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Re: Hot brains

On Nov. 22, Jeff Martz wrote:

>Elizabeth Vrba has studied some sort of brain cooling system in some kind
>of African ungulate, an antelope of gazelle of some kind.  Does anyone
>know what I am talking about?

        The actual term is selective brain cooling (SBC).  This occurs as
a result of cool venous blood draining from the nasal mucosa and skin of the
head.  This cooled blood flows into the venous sinuses at the base of the 
brain, where heat exchange with warm blood from the carotid artery leads to
brain temperatures which are slightly below core body temperature.
        Though characteristic of many mammals and birds, it is unclear
how widespread this process is.  SBC has been documented in artiodactyls,
horses, dogs, cats, rabbits and some primates and rodents.  Whether SBC
occurs in humans remains controversial.  Selective brain cooling has been
documented in birds, but here the evidence is less complete, and it seems
clear some birds do not regulate their brain temperatures tightly.
Helmeted Guineafowl (_Numida meleagris_), for example, exhibit brain 
temperatures of 36-42C.

        Withers, P.C. & Crowe, T. M. (1980).  Brain temperature fluctuations
in helmeted guineafowl under semi-natural conditions.  Condor, 82, 99-100.
        McConaghy, F. F., Hales, J.R.S., Rose, R.J. & Hodgson, D.R. (1995).
Selective brain cooling in the horse during exercise and environmental
heat stress.  Journal of Applied Physiology, 79 (6), 1849-1854.
        Jessen, C., LaBurn, H.P., Knight, M.H., Kuhnen, G., Goelst, K. &
Mitchell, D. (1994).  Blood and brain temperatures of free-ranging black
wildebeest in their natural environment.  American Journal of Physiology,
267, R1528-1536.
        Mitchell, D., LaBurn, H.P., Nijland, M.J.M., Zurovsky, Y. & Mitchell,
G. (1987).  Selective brain cooling and survival.  South African Journal 
of Science, 83, 598-604.
        Johnson, H.K. & Folkow, L.P. (1988).  Vascular control of brain
cooling in reindeer.  American Journal of Physiology, 254, R730-739.

Guy Leahy
Dept. of PEHR
Western Washington University
Bellingham, WA 98225