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National Institute of Health and Nutrition, Shinjuku 162-8636, Japan
Non-noxious cooling stimuli were delivered to the shaved back of urethane-chloralose-anaesthetized, artificially ventilated rats using a plastic bag containing water at 24–40°C. Cooling of the skin by 2–6°C increased the rate of whole body oxygen consumption 
and triggered electromyographic (EMG) activity recorded from the neck or femoral muscles. The cooling-induced 
responses did not depend on core (colonic) temperature and followed skin temperature in a graded manner. Pretreatment with the ß-blocker propranolol (10 mg kg-1, I.V.) greatly attenuated the 
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 the 
response very slightly but completely abolished the EMG activity. Accordingly, the cooling stimulus activated mainly non-shivering 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 hindpaw elicited changes in EEG similar to those elicited by skin cooling but did not increase the 
. Therefore, there was no relationship between changes in the EEG and the magnitude of thermogenesis. Finally, skin cooling increased the 
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 non-shivering thermogenesis elicited by cooling stimulation of the skin.
(Received 9 August 2003;
accepted after revision 22 October 2004;
first published online 24 October 2003)
Corresponding author T. Osaka: National Institute of Health and Nutrition, Shinjuku 162-8636, Japan. Email: osaka{at}nih.go.jp
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