Biomedical subjects

T Gotow

Publications and source records attributed to T Gotow.

At least 55 records · Page 3Linked to original sources

PubMed1989

Photoresponses of an extraocular photoreceptor associated with a decrease in membrane conductance in an opisthobranch mollusc.

The photoresponse of an extraocular photoreceptor, the photoresponsive neuron (A-P-1) in the abdominal ganglion of Onchidium verruculatum, was studied by using a voltage-clamp with two micropipettes and a monochromatic light. When the A-P-1 was voltage-clamped at resting membrane potential levels, light induced a slowly developing inward current which peaked at about 20 s. A decrease in membrane conductance accompanied this light-induced current which corresponded to the depolarizing photoreceptor potential in the unclamped A-P-1. The relationship between the peak of the current response and light intensity could be predicted by using the modified Michaelis-Menten equation. The spectral sensitivity for the photoresponse had a peak at 490 nm. The steady-state light-induced current was a non-linear function of the membrane potential. The current-voltage relationship for the instantaneous light-induced current was almost linear. In normal (10 mM K+) saline, the polarity of the instantaneous light current reversed from inward to outward at about -67 mV, and doubling the external K+ from 10 to 20 mM shifted the reversal potential to about-50 mV, similar to that predicted by a K+-electrode. These results suggest that the light-induced current or the depolarizing receptor potential of A-P-1 is due to the light suppression of a voltage- and time-dependent K+ current.

Animals↗

PubMed1989

Orthogonal arrays of particles in plasma membranes of Müller cells in the guinea pig retina.

Plasma membranes of guinea pig Müller cells were examined with a freeze-fracture technique to see how orthogonal arrays are distributed in the avascular retina. Examination of the portion approximately intermediate between the optic disc and equator of the eyeball showed that all end-feet of Müller cells were provided with arrays. Orthogonal arrays were concentrated on vitreal end-foot membranes, i.e., membranes that were covered by the basal lamina and contacted the vitreous body, called vitreal membranes here. The arrays were rarely observed in the portions of end-feet that did not contact the vitreous body, called lateral membranes. The distribution density of arrays in the vitreal membranes was 122.5 +/- 45.3/microns2, which was over 10 times higher than that (9.6 +/- 9.6/microns2) in the lateral membranes. The arrays became numerous and extended in shape at the periphery of the vitreal membrane, characteristically aligned in rows at the border where vitreal met lateral membrane, but never intruded into the domain of lateral membrane. Some arrays were composed of loosely attached particles and/or rod-like profiles. Sometimes rod-like profiles, 9-13 nm wide and 20-50 nm long, called linear structures here, were isolated, and sometimes they appeared in rows. Ordinary intramembrane particles (IMPs) were significantly smaller and less numerous in vitreal than in lateral membranes. IMPs larger than 9 nm in diameter were significantly fewer in the vitreal membranes, which suggests that they have been consumed to form the arrays. Although the distribution of orthogonal arrays is similar to that of K+ channels (Newman: J. Neurosci., 7:2423-2432, 1987), we consider the array an unlikely candidate for the ion channel, because its subunit particles do not protrude onto either the inner or outer surface of the membrane (Gotow and Hashimoto: J. Neurocytol., 17:399-413, 1988). Judging from their unique alignment in rows where the membrane is bent and vitreal and lateral membranes meet, the arrays may contribute to some membrane stability, resisting the physical tension at the interface with mesenchymal tissue.

Animals↗

PubMed1989

Substructure of cisternal organelles of neuronal perikarya in immature rat brains revealed by quick-freeze and deep-etch techniques.

Membrane-bounded organelles possessing cisternae, i.e., rough endoplasmic reticulum and Golgi apparatus, in immature rat central neurons were examined by quick-freeze and deep-etch techniques to see how their intracisternal structures are organized and how ribosomes are associated with the membrane of the endoplasmic reticulum. Cisternae of endoplasmic reticulum, 60-100 nm wide, were bridged with randomly-distributed strands (trabecular strands, 12.5 nm in mean diameter). Luminal surfaces of cisternae of the endoplasmic reticulum were decorated with various-sized globular particles, some as small as intramembrane particles, and others as large as granules formed by soluble proteins seen in the cytoplasm. A closer examination revealed much thinner strands (3.3 nm in mean diameter). Such thin strands were short, usually winding toward the luminal surface, and sometimes touching the luminal surface with one end. Ribosomes appeared to be embedded into the entire thickness of cross-fractured membranes of endoplasmic reticulum, that is, their internal portions appeared to be situated at almost the same level as the cisternal luminal surface. From the internal portion of ribosomes, single thin strands occasionally protruded into the lumen, suggesting that these thin strands were newly synthesized polypeptides. A horizontal separation within ribosomes appeared to occur at the same level as the hydrophobic middle of the membrane of the endoplasmic reticulum. Interiors of the Golgi apparatus cisternae, which were much narrower than cisternae of endoplasmic reticulum, were similarly bridged with trabecular strands, but the Golgi trabecular strands were thinner and more frequent. Their cisternal lumina were also dotted with globular particles. No identifiable profiles corresponding to the thin strands in the endoplasmic reticulum were observed. Golgi cisternae showed a heterogeneous distribution of membrane granularity; the membrane in narrow cisternal space was granule-rich, while that in expanded space was granule-poor, suggesting a functional compartmentalization of the Golgi cisternae.

Animals↗

PubMed1989

Developmental alterations in membrane organization of rat subpial astrocytes.

Subpial astrocytic processes were examined in developing rats, mainly with complementary replicas, to see how orthogonal arrays of particles (OAs) are formed and become numerous in membranes covered by basal lamina. Only a few (4.2%) endfeet in the membranes contacting the basal lamina (subpial membranes) had acquired OAs by the 19-day foetal stage. The number of endfeet provided with OAs increased drastically in the prenatal period, continued to increase at birth (P0), and somewhat more slowly in the early postnatal period (P0-P3), reaching 100% at P10. There were neuronal processes as well abutting on the basal lamina at the pial surface but they were easy to distinguish from astrocytic endfeet because of their larger intramembrane particles (IMPs), which are sparsely distributed and in patch-like aggregations. The distribution density of OAs in differentiated astrocytic endfeet also increased very gradually with age until P0, a little faster in the early postnatal period, and drastically from P10 to adult. Ordinary globular IMPs increased in number with age and continued to increase in the lateral membrane where OAs were still very few, though less rapidly in the subpial membrane as OAs became numerous. With maturation, larger IMPs became conspicuous in the lateral membrane but not in the subpial, suggesting that larger IMPs were predominantly used to form OAs. We have proposed the idea that relatively large IMPs line up to form single linear arrays (SLs), appearing as grooves on the E face, and that occasionally some SLs line up in multiple rows [multiple linear arrays (MLs)] and that SLs or MLs fuse with one another to become rod-like strands, then divide into squares to become OAs. SLs and MLs appeared ontogenetically earlier than OAs, and continued to appear in membranes provided with OAs. In areas where membranes were bent, transition of these three structures was observable and the proportion of OAs increased with age. Further, in such areas, alignment of OAs was different according to membrane curvature: concentric in and around protrusions, perpendicular to the edge of invaginations. This unique association of OA alignment with membrane curvature suggests that OAs contribute to some membrane stability in the area covered by the basal lamina and provide the membrane with special resistance to bending.

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PubMed1988

Deep-etch structure of astrocytes at the superficial glia limitans, with special emphasis on the internal and external organization of their plasma membranes.

The cytoskeletal system in rat subpial astrocytes and the relationship between astrocytic plasma membrane and basal lamina or cytoplasmic components were examined with a quick-freeze deep-etch technique, mainly using chemically fixed tissues. Attention was focused on the way intramembrane particles (IMPs), particularly orthogonal arrays, are organized in the membranes and related to extramembrane components. The basal lamina was composed of a sheet-like network of strands (4-9 nm thick), some, which we have called 'trabecular' strands, extending through the lamina lucida to touch the astrocytic membrane at irregular intervals. The trabecular strands usually formed a bulbous structure where they touched the membrane, but sometimes appeared to intrude directly into the external lipid layer. The orthogonal arrays did not extend to the outer true surface, and no special structure was detectable in association with them. Small spherical protrusions (7-9 nm in diameter), related to neither the trabecular strands nor the arrays, were observed in the outer surface. Judging from their size and distribution, these are probably tops of tall globular IMPs. In the inner or cytoplasmic true surface, protrusions were relatively numerous; some were large, 15-20 nm in diameter, while others were small (8-10 nm). Some of the small protrusions were identified as transmembrane components. Although protrusions were more conspicuous in the inner than in the outer surface, none of them provided images related or similar to the orthogonal arrays. Some protrusions in the inner surface were connected with thin (4-5 nm) or thick (approximately 10 nm) filaments constituting the underlying network. The thin filaments were also anchored to the intermediate filaments which lay parallel with the astrocytic membranes. In the cytoplasm, the intermediate filaments were firmly packed to form bundles. Because the orthogonal arrays are probably embedded within the astrocytic membrane, they may not serve as a transmembrane channel but rather contribute to some stabilizing function for the membrane.

Aging↗

PubMed1987

Postnatal development of the inferior olivary complex in the rat: IV. Synaptogenesis of GABAergic afferents, analyzed by glutamic acid decarboxylase immunocytochemistry.

The postnatal maturation of the GABAergic innervation of the rat inferior olive was studied with an antiserum to glutamic acid decarboxylase (GAD), the GABA-synthesizing enzyme. GAD-positive axons were present at a very low density in the periolivary and interlamellar regions of newborn rats, as well as in certain precise areas of the lamellae, at the mediodorsal limit. The immature distribution indicates that the GABAergic projections reach the inferior olive shortly before birth and that the greater part of synaptogenesis and the establishment of the adult organization occurs postnatally. Light and electron microscopic analyses disclosed that the maturation of this system of olivary afferents passes through three well-defined stages: (1) During the first, or immature stage (from PO to P5), GAD immunoreactivity is not confined to axon terminals, as in adult rats. The labeled fibers penetrate progressively into the periphery of the lamellae and reach their centers in an irregular manner by the end of the immature stage. This staggered invasion of the lamellae accentuates intraregional olivary differences and begins to take the adult configuration. As fiber penetration advances, the density of labeled axons establishing synaptic contacts increases, while the number of completely immunostained fibers decreases. This distribution prevails until the end of the immature stage and suggests that the GABAergic afferent projections remain in a "waiting compartment" from their prenatal arrival until the moment they invade the olivary parenchyma. (2). The second stage is designated as an intermediate stage of maturation and lasts from P7 to P10. During this period, GAD axoplasmic compartmentation occurs, and henceforth only axon terminals exhibit GAD immunoreactivity. Concomitantly, intraregional differences in the pattern of innervation become more marked, because of the continuing irregular distribution of the growing labeled axons. This intermediate maturational stage is also characterized by a rapid increase in labeled axon terminals bearing synaptic complexes and by the formation of complex synaptic arrangements, the protoglomeruli. From the beginning of protoglomeruli formation, GAD-positive axon terminals are one of their constituents, and they are systematically localized at the periphery of the incipient dendritic protrusions. (3) The final stage of maturation takes place from P10 to P15. During this stage, the adultlike pattern of GABAergic innervation of the inferior olive is attained. Toward P15, intraregional differences in GAD immunoreactivity are similar to those of the adult rat.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1986

Localization of glutamic-acid-decarboxylase-immunoreactive axon terminals in the inferior olive of the rat, with special emphasis on anatomical relations between GABAergic synapses and dendrodendritic gap junctions.

Immunocytochemical and electron microscopic methods were used to examine the GABAergic innervation of the inferior olivary nucleus in adult rats. This neuronal system was visualized with an antibody against glutamic acid decarboxylase (GAD, EC 4.1.1.15), the GABA-synthesizing enzyme. A GAD-positive reaction product was encountered only in short segments of preterminal axons and in axon terminals. Their relative number per unit area of neuropil was very similar in all olivary subnuclei. Despite this homogeneity in density, obvious intraregional differences existed. Some regions were strongly immunoreactive (the "c" subgroup, the beta nucleus, and the mediolateral outgrowth of the medial accessory olive), whereas others were weakly labeled (the dorsomedial cell column and the central zones of the medial accessory and principal olives). The strongly immunoreactive areas contained the largest and most intensively labeled axon terminals. Areas of weak labeling were filled with small, weakly immunoreactive nerve terminals. Thus, variations in size and in intensity of labeling create a specific pattern of GABA innervation, revealed by an almost continuous gradient between the above-mentioned extremes. The GAD-positive axon terminals established conventional synapses with dendrites (94% of the samples) or with cell bodies (6%). The vast majority of these synapses were type II (84%) and only a small proportion formed type I synaptic contacts (16%), regardless of the nature of the postsynaptic element. Immunoreactive terminals were also involved in the complex synaptic arrangements--the glomeruli, which characterize the olivary neuropil. Within these formations, olivary neurons were electrotonically coupled through dendrodendritic gap junctions. There was a constant association between GAD-positive axon terminals and small dendritic appendages linked by gap junctions. This association was revealed not only by the systematic presence of immunolabeled terminals directly apposed to the dendritic appendages but, more importantly, by the frequent presence of type II synapses straddling both elements. These synapses were in close proximity to the low-resistance pathways represented by the gap junctions. The strategic location of these GABA synapses is discussed in relation to recent findings indicating the possibility of a synaptic modulation of the electrical coupling: the release of GABA, by increasing nonjunctional membrane conductance, could shunt the coupling between olivary neurons. The functional decoupling of selected gap junctions would be responsible for the spatial organization of the olivary electrotonic coupling.

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PubMed1985

Characterization of long-lasting histaminergic inhibition in a beating pacemaker neuron of Onchidium.

A single BPSP (excitatory-inhibitory postsynaptic potential) was monosynaptically produced in an identified Onchidium neuron, Be-1, with a beating rhythm upon stimulation of the cardiac nerve. The BPSPs summated to produce an inhibition of long duration (ILD) upon blockage of the beating rhythm after repeated stimulation, so that the BPSPs seemed to be functionally inhibitory. Ten stimuli (1-2 Hz) applied to the cardiac nerve usually evoked an ILD (0.5-1 min) of about 10 mV. The early and middle phases of this ILD reversed near -80 to -85 mV, but the late phase did not reverse at more negative potentials. None of the phases was significantly affected by low Cl or Na solutions or by high Ca solutions. However, by changing the external K, the shift of the reversal potentials for the early and middle phases reached about 65% of that predicted for the K electrode, although the late phase was insensitive to the external K. Intracellular tetraethylammonium (TEA) attenuated the amplitude of the ILD but did not shorten the duration. These suggest that the ILD has another conductance-independent mechanism simultaneously with the increase in K conductance. Several lines of evidence suggested that a ouabain-sensitive Na pump does not contribute to the ILD. Inhibitors of energy supply, 2,4-dinitrophenol sodium salt (DNP) and cyanide, selectively and reversibly reduced the ILD. Simultaneous applications of intracellular TEA and DNP completely abolished the ILD. As for the ionic basis, the histamine-induced inhibitory response in Be-1 was closely related to the ILD. Cimetidine specifically blocked the ILD and histamine-induced inhibitory response, which were mimicked by 2-methylhistamine, but not by dimaprit. It is concluded that the ILD, mediated by some histamine receptor other than the H1 or H2 type, results from an increase in K conductance and a hyperpolarizing ion pump insensitive to ouabain.

Animals↗

PubMed1985

Distribution patterns of orthogonal arrays and alkaline phosphatase in plasma membranes of satellite cells in rat spinal ganglia.

The plasmalemmal structure of satellite cells in the lumbar spinal ganglia of rat was examined by freeze-fracture and by a cytochemical method for the demonstration of alkaline phosphatase activity. Plasma membranes of satellite cells are the only ones in the ganglia to contain, in addition to globular intramembrane particles, orthogonal arrays of particles 6-7 nm in diameter. The arrays are most concentrated in the portions of the membranes contacting the basal lamina, or outer membranes; they decrease considerably in number in lateral membranes, and are rare in the membrane regions adjacent to the neuronal perikaryon, or inner membranes. Such gradual decrease in array density in satellite cells suggests regional differences of plasma membrane properties within the same cell. Alkaline phosphatase, which was chosen as a cytochemical marker for membrane activity because of its relation to transport function, localizes to inner and lateral membranes, and not to outer membranes of satellite cells. The absence of correlation between localization of orthogonal arrays and such enzymatic activity suggests that the membranes provided with many arrays possess some characteristics different from other membranes that may exclude transport activity. The possible significance of orthogonal arrays and their close association with the basal lamina are discussed.

Alkaline Phosphatase↗

PubMed1985

Visualization of the cerebrospinal fluid drainage into the Galen's vein.

Arachnoid granulations are not always present in lower mammals and primate newborns. In order to visualize the route for the cerebrospinal fluid (CSF) to drain into the venous system, horseradish peroxidase (HRP) was injected into the lateral ventricle or cisterna cerebellomedullaris of the mouse and rat. From 30 to 60 min after the commencing of a slow infusion for 15-30 min of 0.05-0.1 ml solution containing 10-20 mg HRP, the mouse, whose skull had been exposed, was dropped into cold acetone at dry ice temperature; other animals were fixed by perfusion with aldehyde solution. The frozen head was dissected in a cryostat kept at -18 degrees C to remove the skull, but leave the dura mater and the falx cerebri. The brain with meninges was cut into 30-45 microns sagittal sections in the cryostat, and processed for peroxidase reaction. The perfusion-fixed brains were used for scanning electron microscopy and for electron microscope observation of the tracer. The reaction product was found within fenestrated venous capillaries of the choroid plexus. The route for the HRP in the CSF to drain into the sinus rectus via the vena choroidea and vena cerebri magna was directly visualized in the mouse.

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PubMed1984

Cytochemical characteristics of astrocytic plasma membranes specialized with numerous orthogonal arrays.

Astrocytic membranes contacting the basal lamina are found to be less affected by filipin than subjacent lateral membranes. An abrupt change in density of lesions induced by filipin creates a border between subpial and lateral membranes at the glia limitans. This means that orthogonal array-crowded membranes may contain relatively less cholesterol than other astrocytic membrane domains. Another possible explanation for filipin resistance is also considered in relation to aggregated intramembrane particles of orthogonal arrays and/or membrane-associated filamentous elements including the basal lamina. The polygonal particle junction between astrocytic processes located just below the subpial membrane is strongly resistant to the action of filipin. Both membrane-associated enzymes, i.e. alkaline phosphatase (AlkPase) and Na+,K+-ATPase are commonly detected only in perivascular astrocytic membranes, and not in subpial membranes, suggesting a regional differentiation in function of astrocytic membranes. There are variations in the reactive deposits particularly of those for Na+,K+-ATPase. It is apparent that the distribution polarity of orthogonal arrays is not connected with that of either AlkPase or Na+,K+-ATPase. Judging from the relative resistance to filipin, however, astrocytes throughout the C.N.S., having domains specialized with orthogonal arrays, may possess a unique stabilizing mechanism for their own membranes contacting the basal lamina.

Alkaline Phosphatase↗

PubMed1984

Plasma membrane organization of astrocytes in elasmobranchs with special reference to the brain barrier system.

The structural machinery contributing to the blood-brain barrier in elasmobranchs has been examined mainly using freeze-fracture techniques. Capillary endothelial cells, which show local aggregations of pinocytotic vesicles and infrequent fenestrations, are connected by poorly developed tight junctions. Astrocytic processes investing the capillary are linked by well-developed tight junctions between lateral membranes immediately beneath the perivascular space. The tight junctions consist of continuous strands of multiple layers coursing circumferentially around the astrocytic processes parallel to one another as well as to the perivascular space. The presence of intramembrane particles (IMPs) within E-face grooves may result in discontinuities in IMP rows on the P-face. Thus, in compensation for the capillary endothelium, perivascular astrocytes constitute the morphological site of the blood-brain barrier in elasmobranchs. Continuous strands of tight junctions are also detected between astrocytic processes forming the glia limitans at the brain surface. These may act as a barrier between meningeal connective tissue and brain parenchyma. Astrocytic membranes have numerous IMPs of 8-9 nm in diameter on their P-faces. These IMPs are uniformly distributed so that astrocytic membranes are easily distinguished from neuronal membranes even in the neuropil. Ependymal cells also have numerous IMPs in all their membrane domains. Orthogonal arrays are not detected in either astrocytic or ependymal plasma membranes.

Animals↗

PubMed1984

Modulation of the histaminergic inhibitory synaptic potential in the Onchidium neuron by cyclic nucleotides.

In the identified molluscan neuron, the presynaptic stimulation evokes a histaminergic inhibition of long duration (HILD), resulting from an increase in K conductance followed by a conductance-independent hyperpolarizing process. The latter component of HILD was enhanced by cyclic AMP but depressed by cyclic GMP. However, neither agent alone altered the resting membrane potential nor the conductance.

Animals↗

PubMed1983

Regional difference in effect of filipin in plasma membranes of epithelial cells and surrounding free cells in the choroid plexus.

Epithelial cells and surrounding free cells in the choroid plexus were examined cytochemically using filipin to clarify the distribution pattern of cholesterol within plasma membranes. The apical and basal membranes of the choroid epithelial cell are less susceptible to filipin than the lateral epithelial membrane and plasma membranes of adjacent mesenchymal cells such as macrophages and fibroblasts. Apical and basal domains of the epithelial membranes, which are relatively resistant to action of filipin, appear to have a slightly lower cholesterol content. We suggest that the apical and basal membranes may possess a unique membrane fluidity or stability that differs from that of the lateral epithelial, macrophage or fibroblast membranes.

Animals↗

PubMed1983

Filipin resistance in intermediate junction membranes of guinea pig ependyma: possible relationship to filamentous underlying.

Plasma membranes in intermediate junctions of ependymal cells are found to show considerable resistance to the antibiotic filipin, suggesting low cholesterol in these membranes. Further, ependymal cells were treated with cytochalasin B (CB) infused into the cerebral ventricle in vivo, and then incubated with filipin. When treated with CB, intermediate junctions show a decrease in their underlying density, mainly composed of microfilaments, and their membranes are found to be more affected by filipin. This reduction of resistance to the antibiotic is clearly demonstrated by thin-section and freeze-fracture as well as quantitative analysis. Nonjunctional lateral membranes, however, show no significant difference in the degree of filipin effect whether treated with CB or not. Although biochemical data on lipid composition have not been available for the intermediate junction membranes, we bring forward a possibility that resistance to filipin in these membranes may come not from less cholesterol but from morphological membrane stability brought about by the filamentous underlying.

Animals↗

PubMed1982

Modulation of the histamine-induced inhibitory response in an identified Onchidium neuron by cyclic nucleotides.

Intrinsic beating activity in the identified molluscan neuron Be-1 can be inhibited for a relatively long time by a short application of histamine. Cyclic AMP enhanced both the amplitude and duration of this inhibitory histamine response (H2-response), while cyclic GMP depressed the H2-response. However, when only these nucleotides were applied, they produced no significant, change in the beating spike activity.

Animals↗

PubMed1982

Intercellular junctions between specialized ependymal cells in the subcommissural organ of the rat.

The permeability of intercellular junctions in specialized ependymal cells in the rat subcommissural organ (SCO) has been studied ultrastructurally by freeze-fracturing and tracer experiments with horseradish peroxidase (HRP). In addition to normal smooth membrane, areas which could be classified as a leaky tight junction are found within the ependymal junctional region. This consists of only one or two relatively continuous strands but with interruptions in the apical portion. Some strands are perpendicular to the apical membrane surface and often form hairpin-like bends in the basal portion of the junction. The junctional region also shows areas with no strands but only a rippled membrane structure which may be equivalent to very close appositions without fusion of adjacent ependymal cell membranes. The relative proportions of normal smooth membrane, strands and rippled structure in the junctional region is approximately 3:4:6 including two parts overlapping of the strands and rippled structure. Intraventricularly infused HRP passes through many junctions but is occasionally stopped, leaving unstained intercellular spaces of various lengths between membrane fusions of tight junctions. Even when it is stopped, the intercellular space below the junction is densely stained by the enzyme. Orthogonal arrays of intramembrane particles are found to be distributed on the basal and lateral cell membranes below the junctional region in the SCO ependyma.

Animals↗

PubMed1982

Fine structural studies on ependymal paracellular and capillary transcellular permeability in the subcommissural organ of the guinea pig.

Morphological investigations on the permeability of intercellular junctions between ependymal cells and between capillary endothelial cells in the subcommissural organ (SCO) of the guinea pig have been carried out using freeze-fracturing and tracer experiments with horseradish peroxidase (HRP). The ependymal junction reveals a moderately developed network of tight junctional strands surrounding the tall ependymal cell. The apical portion of this junctional network tends to form nearly complete strands, whereas the basal portion usually shows irregular, fragmented strands often arranged in hairpin-like structures. The passage of intraventricularly infused HRP is blocked, leaving unstained areas, at the level of membrane fusions. At the same time the lateral intercellular space below the junction is densely stained, probably due to invasion from the basal side through adjacent ordinary ependymal junctions. The SCO capillary endothelium shows a high distribution density of pinocytotic vesicles. Vesicular transport of intravascularly injected HRP is observed, but no HRP penetration occurs through the endothelial junction. The active participation of vesicles in tracer movement is shown in preparations fixed before administration of HRP. Extravasation of this tracer is indicated to some degree in the SCO capillary, but permeability here appears to be comparable to that of ordinary brain capillaries. Accordingly, the SCO ependymal tight junction seems to form an effective barrier not to blood plasma or similar materials but to apically secreted substances, preventing them from spreading back into SCO intercellular spaces.

Animals↗