Erythrocyte flow through the interendothelial slits of the splenic venous sinus.

The flow patterns of red blood cells through the spleen are intimately linked to clearance of senescent RBCs, with clearance principally occurring within the open flow through the red pulp and slits of the venous sinus system that exists in humans, rats, and dogs. Passage through interendothelial slits (IESs) of the sinus has been shown by MacDonald et al. (Microvasc Res 33:118-134, 1987) to be mediated by the caliber, i.e., slit opening width, of these slits. IES caliber within a given slit of a given sinus section has been shown to operate in an asynchronous manner. Here, we describe a model and simulation results that demonstrate how the supporting forces exerted on the sinus by the reticular meshwork of the red pulp, combined with asymmetrical contractility of stress fibers within the endothelial cells comprising the sinus, describe this vital and intriguing behavior. These results shed light on the function of the sinus slits in species such as humans, rats, and dogs that possess sinusoidal sinuses. Instead of assuming a passive mechanical filtering mechanism of the IESs, our proposed model provides a mechanically consistent explanation for the dynamically modulated IES opening/filtering mechanism observed in vivo. The overall perspective provided is also consistent with the view that IES passage serves as a self-protective mechanism in RBC vesiculation and inclusion removal.

Individualized tissue-engineered veins as vascular grafts: A proof of concept study in pig.

Personalized tissue engineered vascular grafts are a promising advanced therapy medicinal product alternative to autologous or synthetic vascular grafts utilized in blood vessel bypass or replacement surgery. We hypothesized that an individualized tissue engineered vein (P-TEV) would make the body recognize the transplanted blood vessel as autologous, decrease the risk of rejection and thereby avoid lifelong treatment with immune suppressant medication as is standard with allogenic organ transplantation. To individualize blood vessels, we decellularized vena cava from six deceased donor pigs and tested them for cellular removal and histological integrity. A solution with peripheral blood from the recipient pigs was used for individualized reconditioning in a perfusion bioreactor for seven days prior to transplantation. To evaluate safety and functionality of the individualized vascular graft in vivo, we transplanted reconditioned porcine vena cava into six pigs and analyzed histology and patency of the graft at different time points, with three pigs at the final endpoint 4-5 weeks after surgery. Our results showed that the P-TEV was fully patent in all animals, did not induce any occlusion or stenosis formation and we did not find any signs of rejection. The P-TEV showed rapid recellularization in vivo with the luminal surface covered with endothelial cells. In summary, the results indicate that P-TEV is functional and have potential for use as clinical transplant grafts.

3D-Reconstruction of the human conventional outflow system by ribbon scanning confocal microscopy.

PURPOSE: The risk for glaucoma is driven by the microanatomy and function of the anterior segment. We performed a computation-intense, high-resolution, full-thickness ribbon-scanning confocal microscopy (RSCM) of the outflow tract of two human eyes. We hypothesized this would reveal important species differences when compared to existing data of porcine eyes, an animal that does not spontaneously develop glaucoma. METHODS: After perfusing two human octogenarian eyes with lectin-fluorophore conjugate and optical clearance with benzyl alcohol benzyl benzoate (BABB), anterior segments were scanned by RSCM and reconstructed in 3D for whole-specimen rendering. Morphometric analyses of the outflow tract were performed for the trabecular meshwork (TM), limbal, and perilimbal outflow structures and compared to existing porcine data. RESULTS: RSCM provided high-resolution data for IMARIS-based surface reconstruction of outflow tract structures in 3D. Different from porcine eyes with an abundance of highly interconnected, narrow, and short collector channels (CCs), human eyes demonstrated fewer CCs which had a 1.5x greater cross-sectional area (CSA) and 2.6x greater length. Proximal CC openings at the level of Schlemm's canal (SC) had a 1.3x larger CSA than distal openings into the scleral vascular plexus (SVP). CCs were 10.2x smaller in volume than the receiving SVP vessels. Axenfeld loops, projections of the long ciliary nerve, were also visualized. CONCLUSION: In this high-resolution, volumetric RSCM analysis, human eyes had far fewer outflow tract vessels than porcine eyes. Human CCs spanned several clock-hours and were larger than in porcine eyes. These species differences may point to factors downstream of the TM that increase our vulnerability to glaucoma.

Vascular Supply of the Human Spiral Ganglion: Novel Three-Dimensional Analysis Using Synchrotron Phase-Contrast Imaging and Histology.

Human spiral ganglion (HSG) cell bodies located in the bony cochlea depend on a rich vascular supply to maintain excitability. These neurons are targeted by cochlear implantation (CI) to treat deafness, and their viability is critical to ensure successful clinical outcomes. The blood supply of the HSG is difficult to study due to its helical structure and encasement in hard bone. The objective of this study was to present the first three-dimensional (3D) reconstruction and analysis of the HSG blood supply using synchrotron radiation phase-contrast imaging (SR-PCI) in combination with histological analyses of archival human cochlear sections. Twenty-six human temporal bones underwent SR-PCI. Data were processed using volume-rendering software, and a representative three-dimensional (3D) model was created to allow visualization of the vascular anatomy. Histologic analysis was used to verify the segmentations. Results revealed that the HSG is supplied by radial vascular twigs which are separate from the rest of the inner ear and encased in bone. Unlike with most organs, the arteries and veins in the human cochlea do not follow the same conduits. There is a dual venous outflow and a modiolar arterial supply. This organization may explain why the HSG may endure even in cases of advanced cochlear pathology.

Structure and tensile properties of the forewing costal vein of the honeybee Apis mellifera.

In this study, we investigated the morphological features and tensile properties of the forewing costal vein of the honeybee (Apis mellifera) under fresh, dry and in vitro-time varied conditions. The costal vein is composed of an outer sub-vein and an inner vein starting from the wing base to nearly 50% of the wing span and then they are fused into one vein extending to the wing tip. Confocal laser scanning microscopy revealed that the outer sub-vein with red autofluorescence is stiffer than the inner one with green autofluorescence, and the membrane in the gap between the sub-veins exhibited a long blue-autofluorescence resilin stripe. Considering the irregular cross-sectional shape of the costal vein, cross-sections of the tested specimens after tensile failure were analysed using scanning electron microscopy, to precisely calculate their cross-sectional areas by a customized MATLAB program. The Young's modulus and tensile strength of fresh specimens were ∼4.78 GPa and ∼119.84 MPa, which are lower than those of dry specimens (∼9.08 GPa and ∼154.45 MPa). However, the tensile strain had the opposite relationship (fresh: ∼0.031, dry: ∼0.018). Thus, specimen desiccation results in increasing stiffness and brittleness. The morphological features and material properties of the costal vein taken together represent a tradeoff between both deformability and stiffness. Our study provides guidance for material selection and bionic design of the technical wings of flapping micro aerial vehicles.

Investigation of the morphological cell structures and their optical significances of Aeshna cyanea.

The transparent wing of the dragonfly Aeshna cyanea has been investigated using scanning electron microscopy (SEM), optical microscopy (OPM), energy-dispersive X-ray spectroscopy (EDS) and reflectance spectroscopy. Four cells (D1-D4) were studied and classified according to their general morphology. The OPM depicted the vein-joint characterised by the distribution of resilin. EDS technique showed common elements such as carbon, oxygen, and chlorine. SEM analysis revealed thin membranes reinforced with a network of hallow veins. Spikes and round shape of microstructures were identified. The roughness of the pruinosity was estimated, which indicates the shape and curvature of the microstructures that essentially play a significant role in the optical response observed. The study can be essential to design and improve micro-air vehicles.

A simple ex vivo model of human renal allograft preservation using the gonadal vein.

INTRODUCTION: Hypothermic machine perfusion, an organ preservation modality, involves flow of chilled preservation fluid through an allograft's vasculature. This study describes a simple, reproducible, human model that allows for interrogation of flow effects during ex vivo organ perfusion. MATERIALS AND METHODS: Gonadal veins from deceased human renal allografts were subjected to either static cold storage or hypothermic machine perfusion for up to 24 hours. Caspase-3, Krüppel-like factor 2 expression and electron microscopic analysis were compared between 'flow' and 'no-flow' conditions, with living donor gonadal vein sections serving as negative controls. RESULTS: The increase in caspase-3 expression was less pronounced for hypothermic machine-perfused veins compared with static cold storage (median-fold increase 1.2 vs 2.3; P < 0.05). Transmission electron microscopy provided ultrastructural corroboration of endothelial cell apoptosis in static cold storage conditions. For static cold storage preserved veins, Krüppel-like factor 2 expression diminished in a time-dependent manner between baseline and 12 hours (P < 0.05) but was abrogated and reversed by hypothermic machine perfusion (P < 0.05). CONCLUSIONS: Our methodology is a simple, reproducible and successful model of ex vivo perfusion in the context of human organ preservation. To demonstrate the model's utility, we establish that two widely used markers of endothelial health (caspase-3 and Krüppel-like factor 2) differ between the flow and no-flow conditions of the two predominant kidney preservation modalities. These findings suggest that ex vivo perfusion may mediate the induction of a biochemically favourable endothelial niche which may contribute tohypothermic machine perfusion's association with improved renal transplantation outcomes.

Microglia contribute to the glia limitans around arteries, capillaries and veins under physiological conditions, in a model of neuroinflammation and in human brain tissue.

Microglia represent resident immune cells of the central nervous system (CNS), which have been shown to be involved in the pathophysiology of practically every neuropathology. As microglia were described to participate in the formation of the astroglial glia limitans around CNS vessels, they are part of the neurovascular unit (NVU). Since the NVU is a highly specialized structure, being functionally and morphologically adapted to differing demands in the arterial, capillary, and venous segments, the present study was aimed to systematically investigate the microglial contribution to the glia limitans along the vascular tree. Thereby, the microglial participation in the glia limitans was demonstrated for arteries, capillaries, and veins by immunoelectron microscopy in wild-type mice. Furthermore, analysis by confocal laser scanning microscopy revealed the highest density of microglial endfeet contacting the glial basement membrane around capillaries, with significantly lower densities around arteries and veins. Importantly, this pattern appeared to be unaltered in the setting of experimental autoimmune encephalomyelitis (EAE) in CX3CR1CreERT2:R26-Tomato reporter mice, although perivascular infiltrates of blood-borne leukocytes predominantly occur at the level of post-capillary venules. However, EAE animals exhibited significantly increased contact sizes of individual microglial endfeet around arteries and veins. Noteworthy, under EAE conditions, the upregulation of MHC-II was not limited to microglia of the glia limitans of veins showing infiltrates of leukocytes, but also appeared at the capillary level. As a microglial contribution to the glia limitans was also observed in human brain tissue, these findings may help characterizing microglial alterations within the NVU in various neuropathologies.

Survival after Digit Replantation and Revascularization Is Not Affected by the Use of Interpositional Grafts during Arterial Repair.

BACKGROUND: Interpositional grafts can be used to reconstruct the digital artery during revascularization and replantation when primary repair is not possible. The purpose of this study was to determine the effect of using interpositional grafts on the rate of digit survival. METHODS: A retrospective review of all patients from 2007 to 2016 that required revascularization and/or replantation of one or more digits was performed. RESULTS: One hundred twenty-seven patients were identified with 171 affected digits (118 digital revascularizations and 53 digital replantations). A graft was used to repair the digital artery in 50 percent of revascularizations (59 of 118) and in 49 percent of replantations (26 of 53). There was no difference in digit survival with use of an interpositional graft for arterial repair versus primary repair in revascularization (91.5 percent in both groups) or replantation (48.1 percent versus 46.2 percent; p = 0.88). Regression analysis demonstrated no association between the use of interpositional grafts and digit survival. Interpositional grafting was more likely to be used in crush (62.5 percent) and avulsion injuries (72.2 percent) compared with sharp laceration injuries (11.1 percent), with a relative risk of 5.6 (p = 0.01) and 6.5 (p = 0.006), respectively. CONCLUSIONS: There was no difference in the survival rate of amputated digits that required interpositional grafting for arterial repair. The need for an interpositional graft in a large zone of injury should not be considered a contraindication to performing revascularization or replantation. Furthermore, hand surgeons should have a low threshold for using interpositional grafts, especially in crush or avulsion injuries. CLINICAL QUESTION/LEVEL OF EVIDENCE: Therapeutic, III.

Microvascular anatomy of the brain of the adult pipid frog, Xenopus laevis (Daudin): A scanning electron microscopic study of vascular corrosion casts.

To demonstrate the 3D microvascular anatomy of the brain of the model organism Xenopus laevis Daudin scanning electron microscopy of vascular corrosion casts was correlated with light microscopy of stained 7 µm thick serial tissues sections. Results showed that supplying arteries descended from the leptomeningeal surface without remarkable branchings straight to the subventricular zone where they branched and capillarized. Capillaries showed few H- and/or Y-shaped anastomoses during their centrifugal course toward the leptomeningeal surface where they drained into cerebral venules and veins. Apart from the accessory olfactory bulb and the vestibule-cochlear nucleus where capillaries were densely packed, capillaries formed a wide-meshed 3D network throughout the brain parenchyma and thus contrasted to urodelian brains where hairpin-shaped capillaries descend from the leptomeningeal vessels into varying depths of the brain parenchyma. In about two-third of specimens, a closed arterial circle of Willis was found at the base of the brain. If this circle in Xenopus might serve the same two functions as in men is briefly discussed. Choroid plexuses of third and fourth ventricle were found to have a high venous, but a low arterial inflow via one small choroidal artery only. Findings are compared with previous studies on the vascularization of the anuran brain and discrepancies in respect to presence or absence of particular arteries and/or veins in Ranids, Bufonids, and Pipids studied so far are discussed with particular emphasis on the techniques used in the various studies published so far.

Morphology of hindwing veins in the shield bug Graphosoma italicum (Heteroptera: Pentatomidae).

Light, fluorescence, and electron microscopy were applied to cross sections and -breakage and whole-mount preparations of the anterior hindwing vein of the shield bug Graphosoma italicum. These analyses were complemented by investigations of the basal part of the forewing Corium and Clavus. The integration of structural, histological, and fluorescence data revealed a complex arrangement of both rigid and elastic structures in the wall of wing veins and provided insights into the constitution of transition zones between rigid and elastic regions. Beneath the exocuticular layers, which are continuous with the dorsal and ventral cuticle of the wing membrane, the lumen of the veins is encompassed by a mesocuticular layer, an internal circular exocuticular layer, and an internal longitudinal endocuticular layer. Separate parallel lumina within the anterior longitudinal vein of the hindwing, arranged side-by-side rostro-caudally, suggest that several veins have fused in the phylogenetic context of vein reduction in the pentatomid hindwing. Gradual structural transition zones and resilin enrichment between sclerotized layers of the vein wall and along the edges of the claval furrow are interpreted as mechanical adaptations to enhance the reliability and durability of the mechanically stressed wing veins.

Morphological and mechanical properties of flexible resilin joints on damselfly wings (Rhinocypha spp.).

Resilin functions as an elastic spring that demonstrates extraordinary extensibility and elasticity. Here we use combined techniques, laser scanning confocal microscopy (LSCM) and scanning electron microscopy (SEM) to illuminate the structure and study the function of wing flexibility in damselflies, focusing on the genus Rhinocypha. Morphological studies using LSCM and SEM revealed that resilin patches and cuticular spikes were widespread along the longitudinal veins on both dorsal and ventral wing surfaces. Nanoindentation was performed by using atomic force microscopy (AFM), where the wing samples were divided into three sections (membrane of the wing, mobile and immobile joints). The resulting topographic images revealed the presence of various sizes of nanostructures for all sample sections. The elasticity range values were: membrane (0.04 to 0.16 GPa), mobile joint (1.1 to 2.0 GPa) and immobile joint (1.8 to 6.0 GPa). The elastomeric and glycine-rich biopolymer, resilin was shown to be an important protein responsible for the elasticity and wing flexibility.

Cross talk between TGF beta and TNF alfa in regression of myointimal hyperplasia.

BACKGROUND: The phenomena involved in regression of arterial myointimal hyperplasia have not been analyzed in detail. MATERIALS AND METHODS: In 24 Lewis rats, a 1-cm-long venous graft, obtained from syngenic Lewis rats, was implanted in the infrarenal aorta. After 4 wk, the grafts were removed and analyzed using scanning electron microscopy and histochemistry. The grafts showed evidence of myointimal hyperplasia; 16 of these explanted grafts were reimplanted in the vein circulation of syngenic Lewis rats. These grafts were harvested 2 wk (8 animals) and 8 wk (8 animals) later, showing complete regression of myointimal hyperplasia. RESULTS: Regression of experimental myointimal hyperplasia was correlated with the simultaneous and complementary action of Transforming Growth Factor beta and Tumor Necrosis Factor alfa. Inflammatory cytokines (IL1, IL2, and IL6) inhibit Tumor Necrosis Factor alfa-induced apoptosis. CONCLUSIONS: Regression of myointimal hyperplasia is an active process, which implies the action of several inhibitory factors. The analysis of these phenomena can lead to new therapeutic approaches to prevent myointimal hyperplasia progression.

Resilin microjoints: a smart design strategy to avoid failure in dragonfly wings.

Dragonflies are fast and manoeuvrable fliers and this ability is reflected in their unique wing morphology. Due to the specific lightweight structure, with the crossing veins joined by rubber-like resilin patches, wings possess strong deformability but can resist high forces and large deformations during aerial collisions. The computational results demonstrate the strong influence of resilin-containing vein joints on the stress distribution within the wing. The presence of flexible resilin in the contact region of the veins prevents excessive bending of the cross veins and significantly reduces the stress concentration in the joint.

Vascular Telocytes.

Telocyte, different to fibroblast and dendritic cell, is a novel type of interstitial cell, whose key features are their smaller cell body with very long prolongations of uneven caliber, termed telopodes. The telocytes have been continuously discovered to be present in many tissues and organs. Whether telocytes exist in the blood and vascular wall is not clear. Our research group, for the first time, testified that telocytes also exist in the blood and large sized arterial and venous wall under scanning and transmission electron microscope. In static condition, blood telocytes and their prolongations usually attach on endothelial surface. We speculate that the blood telocyte maybe come from the bone marrow, because most of formed element in the blood originated from bone marrow. The telocytes within arterial wall locate in the tunica adventitia and close to outer elastic lamina. And, the telocytes in venous wall commonly situate in the subendothelial layer. The morphological features of blood and vascular telocytes are consistent with the telocytes in other organs and tissues. Their real function of telocytes in cardiovascular system preserved to be further investigated.

Microvascularization of the spleen in larval and adult Xenopus laevis: Histomorphology and scanning electron microscopy of vascular corrosion casts.

Microvascular anatomy and histomorphology of larval and adult spleens of the Clawed Toad, Xenopus laevis were studied by light microscopy of paraplast embedded serial tissue sections and scanning electron microscopy (SEM) of vascular corrosion casts (VCCs). Histology showed i) that white and red pulp are present at the onset of metamorphic climax (stage 57) and ii) that splenic vessels penetrated deeply into the splenic parenchyma at the height of metamorphic climax (stage 64). Scanning electron microscopy of VCCs demonstrated gross arterial supply and venous drainage, splenic microvascular patterns as well as the structure of the interstitial (extravasal) spaces representing the "open circulation routes." These spaces identified themselves as interconnected resin masses of two distinct forms, namely "broccoli-shaped" forms and highly interconnected small resin structures. Arterial and venous trees were clearly identified, as were transitions from capillaries to interstitial spaces and from interstitial spaces to pulp venules. Venous sinuses were not diagnosed (nonsinusal spleen). The splenic circulation in Xenopus laevis is "open." It is hypothesized that red blood cells circulate via splenic artery, central arteries, penicillar arteries, and red pulp capillaries primarily via "broccoli-shaped" interstitial spaces, pulp venules and veins into subcapsular veins to splenic veins while lymphocytes circulate also via the interstitial spaces represented by the highly interconnected small resin structures in vascular corrosion casts. In physiological terms, the former most likely represent the fast route for blood circulation, while the latter represent the slow route. J. Morphol. 277:1559-1569, 2016. © 2016 Wiley Periodicals, Inc.

Dimensions of compartments and membrane surfaces in the intact rabbit heart of importance in studies on intramyocardial transfer of blood-borne substances.

Cardiac studies on the uptake, storage and intramyocardial transfer of blood-borne substances require detailed information on the geometric ultrastructural dimensions of myocardial compartments and parts thereof, and the membranes separating these compartments. Such a specific ultrastructural set of data of the heart is yet lacking. In the present study, we quantitatively assessed these dimensions in glutaraldehyde-perfusion fixed rabbit hearts by means of histological and tailored mathematical techniques. We showed the true ellipsoid nature of the myocardial capillary cross section and estimated the mean capillary diameter dcap. After correction for the ellipsoid shape, dcap was found to be 5.21±1.41 µm. Effective widths of the endothelial cell and the pericapillary interstitium (is1), dimensions of importance in diffusion, amounted to 187±7 and 160±10 nm, respectively. The fractional volume of the large vessels (arteries and veins larger than 10 µm), capillaries, endothelium, is1, cardiomyocytes, non-pericapillary interstitium is2, t-tubular compartment and interstitial cells amounted on average to 5.92%, 9.36%, 1.83%, 1.94%, 73.07%, 5.97%, 0.95% and 0.96%, respectively, of total myocardial volume, defined as the cardiac tissue volume, the large blood vessels included. Normalized to total myocardial volume, the surface area of the luminal and abluminal endothelial membranes and of the cardiomyocyte membrane opposing the endothelial cells amounted to 75.2±5.5·10³, 82.2±6.0·10³ and 89.1±6.5·10³ m²/m³, respectively. The present study provides quantitative information about ultrastructural dimensions of the adult rabbit heart, among others, of importance for studies on cardiac uptake, and intramyocardial transfer and storage of blood-supplied substances.

Ultrastructure of dragonfly wing veins: composite structure of fibrous material supplemented by resilin.

Dragonflies count among the most skilful of the flying insects. Their exceptional aerodynamic performance has been the subject of various studies. Morphological and kinematic investigations have showed that dragonfly wings, though being rather stiff, are able to undergo passive deformation during flight, thereby improving the aerodynamic performance. Resilin, a rubber-like protein, has been suggested to be a key component in insect wing flexibility and deformation in response to aerodynamic loads, and has been reported in various arthropod locomotor systems. It has already been found in wing vein joints, connecting longitudinal veins to cross veins, and was shown to endow the dragonfly wing with chordwise flexibility, thereby most likely influencing the dragonfly's flight performance. The present study revealed that resilin is not only present in wing vein joints, but also in the internal cuticle layers of veins in wings of Sympetrum vulgatum (SV) and Matrona basilaris basilaris (MBB). Combined with other structural features of wing veins, such as number and thickness of cuticle layers, material composition, and cross-sectional shape, resilin most probably has an effect on the vein's material properties and the degree of elastic deformations. In order to elucidate the wing vein ultrastructure and the exact localisation of resilin in the internal layers of the vein cuticle, the approaches of bright-field light microscopy, wide-field fluorescence microscopy, confocal laser-scanning microscopy, scanning electron microscopy and transmission electron microscopy were combined. Wing veins were shown to consist of up to six different cuticle layers and a single row of underlying epidermal cells. In wing veins of MBB, the latter are densely packed with light-scattering spheres, previously shown to produce structural colours in the form of quasiordered arrays. Longitudinal and cross veins differ significantly in relative thickness of exo- and endocuticle, with cross veins showing a much thicker exocuticle. The presence of resilin in the unsclerotised endocuticle suggests its contribution to an increased energy storage and material flexibility, thus to the prevention of vein damage. This is especially important in the highly stressed longitudinal veins, which have much lower possibility to yield to applied loads with the aid of vein joints, as the cross veins do. These results may be relevant not only for biologists, but may also contribute to optimise the design of micro-air vehicles.

Regional differences in statistical geometry of endothelial dense granules in human extremity veins.

OBJECTIVES: Leg and arm human veins are exposed to different gravitational stresses. We investigated if there is difference in the amount and geometry of secretory vesicles in their endothelium. METHODS: Superficial small vein segments were removed during vascular operations for electromicroscopic analysis. Vesicular area/total endothelial cross-sectional area was determined by computer-based morphometry. Long and short axes of granule cross sections were measured by image analyzing software. RESULTS: Vesicular density in all samples was 2.26 ± 0.34%. There was no significant difference between the vesicular densities of upper extremity and leg. The shape of the vesicles was more frequently elongated in leg than in arm sections (p < 0.01). CONCLUSIONS: The density of the vesicles does not depend on vascular region or orthostatic load. Ellipticity of these granules is significantly different in areas exposed to different gravitational stresses. This might contribute to the differences of thrombotic and hemodynamic properties of leg and upper body veins.