[Heart innervation in rats (an immunohistochemical study)]

The aims of the present study were to investigate the structure of the nervous apparatus in different heart regions using the immunohistochemical methods. The study was performed in Wistar rats (n - 5). For selective staining of synaptic structures, synaptophysin (Syn) demonstration was used, while neurofilament proteins (NF-M) were used to detect axonal neurofilaments. The innervation apparatuses in the heart were shown to be unevenly distributed. High density of Syn- and of NF-M-positive axons was found in the myocardium near the atrial sinus, vena cava superior and inferior, pulmonary veins, aorta, truncus pulmonalis, as well as in the deep layers of atrial myocardium, and in the myocardium of anterior and posterior ventricle walls. In the heart apex, within the ventricular myocardium, the density of immunopositive axons was low. Using the antibodies against Syn, only the synaptic terminals of the efferent postganglionic nerve fibers and of the parasympathetic vegetative nerve fibers were selectively demonstrated in the heart, as well as the pericellular synapses on the parasympathetic neurons of intracardiac ganglia. NF-M-immunopositive axons, unlike Syn-positive terminals, were found not only in the myocardium, but also in the epicardium and the endocardium within the same regions of the heart. The authors believe that these axons belong to afferent sensory and efferent preganglionic myelinated nerve fibres of PNS.