INVESTIGATION OF THE EFFECT OF LIGHT REGIME AND MELATONIN ON THE INTENSITY OF THYMUS INVOLUTION IN RATS MEDIATED BY SEROTONIN-CONTAINING MAST CELLS

Abstract

The purpose of this work was to study the effect of melatonin on serotonin-containing mast cells of rat thymus and their role in thymus involution in different light conditions. Materials and methods. Male Wistar rats (n = 60) were divided into six groups: the first and second were kept under conditions of natural photoperiod, the third and fourth – under conditions of constant obscuring, the fifth and sixth groups – under conditions of continuous illumination for 4 weeks. Melatonin was received by animals of the second, fourth and sixth groups in the form of the drug "Melaxen" ad libium at the concentration of 4 mg / l with drinking water for 4 weeks. Immunocytochemical reaction (5-hydroxytryptamine, 5-HT) and luminescent histochemical methods were used for selective detection of serotonin, catecholamines and histamine. Results and discussion. Continuous illumination (24/24) leads to a decrease in the number of mast cells in the areas of thymus atrophy in rats. Administration of melatonin increases the number of mast cells regardless of lighting conditions. The content of serotonin in MCs decreases in conditions of constant obscuring and increases in conditions of continuous illumination. Melatonin increases the content of serotonin in mast cells only in conditions of constant obscuring. Constant obscuring (0/24) results in a decrease in the number of white adipocytes, and continuous illumination (24/24) leads to an increase in the number of white adipocytes in the involution zones. Melatonin introduction reduces the number of white adipocytes regardless of lighting conditions. Measurement of serotonin optical density in white adipocytes showed that continuous illumination reduces the content of serotonin in the cells under study. Exogenous melatonin increases the serotonin content in adipocytes in constant obscuring and decreases it in continuous illumination. We revealed a direct strong correlation dependence between the content of serotonin in mast cells and adipocytes of perithymic white adipose tissue (r = 0.82; p < 0.05) in the group of control animals, which increased if the test animals were in continuous lighting conditions (r = 0.99; p < 0.05). Conclusions. A decrease in the number of adipocytes in the involution sites in obscuring conditions was found to be associated with a decrease in the production of serotonin by mast cells, and an increase in the number of adipocytes under continuous illumination is associated with an increase in serotonin secretion by mast cells.