Selective brain cooling after bilateral superior cervical sympathectomy in sheep (Ovis aries)

Nijland, Mark J.; Mitchell, Duncan; Mitchell, G.

doi:10.1007/bf00370656

Cited by 13 publications

(13 citation statements)

References 27 publications

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“…Our protocol required that the animals be housed communally, with as little interference from human observers as possible. That requirement was imposed because of the well-described effects of sympathetic stress on selective brain cooling in sheep (4,25,31) and other ungulates (30). Sympathetic stimulation inhibits selective brain cooling, and, in sheep, appears to do so either Fig.…”

Section: Discussionmentioning

confidence: 99%

Dehydration increases the magnitude of selective brain cooling independently of core temperature in sheep

Fuller¹,

Meyer²,

Mitchell³

et al. 2007

American Journal of Physiology-Regulatory, Integrative and Comp

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By cooling the hypothalamus during hyperthermia, selective brain cooling reduces the drive on evaporative heat loss effectors, in so doing saving body water. To investigate whether selective brain cooling was increased in dehydrated sheep, we measured brain and carotid arterial blood temperatures at 5-min intervals in nine female Dorper sheep (41 +/- 3 kg, means +/- SD). The animals, housed in a climatic chamber at 23 degrees C, were exposed for nine days to a cyclic protocol with daytime heat (40 degrees C for 6 h). Drinking water was removed on the 3rd day and returned 5 days later. After 4 days of water deprivation, sheep had lost 16 +/- 4% of body mass, and plasma osmolality had increased from 290 +/- 8 to 323 +/- 9 mmol/kg (P < 0.0001). Although carotid blood temperature increased during heat exposure to similar levels during euhydration and dehydration, selective brain cooling was significantly greater in dehydration (0.38 +/- 0.18 degrees C) than in euhydration (-0.05 +/- 0.14 degrees C, P = 0.0008). The threshold temperature for selective brain cooling was not significantly different during euhydration (39.27 degrees C) and dehydration (39.14 degrees C, P = 0.62). However, the mean slope of lines of regression of brain temperature on carotid blood temperature above the threshold was significantly lower in dehydrated animals (0.40 +/- 0.31) than in euhydrated animals (0.87 +/- 0.11, P = 0.003). Return of drinking water at 39 degrees C led to rapid cessation of selective brain cooling, and brain temperature exceeded carotid blood temperature throughout heat exposure on the following day. We conclude that for any given carotid blood temperature, dehydrated sheep exposed to heat exhibit selective brain cooling up to threefold greater than that when euhydrated.

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Section: Discussionmentioning

confidence: 99%

Dehydration increases the magnitude of selective brain cooling independently of core temperature in sheep

Fuller¹,

Meyer²,

Mitchell³

et al. 2007

American Journal of Physiology-Regulatory, Integrative and Comp

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“…In artiodactyls, the extent of heat exchange in the carotid rete, and consequently the extent of selective brain cooling, depends on diverting cool venous blood from the evaporating surfaces in the nasal mucosa through the angularis oculi and associated veins to the cavernous sinus, or into the facial vein where it bypasses the venous lakes and the carotid rete [16,23]. Sympathetic stimulation of the cranial vasculature therefore reduces or abolishes selective brain cooling [2], whereas interruption of sympathetic supply augments selective brain cooling [26]. Sympathetic stimulation of the cranial vasculature therefore reduces or abolishes selective brain cooling [2], whereas interruption of sympathetic supply augments selective brain cooling [26].…”

Section: Relationship Between External Thermal Loads and Internal Bodmentioning

confidence: 99%

Brain, abdominal and arterial blood temperatures of free-ranging eland in their natural habitat

Fuller¹,

Moss²,

Skinner³

et al. 1999

Pfl�gers Archiv European Journal of Physiology

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Using implanted miniature data loggers we measured brain, arterial blood and abdominal temperatures at 5-min intervals in two free-ranging eland (Tragelaphus oryx) in their natural habitat. The animals were subjected to a nychthemeral range of globe temperature which exceeded 40 degrees C. Arterial blood exhibited a moderate amplitude (2.3 degrees C) nychthemeral rhythm, with a temperature peak at 1600-1800 hours, and a trough in the early morning at 0600-0800 hours. Mean abdominal temperature was 0.2-0.3 degrees C lower than the corresponding blood temperature, and had a peak-to-trough amplitude of 2.6 degrees C. Brain temperature closely paralleled changes in blood temperature but usually exceeded blood temperature by about 0.5 degrees C. Sporadic episodes of selective brain cooling occurred in one animal, but the duration and magnitude of such cooling was small (less than 0.4 degrees C), and took place only well above the mode of blood temperature. Our results do not support the concept that eland routinely employ adaptive heterothermy and selective brain cooling to survive in their natural environment.

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“…The magnitude of this selective brain cooling (SBC) is usually seen to be related directly to the rate of respiratory evaporative heat loss (REHL) and to the rate of blood flow through the upper respiratory passages (Baker & Hayward, 1968;Jessen & Pongratz, 1979;Baker, 1982;Bamford & Eccles, 1983). Selective brain cooling may also be affected by muscular venous sphincters BS 2016 which can change the direction of flow of blood draining the nasal passages (Johnsen, Blix, Mercer & Bolz, 1987;Nijland, Mitchell & Mitchell, 1990). Selective brain cooling has been viewed as a mechanism which can protect the brain from overheating (Carithers & Seagrave, 1976) and extend the range of body core temperature over which an animal can function in hot environments and during exercise (Taylor & Lyman, 1972).…”

Section: Introductionmentioning

confidence: 99%

Selective brain cooling in goats: effects of exercise and dehydration.

Baker

Nijland

1993

The Journal of Physiology

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SUMMARY1. Measurements of brain and central blood temperature (Tbr and Tbl), metabolic rate (MR) and respiratory evaporative heat loss (REHL) were made in trained goats walking on a treadmill at 4'8 km h-' at treadmill inclines of 0, 5, 10, 15 and 20 % when they were fully hydrated and at 0 % when they had been deprived of water for 72 h.2. In hydrated goats, exercise MR increased progressively with increasing treadmill incline. Both Tbl and Tbr rose during exercise, but Tbl always rose more than Tbr, and selective brain cooling (SBC = Tbl-Tbr) increased linearly with Tbl. Significant linear relationships were also present between REHL and Tbl and between SBC and REHL. Neither the slope of the regression relating SBC to Tbl nor the threshold Tbl for onset of SBC was affected by exercise intensity. Manual occlusion of the angularis oculi veins decreased SBC in a walking goat, while occlusion of the facial veins increased SBC. 3. Dehydrated goats had higher levels of Tbl, Tbr and SBC during exercise, but the relationship between SBC and Tbl was the same in hydrated and dehydrated animals. In dehydrated animals, REHL at a given Tbl was lower and SBC was thus maintained at reduced rates of REHL.4. It is concluded that SBC is a linear function of body core temperature in exercising goats and REHL appears to be a major factor underlying SBC in exercise. The maintenance of SBC in spite of reduced REHL in dehydrated animals could be a consequence of increased vascular resistance in the facial vein and increased flow of cool nasal venous blood into the cranial cavity.

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Selective brain cooling after bilateral superior cervical sympathectomy in sheep (Ovis aries)

Cited by 13 publications

References 27 publications

Dehydration increases the magnitude of selective brain cooling independently of core temperature in sheep

Dehydration increases the magnitude of selective brain cooling independently of core temperature in sheep

Brain, abdominal and arterial blood temperatures of free-ranging eland in their natural habitat

Selective brain cooling in goats: effects of exercise and dehydration.

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