The effect of motion sickness on the sleep–wake cycle in rats exposed to prenatal hypoxia

Abstract

This study is a continuation of our research of phenomenology and mechanisms of motion sickness (MS) and the relation of this phenomenon to features of sleep-wake cycle (SWC) changes. It presents data about the effect of MS on SWC in 30-day-old intact rats and rats exposed previously to prenatal hypoxia on days 13 and 19 of gestation. In all groups of animals MS was shown to reduce significantly the waking time and to increase the time of paradoxical sleep (PS). For the first time it became possible to reveal a connection between hypothalamic mechanisms controlling MS and SWC and to suggest the role of this connection in mechanisms of development of the sopite syndrome which may be the only manifestation of MS in some animals and man. The results obtained demonstrate that hypoxia on day 19 of gestation has a greater damaging effect on the thalamocortical sleep-regulating structures than hypoxia on day 13 when only hypothalamic-hippocampal systems controlling slow-wave sleep were found disturbed. Against this background MS substantially suppresses the activity of the brain excitatory systems which provide wake- fulness maintenance (it appears to be the ascending reticular activating system) and enhances the work of those activating systems that control PS. It is in rats exposed to preliminary hypoxia on day 19 of gesta- tion, where it was possible to show the role of the evolutionary young thalamocortical system in the control of PS.