Peripheral vascularization of the dermal laminae of the equine hoof

The vascular architecture of the dermal laminae was studied by scanning electron microscopy of vascular corrosion casts. Ultrastructurally, the laminar vasculature consisted of arterioles, capillaries, venules and veins, arranged in a sheet-like network. Through the laminae, arterioles ran parallel to the solar surface and branched at two levels to form a continuous arteriolar arcade, parallel to the hoof wall. Capillaries originating from these arcades formed hairpin loops joining the marginal vein prior to forming an axially situated venous network. Additional capillaries were also given off by the arterioles, forming an abaxially arranged capillary plexus.     

Surface of the vascular plexuses of human cerebral ventricles

The racemose part of vascular plexuses of the lateral ventricles has been studied in fetuses and persons at various age in the scanning and transmissive electron microscopes. In the magistral arteries of the vascular plexuses the neural trunks have been studied. They form the periadventitial plexus with a more complex network of connections in mature persons. The sulci and the elongated folds between them make the relief of the plexus. A rough surface of epitheliocytes has deep craters and irregular protrusions, microvilli, cilia and spherical bodies. The epitheliocytes are arranged in a single layer and connected with each other by means of protoplasmic peduncles. Over the epithelial layer, as single groups, Kolmer cells are situated.     

Structural organization and neuropeptide distributions in the equine enteric nervous system: an immunohistochemical study using whole-mount preparations from the small intestine

The architecture and neurochemistry of the enteric nervous system was studied by use of whole-mount preparations obtained by microdissection of the horse jejunum. A myenteric plexus and two plexuses within the submucosa were identified. The external submucosal plexus lying in the outermost region of the submucosa had both neural and vascular connections with the inner submucosal plexus situated closer to the mucosa. Counts of neurones stained for NADH-diaphorase demonstrated the wide variation in size, shape and neurone content of individual ganglia in both the external and internal submucosal plexuses. The average number of cells/ganglion was similar in each plexus (about 25 cells). Immunoreactivities for galanin, vasoactive intestinal peptide and neuropeptide Y were observed in nerve cell bodies and fibres of each of the plexuses. Immunoreactivity for substance P was extensive and strong in nerve fibres of all plexuses but was weaker in cell bodies of the submucosal neurones and absent in the cell bodies of the myenteric plexus. Comparative quantitative analysis of immunoreactive cell populations with total cell numbers (enzyme staining) was indicative of neuropeptide colocalization in the external submucosal plexus.     

Topsy-turvy: turning the counter-current heat exchange of leatherback turtles upside down

Counter-current heat exchangers associated with appendages of endotherms feature bundles of closely applied arteriovenous vessels. The accepted paradigm is that heat from warm arterial blood travelling into the appendage crosses into cool venous blood returning to the body. High core temperature is maintained, but the appendage functions at low temperature. Leatherback turtles have elevated core temperatures in cold seawater and arteriovenous plexuses at the roots of all four limbs. We demonstrate that plexuses of the hindlimbs are situated wholly within the hip musculature, and that, at the distal ends of the plexuses, most blood vessels supply or drain the hip muscles, with little distal vascular supply to, or drainage from the limb blades. Venous blood entering a plexus will therefore be drained from active locomotory muscles that are overlaid by thick blubber when the adults are foraging in cold temperate waters. Plexuses maintain high limb muscle temperature and avoid excessive loss of heat to the core, the reverse of the accepted paradigm. Plexuses protect the core from overheating generated by muscular thermogenesis during nesting.     

Cytokeratins of the bovine hoof: classification and studies on expression

The bovine hoof has been examined as a model for the study of keratinized skin appendages. We characterized the keratin polypeptides of hoof bed and matrix and compared them to epidermis using two-dimensional electrophoresis and immunoblot techniques. Both hoof tissues express keratins 6 and 16 (as described by Franke et al. (1981) J. Mol. Biol. 153, 933-959) and b2 and a1-4 which are previously undescribed proteins unique to the bovine hoof. Keratins of hoof matrix and bed share one or more common antigenic components as defined by immunoblot analysis. Hoof matrix expresses keratins 7 and 14, which are absent in hoof bed, and also expresses a greater number of isoelectric variants of keratin 6. Biopsies of hoof bed and matrix transplanted onto athymic mice both made hard hoof and underwent active keratin synthesis as evidenced by incorporation of [3H]leucine. Indirect immunofluorescence studies of the grafts showed that they had the histology and immunoreactivity previously noted for hoof bed and matrix. The two-dimensional gel electrophoretic patterns of both grafts were similar and expressed keratins b2 and a1-4. We conclude that a unique group of keratins exists in hoof. Furthermore, while hoof matrix is the major contributor to hard hoof, hoof bed epidermis maintains the capacity to make hard hoof and may contribute to the synthesis of the hoof plate in vivo. The ability to graft hoofs onto athymic mice provides an opportunity for the study of a number of aspects of hoof formation.     

Vasoactive intestinal peptide and substance P-like immunoreactivities in the enteric nervous system of the pig correlate with the severity of pathological changes induced by Schistosoma japonicum

Limited studies have shown that in intestinal schistosomosis, the enteric nervous tissue becomes inflamed, disrupted and destroyed by granulomas and peptides, amines and neurofilaments contents are altered. Therefore, immunoreactivities of vasoactive intestinal peptide and substance P were correlated to pathological lesions in the large intestine from pigs infected with Schistosoma japonicum. Ganglia situated within or near granulomas showed ganglionitis, and necrosis of neurons as well as infiltration by eosinophils, mast cells, lymphocytes, plasma cells, neutrophils and macrophages. The inner submucous and mucous plexuses were the most damaged. In all categories of inflamed areas, the vasoactive intestinal peptide-like immunoreactive was reduced in all plexuses whereas, that of substance P was increased both in the enteric nerve plexuses and enterochromaffin cells in lightly, moderately and severely inflamed tissues. However, both peptides were highly diminished or absent in very severe lesions and areas surrounding schistosome eggs and mature worms laying eggs in the submucosal veins. The alterations of the levels of vasoactive intestinal peptide and substance P were correlated with severity of inflammation. Our observations show alterations of vasoactive intestinal peptide and substance P contents in the local microenvironment in the vasoactive intestinal peptide- and substance P-mediated reflex pathways which regulate intestinal motility, epithelial transport and modulate immunity. These changes could cause alterations in bowel motility, electrolyte and fluid secretion, vascular and immune functions during S. japonicum infections in the pig. This may, therefore, partly play a role in the pathobiology of migration and egress of schistosome eggs as well as influence trapping of eggs in granulomas, and account for diarrhoea, loss of body weight and failure to thrive, which are recorded in schistosomosis.     

The early development of the lymphatic system in mouse embryos.

The early development of the lymphatic system was studied in embryos of an inbred strain of the laboratory mouse. During the first stage of its development the system is represented by a more or less regular series of small and blind-ending outgrowths of the major embryonic veins which develop in a cranio-caudalward direction from the jugular to the pelvic region. As a result of differences in growth rates of adjacent anatomical structures this series of early lymphatic primordia becomes subdivided into 4 singular primordia and 12 groups of primordia. After the constituents of each group of early primordia have fused, 16 isolated lymphatic plexuses (sacs) are formed of which 14 are in bilaterally symmetric and 2 are in a median line position: i.e. bilaterally: (1) the jugulo-axillary lymph sac situated lateral to the anterior cardinal vein and dorsal to the primitive ulnar vein and its major branch, the external mammary vein, (2) the paratracheal lymph plexus situated medial to the anterior cardinal vein, (3) the internal thoracic lymph plexus situated lateral to the thoracic part of the posterior cardinal vein, (4) the thoracic ducts situated medial to the thoracic part of the posterior cardinal vein, (5) the lumbar lymph plexus situated dorso-lateral to the abdominal part of the posterior cardinal vein, (6) the subcardinal lymph plexus and (7) the iliac lymph plexus situated ventro-lateral to the abdominal part of the posterior cardinal vein; and in the median line: (8) the subtracheal lymph plexus situated at the confluence of the pulmonary veins and (9) the mesenteric lymph plexus situated near the confluence of the splenic and the superior mesenteric veins. Except for some openings at the jugulo-subclavian confluence all connections with the veins disappear. From the primordia extensions grow out centrifugally. They invade the surrounding tissues and, in part, fuse with similar sprouts of adjacent primordia. In this way a continuous system of lymph truncs is formed that opens into the venous system at the jugulo-subclavian confluence.     

Accelerated Coronary Angiogenesis by Vegfr1-Knockout Endocardial Cells

During mouse heart development, ventricular endocardial cells give rise to the coronary arteries by angiogenesis. Myocardially-derived vascular endothelial growth factor-a (Vegfa) regulates embryonic coronary angiogenesis through vascular endothelial growth factor-receptor 2 (Vegfr2) expressed in the endocardium. In this study, we investigated the role of endocardially-produced soluble Vegfr1 (sVegfr1) in the coronary angiogenesis. We deleted sVegfr1 in the endocardium of the developing mouse heart and found that this deletion resulted in a precocious formation of coronary plexuses. Using an ex vivo coronary angiogenesis assay, we showed that the Vegfr1-null ventricular endocardial cells underwent excessive angiogenesis and generated extensive endothelial tubular networks. We also revealed by qPCR analysis that expression of genes involved in the Vegf-Notch pathway was augmented in the Vegfr1-null hearts. We further showed that inhibition of Notch signaling blocked the formation of coronary plexuses by the ventricular endocardial cells. These results establish that Vegfr1 produced in the endocardium negatively regulates embryonic coronary angiogenesis, possibly by limiting the Vegf-Notch signaling.     

Fetal development of the segment-specific papillary body in the equine hoof

Fetal development of the unique papillary body and its localized peculiarities in the equine hoof are described based on the study of 51 fetuses, nine newborn foals, and five adult horses. The shape and dimensions of the dermal papillae and lamellae have a formative influence on the structure and physical quality of the corneous hoof capsule with its horn tubules and lamellae. The size and arrangement of these horn structures determine the mechanical quality of hoof horn. Proper horn quality is a prerequisite for the various functions of the hoof capsule, such as protecting the living dermis supporting the hoof capsule, shock absorption, and formation of the suspensory apparatus of the distal phalanx. Development of the segment-specific papillary body is initiated by the increasing mitotic activity of the epidermal cells invaginating the dermal surface, thus forming dermal microridges. These microridges are transformed into single dermal papillae, which are arranged in rows, or enlarged to become primary and secondary dermal lamellae. The formation of a segment-specific papillary body enables the increasing keratinization ratio in the hoof epidermis and the formation of the characteristic tubular and lamellar horn responsible for the special mechanical properties of hoof horn.     

Degradation of annular gap junctions of the equine hoof wall

Annular gap junctions interiorized within cells of the stratum spinosum of the coronary border of the equine hoof were degraded by two methods. Some were autophagocytized and some appeared to fuse with lysosomes to form heterophagosomes. Structural changes of partially degraded annular gap junctions included increased density of the enclosed cytoplasm, formation of filamentous or membrane-like material within the annular gap junction, and disruption of the circular or oval profile of the gap junction. The annular gap junctions are apparently incorporated into the fully keratinized cells of the stratum corneum.     

Topography, architecture and structure of the plexus submucosus externus (Schabadasch) of the porcine small intestine in scanning electron microscopy

Whole-mount preparations of the porcine small intestine, consisting of the tela submucosa and the adjacent lamina muscularis mucosae, were used for scanning electron-microscopic investigation of the plexus submucosus externus (Schabadasch) after enzymatic digestion, fixation and HCI hydrolysis. The present results confirm previous light-microscopic data and provide irrefutable proof that within the submucosal plexus, considered by most authors as one ganglionated nerve plexus situated in the entirety of the tela submucosa, two distinct nerve meshworks can be distinguished, one lying close to the lamina muscularis mucosae, i.e., the plexus submucosus internus (Meissner), and the other, i.e., the plexus submucosus externus (Schabadasch), situated in the outer region of the tela submucosa against the circular smooth muscle layer. In addition to the distinct location of both plexuses, they are quite different with regard to the pattern and diameter of their nerve strands and the number and appearance of their ganglia.     

Eimeria stiedai in rabbits: the presence of an oocyst residuum

Observations on 5 different isolates of Eimeria stiedai from pure infections in laboratory-reared rabbits have confirmed the presence of an oocyst residuum. This structure was seen in 89--100% of the oocytes in cultures prepared both from the liver and from the faeces at different times during the patent period. The residuum consisted of 1--7 or more granules situated centrally in the oocyst and partially concealed by 4 sporocysts. The differential diagnosis of E. stiedai and E. coecicola is discussed.     

Presence and distribution of serotonin immunoreactivity in the cyprids of the barnacle Balanus amphitrite

In this work, the presence and distribution of serotonin in the cyprid of the barnacle Balanus amphitrite were investigated by immunohistochemical methods. Serotonin-like immuno-reactive neuronal cell bodies were detected in the central nervous system only. Various clusters of immunoreactive neuronal cell bodies are distributed in the brain (protocerebrum, deutocerebrum, optical lobes), and at least, four pairs of neuronal cell bodies were detected in the centrally positioned neuropil of the posterior ganglion. Rich plexuses of immunoreactive nerve fibers in the neuropil area were also observed. Furthermore, bundles of strongly immunoreactive nerve fibers surrounding the gut wall were localized, and immunoreactive nerve terminals in the antennules and compound eyes were observed. These data demonstrate the presence of a serotonin-like immunoreactive substance in the barnacle cyprids; furthermore, its immunolocalization in the cephalic nerve terminals allows us to postulate the involvement of this bioactive molecule in substrate recognition during the settlement process.     

An electrogenic NA+/K+ pump in the choroid plexus.

Intracellular electrical potential and potassium activity was measured by means of microelectrodes in the epithelial cells of choroid plexus from bullfrogs (Rana catesbeiana). Ouabain applied from the ventricular side caused an abrupt depolarisation of 10 mV but only a gradual loss of potassium from the cells. Readministration of potassium to the ventricular solution of plexuses which were previously depleted of potassium, caused a hyperpolarisation of about 4 mV. These two experiments are consistent with the notion of an electrogenic Na+/K+ pump situated at the ventricular membrane and which pumps potassium into the cell and sodium into the ventricle. The numerical values obtained suggest that 3 sodium ions are pumped for 2 potassium ions. The permeability coefficient for potassium exit from the cell is calculated to be 1.24 . 10(-5) cm-1 . s-1 expressed per cm2 of flat epithelium.     

The dynamics of hoof growth of the primitive Konik horses (Equus caballus gmelini Ant.) in an annual cycle

The annual growth rate of the horny wall of the hoof was investigated in 38 horses—31 mares and seven stallions. Experimental subjects were Konik horses kept in a conservative breeding herd. The horses hooves of both limbs: the right fore limb and the right hind limb were measured and next growth rate of the horny wall was analysed at five points of the hoof capsule. On the basis of Principal Component Analysis it was found that the subjects needed to be considered in three groups: three-year old mares, older mares and stallions. Next the growth increments were averaged in each investigated group and compared. The dynamics of hoof horn growth turned out to be the highest in the group of young mares, followed by the group of stallions and the group of adult mares. In the winter months the lowest growth increment of the hoof horn was observed in all the analysed groups. In the period of the elongating solar day, i.e. from May to July, the growth was rapid and reached the highest values. Starting from August the growth of the hoof horn decreased.     

Immunocytochemical localization of substance P in mammalian intestine

Summary In mammalian intestine immunoreactive Substance P is localized not only in the plexuses of Auerbach and Meissner, as could be anticipated, but also in a number of basally situated, often basigranular, endocrine cells which have been identified tentatively as enterochromaffin.The presence of a neurohormone in cells of this type confirms their close association with the nervous system, noted by Masson (1924), and suggests that their postulated origin from the nervous system (Danisch, 1924) may well be correct.     

Nerve endings in the heart of teleosts

The nerve endings in the heart of fishes were studied using silver impregnation techniques. The heart chambers are profusely innervated by the sympathetic, parasympathetic (vagal) and postganglionic fibers of the intracardiac ganglia situated at the sinuatrial and the atrioventricular junctions. The plexuses are composed of medullated and nonmedullated fibers. The nerve fibers generally end freely and are slightly branched or unbranched terminations of myelinated and unmyelinated fibers. Moreover, a few nerve fibers end redundant in the form of end-rings, bulb-like, bush-like, club-shaped end end-coil like structures. The complex unencapsulated types of endings are also found in the myocardium of the atrium and the ventricle. The encapsulated endings (Vater-Pacinian; Krause end-bulb) could not be observed.     

Histology and ultrastructure of the hepatopancreas of the tigerfish,Hydrocynus forskahlii

Study of the histology and ultrastructure of the hepatopancreas of the tigerfish, Hydrocynus forskahlii shows that the liver parenchyma is divided into irregularly shaped lobules, separated by the exocrine pancreas and associated connective tissue. The hepatocytes are arranged in interconnecting cords or laminae, two to three cell layers in thickness. Sinusoids separate the laminae. The spherical to oval-shaped hepatocytes contain large, round, centrally situated nuclei with prominent nucleoli. The cytoplasm of the hepatocytes contains abundant rough and smooth endoplasmic reticulae, free polysomes, and mitochondria. Exocrine pancreatic tissue is scattered throughout the liver. This tissue is encapsulated by an endothelium resting on a thin layer of connective tissue and is separated from the liver parenchyma by a sinusoid. The nuclei of the exocrine pancreas cells are spherical, basally situated within the cells, and contain dark nucleoli. Vesicular rough endoplasmic reticulae and secretory granules lie in the apical regions of the exocrine pancreas cells. © 1996 Wiley-Liss, Inc.     

On testing the activity of proteases from human polymorphonuclear neutrophils on blood smears.

A cytochemical method is presented for the demonstration of proteases in human polymorphonuclear (PMN) neutrophils on fixed blood smears. This new technique is based on solubilization of proteases from PMN neutrophils by incubation with 0.25 M NaCl in borate buffer at pH 8.5 which leads to degradation of erythrocytes and plasma in a disclike zone (halo) around centrally situated PMN neutrophils, an effect that is visualized by staining smears using a modified colloidal iron reaction. Halo formation is inhibited by trypsin inhibitors of soya-bean as well as of chicken egg white mucoid and by phenylmethyl-sulfonylfluoride.     

Intercellular bridges and factors determining their patterns in the grasshopper testis

Intercellular bridges joining cells contained in cysts of Chortophaga viridifasciata testes were studied with light and electron microscopy. Preparations consisted of expressed whole cells (living, or fixed and stained) as well as sections. The secondary spermatogonia of each cyst are joined centrally by persisting fused interzonal bodies (fusomes) of incompletely cleaved cells. Shifts in cell orientation during anaphase are apparently responsible for central as opposed to chain linkage of cells. In the primary spermatocytes, the central fusome is replaced by a chain linkage, apparently resulting from the breakdown of the fusome into its original interzonal body components. Intercellular bridges are also present in spermatids, but there is no evidence to indicate the time of their formation (in the immediately preceding meiotic divisions or in the secondary spermatogonial divisions). The function of the compact centrally situated fusome in the secondary spermatogonial cyst is discussed as it relates to synchrony, number of cell divisions, spermatodesm formation, and fertility.