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

Abstract

Background: The present study was conducted to determine the location, the morphology and distribution of NADPH-diaphorase positive neurons in the cardiac nerve plexus of the atria of mice (ASn). This plexus lies over the muscular layer of the atria, dorsal to the muscle itself, in the connective tissue of the subepicardium. NADPH- diaphorase staining was performed on whole-mount preparations of the atria mice. For descriptive purposes, all data are presented as means +/- SEM.

Results: 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 microm2 to about 220 microm2. 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.

Conclusion: 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.

Figure 1

Diagram of epicardial surface of right and left atria of mouse heart viewed from their cranial aspect showing the 3 major regions in which NADPH-diaphorase positive neurons were located. The neurons are represented by dots. La= left atrium; Ra = right atrium; Pv = pulmonary veins; Svc = superior vena cava; Ivc = inferior vena cava; Lv = left ventricle; Rv = right ventricle. Calibration bar: 0.1 mm.

Figure 2

NADPH-diaphorase positive cardiac neurons of the mouse atria: (A) One of the NADPH-diaphorase positive neurons is unipolar (arrow) and the other is bipolar (arrowhead). (B) Note the unipolar NADPH-diaphorase positive neuron (arrow) and the nonreactive neurons (arrowheads). (C) An ovoid bipolar neuron with two short processes (arrow), and one multipolar neuron with three short processes (arrowhead). The neurons are pear-shaped with a round or oval nucleus. (D) A multipolar neuron with three processes. (E) A ganglion stained for NADPH-diaphorase. The ganglion contains both NADPH-diaphorase positive neurons (arrow) and nonreactive perikarya (arrowhead). (F) The two NADPH-diaphorase positive neurons are unipolar neurons. (G) A single NADPH-diaphorase positive neuron with two large processes. (H) Cardiac ganglion showing a cluster of unipolar NADPH-diaphorase positive neurons. Calibration bar: 20 μm.

Figure 3

Relation between mean, standard error of mean and deviation values of sizes (μm²) of the three types of NADPH-positive cardiac neurons (unipolar, bipolar and multipolar) of the mouse atria.