J. Moravec

Heart failure: an electron microscopic study of the left ventricular papillary muscle in aortic insufficiency in the rabbit.

The left ventricular papillary muscle was studied by electron microscopy in 31 rabbits subjected to experimental aortic insufficiency and sacrificed at different stages (from 2 days to 10 months) after valvulotomy. The fixation was performed quickly after stopping the heart in diastole, by means of an intra-coronary venous injection of iso- or slightly hyper-osmotic fixative. The electron microscopic appearances were quite different depending on the date of death. From the second to the twenty-first days, there were many modifications of the cellular picture, related to increased protein synthesis, or to disturbances in cellular metabolism. Myofibrillar “lesions” (stretching of the I-band and Z-line, which predominate beneath the intercalated disc) may represent either growth of the myofilaments or true lesions of contractile proteins. During the later stages (from 1 to 10 months after valvulotomy), there were two types of modifications: the “usual” appearances of hypertrophy, and “clarification” of certain cells with a decrease in the density of structural proteins and an increase of the surface occupied by sarcoplasm. There was no longer any myofibrillar or cellular damage, apart from some appearances thought to be covered by a state of under-contractility. Heart failure, which was not always easy to establish, was correlated with the extent of cellular alterations in the early stages, but poorly in the later ones. Throughout the whole experiment the average sarcomere length, apart from very localized stretching of the I band in the early stages, never differed from controls.

Catecholamine-synthesizing enzymes and neuropeptides in rat heart epicardial ganglia; an immunohistochemical study

SummaryThe subepicardial atrial ganglia of rat hearts were examined using immunohistochemical techniques and antibodies against the catecholamine-synthetic enzymes tyrosine hydroxylase (TH) and dopamine-β-hydroxylase (DBH), and the neuropeptides substance P (SP), calcitonin gene-related peptide (CGRP), neuropeptide Y (NPY), vasoactive intestinal polypeptide (VIP) and met-5-enkephalin (ENK). Some of the ganglion cells present in the ganglia exhibited DBH-like immunoreactivity (LI) and NPY-LI, whilst these cells nerver exhibited TH-, VIP-, CGRP-, SP- or ENK-LI. Groups of small cells exhibiting an intense TH-LI, corresponding to cells referred to as catecholamine-containing cells and sometimes small intensely fluorescent cells in the literature, were observed in the ganglia. A subpopulation of these cells exhibited immunoreactivity to one of the neuropeptides tested, namely SP. Only a few of the cells showing TH-LI displayed DBH-LI. Nerve fibres showing SP-, CGRP-, DBH- and TH-LI were present in the ganglia; some of these fibres being closely associated with the ganglion cells or with the cells showing TH-LI. The observations provide new information on the catecholaminesynthetic enzyme/neuropeptide expression of the ganglion and catecholamine-containing cells and of the associated nerve fibres of rat heart subepicardial ganglia.

Catecholaminergic and peptidergic nerve components of intramural ganglia in the rat heart

SummaryImmunohistochemical properties of the terminal nerve network in the rat heart were assessed by use of the elution-restaining method. The colocalization of the enzymes involved in catecholamine synthesis (tyrosine hydroxylase — TH, dopamine-β-hydroxylase — DBH) as well as the respective distributions of the neuropeptides associated with the adrenergic nervous system (neuropeptide tyrosine — NPY, C-terminal flanking peptide of neuropeptide Y — C-PON) were studied in series of serial sections throughout the interatrial septum and the atrioventricular junction. Our data suggest that ganglion cells of sulcus terminalis as well as the epicardial ganglia enclosed between the superior vena cava and ascending aorta are VIP- and TH-negative, but neuropeptide Y- and DBH-immunoreactive. They give rise to three intraseptal nerves directed towards the specialised structures of the atrioventricular junction. These nerve fascicles contain abundant, thick TH-immunoreactive nerve fibres and scarce, thin NPY- and DBH-immunoreactive fibres. The cell bodies of the intramural ganglion cells localized between the right and left branches of the bundle of His (Moravec and Moravec 1984) are strongly TH- and DBH-immunoreactive. They are innervated by thick nerve fibres having the same immunohistochemical properties (NPY- and DBH-immunoreactivities) as those of a subpopulation of the epicardial ganglion cells and seem to supply some of the TH-immunoreactive nerve fibres directed via the intraseptal nerves to the epicardial ganglia. The existence of a multicomponent nerve network, characterized by a reciprocal innervation of the sinus node and atrioventricular node areas, is suggested by our immunohistochemical data.

The ultrastructure of rat conductive tissue; An electron microscopic study of the atrioventricular node and the bundle of His

Abstract An electron microscope study of the atrioventricular node and the bundle of His was done after an in vivo fixation. Three types of cells have been described: (1) pacemaker cells localized in the atrioventricular node and the upper parts of both branches, (2) conduction, or “transitional” cells found at any level of conduction system examined, (3) Purkyne like cells with clear sarcoplasm, but small diameter found mostly in the bundle of His. In the node the cells are randomly organized, forming an irregular network of trabecular or nodular appearance. The number of nerves, as well as of collagen fibres is striking. Close interactions between the different kinds of tissues are of particular interest. In the bundle of His the cells are well organized, parallel to its longitudinal axis. The nerves and connective tissue are mostly on the periphery of the bundle. The ultrastructure of specialized cells shows a gradation along the conduction system from typically nodal towards myocardium like cells, which puts in doubt the real entity of cells called usually as pacemaker or conduction ones. No morphological substratum of spontaneous activity nor conductibility could be found. The presence of well developed Golgi apparatus, rough sarcoplasmic reticulum, numerous proteic inclusions and pinocytic vesicles might reflect an excretory activity of conduction system.

Intrinsic Nerve Plexus of Mammalian Heart: Morphological Basis of Cardiac Rhythmical Activity?

Publisher Summary This chapter reveals that the generation of rhythmical heartbeats in mammals has been considered essentially myogenic, resulting from slow diastolic depolarization of pacemaker cells or from subthreshold oscillations of their membrane potentials. The role of the nervous system is often restricted to an external modulation of the inherent muscular pacemaker. This situation results from the fact that current knowledge of cardiac innervation of the mammalian heart has been derived from classical, physiological, and microanatomical observations. According to these studies, the pacemaker area of the heart receives abundant cholinergic and adrenergic postganglionics originating from the extracardiac ganglia. A majority of the ganglionic cells is concentrated in the subepicardium of the base of the heart, around the ostia of great vessels and in the coronary sulcus, where they form more or less delimitated subepicardial ganglia. Isolated ganglionic cells can also be found scattered in the meshes of the terminal nerve plexus located in the wall of the right atrium and in the interatrial septum all along the sulcus terminalis.

Development and reversal of pressure-induced cardiac hypertrophy

SummaryLight and electron microscopy, combined with morphometry, were utilized to study myocardial cell modifications induced by a temporary abdominal aortic constriction in the rat.During the early stage of active hypertrophy, cell enlargement in the subendocardial layers of the left ventricle was predominant. This enlargement may be partly due to intracellular edema, characteristic of cell damage. Degenerative foci leading to fibrous scars were found primarily in the subendocardium and midwall layers.The times taken by the different cell structures to adapt to modifications of the load were rather different; some adapted very rapidly (nucleoli, intercalated discs), while others were much slower (cell diameter, mitochondria).ZusammenfassungLichtmikroskopische und elektronenoptische Untersuchungen, kombiniert mit morphometrischen Verfahren, wurden benutzt, um myokardiale Zellveränderungen zu studieren, die durch eine temporäre Konstriktion der abdominalen Aorta bei der Ratte hervorgerufen wurden.Während des frühen Studiums der “aktiven” Hypertrophie war die Verbreiterung der Zellen in den subendokardialen Schichten des linken Ventrikels vorherrschend. Diese Dickenzunahme könnte teilweise auf ein intrazelluläres Ödem zurückgehen, das für eine Zellschädigung charakteristisch ist. Degenerative Herde, die zu Narbenbildungen führten, wurden in erster Linie subendokardial und in den mittleren Muskelschichten gefunden.Die Zeit, welche unterschiedliche Zellstrukturen benötigen, um sich an Anderungen der Belastung anzupassen, war ziemlich verschieden; einige Strukturen adaptierten sich sehr schnell (Nucleolen, Disci intercal.), andere wesentlich langsamer (Zelldurchmesser, Mitochondrien).

Subacute myocardial hypoxia in the rat. An electron microscopic study of the left ventricular myocardium.

Abstract Electron microscopic analysis of left ventricular myocardium from rats made hypoxic for 2h, 10 and 30 days showed focal intracellular oedema as the only alteration in acute severe hypoxia (6% oxygen). No mitochondrial lesions were seen. In chronically hypoxic hearts (9% oxygen) the mitochondrial structure also remained normal. Morphometric analysis has showed a significant increase in capillary density and in the number of mitochondria. The mean diameter of the latter seems to be smaller in hypoxic than in control hearts.

Effect of increased aortic perfusion pressure on fluorescent emission of the isolated rat heart

When the isolated rat heart was perfused at a range of aortic pressures, left ventricular peak systolic pressure varied from 40 to 140 mmHg. The fluorescent emission at 481 nm decreased, which was interpreted as an increased myocardial tissue NAD+NADH ratio at higher pressures. Because the perfusion conditions (fasted rats, β-hydroxybutyrate 5 mm substrate) were such as to minimize glycolytic flux and because the cytoplasmic NAD pool did not change as assessed by perfusate and tissue lactate/pyruvate ratios, it was probable that the mitochondrial NAD pool had changed towards NAD+. The effect of increased perfusion pressure on the fluorescent emission was dependent on the substrate of the heart.

Intrinsic neurosecretory neurons of the rat heart atrioventricular junction: Possibility of local neuromuscular feed back loops

The microanatomy and ultrastructure of rat heart atrioventricular junction were studied on serial sections of both paraffin and epoxy embedded samples. The animals were pretreated with 5-hydroxy-dopamine in order to differentiate the adrenergic component of the terminal nerve plexus. Two kinds of ganglia could be identified throughout the interatrial septum by the optical microscope. The first was composed of large pale cells with voluminous nuclei. The other resembled acini-like clusters of osmophilic cells. Another small ganglion was invariably present between right and left branches of the bundle of His. The electron microscopic examination of this structure revealed, apart from small pale neurons (10 microns in diameter), several large 5-hydroxy-dopamine contrasted neurosecretory cells (up to 30 microns) with abundant electron dense vesicles typical for sympathetic neurons. Numerous glomeruli with dendrodendritic and axodendritic connections, some of which exhibit the same 5-hydroxy-dopamine loaded vesicles, could be found in the vicinity of the specialized conducting tissue. The functional implications of the above morphological data are not clear. However, the intrinsic neurosecretory component can be expected to modulate both specialized cells and neighbouring neurons. The heterogeneity of neuro-neuronal and neuro-muscular relations, such as perinodal mechanoreceptors, may suggest that the terminal nerve plexus not only distributes the efferent stimuli, but that it also has an integrative function which is the necessary prerequisite for a local feed back autoregulation.

Adrenergic neurons and short proprioceptive feedback loops involved in the integration of cardiac function in the rat

SummarySerial cryostat and paraffin-embedded sections through the atrioventricular junction of the rat heart were studied at the light-microscopic level after indirect immunohistochemical staining (tyrosine hydroxylase, neuropeptide Y, C-terminal flanking peptide of neuropeptide Y immunoreactivities) or silver impregnation. The distribution of these immunoreactivities in the Hissian ganglion (Moravec and Moravec 1984) as well as the relationships of the Hissian ganglion cells with the surrounding structures have been studied to assess its function. The results suggest that the Hissian ganglion is composed of large multipolar neurons displaying both tyrosine hydroxylase (TH) and related peptide (neuropeptide Y, C-terminal flanking peptide of neuropeptide Y) immunoreactivities. The dendritic projections of these adrenergic cells penetrate the reticular portion of the atrioventricular node and the upper segments of the interventricular septum where they constitute sensory-like corpuscles. The hypothesis that the adrenergic neurons of the atrioventricular junction are involved in short proprioceptive feedback loops necessary for beat-to-beat modulation of cardiac excitability and intracardiac conduction can thus be suggested.