Brain Temperatures in the Rat during Exposure to Low Environmental Temperatures.

LOMAX, PETER, E. MALVEAUX, AND R. E. SMITH. Brain temperatures in the rat during exposure to low environmental temperatures. Am. J. Physiol. 207(s) : 736-739. 1g64.-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 coldacclimated 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.