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Phenotypes and probable function of autonomic neurons of cardiac ventricles
Date Issued |
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2013-03-22 |
The function of neurons distributed on cardiac ventricles is unknown so far. Therefore, chemical phenotype of epicardial nerve cells was demonstrated employing double labeling for tyrosine hydroxylase (TH), choline acetyltransferase (ChAT), substance P (SP), calcitonin gene related peptide (CGRP) and protein gene product 9.5 (PGP) in order to identify the sympathetic, parasympathetic and sensory neural structures, respectively. Ventricular ganglionic cells positive for PGP were found within epicardium both in birds and mammalians. The examined epicardial neurons in mammals were positive for ChAT, TH or were biphenotypic (i.e. immunoreactive for ChAT and TH), while in birds they were immunoreactive for ChAT exclusively. On cardiac ventricles of mammals, there were identified numerous SIF cells. Ventricular epicardial nerves and nerve bundles possessed nerve fibers, but not somata, immunoreactive for CGRP and SP. Morphology of autonomic ganglia on ventricles of birds differed from those on mammalian ventricles as ganglionic cells in birds were smaller in size and distributed more compactly within ganglia compared with mammalians. Ventricular neurons immunoreactive for PGP, but negative for cholinergic, adrenergic and peptidergic neuronal markers, were found in birds only. In conclusion, the present findings demonstrate that ventricular ganglia distributed up to the heart apex possess the ChAT(+), TH(+) neurons and CGRP(+), SP(+) nerve fibers. In mammals, ventricular ganglionic cells are presumably involved both in parasympathetic and sympathetic control of ventricles, but role of many ventricular ganglionic cells in birds remains unclear and deserve further investigations.