The role of the medial preoptic area in the organization of paradoxical sleep

Influence of electrical stimulation of the medial preoptic area of cats on characteristics of paradoxical sleep and activity of medial preoptic neurons were studied in the course of sleep-waking cycle. Low-frequency stimulation of this structure in the state of slow-wave sleep evoked short-latency electrocortical desynchronization and induced transition to paradoxical sleep or paradocical sleep-like state. The same stimulation during the whole period of paradoxical sleep results in a reduction of its duration, practically complete disappearance of tonic stage, and increase in the density of rapid eye movements in phasic stage. The vast majority of meurons in the medial preoptic area decreased their firing rates during quiet waking and slow-wave sleep and dramatically increased their activity during paradoxical sleep. More than 50% of such neurons displayed activation 20-70 s prior to the appearance of electrocorticographic correlates of paradoxical sleep. Some neurons were selectively active during paradoxical sleep. Approximately 50% of cells increased their firing rates a few seconds prior to and/or during series of rapid eye movements. The results suggest that the medial preoptic area contains the units of the executive system (network) of paradoxical sleep and are involved in the mechanisms of neocortical desynchronization.