AJP - Regulatory, Integrative and Comparative Physiology, Vol 267, Issue 6 1528-R1536, Copyright © 1994 by American Physiological Society
Blood and brain temperatures of free-ranging black wildebeest in their natural environment
C. Jessen, H. P. Laburn, M. H. Knight, G. Kuhnen, K. Goelst and D. Mitchell
Physiologisches Institut, Justus-Liebig-Universitat, Giessen, Germany.
Using miniature data loggers, we measured the temperatures of carotid blood
and brain in four wildebeest (Connochaetes gnou) every 2 min for 3 wk and
every 5 min, in two of the animals, for a further 6 wk. The animals ranged
freely in their natural habitat, in which there was no shelter. They were
subject to intense radiant heat (maximum approximately 1,000 W/m2) during
the day. Arterial blood temperature showed a circadian rhythm with low
amplitude (< 1 degree C) and peaked in early evening. Brain temperature
was usually within 0.2 degrees C of arterial blood temperature. Above a
threshold between 38.8 and 39.2 degrees C, brain temperature tended to
plateau so that the animals exhibited selective brain cooling. However,
selective brain cooling sometimes was absent even when blood temperature
was high and present when it was low. During helicopter chases, selective
brain cooling was absent, even though brain temperature was near 42 degrees
C. We believe that selective brain cooling is controlled by brain
temperature but is modulated by sympathetic nervous system status. In
particular, selective brain cooling may be abolished by high sympathetic
activity even at high brain temperatures.
