The effect of photoperiod on the serotoninergic system of the thymus and its role in implementing the effects of exogenous melatonin

Abstract

Serotonin‐containing cells of the thymus in Wistar rats were studied, which were kept during 4 weeks of the experiment under the conditions of a natural photoperiod, under the conditions of constant blackout, under the conditions of continuous illumination. The effect of melatonin (“Melaxen” Unipharm, Inc., USA) ad libitum at a concentration of 4 mg / liter with drinking for four weeks) on serotonin‐positive cells of the thymus was studied.ResultsThe absence of light does not affect serotonin synthesis in the amine‐producing cells of the diffuse endocrine system in the border of the cortical and medullary lobules, but it suppresses the amine‐absorbing properties in the cortical substance cells of the thymus lobules. Continuous illumination does not affect the amine‐absorbing properties of the cells of the diffuse endocrine system in the cortical lobular substance, but promotes serotonin accumulation in the amine‐producing cells at the border of the thymus cortical and medullary lobules. Regardless of the photoperiod, exogenous melatonin increases the content of serotonin in the cells of the thymic diffuse endocrine system, which is more pronounced in continuous light conditions.ConclusionsOur studies have shown that changes in the photoperiod stimulate the serotoninergic system of the thymus, and exogenous melatonin smooths out these effects.