Ventskovska O. Influence of cooling on sleep-wake cycle structure in rats

The object of the research is sleep-wake cycle under the influence of rhythmic cold exposures. The aim of the research is to determine the characteristics of rat's sleep-wake cycle changes under the influence of various types of rhythmic cold exposures to justify the possibility of correction of sleep-wake cycle disturbances. Research methods: cryobiological, electrophysiological, biochemical, radioimmunoassay and statistics. The aim of the thesis was to investigate the effects of either long-term continuous (LTCE) or rhythmic cold exposures (RCE) on the sleep-wake cycle of rats. The different types of cold exposures differed in their levels of thermal load and in their ability to activate the thyroid hormone axis. Both LTCE and RCE induced cold acclimation, but the activation of the thyroid hormone axis was stronger by LCTE. This difference was reflected to the changes in sleep. LTCE increased the depth and duration of both slow wave sleep (SWS) and rapid eye movement (REM) sleep, while RCE (-12°С) increased only REM sleep duration, and RCE (10°С) only the duration of SWS. There has been shown that the skin surface temperature rise after each series of RCE (10°С) combined with an increased level of nitric oxide metabolism products in blood serum, promoted SWS amount augmentation. The compensatory increase of REM sleep amount after RCE (-12°С) was of a rhythmic character, indicating the ability of RCE to adjust sleep biorhythm. RCE accelerated the recovery of daily sleep distribution after light-dark inversion, but the final restoration of sleep hourly dynamics has not been observed.