Brain temperatures in the rat during exposure to low environmental temperatures

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Abstract
Exposure to cold is known to elicit a rise in metabolic rate in various tissues of homeothermic animals. The role of the hypothalamus in this response was investigated by exposing normal and cold-acclimated rats to environmental temperatures of 26 C, 6 C, and –8 C and comparing the temperature changes in the thalamus, hypothalamus, and rectum using chronically implanted thermocouples. At all environmental temperatures the cold-acclimated rats had lower hypothalamic temperatures than did the normal animals. Apart from this, pattern of response was similar in all animals; the hypothalamic temperature tends to increase on exposure of the animal to cold while the adjacent thalamic region shows a marked fall in temperature, the rectal temperature staying fairly constant. This difference in response suggests increased metabolic heat production in the hypothalamus on exposure of the rat to low temperatures.