NEURONAL DISCHARGE OF PREOPTIC-ANTERIOR HYPOTHALAMIC THERMOSENSITIVE NEURONS - RELATION TO NREM SLEEP

Thermosensitive neurons of the preoptic/anterior hypothalamic area (PO AH) have been implicated in the regulation of non-rapid eye movement(N REM) sleep. We attempted to identify those medial POAH thermosensitive neurons that may be involved in NREM sleep regulation. The thermosens itivity of medial POAH neurons was studied in five freely moving adult cats by local cooling or warming of the medial POAH with a water-perf used thermode. Of 308 neurons, 65 (21%) were classified as thermosensi tive, including 31 (10%) warm-sensitive and 34 (11%) cold-sensitive ne urons. The spontaneous discharge rates of 28 warm-sensitive, 34 cold-s ensitive, and 115 randomly selected thermoinsensitive neurons were rec orded through one to three sleep-waking cycles. Patterns of spontaneou s activity for warm- and cold-sensitive neurons were different. Of 28 warm-sensitive neurons, 18 (64%) exhibited increased discharge rate du ring NREM sleep compared with waking (NREM/wake, greater than or equal to 1.2). This subpopulation of warm-sensitive neurons also exhibited significantly increased thermosensitivity when tested during NREM slee p. Of 34 cold-sensitive neurons, 25 (74%) discharged more slowly durin g NREM sleep compared with waking (NREM/wake, less than or equal to 0. 8). This subpopulation of cold-sensitive neurons exhibited decreased t hermosensitivity during NREM sleep. These results are consistent with a hypothesis that the activation of sleep-related warm-sensitive neuro ns and the deactivation of wake-related cold-sensitive neurons may pla y a key role in the onset and regulation of NREM sleep.