Preoptic/anterior hypothalamic neurons: thermosensitivity in wakefulness and non rapid eye movement sleep.

Thermosensitive neurons of the preoptic/anterior hypothalamic area (POAH) have been implicated in the regulation of both body temperature and non rapid eye movement (NREM) sleep. During NREM sleep, a majority of POAH warm-sensitive neurons (WSN) exhibit increased discharge compared to wakefulness. Cold-sensitive neurons (CSN) exhibit reduced discharge in NREM sleep compared to wakefulness. To further study the mechanism underlying these processes, the present study compared discharge rate and thermosensitivity (discharge rate change/degree C) of WSNs and CSNs in NREM sleep and wakefulness in freely moving adult cats. The thermosensitivity of 24 WSNs and 31 CSNs from the medial POAH was determined from responses to local POAH warming and cooling. WSNs with increased discharge in NREM sleep exhibited increased thermosensitivity during NREM sleep compared to wakefulness. CSNs with decreased discharge during NREM sleep exhibited decreased thermosensitivity in NREM sleep. The change in thermosensitivity from wakefulness to NREM sleep was correlated with the change in discharge rate in WSNs but not in CSNs. In addition, 9 of 47 neurons that were thermo-insensitive during wakefulness became warm-sensitive during NREM sleep. Changes in POAH neuronal thermosensitivity could be a component of the mechanism for stabilization of state after state transition.