ON THE INFLUENCE OF PRENATAL HYPOXIA ON FORMATION OF THE OREXINERGIC SYSTEM AND SLEEP-WAKEFULNESS CYCLE IN EARLY POSTNATAL ONTOGENESIS OF RATS
The role of orexin in the organization of sleep-wakefulness cycle (SWC) is well known. The aim of this study was to examine the terms of formation of the orexinergic system in the rat postnatal ontogenesis and to assess the role of orexin A in SWC organization under normal conditions and after prenatal hypoxia realized on days 14 and 19 of the embryogenesis. SWC was investigated in 30-day-old rats with electrodes implanted into the somatosensory and occipital cortex. Immunoreactivity in the orexinergic structures of the lateral hypothalamus was also studied. It was shown that in the control 14-day-old animals the orexinergic structures were at the formation stage whereas in the 30-day-old ones they were already formed as in adults. In the 14-day-old rats prenatal hypoxia evoked retardation of the orexinergic system formation terms. In the 30-day-old rats the orexinergic system activity after hypoxia was increased, with hypoxia on day 19 activating this system stronger than hypoxia on day 14 of gestation. These changes were reflected in the SWC formation in the 30-day-old rats as shortening of the slow-wave phase of sleep, increase in the fitful sleep and in the number of transitions from the slow-wave to the fast-wave phase of sleep. The results obtained are discussed in the light of the adaptation-compensatory role of the orexinergic system in the postnatal ontogenesis after prenatal damage affecting the central neural system.