Project Title

Exploration of Cholinergic and Noradrenergic Innervation of the Human Atrioventricular Node

Authors' Affiliations

Logan Kirkland, Department of Biomedical Sciences, Quillen College of Medicine, East Tennessee State University, Johnson City, TN Chloe Garbe, Department of Biomedical Sciences, Quillen College of Medicine, East Tennessee State University, Johnson City, TN Elizabeth Smith, Department of Biomedical Sciences, Quillen College of Medicine, East Tennessee State University, Johnson City, TN Igor Efimov, Department of Biomedical Engineering, George Washington University, Washington, DC Kalyanam Shivkumar, Department of Cardiology, UCLA, Los Angeles, CA Peter Hanna, Department of Cardiology, UCLA, Los Angeles, CA Donald Hoover, Department of Biomedical Sciences, Quillen College of Medicine, East Tennessee State University, Johnson City, TN

Location

Culp Ballroom

Start Date

4-7-2022 9:00 AM

End Date

4-7-2022 12:00 PM

Poster Number

114

Faculty Sponsor’s Department

Biomedical Sciences

Name of Project's Faculty Sponsor

Donald Hoover

Classification of First Author

Undergraduate Student

Competition Type

Competitive

Type

Poster Presentation

Project's Category

Cardiovascular System

Abstract or Artist's Statement

In the normal heart, the atrioventricular node (AVN) is part of the sole pathway between the atria and ventricles and is responsible for transmitting and coordinating atrial and ventricular contractions. The AVN electrically connects the atria and ventricles of the heart and is part of the electrical conduction system. Conduction within this system is highly regulated by the autonomic nervous system. The complex neurochemical anatomy of this region has been studied extensively in mice and other small animals but not in humans. The goal of this study was to provide detailed neurochemical characterization of parasympathetic (cholinergic) and sympathetic (noradrenergic) innervation of the human AVN, which is the lead component of the conducting system. Using immunohistochemistry, we have investigated the innervation of the AVN region in samples collected from human hearts that were rejected for transplantation. Tissues were fixed in 4% paraformaldehyde, cryoprotected, and sectioned frozen at 30um thickness. Sections through the AVN were cut in the horizontal plane and collected in representative sets on charged slides. Each set of slides was stained for a different phenotypic marker using the VECTOR Elite ABC kits and ImmmPACT VIP Chromogen. To aid in locating the AVN, we used anti-Connexin-43(Cx-43). Unlike surrounding myocardium, nodal tissue lacks significant Cx-43. Cholinergic nerves were stained with anti-vesicular acetylcholine transporter (VAChT).Noradrenergic nerves were stained with anti-tyrosine hydroxylase (TH). We evaluated tissue from two patients and obtained similar results. The AVN received prominent input from cholinergic and noradrenergic nerves, with cholinergic being dominant. The AVN displayed a greater density of parasympathetic and sympathetic innervation compared to surrounding regions. Sympathetic innervation is what causes an increase in conduction speed in the AVN, while parasympathetic innervation is what causes a decrease in conduction speed. Based on previous pharmacological evidence and observation of innervation in other species, the AVN is a highly controlled area for cardiac regulation. Our research implies that parasympathetic innervation is more highly regulated in the AVN and that parasympathetic innervation could play a larger role in cardiac conduction than sympathetic innervation.

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Apr 7th, 9:00 AM Apr 7th, 12:00 PM

Exploration of Cholinergic and Noradrenergic Innervation of the Human Atrioventricular Node

Culp Ballroom

In the normal heart, the atrioventricular node (AVN) is part of the sole pathway between the atria and ventricles and is responsible for transmitting and coordinating atrial and ventricular contractions. The AVN electrically connects the atria and ventricles of the heart and is part of the electrical conduction system. Conduction within this system is highly regulated by the autonomic nervous system. The complex neurochemical anatomy of this region has been studied extensively in mice and other small animals but not in humans. The goal of this study was to provide detailed neurochemical characterization of parasympathetic (cholinergic) and sympathetic (noradrenergic) innervation of the human AVN, which is the lead component of the conducting system. Using immunohistochemistry, we have investigated the innervation of the AVN region in samples collected from human hearts that were rejected for transplantation. Tissues were fixed in 4% paraformaldehyde, cryoprotected, and sectioned frozen at 30um thickness. Sections through the AVN were cut in the horizontal plane and collected in representative sets on charged slides. Each set of slides was stained for a different phenotypic marker using the VECTOR Elite ABC kits and ImmmPACT VIP Chromogen. To aid in locating the AVN, we used anti-Connexin-43(Cx-43). Unlike surrounding myocardium, nodal tissue lacks significant Cx-43. Cholinergic nerves were stained with anti-vesicular acetylcholine transporter (VAChT).Noradrenergic nerves were stained with anti-tyrosine hydroxylase (TH). We evaluated tissue from two patients and obtained similar results. The AVN received prominent input from cholinergic and noradrenergic nerves, with cholinergic being dominant. The AVN displayed a greater density of parasympathetic and sympathetic innervation compared to surrounding regions. Sympathetic innervation is what causes an increase in conduction speed in the AVN, while parasympathetic innervation is what causes a decrease in conduction speed. Based on previous pharmacological evidence and observation of innervation in other species, the AVN is a highly controlled area for cardiac regulation. Our research implies that parasympathetic innervation is more highly regulated in the AVN and that parasympathetic innervation could play a larger role in cardiac conduction than sympathetic innervation.