QUANTITATIVE STUDY AND ARCHITECTURE OF NERVES AND GANGLIA OF THE RAT-HEART

The cardiac plexus of the Wistar rat was investigated in whole-mount p reparations of the atria by NADH-diaphorase staining and by the acetyl cholinesterase (AChE) histochemical technique. The plexus lies over th e muscular layer of the atria, dorsal to the muscle itself, in the con nective tissue of the subepicardium. The plexus contains on average 97 5 +/- 150 neurons, occurring singly or gathered in packed ganglia. The ganglia are found regularly in certain situations, namely, cranially to the pulmonary veins (44% of total); cranially and to the left of su perior vena cava (10%); in the interatrial groove (21%); to the left o f the left pulmonary vein (11%); caudally to the pulmonary veins (12%) and in the wall of the coronary sinus (1%). Ganglia are never found o n the auricular appendages. For the histochemical demonstration of ACh E, the 'direct coloring' copper ferrocyanide method was used. Extrinsi c nerves enter the atria along the superior vena cava, along the pulmo nary veins and along the coronary sinus, forming ganglion-containing p lexuses. From specific sites of these plexuses, nerves proceed to the ganglia located to the left of the superior vena cava, to the ventral and dorsal ventricular wall and to the wall of the right atrium, where they form a delicate plexus accompanying the muscle fibers. Most of t he neurons of the plexuses displayed AChE activity in the cytoplasm th ough they presented different reaction intensities. The distribution o f cardiac nerves from groups of neurons located at discrete sites may indicate that postganglionic nerves selectively project to and thus co ntrol specific cardiac regions and/or functions.