The innervation of the human myocardium at birth

In order to delineate the type and distribution of autonomic nerves within the atrial and ventricular myocardium of the neonatal human heart, numerous samples of atrial and ventricular myocardium from 4 neonatal human hearts with no cardiac anomaly, freshly obtained at necropsy, were processed and studied using immunohistochemical and enzyme histochemical techniques. The antisera included those used to demonstrate protein gene product (PGP) 9.5 as a general neural marker, dopamine beta-hydroxylase (DBH) and tyrosine hydroxylase (TH) as indicators for presumptive sympathetic neural tissue, and neuropeptide Y (NPY). A histochemical technique was used to reveal tissue cholinesterase activity. Numerous PGP-immunoreactive (PGP-IR) nerves were seen in the atrial myocardium, forming perivascular plexuses and lying in close apposition to myocardial cells. Fewer PGP-IR nerves were found amongst the myocardium of the ventricles. Both DBH-IR and TH-IR nerves demonstrated a similar pattern of distribution as that of PGP-IR nerves; in the atria, however, they were less numerous, while in the ventricles, their density approximated to that of PGP-IR nerves. Relatively few NPY-IR nerves were observed either in the atrial or the ventricular myocardium. The density of acetylcholinesterase (AChE) positive nerves in the walls of the atria was less than that of PGP-IR nerves although their distribution patterns were similar. In the ventricles, AChE positive nerves were rarely observed. It is concluded that the neonatal human heart possesses a rich supply of autonomic nerves. The atria possess at least two populations of nerves, presumably sympathetic and vagal, whereas the walls of the ventricles are innervated principally by presumptive sympathetic nerves.