Changes in sleep-wakefulness in female rats during circadian and estrous cycles

Abstract

Continuous EEG records from chronically implanted cerebral electrodes have been made of sleep-wakefulness in 5 female rats throughout their 4-day or 5-day estrous cycles, under controlled lighting conditions with 14 h light and 10 h darkness per day. Percentages of alertness, slow wave sleep (SS) and paradoxical sleep (PS) in each 10-min period were punched on IBM cards and introduced to a computer system capable of plotting these percentages daily in each rat and averaging across animals for each time period on corresponding days of the estrous cycle. The results reveal rapid shifts from relative alertness to sleep after the lights come on in the morning. Highest levels of alertness generally occur during the early evening and PS during the afternoon, including the afternoon of proestrus. The day of vaginal cornification (‘estrus’) shows a high percentage of PS — after a night characterized by alertness and virtual absence of PS, i.e., the night of behavioral estrus and ovulation. The female rat, like the male, sleeps on the average about two-thirds of the daylight hours and only one-third of the dark period. Hormonal changes during the day of proestrus appear to increase alertness that night, compensated by an increase in sleep, especially PS, the following day.