Atrial Innervation Patterns of Intrinsic Cardiac Autonomic Nerves

BACKGROUND: Although ganglionated plexi (GPs) are important in the pathogenesis of arrhythmia, their patterns of atrial innervation have remained unclear. We investigated patterns of GP innervation to cardiac atria and the neuroanatomical interconnections among GPs in an animal model. METHODS: Atrial innervation by GPs was evaluated in 10 mongrel dogs using a retrograde neuronal tracer (cholera toxin subunit B [CTB] conjugated with fluorescent dyes). In Experiment 1, CTB was injected into the atria. In Experiment 2, CTB was injected into the major GP, including the anterior right GP (ARGP), inferior right GP (IRGP), superior left GP (SLGP), and ligament of Marshall (LOM). After 7 days, the GPs were examined for the presence of tracer-positive neurons. RESULTS: GPs in either right or left-side were innervating to both the same and opposite sides of the atrium. In quantitative analysis, right-sided GPs, especially ARGP, showed numerical predominance in atrial innervation. Based on the proportion of CTB-labeled ganglion in each GP, atrial innervation by GPs showed a tendency of laterality. In Experiment 2, CTB that was injected to a particular GP widely distributed in different GP. ARGP projected the largest number of innervating neurons to the IRGP, SLGP and LOM. CONCLUSION: This study demonstrated that GPs project axons widely to both the same and opposite sides of atria. ARGP played a dominant role in atrial innervation. Furthermore, there were numerous neuroanatomical interconnections among GPs. These findings about neuronal innervation and interconnections of GPs could offer useful information for understanding intrinsic cardiac nervous system neuroanatomy.