Vagal Afferent Innervation of the Atria and Ventricles of the Rat Heart: Anterograde Tracing

Abstract

Vagal afferent innervation of the atria from the nodose ganglion has been shown in previous studies but the innervation of the ventricles remains unknown. In this study, tracer Dextran-Biotin was injected into the left nodose ganglion of SD male rats (n=6; 3 months). The tracer was allowed to transport for 14 days, then the rats were perfused through the left ventricle with 40°C phosphate-buffered saline (PBS, 0.1 M, pH = 7.4). Tissues were then fixed by perfusion with 4% paraformaldehyde in 0.1M PBS (4°C, pH 7.4). Whole rat hearts were harvested, and the atria and ventricles were separated. Then, a cut was made along the interatrial septum to separate the left and right atrium, then either a DAB staining or fluorescent immunohistochemistry staining was performed. Intrinsic cardiac ganglionic (ICG) neurons were stained with Cuprolinic Blue or Fluoro-Gold. Labeled single vagal afferent axons in the flat mounts of the whole heart were traced using the Neurolucida system. Consistent with previous findings using fluorescent tracer 1,1’-dioleyl-3,3,3’,3’ tetramethylindocarbocyaninemethanesulfonate (DiI) injection, afferent axons have been observed in the epi-, myo-, and endocardium and vagal axons formed “flower-spray” and “end-net” terminals in the atria. Also, the afferents displayed contact with cardiac muscles. For the first time, the “flower-spray” and “end-net” vagal afferent terminals have been found in both the left and right ventricles. Neither the “flower-spray” and “end-net” vagal afferent terminals on the heart, nor the vagal afferent terminal structures on the stomach such as intraganglionic laminar endings ( IGLEs) and intramuscular arrays ( IMAs) were found to co-localize with calcitonin gene-related peptide (CGRP) or Substance P (SP) in the three rats with injection followed fluorescent labeling and immunohistochemical analysis. In conclusion, our study provides the foundation for further functional studies of vagal afferent innervation of the whole heart (atria and ventricles) in normal and pathological states. This study was supported by NIH HEAL/SPARC U01 NS113867-01 (ZJC), NIH R15HL137143-01A1 (ZJC). 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.