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Received August 9, 2003
Revised September 12, 2003
Accepted after revision October 22, 2003
1 National Institute of Health and Nutrition
* To whom correspondence should be addressed. E-mail: osaka{at}nih.go.jp.
Non-noxious cooling stimuli were delivered to the shaved
back of urethane-chloralose-anaesthetized, artificially
ventilated rats by a plastic bag containing 24-40°C
water. Cooling of the skin by 2-6°C increased the
rate of whole body oxygen consumption (VO2)
and triggered electromyographic (EMG) activity recorded
from the neck or femoral muscles. The cooling-induced
VO2 responses did not depend on core
(colonic) temperature and followed skin temperature in a
graded manner. Pretreatment with the 
-blocker
propranolol (10 mg kg-1, I.V.) greatly
attenuated the VO2 response but did not
affect the EMG response. On the other hand,
pretreatment with the muscle relaxant pancuronium
bromide (2 mg kg-1, I.V.) affected very
slightly the VO2 response but completely
abolished the EMG activity. Accordingly, the cooling
stimulus activated mainly nonshivering thermogenesis.
Next, the contribution of the cerebral cortex to the
cooling-induced thermogenesis was examined. Power
spectral analysis of the electroencephalogram (EEG)
showed that the cooling stimulus largely inhibited delta
(0.5-3 Hz) waves, enhanced theta (3-8 Hz) waves, and
slightly increased frequencies higher than 8 Hz.
Pinching the hind paw elicited changes in EEG similar to
those elicited by skin cooling but did not increase the
VO2. Therefore, there was no relationship
between changes in the EEG and the magnitude of
thermogenesis. Finally, skin cooling increased the
VO2 of decorticated rats but did not increase
that of decerebrated rats. The results suggest that the
subcortical forebrain structure, but not cortical
activation, is indispensable for nonshivering
thermogenesis elicited by cooling stimulation of the
skin.
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