Chemical phenotypes of intrinsic cardiac neurons in the newborn pig (Sus scrofa domesticus Erxleben, 1777)

Abstract

Intrinsic cardiac neurons (ICNs) are crucial cells in the neural regulation of heart rhythm, myocardial contractility, and coronary blood flow. ICNs exhibit diversity in their morphology and neurotransmitters that probably are age‐dependent. Therefore, neuroanatomical heart studies have been currently focused on the identification of chemical phenotypes of ICNs to disclose their possible functions in heart neural regulation. Employing whole‐mount immunohistochemistry, we examined ICNs from atria of the newborn pigs (Sus scrofa domesticus) as ICNs at this stage of development have never been neurochemically characterized so far. We found that the majority of the examined ICNs (>60%) were of cholinergic phenotype. Biphenotypic neuronal somata (NS), that is, simultaneously positive for two neuronal markers, were also rather common and distributed evenly within the sampled ganglia. Simultaneous positivity for cholinergic and adrenergic neuromarkers was specific in 16.4%, for cholinergic and nitrergic—in 3.5% of the examined NS. Purely either adrenergic or nitrergic ICNs were observed at 13% and 3.1%, correspondingly. Purely adrenergic and nitrergic NS were the most frequent in the ventral left atrial subplexus. Similarly to neuronal phenotype, sizes of NS also varied depending on the atrial region providing insights into their functional implications. Axons, but not NS, positive for classic sensory neuronal markers (vesicular glutamate transporter 2 and calcitonin gene‐related peptide) were identified within epicardiac nerves and ganglia. Moreover, a substantial number of ICNs could not be attributed to any phenotype as they were not immunoreactive for antisera used in this study. Numerous dendrites with putative peptidergic and adrenergic contacts on cholinergic NS contributed to neuropil of ganglia. Our observations demonstrate that intrinsic cardiac ganglionated plexus is not fully developed in the newborn pig despite of dense network of neuronal processes and numerous signs of neural contacts within ganglia.

Topographical mapping of catecholaminergic axon innervation in the flat-mounts of the mouse atria: a quantitative analysis

“…However, recent studies demonstrated that ICG neurons exhibit diverse neurochemical phenotypes (including TH, ChAT, nNOS, VIP, NPY) 58 , 59 that extend beyond the traditional concept of cholinergic neurons. A subpopulation of the ICG neurons were also found to be TH-IR in mice which aligns with our findings 10 , 60 . Similar to previous studies, we have observed the ICG being located primarily on the outer surface of the atria near the entrance of the pulmonary veins to the LA and near the SAN and AVN 25 , 41 .…”

High‐resolution mapping of sensory fibers at the healthy and post‐myocardial infarct whole transgenic hearts

“…In mice, ganglionated plexus were detected only on the atria and aortic arch (Pauza et al, 2013) consistent with our findings. The VGLUT2‐expressing RFP‐IR neuron fibers were exclusively detected within the mouse cardiac ganglia without labeling any soma, similar to the previous reports in piglets (Ragauskas et al, 2022). Although we detected TH‐IR in the neural soma within the intrinsic cardiac ganglia, there were no VGLUT2‐expressing RFP‐IR from the neuron soma, but only afferent axons were detected cross passing the intrinsic ganglia.…”

“…Indeed, the lack of definitive immunochemical markers that could exclusively label afferent nerve fibers prevented the global visualization of the heart. Thus, previous attempts using peptidergic markers such as CGRP or Substance P provided partial visualization of the cardiac afferents (Ragauskas et al, 2022; Rysevaite et al, 2011). Here, we described the global architecture of the vagal and spinal afferents together with sympathetic fibers by using transgenic mouse models and advanced imaging in healthy or post‐MI hearts.…”

“…Indeed, the lack of definitive immunochemical markers that could exclusively label afferent nerve fibers prevented the global visualization of the heart. Thus, previous attempts using peptidergic markers such as CGRP or Substance P provided partial visualization of the cardiac afferents (Ragauskas et al, 2022;Rysevaite et al, 2011).…”

“…In mammals, the majority of intrinsic cardiac ganglia are distributed at the epicardial heart hilum especially embedded in the fat tissue (Inokaitis et al, 2016;Pauza et al, 2013;Saburkina et al, 2014). On both atria, the cardiac ganglia exhibit different shapes and sizes (Ragauskas et al, 2022). Cardiac ganglia at the ventricles were identified in the hearts of piglets (Pauziene et al, 2017), rabbits (Saburkina et al, 2014), and humans (Pauza et al, 2002;Pauza et al,2014;Saburkina & Pauza, 2006), distributing at the basal level, mostly near the coronary groove (Pauza et al, 2000(Pauza et al, , 2002.…”