelles (Gazella subgutturosa marica) in a desert environment. ACTA ACUST UNITED AC 2006; 209:1421-9. [PMID: 16574802 DOI: 10.1242/jeb.02151] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
To test whether free-living desert ungulates employ heterothermy to reduce water loss, we measured core body temperature (T(b)) of six free-living Arabian sand gazelles (Gazella subgutturosa marica), a small desert antelope (12-20 kg) that lives in the deserts of Saudi Arabia, where air temperature (T(a)) often exceeds 40 degrees C. We found that the mean daily T(b) varied by 2.6+/-0.8 degrees C during summer (June-July) and 1.7+/-0.3 degrees C during winter (January-February); over both seasons, mean T(b) was 39.5+/-0.2 degrees C. During the day, in summer, T(b) increased by more than 2 degrees C when T(a)>T(b) and declined at night when T(a)<T(b), suggesting that gazelles stored heat during day and dissipated it by non evaporative means during night. The minimum T(b) was lower in summer (38.2+/-0.5 degrees C) than in winter (38.6+/-0.3 degrees C) despite the fact that the gradient between T(b) and T(a) was larger and solar radiation was lower in winter. Correlation between daily variation of T(b) and mean, maximal T(a)s were significant in summer, but not in winter. To dissipate the amount of heat stored by gazelles would require an evaporative water loss of 33.5 ml H(2)O day(-1) in summer and 23.2 ml H(2)O day(-1) in winter. We tested whether the amplitude of daily variation in T(b) was influenced by the level of water provided to six captive sand gazelles maintained under controlled conditions in summer. The daily amplitude of T(b) was increased by 1.4 degrees C when gazelles were denied drinking water but supplied with pre-formed water in food, and by 1.1 degrees C when they were denied both water and food. Gazelles denied only drinking water increased the amplitude of variation in T(b), whereas when denied both food and water, they seemed to undergo a dehydration-hyperthermia, with increased mean and maximal T(b) values but no decrease of minimal T(b). Free-ranging and captive gazelles surviving on pre-formed water in natural food used heterothermy during summer with no elevation of plasma osmolality, indicating that they were not in a state of dehydration. Our data on variation in T(b) of gazelles provide an example of a small desert ungulate employing heterothermy to reduce evaporative water loss that would otherwise be required to maintain normothermic T(b).
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Fuller A, Kamerman PR, Maloney SK, Matthee A, Mitchell G, Mitchell D. A year in the thermal life of a free-ranging herd of springbok Antidorcas marsupialis. J Exp Biol 2005; 208:2855-64. [PMID: 16043590 DOI: 10.1242/jeb.01714] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
SUMMARY
We used miniature data loggers implanted in the abdominal cavity to measure core body temperatures at 30 min intervals in eight (three males, five females) adult free-ranging springbok Antidorcas marsupialis in their natural habitat, over a period of 11–13 months. The animals were subjected to a nychthemeral range of air temperature that often exceeded 20°C, with an absolute minimum temperature of –6°C and a maximum of 34°C. Abdominal temperature exhibited a low amplitude (∼1.2°C)nychthemeral rhythm, with a temperature peak near sunset and a trough shortly after sunrise. The amplitude of the nychthemeral rhythm of body temperature was not correlated with the 24 h range of air temperature. Although mean 24 h body temperatures were positively correlated with corresponding air temperatures, mean daily body temperature increased, on average, by only 0.02°C per 1°C increase in air temperature, so that it was only∼0.3°C higher in summer than in winter. Mean monthly body temperatures were strongly positively correlated with photoperiod and, in parallel with changes in the time of sunrise, the times at which the minimum and maximum body temperatures occurred were shifted ∼1.2 h earlier in summer than in winter. Annual and daily variations in body temperature of springbok, like those of other free-living African ungulates, therefore appear to reflect an endogenous rhythm, entrained by the light:dark cycle, but largely independent of fluctuations in the environmental thermal load. Springbok exhibit remarkable homeothermy and do not employ adaptive heterothermy to survive in their natural environment.
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Affiliation(s)
- Andrea Fuller
- School of Physiology, University of the Witwatersrand Medical School, 7 York Road, Parktown 2193, South Africa.
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Maloney SK, Moss G, Cartmell T, Mitchell D. Alteration in diel activity patterns as a thermoregulatory strategy in black wildebeest (Connochaetes gnou). J Comp Physiol A Neuroethol Sens Neural Behav Physiol 2005; 191:1055-64. [PMID: 16049700 DOI: 10.1007/s00359-005-0030-4] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2005] [Revised: 06/16/2005] [Accepted: 06/26/2005] [Indexed: 10/25/2022]
Abstract
The nychthemeral activity patterns of a population of female black wildebeest inhabiting a shadeless environment were surveyed periodically over 1 year. The wildebeest fed mostly at night, with the proportion of feeding at night increasing when ambient conditions were hotter. Inactive periods were spent mostly lying during cooler weather but standing as days became hotter. We suggest that the entire suite of behavioural adjustments is beneficial to heat exchange with the environment. Behaviour patterns were markedly different during one warm weather survey, from the other warm weather surveys, when an 8-month dry spell had just been broken. We suggest that this may reflect the availability of water for autonomic thermoregulation, a consequent decreased reliance on behavioural thermoregulation, and a release of the thermal constraints on foraging. Our results help to explain the ability of black wildebeest to maintain body core temperature within a very narrow range despite being exposed to an environment with large nychthemeral variations in thermal conditions and offering little in the way of microclimate selection.
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Affiliation(s)
- Shane K Maloney
- School of Physiology, University of the Witwatersrand Medical School, Johannesburg, 2193, South Africa.
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25
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The eland and the oryx revisited: body and brain temperatures of free-living animals. ACTA ACUST UNITED AC 2004. [DOI: 10.1016/j.ics.2004.08.092] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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26
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27
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28
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In-vitro heat exchange at the rete of the Boer goat under specified laboratory conditions. J Therm Biol 2004. [DOI: 10.1016/j.jtherbio.2004.08.041] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
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29
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30
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Ostrowski S, Williams JB, Ismael K. Heterothermy and the water economy of free-living Arabian oryx (Oryx leucoryx). J Exp Biol 2003; 206:1471-8. [PMID: 12654886 DOI: 10.1242/jeb.00275] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
To test the idea that large, free-living, desert ungulates use heterothermy to reduce water loss, we measured core body temperature (T(b)) of six free-ranging, adult Arabian oryx (Oryx leucoryx) during 2 years in the arid desert of west-central Saudi Arabia. We report the first case of heterothermy in a free-living ruminant in a desert environment: T(b) varied by 4.1+/-1.7 degrees C day(-1) during summer (June to September) and by 1.5+/-0.6 degrees C day (-1) during winter (November to March). Over both seasons, mean T(b) was 38.4+/-1.3 degrees C. During the day in both summer and winter, T(b) increased continually, suggesting that oryx store heat instead of dissipating it by evaporation, whereas at night T(b) decreased. The minimum T(b) was lower in summer (36.5+/-1.16 degrees C) than in winter (37.5+/-0.51 degrees C) despite the fact that the temperature gradient between T(b) and air temperature (T(a)) was larger and solar radiation was lower in winter. Throughout the year, daily variation in T(b) appeared to reflect thermal load (T(a,max)-T(a,min)) rather than an endogenous rhythm. Behavioural thermoregulation was used by oryx to cope with thermal stress during summer: animals lay down in shade in the morning shortly before T(a) exceeded T(b) and remained there until evening when T(b)-T(a) became positive. The use of heterothermy by oryx resulted in storage of 672.4 kJ day(-1) animal(-1) in summer and 258.6 kJ day(-1) animal(-1) in winter, if heat storage is based on calculations involving mean T(b). To dissipate this heat by evaporation would require 0.28 litres H(2)O day(-1) animal(-1) and 0.11 litres H(2)O day(-1) animal(-1) in summer and winter, respectively. Without heat storage in summer, we estimated that oryx would have to increase their water intake by 19%, a requirement that would be difficult to meet in their desert environment. If heat storage was calculated based on the daily change in T(b) rather than on heat storage above mean T(b) then we estimated that oryx saved 0.538 litres H(2)O day(-1) animal(-1) during summer.
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31
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Fuller A, Kamerman PR, Maloney SK, Mitchell G, Mitchell D. Variability in brain and arterial blood temperatures in free-ranging ostriches in their natural habitat. J Exp Biol 2003; 206:1171-81. [PMID: 12604577 DOI: 10.1242/jeb.00230] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
We used implanted miniature data loggers to measure brain (in or near the hypothalamus) and carotid arterial blood temperatures at 5 min intervals in six free-ranging ostriches Struthio camelus in their natural habitat, for a period of up to 14 days. Carotid blood temperature exhibited a large amplitude (3.0-4.6 degrees C) circadian rhythm, and was positively correlated with air temperature. During the day, brain temperature exceeded carotid blood temperature by approx. 0.4 degrees C, but there were episodes when brain temperature was lowered below blood temperature. Selective brain cooling, however, was not present in all ostriches, and was not tightly coupled to the prevailing body temperature. Brain temperature was maintained within narrow daily limits of approx. 2 degrees C, and varied significantly less than blood temperature at short time scales of 5 to 20 min. At night, brain temperature exceeded blood temperature by as much as 3 degrees C. We attribute the elevated brain temperatures to warming of cerebral arterial blood, by reduced heat exchange in the ophthalmic rete or possibly heat gain from cranial structures, before supplying the hypothalamus. Further studies are necessary to elucidate the significance of such variations in brain temperature and the importance of selective brain cooling in free-living birds.
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Affiliation(s)
- Andrea Fuller
- School of Physiology, University of the Witwatersrand Medical School, 7 York Road, Parktown 2193, South Africa.
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32
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Mitchell D, Maloney SK, Jessen C, Laburn HP, Kamerman PR, Mitchell G, Fuller A. Adaptive heterothermy and selective brain cooling in arid-zone mammals. Comp Biochem Physiol B Biochem Mol Biol 2002; 131:571-85. [PMID: 11923074 DOI: 10.1016/s1096-4959(02)00012-x] [Citation(s) in RCA: 99] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Adaptive heterothermy and selective brain cooling are regarded as important thermal adaptations of large arid-zone mammals. Adaptive heterothermy, a process which reduces evaporation by storing body heat, ought to be enhanced by ambient heat load and by water deficit, but most mammals studied fail to show at least one of those attributes. Selective brain cooling, the reduction of brain temperature below arterial blood temperature, is most evident in artiodactyls, which possess a carotid rete, and traditionally has been considered to protect the brain during hyperthermia. The development of miniature ambulatory data loggers for recording body temperature allows the temperatures of free-living wild mammals to be measured in their natural habitats. All the African ungulates studied so far, in their natural habitats, do not exhibit adaptive heterothermy. They have low-amplitude nychthemeral rhythms of temperature, with mean body temperature over the night exceeding that over the day. Those with carotid retes (black wildebeest, springbok, eland) employ selective brain cooling but zebra, without a rete, do not. None of the rete ungulates, however, seems to employ selective brain cooling to prevent the brain overheating during exertional hyperthermia. Rather, they use it at rest, under moderate heat load, we believe in order to switch body heat loss from evaporative to non-evaporative routes.
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Affiliation(s)
- Duncan Mitchell
- School of Physiology, University of the Witwatersrand, Medical School, Parktown, 2193, Johannesburg, South Africa.
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Kamerman PR, Fuller A, Faurie AS, Mitchell G, Mitchell D. Body temperature patterns during natural fevers in a herd of free-ranging impala (Aepyceros melampus). Vet Rec 2001; 149:26-7. [PMID: 11486773 DOI: 10.1136/vr.149.1.26] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022]
Affiliation(s)
- P R Kamerman
- School of Physiology, University of the Witwatersrand, Medical School, Parktown, South Africa
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34
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Maloney SK, Fuller A, Mitchell G, Mitchell D. Rectal temperature measurement results in artifactual evidence of selective brain cooling. Am J Physiol Regul Integr Comp Physiol 2001; 281:R108-14. [PMID: 11404284 DOI: 10.1152/ajpregu.2001.281.1.r108] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Selective brain cooling (SBC) is defined as a brain temperature cooler than the temperature of arterial blood from the trunk. Surrogate measures of arterial blood temperature have been used in many published studies on SBC. The use of a surrogate for arterial blood temperature has the potential to confound proper identification of SBC. We have measured brain, carotid blood, and rectal temperatures in conscious sheep exposed to 40, 22, and 5 degrees C. Rectal temperature was consistently higher than arterial blood temperature. Brain temperature was consistently cooler than rectal temperature during all exposures. Brain temperature only fell below carotid blood temperature during the final few hours of 40 degrees C exposure and not at all during the 5 degrees C exposure. Consequently, using rectal temperature as a surrogate for arterial blood temperature does not provide a reliable indication of the status of the SBC effector. We also show that rapid suppression of SBC can result if the animals are disturbed.
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Affiliation(s)
- S K Maloney
- Department of Physiology, University of the Witwatersrand, Johannesburg 2193, South Africa.
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35
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Abstract
Two winter-insulated Norwegian reindeer (Rangifer tarandus tarandus) were exposed to air temperatures of 10, 20, 30, and 38 degrees C while standing at rest in a climatic chamber. The direction of airflow through nose and mouth, and the total and the nasal minute volumes, respectively, were determined during both closed- and open-mouth panting. The animals alternated between closed- and open-mouth panting, but the proportion of open-mouth panting increased with increasing heat load. The shifts from closed- to open-mouth panting were abrupt and always associated with a rise in respiratory frequency and respiratory minute volume. During open-mouth panting, the direction of airflow was bidirectional in both nose and mouth, but only 2.4 +/- (SD) 1.1% of the air was routed through the nose. Estimates suggest that the potential for selective brain cooling is markedly reduced during open-mouth panting in reindeer as a consequence of this airflow pattern.
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Affiliation(s)
- O Aas-Hansen
- Department of Arctic Biology and Institute of Medical Biology, University of Tromsø, N-9037 Tromsø, Norway
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36
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Grover LM, Yan C. The modulation of excitatory synaptic transmission by adenosine in area CA1 of the rat hippocampus is temperature dependent. Neurosci Lett 1999; 263:77-80. [PMID: 10213139 DOI: 10.1016/s0304-3940(99)00121-4] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We tested the possibility that extracellular adenosine concentration varies with tissue temperature by measuring the tonic adenosinergic inhibition of excitatory synaptic transmission at different temperatures in the in vitro rat hippocampus. Application of the A1 receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX) enhanced population excitatory postsynaptic potentials (EPSPs) by antagonizing tonic adenosinergic inhibition; this effect was greatest at 25 degrees C, and was progressively reduced at 35 and 37.5 degrees C. These results demonstrate that tonic adenosinergic inhibition is inversely related to temperature. In a second experiment, an exogenous A1 agonist, N6-cyclohexyladenosine (CHA), was applied to slices to inhibit evoked EPSPs. CHA inhibition of EPSPs was greater at 35 than at 25 degrees C, demonstrating that the reduced adenosinergic inhibition at higher temperatures is not a result of reduced A1 receptor function.
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Affiliation(s)
- L M Grover
- Department of Physiology, Marshall University School of Medicine, Huntington, WV 25755-9340, USA.
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Jessen C. Brain Cooling: An Economy Mode of Temperature Regulation in Artiodactyls. NEWS IN PHYSIOLOGICAL SCIENCES : AN INTERNATIONAL JOURNAL OF PHYSIOLOGY PRODUCED JOINTLY BY THE INTERNATIONAL UNION OF PHYSIOLOGICAL SCIENCES AND THE AMERICAN PHYSIOLOGICAL SOCIETY 1998; 13:281-286. [PMID: 11390804 DOI: 10.1152/physiologyonline.1998.13.6.281] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Artiodactyls employ selective brain cooling (SBC) regularly during experimental hyperthermia. In free-ranging antelopes, however, SBC often was present when body temperature was low but absent when brain temperature was near 42 degrees C. The primary effect of SBC is to adjust the activity of the heat loss mechanisms to the magnitude of the heat stress rather than to the protection of the brain from thermal damage.
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Affiliation(s)
- Claus Jessen
- Physiologisches Institut, Justus-Liebig-Universität, D-35392 Giessen, Germany
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Fuller A, Carter RN, Mitchell D. Brain and abdominal temperatures at fatigue in rats exercising in the heat. J Appl Physiol (1985) 1998; 84:877-83. [PMID: 9480946 DOI: 10.1152/jappl.1998.84.3.877] [Citation(s) in RCA: 118] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
We measured brain and abdominal temperatures in eight male Sprague-Dawley rats (350-450 g) exercising voluntarily to a point of fatigue in two hot environments. Rats exercised, at the same time of the day, in three different trials, in random order: rest 23 degrees C, exercise 33 degrees C; rest 23 degrees C, exercise 38 degrees C; and rest 38 degrees C, exercise 38 degrees C. Running time to fatigue was 29.4 +/- 5.9 (SD), 22.1 +/- 3.7, and 14.3 +/- 2.9 min for the three trials, respectively. Abdominal temperatures, measured with intraperitoneal radiotelemeters, at fatigue in the three trials (39.9 +/- 0.3, 39.9 +/- 0.3, and 39.8 +/- 0.3 degrees C, respectively) were not significantly different from each other. Corresponding brain temperatures, measured with thermocouples in the hypothalamic region (40.2 +/- 0.4, 40.2 +/- 0.4, and 40.1 +/- 0.4 degrees C), also did not differ. Our results are consistent with the concept that there is a critical level of body temperature beyond which animals will not continue to exercise voluntarily in the heat. Also, in our study, brain temperature was higher than abdominal temperature throughout exercise; that is, selective brain cooling did not occur when body temperature was below the level limiting exercise.
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Affiliation(s)
- A Fuller
- Department of Physiology, University of the Witwatersrand, Medical School, Parktown 2193, Johannesburg, South Africa.
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