Morphological study of the innervation pattern of the rabbit sinoatrial node

The pattern of nerves, ganglia, and fine nerve processes in the adult rabbit sinoatrial node, identified by microelectrode recording, was defined by staining histochemically for cholinesterase followed by silver impregnation. A generalized repeatable pattern of innervation was recognized, including (1) a large ganglionic complex inferior to the sinoatrial node; (2) two or three moderately large nerves traversing the sinoatrial node parallel to the crista terminalis; (3) nerves entering the region from the atrial septum, the superior vena cava, and the inferior vena cava; and (4) a fine network of nerve processes, particularly extensive in the morphologically dense small-cell part of the sinoatrial node. When the site of initial depolarization in the node was located and marked by a broken-off electrode tip, it was found, after cholinesterase staining, to be characterized by a cluster of cells enclosed in a nest or basket of fine nerves. Similar nested cell clusters were observed elsewhere in the sinoatrial node in this same preparation and in other hearts. A complex interweaving of atrial muscle fibers was observed medial and inferomedial to the sinoatrial node, which may form the anatomical basis for the lack of conduction through this region. The morphological pattern of nerves, ganglia, and myocardial cells described in this study emphasizes the complexity of innervation of the sinoatrial node, including its intrinsic neural elements. Cholinesterase/silver staining can be useful in the definition and comparison of electrophysiologically identified sites within the sinoatrial node.     

Contribution of the cervical sympathetic ganglia to the innervation of the pharyngeal arch arteries and the heart in the chick embryo

In the chick heart, sympathetic innervation is derived from the sympathetic neural crest (trunk neural crest arising from somite level 10–20). Since the trunk neural crest gives rise to sympathetic ganglia of their corresponding level, it suggests that the sympathetic neural crest develops into cervical ganglia 4–14. We therefore tested the hypothesis that, in addition to the first thoracic ganglia, the cervical ganglia might contribute to cardiac innervation as well. Putative sympathetic nerve connections between the cervical ganglia and the heart were demonstrated using the differentiation markers tyrosine hydroxylase and HNK‐1. In addition, heterospecific transplantation (quail to chick) of the cardiac and trunk neural crest was used to study the relation between the sympathetic neural crest and the cervical ganglia. Quail cells were visualized using the quail nuclear antibody QCPN. The results by immunohistochemical study show that the superior and the middle cervical ganglia and possibly the carotid paraganglia contribute to the carotid nerve. This nerve subsequently joins the nodose ganglion of the vagal nerve via which it contributes to nerve fibers in cardiac vagal branches entering the arterial and venous pole of the heart. In addition, the carotid nerve contributes to nerve fibers connected to putative baro‐ and chemoreceptors in and near the wall of pharyngeal arch arteries suggesting a role of the superior and middle cervical ganglia and the paraganglia of the carotid plexus in sensory afferent innervation. The lower cervical ganglia 13 and 14 contribute predominantly to nerve branches entering the venous pole via the anterior cardinal veins. We did not observe a thoracic contribution. Heterospecific transplantation shows that the cervical ganglia 4–14 as well as the carotid paraganglia are derived from the sympathetic neural crest. The cardiac neural crest does not contribute to the neurons of the cervical ganglia. We conclude that the cervical ganglia contribute to cardiac innervation which explains the contribution of the sympathetic neural crest to the innervation of the chick heart. Anat Rec 255:407–419, 1999. © 1999 Wiley‐Liss, Inc.     

Morphological pattern of intrinsic nerve plexus distributed on the rabbit heart and interatrial septum

Although the rabbit is routinely used as the animal model of choice to investigate cardiac electrophysiology, the neuroanatomy of the rabbit heart is not well documented. The aim of this study was to examine the topography of the intrinsic nerve plexus located on the rabbit heart surface and interatrial septum stained histochemically for acetylcholinesterase using pressure‐distended whole hearts and whole‐mount preparations from 33 Californian rabbits. Mediastinal cardiac nerves entered the venous part of the heart along the root of the right cranial vein (superior caval vein) and at the bifurcation of the pulmonary trunk. The accessing nerves of the venous part of the heart passed into the nerve plexus of heart hilum at the heart base. Nerves approaching the heart extended epicardially and innervated the atria, interatrial septum and ventricles by five nerve subplexuses, i.e. left and middle dorsal, dorsal right atrial, ventral right and left atrial subplexuses. Numerous nerves accessed the arterial part of the arterial part of the heart hilum between the aorta and pulmonary trunk, and distributed onto ventricles by the left and right coronary subplexuses. Clusters of intrinsic cardiac neurons were concentrated at the heart base at the roots of pulmonary veins with some positioned on the infundibulum. The mean number of intrinsic neurons in the rabbit heart is not significantly affected by aging: 2200 ± 262 (range 1517–2788; aged) vs. 2118 ± 108 (range 1513–2822; juvenile). In conclusion, despite anatomic differences in the distribution of intrinsic cardiac neurons and the presence of well‐developed nerve plexus within the heart hilum, the topography of all seven subplexuses of the intrinsic nerve plexus in rabbit heart corresponds rather well to other mammalian species, including humans.     

Innervation of the rabbit cardiac ventricles

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 provide a basic anatomical background for further functional analysis of the intrinsic nervous system in the cardiac ventricles.     

Architecture and age-related analysis of the neuronal number of the guinea pig intrinsic cardiac nerve plexus.

The aims of the present study have been to determine the architecture of the guinea pig intrinsic cardiac nerve plexus (ICNP) and to test whether or not the heart of this species undergoes decrease in neuronal number with aging. Nine young (3-4 weeks of age) and nine adult (18-24 months of age) animals were examined employing histochemistry for acetylcholinesterase to reveal the ICNP in total hearts. The number of intracardiac neurons in seven animals was assessed via counting of the nerve cells both on total hearts and in serial sections of the atrial walls. The intracardiac neurons from adult guinea pigs were amassed within 329 +/- 15 ganglia. The hearts of young animals contained significantly fewer ganglia, only 211 +/- 27. In adult guinea pigs approximately 60% of the intracardiac neurons were distributed within ganglia of not more than 20 neurons, but the ganglia of such size accumulated only 45% of the neurons in young animals. The total number of the intracardiac neurons estimated per guinea pig heart was 2321 +/- 215, and this number did not differ significantly between young and adult animals. The nerves entering the guinea pig heart were found both in the arterial and venous part of the heart hilum. The nerves from the arterial part of the heart hilum proceeded into the ventricles, but the nerves from the venous part of the hilum formed a nerve plexus of the cardiac hilum located on the heart base. Within the guinea pig epicardium, intrinsic nerves divided into six routes and proceeded to separate atrial, ventricular and septal regions. In conclusion, findings of this study contradict the age-related decrease of the neuronal number in the guinea pig heart and illustrate the remarkable similarity in the architecture of the intracardiac nerve plexuses between guinea pig and rat.     

The adrenergic cardiac nerves of the cat

A fluorescence method was used for study of the adrenergic cardiac nerves of the cat. Sixteen regions of the heart were examined. The sinoatrial and atrioventricular nodes and the interatrial septum were the most richly innervated regions of the heart. There was little difference between the density of innervation in sections of atrial and ventricular portions of the myocardium. Most of the adrenergic nerves supplying the ventricles were derived from large bundles in the atrioventricular sulcus and were distributed through the subepicardial plexus. Each coronary artery was sparsely innervated in its initial elastic segment, but the vasa vasorum were well innervated. The main trunks of the coronary arteries were surrounded by plexuses composed only of preterminal axons; adrenergic vasomotor terminals were plentiful on the external surface of the muscular media of major and minor myocardial branches. Dense plexuses of adrenergic nerves were seen in both atrioventricular valves. The pulmonary valve was well innervated and contained more adrenergic nerves than the aortic valve. Perivascular plexuses and freely ending adrenergic terminals were observed in the pericardium. Small intensely fluorescent cells were grouped around small blood vessels in the interatrial septum. Most were in the vicinity of the atrioventricular node. It is suggested that these cells, under neural control may secrete catecholamines into the microcirculation of the interatrial septum. They may exert local humoral control over the atrioventricular node or the atrial parasympathetic ganglia.     

Contribution of the cervical sympathetic ganglia to the innervation of the pharyngeal arch arteries and the heart in the chick embryo.

In the chick heart, sympathetic innervation is derived from the sympathetic neural crest (trunk neural crest arising from somite level 10-20). Since the trunk neural crest gives rise to sympathetic ganglia of their corresponding level, it suggests that the sympathetic neural crest develops into cervical ganglia 4-14. We therefore tested the hypothesis that, in addition to the first thoracic ganglia, the cervical ganglia might contribute to cardiac innervation as well. Putative sympathetic nerve connections between the cervical ganglia and the heart were demonstrated using the differentiation markers tyrosine hydroxylase and HNK-1. In addition, heterospecific transplantation (quail to chick) of the cardiac and trunk neural crest was used to study the relation between the sympathetic neural crest and the cervical ganglia. Quail cells were visualized using the quail nuclear antibody QCPN. The results by immunohistochemical study show that the superior and the middle cervical ganglia and possibly the carotid paraganglia contribute to the carotid nerve. This nerve subsequently joins the nodose ganglion of the vagal nerve via which it contributes to nerve fibers in cardiac vagal branches entering the arterial and venous pole of the heart. In addition, the carotid nerve contributes to nerve fibers connected to putative baro- and chemoreceptors in and near the wall of pharyngeal arch arteries suggesting a role of the superior and middle cervical ganglia and the paraganglia of the carotid plexus in sensory afferent innervation. The lower cervical ganglia 13 and 14 contribute predominantly to nerve branches entering the venous pole via the anterior cardinal veins. We did not observe a thoracic contribution. Heterospecific transplantation shows that the cervical ganglia 4-14 as well as the carotid paraganglia are derived from the sympathetic neural crest. The cardiac neural crest does not contribute to the neurons of the cervical ganglia. We conclude that the cervical ganglia contribute to cardiac innervation which explains the contribution of the sympathetic neural crest to the innervation of the chick heart.     

Nerve contributions to the pelvic plexus and the umbilical cord

Serial sections of human embryos and fetuses reveal that the sacral nerves which contribute fibers to the pelvic plexus often have dorsal, ventral, and oblique communicating rami. The ventral rami resemble the white rami of upper thoracic nerves and some of their fibers pass close by or through the chain ganglia and into the pelvic plexus. The sizes of the ventral rami are often in inverse proportion to that of the pelvic splanchnic nerves. That is, when the pelvic splanchnic nerves are poorly developed, the ventral rami are large, and conversely, when the pelvic splanchnic nevers are well developed, these rami are small. The pelvic plexus was found to receive fibers from the sympathetic trunk and its ganglia in addition to those from the hypogastric plexus and the pelvic splanchnic nerves. Analysis of the observations made in this study together with a review of the literature in light of the present day classification of nerve fibers raises serious doubts concerning the limits set for the outflow of preganglionic nerve fibers from the spinal cord and the distribution of gray and white rami as described in recent textbooks in terms of their histological and physiological significance. Nerve fibers from the pelvic plexus can be traced along the walls of the bladder and the urachus and along the umbilical arteries into the umbilical cord. In embryos, only a few scattered nerve fibers were found distal to the umbilicus, but in fetuses at term, distinct nerve bundles were identified in the cord. These bundles sent branches to the walls of the umbilical arteries; other branches terminated as “end-nets” in Wharton's jelly. These nets appeared as fine fibers with nodular swellings at irregular intervals. Innervation of the umbilical arteries was richest within the first few inches of the cord. Beyond this region, the nerves rapidly decreased in number. “End-nets” were present as far as four inches from the umbilicus. Granular cells resembling Langerhans' cells were found in the cord. Often these cells were closely associated with fine nerve fibers.     

Localisation and quantitation of autonomic innervation in the porcine heart II: endocardium, myocardium and epicardium

The immunological problems of pig hearts supporting life in human recipients have potentially been solved by transgenic technology. Nevertheless, other problems still remain. Autonomic innervation is important for the control of cardiac dynamics and there is evidence suggesting that some neurons remain intact after transplantation. Previous studies in the human heart have established regional differences in both general autonomic innervation and in its component neural subpopulations. Such studies are lacking in the pig heart. Quantitative immunohistochemical and histochemical techniques were used to demonstrate the pattern of innervation in pig hearts (Sus scrofa). Gradients of immunoreactivity for the general neural marker protein gene product 9.5 were observed both within and between the endocardial, myocardial and epicardial plexuses throughout the 4 cardiac chambers. An extensive ganglionated plexus was observed in the epicardial tissues and, to a lesser extent, in the myocardial tissues. The predominant neural subpopulation displayed acetylcholinesterase activity, throughout the endocardium, myocardium and epicardium. These nerves showed a right to left gradient in density in the endocardial plexus, which was not observed in either the myocardial or epicardial plexuses. A large proportion of nerves in the ganglionated plexus of the atrial epicardial tissues displayed AChE activity, together with their cell bodies. Tyrosine hydroxylase (TH)-immunoreactive nerves were the next most prominent subpopulation throughout the heart. TH-immunoreactive cell bodies were observed in the atrial ganglionated plexuses. Endocardial TH- and NPY-immunoreactive nerves also displayed a right to left gradient in density, whereas in the epicardial tissues they showed a ventricular to atrial gradient. Calcitonin gene-related peptide (CGRP)-immunoreactive nerves were the most abundant peptide-containing subpopulation after those possessing NPY immunoreactivity. They were most abundant in the epicardial tissues of the ventricles. Several important differences were observed between the innervation of the pig heart compared with the human heart. These differences may have implications for the function of donor transgenic pig hearts within human recipients.     

The origins of the adrenergic fibres which innervate the internal anal sphincter, the rectum, and other tissues of the pelvic region in the guinea-pig

Summary The adrenergic innervation of the pelvic viscera was examined by the fluorescence histochemical technique, applied to tissue from untreated guinea-pigs and from guinea-pigs in which nerve pathways had been interrupted at operation. It was found that adrenergic neurons in the inferior mesenteric ganglia give rise to axons which run in the colonic nerves and end in the myenteric and submucous plexuses and around the arteries of the distal colon. In the rectum, part of the innervation of the myenteric plexus and all of the innervation of the submucous plexus comes from the inferior mesenteric ganglia. The rest of the adrenergic innervation of the myenteric plexus comes from the posterior pelvic ganglia or the sacral sympathetic chains. The innervation of the blood vessels of the rectum is from the posterior pelvic ganglia. Adrenergic nerves run from the sacral sympathetic chains and pass via nerves accompanying the rectal arteries to the internal anal sphincter. Other adrenergic fibres to the internal anal sphincter either arise in, or pass through, the posterior pelvic plexuses. The anal accessory muscle is innervated by adrenergic axons arising in the posterior pelvic plexuses. Adrenergic nerves which run in the pudendal nerves, probably from the sacral sympathetic chains, innervate the erectile tissue of the penis.This work was supported by grants from the Australian Research Grants Committee and the National Health and Medical Research Council. We thank Professor G. Burnstock for his generous support.     

Can atrial vagal denervation influence ventricular function in a failing heart?

Atrial fibrillation (AF) and congestive heart failure (CHF) often coexist (AF-CHF), and each adversely affects the other with respect to management and prognosis. Therapy with antiarrhythmic drugs to maintain sinus rhythm was disappointing. Ablation is more successful than antiarrhythmic drug therapy for the prevention of AF with few complications, although in patients with AF-CHF it is noted. Ablating autonomic nerves and ganglia on the large vessels and the heart can result in AF suppression with little damage to healthy myocardium. Our study in patients with AF-CHF found that cardiac function aggravation was more frequent in patients with AF recurrence than that of those who successfully maintain sinus rhythm. The autonomic nervous system is a fine network spreading throughout the myocytes; hence the elimination of atrial vagal with radiofrequency catheter ablation can influence the innervation in sinus and AV nodes even in the ventricular region. Thus we propose that atrial vagal denervation may result in paratherapeutic sympathovagal imbalance in the ventricular region, which has a negative effect in a failing heart, although it is neutralized by the benefit accrued from sinus rhythm after successful ablation.     

Localization of multiple neurotransmitters in surgically derived specimens of human atrial ganglia

Dysfunction of the intrinsic cardiac nervous system is implicated in the genesis of atrial and ventricular arrhythmias. While this system has been studied extensively in animal models, far less is known about the intrinsic cardiac nervous system of humans. This study was initiated to anatomically identify neurotransmitters associated with the right atrial ganglionated plexus (RAGP) of the human heart. Biopsies of epicardial fat containing a portion of the RAGP were collected from eight patients during cardiothoracic surgery and processed for immunofluorescent detection of specific neuronal markers. Colocalization of markers was evaluated by confocal microscopy. Most intrinsic cardiac neuronal somata displayed immunoreactivity for the cholinergic marker choline acetyltransferase and the nitrergic marker neuronal nitric oxide synthase. A subpopulation of intrinsic cardiac neurons also stained for noradrenergic markers. While most intrinsic cardiac neurons received cholinergic innervation evident as punctate immunostaining for the high affinity choline transporter, some lacked cholinergic inputs. Moreover, peptidergic, nitrergic, and noradrenergic nerves provided substantial innervation of intrinsic cardiac ganglia. These findings demonstrate that the human RAGP has a complex neurochemical anatomy, which includes the presence of a dual cholinergic/nitrergic phenotype for most of its neurons, the presence of noradrenergic markers in a subpopulation of neurons, and innervation by a host of neurochemically distinct nerves. The putative role of multiple neurotransmitters in controlling intrinsic cardiac neurons and mediating efferent signaling to the heart indicates the possibility of novel therapeutic targets for arrhythmia prevention.     

Substance P-like immunoreactive nerves in the anterior segment of the rabbit, cat and monkey eye

The indirect immunofluorescence technique demonstrates a substance P-like immunoreactive innervation to the anterior segment of the rabbit, cat and monkey eye. In all three species there is a sparse, but definite, corneal innervation. For the rabbit, substance P-like immunoreactive nerves to the aqueous outflow apparatus are found chiefly in the pectinate ligament. In the cat, this innervation is somewhat more extensive, being seen in the septae of the ciliary cleft as well. The monkey has a more plentiful innervation to the outflow apparatus than either the cat or the rabbit. Substance P-like immunoreactive nerves are visible in the trabecular meshwork and at the inner and outer walls of Schlemm's canal. For all three animals, the iris contains immunoreactive nerve fibers to the sphincter muscle, to the large blood vessels and to the anterior stromal melanocytes. In the ciliary body, the ciliary processes receive a constant innervation; it is somewhat more dense in the rabbit. Some of the large ciliary body blood vessels also are innervated. Ciliary body melanocytes are innervated; it was not possible to determine whether or not immunoreactive fibers innervate the ciliary muscle cells as well. The present study extends prior knowledge of the innervation of the eye. Taken with the known physiologic effects of substance P, it indicates a series of potential roles for this peptide in the vegetative processes of the eye.     

The ramifications of adrenergic nerve terminals in the rectum, anal sphincter and anal accessory muscles of the guinea-pig

Summary The anatomy and the adrenergic innervation of the rectum, internal anal sphincter and of accessory structures are described for the guinea-pig. The distribution of adrenergic nerves was examined using the fluorescence histochemical technique applied to both sections and whole mount preparations. The longitudinal and circular muscle of the rectum and the muscularis mucosae are all supplied by adrenergic nerve terminals. The density of the adrenergic innervation of the muscularis externa increases towards the anal sphincter. There is a very dense innervation of the internal anal sphincter, of the anal accessory muscles and of the corrugator ani. Non-fluorescent neurons in the ganglia of the myenteric plexus are supplied by adrenergic terminals. The ganglia become smaller and sparser towards the internal anal sphincter and non-ganglionated nerve strands containing adrenergic axons run from the plexus to the sphincter muscle. Adrenergic fibers innervate two interconnected ganglionated plexuses in the submucosa. Very few adrenergic nerve cells were found in the myenteric plexus and they were not found at all in the submucosa. The extrinsic arteries and veins of the pelvic region are heavily innervated by adrenergic nerves. Within the gut wall the arteries are densely innervated but there is little or no innervation of the veins.This work was supported by grants from the Australian Research Grants Committee and the National Health and Medical Research Council. We thank Professor G. Burnstock for his generous support.     

The early pattern of cardiac innervation in the fetal guinea pig

Embryonic hearts were obtained from 78 guinea pig embryos at 20–40 days of gestation. They were frozen quickly, freeze-dried and prepared by the Falck catecholamine fluorescent method for demonstration of adrenergic fibers. Other hearts were fixed in 10% formalin and examined after silver impregnation with the Holmes technique. The results of the two methods were correlated to visualize the total neural pattern as well as the specific adrenergic elements of the developing hearts. The present study indicates that vagal fibers, accompanied by the primordia of the cardiac ganglia, reach the atrial wall on the twenty-fifth day of gestation in the guinea pig. They penetrate the wall and are distributed by individual branches throughout the atrial wall from days 26 to 29 inclusive. From day 30 to parturition, the basic pattern of atrial distribution is elaborated by the lengthening, thickening, and branching of individual fibers. Sympathetic fibers pass to the atrial wall from the twenty-fifth to twenty-ninth day, those coursing with the vagus nerve arriving on the twenty-fifth day, while the remaining fibers arrive on the twenty-sixth to the twenty-ninth days. A ventricular ground plexus of sympathetic fibers is present just deep to the epicardium on the twenty-sixth day, and from this point until 30 days of gestation the ground plexus penetrates the ventricular myocardial wall. The sympathetic fibers at first course along the edge of a muscle bundle, but not between muscle fibers. The nerves become thicker at 29 days but do not exceed 2 μ. They branch slightly at 27 days, and at 30 days they are well branched and appear to overlie the surface of the muscle bundles simulating a perimysial plexus. At 40 days a very dense perimysial plexus is visible which contains some fluorescent nerves. Complete autonomic innervation is established by the thirtieth day of gestation.     

Sympathetic nerve pathways to the human heart,and their variations

Stimulated by the needs of surgery, common variations in the sympathetic pathways to the heart have acquired a practical significance. The cervical and upper thoracic sympathetic trunk was dissected on 24 sides in human fetuses at term, and the cardiac rami together with their communications studied and illustrated. To enable us to classify the cervical rami according to their sites of origin, the cervical sympathetic trunk was subdivided midway between ganglia into portions called ganglionic divisions; these divisions keeping the names applied to the ganglia in the Nomina Anatomica. Intermediate ganglia were found on the visceral outflow of the sympathetic trunk and are referred to as “distal intermediate ganglia” to distinguish them from the intermediate ganglia that have been described proximal to the sympathetic trunk. Thoracic cardiac rami were almost invariably present, the third and fourth thoracic ganglia most frequently providing substantial contributions. Some thoracic cardiac rami were traced as far as the left anterior descending coronary plexus. The question of bilateral symmetry was also examined. Whilst a variety of features are commonly present on both sides, the first dissection in a cervicothoracic sympathectomy is no reliable guide to the detailed anatomy of the second side. The sympathetic pathways to the heart are extremely variable in their topography, and the diversity of arrangements encountered accounts for the morphological contradictions in the literature. So numerous are the possible variations that the outcome of a sympathectomy is unpredictable. Where denervation is incomplete, collateral sprouting and regeneration of nerves could even lead to hyperstimulation via the sympathetic pathways.     

Adrenergic innervation of the mammalian choroid plexus

Choroid plexuses from the four cerebral ventricles of mice, rats, guinea-pigs, rabbits, cats, cows, and monkeys were either sectioned after freeze-drying or stretched on microscope slides for subsequent exposure to formaldehyde gas to demonstrate fluorescent adrenergic nerves. All plexuses received a substantial amount of noradrenaline-containing axons which originated in the superior cervical sympathetic ganglia. The nerve terminals enclosed both arterial and venous vessels. Some of the terminals in the tufts of the choroid plexus ran between the base of the epithelial cells and the underlying vascular wall. Thus, there are structural possibilities for a sympathetic innervation of the plexus epithelium, the plexus blood vessels, or both.     

Dual innervation of the mammalian urinary bladder A histochemical study of the distribution of cholinergic and adrenergic nerves

The pattern of autonomic innervation of the urinary bladder was studied in the cat, dog, rabbit and rat, using specific histochemical technics for acetylcholinesterase and norepinephrine. Cholinergic and adrenergic ganglion cells exist in all layers throughout the bladder wall. Large cholinergic and adrenergic nerve trunks coursing in the adventitial coat and deep lamina propria branch into the muscularis. The terminal cholinergic ramifications form a neuroterminal plexus which surrounds every smooth muscle cell in the bladder wall. The terminal adrenergic fibers are less abundant, do not form a plexus, and show regional variations in number at different levels and depths of the muscularis. These variations suggest that two regions of the bladder, namely the base and body, may be distinguished on the basis of differences in muscular innervation. In the lamina propria cholinergic and adrenergic nerves are grouped as deep and superficial subepithelial nerves. The latter form networks of variable complexity and supply fibers to the epithelium. Throughout the bladder wall, the blood vessels have a dual cholinergic and adrenergic perivascular plexus from which fibers extend into the media. Although the basic pattern of innervation is similar in the species studied, certain variations exist in the relative abundance and arrangement of epithelial and subepithelial nerves. The muscularis has a uniform cholinergic and a variable adrenergic innervation in different species.     

A macroscopical study of the subclavius muscle of the rat

The subclavius muscles of Wistar rats were dissected, and the morphological features and innervation of this muscle were macroscopically studied. The subclavius muscles of rats were found to be innervated dually by the dorsal and ventral subclavius nerves. The dorsal subclavius nerve was found to arise, in conjunction with the suprascapular and upper subscapular nerves, from the dorsal division of the superior trunk of the brachial plexus. The ventral subclavius, which was observed for the first time, was discovered to issue, together with the pectoral and the accessory phrenic nerves, from the superior and middle trunks of the brachial plexus. In rats, the appearance of the accessory phrenic nerve seemed to be a almost consistent phenomenon. From the close anatomical relationship of the dorsal and ventral subclavius nerves with the neighbouring nerves, it could be speculated that the subclavius muscle might develop from an anlage of the hypobranchial musculature near and/or in the junctional region between the hypobranchial and the pectoral regions of the body trunk. The region might, phylogenetically and ontogenetically, concomitantly with the development of the heart and lungs, undergo remarkable changes, to which variations of this muscle and its innervation could be attributed.