Cardiac Nitrergic Neurons: Location, Morphology and Functional Role

Aim of the study. To study the distribution and morphological pattern of nitrergic neuronal somata and nerve fibres within the potential extrinsic sources of cardiac innervation. Objectives. 1. To explore the distribution of nitrergic neuronal somata and nerve fibres within the vagal nuclei and vagal nerve rootlets; 2. To examine the distribution of nitrergic neuronal somata within the inferior vagal sensory ganglia and C8-Th5 dorsal root ganglia; 3. To inspect the distribution of nitrergic neuronal somata and nerve fibres within the Th1-5 intermediolateral nuclei and stellate ganglia; 4. To inspect the distribution of nitrergic nerve fibres within the cervical vagal nerve and vagal cardiac branches. Methods. This study includes 28 rats examined. Section of the medulla oblongata, Th1-5 segments of the spinal cord, inferior vagal sensory ganglia, vagal rootlets, cervical vagal nerve, thoracic cardiac branches, C8-Th5 dorsal root ganglia and stellate ganglia were prepared. Immunohistochemical staining for neuronal nitric oxide synthase (nNOS), choline acetyltransferase (ChAT), peripherin, myelin basic protein (MBP), substantia P (SP), calcitonin gene-related peptide (CGRP) and tyrosine hydroxylase (TH) was performed. Preparations were analysed employing laser-scanning microscope. Results. In the nucleus ambiguus, all nitrergic neuronal somata (NS) were biphenotypic with ChAT. They composed 12,4 ± 1,6 % in the compact subnucleus, 4,7 ± 1,2 % in the semicompact subnucleus and were absent in the loose part. In the dorsal nucleus of vagus nerve, biphenotypic nNOS/ChAT NS composed 7,0 ± 1,0 %, while purely nitrergic ones – 2,6 ± 0,4 % only. The small nitrergic NS were abundant in the nuclei of the solitary tract. Nitrergic NFs were plentiful in the rootlets of the vagal nerve. 31,4 ± 0,5 % of NFs in the cervical vagal nerve were nitrergic and an abundant population of them proceeded into cardiac branches. Inferior vagal sensory ganglia involved 37,4 ± 1,3 % of NS immunoreactive for nNOS. In the dorsal root ganglia, nitrergic NS were scarce. In the intermediolateral nuclei, the majority of NS were biphenotypic nNOS/ChAT. Only solitary nitrergic NS were revealed in the stellate ganglia. Conclusions. Since the abundant population of nitrergic NS is distributed in the inferior vagal sensory ganglia, presumably neuronal NO is involved in afferent cardiac innervation. However, the presence of biphenotypic nNOS/ChAT NS in both the vagal and the intermediolateral nuclei suggests that neuronal NO may also regulate the parasympathetic and sympathetic outflow to the heart