Morphological Features of Rat Mediastinum Organs’ Innervation at Different Stages of Postnatal Ontogenesis

The relevance of studying the nervous apparatus of the mediastinal organs during the period of early postnatal ontogenesis is due to the peculiarities of the birth period, when the process of blood circulation switches from placental to pulmonary, and the period of the first days of development, when the establishment of the regulation of respiration and the functioning of the cardiovascular system is observed. The purpose of this study was to comparatively study the innervation of the organs of the rat mediastinum and to elucidate interorgan and neurotissue relationships in the early postnatal period of ontogenesis. Frontal sections through the cardiopulmonary complex of rats at the age of 1, 7, 10, and 14 days were the objects of study. The nervous structures of the mediastinum were studied using neuronal markers: PGP 9.5 protein, tyrosine hydroxylase, and synaptophysin. This study of the nervous apparatus of the mediastinal organs (heart, bronchi, esophagus, aorta, pulmonary artery, adipose tissue, etc.) showed that most nervous structures are cholinergic in the early stages of development. Using an immunohistochemical reaction to synaptophysin, heterochronic development of the main terminal synaptic network en passant was revealed. A high concentration of synaptic structures in the venous sinus and in the His bundle of the rat myocardium at the age 1 and 7 days with a predominance of parasimatic innervation has been described. At the age of 10 and 14 days, widespread superficial active growth of nerve fibers was noted along the entire perimeter of the organ up to its apex. The beginning of the formation of its main nerve plexuses of the heart was noted: subepicardial, myocardial, and endocardium.