Non-thermal signals govern selective brain cooling in pigs |
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Authors: | A Fuller G Mitchell D Mitchell |
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Institution: | (1) Department of Physiology, University of the Witwatersrand, Medical School, 7 York Road, Parktown 2193, South Africa e-mail: 127andy@chiron.wits.ac.za Tel.: +27-11-6472363; Fax: +27-11-6432765, ZA |
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Abstract: | We used implanted miniature data loggers and fine thermistors to measure arterial blood and brain temperatures in four female
pigs, to a resolution of 0.04 °C, every 5 min, for 4 weeks. Within that period, pigs were exposed on different days, and in
random order, to a cold (5 °C) or hot (38 °C) environment. In the thermoneutral environment of the pigs' home pens, brain
temperature was usually lower than blood temperature. Such selective brain cooling was absent for 2 days after surgery, during
handling and transport stress, and on waking. The magnitude of selective brain cooling was greatest when pigs were sleeping
and body temperatures were low, and was smallest, or even absent, during hyperthermia and natural fever. Our results showed
that selective brain cooling was present in pigs, but there was no clear relationship between blood temperature and the magnitude
of selective brain cooling. Instead, the degree of selective brain cooling in pigs was governed by non-thermal factors, especially
those associated with high sympathetic nervous system activity. Our results further support the concept that selective brain
cooling does not serve to protect the brain from thermal damage during heat stress.
Accepted: 14 September 1999 |
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Keywords: | Body temperature Brain temperature Fever Sleep Sympathetic activity |
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