The relationship between sleep circadian rhythm and central feedback mechanism of gonadal steroid in female guinea pigs.

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Abstract
To examine the relationship between the sleep rhythm and the gonadal feedback system in the guinea pig, the effects of estrous cycle, gonadal steroids and brain deafferentations on the sleep rhythm were studied. The guinea pigs did not show an apparent circadian rhythmicity in the sleep-wakefulness cycle but showed an ultradian rhythm, whereas, the activity rhythm was circadian. The rhythm in paradoxical sleep(PS) showed changes associated with the estrous cycle which were characterized by a decrease and rebound-like increase in PS amounts on the day of proestrus. The horizontal deafferentation above the medial preoptic area at the level of the anterior commissure (MPO roof cut) did not disrupt the estrous cycle dependent changes in the PS rhythm, but the prechiasmatic deafferentation of the medial basal hypothalamus (PCD) and the large complete deafferentation of the medial basal hypothalamus (CDL) disrupted them. Ovariectomy (OVX) did not result in any changes in sleep and activity rhythms. An administration of estradiol benzoate (E2) to OVX guinea pig caused a decrease in the amount of PS and an administration of progesterone(P) 48h after E2 caused a more pronounced decrease and rebound-like increase in the amount of PS. The MPO roof cut did not affect the steroidal modification of the PS rhythm and the PCD disrupted it, while the CDL-animal also showed an E2-induced PS decrease. The guinea pig may be a circadian animal, but this may not be seen in the sleep-wakefulness cycle. The estrous cycle dependent changes in the PS rhythm may be the reflection of steroidal modification of the sleep rhythm with the site of action being the inside of the medial preoptic anterior hypothalamic structures, but this area may also be affected by the output from the medial basal hypothalamus.