Spinal Afferent Innervation of the Rat Heart: Anterograde Tracing

Spinal afferent innervation of the heart regulates cardiac function. Understanding the precise distribution and morphology of spinal afferent nerves in the heart is crucial as remodeling of cardiac sensory innervation results in cardiovascular diseases. To specifically study the spinal afferent innervation of the heart, we injected tracer dextran biotin (DB) into the left DRG (C8-T3; 1.5 μl/each ganglion). Rats were allowed to recover for 14 days, then perfused through the left ventricle with 40°C PBS (1M phosphate-buffered saline, pH = 7.4). Tissues were then fixed by perfusion with 4% paraformaldehyde in 0.1M PBS (4°C, pH 7.4). After the perfusion, hearts were harvested, and the atria and ventricles were separated. Then, a cut was introduced along the interatrial septum to separate the left and right atrium, and DAB staining was performed. DB-labeled single spinal afferent axons in the flat-mounts of the left and right atria were traced using the Neurolucida system. We summarized our findings based on morphology, innervation area, and target of individual spinal afferent axons. 1) Morphological characteristics of single spinal afferent axons: DB-labeled single axons entered the atria and bifurcated into many branches with or without varicosities. Varicose branches which arose from a single axon traveled through the atria either in the same direction or a non-preferential direction. 2) Distinct regions received single spinal afferent axons include left and right auricles, the sinoatrial node, the atrioventricular node, left precaval vein, pulmonary veins, and the junction between the left atrium and pulmonary veins. Axons with different terminal structures could be found in all these regions. 3) Single afferent axons were identified on different targets: such as cardiac and smooth muscles, fat tissue, blood vessels, and intrinsic cardiac ganglia. Our work will provide a foundation for specific labeling of spinal afferent innervation of the heart. This study was supported by NIH HEAL/SPARC U01 NS113867-01, NIH R15 R15HL137143-01A1, and UCF dissertation completion Fellowship. 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.