The Omental Pedicle Flap in Dogs Revised and Refined: A Cadaver Study.

OBJECTIVE: To expand current knowledge on the canine omental vasculature and refine the existing lengthening technique of the canine omentum. STUDY DESIGN: Ex vivo study. ANIMALS: Canine cadavers (n=20). METHODS: In 10 canine cadavers the omental arteries were mapped using intravascular latex injection and these results were used to create an omental pedicle flap based on the splenic artery in 10 additional cadavers. The operating range of the flap was recorded with particular attention to the main regions of interest for omental transposition in dogs (axillary and inguinal regions). RESULTS: The superficial and deep omental leaves were each predominantly supplied by a left and a right marginal omental artery that anastomosed near the caudal omental border into a superficial and a deep omental arch, respectively. Anastomoses between arteries of the superficial and the deep omental leaves were weak and inconsistent, except for 1 anastomosis that was found in 8 of 10 dogs. By transposing the intact omentum, the right axilla could be reached in 3 dogs, both axillae in 1 dog, and both groins in all cadavers. In all cases, the omental pedicle reached to and beyond the axillary and inguinal regions. By unfolding the pedicle leaves, the width of the pedicle tip could be doubled. CONCLUSION: When lengthening the omentum is necessary to reach extra-abdominal structures, the omental pedicle flap based on the splenic artery appears to preserve the omental vascular supply. These observations warrant further clinical trials to evaluate this new omtental flap technique in vivo.

Intussusceptive angiogenesis: a biologically relevant form of angiogenesis.

Angiogenesis, i.e. the development and growth of blood vessels, is a major topic of research as it plays an important role in normal development and in various pathologies. Recent evidence revealed the existence of different mechanisms of blood vessel growth, including sprouting and intussusceptive angiogenesis, vascular mimicry, and blood vessel cooption. The latter two have only been observed in tumor growth, but sprouting and intussusceptive angiogenesis also occur in healthy, physiologically growing tissues. Despite this variety of angiogenic mechanisms, most of the current research is focused on the mechanism of sprouting angiogenesis because this mechanism was first described and because most existing experimental models are related to sprouting angiogenesis. Consequently, the mechanism of intussusceptive angiogenesis is often overlooked in angiogenesis research. Here, the mechanism of intussusceptive angiogenesis is reviewed and the current techniques and models for investigating intussusceptive angiogenesis are summarized. In addition, other mechanisms of vascular growth are briefly reviewed.

Perfusion characteristics of the human hepatic microcirculation based on three-dimensional reconstructions and computational fluid dynamic analysis.

The perfusion of the liver microcirculation is often analyzed in terms of idealized functional units (hexagonal liver lobules) based on a porous medium approach. More elaborate research is essential to assess the validity of this approach and to provide a more adequate and quantitative characterization of the liver microcirculation. To this end, we modeled the perfusion of the liver microcirculation using an image-based three-dimensional (3D) reconstruction of human liver sinusoids and computational fluid dynamics techniques. After vascular corrosion casting, a microvascular sample (±0.134 mm(3)) representing three liver lobules, was dissected from a human liver vascular replica and scanned using a high resolution (2.6 µm) micro-CT scanner. Following image processing, a cube (0.15 × 0.15 × 0.15 mm(3)) representing a sample of intertwined and interconnected sinusoids, was isolated from the 3D reconstructed dataset to define the fluid domain. Three models were studied to simulate flow along three orthogonal directions (i.e., parallel to the central vein and in the radial and circumferential directions of the lobule). Inflow and outflow guidances were added to facilitate solution convergence, and good quality volume meshes were obtained using approximately 9 × 10(6) tetrahedral cells. Subsequently, three computational fluid dynamics models were generated and solved assuming Newtonian liquid properties (viscosity 3.5 mPa s). Post-processing allowed to visualize and quantify the microvascular flow characteristics, to calculate the permeability tensor and corresponding principal permeability axes, as well as the 3D porosity. The computational fluid dynamics simulations provided data on pressure differences, preferential flow pathways and wall shear stresses. Notably, the pressure difference resulting from the flow simulation parallel to the central vein (0-100 Pa) was clearly smaller than the difference from the radial (0-170 Pa) and circumferential (0-180 Pa) flow directions. This resulted in a higher permeability along the central vein direction (k(d,33) = 3.64 × 10(-14) m(2)) in comparison with the radial (k(d,11) = 1.56 × 10(-14) m(2)) and circumferential (k(d,22) = 1.75 × 10(-14) m(2)) permeabilities which were approximately equal. The mean 3D porosity was 14.3. Our data indicate that the human hepatic microcirculation is characterized by a higher permeability along the central vein direction, and an about two times lower permeability along the radial and circumferential directions of a lobule. Since the permeability coefficients depend on the flow direction, (porous medium) liver microcirculation models should take into account sinusoidal anisotropy.

The tonsils revisited: review of the anatomical localization and histological characteristics of the tonsils of domestic and laboratory animals.

This paper gives an overview of the anatomical localization and histological characteristics of the tonsils that are present in ten conventional domestic animal species, including the sheep, goat, ox, pig, horse, dog, cat, rabbit, rat, and pigeon. Anatomical macrographs and histological images of the tonsils are shown. Six tonsils can be present in domestic animals, that is, the lingual, palatine, paraepiglottic, pharyngeal, and tubal tonsils and the tonsil of the soft palate. Only in the sheep and goat, all six tonsils are present. Proper tonsils are absent in the rat, and pigeon. In the rabbit, only the palatine tonsils can be noticed, whereas the pig does not present palatine tonsils. The paraepiglottic tonsils lack in the ox, horse, and dog. In addition, the dog and cat are devoid of the tubal tonsil and the tonsil of the soft palate.

Validation of the murine aortic arch as a model to study human vascular diseases.

Although the murine thoracic aorta and its main branches are widely studied to gain more insight into the pathogenesis of human vascular diseases, detailed anatomical data on the murine aorta are sparse. Moreover, comparative studies between mice and men focusing on the topography and geometry of the heart and aorta are lacking. As this hampers the validation of murine vascular models, the branching pattern of the murine thoracic aorta was examined in 30 vascular corrosion casts. On six casts the intrathoracic position of the heart was compared with that of six younger and six older men of whom contrast-enhanced computer tomography images of the thorax were three-dimensionally reconstructed. In addition, the geometry of the human thoracic aorta was compared with that of the mouse by reconstructing micro-computer tomography images of six murine casts. It was found that the right brachiocephalic trunk, left common carotid artery and left subclavian artery branched subsequently from the aortic arch in both mice and men. The geometry of the branches of the murine aortic arch was quite similar to that of men. In both species the initial segment of the aorta, comprising the ascending aorta, aortic arch and cranial/superior part of the descending aorta, was sigmoidally curved on a cranial/superior view. Although some analogy between the intrathoracic position of the murine and human heart was observed, the murine heart manifestly deviated more ventrally. The major conclusion of this study is that, in both mice and men, the ascending and descending aorta do not lie in a single vertical plane (non-planar aortic geometry). This contrasts clearly with most domestic mammals in which a planar aortic pattern is present. As the vascular branching pattern of the aortic arch is also similar in mice and men, the murine model seems valuable to study human vascular diseases.

Topography of the rabbit paranasal sinuses as a prerequisite to model human sinusitis.

BACKGROUND: Anatomical studies of the rabbit paranasal cavities are impelled by the increasing interest in the rabbit model to investigate human sinusitis. Although several such studies have already been performed, the topography of the rabbit dorsal conchal and maxillary sinuses is described ambiguously and the existence of the ethmoidal, frontal and sphenoidal sinuses is controversial. METHODOLOGY: The paranasal cavities were investigated using corrosion casting, gross and histological cross-sectioning, and micro-CT scanning of rabbit noses followed by computerized three-dimensional reconstruction. RESULTS: Micro-CT scanning was most useful to illustrate the dorsal conchal sinus, the large maxillary sinus consisting of a dorsal and a ventral recess, and the sphenoidal sinus. All these sinuses are paired and symmetrical. A large connection is present between the dorsal conchal sinus and the maxillary sinus resulting in one large conchomaxillary cavity. The sphenoidal sinus lies most caudal and is surrounded by the presphenoid bone. The openings from the nasal cavity into the conchomaxillary cavity and the sphenoidal sinus are very small. CONCLUSIONS: The absence of frontal and ethmoidal sinuses in any of the rabbits examined is a major difference between the rabbit and human sinuses. The rabbit maxillary sinus seems most appropriate for experimental work.

Three-dimensional reconstruction of the remodeling of the systemic vasculature in early pig embryos.

Current research on angiogenesis and vascular regression is mainly focused on pathological conditions such as tumor growth and diabetic retinopathy, while a suitable physiological model to study the controlling factors in these processes is still lacking. The remodeling pattern of the embryonic vasculature into the adult configuration, such as the branchial arch arterial system developing into the aorta or the early embryonic veins building the caudal vena cava can potentially serve as a model. However, practical applications of the embryonic vascular patterning are impeded by the current controversy over the exact development of the caudal vena cava in mammals. To elucidate these ambiguities, specific developmental stages of vascular development in pig embryos were mapped by means of computer-assisted 3D reconstructions starting from histological serial sections of Bouin's fixed embryos. Special attention was given to venous segments in the lumbar region, as their origin and fate are equivocally described in literature. Here we demonstrate that these venous segments originate from the caudal cardinal veins which are forced to migrate during development into a more dorsal position due to the expansion of the developing metanephroi and the more dorsal relocation of the umbilical arteries. These findings are in contrast with the generally accepted theory that the venous segments in the lumbar region arise from newly formed veins that are located dorsal to the early caudal cardinal system.

Larynx-associated lymphoid tissue (LALT) in young cattle.

This paper describes the presence of lymphoid tissue in the mucosa of the bovine larynx. A total of 15 bovine larynges were examined both macroscopically after tissue fixation in acetic acid and microscopically using histology. It was found that no paraepiglottic tonsil was present in cattle, although a few lymphoid follicles were present in the mucosa at the base of the epiglottis. This result is in accordance with previous reports. In contrast, numerous lymphoid follicles were seen in the mucosa of the epiglottis and the corniculate processes of the arytenoid cartilages. This suggests that larynx-associated lymphoid tissue is present in cattle. Our observation could be of clinical importance, e.g. in the framework of the development of aerosolized vaccines.

Morphological and immunological characteristics of the bovine temporal lymph node and hemal node.

Anatomical dissection of the temporal regions of 62 cattle demonstrated that lymph nodes and hemal nodes are present in 89% of the animals (bilaterally in 65% and unilaterally in 24% of the cases). Lymph nodes accounted for 60% and hemal nodes for 40% of all examined nodes. They are nearly always round with diameters ranging from 1 to 9mm. Injections of India ink showed that their drainage area consists of the forehead, the upper eyelid, the base of the horn and the temporal muscle. Immunohistochemistry and flow cytometry revealed that the distribution and percentages of the different cell populations in the lymph nodes and hemal nodes are similar to other cranial lymph nodes. Based on its anatomical location the name temporal lymph node (lymphonodus temporalis) is proposed.

Anatomical and histological aspects of the bovine lingual tonsil.

The localization of the bovine lingual tonsil is described as a prerequisite for the removal of specified risk material from the tongue meat in order to restrict the risk arising from bovine spongiform encephalopathy (BSE) to public health. The major part of this tonsil can be located macroscopically by the openings of its follicular crypts at the root of tongue. This part consists of organized aggregations of lymph nodules. Additional solitary primary lymph nodules and diffuse accumulations of lymphocytes are macroscopically invisible but are bilaterally present in the area extending 2 cm caudal to 3 cm rostral to the last vallate papillae. By sectioning the tongue 3 cm rostral to the last vallate papillae, undermining the lingual mucosa to the level of these papillae and making a transverse cut towards the lingual process of the basihyoid bone, the greater part of the lingual tonsil can efficiently be removed. Finally, immunohistochemical staining demonstrated the presence of T and B lymphocytes, suggesting that the bovine lingual tonsil can be considered as a site where an immune response can be induced.

The buccal lymph node (lymphonodus buccalis) in dogs: occurrence, anatomical location, histological characteristics and clinical implications.

Three dogs were presented for clinical examination with bilateral buccal nodules which were identified as enlarged buccal lymph nodes. As little is known about this pathology, 150 dogs were examined by anatomical dissection for the presence of buccal lymph nodes. They were found in 13 dogs, occurring bilaterally in six dogs and unilaterally in seven dogs. Two buccal lymph nodes were bilobulated and one was double. The lymph nodes were always located dorsal to the zygomatic muscle and rostral to the masseter muscle in the region where the superior labial vein drains into the facial vein. Histology demonstrated a large amount of intranodal adipose tissue scattered throughout the lymphoid tissue. The canine buccal lymph node should not be confused with the accessory parotid or ventral buccal salivary gland and is clinically important as it can enlarge due to tumour metastasis or inflammation of the buccal region.

Mechanical strain determines the site-specific localization of inflammation and tissue damage in arthritis.

Many pro-inflammatory pathways leading to arthritis have global effects on the immune system rather than only acting locally in joints. The reason behind the regional and patchy distribution of arthritis represents a longstanding paradox. Here we show that biomechanical loading acts as a decisive factor in the transition from systemic autoimmunity to joint inflammation. Distribution of inflammation and erosive disease is confined to mechano-sensitive regions with a unique microanatomy. Curiously, this pathway relies on stromal cells but not adaptive immunity. Mechano-stimulation of mesenchymal cells induces CXCL1 and CCL2 for the recruitment of classical monocytes, which can differentiate into bone-resorbing osteoclasts. Genetic ablation of CCL2 or pharmacologic targeting of its receptor CCR2 abates mechanically-induced exacerbation of arthritis, indicating that stress-induced chemokine release by mesenchymal cells and chemo-attraction of monocytes determines preferential homing of arthritis to certain hot spots. Thus, mechanical strain controls the site-specific localisation of inflammation and tissue damage in arthritis.

Histological characteristics and stereological volume assessment of the ovine tonsils.

Tonsils form a first line of defence against foreign antigens and therefore play a key role in immunity. Since documented information about ovine tonsils is limited, a study was performed in which the morphological characteristics and the volume of lymphoid tissue present in each ovine tonsil were determined. The tonsils of five adult healthy sheep were examined histologically and the volumes were estimated using the Cavalieri method. The pharyngeal tonsil had a mean volume of 1296.1+/-205.9 mm3 and was by far the largest ovine tonsil, followed by the paired palatine tonsil with a mean volume of 715.0+/-110.5 mm3. The tonsil of the soft palate, the paired tubal and paraepiglottic tonsils and the lingual tonsil were much smaller with a mean volume of, respectively, 90.3+/-24.9 mm3, 80.1+/-24.3 mm3, 29.7+/-11.8 mm3 and 10.1+/-2.8 mm3. The folds and crypts of the pharyngeal and palatine tonsils were covered by a reticular and a non-reticular epithelium. Both tonsils were mainly composed of primary and secondary lymph follicles. The palatine tonsils contained 1-3 crypts with a few secondary infoldings. Lymphoid tissue in the tonsil of the soft palate was located at the nasopharyngeal (dorsal) side of the soft palate. The tubal tonsil was lined with a pseudostratified columnar ciliated epithelium and consisted of scattered lymphoid cells and lymph follicles. The paraepiglottic tonsil consisted of lymph follicles and aggregated lymphoid cells. Its overlying keratinized stratified squamous epithelium was folded and often heavily infiltrated by lymphocytes. The ovine lingual tonsil was not macroscopically visible and did not contain clearly distinguishable lymph follicles. It consisted of aggregations of lymphoid cells that were mainly located within the vallate lingual papillae.

Stereological and immunogold studies on TIE1 and TIE2 localization in glomeruli indicate angiopoietin signaling in podocytes.

Angiopoietins and their TIE receptors are important regulators of vascular stability and remodeling. These molecules are involved not only in the normal development of kidney glomeruli, but also in disease, thus making them promising targets for therapies. Although TIE receptors are mainly found in endothelial cells, some reports observed TIE2 expression in glomerular podocytes as well. This suggests a role of angiopoietins in the regulation of podocytes. In the present study, we aimed to map the subcellular localization of TIE receptors in metanephric glomeruli of fetal pigs using high-resolution immunogold electron microscopy and the relative labeling index stereological approach. TIE1 and TIE2 antibody labeling was detected on the abluminal side of endothelial cell membranes. In endothelial cells, 4.5% of TIE2 was observed close to cell-cell contacts and 11.9% of TIE2 was found in closely associated pairs, which suggests the presence of homodimers. Interestingly, both receptors were also expressed in podocyte foot processes indicating that TIE1 and TIE2 may play a similar role in podocytes as in endothelial cells.

Anatomy and nomenclature of murine lymph nodes: Descriptive study and nomenclatory standardization in BALB/cAnNCrl mice.

Murine lymph nodes are intensively studied but often assigned incorrectly in scientific papers. In BALB/cAnNCrl mice, we characterized a total of 22 different lymph nodes. Peripheral nodes were situated in the head and neck region (mandibular, accessory mandibular, superficial parotid, cranial deep cervical nodes), and at the forelimb (proper axillary, accessory axillary nodes) and hindlimb (subiliac, sciatic, popliteal nodes). Intrathoracic lymph nodes included the cranial mediastinal, tracheobronchal and caudal mediastinal nodes. Abdominal lymph nodes were associated with the gastrointestinal tract (gastric, pancreaticoduodenal, jejunal, colic, caudal mesenteric nodes) or were located along the major intra-abdominal blood vessels (renal, lumbar aortic, lateral iliac, medial iliac and external iliac nodes). Comparative and nomenclative aspects of murine lymph nodes are discussed. The position of the lymph nodes of BALB/cAnNCrl mice is summarized and illustrated in an anatomical chart containing proposals for both an official nomenclature according to the Nomina Anatomica Veterinaria and English terms.

Computed tomography and cross-sectional anatomy of the thorax in clinically normal dogs.

OBJECTIVE: To provide a detailed anatomic description of the thorax in clinically normal dogs by means of computed tomography. ANIMALS: 4 clinically normal adult German Shepherd Dogs weighing 28 to 37 kg. PROCEDURE: Dogs were anesthetized and positioned in ventral recumbency for computed tomographic (CT) examination of the thorax. A CT image from the thoracic inlet to the diaphragm was made by use of a third-generation scanner with a slice thickness of 5 mm. Individual images were reviewed by use of soft tissue (window width, 250 Hounsfield units; window level, 35 Hounsfield units) and lung (window width, 1,000 Hounsfield units; window level, -690 Hounsfield units) settings. One dog, weighing 28 kg, was euthanatized, bound on a wooden frame in the same position as used for CT examination, and frozen at -14 degrees C until solid. By use of an electric band saw, the frozen thorax was sectioned at 10-mm-thick intervals. Slab sections were immediately cleaned, photographed, and compared with corresponding CT images. RESULTS: Anatomic sections were studied, and identified anatomic structures were matched with structures on corresponding CT images. Except for some blood vessels and details of the heart, most of the bony and soft tissue structures of the thorax discerned on anatomic slices could be found on matched CT images. CONCLUSIONS AND CLINICAL RELEVANCE: Because CT images provide detailed information on most structures of the canine thorax, results of our study could be used as a guide for evaluation of CT images of the thorax of dogs with thoracic diseases.

Computed tomography and cross-sectional anatomy of the brain in clinically normal dogs.

OBJECTIVE: To provide a detailed anatomic description of brain structures in clinically normal dogs by means of computed tomography (CT). ANIMALS: 4 clinically normal adult German Shepherd Dogs weighing 30 to 35 kg. PROCEDURE: Each dog was anesthetized and positioned in ventral recumbency for CT examination of the brain; transverse scans were completed at 2-mm intervals from the cribriform plate of the ethmoid bone to the cranial part of the atlas by use of a third-generation CT scanner. Contrast material was injected IV, and a second series of scans was completed. Images (with or without contrast) from all dogs were reviewed by use of a soft tissue setting (window width, 150 Hounsfield units; window level, 50 Hounsfield units). One of the dogs was euthanatized, and a 3.5% formaldehyde solution was perfused via the common carotid arteries. After fixation, the brain was embedded in gelatin and sectioned into 5-mm-thick transverse sections by use of a stainless-steel knife. Anatomic sections were photographed and compared with the corresponding CT views. RESULTS: Most features of the brain that were identified on anatomic sections could be identified on the corresponding CT scans despite the low contrast between structures, particularly if adjacent bony and soft tissue structures were used as landmarks. Additional anatomic structures surrounding the brain were also identifiable on the CT images. CONCLUSIONS AND CLINICAL RELEVANCE: Images obtained in this study could be used as a guide for evaluation of CT images of the brain in dogs with brain diseases.

Immunolocalization of sex steroid hormone receptors in canine vaginal and vulvar tissue and their relation to sex steroid hormone concentrations.

The aim of this immunohistochemical study was to describe the cellular distribution of the estrogen receptor-alpha (ERalpha), progesterone receptor (PR) and androgen receptor (AR) in canine vaginal and vulvar tissue. Samples were taken from dogs in different stages of the estrous cycle. Nuclear staining for ERalpha, PR and AR was observed in surface epithelium, stromal and smooth muscle cells. Receptors were also expressed in vulvar skin. Cytoplasmic staining for AR was observed in basal and parabasal cell layers of vulvar and vaginal epithelium. For all three receptors, staining intensity was generally higher in stromal cells compared with epithelial cells, suggesting that stromal cells may be more receptive to steroid hormone action. Therefore, as in other tissues of the female genital tract, stromal-epithelial interactions induced by sex steroid hormones may be of importance in canine vaginal and vulvar tissues. No cyclic changes in receptor immunostaining were observed. Significant positive correlations were found between receptor immunostaining in some vaginal and vulvar cell groups and the serum concentrations of estradiol-17beta and testosterone, but not with the serum progesterone concentration. Significant negative correlations were found between ERalpha immunostaining in epithelial and stromal cells of the vagina and the serum estradiol-17beta concentration, suggesting a negative feedback mechanism between estradiol-17beta and its receptor. Both cell types play a role in the differentiation of vaginal epithelium, under the influence of estradiol-17beta.

Immunolocalization of sex steroid hormone receptors in the canine uterine tube and their relation to sex steroid hormone concentrations.

The aim of this immunohistochemical study was to describe the cellular distribution of the estrogen receptor-alpha (ERalpha), progesterone receptor (PR) and androgen receptor (AR) in canine uterine tubes. Samples of uterine tubes were taken from dogs in different stages of the estrous cycle, and dogs that were pregnant or had just delivered. Nuclear staining for sex steroid hormone receptors was observed in the surface epithelium, stromal cells and smooth muscle cells of the muscular layer. Only slight differences in staining pattern were observed between the ampulla and fimbriae. The staining for ERalpha and PR showed changes throughout the estrous cycle. Some of these changes were related to changing concentrations of sex steroid hormones. High staining scores for ERalpha and PR were found during proestrus and low scores during early metestrus. The staining for AR showed only minor cyclic changes. However, during proestrus and estrus, cytoplasmic staining for AR was observed in differentiated secretory epithelial cells, when nuclear staining in these cells was nearly absent. For the three hormone receptors, stromal cells generally stained with a higher intensity than epithelial cells. It is likely that many steroid hormone actions on the epithelium are mediated through stromal cells. During pregnancy, rather high staining scores were found for ERalpha and AR in the uterine tube. This is in contrast to observations in the canine pregnant uterus.

Immunohistochemical detection of androgen receptors in the canine uterus throughout the estrus cycle.

Serum androgen levels in the bitch increase during proestrus and remain elevated until metestrus. To find out whether androgens can have a direct impact on the canine uterus, androgen receptors (AR) were identified immunohistochemically in uterine tissue. Androgen receptor distribution in the uterine horns, body and cervix was described during different cycle stages, during pregnancy and in the postpartum period. Nuclear staining for AR was observed in cells of the surface epithelium, glandular ducts, basal glands and stroma of the endometrium, and in myometrial smooth muscle cells. In addition, cytoplasmic staining was observed in epithelial cells from proestrus to early metestrus, when the cells were secretory active, and in stroma cells during pregnancy, suggesting a role for androgens in decidualization. During pregnancy and in the postpartum period nuclear staining for AR was nearly absent. During the estrus cycle stroma cells stained with higher intensities for AR than epithelial cells, supporting the idea that stroma cells mediate some effects of steroid hormones on epithelial cells in the genital tract. In contrast with earlier findings on estrogen receptor-alpha and progesterone receptors, no significant changes in androgen receptor expression were observed during the estrus cycle. Few correlations were found between the staining for AR and serum levels of the sex steroids. The present findings suggest that there is a basal expression of AR in the canine uterus throughout the estrus cycle that may not be influenced by sex steroid hormones.