Wakefulness–;Sleep Cycle and hypothalamo-Pituitary System of Young Rat Pups on the Background of Photostimulation

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Abstract

Effects of multiple photostimulations (PS) on behavioral reactions of the 30-day old rats were studied in the “open field” test, on the dynamics of the time EEG parameters of the wakefulness-sleep cycle, and on morpho-functional characteristics of the hypothalamo-pituitary neuroendocrine system. It has been revealed that PS promotes the gradual inhibition of the locomotor activity and exploratory behavior (p < 0.05) and an enhancement of autonomic reactions (p < 0.05) as well as an initial increase of intensity of orientation reactions with a subsequent decrease of their number (in connection with adaptation to a light stimulus), A comparative analysis of time parameters of the wakefulness-sleep cycle (WSC) shows a decrease of the part of wakefulness, the slow-wave and rapid-wave sleep phases with a simultaneous increase of the cataleptic stage and the sleep stage transient to the rapid-wave stage, as well as of the number of microactivations appearing on the sleep background at once after the several first PS. By the 4–5th photostimulations the CWS parameters on the whole are restored, except for the cataleptic stage, whose value remains statistically significantly high. The obtained data indicate the initial total CNS excitation and a decrease of the CWS stability. This conclusion is confirmed by the data of analysis of spectral characteristics of electrograms of cortical, hippocampal, hypothalamic brain parts and of caudate nucleus, which revealed only a brief small increase of δ-waves in the slow-wave sleep phase, but a statistically significant long decrease of power of the EEG δ-and θ-oscillations with a simultaneous power increase of α-components in the rapid-wave sleep. The quantitative parameters of changes of the morpho-functional state of neurosecretory cells of the hypothalamus supraoptic and paraventricular nuclei indicate the stress effect of this performed stimulation. The aspects of interaction of the hypothalamic-cortical and thalamo-cortical levels of the CWS integration on the background of chronic stress are discussed.

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