Figure 12.

The distribution of different chemical phenotypes of neuronal somata (NS) and nerve fibers (NFs) among the presumed sources of extrinsic cardiac innervation [modified from Navickaite et al., 2021 [83]]. The nodose ganglion contains a significant population of nitrergic neuronal somata (37%); this ganglion is most likely the principal source of nitrergic nerve fibers throughout the vagal nerve and its cardiac branches. However, approximately 7% of neuronal cell bodies in the dorsal vagal nucleus co-express both ChAT and nNOS, indicating that this nucleus may be the origin of a small number of cardiac nitrergic nerve fibers. Furthermore, the dorsal vagal nucleus (DNV) contains tiny interneurons that are positive for nNOS (about 3%), physically resemble conventional interneurons, and most likely act around the nucleus. In the nucleus ambiguous (NAm), approximately 6% of neuronal somata display the biphenotypic characteristics of nNOS and ChAT, although only cholinergic nerve fibers have been observed exiting the nucleus. In both the dorsal vagal nucleus and nucleus ambiguous, a network of nNOS-IR nerve fibers is identified, which, according to existing literature, may originate from the solitary tract nuclei (indicated by the dashed line), where a crowded group of little nitrergic neuronal somata is found. Most sympathetic neuronal somata in the intermediolateral nucleus of the spinal cord co-express choline acetyltransferase and neuronal nitric oxide synthase, indicating that neuronal nitric oxide synthase is involved in the neuromodulation of preganglionic sympathetic neurotransmission. Nevertheless, only a single neuronal soma in the stellate ganglia has positivity for both tyrosine hydroxylase and neuronal nitric oxide synthase. Nitrergic neuronal somata are likewise rare in the dorsal root ganglia, suggesting that merely solitary nitrergic nerve fibers for the heart may come from this ganglionic station. Studies by Rysevaite et al. (2011) [84] and Pauziene et al. (2015, 2017) [85,86] form the basis for the anatomical map of the intrinsic cardiac ganglia’s makeup. Respectively, the following abbreviations (DNV), stand for the dorsal nucleus of the vagal nerve, (X), the hypoglossal nucleus, (Nam), the nucleus ambiguous, and (SIF cells), the tiny, highly fluorescent cells [83].