CHANGES IN HYPOTHALAMIC PROSTAGLANDIN E(2) MAY PREDICT THE OCCURRENCEOF SLEEP OR WAKEFULNESS AS ASSESSED BY PARALLEL EEG AND MICRODIALYSISIN THE RAT

Prostaglandin (PG) E(2) is produced by mammalian hypothalamus and when administered exogenously prolongs wakefulness. In order to study the relation of endogenous hypothalamic PGE(2) to sleep and wakefulness, w e have used microdialysis in freely moving rats associated with EEG re cording. Male Wistar rats were implanted with three cortical electrode s and with a guide cannula for microdialysis in the space between the paraventricular nucleus (PVN) and the ventromedial hypothalamus (VMH). PGE(2) was measured by RIA in 3-or 6-min dialysates 15 days after sur gery, when sleep patterns were normal again and PGE(2) production stab ilised. PGE(2) levels were significantly higher during wakefulness (60 1 +/- 35 pg/ml, 5 experiments, 35 samples) than during slow-wave sleep (487 +/- 24 pg/ml, 5 experiments, 49 samples). Samples corresponding to paradoxical sleep showed a tendency towards higher PGE(2) values co mpared to slow-wave sleep but lower compared to wakefulness. In epochs of wakefulness or sleep lasting at least 12 min, high PGE(2) levels i n the middle of wakefulness regularly dropped, thus announcing the occ urrence of sleep. During sleep, PGE(2) first went on dropping and then reincreased towards the values that characterize early periods of wak efulness. In its turn, this reincrease in PGE(2) announced the end of sleep and the imminent occurrence of wakefulness. It is the first stud y to our knowledge showing that the evolvement in endogenous PG profil e may predict the occurrence of sleep or wakefulness.