Regulation of brain temperature in pigeons: effects of corneal convection

Pinshow, Berry; Bernstein, Marvin H.; López, Gloria Esperanza; Kleinhaus, Shani

doi:10.1152/ajpregu.1982.242.5.r577

Cited by 22 publications

(24 citation statements)

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“…Heat loss from the head may be further reduced if the eyes of the bird are closed. Pinshow et al (1982) showed that heat loss from the eye plays a significant role in reducing brain temperature of pigeons. The ostrich has a relatively large eye, which potentially is a large heat sink for arterial blood supplying the brain.…”

Section: Discussionmentioning

confidence: 99%

Variability in brain and arterial blood temperatures in free-ranging ostriches in their natural habitat

Fuller

Kamerman

Maloney

et al. 2003

Journal of Experimental Biology

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The main determinant of deep brain temperature, measured in or near the hypothalamus, is the temperature of the arterial blood supplying the brain (Hayward and Baker, 1968). In most mammals, therefore, brain temperature changes in parallel with carotid blood temperature but, because of its high metabolic rate, exceeds the temperature of arterial blood by 0.2-0.5°C (Hayward and Baker, 1969). However, some mammals, particularly artiodactyls and felids, are able to lower brain temperature below carotid blood temperature, a process termed selective brain cooling (for reviews, see Jessen, 2001;Mitchell et al., 2002). In these mammals, selective brain cooling is facilitated by the carotid rete, a bilateral network of intertwining arteries in the main arterial supply to the brain, situated on either side of the pituitary body within cool venous lakes derived from veins draining the nasal mucosa (Gillilan, 1974;Simoens et al., 1987). Moderate exercise on a treadmill or exposure to heat in a laboratory uncouples brain and carotid blood temperatures, so that the gradient between brain and blood temperatures narrows until, at a threshold temperature of approximately 39°C, brain temperature equals carotid blood temperature (Baker, 1982;Kuhnen and Jessen, 1991;Kuhnen and Mercer, 1993). Beyond that threshold, brain temperature rises at a slower rate than does blood temperature, establishing selective brain cooling with a magnitude, at most, of about 1°C.In mammals that are free-living in their natural habitat and exposed to a variety of complex stressors, however, a similar tight thermal relationship between brain and arterial blood temperatures is apparently absent. In free-ranging antelope, selective brain cooling occurs within the normothermic range of body temperature, and only sporadically in response to high heat loads (Jessen et al., 1994;Mitchell et al., 1997;Fuller et al., 1999b;Maloney et al., 2002). During high-intensity exercise, when brain temperatures reach their highest levels, selective brain cooling is abolished. Indeed, for any given blood temperature, brain temperature is highly variable and unpredictable. Large-amplitude, transient deviations in brain temperature, independent of any changes in the temperature of arterial blood supplying the brain, have also been observed in several laboratory animals in response to non-thermal stimuli (Fuller et al., 1999a;Maloney et al., 2001). This variability arises because the efferent arm of the control mechanism 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°C) circadian rhythm, and was positively correlated with air temperature. During the day, brain temperature exceeded carotid blood temperature by approx. 0.4°C, but there were episodes when brain temperature was lowered below blood temperature. Selecti...

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Section: Discussionmentioning

confidence: 99%

Variability in brain and arterial blood temperatures in free-ranging ostriches in their natural habitat

Fuller

Kamerman

Maloney

et al. 2003

Journal of Experimental Biology

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“…However, there is no evidence, especially at shallow depth, for this mechanism of T. Knower Stockard and others (Kooyman et al, 1973). Oxygenation of carotid blood via the avian ophthalmic rete (Bernstein et al, 1984;Pinshow et al, 1982) is unlikely since continued passage of fresh air over nasal and oral mucosa will not occur during a dive. On the other hand, adaptations in the brain may also contribute to increased cerebral hypoxemic tolerance.…”

Section: Hypoxic Tolerancementioning

confidence: 99%

Air sacPO2 and oxygen depletion during dives of emperor penguins

Stockard

Heil

Meir

et al. 2005

Journal of Experimental Biology

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“…Evaporative heat dissipation is of particular significance to species that routinely encounter environmental temperatures approaching or exceeding their body temperature (T b ), with birds and mammals typically responding to hot conditions with large increases in their rates of evaporative water loss (EWL) to prevent potentially lethal increases in T b (King and Farner 1961;Herreid and Schmidt-Nielsen 1966;Licht and Leitner 1967). Total evaporative water loss (TEWL) is the sum of cutaneous evaporative water loss (CEWL) and respiratory evaporative water loss (REWL), although there is empirical evidence that other avenues of evaporation, including the ocular surfaces and the avian cloaca, may also contribute significantly to total rates of evaporation (Pinshow et al 1982;Hoffman et al 2007).…”

Section: Introductionmentioning

confidence: 99%

Partitioning of Evaporative Water Loss into Respiratory and Cutaneous Pathways in Wahlberg's Epauletted Fruit Bats (Epomophorus wahlbergi)

Minnaar¹,

Bennett²,

Chimimba³

et al. 2014

Physiological and Biochemical Zoology

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The relative contributions of respiratory and cutaneous evaporation to total evaporative water loss (TEWL) and how the partitioning of these two avenues varies with environmental temperature has received little attention in bats. We trained Wahlberg's epauletted fruit bats (Epomophorus wahlbergi) captured in Pretoria, South Africa, to wear latex masks while hanging in respirometry chambers, and we measured respiratory evaporative water loss (REWL) and cutaneous evaporative water loss (CEWL) over air temperatures (T a ) from 10Њ to 40ЊC. The bats' normothermic body temperature (T b ) was approximately 36ЊC, which increased at higher T a to 40.5Њ ‫ע‬ 1.0ЊC at T a ≈ 40ЊC. Both TEWL and resting metabolic rate (RMR) increased sharply at T a 135ЊC, with a mean TEWL at 40ЊC equivalent to 411% of that at 30ЊC. The increase in TEWL was driven by large increases in both CEWL and REWL. CEWL comprised more than 50% of TEWL over the entire T a range, with the exception of T a ≈ 40ЊC, where REWL accounted for 58% of evaporative water loss. Surface area-specific CEWL increased approximately sixfold with increasing T a . Thermoregulation at T a approaching or exceeding T b involved a considerable energetic cost, with RMR at T a ≈ 40ЊC exceeding by 24% that measured at T a ≈ 10ЊC. Our data do not support recent arguments that respiratory gas exchange across the wing membranes represents 5%-10% of the total in E. wahlbergi.

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Regulation of brain temperature in pigeons: effects of corneal convection

Cited by 22 publications

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Variability in brain and arterial blood temperatures in free-ranging ostriches in their natural habitat

Variability in brain and arterial blood temperatures in free-ranging ostriches in their natural habitat

Air sacPO2 and oxygen depletion during dives of emperor penguins

Partitioning of Evaporative Water Loss into Respiratory and Cutaneous Pathways in Wahlberg's Epauletted Fruit Bats (Epomophorus wahlbergi)

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