Morphological reaction of GFAP+ thymus cells to melatonin supply under different light conditions

Introduction. The neural crest-derived thymic cell population can be detected using glial fibrillary acidic protein (GFAP) antibodies and it does not overlap with the neuron-specific enolase (NSE+) cell population. We focused on investigating the response of GFAP+ thymic cells to photoperiod changes and melatonin administration. Materials and methods. We performed a 4-week experiment on sixty 3-week-old male Wistar rats, which were divided into 6 groups: groups I and II were kept in the natural photoperiod; groups III and IV were in constant darkness; and groups V and VI were observed under constant light (24 hours). Subjects from groups II, IV, and VI were given ad libitum access to drinking water with “Melaxen” at a concentration of 4 mg/L. Antibodies to GFAP were used to detect astrocyte-like cells in the thymus. Results. In the thymus lobule, GFAP+ cells were found in the corticomedullary and subcapsular zones, as well as in the cortical thickness of the lobules. Under the conditions of constant light, the number of the studied cells increased in the premedullary zone of the lobules, whereas the optical density of glial fibrillary acidic protein decreased in all studied cell zones. In groups V and VI, we observed a decrease in the total number of the studied cells and thymus involution area, as well as an increase in the content of glial fibrillary acidic protein in the cells of the diffuse endocrine system. Conclusion. Our study has shown that GFAP+ cells of the thymus gland are sensitive to photoperiod changes. Under conditions of constant light, pronounced morphological changes are observed in GFAP+ cells. The changes are accompanied by destructive changes in the thymus lobules and can be leveled by melatonin introduction. Keywords: glial fibrillary protein, diffuse endocrine system, thymus gland, melatonin, photoperiod