Innervation and Neuronal Control of the Mammalian Sinoatrial Node a Comprehensive Atlas

Abstract

Rationale: Cardiac function is under exquisite intrinsic cardiac neural control. Neuroablative techniques to modulate control of cardiac function are currently being studied in patients, albeit with variable and sometimes deleterious results. Objective: Recognizing the major gaps in our understanding of cardiac neural control, we sought to evaluate neural regulation of impulse initiation in the sinoatrial node as an initial discovery step. Methods and Results: We report an in-depth, multi-scale structural and functional characterization of the innervation of the sinoatrial node (SAN) by the right atrial ganglionated plexus (RAGP) in porcine and human hearts. Combining intersectional strategies including tissue clearing, immunohistochemical and ultrastructural techniques, we have delineated a comprehensive neuroanatomic atlas of the RAGP-SAN complex. The RAGP shows significant phenotypic diversity of neurons while maintaining predominant cholinergic innervation. Cellular and tissue-level electrophysiologic mapping and ablation studies demonstrate interconnected ganglia with synaptic convergence within the RAGP to modulate SAN automaticity, atrioventricular (AV) conduction and left ventricular (LV) contractility. Using this approach, we comprehensively demonstrate that intrinsic cardiac neurons influence the pacemaking site in the heart. Conclusions: This report provides an experimental demonstration of a discrete neuronal population controlling a specific geographic region of the heart (SAN) that can serve as a framework for further exploration of other parts of the intrinsic cardiac nervous system (ICNS) in mammalian hearts and for developing targeted therapies.

The Organization of the Sinoatrial Node Microvasculature Varies Regionally to Match Local Myocyte Excitability

“… 47 , 48 This disparity between in vivo and isolated single cell firing rates reflects strong input from the sympathetic arm of the autonomic nervous system, which increases firing rate through the activation of cAMP/protein kinase A signaling. Indeed, recent studies by Brennan et al 23 and Hanna et al 49 suggested that sympathetic innervation and drive is larger in the superior compared with the inferior SAN. Thus, a combination of higher AP firing, Ca 2+ cycling, and contraction rates as well as cAMP production may conspire to produce a much larger energetic load in superior than inferior SAN myocytes.…”

A single cell transcriptomics map of paracrine networks in the intrinsic cardiac nervous system

“…In addition, our study provides the data needed to begin a modeling effort focused on neuroanatomical and electrophysiological properties of the intrinsic cardiac neurons. Integrating these findings with other data obtained from our collaborative SPARC consortium will enable development of computational models of neurons and networks in the RAGP as a critical mediator of vagal control of the heart (Hanna et al, 2021). With the RAGP as a starting point, the RAGP network model can be further expanded into a systems model of autonomic control of cardiovascular function to test novel control strategies for neuromodulation and to open the door to more effective therapeutics.…”

“…We now find consistent neuroanatomical structure and diverse molecular properties of ganglia in the ICNS of a large porcine mammal, accepted as close to human. Our newly developed data demonstrate that the local cardiac ganglia harbor anatomical and molecular features necessary to function as complex signal processing units that critically mediate vagal control of heart function and health (Hanna et al, 2021).…”

“…Immunohistochemistry for TH and VAChT revealed that a majority of neurons showed robust protein expression of VAChT with a subset co-staining for TH (Figures 5G-5I). A more detailed quantitative analysis of TH and VAChT protein co-expression are included in a complementary study (Hanna et al, 2021). This finding suggests that post-transcriptional regulation plays a key role in shaping the neurotransmitter patterns within RAGP.…”

3D single cell scale anatomical map of sex-dependent variability of the rat intrinsic cardiac nervous system

“…The ICNS neurons utilize a variety of neurotransmitters and modulators and receive the inputs of both local afferent and extrinsic autonomic (parasympathetic and sympathetic) nerves, performing very complicated integration in controlling cardiac functions ( Achanta et al., 2020 ; Ardell and Armour, 2016 ; Hanna et al., 2021 ; Moss et al., 2021 ). We previously identified multiple clusters of ICNS neurons on the epicardium of the superior surface of the heart and on the posterior left atrium ( Achanta et al., 2020 ; Ai et al., 2007 ; Cheng et al., 1999 ; Lin et al., 2008 ; Pauza et al., 2000 ; Richardson et al., 2003 ).…”