CIRCADIAN SLEEP-WAKEFULNESS PATTERNS IN RATS AFTER OVARIECTOMY AND TREATMENT WITH ESTROGEN

Electroencephalographic records were obtained from unanesthetized freely moving rats with electrodes permanently implanted in the olfactory bulb, hippocampus, and frontal cortex while the animals were housed in large glass cylinders within a sound-, temperature-, and light-controlled chamber. The EEG records were converted to percentages of alertness, slow-wave sleep, and paradoxical sleep for each 10-min. interval around the clock and analyzed by computer. After ovariectomy, the records showed greater amounts of slow-wave sleep per day largely because of major increases in nighttime slow-wave sleep levels. Furthermore, the circadian pattern of paradoxical sleep was altered by ovariectomy: the daily (24-hour) amounts of paradoxical sleep remained constant but the night-time hours contained more and the daylight hours concomitantly less, almost obscuring the circadian rhythm. Estrogen injections restored the circadian pattern by sharply reducing the amount of paradoxical sleep at night, resulting in significant diminution in total paradoxical sleep per 24 hours. © 1969.