Mechanisms underlying hypothalamic temperature changes during sleep in mammals.

The mechanisms underlying hypothalamic temperature (Thy) changes across the ultradian wake-sleep cycle were analyzed in cats chronically implanted with EEG and EMG electrodes, and transducers that measured Thy and pontine temperature (Tp). The influence of artificially induced changes in (i) systemic blood temperature, (ii) heat loss from the specific heat exchangers of the head, and (iii) carotid artery occlusion, on Thy, Tp and ear pinna temperature (Ts) during waking (W), synchronized sleep (SS) and desynchronized sleep (DS) were assessed in animals maintained in a thermoneutral environment. The results show that the decrease in Thy during SS is dependent on increased heat loss from heat exchangers (ear pinna), whereas the increase in Thy during DS is due to an alteration in the arterial blood perfusion of the circle of Willis receiving an increased supply of warm vertebral blood that replaces a decrease in supply of cool carotid blood.