Morphological study of neurons in the nerve plexus on heart base of rats and guinea pigs.

The paper describes the morphological pattern of neurons in the nerve plexus on the heart base of rats and guinea pigs. The nerve plexus, containing the investigated neurons, lies beneath the pulmonary arteries on the myocardium of the left atrium. This plexus is not covered by the epicardium. Therefore, contrary to the subepicardiac nerve plexus the investigated plexus was termed the nerve plexus of the cardiac hilum (NPCH). The morphology of neurons in the NPCH was revealed by ionophoretic injection of Lucifer Yellow via an intracellular microelectrode in vitro. A total of 139 neurons in 31 rats and 15 guinea pigs were labeled with dye and examined without chemical fixation with a fluorescent microscope. In the NPCH of both species, two types of neuron were revealed: unipolar and multipolar. The unipolar predominated (61.2% of the labeled nerve cells), whereas the multipolar were encountered less frequently (38.8% of the sampled neurons). Morphometrically, both types were similar and there was no significant difference in their length or width. The dyed neurons of both types were divided into separate groups according to indentations on the surface of their soma. Most of the unipolar nerve cells were encompassed into a group of "smooth' neurons because the surface of their soma was without noticeable prominences or grooves. The rest of the unipolar neurons were distinguished from the 'smooth' by various types of unevenness of the surface of their body, such as spine-like sprouts and grooves of different depth. The latter were attached to another group, the 'unsmooths', which made up 22.4% of all the labeled cells. The multipolar neurons were subdivided into two groups according to the number of long processes. The first group included neurons with a single long process, whereas the other group encompassed the nerve cells with two or more processes. The latter groups made up 31.6% and 7.2%, respectively, of the total number of labeled nerve cells. The obtained data have shown that the neurons in the NPCH of the rats and guinea pigs are morphologically different, and therefore it is proposed that the function of the neurons in the diverse groups may also be different.