Stellate Ganglion Sympathetic postganglionic efferent innervation in the flat-mount of the whole heart of rats: Anterograde Tracing

Abstract

The autonomic nervous system (sympathetic and parasympathetic) plays an essential role in controlling cardiac functions. Previously, we used anterograde tracing to examine the vagal afferent and efferent (preganglionic) innervations of the normal heart, their anatomical remodeling and their functional changes in disease models of rats and mice. In addition, we used vesicular acetylcholine transporter (VAChT, a parasympathetic marker;) and tyrosine hydroxylase (TH, a sympathetic marker,) to determine the parasympathetic and sympathetic postganglionic innervation of the whole heart (atria and ventricles). Immunohistochemical labeling with TH is useful for determining the broad distribution of sympathetic efferent axons in the heart. However, it is difficult to distinguish its extrinsic and intrinsic origins using TH labeling. Furthermore, the topographical organization and morphological terminal structures of cardiac sympathetic postganglionic efferent axons from the stellate ganglia (SG) remains unknown. To address this we anterogradely labeled individual sympathetic postganglionic axons projecting to the heart, using tracer Dextran-Biotin microinjections into the right SG of Sprague-Dawley rats (male, n=6, 3-6 months). Fourteen days after the injection, animals were euthanized, and their hearts were dissected into the left/right atria (LA and RA) and ventricles and prepared as flat-mounts. The tracer-labeled axons were digitized and analyzed using The Neurolucida 3D tracing system and imaged using a Zeiss M2 Imager. We found that stellate sympathetic neurons had projections to the LA and RA and left and right ventricles. Individual sympathetic axons formed complex arbors of varicose neurites in the areas of the sinoatrial node (SAN) and atrioventricular node (AVN) as well as the other areas of the atria and throughout the ventricles. Sympathetic axons also innervated blood vessels. Using the Neurolucida Digitization and Tracer system, we determined the regional density and characterized different types of axons. Some axons formed relatively simple terminal structures with only a few branches, whereas other axons produced very complex terminals with extensive branching. For the first time, we anterogradely labeled the sympathetic postganglionic axons and characterized their terminal architecture in the whole heart. These results will provide an anatomical foundation for future study This study was supported by NIH HEAL/SPARC U01 NS113867-01 and NIH R15HL137143-01A1. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.