Cerebral vessels cryofixed after hyperosmosis or cold injury in normothermic and hypothermic frogs

Form and Function of the Vertebrate and Invertebrate Blood-Brain Barriers

The need to protect neural tissue from toxins or other substances is as old as neural tissue itself. Early recognition of this need has led to more than a century of investigation of the blood-brain barrier (BBB). Many aspects of this important neuroprotective barrier have now been well established, including its cellular architecture and barrier and transport functions. Unsurprisingly, most research has had a human orientation, using mammalian and other animal models to develop translational research findings. However, cell layers forming a barrier between vascular spaces and neural tissues are found broadly throughout the invertebrates as well as in all vertebrates. Unfortunately, previous scenarios for the evolution of the BBB typically adopt a classic, now discredited 'scala naturae' approach, which inaccurately describes a putative evolutionary progression of the mammalian BBB from simple invertebrates to mammals. In fact, BBB-like structures have evolved independently numerous times, complicating simplistic views of the evolution of the BBB as a linear process. Here, we review BBBs in their various forms in both invertebrates and vertebrates, with an emphasis on the function, evolution, and conditional relevance of popular animal models such as the fruit fly and the zebrafish to mammalian BBB research.

Frog Virus 3 dissemination in the brain of tadpoles, but not in adult Xenopus, involves blood brain barrier dysfunction

While increasing evidence points to a key role of monocytes in amphibian host defenses, monocytes are also thought to be important in the dissemination and persistent infection caused by ranavirus. However, little is known about the fate of infected macrophages or if ranavirus exploits immune privileged organs, such as the brain, in order to establish a reservoir. The amphibian Xenopus laevis and Frog Virus 3 (FV3) were established as an experimental platform for investigating in vivo whether ranavirus could disseminate to the brain. Our data show that the FV3 infection alters the BBB integrity, possibly mediated by an inflammatory response, which leads to viral dissemination into the central nervous system in X. laevis tadpole but not adult. Furthermore, our data suggest that the macrophages play a major role in viral dissemination by carrying the virus into the neural tissues.

Human Cerebral Microvessel Endothelial Cell Culture as a Model System to Study the Blood–Brain Interface in Ischemic/Hypoxic Conditions

(1) Cerebral ischemia and reperfusion induce several changes on the endothelial cells at the microcirculatory level. (2) Vasogenic brain edema due to compromised blood-brain barrier, transformation of the endothelial cell surface from an anticoagulant to a procoagulant surface are important factors in the pathogenesis of ischemic stroke. (3) Release of prostaglandins, endothelin-1, complement proteins, and matrix metalloproteinase-9 by microvascular endothelial cells are other components in the complex mechanism of brain ischemia/hypoxia. (4) Ultrastructural studies documented the opened paracellular avenues in the course of vasogenic edema in different experimental models (5) Tight junctions of endothelial cells have been characterized with freeze fracture electron microscopy, and the process of transvesiculation was analyzed using rapid freeze and freeze substitution procedure before electron microscopy studies (6) In endothelial cell-culture experiments, we used rodent and later human brains. (7) Endothelial cells co-cultured with astroglia resulted in an elaborate tight junctional complex. (8) This co-culture technique becomes the basis of in vitro blood-brain barrier studies On endothelial cells of human brain origin, different regulatory factors found to be responsible for the complex mechanism of ischemic stroke.

Ionic permeability of the opossum sciatic nerve perineurium, examined using electrophysiological and electron microscopic techniques

A parallel electrophysiological and electron microscopic study was used to assess the ionic permeability of the sciatic nerve perineurium of the opossum Monodelphis domestica. The electrophysiological method was used to monitor permeability to K(+), followed by combined electron microscopy and X-ray probe analysis to monitor permeability to the electron-dense tracer lanthanum. Isolated but intact nerves were mounted in a 'grease gap' chamber for extracellular measurement of DC potential and compound action potential (CAP). Challenge with 100 mM [K(+)] Ringer was used to assess the K(+) permeability of the perineurium, since a change in DC potential (DeltaDC) under these conditions reflected changes in the axonal resting membrane potential. There was no detectable change in DC potential or CAP to the first K(+) challenge (n=71 nerves) indicating negligible K(+) permeability under control conditions. The inflammatory mediators histamine 0.1-40 mg/ml (1. 3-130 mM), bradykinin (0.1-4.7 mM) and 5HT (serotonin) 0.1-5.0 mg/ml (0.5-23.5 mM) caused no measurable DeltaDC on subsequent challenge with 100 mM [K(+)] Ringer, indicating no effect on perineurial K(+) permeability. In nerves exposed to the bile salt sodium deoxycholate (DOC, 6 min, 4 mM), challenge with elevated K(+) Ringer caused a dose-dependent DeltaDC in the range 10-100 mM [K(+)] (1.67+/-0.17 mV in 100 mM [K(+)], n=20), indicating increased perineurial permeability caused by DOC, but the response was smaller than that previously reported for the frog perineurium. Lanthanum was observed in the outer layers of the perineurium, but was not seen to penetrate the endoneurium in any of the nerves examined (n=51), even after DOC application. This study shows that the combined electrophysiological and electron microscopic technique for monitoring ionic permeability can be applied to mammalian nerve, and suggests that the opossum perineurium is more resistant to tight junction opening by chemical modulators than is the frog perineurium.

Electron microscopy of the blood-brain barrier in disease

The anatomical site of the blood-brain barrier (BBB) is at the capillary endothelium mainly, with some contribution from astrocytes. Electron microscopic observations of endothelial cells and perivascular astrocytes comprising the BBB in brain edema and other pathological conditions are reviewed in this article. The tight junctions of cerebral endothelial cells open under several conditions such as infusion of hyperosmolar solutions. Pinocytotic vesicles increase under various pathological conditions and fenestrae appear in blood vessels of certain brain tumors and several non-neoplastic lesions. Inflammatory cells penetrate between or through endothelial cells. In long standing lesions, endothelial cells containing various tubular structures such as Weibel-Palade bodies proliferate. Other alterations include surface infoldings of endothelial cells and fluid diffusion through damaged endothelium. Astrocytic alterations include abnormal junctions between astrocytic processes in certain gliomas. In vivo and in vitro studies suggest that astrocytes maintain or develop certain functions of BBB. As the BBB is disrupted, edema fluid infiltrates the brain parenchyma. Because the white matter consists of nerve fibers without demonstrable junctions, it invades between nerve fibers. In the gray matter, expansion of the fluid is limited by complicated anatomical structures. In myelinated nerve fibers, edema fluid accumulates in five separate compartments of extracellular space.

Transport pathways for macromolecules in the aortic endothelium. II. The distribution analysis of plasmalemmal vesicles reconstructed by serial sections

Three-dimensional organization of vesicles was examined to elucidate the transendothelial transport properties for macromolecules in rat aortic endothelium using ultrathin serial sections and horseradish peroxidase (HRP) as a tracer molecule. A total number of reconstructing vesicles was 1,298 in nine series of serial electron micrographs, if each vesicular entity was counted as one regardless of composite number of vesicles. The vesicles could be classified into the following six types: HRP-positive luminal, abluminal and intercellular invaginations; HRP-positive channels; HRP-positive and -negative vesicles. The vesicular invaginations and the channels occupied 97.8% and 0.9% of the total vesicles, whereas HRP-positive and -negative free vesicles were found in 0.8% and 0.5%, respectively. The average numerical density of the luminal invagination was 41.1/microns 2 and approximately equal to that of the abluminal invagination (42.0/microns 2), whereas the frequency of the latter was 1.4 times higher than that of the former since the abluminal surface of the endothelium was more irregular to increase a surface area. Each endothelial region varied in the vesicular density and the peripheral region generally showed the higher density, although the transendothelial channels composed of vesicles were not always found in every peripheral region. These results suggest that the shuttle hypothesis is unsuitable to explain "vesicular transport" in the arterial endothelium as well as in the capillary endothelium and that the channels in the peripheral region mainly control transendothelial transport for macromolecules via vesicles.

Effect of temperature change on the permeability of eel rete capillaries

The changes in the permeability properties of the rete capillaries of the eel in response to temperature shifts were studied during countercurrent perfusion at constant flow and pressure. Tracers and oxygen were added to the arterial perfusate. From the ratio of end concentrations of arterial to venous capillaries divided by surface area, calculated from rete weight, a value for the ratio of permeability to flow, P/F, with dimensions in centimeters-2 was estimated. Because flow and surface area are constant, this provides an index of how permeability varies with time. A group of paracellular (albumin, sucrose, and sodium) and cellular (antipyrine, water, and oxygen) probes were used. When the temperature of the perfusate was raised abruptly from 25 degrees C to 35 degrees C, P/F values rose continuously and irreversibly from 0.042 +/- 0.009 to 0.281 +/- 0.112 cm-2 (mean +/- SEM) for 125I-albumin, from 0.082 +/- 0.006 to 1.74 +/- 0.070 cm-2 for [14C]sucrose, and from 0.32 +/- 0.06 to 2.78 +/- 0.62 cm-2 for 22Na, whereas they were not modified for [14C]antipyrine, [3H]water, and O2. Gradual increase of temperature was accompanied by a smaller rise in sucrose and sodium permeability and no change in albumin permeability; with decrease, the change was reversible.(ABSTRACT TRUNCATED AT 250 WORDS)

Isolation and characterization of endothelial cells from bovine cerebral arteries

For our laboratory's investigation into the role of the endothelial cells in vasospasm following subarachnoid hemorrhage and in inflammatory diseases, we found it necessary to devise a modified method of cell culture, which would be appropriate for studying human endothelial cells from lobectomized brain. We report our techniques to increase cell harvest and ensure reproducibility, our method of culturing endothelial cells from bovine major cerebral arteries, and our morphologic and immunocytochemical characterization of these cells. To increase the harvest of endothelial cells, the blood cells were washed from the lumen of the major cerebral arteries at the slaughterhouse and a modified reversed vessel technique was employed. The monolayer of cultured endothelial cells displayed a cobblestone appearance when it reached confluency and transmission electron microscopy revealed junctional complexes and interdigitation of cytoplasm at Passages 10 and 17. The cells stained positively for Factor VIII-related antigen at Passages 3, 5, 7, 10, and 15. Also the cells metabolized acetylated low-density lipoprotein at Passage 8. To determine the purify of the cultured endothelial cells, an immunocytochemical study of the cytoskeleton was performed on Passage 5 cells using either rhodamine-phalloidin or antibodies against smooth muscle myosin, desmin, and vimentin.

Vascularization of fetal cell suspension grafts in the excitotoxically lesioned adult rat thalamus

Several studies have considered the establishment of vascularization in intracerebral solid transplants of neural tissue. The widely supported interpretation of the results is that the vascular network of the solid grafts is already present before implantation into the host brain. The situation is different when dissociated fetal tissue is transplanted as a cell suspension because in these conditions the fetal vascular network is disrupted. The present study has, therefore, been undertaken to follow the angiogenesis in a transplant of dissociated fetal cells implanted into the excitotoxically neuron-depleted thalamus. The vascular network is compared to that observed in the intact and in the lesioned thalamus both in terms of morphology of the capillaries and of the function of the blood-brain barrier (BBB). In the transplant, capillaries, stained by Indian ink, are very few in number and have very fine calibers during the first 20 days after grafting. Some structures can be identified as immature blood vessels at the electron microscopic level. The blood vessels are progressively more numerous in the graft and they demonstrate mature ultrastructural features 2 months after grafting. Last, there is no leakage of the BBB for peroxidase. The vascularization seems to follow a pattern of maturation comparable to that described during development in the literature. In contrast, in the lesioned area, there is a reactive angiogenesis: 10 days after the excitotoxic injection (shortest time studied), there are many wide caliber vessels with expanded perivascular spaces engorged with mesodermal cells. A microvascularization also develops transiently during the first two months. Capillaries are abnormal from the functional point of view, since there is a leakage of the BBB to macromolecules. The use of an experimental model in which transplant had to grow in a lesioned area permits to determine two types of vascularization: an apparently normal developmental timetable, normal morphological and functional characteristics, in the transplant; a reactive angiogenesis, in the lesioned area.