Neurochemical and morphological characterization of porcine atrial intracardiac ganglia

Abstract

Study Highlights. 1) The majority of porcine atrial intracardiac ganglia neurons are cholinergic; 2) Few neurons are adrenergic or nitrergic; 3) Neurons of almost all phenotypes were evenly distributed across atria. Background. Intracardiac ganglia (ICG) are important component of the regulation of heart rhythm and contractile properties. Neurochemical and morphological phenotypes of ICG neurons play important role in this regulation. Porcine heart is important for cardiac translational medicine because of its high similarity with human heart. However, knowledge of porcine ICG neuronal phenotype and morphology is limited. Regional distribution of atrial ICG neurons of distinct phenotypes have not been studied. To this purpose we investigated ICG from porcine whole atria. Material and Methods. Hearts from 11 adult pigs were used in the study. Whole-mount preparations of epicardium from atria were double labelled for choline acetyltransferase (ChAT), tyrosine hydroxylase (TH), neuronal nitric oxide synthase (nNOS), calcitonin gene-related peptide (CGRP) and vesicular glutamate transporter 2 (VGLUT2) using immunohistochemical procedures and imaged using confocal microscope. ICG neurons of distinct phenotype were calculated and area of ICG neurons were measured. Results. Majority of porcine ICG neurons were cholinergic. 96.3% of neurons were positive for ChAT but not for TH (n=9206), 2,7% were positive both for ChAT and TH (n=256), while 0.1% were positive only for TH, but not for ChAT (n=8). 96,2% of ICG neurons were positive for ChAT but not for nNOS (n=10.907), 3.3% were positive both for ChAT and nNOS (n=379) and 0.5% positive only for nNOS but not for ChAT (n=53). There were minor differences in abundance of neurons of particular phenotype between atrial regions. Specifically, only ChAT/nNOS biphenotypic neurons in ventral regions of atria were less abundant than in dorsal. 4.5% of ICG contained TH positive c[...].