THE INNERVATION OF THE HUMAN MYOCARDIUM AT BIRTH

In order to delineate the type and distribution of autonomic nerves wi thin the atrial and ventricular myocardium of the neonatal human heart , numerous samples of atrial and ventricular myocardium from 4 neonata l human hearts with no cardiac anomaly, freshly obtained at necropsy, were processed and studied using immunohistochemical and enzyme histoc hemical techniques. The antisera included those used to demonstrate pr otein gene product (PGP) 9.5 as a general neural marker, dopamine beta -hydroxylase (DBH) and tyrosine hydroxylase (TH) as indicators for pre sumptive sympathetic neural tissue, and neuropeptide Y (NPY). A histoc hemical technique was used to reveal tissue cholinesterase activity. N umerous PGP-immunoreactive (PGP-IR) nerves were seen in the atrial myo cardium, forming perivascular plexuses and lying in close apposition t o myocardial cells. Fewer PGP-IR nerves were found amongst the myocard ium of the ventricles. Both DBH-IR and TH-IR nerves demonstrated a sim ilar pattern of distribution as that of PGP-IR nerves; in the atria, h owever, they were less numerous, while in the ventricles, their densit y 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 distribu tion patterns were similar. In the ventricles, AChE positive nerves we re rarely observed. It is concluded that the neonatal human heart poss esses a rich supply of autonomic nerves. The atria possess at least tw o populations of nerves, presumably sympathetic and vagal, whereas the walls of the ventricles are innervated principally by presumptive sym pathetic nerves.