NADPH- Diaphorase positive cardiac neurons in the atria of mice. A morphoquantitative study

The majority of the NADPH-diaphorase positive neurons were observed in the ganglia of the plexus. A few single neurons were also observed. The number of NADPH-d positive neurons was 57 ± 4 (ranging from 39 to 79 neurons). The ganglion neurons were located in 3 distinct groups: (1) in the region situated cranial to the pulmonary veins, (2) caudally to the pulmonary veins, and (3) in the atrial groove. The largest group of neurons was located cranially to the pulmonary veins (66.7%). Three morphological types of NADPH-diaphorase neurons could be distinguished on the basis of their shape: unipolar cells, bipolar cells and cells with three processes (multipolar cells). The unipolar neurons predominated (78.9%), whereas the multipolar were encountered less frequently (5,3%). The sizes (area of maximal cell profile) of the neurons ranged from about 90 μm2to about 220 μm2. Morphometrically, the three types of neurons were similar and there were no significant differences in their sizes. The total number of cardiac neurons (obtained by staining the neurons with NADH-diaphorase method) was 530 ± 23. Therefore, the NADPH-diaphorase positive neurons of the heart represent 10% of the number of cardiac neurons stained by NADH.The obtained data have shown that the NADPH-d positive neurons in the cardiac plexus of the atria of mice are morphologically different, and therefore, it is possible that the function of the neurons may also be different.The heart of mammals is innervated by nerve fibers from the vagus and the sympathetic chain. In addition, a group of neurons situated at the dorsal surface of the atria contribute to the innervation of the heart. These neurons play an important role in the regulation of cardiac output during rest, exercise and cardiovascular disease [1].Recent evidences suggest that nitric oxide (NO), acts as a neurotransmitter in both the central [2,3] and peripheral nervous system [4-6]. Nitric oxide is synthesized by the enzyme nitric oxide synthase (NO