Release of heat-loss responses in paradoxical sleep by thermal loads and by pontine tegmental lesions in cats.

Thermoregulatory heat-loss responses at high ambient temperatures were studied in intact cats and those with bilateral electrolytic lesions in the pontine tegmentum during wakefulness (W), slow-wave sleep (SWS), paradoxical sleep (PS) and PS without atonia induced by the lesions. Panting (respiratory rate greater than or equal to 90/min) was present during W, SWS, and in some cases, during PS. The percentage of the PS episodes with panting was directly related to ambient temperature. In intact cats at 30 degrees C, panting occurred in 8% of the PS episodes; at 35 degrees C, in 52%, and at 40 degrees C, in 77%. The percentage of PS episodes with panting was higher in the pontine-lesioned cats (90% at 35 degrees C), probably another indication of the altered thermoregulation of such animals. Thermoregulatory responses to heat load, and thermoregulation in general, have previously been shown to be suppressed in PS. Because hypothalamic thermosensitive neurons lack thermal responses during PS, the partial activation of heat-loss responses observed here may depend upon the function of extrahypothalamic brainstem areas.