© 2004 by European Society of Cardiology
Copyright © 2004, European Society of Cardiology
Localization of cholinergic innervation in guinea pig heart by immunohistochemistry for high-affinity choline transporters
aDepartment of Pharmacology, James H. Quillen College of Medicine, East Tennessee State University, Johnson City, TN 37614, USA
bDepartment of Pathology, James H. Quillen College of Medicine, East Tennessee State University, Johnson City, TN 37614, USA
cJames H. Quillen Veterans Affairs Medical Center, Mountain Home, TN 37684, USA
dNeuroscience Graduate Program, Center for Molecular Neuroscience, Vanderbilt University, Nashville, TN 37232, USA
eCenter for Molecular Neuroscience, Vanderbilt University, Nashville, TN 37232, USA
fDepartment of Pharmacology, Vanderbilt University, Nashville, TN 37232, USA
gDepartment of Anatomy and Neurobiology, University of Vermont College of Medicine, Burlington, VT 05405, USA
* Corresponding author. Tel.: +1-423-439-6322; fax: +1-423-439-8773. Email address: hoover{at}mail.etsu.edu
Objective: Previous studies have used acetylcholinesterase (AChE) histochemistry to identify cholinergic nerves in the heart, but this enzyme is not a selective marker for cholinergic neurons. This study maps cholinergic innervation of guinea pig heart using a new antibody to the human high-affinity choline transporter (CHT), which is present only in cholinergic nerves. Methods: Immunohistochemistry was used to localize CHTs in frozen and paraffin sections of heart and whole mount preparations of atrial ganglionated nerve plexus. AChE-positive nerve fibers were identified in sections from separate hearts for comparison. Results: Control experiments established that the antibody to human CHT selectively labeled cholinergic neurons in the guinea pig. CHT-immunoreactive nerve fibers and AChE-positive nerves were very abundant in the sinus and AV nodes, bundle of His, and bundle branches. Both markers also delineated a distinct nerve tract in the posterior wall of the right atrium. AChE-positive nerve fibers were more abundant than CHT-immunoreactive nerves in working atrial and ventricular myocardium. CHT-immunoreactive nerves were rarely observed in left ventricular free wall. Both markers were associated with numerous parasympathetic ganglia that were distributed along the posterior atrial walls and within the interatrial septum, including the region of the AV node. Conclusions: Comparison of labeling patterns for CHT and AChE suggests that AChE histochemistry overestimates the density of cholinergic innervation in the heart. The distribution of CHT-immunoreactive nerve fibers and parasympathetic ganglia in the guinea pig heart suggests that heart rate, conduction velocity, and automaticity are precisely regulated by cholinergic innervation. In contrast, the paucity of CHT-immunoreactive nerve fibers in left ventricular myocardium implies that vagal efferent input has little or no direct influence on ventricular contractile function in the guinea pig.
KEYWORDS Acetylcholine; Autonomic nervous system; AV-node; Innervation; Purkinje fiber; Conduction system; Neurotransmitters; Sinus node; High-affinity choline transporter; Immunohistochemistry; Guinea pig
Time for primary review 21 days
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