Fine structure of tight junctions between rat choroidal cells after osmotic opening induced by urea and sucrose

Whole-body hyperthermia in the rat disrupts the blood-cerebrospinal fluid barrier and induces brain edema

The present investigation was undertaken to find out whether whole-body hyperthermia (WBH) alters blood-cerebrospinal fluid barrier (BCSFB) permeability to exogenously-administered tracers and whether choroid plexus and ependymal cells exhibit morphological alterations in hyperthermia. Rats subjected to 4 hours of heat stress at 38 degrees C in a biological oxygen demand (BOD) incubator exhibited a profound increase in the BCSFB to Evans blue and radioiodine. Blue staining of the dorsal surface of the hippocampus and caudate nucleus and a significant increase in Evans blue and [131]Iodine in cisternal cerebrospinal fluid were seen following 4-hour heat stress compared to control. Degeneration of choroidal epithelial cells and underlying ependyma, a dilated ventricular space, and degenerative changes in the underlying neuropil were frequent. Hippocampus, caudate nucleus, thalamus, and hypothalamus exhibited profound increases in water content after 4 hours of heat stress. These observations suggest that hyperthermia induced by WBH is capable of breaking down the BCSFB and contributing to cell and tissue injury in the central nervous system.

Enhanced Prospects for Drug Delivery and Brain Targeting by the Choroid Plexus–CSF Route

The choroid plexus (CP), i.e., the blood-cerebrospinal fluid barrier (BCSFB) interface, is an epithelial boundary exploitable for drug delivery to brain. Agents transported from blood to lateral ventricles are convected by CSF volume transmission (bulk flow) to many periventricular targets. These include the caudate, hippocampus, specialized circumventricular organs, hypothalamus, and the downstream pia-glia and arachnoid membranes. The CSF circulatory system normally provides micronutrients, neurotrophins, hormones, neuropeptides, and growth factors extensively to neuronal networks. Therefore, drugs directed to CSF can modulate a variety of endocrine, immunologic, and behavioral phenomema; and can help to restore brain interstitial and cellular homeostasis disrupted by disease and trauma. This review integrates information from animal models that demonstrates marked physiologic effects of substances introduced into the ventricular system. It also recapitulates how pharmacologic agents administered into the CSF system prevent disease or enhance the brain's ability to recover from chemical and physical insults. In regard to drug distribution in the CNS, the BCSFB interaction with the blood-brain barrier is discussed. With a view toward translational CSF pharmacotherapy, there are several promising innovations in progress: bone marrow cell infusions, CP encapsulation and transplants, neural stem cell augmentation, phage display of peptide ligands for CP epithelium, CSF gene transfer, regulation of leukocyte and cytokine trafficking at the BCSFB, and the purification of neurotoxic CSF in degenerative states. The progressively increasing pharmacological significance of the CP-CSF nexus is analyzed in light of treating AIDS, multiple sclerosis, stroke, hydrocephalus, and Alzheimer's disease.

Structural characteristics and barrier properties of the choroid plexuses in developing brain of the opossum (Monodelphis Domestica)

The structural and functional development of the choroid plexuses, the site of the blood-cerebrospinal fluid (CSF) barrier, in an opossum (Monodelphis domestica) was studied. Marsupial species are extremely immature at birth compared with more conventional eutherian species. Choroid plexus tissue of each brain ventricle, from early stages of development, was collected for light and electron microscopy. During development, the choroidal epithelium changes from a pseudostratified to a cuboidal layer. Individual epithelial cells appear to go through a similar maturation process even though the timing is different between and within each plexus. The ultrastructural changes during development in the choroidal epithelial cells consist of an increase in the number of mitochondria and microvilli, and changes in structure of endoplasmic reticulum. There are also changes in the core of plexuses with age. In contrast, the structure of the tight junctions between epithelial cells does not appear to change with maturation. In addition, the route of penetration for lipid insoluble molecules from blood to CSF across the choroid plexuses was examined using a small biotin-dextran. This showed that the tight junctions already form a functional barrier in early development by preventing the paracellular movement of the tracer. Intracellular staining shows that there may be a transcellular route for these molecules through the epithelial cells from blood to CSF. Apart from lacking a glycogen-rich stage, cellular changes in the developing opossum plexus seem to be similar to those in other species, demonstrating that this is a good model for studies of mammalian choroid plexus development.

Transcytosis of protein through the mammalian cerebral epithelium and endothelium. I. Choroid plexus and the blood-cerebrospinal fluid barrier

The potential for transcytosis (endocytosis----intracellular transport----exocytosis) of protein and membrane events associated with fluid phase and adsorptive endocytic processes within epithelia of the choroid plexus [blood-cerebrospinal fluid (CSF) barrier] were investigated in mice injected intravenously or into the lateral cerebral ventricle with native horseradish peroxidase (HRP) or the lectin wheatgerm agglutinin (WGA) conjugated to HRP. WGA binds to specific cell surface oligosaccharides and enters cells by the process of adsorptive endocytosis; native HRP is taken into cells non-specifically by fluid phase endocytosis. The lysosomal system of organelles and the endoplasmic reticulum, identified by enzyme cytochemical markers applied to choroid epithelia, were analysed for possible participation in transcytosis and compared to epithelial organelles harbouring the exogenous tracer proteins. Blood-borne native HRP was endocytosed readily by choroid epithelia whereas WGA-HRP was not, perhaps because WGA-HRP does not escape fenestrated endothelia as easily as native HRP. The blood-borne proteins incorporated within endocytic vesicles by choroid epithelia were directed to endosomes (prelysosomes) and secondary lysosomes (e.g. tubules, multivesicular/dense bodies) for eventual degradation and did not reach the apical/microvillus surface. Both CSF-borne native HRP and WGA-HRP entered choroid epithelia within endocytic vesicles derived from the microvillus border. Native HRP, ultimately sequestered within endosomes and secondary lysosomes, failed to undergo transcytosis through the epithelia into the basolateral clefts. Conversely, CSF-borne WGA-HRP was transported through the epithelia and released into the basolateral clefts within 10 min post-injection. The lectin conjugate labelled epithelial vesicles, endosomes, secondary lysosomes and, at 30 min post-injection, the transmost saccule of the Golgi complex which exhibits acid hydrolase activity. Tubular profiles, related either to the endosome apparatus or to the lysosomal system, and the endoplasmic reticulum did not appear involved in the transcytotic pathway. The data suggest that CSF-borne protein entering the choroid epithelium by adsorptive endocytosis can undergo rapid transcytosis through the cell. The results provide insight to transcytotic pathways utilizing vesicles, the endosomal apparatus, and the Golgi complex within the choroid epithelium for circumventing the blood-CSF barrier. Hypothesized membrane events and morphological associations among constitutents of the endomembrane system within the choroid epithelium are summarized diagrammatically.

Selective and reversible breakdown of the tight junctional barrier in the rabbit ciliary body induced by arachidonic acid. A tracer and freeze-fracture study

Arachidonic acid induced a reversible breakdown of the blood-aqueous barrier in the iridial processes of the rabbit ciliary body, whereas the ciliary processes were not affected under the conditions of this study. The focal passage of horseradish peroxidase through the tight junctions was demonstrated. In freeze-fracture images, this breakdown of the barrier function was associated with focal changes: an alteration in the geometry of the tight junctional network; an increase in the number of discontinuities of the P-face ridges and particles and short bars in the E-face furrows; an increase in the density of intramembranous particles within the junctional area. The significance of the ultrastructural alterations of the tight junctions as a structural counterpart of the physiological changes is discussed.

Lanthanum and freeze-fracture studies of retinal pigment epithelial cell junctions in the streptozotocin diabetic rat

The blood-retinal barrier breaks down early in diabetes and previous morphological studies suggest that the retinal pigment epithelium (RPE) is the site of this defect. In the present study the electron microscope lanthanum nitrate tracer technique has been used to study RPE cell permeability in the streptozotocin diabetic rat retina. The freeze-fracture technique has been used to study RPE cell tight junction structure as permeability increases. In the lanthanum experiments, RPE cell permeability is normal in control rats and in diabetic rats 3 weeks after the injections. After 8 or 16 weeks of diabetes, however, the RPE cell layer no longer forms a barrier to the tracer and electron dense material is present in the subretinal space, in the apical and basal regions of the RPE cell junctions and intracellularly within the RPE. Freeze-fracture studies of tight junctions during this period show (1) an increase in the complexity of the tight junction network due to an increase in anastomoses between the tight junctions; (2) a change in membrane fracturing properties such that the tight junctional intra-membrane particles adhering to the E-face grooves are more numerous than in the control junctions; (3) no change in the number or size of the tight and gap junctional elements. These results suggest that the blood-retinal barrier breakdown in the diabetic RPE is due to alteration of plasma membrane permeability rather than to a loss of tight junctions.

Ca2+ depletion-induced disconnection of tight junctions in isolated rat brain microvessels

Cerebral microvessels were isolated from rat brains. One part of the microvessel pellets was incubated for 25 or 90 min in Krebs-Henseleit bicarbonate buffer (KHB) at pH 7.5 (control group). The other part of the pellets was treated for the same periods of time with Ca2+-free KHB, containing 2.2 mM EGTA and 2 mM glucose (experimental group). Morphological changes of endothelial tight junctions were evaluated in 100 randomly selected interendothelial clefts from isolated cerebral microvessels of each groups by electron microscopy. Following 25 min of incubation time, either with Ca2+-containing or with Ca2+-free KHB, no significant changes of tight junctions were observed. After 90 min of incubation in Ca2+-free medium, 58% of tight junctions were altered (in 42% partial, and in 16% complete disconnection of tight junctions were found). This contrasted the control group, where only 14% of tight junctions were disconnected (12% partially and 2% completely). Our results are consistent with a role for intercellular Ca2+ in maintaining structural integrity of cerebral tight junctions.

Electron-microscopic immunohistochemical study of the localization of immunoglobulin G in the choroid plexus of the rat

The localization of autologous antiperoxidase immunoglobulin G (IgG) was studied in the choroid plexus of Lewis rats immunized against horseradish peroxidase (HRP). This experiment was performed to study the permeability of the choroid plexus to intravascular IgG. It was shown that autologous IgG was present in the extravascular spaces. The transendothelial transfer appeared to occur mainly via the fenestrations and some interendothelial junctions. No transfer of IgG at the level of epithelial cells toward the cerebrospinal fluid was demonstrated. Interstitial spaces in contact with the connective-tissue cells of the choroid stroma were strongly labeled. The significance of these spaces remains hypothetical and raises the question of the fate of IgG from the interstitial space.

Effects of extracellular calcium depletion on membrane topography and occluding junctions of mammary epithelial cells in culture

Ca2+ dependence of occluding junction structure and permeability, well documented in explanted or cultured epithelial sheets, presumably reflects inherent control mechanisms. As an approach to identification of these mechanisms, we induced disassembly of zonulae occludentes in confluent monolayers of mouse mammary epithelial cells by exposure to low concentrations of the chelators, EGTA or sodium citrate. Stages in disassembly were monitored during treatment by phase-contrast microscopy and prepared for transmission and scanning electron microscopy. Cellular response included several events affecting occluding junctions: (a) Centripetal cytoplasmic contraction created tension on junction membranes and displaced intramembrane strands along lines determined by the axis of tension. (b) Destabilization of junction position, probably through increased membrane fluidity, augmented tension-induced movement of strands, resulting in fragmentation of the junction belt. (c) Active ruffling and retraction of freed peripheral membranes remodeled cell borders to produce many filopodia, distally attached by occluding-junction fragments to neighboring cell membranes. Filopodia generally persisted until mechanically ruptured, when endocytosis of the junction and adhering cytoplasmic bleb ensued. Junction disassembly thus resulted from mechanical tensions generated by initial centripetal contraction and subsequent peripheral cytoskeletal activity, combined with destabilization of the junction's intramembrane strand pattern.

A survey of the effects of loop diuretics on the zonulae occludentes of the perilymph-endolymph barrier by freeze fracture

The acute (30 min) effects of the loop diuretics piretanide, ethacrynic acid, bumetanide, furosemide, and azosemide, and the chronic (8 days) effects of furosemide and bumetanide on the zonulae occludentes (tight junctions) of the perilymph-endolymph barrier in the stria vascularis and in Reissner's membrane of the basal cochlear turns were studied by freeze-fracture. Quantitative analysis of their effects indicated that the structural integrity of the barrier was modified by either as increase or a decrease in the number, depth, and density of the strands of the tight junctions of the strial marginal cells. Only azosemide appeared to modify the tight junctions between the epithelial cells of Reissner's membrane, but it had little effect on the strial junctions. The tight junctions between the basal cells of the stria appeared to be the least affected by the various loop diuretics, although piretanide appeared to increase randomly the intercellular spaces lying between the strands.

Tissue connections in a transplantable virus-producing sebaceous adenoma of the mouse. II. A freeze-fracture study in conjunction with filipin

The distribution, size, and configuration of intercellular junctions in the sebaceous tumor of mice were examined using the freeze-fracture technique. Three types of junctions were observed: desmosomes, gap, and tight junctions. Tight junctions in general consisted of short linear unbranched fibrils, and macular or complex tight junctional patterns were present only occasionally. Gap junctions ranged from small sports of 0.9 x 10(-3) micrometer2 to areas of approximately 0.46 micrometers2. Desmosomes were the most frequent junctional specializations, and it is concluded that they are at least partially responsible for this tumor not being metastatic. Filipin in conjunction with freeze-fracture showed filipin-sterol complexes on the plasma membrane, the nuclear envelope, and the membranes of the endoplasmic reticulum and mitochondria. The intercellular junctions were devoid of these complexes indicating that these regions are low in cholesterol.

Thin section and freeze-fracture studies of hexachlorophene induced alterations in the rat liver with special regard to intercellular junctions

The ultrastructural changes in the liver cells of male Wistar rats induced by the oral and intraperitoneal application of hexachlorophene (HCP) were studied by using the freeze-fracture technique and by producing ultrathin sections. The rats were given the HCP once at a dose of 30 mg/kg body weight and were sacrificed 60 hours after treatment. The enlargement of bile canaliculi, the disorganization of tight junctions and the increase in number of gap junctions were the most prominent alterations observed in the liver cells. Furthermore, an increase in the smooth and rough endoplasmic reticulum and the microbodies were found. Pathological alterations in the mitochondria were also seen. In general, the effects of the intraperitoneal application on the liver were more pronounced than the effects of the oral application.