Structural and cytochemical features of the process of formation of innervation of the airways and lungs of the rat

The aim of the work is to study the development of the nervous apparatus and muscle structures of the rat lung in the early stages of postnatal development. The objects of study were extramural and intramural parts of the lung (trachea, main bronchi and lobar parts of the lung, including the respiratory section) of Wistar rats aged from one to fourteen days. Nervous structures were studied using immunohistochemical markers: PGP 9.5 protein, tyrosine hydroxylase, synaptophysin. Sarcomeric actin was used to identify muscle cells. It was found that in newborn rats, the distribution density of cholinergic structures (parasympathetic ganglia, microganglia of the nerve plexuses and terminal synaptic networks) prevails over catecholaminergic (sympathetic neurons and bundles of postganglionic fibers). Ganglionic plexuses are located around the trachea and main bronchi. Changes in tissue innervation in the bronchial wall of the lung in the cranio-caudal direction were detected. High density of distribution of nerve plexuses is characteristic of the proximal sections. They are absent in the alveolar regions. Close relationships of the main terminal nerve plexus with muscle tissue cells of the bronchial wall of different calibers up to the bronchioles are shown. Low innervation of cellular elements in the lobules around the pulmonary sacs and the absence of nerve terminals in the interalveolar septa are noted. Using the reaction to the S100β protein, cellular elements morphologically similar to the glial cells of Cajal, without axons included in their cytoplasm, were revealed in these places. An important feature is noted: the presence of cardiomyocytes in the muscular wall of the main pulmonary veins of the mediastinum and the cranial section of the lung. In the alveolar parts of the lungs, the wall of the pulmonary vein consists of smooth myocytes and the sphincters formed by them. The issues of differences in the histological structure and innervation of the afferent, efferent and exchange arterial and venous vessels of the microcirculatory bed of the lung require further special study. The absence of broncho-associated lymphoid tissue, characteristic of sexually mature animals, in the studied material at early stages of development was noted. The synchronicity of the formation of interneuronal and neuromuscular synapses, which are important for regulating the onset of the respiratory process in animals, was established.