A pontine-hypothalamic temperature difference correlated with cutaneous and respiratory heat loss

The role of cutaneous and respiratory heat loss for selective brain cooling in different species is discussed and new experimental results from a comparative study are summarized. In three species (cat, rabbit and rat) the difference between pontine and hypothalamic temperatures was studied as a function of head heat exchanger vasomotion appraised by the difference between hypothalamic and ear pinna (cats and rabbits) or nasal mucosa (rats) temperatures during the behavioral states of wakefulness and slow wave sleep at an ambient temperature of 24+/-1 degrees C. The results show that: (i) the pontine-hypothalamic temperature difference is an useful indicator of selective brain cooling since it is positive and inversely correlated with the hypothalamic-ear pinna temperature difference in cats and rabbits and with the hypothalamic-nasal mucosa temperature difference in rats; (ii) respiratory heat loss prevails quantitatively over cutaneous heat loss in maintaining this difference.