DEVELOPMENT OF RAT SUBEPICARDIAL NERVE PLEXUS IN THE POSTNATAL PERIOD

Objective - to study the formation of a subepicardial nerve plexus at different stages of postnatal development in a rat, to examine the nature of neurotransmitters in its nerve fibers and the interrelation of epicardial nervous structures and blood vessels. Materials and methods. The composition of nerve ganglia and the neurotransmitter nature of nerve fibers in subepicardial nerve plexus was studied in the newborn, 2 weeks, 1 and 3 months-old Wistar rats (a total of 16 observations). For identification of the nervous structures, immunohistochemical techniques were applied that demonstrated PGP 9.5 neural marker of together with the demonstration of synaptophysin tyrosine hydroxylase to characterize the localization of synaptic vesicles and catecholaminergic structures. Results. It was shown that the pericardiac area of the newborn rats already contained well developed ganglia, microganglia, nerve plexuses formed by the mixture of parasympathetic and sympathetic bundles, as well as the aggregates of chromaffin cells, with the prevalence of parasympathetic elements over the sympathetic ones. For the first time, the nerve plexus forming from bundles of unmyelinated parasympathetic fibers was detected in a subepicardial layer of a newborn rat. It was found that at the early stages of development, the the epicardial epithelial cells transiently expressed PGP 9.5protein. In 2-4 week-old rats the epicardial epithelium lost PGP 9.5 immunoreactivity. In 3 month-old rats, the nerve plexuses in various parts of the heart attained a definitive structure. Conclusions. During postnatal ontogenesis, the relationship between the subepicardial nerve plexus and the underlying connecting tissue has a heterochronous developmental pattern. This was also found in the various parts of rat heart. They include the stage of formation of subepicardial nerve plexus in the newborns that consists mainly of the unmyelinated parasympathetic axons.

heart, subepicardial nerve plexus PGP 9.5, protein, synaptophysin, tyrosine hydroxylase