Electric lighting at night has become an essential part of the lifestyle of a modern person. Its change is one of the strongest external synchronizers of biorhythms. Long-term illumination at night causes serious disorder of behavior and functional state at the molecular, cellular and organizational levels. There is no detail analysis in the scientific literature of the level of emotional and behavioral reactivity of rats, which were maintained when the mode of illumination was changed. Therefore, based on the relevance of the problem, the purpose of the study is to examine the functional changes in behavioral responses of rat females in the "open field" caused by different modes of illumination. Material and methods. At the beginning of research, we formed 3 groups based on the nature and intensity of light: C - control, 12/12 and 24/00 groups. Female rats of the control C-group were in day light. Rats of 12/12 group were being held by the action of artificial light for 12 hours a day; animals of 24/00-group were under the influence of round-the-clock artificial lighting. Behavioral reactions in the "open field" test were investigated in 30 sexually mature Wistar females at the age of 5.5-6 months, weighing 160-284 grams according to the generally accepted method. Results and discussion. During the test in the "open field" it was found out that the motor behavior of rat females in the control group was different from the behavior dynamics of rat females kept in conditions of changing the mode of illumination: their horizontal activity to the third experimental day decreased and the number of washes statistically significant increased (P≤0.05). Despite the lack of consistency in the changes in locomotor and rudder indices of 12/12 group rats during testing, based on the final results, it can be concluded that they had similar dynamics with the 24/00 group females. The horizontal motor activity of the animals, which was maintained at round-the-clock light, gradually increased statistically significant (P≤0.05) to the third experimental day, and the grooming behavior decreases. The level of research activity in females of 12/12-group and 24/00-group was higher compared to the control group. The high level of research behavior of 12/12-group and 24/00-group of rats, in conditions of increased anxiety (indicators of grooming behavior are rising), in the last day, as compared to the control group, indicates a low resistance of rat females of these groups to the stress factors and possible adaptation to them. Negative correlation of horizontal and vertical activity in 12/12 group of rats (r = -0.97) and 24/00 (r = -0.64) indicates that these indicators have moved to a new qualitative state. It means that rat females, which were in change of light conditions, possibly could have the formation of a new model of behavioral reactions on the neuronal level with changes in ensembles of neurons. Rat females of the control group had a decrease in the level of fear and gradual adaptation to unusual conditions development, due to a statistically significant increase in the number of boluses (Р≤0.05). Compared to the C-group, the 12/12 rats group did not tend to become addicted to vulnerable conditions, but their level of anxiety decreased. Compared to other groups, the 24/00-group rat females were characterized by less pronounced adaptation to adverse conditions, which manifested itself as an increase in motor activity with a decrease in the level of bowel movements and more severe aggressiveness. Conclusions. Thus, the change in the mode of illumination has led to the advantage of the active-defensive type of behavior in females of 12/12- and 24/00-groups. Animals of the control group were characterized by passive-defensive behavior. In general, rats, which were kept under conditions of changing the mode of illumination, got inherent low adaptive capacity, activity, aggressiveness and ability to self-regulation. Rats kept at round-the-clock illumination were less resistant to the action of the stress factor of the "open field", their behavioral reactions were not accompanied by the search for new information.
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