Sleep in the opossum Didelphis marsupialis.

Abstract Polygraphic correlates of waking and sleep were studied under carefully controlled conditions in five opossums ( Didelphis marsupialis ). On the basis of many criteria, slow wave sleep (SWS) and paradoxical sleep (PS) were judged to be very similar to these states in placental mammals. Cortical and hippocampal activity during waking and both states of sleep were typically mammalian. During PS, brain temperature increased and blood pressure decreased, whereas heart and respiration rates became irregular. Neck muscle tonus was always minimal during PS but was usually minimal during SWS. Using electrical shocks to the chest, thresholds for eliciting behavioral arousal were lowest during waking and highest during PS. Based on 24 h recordings, total sleep time averaged 80.8% of total recording time and PS occupied 29.1% of total sleep time. It is concluded that the polygraphic manifestations of sleep are essentially identical in marsupial and placental mammals. The large amount of PS is probably not due to the fact that the opossum is a primitive mammal, but rather reflects differences in behavioral characteristics of sleep.

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