The mRNA for dopamine receptors of type D1, D3, D5, but not type D2, was 
detected in the thymus of rats starting from day 16 of embryonic development 
(E16). Dopamine at concentrations of 10-8-10‒6 M inhibited fetus thymocyte 
response to mitogen, confirming the functionality of the receptors and the 
possibility of a direct effect of dopamine on the developing thymus. 
Pharmacological inhibition of catecholamine synthesis in the crucial period of 
thymus development leads to long-term changes in the T-system immunity due to 
increased production of natural regulatory T-lymphocytes. The presence and 
functional activity of dopamine receptors in the fetal thymus indicates its 
ability to influence the development of the immune system of rats during 
ontogeny.