Morphofunctional state of pinealocytes during dark deprivation

The aim of the study is to investigate the impact of dark deprivation on morphometric parameters of pinealocytes in rats. Materials and methods. The experiment was conducted on male rats (n=36). Animals of the control group (n=12) were kept under the standard light-dark regime (12/12 h), animals of experimental groups 1 (n=12) and 2 (n=12) were subjected to 24-hour dark deprivation (24/0 h). The dark deprivation lasted for 30 days. After the dark deprivation, rats of experimental group 2 were kept under the standard light-dark regime (12/12 h). After the experiment, pineal gland samples were placed in 10 % buffered formalin solution and subjected to automated histological processing. The prepared sections were stained with hematoxylin and eosin. Immunohistochemical study for antibodies to caspase-3 and Klotho protein was performed according to manufacturers' recommendations. Morphometry of pinealocytes and gliocytes was performed using LAS Software Version 4.7.1. Results. It was found that 30-day dark deprivation caused a decrease in the number of light pinealocytes by 23.2 %, their hypertrophy by 12.7 % and an increase in nuclei size by 20.5 %. Fourteen days after dark deprivation, the number of light pinealocytes increased by 5.5 %. Morphometric parameters of light pinealocytes of the pineal gland returned to the initial level: the volume of light pinealocytes and their nuclei decreased by 2.8 % and 5.8 %, respectively. Signs of apoptosis appeared under morphofunctional exhaustion: a decrease in Klotho protein activity and an increase in caspase-3 activity. Conclusion. Dark deprivation should be considered as a factor contributing to accelerated aging of the pineal gland.