The perfect knowledge of the microscopic structure of the appropriate organ is crucial in the solution of many urgent problems of clinical medicine. Better preservation of tissue structures is achieved when the tissues are embedded into epoxy resins followed up with the semi-thin section making. In contrast to the thick sections that are used for light microscopy, due to the greater awareness and relative cost effectiveness without the need of complicated expensive equipment, the method of semithin sections today is currently used in morphological studies. The paper was aimed at the study of the prospects of using the semi-thin section method to evaluate the immobilization stress-induced structural changes in the lungs. The resulting study showed the appropriateness of the use of semi-thin sections to study structural changes in lungs, induced by the experimental stress. The study of the semi-thin sections is the beneficial technique of the morphological analysis that permits to evaluate the structure of the studied material at the tissue and cellular level.

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Notwithstanding the long history of research, versatile studies of stress effect on living organisms are relevant to date. The stress response that arose in the process of evolution as a component of the adaptation process, in case of its unfavorable course, can trigger pathogenetic mechanisms of numerous pathologies. Investigation of the effect of stress reactions on living organisms requires the use of laboratory animals in the experimental studies, to which there is currently no alternative. In our opinion, special attention should be paid to those experimental models of stress that are easy-to-use, cost effective and are in concordance with current principles of bioethics. The purpose of the study was to study the impact of 6-hour-long cervical fold suspension experimental model of acute immobilization stress on the albino rat spleen. Material and methods. Based on the international bioethical principles, 10 male albino rats were involved in the study. The intact animals were assigned into control Group I (n=5); experimental Group II (n=5) involved animals, exposed to 6-hour-long cervical fold suspension model of acute immobilization stress. After euthanasia, macro- and microscopic examination of the spleen was made. Microspecimens were stained with hematoxylin and eosin. Results and discussion. The macroscopic analysis of the spleen revealed no visual differences in the rats of the experimental group compared to control ones. Histological study of the spleen specimens of the rat of Group II has shown sparse perivascular swellings of the central arteries, thickening of the periarterial zone, narrowing of the diameter of the germinal center due to the cell redistribution that was detected in the white pulp in the medium and large lymphoid nodules under the effect of the acute immobilization stress induced by the atraumatic cervical fold suspension for 6 hours. The above changes led to a relatively slight increase in the volume of the white pulp of the spleen by 4.23 ± 1.52%. A clear boundary between the white and red pulp was noted. In addition, disturbances in the microcirculation in the vessels of the hemomicrocirculatory bed, manifested by edema of the splenic stroma, plethora of vessels and a decrease in the number of erythrocytes in these areas in the subcapsular departments were noted. In the deeper layers of the spleen, foci of sparse perivascular diapedetic hemorrhages were found with the phenomena of blood stasis in the microcirculatory bed, leukostasis and sludge phenomenon. The described changes led to blood flow slowing in the microcirculatory bed with subsequent adhesion of erythrocytes and the formation of blood clots in the vessels of larger diameter. Thus, histologically, acute stress induced by cervical fold suspension causes minor morphological changes in the spleen of rats of the experimental group, the moderate severity of which indicates the relative resistance of splenic structures to the action of 6-hour-long immobilization. Conclusion. The findings of the study showed the relative resistance of the rat spleen to 6-hour-long stress caused by cervical fold suspension, with minor morphological changes in the white pulp and impaired hemomicrocirculation