Light-Induced Functional Pinealectomy. Effect on the Thymus of C57BL/6 Mice

Light-induced functional pinealectomy was simulated in C57BL/6 mice by 14-day exposure to constant lighting. Immunophenotyping of CD3^hi and CD3^low thymocytes was performed by staining with CD3-APC antibodies followed by flow cytofluorometry. To study the cell cycle distribution of thymus cells, the content of intracellular DNA was measured by the level PI inclusion. In animals with light-induced functional pinealectomy, blood leukocyte content, the relative number of CD3^low and CD3^hi T cells in the thymus, and the ratio of CD3^low/CD3^hi thymocytes decreased. The number of G0/G1-phase thymus cells (non-dividing cells) increased and the content of S-phase cells (division phase) decreased. Continuous lighting stimulated the development of thymocyte apoptosis. The results obtained indicate that prolonged 24-h illumination inhibits differentiation and maturation of young CD3^low thymocytes into mature CD3^hi forms and leads to the development of T-cell apoptosis in the thymus and, as a consequence, to leukopenia.