Development of the nerve supply to the human heart

Developmental Progression of the Coronary Vasculature in Human Embryos and Fetuses

Although considerable advances in our understanding of mammalian and avian embryonic coronary development have occurred during the last decade, our current knowledge of this topic in humans is limited. Accordingly, the aim of this study was to determine if the development of the human coronary vasculature in humans is like that of other mammals and avians. The data document a progression of events involving mesenchymal cell-containing villi from the proepicardium, establishment of blood islands and a capillary network. The major finding of the study is direct evidence that the capillary plexus associated with spindle cells and erythroblasts invades the base of the aorta to form coronary ostia. A role for the dorsal mesocardium is also indicated by the finding that cells from this region are continuous with the aorta and pulmonary artery. The development of the tunica media of the coronary arteries follows the same base-apex progression as in other species, with the development of branches occurring late in the embryonic period. The fetal period is characterized by 1) growth and a numerical increase in the smallest arterial branches, veins, and venules, 2) innervation of arteries, and 3) inclusion of elastic fibers in the tunica media of the coronary arteries and development of the tunica adventitia. In conclusion, the data demonstrate that the development of the coronary system in humans is similar to that of other mammalian and avian species, and for the first time documents that the formation of the ostia and coronary stems in humans occurs by ingrowth of a vascular plexus and associated cells from the epicardium.

Venous endothelin guides sympathetic innervation of the developing mouse heart

The mechanisms responsible for establishing correct target innervation during organ development are largely unknown. Sympathetic nerves traverse or follow blood vessels to reach their end-organs, suggesting the existence of vascular guidance cues that direct axonal extension. The sinoatrial node and the ventricle of the heart receive sympathetic innervation from the stellate ganglia (STG). Here we show that STG axons follow veins, specifically the superior vena cavae and sinus venosus, to reach these targets. We find that the election of these routes is determined by venous endothelium-derived endothelin-1, acting through its specific receptor Ednra expressed within a subpopulation of STG neurons. Furthermore, we demonstrate that Edn1-Ednra signaling is essential for functional regulation of the heart by sympathetic nerves. Our findings present venous Edn1 as a sympathetic guidance cue, and show how axon guidance mechanisms are coordinated with end-organ morphogenesis.

Gross anatomical study of the sympathetic cardiac nerves in the house musk shrew (Suncus murinus)

The sympathetic cardiac nerves originating from the cervical and upper thoracic sympathetic ganglia in the house musk shrew (Suncus murinus) were examined using macroscopic and whole-mount immunohistochemical methods. Based on the results, the nerves were macroscopically classified into the following three groups: nerves innervating the cervical sympathetic ganglia mainly to the arterial porta of the heart; nerves supplying the stellate and thoracic sympathetic ganglia at the level of T2-T5 or T6 for both the arterial and venous portae of the heart; and nerves innervating the thoracic sympathetic ganglia at the level of T4-T9 to the esophagus and lung and then the heart via the blood vessels within the mediastinal pleura. These findings in the house musk shrew suggest a possible primitive morphological pattern of the cervical and thoracic sympathetic nervous system that may be related to those in other mammals, including humans.

Location and variability of epicardiac ganglia in human fetuses

The aim of the study was to determine the morphology of epicardiac ganglia in human fetuses at different stages of their development as these ganglia are considered to be of a pivotal clinical importance. Twenty-one fetal hearts were investigated applying a technique of histochemistry for acetylcholinesterase to visualize the epicardiac neural ganglionated plexus with its subsequent stereoscopic examination on total organs. In all of the examined fetuses, epicardiac neural plexus with numerous ganglia was well recognizable and could be clearly differentiated into seven ganglionated subplexuses, topography and structural organization of which were typical for hearts of adult human. The largest ganglion number comprising 77% of all counted ganglia was identified on the dorsal atrial surface. Fetal epicardiac plexus in gestation period of 15-40 weeks contained 929 +/- 62 ganglia, but ganglion amount did vary substantially from heart to heart. In conclusion, this study implies that the human fetal epicardiac ganglia occupy their definitive location already at gestation period from 15 weeks and their number as well as distribution on heart surface presumably is not age dependent.

Morphology and development of the distal ganglion of the vagus nerve (ganglion distale n. vagi) in sheep during the prenatal period

This study was carried out on 31 sheep fetuses, which were divided into four developmental groups. It was established that the development and morphology of the investigated part of vagus nerve is strongly correlated with the developing organs of the fetuses. The very distinct 'translocation' of the distal ganglion of the vagus nerve in the caudoventral direction was observed in the course of development. There was no influence of sex on the results of investigation.

Topography of cardiac ganglia in the adult human heart

Published descriptions of the topography of cardiac ganglia in the human heart are limited and present conflicting results. This study was carried out to determine the distribution of cardiac ganglia in adult human hearts and to address these conflicts. Hearts obtained from autopsies and heart transplant procedures were sectioned, stained, and examined. Results indicate that the largest populations of cardiac ganglia are near the sinoatrial and atrioventricular nodes. Smaller collections of ganglia exist on the superior left atrial surface, the interatrial septum, and the atrial appendage-atrial junctions. Ganglia also exist at the base of the great vessels and the base of the ventricles. The right atrial free wall, atrial appendages, trunk of the great vessels, and most of the ventricular myocardium are devoid of cardiac ganglia. These findings suggest modifications to surgical procedures involving incisions through regions concentrated with ganglia to minimize arrhythmias and related complications. Repairs of septal defects, valvular procedures, and congenital reconstructions, such as the Senning and Fontan operations, involve incisions through areas densely populated with cardiac ganglia. The current standard procedure for orthotopic heart transplantation severs cardiac ganglia and their projections to nodal and muscular tissue. One modification of the current heart transplantation procedure, involving bicaval anastomosis, preserves atrial anatomy and the cardiac ganglia. Preservation of cardiac ganglia within the donor heart may provide additional neuronal substrate for intracardiac processing and targets for regenerating nerve fibers to the donor heart.

Cardiac neurones of autonomic ganglia

The properties of the postganglionic sympathetic neurones supplying the heart and arising in the stellate and adjacent paravertebral ganglia of various species are discussed with respect to their location, morphology, synaptic input and membrane characteristics. Results from our laboratory on the morphology of rat stellate neurones projecting to the heart were obtained either by intracellular injection of hexammine cobaltic (III) chloride or by retrograde labelling of cells using cobalt-lysine complex. Intracellular recordings were made from cells using electrodes filled either with potassium chloride plus hexammine cobaltic chloride or potassium acetate. Neurones which projected axons into cardiac nerve branches arising from the stellate ganglion were termed putative cardiac neurones, because of the possibility that some supply pulmonary targets. Putative cardiac neurones had unbranched axons and were ovoid or polygonal in shape, but showed considerable variation in soma size and in the complexity of dendritic trees. The mean two-dimensional surface area was 463 microns2 and the mean number of primary dendrites was seven. Other studies have found that the morphology of rat stellate ganglion neurones is similar to that of superior cervical ganglion cells. However, in strains of rat displaying spontaneous hypertension, dendritic length may be increased. Histochemical studies do not, as yet, seem to have demonstrated a distinctive neurochemical profile for stellate cardiac neurones, but various types of peptide-containing intraganglionic nerve fibres have been identified in the guinea pig. In our electrophysiological studies, putative cardiac neurones were found to receive a complex presynaptic input arising from the caudal sympathetic trunk and from T1 and T2 thoracic rami. In addition, 16% of cardiac neurones received a synaptic input from the cardiac nerve. The properties of postganglionic parasympathetic neurones distributed in the cardiac plexus and termed intrinsic cardiac neurones are discussed, including the results of studies on cultures of these neurones.

Innervation of the human cardiac conduction system. A quantitative immunohistochemical and histochemical study

BACKGROUND

Cardiac conduction is influenced by peptidergic mechanisms as well as classic neurotransmitters. The distribution of peptide-containing nerves has not been well defined.

METHODS AND RESULTS

Immunofluorescence and histochemical techniques were used to visualize the innervation of the human conduction system and to distinguish nerve subpopulations according to their peptide and enzyme content. Nerve fibers and fascicles displaying immunoreactivity for protein gene product 9.5 (PGP 9.5) were more numerous in the sinus and atrioventricular nodes than in the penetrating bundle, bundle branches, and adjacent myocardium. The relative density of innervation was greater in the central region of the sinus node than in the peripheral regions. Nerve densities were also higher in the transitional region of the atrioventricular node compared with its compact region. Acetylcholinesterase (AChE)-positive nerves were the main subtype identified in the sinus and atrioventricular nodes, representing half to two thirds of the stained area occupied by PGP 9.5-immunoreactive nerves. Neuropeptide Y-immunoreactive nerves represented the main peptide-containing subpopulation and occurred throughout the conduction system, displaying a similar pattern of distribution and relative density to those demonstrating tyrosine hydroxylase immunoreactivity. Nerve fibers showing immunoreactivity for vasoactive intestinal polypeptide, somatostatin, substance P, or calcitonin gene-related peptide exhibited distinct patterns of distribution and comprised a relatively minor component of the innervation, the percentage of stained area being 10- to 40-fold lower than that occupied by neuropeptide Y- and PGP 9.5-immunoreactive nerves, respectively.

CONCLUSIONS

The innervation of human conduction tissues exhibits significant regional variation and comprises putative parasympathetic nerves and intrinsic neurons (AChE positive), sympathetic efferent nerves (neuropeptide Y- and tyrosine hydroxylase-immunoreactive nerves), and other peptide-containing nerves, some of which (substance P and calcitonin gene-related peptide containing) are considered to represent afferent nerves. Locally released peptides may be involved in the neural modulation of the human conduction system.

Development of the peptidergic innervation of human heart

The aim of the present investigation was to study the developing peptidergic innervation of the human fetal heart of 7-24 wk gestational age. An immunohistochemical approach was adopted and the total innervation visualised with antisera to general neuronal and Schwann cell markers, while the onset and development of specific neuropeptide-containing subpopulations were investigated using antisera to neuropeptide Y (NPY), somatostatin, vasoactive intestinal polypeptide (VIP), calcitonin gene-related peptide (CGRP) and substance P (SP). Cardiac ganglia and nerves were demonstrated from 7 wk of gestation whereas peptide-immunoreactive nerves were not observed until the 10th week of gestation. NPY-immunoreactive nerve fibres constituted the major subpopulation of peptide-containing nerves identified in the fetal heart, exhibiting a descending atrial to ventricular density gradient, and were first identified during the 10th wk of gestation. Somatostatin- and VIP-immunoreactive nerves appeared at 10-12 wk of gestation and were mainly distributed in the atria. Somatostatin immunoreactivity was localised to cell bodies in cardiac ganglia, as well as to nerve fibres, indicating an intrinsic origin for this nerve subpopulation. Conversely, the other peptide-containing nerves appear to be of extrinsic origin, including those immunoreactive for VIP. Intracardiac neurons exhibit a transient expression of tyrosine hydroxylase immunoreactivity. Putative sympathetic nerve fibres, displaying tyrosine hydroxylase and NPY immunoreactivity, were demonstrated before the adrenergic innervation has previously been shown to be present by formaldehyde-induced fluorescence staining of catecholamines. The onset of the CGRP- and SP-immunoreactive innervation, at 18-24 wk of gestation, followed the appearance of other peptide-containing nerves, suggesting that the sensory, afferent innervation occurs later than the autonomic. The differential appearance and distribution of peptide-containing nerve subpopulations indicate that there is a chronological order to the development of the autonomic and sensory components of human cardiac innervation.

The intracardiac neurones of the fetal human heart in culture

Dissociated cell culture preparations were employed to study intracardiac neurones of the atria from human fetal hearts at 9 to 21 weeks' gestation. Intracardiac neurones were not observed in cultures dissociated from the ventricles. Single neurones, as well as groups, could be identified by phase-contrast microscopy in all of the atrial cultures prepared from 14 to 21 weeks' gestation, and protein gene product 9.5-like immunoreactive neurones were detected in cultures from as early as 10 weeks' gestation. The neurones were mononucleate, with a prominent nucleolus or multiple nucleoli, and often had extensive neurites. Neurones tended to be bigger in cultures from later stages in gestation, and these cells appeared to be more mature with a complex pattern of neurite outgrowth. Many neurones from 15 to 20 weeks' gestation expressed somatostatin-like immunoreactivity in culture. A very low proportion of cultured neurones was immunoreactive for neuropeptide Y and its C-terminal flanking peptide. Neuropeptide Y-like immunoreactive neurones also contained 5-hydroxy-tryptamine-like immunoreactivity in culture, but dopamine beta-hydroxylase-like immunoreactive neurones were not detected. This study is the first description of human intracardiac neurones in culture and forms the essential baseline for further direct investigation of these cells.

The development of cholinergic ganglia in the chick embryo heart

Cholinesterase activity was investigated in the heart of the developing chick from the 6th to 20th day of incubation. The earliest cholinesterase-positive nerve cells and fibers could be demonstrated between the 7th and 9th day. On the 13th day the nervous structure attained full development comparable with that seen in the hatched chicken. The number of ganglia increases up to the 15th day, and remains constant thereafter. The right ventricle is associated with the largest number of ganglia.

Innervation of the sinu-atrial node and neighbouring regions in two human embryos

In human embryos of 20 to 23 mm (36 to 40 days) it is possible to identify on the right side a nerve that we may call the sinusal, which originates by several roots from the nervus vagus dexter (Figs. 1A, B, D), descending through the right ventrolateral face of the primary trachea and right bronchus (Fig. 2, arrows). Beaded in appearance, it gives a fine anastomotic branch which, passing in front of the arteria pulmonalis dextra, passes to the left side (Figs. 2B, C, D; AN). At this level it gives the large branch for the nodus sinoatrialis which, penetrating through the wall of the superior vena cava, provides a rich innervation for the nodus sinoatrialis which is already in an advanced stage of differentiation (Fig. 3, 2; Cy, D, AN). Afterwards it gives fine branches which, following the atrial fold, are distributed throughout the posterior face of the atrium dextrum (Fig. 3). It increases in diameter and, passing through the angle formed by the right pulmonary veins with the atrium dextrum, reaches the intrapericardial portion of the inferior vena cava in the vicinity of its outlet from the atrium (Fig. 3, arrows). The whole innervation is parasympathetic at the stages studied.

The nerve supply and conducting system of the human heart at the end of the embryonic period proper

The nerve supply and conducting system were studied in a stage 23 human embryo of exceptional histological quality. The nerves on the right side arose from cervical sympathetic and from cervical and thoracic vagal filaments. Out of their interconnexions vagoxympathetic nerves emerged, which (1) sent a branch in front of the trachea to the aorticopulmonary ganglion, thereby supplying arterial and venous structures, and (2) formed the right sinal nerve, which supplied the sinu-atrial node, and gave filaments to the interatrial septum which could be traced to the atrioventricular node and pulmonary veins. The nerves on the left side arose similarly from cervical sympathetic and from cervical and thoracic vagal filaments. These formed several descending, ganglionated, vagosympathetic filaments that descended to the right of the arch of the aorta and entered the aorticopulmonary ganglion. Filaments leaving the ganglion supplied the pulmonary trunk, ascending aorta, interatrial septum, pulmonary veins, and, as the left sinal nerve, the fold of the left vena cava. The thoracic vagal filaments descended to the left of the arch of the aorta and supplied chiefly the arterial end of the heart. No thoracic sympathetic cardiac filaments were found. The sinu-atrial node began as a crescentic mass in front of the lower part of the superior vena cava. It gradually extended on each side of the superior vena cava and came to form its posterior wall at a more caudal level. The atrial myocardium that formed the septum spurium, venous valves, and interatrial septum could be traced from the sinu-atrial to the atrioventricular node. Myocardium also encircled the atrial aspects of the atrioventricular orifices, and could be traced caudally to the atrioventricular nde. The atrioventricular node was a conspicuous mass in the anterior and lower part of the interatrial septum, from which a clearly defined bundle left to enter the interventricular septum. Right and left limbs were observed, the former being a rounded bundle that passed immediately in front of the root of the aorta.

Comparison of cardiac refractory periods in children and adults

Atrial (A) and A-V nodal (AVN) effective and functional refractory periods (ERP & FRP) were determined by atrial extrastimulus technique in 40 children, aged 7 months to 16 years, with normal P-R intervals and QRS durations. These data were compared to adult data at longest cycle lengths (CL) assuring atrial capture. All values are listed in msec as means plus or minus standard errors of the means. CL was 566 plus or minus 15 in children and 699 plus or minus 29 in adults (P less than .001). Refractory periods (RP) in children and adults were, respectively: AERP 196 plus or minus 9 and 239 plus or minus 13 (P less than .01), AFRP 225 plus or minus 8 and 284 plus or minus 11 (P less than .001), AVNERP 239 plus or minus 11 and 293 plus or minus 7 (P smaller than .001), AVNFRP 360 plus or minus 13 and 403 plus or minus 7 (P smaller than .005). RP were then compared at three equivalent CL ranges: CL1, 850-600; CL2 599-460; CL3 459-280. The following RP were significantly shorter in children (P smaller than .05-.001): AERP, AFRP, AVENERP and AVNFRP at CL2 and CL3. RP of the bundle branches were compared and tended to be shorter in children. In conclusion, atrial and A-V nodal ERP and FRP are shorter in children than adults. This shortening is only partially related to the shorter CL in children. These data are germane to understanding the maturation of the conduction system in man.

The development of the intrinsic innervation of the human heart between the 10 and 70 mm stages

Images

Development of innervation of coronary arteries in human foetus up until 230 mm. stage (mid-term)

Images

Notched T waves in young persons with central nervous system lesions

Eighty-nine abnormal electrocardiograms taken on young persons with central nervous system (CNS) lesions were reviewed. Most had S-T segment and T-wave abnormalities of a nonspecific type. A high incidence of notched T waves was also noted. In this group of patients with CNS lesions the notching may be due to asymmetrical alterations in sympathetic tone to the ventricle.