Selective brain cooling of reindeer during rest and exercise

Selective brain cooling was determined in three reindeer (Rangifer tarandus tarandus) during rest and during exercise. Brain temperature was measured in the hypothalamus and blood temperature in the right carotid artery. To induce selective brain cooling during rest, body temperature was increased by means of a heat exchanger introduced into the rumen via a chronically implanted rumen cannula. During exercise the reindeer I an on a treadmill at a speed of 5.5 to 8 km/h and a slope of 13.5 degrees for 30 to 60 minutes. The threshold temperature for the activation of selective brain cooling was 38.7 +/- 0.2 degrees C (mean +/- SD, N = 3, n = 18) during rest and was significantly (p < 0.001) elevated to 39.6 +/- 0.3 degrees C (N = 3, n = 18) during exercise. The result does not fit with the general belief that the main objective of selective brain cooling is to prevent heat damage but it supports the hypothesis that selective brain cooling may work to modify the general thermoregulation of the body.