Intrinsic Cardiac Ganglionic Neurons Projecting to the SA node in the Rat and Pig Hearts: Retrograde Labeling and Neurolucida 3‐D Reconstruction

Abstract

Intrinsic cardiac ganglionic neurons (ICNs) within the heart are essential for regulation of cardiac function. ICNs include afferent, efferent neurons and interneurons and constitute a local integration center. In rat and pig hearts, there are multiple cardiac ganglia. Among these ganglia, the largest ganglionated plexus in the rat heart and the right atrial ganglionic plexus (RAGP) in the pig heart are near the sinoatrial node (SAN). However, it is not clear whether both plexi project to the SAN. In this study, retrograde tracer Fast DiI was injected into the SAN in rats (n=5) and a pig. SAN cells were identified by immunostaining for pacemaker channel HCN4. Fluorogold (FG) was injected (i.p.) to label all of the ICNs in rats. FG‐ and DiI‐labeled ICNs were identified and analyzed using a confocal microscopic system and a Neurolucida Tracing and Digitization System. Sixteen days after Fast DiI injection in rats, the animals were perfused with paraformaldehyde, and the whole‐mount atria were prepared. There were multiple ganglionated plexi and the DiI‐labeled neurons were mainly found in the largest ganglionated plexus near the SAN in all these rats. Twenty‐one days after Fast DiI injection in the pig, the animal was sacrificed, and the RAGP was removed and sectioned at 40 μm. Numerous DiI‐labeled neurons were found in the RAGP of this pig. Interestingly, these DiI‐labeled neurons were organized in five spatially‐separated columns perpendicular to the epicardial surface. Our data suggest that the largest ganglionated plexus in rat indeed projects mainly to the SAN, and the pig RAGP projects very heavily to the SAN. The functional significance of this large ganglionated plexus in rat and the five spatially‐separated columns of RAGP ICN projecting neurons in the pig will be elucidated in the future.Support or Funding InformationSupported by NIH SPARC grant OT2OD023848, NIH R15HL137143‐01A1.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.