Age-Related Differences of Porcine Atrial Intracardiac Ganglia

Abstract

Background and aim: Intracardiac ganglia (ICG) is important component of the regulation of heart rhythm and contractile properties. Neurochemical phenotype and morphology of ICG neurons play important role in this regulation. For example, adrenergic system is known to increase heart rhythm and younger animals usually demonstrate higher heart rhythm compared with older. However, the knowledge whether this translates to ICG neuronal phenotype is limited. We investigated if age-related differences of adrenergic and nitrergic phenotypes exists in porcine atrial ICG. Materials and methods: Hearts from 11 adult pigs and 8 newborn piglets were used in the study. Whole-mount preparations of epicardium from five atrial regions were double labelled for choline acetyltransferase (ChAT) and tyrosine hydroxylase (TH) or nitric oxide synthase (nNOS) using immunohistochemical procedures and imaged using confocal microscope. Results: Newborn piglet atrial ICG contained markedly more biphenotypic neurons positive for both ChAT and TH (ChAT+/TH+) (16.2 %) than adult pig (3.6 %) and those positive only for TH (ChAT-/TH+) (12.8 % and 0.1 %, respectively). Comparing abundance of small intensely fluorescent (SIF) cells, positive for TH, clusters also revealed age-related differences. 20.8 % of newborn piglet and 4.5 % of adult pig atrial ICG contained at least one SIF cells cluster. Differences of nitrergic phenotype were not so marked, as neurons positive for nNOS constituted 6.9 and 3.7 % of all neurons within younger and older animals, respectively. While ChAT+/TH+ and ChAT+/nNOS+ neurons were evenly distributed across newborn piglet atrial regions, adrenergic phenotype was more abundant within right atrium and nitrergic within dorsal atrial regions of adult pig. Overall, adult pig possessed more than twofold bigger neurons compared with younger conspecifics. ChAT+/TH-, ChAT+/nNOS+ and ChAT+/TH+ neurons of newborn piglet and ChA [...].