ABSTRACT
Ten to twenty ?l of 20-50% horseradish peroxidase (HRP) in normal saline solution was injected into the myocardium of the anterior wall of left and right ventricles in 11 rabbits. The areas containing sino-atria as well as atrio-ventricular nodes and the dorsal wall of the atria were removed separately. Frozen or cryostate sections of these tissues 25-40?m thick, were incubated according to the HRP (tetramethylbenzidine "TMB" method)-AChE combined method. The blue granules produced by the HRP with TMB were observed in the perikarya of a few AChE intensely positive ganglion cells which were located in the epicardium of the dorsal wall of the atria. This indicated the processes of the HRP-AChE double labeled cells distributed to the myocardium of the anterior wall of the ventriculum. It is generally believed that the nerve cells of strong AChE activity can be referred as cholinergic neurons. For this reason, the present study may give further identification to assert the parasympathetic innervation of the ventricular myocardium. The parasympathetic postganglionic neurons innervated the anterior wall of left and right ventriculi are situated primarily in the epicardium of the posterior wall of the atria.