[Intracerebral sites of action of estrogen on the sleep-wakefulness circadian rhythm in female rats].

Effects of estradiol on the sleep-wakefulness circadian rhythm were studied in ovariectomized female rats under a 12: 12 light-dark schedule. In rats that were subcutaneously injected with 20 micrograms of estradiol benzoate (EB) or that had crystalline EB implanted into the third ventricle (III V), the total time of slow wave sleep (SWS) and paradoxical sleep (PS) in the night time was significantly decreased on the third day after the EB administration. The suppression of PS was more remarkable than that of SWS. Slight increases were observed in the total time of SWS and PS in the day time. These effects of estrogen on the appearance patterns of SWS and PS in the night and day time could be elicited in spayed rats after crystalline EB was implanted into the medial preoptic area (MPO) or the medial amygdala (mAMYG), but the implant into the latter proved less effective. Cholesterol implants into IIIV, MPO or mAMYG produced no change in the sleep-wakefulness circadian pattern. Implantations of crystalline EB into the ventromedial hypothalamic nucleus or the dorsomedial thalamic nucleus were ineffective. These results indicate that MPO is probably the most effective site of estrogen on the sleep-wakefulness circadian rhythm of female rats.