New ultrastructural evidence for a protein transport system in endothelial cells of gerbil brains

Animal models of cerebral arterial gas embolism

Cerebral arterial gas embolism is a dreaded complication of diving and invasive medical procedures. Many different animal models have been used in research on cerebral arterial gas embolism. This review provides an overview of the most important characteristics of these animal models. The properties discussed are species, cerebrovascular anatomy, method of air embolization, amount of air, bubble size, outcome parameters, anesthesia, blood glucose, body temperature and blood pressure.

Emboli formation rather than inflammatory mediators are responsible for increased cerebral water content after conventional and assisted beating-heart myocardial revascularization in a porcine model

BACKGROUND AND PURPOSE

Emboli and proinflammatory mediators are suspected of generating cerebral edema after coronary surgery. In contrast to cardiopulmonary bypass (CPB), off-pump coronary artery bypass surgery (OPCAB) reduces microemboli count and proinflammatory mediator release but carries the risk of hemodynamic instability. A microaxial blood pump can augment cardiac output.

METHODS

Coronary bypasses were constructed in pigs with CPB and cardioplegia (n=9), OPCAB (n=9), or blood-pump support CAB (n=9). Nine animals underwent sham operation. Embolus count was monitored and regional cerebral blood flow was assessed with microspheres in 21 brain specimens per animal (n=189 per group). Interleukins 6 and 8 and tumor necrosis factor-alpha concentrations were determined. These variables were studied before, during, and for 4 hours after surgery. Finally, cerebral water content was determined.

RESULTS

During CPB and blood-pump CAB, a significant number of emboli were counted in contrast to OPCAB and controls (P<0.05). During CPB, regional cerebral blood flow was affected (32 of 189) and showed reactive hyperemia except in 10 specimens after aortic cross-clamp release. This impairment persisted in 20 specimens. During and after OPCAB, regional cerebral blood flow remained nearly unchanged but showed low flow during (58 of 189) and after (35 of 189) the blood-pump run. A significant increase in proinflammatory mediators was observed only in the CPB group. CPB and blood-pump CAB significantly increased cerebral water content (P<0.05). A strong correlation between embolic load and cerebral water content was observed in all groups. No correlation between proinflammatory mediator release and cerebral water content was detected.

CONCLUSIONS

Emboli formation rather than inflammatory mediators are responsible for increased cerebral water content after conventional and assisted beating-heart myocardial revascularization.

Lonomia obliqua caterpillar venom increases permeability of the blood-brain barrier in rats

Human envenoming by caterpillars of the saturniid moth Lonomia obliqua in southern Brazil produces a mild local response (erythema, some edema, and pain) and systemic effects that include incoagulable blood, renal failure and in severe accidents intracerebral hemorrhage. In this work, we used light and electron microscopy to investigate the morphological alterations in the brain and blood-brain barrier of rats injected intravenously with venom from L. obliqua spicules (200 microg/kg). Five semi-purified fractions of venom (200 microg/kg each) were also assayed. Quantitative morphological and ultrastructural analyses were done 6, 18, 24 and 72 h after the i.v. injection of venom and its fractions. Light microscopy showed that 6h after envenoming there was cerebellar edema, which decreased by 72 h. Intracerebral hemorrhage occurred in only one rat 24h after the injection of venom. Blood-brain barrier (BBB) breakdown, assessed by transmission electron microscopy based on the passage of an extracellular tracer (lanthanum nitrate) between brain capillary endothelial cells, was observed in the cerebellum and hippocampus 18 h after venom injection. At this time, the cerebellum was more sensitive to the venom than the hippocampus, as shown by the greater number of leaky vessels. The number of capillaries showing breakdown was lower after 72 h than after 18 h. None of the semi-purified fractions significantly increased the number of leaky vessels. These results indicate that L. obliqua caterpillar venom has a deleterious action on the rat BBB. The lack of effect of the venom fractions when administered alone suggested that a synergistic action of venom components may be responsible for the damage seen in the central nervous system, but this was not confirmed when three combinations of the fractions were tested.

Morphological and cytochemical aspects of capillary permeability

Transport of plasma soluble constituents across the capillary wall is of primordial importance in cardiovascular physiology. While physiological experiments have concluded with the existence of two sets of pores, a large one responsible for the transport of proteins and a small one designed for the diffusion of small solutes, the morphological counterparts have yet to get general agreement. In this review, we present the different proposed paths within and between the endothelial cells that do allow passage of plasma constituents and may respond to the definitions established by physiological means. The vesicular system existing in endothelial cells has been the first transendothelial path to be proposed. Several data have demonstrated the involvement of this system in transport, although others have systematically brought controversy. One alternative to the vesicles has been the demonstration of membrane-bound tubules creating, in certain cases, transendothelial channels that would allow diffusion of plasma proteins and other constituents across the capillary wall. Access to this tubulo-vesicular system could be restrained by the stomatal diaphragm and facilitated by specific membrane receptors. Further, we have demonstrated for the first time with morpho-cytochemical tools, that the intercellular clefts are the site of diffusion for small molecules such as peptides having a molecular weight inferior to 3,000. For the fenestrated capillary bed, we have shown that fenestrae are the site through which plasma constituents cross the capillary wall. However, and in spite of the existence of these large open pores, the endothelial cells still display the tubulo-vesicular system involved in transport of large molecules and their intercellular clefts are also the site of diffusion of small molecules. Making consensus on the existence of an intracellular tubulo-vesicular system in non-fenestrated capillaries, responsible for the transport of large molecules by the endothelial cells, and understanding the rational for the fenestrated capillary to have three paths for transport--the fenestrae, the tubulo-vesicular system, and the inter-endothelial clefts--require further investigation.

Blood-brain barrier damage in reperfusion following ischemia in the hippocampus of the Mongolian gerbil brain

Vascular permeability to intravenously injected horseradish peroxidase (HRP) was qualitatively examined in the hippocampus of ischemic Mongolian gerbil brains by light and electron microscopy. After 30 min of right common carotid artery occlusion followed by 90 min of reperfusion, the animal was perfused with a fixative and killed. Before the perfusion of the fixative, HRP was injected into the femoral vein. HRP was visualized with tetramethyl benzidine (TMB) and diamino-benzidine (DAB) for light and electron microscopy, respectively. Staining reaction with TMB for HRP appeared in medial or dorsal portions of the operated side of the hippocampus, especially around some vessels along the hippocampal fissure. Ultrastructural examination in the vessels along hippocampal fissure revealed that the endothelial cytoplasm contained HRP-filled vesicles or vacuoles in close proximity to the basal lamina, and seemed to be slightly electron-dense. Swollen pericytes, swollen astrocytic foot processes and perivascular cells with HRP-filled cytoplasm were also observed in that area. In this study, it was clearly demonstrated that intravascular macromolecules leaked transendothelially, through vessel walls in the hippocampal fissure, from the blood stream in the medial portions of the hippocampus during reperfusion following ischemia. These findings suggest that the blood-brain barrier in some vessels along the hippocampal fissure in the medial parts of the hippocampus is more vulnerable to ischemic insults than those in other brain areas.

Changes in local microvascular permeability and in the effect of intervention with 21-aminosteroid (Tirilazad) in a new experimental model of focal cortical injury in the rat

In a new, reproducible model of rodent focal cortical injury, we have shown that in the absence of early traumatic disruption of the microvasculature and subsequent hemorrhage, delayed perivascular protein leakage and polymorphonuclear leukocyte infiltration of the injured cortex occur. In this study we employed a sensitive quantitative autoradiographic technique (using alpha-aminoisobutyric acid as a tracer) to investigate the focal changes in microvascular permeability with time and to determine the effects of administration of a 21-aminosteroid (Tirilazad) initiated 5 min after induction of the cortical injury. At all time points studied, there was a significant increase in perilesional blood-brain barrier permeability in lesioned animals treated with vehicle, compared to shamoperated animals, with the most marked increase in blood-brain barrier permeability at 4 h postinjury (mean Ki +/- SE = 19.2 +/- 2.4/1000 min with cortical injury, 1.5 +/- 0.3/1000 min in shams) (mean volume +/- SE = 15.48 +/- 0.7 mm3). In animals with cortical injury treated with Tirilazad (10 mg/kg), there was a significant reduction in microvascular permeability at the site of injury (Ki = 3.1 +/- 0.5, p < 0.001) and a significant reduction in volume of increased permeability (4.86 +/- 0.7 mm3, p < 0.01) at 4 h postinjury. In this model of cortical injury, a delayed increase in microvascular permeability occurs, which is significantly attenuated by postinjury treatment with Tirilazad.

Intercellular adhesion molecule-1 (ICAM-1) upregulation in human brain tumors as an expression of increased blood-brain barrier permeability

The distribution of intercellular adhesion molecule (ICAM-1) binding sites was studied in the microvasculature of several types of human brain tumor biopsies (angioma, glioblastoma multiforme and meningioma). Immunoelectron microscopy was performed with the application of immuno-HRP or -gold probes using a pre-embedding technique. Ultrastructural analysis demonstrated a pronounced ICAM-1 upregulation on the luminal EC and/or perivascular surfaces. Reaction product for ICAM-1 was observed associated with some but not all blood vessels of the tumors examined. The strongest reaction product was noted associated with the angioma cases with lesser expression observed on the glioblastoma multiforme and meningioma cases. The reaction product using immuno-HRP probe was observed most pronounced on the luminal endothelial cell surface and also within vesiculo-tubular structures. Concentrated immunosignals with gold label were often expressed on EC microvilli. These data suggest that several types of brain tumors are actively involved in the process of upregulating ICAM-1, presumably for tumor cell adhesion and trafficking, the process of angiogenesis or both. We suggest that the ICAM-1-positive vesiculo-tubular structures reflect specialized, targeted regions on the ECs for tumor cell adhesion and eventual trans-BBB passage. Further, our studies also provide evidence that adhesion molecules may be a useful tool for the study of blood-brain barrier injury.

Scanning and transmission electron microscopic studies of microvascular pathology in the osmotically impaired blood-brain barrier

The present investigation focused on the structural events occurring in endothelial cells lining the lumina of brain microvessels in rats subjected to a single intracarotid injection of hypertonic 1.8 M L (+) arabinose solution with or without intravenous injection of horseradish peroxidase. Blood vessels from cerebral cortex and thalamus were evaluated by transmission and scanning electron microscopy. After short-term exposure (10-12 min) there was widespread flooding of peroxidase into the brain neuropil of the ipsilateral hemisphere. Peroxidase tracer was frequently observed within vesiculo-tubular profiles, and occasionally within widened interendothelial junctional clefts. Partially fragmented, necrotic endothelial cells appeared to be in the process of desquamation. Individual endothelial cells appeared to be shrunken with widened interendothelial spaces. Some healthy endothelial cells appeared to be involved in repair processes, manifested by the extension of thin cellular processes towards the area of vessel injury. Other pathological alterations included a conspicuous increase in the number of endothelial cell microvilli, large crater-like invaginations of the endothelial plasma membranes and muscular blood vessels in the process of spasm. We also observed a platelet reaction with or without endothelial cell necrosis and attached microthrombi in some arterial segments.

Early blood-brain barrier changes in the rat following transient complete cerebral ischemia induced by cardiac arrest

This study examined regional patterns of increased vascular permeability following transient global cerebral ischemia. Rats underwent 3.5, 5 or 10 min of cardiac vessel bundle occlusion, i.e. cardiac arrest. The animals were killed at 2, 3, 5 and 15 min, or 1, 3, 6 and 24 h after global cerebral ischemia. Thirty minutes before the end of each blood recirculation period, the electron dense protein tracer--horseradish peroxidase (HRP) was intravenously injected and rats were perfusion-fixed for light and electron microscopic analysis. Control rats showed no HRP leakage. Post-ischemic rats demonstrated random blood-brain barrier (BBB) alterations. Permeability alterations were spotty and widespread in cortical, thalamic, basal ganglia, hippocampal, brain stem regions, cerebellum and white matter. Peroxidase extravasation frequently involved arterioles, veins and venules surrounded by perivascular spaces. Routes of increased HRP permeability included endothelial cell (EC) vesiculo-canalicular profiles and diffuse leakage through damaged ECs. Barrier damage determined by HRP permeability revealed a biphasic nature. The first stage appeared immediately after ischemia at the 2nd min and involved the 1st post-insult hour. There was no HRP leakage in rats sacrificed 3 h after insult. BBB opening appeared again 6 h after ischemia and remained open 24 h after cardiac arrest. The openings of BBB did not increase in frequency with longer periods of ischemia and recirculation. These results demonstrate that cardiac arrest produces a spotty BBB disturbances at vessel bifurcations and suggest that BBB changes associated with cardiac arrest may be multifactorial in time course and location.

Abnormalities of the blood-brain barrier in global cerebral ischemia in rats due to experimental cardiac arrest

The aim of the study was to characterize the impact of global cerebral ischemia resulting from cardiac arrest on the BBB permeability. Survival time of experimental animals after 3.5, 5 or 10 min ischemia range from 3.5-10 min to 24 h. Vascular permeability was evaluated with horseradish peroxidase (HRP). BBB disturbances were of biphasic nature. In the first phase, appearing immediately after ischemia and persisting till 1st postischemic hour, HRP extravasation involved mainly venous site of microcirculation and was limited to the cerebral and cerebellar cortex and the central periventricular structures. The second phase covering the period between 6 and 24 h after resuscitation was characterized by random HRP leakage in all the CNS structures. HRP penetrated through increased microvesicular and canalicular endothelial systems, through interendothelial junctions and via disintegrated endothelial cells. Distribution and perivenous localization of BBB changes in early phase suggests their connection with venostasis resulting from cardiac arrest. The second phase seems to be pathogenetically related with the consequences of the ischemic process.

Reassessment of a new model of complete cerebral ischemia in rats. Method of induction of clinical death, pathophysiology and cerebrovascular pathology

The present study was undertaken to ascertain the role of the microcirculation in the phenomenon of hypoperfusion following complete cerebral ischemia. The experiments were performed on rats under superficial ether anesthesia. Cerebral ischemia was induced by cardiac arrest for 3.5 or 10 min, with survival periods that lasted from 3 min to 7 days. A special metal hook-like device was inserted into the chest cavity at the third intercostal spaces for occluding the cardiac vessel bundle. The effect of this procedure was total cessation of systemic circulation, i.e., clinical death. In 52% of animals with 10-min clinical death, resuscitation (external heart massage and artificial ventilation) restored heart activity. When brain circulation was restored, respiratory activity, pain reaction, corneal reflex, bioelectric activity of the cortex, and normal activities of the rats returned. Scanning electron microscopy was applied to study the effect of ischemia on the vessel wall and endothelial cells (EC). Ischemia produced a remarkable increase in the numbers of microvilli and pit-like invaginations on the luminal EC surface. The luminal wall surface of many of the microvessels (MV) formed ridges. Frequently, microthrombi of varying sizes were observed. The most prominent changes were noted from 3 min to 6 h of recirculation, and they correlated with hypoperfusion after ischemia. Seven days later, these changes completely disappeared. The data presented here indicate that progressive hypoperfusion after ischemia occurs with significant alterations in the MV walls. These studies collectively suggest that the focal responses in select MVs may be associated with receptor molecule up-regulation of some, but not all, affected ECs. Our data provide further characterization of a new and unique chronic model of brain ischemia that can be applied to relevant clinical studies.

Ultrastructural changes in the blood-brain barrier after nimodipine treatment and induced hypertension

Fourty-four narcotized rats were split into two equal groups, one being treated with nimodipine and the other with a placebo. By use of norfenefrine the blood pressure was raised to values of 150 and 180 mm Hg within the limits of the autoregulation of brain perfusion and under continuous measurement. Fifteen minutes after application of the standard tracer, horseradish peroxidase, the animals were exsanguinated using a saline perfusion and then perfusion-fixed with Karnovsky's solution. After development of the peroxidase staining the brain sections were evaluated and then allocated to their respective groups. In brain tissues from the experimental group significantly more frequent perivascular accumulations of horseradish peroxidase reaction product were found (P less than 0.001). In electron micrographs it could be seen that the tight junctions were intact and that there was a neuroendothelial transport, with horseradish peroxidase-filled vesicles, in the endothelium, muscle cells, and brain parenchyma. These vesicles represent a medium of transport for all proteins of high molecular weight and can therefore result in brain edema. It is concluded that nimodipine damages the blood-brain barrier by disturbance of the autoregulation of the cerebral blood flow.

Mechanisms of inflammatory cell attachment in chronic relapsing experimental allergic encephalomyelitis: a scanning and high-voltage electron microscopic study of the injured mouse blood-brain barrier

Brain and spinal cord blood vessels from mice subjected to chronic relapsing experimental allergic encephalomyelitis were examined by scanning (SEM) and high-voltage electron microscopy (HVEM). SEM analysis of veins and venules from affected tissue regions demonstrated inflammatory cells (ICs), primarily lymphocytes or monocytes, attached to the luminal endothelial cell (EC) surface adjacent to the junctional complexes. In transverse section these cells were shown by HVEM to extend and to insert filopodia (lymphocytes) or flap-like lamellapodia (monocytes) into the luminal EC surfaces. Affected ECs often expressed increased microvillar projection as well as parajunctional crater-like structures on their luminal surfaces. Based on scanning and high-voltage electron microscopy, we present morphological evidence that some populations of sensitized ICs do not penetrate the EC junctions initially during EC attachment but instead insert pseudopodial projections into specialized openings in the ECs that are formed in response to chronic inflammation.

Delayed institution of hypertension during focal cerebral ischemia: effect on brain edema

The effect of induced hypertension instituted after a 2-h delay following middle cerebral artery occlusion (MCAO) on brain edema formation and histochemical injury was studied. Under isoflurane anesthesia, the MCA of 14 spontaneously hypertensive rats was occluded. In the control group (n = 7), the mean arterial pressure (MAP) was not manipulated. In the hypertensive group (n = 7), the MAP was elevated by 25-30 mm Hg beginning 2 h after MCAO. Four hours after MCAO, the rats were killed and the brains harvested. The brains were sectioned along coronal planes spanning the distribution of ischemia produced by MCAO. Specific gravity (SG) was determined in the subcortex and in two sites in the cortex (core and periphery of the ischemic territory). The extent of neuronal injury was determined by 2,3,5-triphenyltetrazolium staining. In the ischemic core, there was no difference in SG in the subcortex and cortex in the two groups. In the periphery of the ischemic territory, SG in the cortex was greater (less edema accumulation) in the hypertensive group (1.041 +/- 0.001 vs 1.039 +/- 0.001, P less than 0.05). The area of histochemical injury (as a percent of the cross-sectional area of the hemisphere) was less in the hypertensive group (33 +/- 3% vs 21 +/- 2%, P less than 0.05). The data indicate that phenylephrine-induced hypertension instituted 2 h after MCAO does not aggravate edema in the ischemic core, that it improves edema in the periphery of the ischemic territory, and that it reduces the area of histochemical neuronal dysfunction.

Structural and functional aspects of the interaction of inflammatory cells with the blood-brain barrier in experimental brain inflammation

Interaction between various subclasses of inflammatory cells (ICs) and endothelial cells (ECs) lining selective blood vessels of the mammalian blood-brain barrier (BBB) is an initial, important event during inflammatory conditions of the central nervous system (CNS). In this review, we will present a brief ultracytochemical and immunocytochemical assessment of our perspective on this intimate cellular interaction which has been described recently in conditions that involve immunological alterations of the BBB. We will discuss some morphological aspects of what is currently known about acute and chronic inflammatory BBB disorders that are involved in inflammatory processes. We will focus, in particular, on experimental allergic encephalomyelitis (EAE), an animal model for human multiple sclerosis (MS). Many of the past and more recent concepts found in the literature concerning IC attachment and diapedesis, as well as our own experimental efforts over more than two decades will be presented.

High voltage electron microscopic studies of endothelial cell tubular structures in the mouse blood-brain barrier following brain trauma

High-voltage electron microscopy was applied to the study of endothelial cell (EC) transport of macromolecules in a murine model of blood-brain barrier injury to study the role of the EC canalicular system following brain insult. Semithick sections from mouse brains subjected to acute (2-3 h) mechanical trauma demonstrated permeation of intravenously injected horseradish peroxidase via tubular structures either (a) in the absence of lysosome-associated structures in close proximity, or (b) in association with lysosomes, dense bodies or multivesicular bodies. Our data suggest a dual-purposed system of tubules, one portion that supplies the metabolic requirements of the cell and another portion, suggested to be more limited, that opens up as a result of brain injury.

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

Three purported means by which large solutes may penetrate the blood-brain barrier are: permeabilized tight junctions; vesicular transport; or channel formation across cerebral blood vessels. The role of vesicular transport has been questioned, in part, because many cytoplasmic vesicles are induced by aldehyde fixation. Cryofixation reduces this artefact and was used to see structural changes in frog cerebral endothelium made permeable to plasma solutes after perivascular exposure to hyperosmotic (3 M) urea, or injury with a cold probe (-50 degrees C). Some control and experimental frogs were made hypothermic so as to inhibit endocytosis and autolytic changes. The brains of some untreated controls were immerse-fixed in aldehydes. Other controls and all other brains of normothermic or hypothermic animals were rapidly frozen, then substituted with acetone-fixative. The interendothelial tight junctions separate partially or completely, after hyperosmotic exposure, in one third of the junctions. Blood-borne ferritin and Evans blue pass through some of the patent junctions. Junctional opening is caused by cell shrinkage, because the perimeter/area ratio of individual endothelial cells in the hyperosmotic group is significantly greater than in the control, due to a decreased area. Large 0.08-0.32-micron-wide invaginations or pits of the endothelial cell membrane characterize both cryofixed and aldehyde-fixed vessels. The pits often appear as isolated vesicles in the cytoplasm, but serial sections reveal that many communicate with either the capillary lumen or subendothelial space. No series of pits opened onto both lumen and space to form a transendothelial channel. The number of vesicles in aldehyde-fixed specimens is about 4 times greater (P less than 0.01) and in the cold injured, cryofixed brain capillary, about two times greater (P less than 0.01), than in the cryofixed control. Hyperosmotic exposure does not increase the number of pits. The permeabilization of anuran cerebral endothelium by hyperosmotic treatment or cold injury is thus by means of an intercellular rather than a transcellular route.

Effect of aging on the blood-brain barrier

Aging is commonly associated with progressive deterioration in central nervous system (CNS) function. Nutritional factors or environmental toxins have important effects on CNS degenerative changes. The blood-brain barrier (BBB) is a major modulator of nutrient delivery to the CNS. The tight junctions and the paucity of pinocytosis or fenestrations in brain capillary endothelium act as an effective barrier between the CNS and the circulating toxic agents. Senescence is associated with significant, though often subtle, changes in BBB. Conditions which are commonly associated with aging, such as hypertension and cerebrovascular ischemia, aggravate the age-related alterations in BBB function. The histologic changes in brain vasculature with aging is region selective and species specific. The common age-related histologic changes include loss of capillary endothelial cells, elongation of the remaining endothelial cells, and decreased capillary diameter in rat cortex, but not in the monkey or human cortex, and a decrease in the number of mitochondria in endothelial cells of the brain capillaries in the monkey but not in the rat. The age-related alterations in BBB transport function include a decrease in BBB choline transport with aging and decreased brain glucose influx. The BBB neutral amino acid transport appears to be unaltered in the aged mice. Most of the studies reported so far have failed to show a significant age-related alteration in BBB permeability to water-soluble substances and high molecular weight solutes in the absence of neurological disease. A more profound change in BBB permeability appears to be associated with Alzheimer's disease. Immunohistological studies have demonstrated the presence of serum proteins in the cerebrovascular amyloid in patients with Alzheimer's disease.(ABSTRACT TRUNCATED AT 250 WORDS)

Tubular profiles do not form transendothelial channels through the blood-brain barrier

The contribution of tubular profiles within the mammalian cerebral endothelium to the formation of transcellular channels was analysed following exposure of the endothelium to native horseradish peroxidase (HRP) dissolved in saline or dimethyl sulphoxide (DMSO) administered intravenously in mice. Within 5-15 min, but not at 30 min to 2 h postinjection, peroxidase-positive extravasations were evident within the parenchyma of the forebrain and brainstem of mice exposed and not exposed to DMSO. The extravasations may be associated with the rupture of interendothelial tight junctions at the level of arterioles as a consequence of the perfusion-fixation process. Ultrastructural inspection of endothelia within and away from areas of peroxidase extravasation revealed the following intraendothelial, peroxidase-positive organelles: presumptive endocytic vesicles, endosomes (a prelysosomal compartment), multivesicular and dense bodies, and tubular profiles. Statistical analysis of the concentration of HRP-labelled presumptive endocytic vesicles, which may coalesce to form tubules, within endothelia from mice injected intravenously with HRP-DMSO compared to mice receiving HRP-saline revealed no significant difference. HRP-positive tubular profiles were blunt-ended, variable in length and width, and appeared free in the cytoplasm or in continuity with dense bodies. Labelled tubules free in the cytoplasm were positioned parallel to the luminal and abluminal plasma membranes and were less frequently oblique or perpendicular to these membranes. Tubular profiles analysed in serial thin sections or with a goniometer tilt stage did not establish membrane continuities with the luminal and abluminal plasma membranes. Peroxidase-positive tubular profiles were similar morphologically to those exhibiting acid hydrolase activity but did not share morphological and enzyme cytochemical similarities with the endoplasmic reticulum that stained for glucose-6-phosphatase (G6Pase) activity. G6Pase-positive profiles of endoplasmic reticulum were not observed to contribute to a transendothelial canalicular network. Our results suggest that: (i) peroxidase-labelled tubules, acid hydrolase-positive tubules, and G6Pase-positive endoplasmic reticulum do not form transcellular channels through the cerebral endothelium; (ii) tubular profiles labelled with blood-borne HRP in the cerebral endothelium are associated with the endosome apparatus and/or the lysosomal system of organelles; and (iii) DMSO does not appear to alter the permeability of the blood-brain barrier to blood-borne protein.

Avenues for entry of peripherally administered protein to the central nervous system in mouse, rat, and squirrel monkey

Pathways traversed by peripherally administered protein tracers for entry to the mammalian brain were investigated by light and electron microscopy. Native horseradish peroxidase (HRP) and wheat germ agglutinin (WGA) conjugated to peroxidase were administered intranasally, intravenously, or intraventricularly to mice; native HRP was delivered intranasally or intravenously to rats and squirrel monkeys. Unlike WGA-HRP, native HRP administered intranasally passed freely through intercellular junctions of the olfactory epithelia to reach the olfactory bulbs of the CNS extracellularly within 45-90 minutes in all species. The olfactory epithelium labeled with intravenously delivered HRP, which readily escaped vasculature supplying this epithelium. Blood-borne peroxidase also exited fenestrated vessels of the dura mater and circumventricular organs. This HRP in the mouse, but not in the other species, passed from the dura mater through patent intercellular junctions within the arachnoid mater; in time, peroxidase reaction product in the mouse brain was associated with the pial surface, the Virchow-Robin spaces of vessels penetrating the pial surface, perivascular clefts, and with phagocytic pericytes located on the abluminal surface of superficial and deep cerebral microvasculature. Blood-borne HRP was endocytosed avidly at the luminal face of the cerebral endothelium in all species. WGA-HRP and native HRP delivered intraventricularly to the mouse were not endocytosed appreciably at the abluminal surface of the endothelium; hence, the endocytosis of protein and internalization of cell surface membrane within the cerebral endothelium are vectorial. The low to non-existent endocytic activity and internalization of membrane from the abluminal endothelial surface suggests that vesicular transport through the cerebral endothelium from blood to brain and from brain to blood does not occur. The extracellular pathways through which probe molecules enter the mammalian brain offer potential routes of passage for blood-borne and air-borne toxic, carcinogenic, infectious, and neurotoxic agents and addictive drugs, and for the delivery of chemotherapeutic agents to combat CNS infections and deficiency states. Methodological considerations are discussed for the interpretation of data derived from application of peroxidase to study the blood-brain barrier.

A comparative ultrastructural study of endothelial cell tubular structures from injured mouse blood-brain barrier and normal hepatic sinusoids demonstrated after perfusion fixation with osmium tetroxide

Mice subjected to surgical leptomeningeal traumatic injury were fixed by perfusion with solutions containing either: (1) osmium tetroxide, (2) a mixture (cocktail) of osmium tetroxide and glutaraldehyde, or (3) a standard aldehyde fixative following the circulation of intravenously injected solutions of native ferritin (NF) or horseradish peroxidase (HRP) tracers. Endothelial cells (ECs) from injured cerebral cortex from all the above groups were examined ultrastructurally for the presence of tubular transport structures. These ECs were compared to endothelia of hepatic sinusoids which normally express numerous EC tubular profiles. Because we observed EC tubular structures in ECs of both injured brain and from liver sinusoids irrespective of fixation regime employed, we present evidence that the tubular profiles are real structures that form in vivo and which do not represent postmortem fixation artifacts.

Brain oedema and blood-brain barrier permeability in pulsatile and nonpulsatile cardiopulmonary bypass

In pigs subjected to pulsatile or nonpulsatile cardiopulmonary bypass (CPB) at normothermia for 3 hours, evaluation was made of water content in brain tissue (specific gravity measurements), blood-brain permeability to serum proteins (immunocytochemical demonstration of extravasated proteins, using peroxidase-antiperoxidase technique) and histopathology (paraffin sections). The specific gravity in parietal cortex was higher after pulsatile than after nonpulsatile CPB or in control pigs, the change corresponding to a 6.3% water increase. The tissue water content was unchanged in the internal capsule, basal ganglia and nucleus accumbens after CPB. The vascular permeability to serum proteins was unchanged after nonpulsatile CPB, but after pulsatile CPB minute foci of extravasated serum proteins appeared. All the animals showed dark neurons in cortical and subcortical regions, but these could have been artefacts in immersion-fixed tissue. There were no other signs of ischaemic tissue damage. The study indicated that cortical oedema may follow pulsatile CPB, the cause being altered permeability of the blood-brain barrier to serum proteins.

Barrier disruption in the major cerebral arteries following experimental subarachnoid hemorrhage

The effects of experimental subarachnoid hemorrhage (SAH) on the blood-arterial wall barrier in the major cerebral arteries were studied in 20 normotensive dogs. Horseradish peroxidase (HRP) was given intravenously before the animals were sacrificed to assess the integrity of the barrier. Transient elevation of intracranial pressure (ICP) produced by cisternal injection of saline solution resulted in HRP leakage at the branching points of the major cerebral arteries. Extensive disturbance of the blood-arterial wall barrier was consistently observed in the major cerebral arteries after SAH, with or without elevation of ICP. These results suggest that both subarachnoid clot and a sudden rise in the ICP are important factors causing the breakdown of the blood-arterial wall barrier, but that the effect of the clot is the most profound. Electron microscopy revealed that opening of the interendothelial junctions is one of the important mechanisms responsible for the HRP leakage in the major cerebral arteries following SAH. Disturbance of arterial permeability in the major cerebral arteries following SAH probably accounts for the abnormal post-contrast enhancement that occurs in patients who are prone to develop vasospasm following aneurysm rupture, and is probably involved in the pathogenesis of vasospasm.

Freeze-fracture replica study of capillary endothelium after embolization in the dog

The underlying mechanisms that lead to brain edema following ischemic insult have been subject to much debate. In this study, experimental cerebral infarction was produced in 25 dogs by injecting 1 or 2 silicone rubber cylinders through the cervical internal carotid artery. The animals were sacrificed 24 hours after embolization. Freeze-fracture studies were conducted on the plasma membrane of the capillary endothelium from 15 control and 25 ischemic dogs. No definite findings of tight junction opening were made in the ischemic preparations. Pinocytotic vesicles were seen as concave areas on the protoplasmic face (PF) of the plasma membrane and as protrusions on the extracellular face (EF). The average pinocytotic vesicle count per square micron was increased in ischemic animals. On the luminal side, it reached 22.0 +/- 1.2/sq mu in the 50 PF samples and 29.5 +/- 1.3/sq mu in the 50 EF samples in the experimental preparations, as compared to 7.2 +/- 0.5 sq mu in the 50 PF samples and 9.0 +/- 0.6 sq mu in the 50 EF samples in normal cortex. The average area of the vesicles was also enlarged in experimental animals: 4990.7 +/- 798 sq nm in the 50 PF samples and 4762.8 +/- 878 sq nm in the 50 EF samples, as compared to 3567.7 +/- 570 sq nm in the 50 PF samples and 3404.5 +/- 573 sq nm in the 50 EF samples in normal cortex (p greater than 0.01). These results indicate that transcellular transportation by pinocytotic vesicles plays an important role in the increase of capillary permeability observed in an ischemic model.

Ultrastructural studies of concanavalin A receptors and 5'-nucleotidase localization in normal and injured mouse cerebral microvasculature

Plant lectin concanavalin A conjugated with ferritin (Con A-F) injected i.v. was used for the detection of the specific monosaccharide residues (alpha-D-mannosyl and alpha-D-glucosyl) on the luminal surface of endothelial cells (ECs) in brain micro-blood vessels (MBVs). Both normal mice and animals with mechanically damaged blood-brain barrier (BBB) were used in this study. In addition, the activity of 5'-nucleotidase (5'N), the putative receptor for Con A, was studied cytochemically. Various methodologic experiments indicated that the reaction product formed on the luminal plasmalemma of ECs after incubation of samples in the cytochemical medium for the detection of 5'N activity results from the action of unspecific phosphatase hydrolyzing both specific and nonspecific substrates. The abluminal side of the wall of MBVs seems to be a major location of 5'N activity. Thus, no correlation between cytochemically demonstrable 5'N activity and Con A receptor sites on the luminal surface of ECs was noted. After damage of the BBB, extensive internalization of the luminal plasmalemma forming the limiting membranes of pinocytotic vesicles, vacuoles, and endothelial channel-like structures was observed. This process was represented by a relatively rapid translocation of Con A receptors from luminal surface into the interior of the ECs and to the abluminal side of the vessel wall.

Capillary junctions of the rat are not affected by osmotic opening of the blood-brain barrier

Osmotic opening of the blood-brain barrier had no effect on the structure of the interendothelial tight junctions located within approximately 9 micron 2 of brain capillary endothelial plasma membrane (junction-containing) examined in this study. These tight junctions restrict the passive diffusion between the blood and the brain and constitute the anatomic basis of the blood-brain barrier. Increased permeability of the blood-brain barrier in the cerebral cortex of the right hemisphere of rats, induced by an infusion of a hypertonic solution of arabinose and monitored with the protein tracer horseradish peroxidase (HRP), was evidenced by the extravasation of the tracer into the extracellular compartment of the brain. Freeze-fracture analysis of the capillaries from the same tissue revealed no alterations in the intramembrane components of the endothelial tight junctions. The junctions, which consist of 8-12 highly anastomosed parallel ridges situated on the PF fracture face of the endothelial plasmalemma, showed no loss of ridge continuity or intra-ridge connections, and were identical to zonulae occludentes from control capillaries. Consistent labeling of numerous vesiculo-tubular elements by HRP in the endothelia of experimental tissue and the three-dimensional nature of these elements observed in platinum replicas support the interpretation that these structures represent transendothelial conduits which are continuous with the luminal and abluminal surfaces of the endothelial cells. Absence of similar structures in control endothelia is taken as evidence that their presence in experimental tissues is a direct response to the osmotic insult. It was concluded, therefore, that during osmotic opening of the blood-brain barrier passage of HRP across the endothelium of brain capillaries is not by an inter-endothelial route due to disruption of tight junctions but rather by a transendothelial route due to amplified vesicular activity.

Disruption of blood-brain barrier following bilateral carotid artery occlusion in spontaneously hypertensive rats. A quantitative study

The present study was designed to clarify the relationship of cerebral blood flow (CBF) to blood-brain barrier (BBB) in the ischemic brains with or without recirculation, which were produced by clipping of both common carotid arteries in spontaneously hypertensive rats. CBF was measured by the hydrogen clearance method and BBB function was evaluated by the permeability of 131I-albumin and Evans blue dye. Cortical CBF was reduced from 48.8 +/- 9.5 to 4.0 +/- 1.2 ml/100 gm/min during 1 hr ischemia and further to 2.6 +/- 0.3 ml/100 gm/min during 3 hrs ischemia, while thalamic CBF was reduced much less from 50.0 +/- 3.6 to 17.9 +/- 6.5 ml/100 gm/min and to 17.5 +/- 11.0 ml/100 gm/min, respectively. There was no increase in permeability to protein tracers observed in such 1 hr or 3 hrs ischemic brain. Both cortical and thalamic CBF were markedly increased 2.5 to 6 fold of resting values at 5 min after recirculation in the 1 hr ischemic brain. In the 3 hrs ischemic brain, however, both CBF were only slightly increased but never restored to the resting level even at 30 min after recirculation. In such reperfused brains, exudation to Evans blue dye was observed in none of 16 animals with 1 hr ischemia, but in 18 of 23 with 3 hrs ischemia. Disruption of BBB was twice more frequent in the cortex (77.8%) than in either thalamus (33.3%) or hippocampus (33.3%). Permeability index of 131I-albumin (brain albumin/blood albumin) was significantly higher in the ischemic areas stained with blue dye (2.07 +/- 0.45%) than in non-ischemic control brain (0.10 +/- 0.01%).(ABSTRACT TRUNCATED AT 250 WORDS)

Increased transendothelial channel transport of cerebral capillary endothelium in stroke-prone SHR

Permeability of brain capillaries of stroke-prone spontaneously hypertensive rats (SHRSP) was studied using labelling (horseradish peroxidase) and cytochemical techniques at the cellular level. In the cerebral capillary endothelium the tracer molecules were quickly transported by abundant transendothelial channels which directly connected the capillary lumen to the subendothelial space. Transendothelial channels are abundant and should be postulated as structural formations engaged in the increased transport of proteins across the capillary endothelium. Ultracytochemical studies revealed that the channels, bounded by indistinct delimiting membranes, initially had no acid phosphatase activity. With the passage of time, however, the channels showed acid phosphatase activity and were lined with distinct membranes. These observations suggested that the lysosomes might fuse with the transendothelial channels and might play an important part in the transport of macromolecules.

The blood-brain barrier following experimental subarachnoid hemorrhage. Part 2: Response to mercuric chloride infusion

Under controlled physiological conditions, fresh blood was injected into the cisterna magna of 10 adult cats to produce subarachnoid hemorrhage (SAH). Damage to the blood-brain barrier (BBB) was induced 30 minutes after SAH by the intracarotid injection of a 6 x 10(-5)M solution of mercuric chloride (HgCl2). A control series of five cats received the same injection of HgCl2. Intravenously injected Evans blue dye was used to indicate areas of BBB damage. The lesions were confirmed by fluorescence microscopy. All control animals showed BBB damage in the hemisphere injected with HgCl2. Of the animals in the test group with SAH, 90% were free from lesions. When lesions were present, the distribution differed from that in the control group. These results bear a similarity to the reported absence of HgCl2 lesions during the acute stages after total cerebral ischemia. This suggests that the cellular components of the BBB participate in a general metabolic inhibition following SAH.

Morphology of cerebral endothelium and astrocytes as determinants of the neuronal microenvironment

The morphological features of the blood-brain barrier to macro-molecules under normal and perturbed conditions are reviewed in the context of some recent investigations. The electric charge on molecules of horseradish peroxidase (HRP) affect its pinocytosis and intracellular fate which pertains to problems of distinguishing endocytosis from vesicular transport across endothelium. When the barrier is opened, the number of pits, vesicles and tubules increases. Such cerebral endothelium resembles normal endothelium of certain fish where numerous membrane invaginations do not signify vesicular or tubular transport. However, such transport has not been entirely ruled out in reactive endothelium. Another route of exudation during barrier opening may be via patent endothelial junctions, especially during intravascular infusion of hyperosmotic solutions. The permeability of the tight junctions, however, is not reflected unequivocally by its intramembranous structure. Although astrocytes do not provide a barrier to the extracellular flow of solutes, their ubiquity may enable them to modify the composition of perineuronal fluid. Their orthogonal arrays of intramembranous particles may be involved. The number of assemblies increases in astrocytes reacting to trauma and to the extracellular accumulation of lactate and CO2. The assemblies might thus participate in the transport of catabolites to and from extracellular fluid.

Disturbances of the blood-brain barrier in cerebrovascular disorders

The disturbances of the BBB in cerebrovascular disorders may affect adversely an underlying basic pathological condition. Breakdown of the barrier associated with extravasation of serum proteins leads to development of vasogenic edema in the brain tissue. An abnormal passage of pharmacologically active substances, such as biogenic amines, may significantly affect cerebral blood flow and metabolism and activate neurons equipped with receptors for these substances. Also, a barrier dysfunction related to faulty out-transport of metabolites may contribute to edema and tissue damage. In cerebral ischemia, following release of arterial occlusion there can be two separate openings of the barrier: the first - occurring promptly after recirculation and related to ensuing reactive hyperemia, the second - after some delay and related to pathological changes in the brain tissue. In some circumstances, such as epileptic seizures, both "hemodynamic" and "tissue" factors may be operative at the same time. The selective features of BBB changes are related to multiplicity of barrier systems residing in cerebral endothelium. These selective features are demonstrable during development and during reversibility of postichemic barrier disturbances. Intermittent openings of the barrier observed in chronic hypertension may lead to accumulation of extravasated serum proteins and be responsible for frequently observed edematous changes in this condition.

Ultracytochemical studies of vesicular and canalicular transport structures in the injured mammalian blood-brain barrier

An ultracytochemical investigation was performed to study the origin of pinocytic vesicles and canalicular structures within endothelial cells (EC) of the injured mammalian blood-brain barrier (BBB). To accomplish this goal, two electron-dense tracers, native ferritin (NF) and horseradish peroxidase (HRP), were used in conjunction with the detection of alkaline phosphatase (AP) activity, a known marker of EC plasmalemma of brain micro-blood vessels. Brain ECs from (1) mice subjected to crude leptomeningeal damage for 1, 2, or 3 days and (2) cats subjected to cold lesion injury for 1, 4, or 24 h were evaluated for tracer transport and AP activity. Fine structural analysis of leaking segments of micro-blood vessels from damaged cerebral cortex or basal ganglia demonstrated pinocytic vesicles, deep invaginations of the luminal plasmalemma and elongated, tubular profiles, all containing tracer. Because we observed in ECs from both experimental models of brain injury a positive reaction for AP activity in the luminal plasmalemma, in its deep invaginations, in delimiting membranes of pinocytic vesicles, and in tubulo-canalicular structures, we conclude that all types of transport structures derive from the same 100A thick exoplasmic plasmalemmal membranes. Further, besides the pinocytic vesicular transport system (PTS), the canalicular transport system (CTS) appears to serve as an additional important mechanism for macromolecular transport across the damaged mammalian BBB.

Ionic lanthanum passage across cerebral endothelium exposed to hyperosmotic arabinose

Hyperosmotic media infused into the cerebral circulation open the blood-brain barrier to protein and colloid. The mechanism whereby such substances cross the affected vessels is still disputed. We describe here the transendothelial route taken by ionic lanthanum (La3+), a small electron-dense tracer which, unlike colloidal lanthanum, can be administered to the living animal. In adult rats, 2.9 ml of hyperosmotic (1.4 M) arabinose was infused into the internal carotid artery as a 30-s bolus, followed by 5 mM LaCl3. To find the extravasated La3+, which is invisible by light microscopy, horseradish peroxidase (HRP) was injected simultaneously into the femoral vein. The hyperosmotic treatment resulted in exudation of both HRP and La3+ primarily around cerebral arterioles. The La3+ crossed arterioles through successive tight junctions between endothelial cells. Although the tight junctions were not discernibly opened, they must have become permeable because the extracellular pools between successive tight junctions were penetrated by the La3+. These pools are normally inaccessible to La3+. Luminal and abluminal pits and cytoplasmic vesicles, some of them containing La3+, formed intraendothelial clusters. Their role, if any, in the transfer of ion remains uncertain.

Cerebrovascular permeability following MCA occlusion in the rat. The effect of halothane-induced hypotension

A quantitative autoradiographic technique that utilizes carbon-14-aminoisobutyric acid (14C-AIB) as a tracer was used to study alterations in cerebral microvascular permeability in 15 rats. Five were "sham-operated" controls and 10 underwent microsurgical, unilateral occlusion of the proximal middle cerebral artery (MCA). Histological changes indicative of focal cerebral ischemia were observed in only the latter 10 animals. These changes were confined to tissue normally perfused by the occluded MCA. After MCA occlusion, five animals were also subjected to transient halothane-induced hypotension (mean arterial blood pressure 50 mm Hg) for 20 to 30 minutes. Only in these five animals were blood-to-brain transfer constants (ki) significantly increased (by approximately 100%) at 4 hours after MCA occlusion. The topographical distribution of this alteration in cerebral microvascular permeability corresponded closely with the histological changes. Neither proximal MCA occlusion nor halothane-induced hypotension alone was associated with any focal or diffuse increase in ki after 4 hours.

Expanding the definition of the blood-brain barrier to protein

Tight junctions between cerebral endothelial cells and the near absence of pinocytosis and vesicular transport of blood-borne protein into and across these cells are believed to constitute the mammalian blood-brain barrier. In the present investigation evidence is provided to indicate that the capillary endothelium of the mouse brain pinocytosis the enzymatic tracer horseradish peroxidase (EC 1.11.1.17) from cerebral blood under normal conditions. This protein and the internalized endothelial surface membrane associated with it are directed, for the most part, to acid hydrolase-positive lysosomes for degradation. Although peroxidase was never seen in the perivascular clefts, the lysosomes of pericytes were peroxidase-positive. Pericytes are macrophage-like cells located on the abluminal surfaces of cerebral microvasculature; these cells may serve as the first line of defense once the blood-brain barrier is breached. The definition of the blood-brain barrier should be expanded to include consideration of the lysosomal system of organelles in endothelial cells and pericytes.

Permeability of intracranial extracerebral vessels in stroke-prone SHR

Permeability of intracranial extracerebral arteries of stroke-prone spontaneously hypertensive rats (SHRSP) was studied using labeling techniques (ferritin and horseradish peroxidase), at the cellular level. In the arterial endothelial cells, the tracer molecules were slowly but constantly transported by the plasmalemmal vesicles to the subendothelial space. This endothelial transportation of the tracers into these cerebral arteries did not seem to be significantly influenced by aging, increased blood pressure, hyperlipidemia or the existence of cerebral bleeding and infarction. Around the adventitia, there were a great number of periadventitial capillaries, especially near bifurcations. In the periadventitial capillaries, the tracer molecules were readily trapped by endothelial cells and were quickly transported to pericapillary spaces. The tracer molecules were then detected in the phagocytes adjacent to the deeper layers of the media, and further in the medial smooth muscle cells. The possibility that large amounts of plasma components are supplied to the media from periadventitial capillaries in the intracranial extracerebral arteries has to be considered in the pathogenic mechanisms of cerebrovascular lesions.

Cerebrovascular permeability in mechanically induced hypertension

Our previous studies of cerebrovascular permeability in angiotensin-induced acute hypertension demonstrated that the principal mechanism resulting in increased permeability is enhanced pinocytosis. In order to exclude the possibility that the enhanced pinocytosis was a direct effect of exogenous angiotensin, cerebrovascular permeability alterations were studied in nonpharmacologically induced acute hypertension. Rats receiving horseradish peroxidase (HRP) intravenously, were sacrificed 2 1/2 minutes after the onset of hypertension induced by placing a clip on the abdominal aorta. These animals showed the same pattern of permeability alterations as had been observed previously in animals with angiotensin-induced acute hypertension. Focal segments of penetrating arterioles in the temporal and parietal cortex showed increased permeability to HRP. Permeable vessels showed increased numbers of pinocytotic vesicles and the interendothelial junctions revealed no alterations. Enhanced pinocytosis appears to be the principal mechanism resulting in increased cerebrovascular permeability in this model as well as suggesting that the alterations of cerebrovascular permeability observed previously in angio-tensin-induced acute hypertension occur due to the hypertensive state and are not a direct drug effect of exogenous angiotensin.

Arterial air embolism: structural effects on the gerbil brain

Air injection into the carotid artery of adult mongolian gerbils caused, within 10 minutes, multifocal brain lesions. The extracellular spaces were widened and neurons, oligodendrocytes and myelin sheaths remained unchanged. The "delayed" effects of air embolism (first seen after 3 h) were similar to those observed in gerbils after unilateral carotid ligation. The histologic alterations after 3 h consisted of astrocytic swelling and shrinkage/necrosis of neuronal soma. The observations reported here illustrate the temporal and spatial separations that exist between a) brain water retention, and b) intraparenchymal entry of horseradish peroxidase. Both alterations can be a consequence of either decreased blood flow or arterial air embolism. Edema and protein leakage in each situation may be initiated by different mechanisms.

Ultracytochemical evidence for endothelial channel-lysosome connections in mouse brain following blood-brain barrier changes

An investigation designed to define relationships between endothelial channels and lysosomes was conducted in the mammalian brain microvasculature. Microvessels from normal and mechanically injured mouse brains were studied ultracytochemically for: (1) transport of horseradish peroxidase (HRP) protein tracer through endothelial channels, and (2) for acid phosphatase (AcP) activity as an enzymatic marker of lysosomes. Following traumatic brain injury for 1 week with 2 h circulation of intravenously injected HRP, selected brain slices were processed for ultrastructural localization of either HRP, AcP, or for both reactions together within the same tissue slices. One week after blood-brain barrier (BBB) damage, the presence of HRP reaction product (RP) was observed within endothelial channels and vesicles of capillaries and arterioles with concomitant increase in lysosomal enzymatic activity of the endothelial cells bordering regions of brain damage. Lysosomes were observed to be directly connected to the endothelial channels. Our observations present cytochemical evidence for endothelial channel-lysosome connections which may suggest intralysosomal modification of blood-born materials before entering the neuropil. Such modification could have important immunological and/or metabolic significance.

Ultracytochemical studies of the blood-meningeal barrier (BMB) in rat spinal cord

Alkaline phosphatase(AP),5'-nucleotidase(5'N) and nucleoside diphosphatase (NDPase) activities were studied by cytochemical methods applied to light and electron microscopy in the microvasculature of spinal cord leptomeningeal strips of normal and protamine sulfate (PS) treated rats. The increased permeability to intravenously injected horseradish peroxidase was observed in some segments of microvessels of PS treated rats. Enhanced formation of plasmalemmal pits and deep invaginations, formation of numerous pinocytic vesicles and the appearance of channel-like structures in the cytoplasm of endothelial cells were the most striking ultrastructural evidence of increased permeability of the affected microvessels. All of these structures also showed activity of AP, and to lesser extent, of NDPase; 5'N activity was mainly associated with the delimiting membranes of pinocytic vesicles. Our data present evidence that a shift of enzymatic activity from luminal to abluminal surface of affected endothelial cells results from membrane flow accompanying increased transport activity via formation of pinocytic vesicles and channel-like structures.

Ultrastructural cytochemical studies of cerebral microvasculature in scrapie infected mice

Alkaline phosphatase, 5'-nucleotidase nucleoside diphosphatase and thiamine pyrophosphatase activities were studied by cytochemical method applied to electron microscopy of brain microvasculature in normal and scrapie infected mice. In control mice, the major location of all phosphatases studied was the luminal plasma membrane of the endothelial cells. In scrapie infected mice, changes in activity and distribution of the above mentioned phosphatases manifested themselves in the appearance of the reaction product on the abluminal side of the vessel wall. Our data presents evidence that following scrapie infection, these enzymes change their specific localization along the endothelial cell membranes. These enzymatic changes may serve as useful indicators of some alterations in the mammalian blood-brain barrier following infection by scrapie agent in the mouse.

Effect of hypertension on blood-brain barrier. Change after restoration of blood flow in post-ischemic gerbil brains. An electronmicroscopic study

The effect of induced hypertension on the blood-brain barrier (BBB) change in Mongolian gerbils exposed to various periods of ischemia was studied. Evans blue dye was used to determine the BBB change in animals subjected to different levels of hypertension after 3 h ischemia. Horseradish peroxidase (HRP) was used in electronmicroscopic studies of animals subjected to 30 min, 1, 3 or 6 h ischemia and subsequently exposed for 30 min to varying periods and sequences of normo- and hypertension. Furthermore, HRP-labeled vesicle counts were performed in animals from the 30-min ischemia group. Our findings revealed that hypertension, after blood flow restoration following ischemia, induces and/or accelerates BBB damage by enhancing endothelial vesicular and/or tubulo-channel transport.

Morphological changes in spontaneously hypertensive rats

Our previous studies of angiotension-induced acute hypertension showed increased intracerebral arteriolar permeability associated with markedly enhanced pinocytosis. This study was performed to determine whether similar findings occurred in spontaneous non-pharmacologically induced chronic hypertension. Cerebrovascular permeability to horseradish peroxidase (HRP) was studied over an 82-week period in spontaneously hypertensive rats (SHR) derived from a strain that originated from Japan. In a few animals increased cerebrovascular permeability to HRP was observed, associated with enhanced pinocytosis. Quantitatively, the number of pinocytotic vesicles in permeable arteriolar segments was significantly increased suggesting that enhanced pinocytosis is the principal mechanism of early cerebrovascular changes in SHR. Light microscopy of renal, ocular and cerebral vessels revealed medial hyperplasia affecting renal vessels at 16 weeks and occurring later in ocular and cerebral vessels. Deposition of fibrin in renal vessels was observed from 64 weeks onwards but was not associated with renal failure.