Elvira Colvee

Bulbus arteriosus of the antarctic teleosts. I. The white-blooded Chionodraco hamatus.

The bulbus arteriosus of teleost fish is a thick‐walled chamber that extends between the single ventricle and the ventral aorta. The functional importance of the bulbus resides in the fact that it maintains a steady blood flow into the gill system through heart contraction. Despite of this, a thorough study of the structure of the bulbus in teleost fish is still lacking. We have undertaken a morphologic study of the bulbus arteriosus in the stenothermal teleosts of the Antarctic sea. The structural organization of the bulbus arteriosus of the icefish Chionodraco hamatus has been studied here by conventional light, scanning, and transmission electron microscopy.

Origin and course of the coronary arteries in normal mice and in iv/iv mice

This paper reports on the origin and distribution of the coronary arteries in normal mice and in mice of the iv/iv strain, which show situs inversus and heterotaxia. The coronary arteries were studied by direct observation of the aortic sinuses with the scanning electron microscope, and by examination of vascular corrosion casts. In the normal mouse, the left and right coronaries (LC, RC) arise from the respective Valsalva sinus and course along the ventricular borders to reach the heart apex. Along this course the coronary arteries give off small branches at perpendicular or acute angles to supply the ventricles. The ventricular septum is supplied by the septal artery, which arises as a main branch from the right coronary. Conus arteries arise from the main coronary trunks, from the septal artery and/or directly from the Valsalva sinus. The vascular casts demonstrate the presence of intercoronary anastomoses. The origin of the coronary arteries was found to be abnormal in 84% of the iv/iv mice. These anomalies included double origin, high take‐off, slit‐like openings and the presence of a single coronary orifice. These anomalies occurred singly or in any combination, and were independent of heart situs. The septal artery originated from RC in most cases of situs solitus but originated predominantly from LC in situs inversus hearts. Except for this anomalous origin no statistical correlation was found between the coronary anomalies and heart situs or a particular mode of heterotaxia. The coronary anomalies observed in the iv/iv mice are similar to those found in human hearts. Most coronary anomalies appear to be due to defective connections between the aortic root and the developing coronaries. iv/iv mice may therefore constitute a good model to study the development of similar anomalies in the human heart.

The structure of the conus arteriosus of the sturgeon (Acipenser naccarii) heart: II. The myocardium, the subepicardium, and the conus-aorta transition.

Sturgeons constitute a family of living “fossil” fish whose heart is related to that of other ancient fish and the elasmobranches. We have undertaken a systematic study of the structure of the sturgeon heart aimed at unraveling the relationship between the heart structure and the adaptive evolutionary changes. In a related paper, data were presented on the conus valves and the subendocardium. Here, the structure of the conus myocardium, the subepicardial tissue, and the conus‐aorta transition were studied by conventional light, transmission, and scanning electron microscopy. In addition, actin localization by fluorescent phalloidin was used. The conus myocardium is organized into bundles whose spatial organization changes along the conus length. The variable orientation of the myocardial cell bundles may be effective in emptying the conus lumen during contraction and in preventing reflux of blood. Myocardial cell bundles are separated by loose connective tissue that contains collagen and elastin fibers, vessels, and extremely flat cells separating the cell bundles and enclosing blood vessels and collagen fibers. The ultrastructure of the myocardial cells was found to be very similar to that of other fish groups, suggesting that it is largely conservative. The subepicardium is characterized by the presence of nodular structures that contain lympho‐hemopoietic (thymus‐like) tissue in the young sturgeons and a large number of lymphocytes after the sturgeons reach sexual maturity. This tissue is likely implicated in the establishment and maintenance of the immune responses. The intrapericardial ventral aorta shows a middle layer of circumferentially oriented cells and internal and external layers with cells oriented longitudinally. Elastin fibers completely surround each smooth muscle cell, and the spaces between the different layers are occupied by randomly arranged collagen bundles. The intrapericardial segment of the ventral aorta is a true transitional segment whose structural characteristics are different from those of both the conus subendocardium and the rest of the ventral aorta. Anat Rec 268:388–398, 2002.

Bulbus arteriosus of the antarctic teleosts. II. The red‐blooded Trematomus bernacchii

The structure of the bulbus arteriosus of the Antarctic teleost, Trematomus bernacchii, has been studied by light, scanning, and transmission electron microscopy. The wall of the bulbus arteriosus is divided into endocardial, subendocardial, middle and external layers. The endocardial endothelium covers the inner surface of the bulbus wall and invaginates into the subendocardium to form solid epithelial cords that show secretory activity. The subendocardial tissue is divided into finger‐like ridges. Ridge cells located under the endocardium appear in niches limited by collagen fibers and thin cell extensions. Away from the endocardium ridge cells cluster into small groups, show some of the characteristics of smooth muscle cells, and appear enmeshed in a filamentous meshwork that lacks collagen and elastin fibers. The middle bulbus layer is formed by typical smooth muscle cells that are enmeshed in a filamentous meshwork similar to that observed in the ridges. The ridges and the middle layer appear to be formed by the same cell type, smooth muscle, with a gradient of differentiation from the endocardium toward the middle layer. In the absence of elastin fibers the filamentous meshwork should confer elastic properties to the bulbus wall. The stretching of the meshwork along the main axis of the middle layer cells, and between different cellular layers, suggests the existence of tensile stress and, hence, the involvement of smooth muscle cells in bulbus wall dynamics. The external layer is formed by numerous cellular types embedded in a collagenous matrix. Among these cellular types, myofibroblasts, macrophages, granulocytes, lymphocytes, dendrite‐like cells, degenerating cells, and plasma cells can be recognized. The subepicardial tissue appears to be a specialized site involved in the production of the humoral immune response and displays many of the morphological characteristics of a germinal center. The outer limiting layer of the bulbus, the visceral pericardium, is formed by epithelial cells that show desmosomes and tight junctions. This suggests a close control of permeability with respect to the pericardial fluid. Anat Rec 256:116–126, 1999.

Structure of the conus arteriosus of the sturgeon (Acipenser naccarii) heart. I: The conus valves and the subendocardium

Sturgeons are bony fish that retain structural traits typical of the more primitive Chondrostei. From an evolutionary viewpoint, sturgeons are considered relic fish. However, they show remarkable ecological plasticity and are well adapted to contemporary environmental conditions. Although development of the cardiovascular system is critical for all organs and systems, and is affected by evolutionary changes, the structure of the sturgeon heart has been mostly overlooked. This is also true for the conus arteriosus, which, as in Chondrostei, is endowed with several rows of valves and a layer of contractile myocardium. This work reports on the structure of the valves, the endocardium, and the subendocardium of the conus arteriosus of the sturgeon (Acipenser naccarii) heart. It is part of a broader study that aims to cover the entire structure of the sturgeon heart. The conus arteriosus of 15 A. naccarii hearts, ranging in age from juveniles to sexually‐differentiated adults, has been studied by conventional light, transmission (TEM), and scanning electron microscopy (SEM). In addition, maceration of the soft tissues with NaOH, and actin localization by fluorescent phalloidin has been used. The conus is a tubular chamber that arises from the right ventricular side and presents two constrictions at the conus‐ventricle and conus‐aorta junctions. The conus is endowed with three rows of valves: one distal and two proximal. The segment of the conus located between the distal and the two proximal rows is devoid of valvular structures. The distal row has four leaflets, while the two proximal rows show the greatest variation in leaflet number, size, and shape. All leaflets have collagenous chordae tendineae arising from the free border and from the parietal side of the leaflets. The endocardium is a flat endothelium which shows a thick, irregular basement membrane. The leaflet body is formed by a loose connective tissue which blends with the subendocardium. The subendocardium is a connective tissue consisting of myofibroblasts, collagen, and elastin. It is divided into two distinct areas: one proximal, which shows little elastin and poorly organized collagen; and one distal, which is rich in elastin, with cells and extracellular fibers organized into layers that are oriented in alternative circumferential and longitudinal directions. The present report is the first systematic analysis of the structure of the sturgeon conus. Descriptions of the conus valves should recognize the existence of three valve rows only. The variability in valve morphology, and the loose structure of the leaflet tissue make it unlikely that the valves play an effective role in preventing blood backflow. In this regard, the ventricle‐conus constriction may act as a sphincter. The subendocardium is an elastic coat capable of actively sustaining the tissue deformation that accompanies the heart contractile cycle. Further comparative studies are needed to provide deeper insight into the structural changes that accompany phyletic diversification. Anat Rec 267:17–27, 2002.

The conus arteriosus of the adult gilthead seabream ( Sparus auratus )

This paper reports on the presence of the conus arteriosus in the heart of the adult gilthead seabream, Sparus auratus (Perciformes, Teleostei). The junctional region between the single ventricle and the bulbus arteriosus has been studied by conventional light microscopy, and by scanning and transmission electron microscopy. In addition, fluorescent phalloidin and antibodies against the muscle myosin heavy chains, laminin and collagen type IV have been used. The conus arteriosus is a distinct muscular segment interposed between the ventricle and the bulbus arteriosus. It is clearly different from the bulbus arteriosus due to its myocardial nature. It can also be distinguished from the ventricular myocardium because: (1) it has a conus shape; (2) it is formed by compact, well‐vascularized myocardium; (3) it is surrounded on its inner and outer faces by fibrous layers rich in collagen and elastin; (4) it constitutes the anatomical support of the so‐termed conus valves; (5) it shows intense staining for laminin and type‐IV collagen; and (6) the myocardial cells located close to the inner fibrous layer are helicoidally arranged. By contrast, the ventricular myocardium is highly trabecular, lacks a compacta, shows no vessels, and presents barely detectable amounts of laminin and collagen type IV. The presence of a distinct conus arteriosus in the heart of an evolutionary advanced teleost species indicates that the conus is not a vestigial segment from the evolutionary or embryological points of view. The characteristic spatial arrangement of the conus myocytes strongly suggests that the conus is implicated in the mechanical performance of the conus valves.

The structural characteristics of the heart ventricle of the African lungfish Protopterus dolloi: freshwater and aestivation

This paper reports on the structure and ultrastructure of the ventricular myocardium of the African lungfish Protopterus dolloi in freshwater (FW), in aestivation (AE), and after the AE period. The myocardium shows a conventional myofibrillar structure. All the myocytes contain large intracytoplasmic spaces occupied by a pale material that could contain glycosaminoglycans and/or glycogen, which may be used as food and water reservoirs. In FW, the myocytes in the trabeculae associated with the free ventricular wall show structural signs of low transcriptional and metabolic activity (heterochromatin, mitochondria of the dense type). These signs are partially reversed during the AE period (euchromatin, mitochondria with a light matrix), with a return to the FW appearance after arousal. The myocytes in the septum show, in FW conditions, nuclear polymorphism (heterochromatin, euchromatin), and two types (colliquative and coagulative) of necrosis. In AE, all the septal myocytes show euchromatin, and the number of necrotic cells increases greatly. Cell necrosis appears to be related to the septal architecture. After arousal, the septal myocytes exhibit a heterochromatin pattern, the number of necrotic cells decreases, cell debris accumulates under the endocardium, and phagocytosis takes place. Despite being a morphologic continuum, the trabeculae associated with the free ventricular wall appear to constitute a different compartment from that formed by the trabeculae in the ventricular septum. Paradoxically, AE appears to trigger an increase in transcriptional and synthetic myocardial activities, especially at the level of the ventricular septum. This activity may be involved in mechanisms of autocrine/paracrine regulation. Aestivation cannot be regarded as the result of a general depression of all cellular and organic activities. Rather, it is a much more complex state in which the interplay between upregulation and downregulation of diverse cell activities appears to play a fundamental role.

COLLAGENOUS SKELETON OF THE HUMAN MITRAL PAPILLARY MUSCLE

The papillary muscles (PM) of the heart have been the subject of numerous structural and functional studies. However, despite the importance of the collagenous compartment of the heart in the mechanical and electrical properties of the myocardium, little information is available on the structural organization of collagen within the PM. We study here the structural organization of collagen within the mitral papillary muscles (PM) of the human heart. Fragments of human mitral PM from normal and hypertensive subjects were macerated in NaOH to eliminate the cellular components. Macerated and nonmacerated samples were then studied with the scanning electron microscope (SEM).

Light and Electron Microscopy of the Bulbus arteriosus of the European Eel (Anguilla anguilla)

The bulbus arteriosus of teleost fish acts as an elastic reservoir that dilates during ventricular systole to store a large part of the cardiac stroke volume. Despite its functional importance, the knowledge of the structure of the bulbus wall is still fragmentary. We have undertaken a series of studies in order to establish a general morphological plan of the teleost bulbus. The bulbus arteriosus of the European eel is studied here by means of conventional light, and transmission and scanning electron microscopy. The inner surface of the bulbus wall is irregular due to the presence of branching ridges that flatten and disappear toward the ventral aorta. The ridge surface is covered by flattened endocardial cells that show moderately dense bodies. In the ridge tissue, cells near the endocardium are mostly undifferentiated and appear isolated in a loose filamentous matrix. Ridge cells progressively cluster toward the middle layer, become surrounded by a dense matrix, and adopt characteristics typical of smooth muscle cells. This suggests the existence of a differentiation gradient. The middle layer is formed by typical smooth muscle cells embedded in a meshwork matrix that contains thin and thick filaments. Stretching of this meshwork suggests an active role of smooth muscle cells in bulbus wall dynamics. Furthermore, large areas of the extracellular space are occupied by elastin-like material. The amount of this material decreases toward the external layer. Collagen is demonstrated across the entire thickness of the bulbus wall, its amount and organization increasing from the inner toward the outer bulbus surface. The existence of matrix gradients should progressively increase wall strength, maintaining bulbus dilation within safe physiological parameters. The epicardium is formed by flattened cells that contain numerous pinocytotic vesicles, suggesting an active interchange of solutes with the pericardial cavity.

The Alimentary Canal of the African Lungfish Protopterus annectens During Aestivation and After Arousal

We describe the structural modifications that occur in the alimentary canal of the African lungfish Protopterus annectens during aestivation and after arousal. With fasting, all gut segments undergo structural modifications. The epithelium covering the intestinal vestibule undergoes bursts of activation at 4 months of aestivation, adopting a more quiescent appearance at 6 months. The ridge area of the spiral intestine shows, at 4 months of aestivation, epithelial disintegration, cell desquamation, cell death, and loss of the freshwater phenotype. Surprisingly, the epithelium adopts a stratified appearance at 6 months of aestivation. Except for epithelial disintegration, the smooth portion of the spiral intestine follows a similar pattern of modifications than the ridge area. The entire epithelium of spiral intestine appears to be renewed during aestivation. The presence of intraepithelial mast cells suggests that inflammation is part of the cellular response to aestivation. After arousal, cell phenotypes are restored in about 6 days, but full structural recovery is not attained during the experimental period (15 days post‐aestivation). Several aspects of the cellular response to fasting are shared by a wide range of animal groups. This commonality agrees with the presence of a character that allows to adjust the structural and functional properties of the gut to food availability and food quality, and to the characteristics of the fasting episodes. Anat Rec, 2012.