Abstract
Sleep cycles were studied by electroencephalographic (EEG) methods during the estrous cycle in female rats with chronic electrodes implanted in their brains. Results were expressed as percentages of EEG arousal (AR), spindle or slow-wave sleep (SS), and activated or paradoxical sleep (PS). Sleep cycles were not completely regular, but 40%–50% of the PS episodes were separated by AR-SS intervals of 10–20 minutes duration in all stages of the estrous cycle. During proestrus the rats showed maximal AR and minimal PS even though running activity had increased the previous night. Running activity was maximal on the night between proestrus and estrus, and the latter day (vaginal cornification) appeared to be a period of recovery, with increased amounts of both types of sleep. Results of ovariectomy and estrogen replacement suggest that the primary influence of hormone is upon activity, from which recovery by sleep is a secondary effect. This suggestion is supported by results of forced-running (sleep-deprivation) experiments in spayed rats in which recovery involved amounts of SS and PS similar to those encountered on the day of vaginal cornification in cyclic rats.
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