Summary BACKGROUND The intrinsic neural plexus of the mouse heart has not been adequately investigated despite the extensive use of this species in experimental cardiology. OBJECTIVE We determined the distribution of cholinergic, adrenergic and sensory neural components in whole-mount mouse heart preparations using double immunohistochemical labeling. METHODS AND RESULTS Intrinsic neurons were concentrated within 19±3 ganglia (n = 20 mice) of varying size, scattered on the medial side of the inferior caval (caudal) vein on the right atrium and close to the pulmonary veins on the left atrium. Of a total of 1082±160 neurons, most somata (83%) were choline acetyltransferase (ChAT)-immunoreactive, while 4% were tyrosine hydroxylase (TH)-immunoreactive; 14% of ganglionic cells were biphenotypic for ChAT and TH. The most intense ChAT staining was observed in axonal varicosities. ChAT was evident in nerve fibers interconnecting intrinsic ganglia. Both ChAT and TH immunoreactivity were abundant within the nerves accessing the heart. However, epicardial TH-immunoreactive nerve fibers were predominant on the dorsal and ventral left atrium, whereas most ChAT-positive axons proceeded on the heart base toward the large intrinsic ganglia and on the epicardium of the root of the right cranial vein. Substance P-positive and calcitonin gene-related peptide-immunoreactive nerve fibers were abundant on the epicardium and within ganglia adjacent to the heart hilum. Small intensely fluorescent cells were grouped into clusters of 3–8 and dispersed within large ganglia or separately on the atrial and ventricular walls. CONCLUSIONS While some nerves and neuronal bundles of the mouse epicardial plexus are mixed, most express either adrenergic or cholinergic markers. Therefore, selective stimulation and/or ablation of the functionally distinct intrinsic neural pathways should allow the study of specific effects on cardiac function.

Summary BACKGROUND Both normal and genetically modified mice are excellent models to investigate molecular mechanisms of arrhythmogenic cardiac diseases that may associate with an imbalance between the sympathetic and the parasympathetic nervous input to the heart. OBJECTIVE We sought to: (1) determine the structural organization of the mouse cardiac neural plexus; (2) identify extrinsic neural sources and their relationship with the cardiac plexus; and (3) reveal any anatomical differences in the cardiac plexus between mouse and other species. METHODS Cardiac nerve structures were visualized employing histochemical staining for acetylcholinesterase (AChE) on whole heart and thorax-dissected preparations derived from 25 mice. To confirm reliability of staining parasympathetic and sympathetic neural components in the mouse heart we applied a histochemical method for AChE and imunohistochemistry for tyrosine hydroxylase (TH) and/or choline acetyltransferase (ChAT) on whole mounts preparations from 6 mice. RESULTS The double immunohistochemical labeling of TH and ChAT on AChE positive neural elements in mouse whole mounts demonstrated equal staining of nerves and ganglia for AChE that were positive for both TH and ChAT. The extrinsic cardiac nerves access the mouse heart at the right (RCV) and left (LCV) cranial veins and interblend within the ganglionated nerve plexus of the heart hilum that is persistently localized on the heart base. Nerves and bundles of nerve fibers extend epicardially from this plexus to atria and ventricles by left dorsal, dorsal right atrial, right ventral, and ventral left atrial routes or subplexuses. The RCV received extrinsic nerves mainly originated from the right cervicothoracic ganglion and a branch of the right vagus nerve, while the LCV was supplied by extrinsic nerves from the left cervicothoracic ganglion and the left vagus nerve. The majority of intrinsic cardiac ganglia were localized on the heart base at the roots of pulmonary veins. These ganglia were interlinked by interganglionic nerves into the above mentioned nerve plexus of the heart hilum. In general, the examined hearts contained 19 ± 3 ganglia, which gave a cumulative ganglion area of 0.4 ± 0.1 mm2. CONCLUSION Despite substantial anatomical differences in ganglion number and distribution, the structural organization of the intrinsic ganglionated plexus in the mouse heart corresponds in general to other mammalian species, including human.

SummaryBACKGROUND-The sheep is routinely used in experimental cardiac electrophysiology and surgery.

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The rabbit is widely used in experimental cardiac physiology, but the neuroanatomy of the rabbit heart remains insufficiently examined. This study aimed to ascertain the architecture of the intrinsic nerve plexus in the walls and septum of rabbit cardiac ventricles. In 51 rabbit hearts, a combined approach involving: (i) histochemical acetylcholinesterase staining of intrinsic neural structures in total cardiac ventricles; (ii) immunofluorescent labelling of intrinsic nerves, nerve fibres (NFs) and neuronal somata (NS); and (iii) transmission electron microscopy of intrinsic ventricular nerves and NFs was used. Mediastinal nerves access the ventral and lateral surfaces of both ventricles at a restricted site between the root of the ascending aorta and the pulmonary trunk. The dorsal surface of both ventricles is supplied by several epicardial nerves extending from the left dorsal ganglionated nerve subplexus on the dorsal left atrium. Ventral accessing nerves are thicker and more numerous than dorsal nerves. Intrinsic ventricular NS are rare on the conus arteriosus and the root of the pulmonary trunk. The number of ventricular NS ranged from 11 to 220 per heart. Four chemical phenotypes of NS within ventricular ganglia were identified, i.e. ganglionic cells positive for choline acetyltransferase (ChAT), neuronal nitric oxide synthase (nNOS), and biphenotypic, i.e. positive for both ChAT/nNOS and for ChAT/tyrosine hydroxylase. Clusters of small intensely fluorescent cells are distributed within or close to ganglia on the root of the pulmonary trunk, but not on the conus arteriosus. The largest and most numerous intrinsic nerves proceed within the epicardium. Scarce nerves were found near myocardial blood vessels, but the myocardium contained only a scarce meshwork of NFs. In the endocardium, large numbers of thin nerves and NFs proceed along the bundle of His and both its branches up to the apex of the ventricles. The endocardial meshwork of fine NFs was approximately eight times denser than the myocardial meshwork. Adrenergic NFs predominate considerably in all layers of the ventricular walls and septum, whereas NFs of other neurochemical phenotypes were in the minority and their amount differed between the epicardium, myocardium and endocardium. The densities of NFs positive for nNOS and ChAT were similar in the epicardium and endocardium, but NFs positive for nNOS in the myocardium were eight times more abundant than NFs positive for ChAT. Potentially sensory NFs positive for both calcitonin gene-related peptide and substance P were sparse in the myocardial layer, but numerous in epicardial nerves and particularly abundant within the endocardium. Electron microscopic observations demonstrate that intrinsic ventricular nerves have a distinctive morphology, which may be attributed to remodelling of the peripheral nerves after their access into the ventricular wall. In conclusion, the rabbit ventricles display complex structural organization of intrinsic ventricular nerves, NFs and ganglionic cells. The results pr...