Responses of extrahypothalamic neurons to short temperature transients during the ultradian wake-sleep cycle

The thermosensitivity of neurons in thalamo-striate-limbic structures located dorsally to the classical thermosensitive anterior hypothalamic-preoptic region was studied in cats during the natural ultradian wake-sleep cycle. Direct cooling or warming of the brain tissue by means of water-perfused thermodes was combined with tonic cooling or warming of the abdominal wall using a water-perfused heat exchanger on which the animal was lying. Out of 482 neurons, 116 (24.1%) were thermosensitive. They were located in the nuclei reticularis and ventralis anterior of the thalamus, the fundus of the caudate nucleus, the bed nucleus of the stria terminalis, the bed nucleus of the inferior thalamic peduncle, and the nucleus of the anterior commissure. Abdominal warming increased the effect of direct brain warming and decreased the effect of direct brain cooling; opposite effects were obtained by abdominal cooling. Thermosensitivity was present during wakefulness and synchronized sleep, but depressed or altered during desynchronized sleep.