Ultrastructural studies on cerebrovascular permeability in acute hypertension

Posterior reversible encephalopathy syndrome: A neuropsychiatric manifestation of systemic lupus erythematosus

Posterior Reversible Encephalopathy Syndrome (PRES) is an acute neurological syndrome clinically characterized by seizures, altered mental status, headache, and visual disturbances. It is caused by a variety of abnormalities in the endothelial function that ultimately result in vasogenic edema in the circulation of the central nervous system. This is reflected by the neuroimaging findings, that most often show reversible parieto-occipital edema. An important proportion of patients with PRES present with Systemic Lupus Erythematosus (SLE), and its complications, as their sole risk factors. This review describes the relationship between these two clinical entities and explains the pathophysiological models that have been proposed to describe the development of PRES. We explain how SLE can cause alterations in every pathway implicated in the development of PRES. Given the relatively high frequency and the distinct clinical course, PRES in the setting of SLE might be best described as a distinct neuropsychiatric syndrome associated with SLE.

Neurotoxicity Associated with Radiological Contrast Agents Used during Coronary Angiography: A Systematic Review

Contrast media enhances the visualization of the anatomic structures in radiological studies, allowing internal tissues such as blood vessels, kidney, ureters, adrenals and other organs to be identified. The evolution of contrast media highlights the efforts to develop less toxic chemical agents that possess low viscosity and osmolality. However, adverse effects such as idiosyncratic reactions, and organ specific damage are well characterized. Neurotoxicity, an important and dose related effect, appears to be due to disruption of the blood-brain-barrier by the high osmolarity of the contrast agent. From devastating cortical blindness to paralysis and seizures, an array of neurological manifestations has been described. In this systematic review, we describe the contrast-induced neurologic injury following coronary angiography and discuss the proposed mechanisms of injury leading to neurotoxicity.

A Case of Unusual Presentation of Contrast-induced Encephalopathy after Cerebral Angiography Using Iodixanol

Contrast-induced encephalopathy after cerebral angiography is a rare complication and until now, only few cases have been reported. This paper reports on contras-induced encephalopathy mimicking meningoencephalitis after cerebral angiography by using iodixanol, an iso-osmolar non-ionic contrast agent. A 58-year-old woman underwent cerebral angiography for the evaluation of multiple intracranial aneurysms. A few hours later, she had persistent headache, vomiting, fever, and seizures. Brain computed tomography (CT) showed sulcal obliteration of right cerebral hemisphere and cerebrospinal fluid profile was unremarkable. The next day, she developed left side hemiparesis, sensory loss, and left-sided neglect with drowsy mentality. Brain magnetic resonance imaging (MRI) showed cerebral swelling with leptomeningeal enhancement in the right parieto-occipital lobe without sign of ischemia or hemorrhage. The patient was managed with intravenous dexamethasone, mannitol and anticonvulsant. There was a progressive neurological improvement with complete resolution of the symptoms at day 6. This observation highlights that contrast-induced encephalopathy can be caused by an iso-osmolar non-ionic contrast agent. This rare entity should be suspected if neurologic deterioration after cerebral angiography is not explained by other frequent causes such as acute infarction or hemorrhage.

Other cerebrovascular occlusive disease

In this chapter we review the optimal imaging modalities for subacute and chronic stroke. We discuss the utility of computed tomography (CT) and multimodal CT imaging. Further, we analyze the importance of specific magnetic resonance imaging sequences, such as diffusion-weighted imaging for acute ischemic stroke, T2/fluid-attenuated inversion recovery for subacute and chronic stroke, and susceptibility imaging for detection of intracranial hemorrhages. Different ischemic stroke mechanisms are reviewed, and how these imaging modalities may aid in the determination of such. Further, we analyze how topographic patterns in ischemic stroke may provide important clues to the diagnosis, in addition to the temporal evolution of the stroke. Lastly, specific cerebrovascular occlusive diseases are reviewed, with emphasis on the optimal imaging modalities and their findings in each condition.

Leukoencephalopathy resolution after atypical mycobacterial treatment: a case report

Background

Association of leukoencephalopathy and atypical mycobacteriosis has been rarely reported. We present a case that is relevant for its unusual presentation and because it may shed further light on the pathogenic mechanisms underlying reversible encephalopathies.

Case report

We report the case of a Hispanic 64-year-old woman with cognitive decline and extensive leukoencephalopathy. Magnetic resonance imaging revealed white-matter lesions with increased water diffusivity, without blood–brain-barrier disruption. Brain biopsy showed tissue rarefaction with vacuolation, mild inflammation, few reactive astrocytes and decreased aquaporin water-channel expression in the lesions. Six months later, she was diagnosed with atypical mycobacterial pulmonary infection. Brain lesions resolved after antimycobacterial treatment.

Conclusion

We hypothesize leukoencephalopathic changes and vasogenic edema were associated with decreased aquaporin expression. Further studies should clarify if reversible leukoencephalopathy has a causal relationship with decreased aquaporin expression and atypical mycobacterial infection, and mechanisms underlying leukoencephalopathy resolution after antimycobacterial treatment. This article may contribute to the understanding of pathogenic mechanisms underlying magnetic resonance imaging subcortical lesions and edema, which remain incompletely understood.

Posterior reversible encephalopathy syndrome--Insight into pathogenesis, clinical variants and treatment approaches

Posterior reversible encephalopathy syndrome is a rare clinicoradiological entity characterized by typical MRI findings located in the occipital and parietal lobes, caused by subcortical vasogenic edema. It was first described as a distinctive syndrome by Hinchey in 1996. Etiopathogenesis is not clear, although it is known that it is an endotheliopathy of the posterior cerebral vasculature leading to failed cerebral autoregulation, posterior edema and encephalopathy. A possible pathological activation of the immune system has been recently hypothesized in its pathogenesis. At clinical onset, the most common manifestations are seizures, headache and visual changes. Besides, tinnitus and acute vertigo have been frequently reported. Symptoms can be reversible but cerebral hemorrhage or ischemia may occur. Diagnosis is based on magnetic resonance imaging, in the presence of acute development of clinical neurologic symptoms and signs and arterial hypertension and/or toxic associated conditions with possible endotheliotoxic effects. Mainstay on the treatment is removal of the underlying cause. Further investigation and developments in endothelial cell function and in neuroimaging of cerebral blood flow are needed and will help to increase our understanding of pathophysiology, possibly suggesting novel therapies.

The Cerebral Endothelium During Pregnancy: A Potential Role in the Development of Eclampsia

The authors investigated the influence of pregnancy on cerebral endothelial cell permeability in response to an acute elevation in intravascular pressure that caused forced dilatation of myogenic tone. Third-order branches of the posterior cerebral artery (PCA) were dissected from nonpregnant (NP) and late-pregnant (LP, days 19 to 20) Sprague-Dawley rats and mounted on glass cannulas in an arteriograph chamber that allowed control over intravascular pressure and measurement of both diameter and permeability to fluorescent dextran (3000 Da). Permeability was determined at 75 mm Hg and after a step increase in pressure to 200 mm Hg. The extent of pinocytosis and transcellular transport in response to pressure was evaluated separately in the same groups of animals at 75 and 200 mm Hg using transmission electron microscopy. All arteries developed myogenic tone at 75 mm Hg that was lost when pressure was increased to 200 mm Hg to cause forced dilatation. The increased pressure caused a significant increase in permeability to dextran and enhanced pinocytosis in arteries from LP animals, but not in NP animals whose permeability remained constant at both pressures. These results suggest a pregnancy-specific effect on the cerebral endothelium that may promote enhanced vascular permeability during acute hypertension and may contribute to the edema formation and neurologic complications of eclampsia.

PROTECTION OF BLOOD-BRAIN BARRIER BREAKDOWN BY NIFEDIPINE IN ADRENALINE-INDUCED ACUTE HYPERTENSION

The question of whether influxes of ionic Ca+2 into cerebral endothelium plays an important role in increased vascular permeability consequent to an acute hypertension is not accurately resolved. We tested the effect of nifedipine, a calcium entry blocker, on the cerebrovascular permeability for proteins in adrenalin-induced acute hypertension. The experiments were carried out on male Wistar rats. The experimental groups consisted of normotensive saline controls, adrenaline-induced hypertensive rats, and adrenalin-induced hypertensive rats as pre-treated or post-treated with a bolus of nifedipine. Brains of hypertensive rats showed increased permeability to Evans Blue-Albumin complex, when blood pressure elevated rapidly to more than 170 mmHg. The number and size of areas of Evans-Blue extravasation were smaller if an increase in blood pressure was prevented. The short lasting elevation of blood pressure did not result in protein extravasation in brains of hypertensive rats. The results suggest that nifedipine can modify the permeability disruptions observed in acutely hypertensive rats. The data also support the hypothesis that Ca+2 may be responsible for the changes in permeability of BBB in hypertension by mediating the contraction of vascular muscles.

Regulation of cerebral vasculature in normal and ischemic brain

We outline the mechanisms currently thought to be responsible for controlling cerebral blood flow (CBF) in the physiologic state and during ischemia, focusing on the arterial pial and penetrating microcirculation. Initially, we categorize the cerebral circulation and then review the vascular anatomy. We draw attention to a number of unique features of the cerebral vasculature, which are relevant to the microcirculatory response during ischemia: arterial histology, species differences, collateral flow, the venous drainage, the blood-brain barrier, astrocytes and vascular nerves. The physiology of the arterial microcirculation is then assessed. Lastly, we review the changes during ischemia which impact on the microcirculation. Further understanding of the normal cerebrovascular anatomy and physiology as well as the pathophysiology of ischemia will allow the rational development of a pharmacologic therapy for human stroke and brain injury.

Blood-brain barrier studies with special reference to epileptic seizures

A review is given of the structure and function of the blood-brain barrier (BBB) with special reference to the situation during and after epileptic seizures including electroconvulsive therapy (ECT). Based on the literature describing different models of epilepsy the development of the theories concerning the early observations of a BBB dysfunction in connection with seizure activity is given, and gross morphology, ultrastructural and dynamic findings are briefly reviewed.

Extravasation of blood-borne immunoglobulin G through blood-brain barrier during adrenaline-induced transient hypertension in the rat

The effect of transient hypertension on blood-brain barrier (BBB) permeability, particularly on extravasation of immunoglobulin G (IgG), has not been fully understood. In the present experiment, we investigated the time course of endogenous albumin and IgG extravasation through BBB and the localization of extravasated IgG in brain parenchyma during adrenaline(AD)-induced transient hypertension in the rat by using Evans blue fluorescence, immunohistochemistry, and Western blot. The results showed that a bolus injection of AD (10 microg/kg) induced a transient elevation of arterial pressure lasting about 1 min. The endogenous albumin and IgG entered the brain parenchyma via BBB only when hypertension occurred. Electron microscopically, the IgG-like immunoreactivities were predominantly seen in the cytoplasm of endothelia of capillaries, pericytes, extracellular space of parenchyma, and the cytoplasm of glial cells. The results suggest that circulating IgG or antibodies might contact the structures of brain parenchyma through passage of BBB when its permeability is temporally changed by transient hypertension. This phenomenon implies a possible mechanism of pathogenesis for immune-mediated diseases in the brain.

Regulation of blood-brain barrier permeability

The blood-brain barrier minimizes the entry of molecules into brain tissue. This restriction arises by the presence of tight junctions (zonulae occludens) between adjacent endothelial cells and a relative paucity of pinocytotic vesicles within endothelium of cerebral arterioles, capillaries, and venules. Many types of stimuli can alter the permeability characteristics of the blood-brain barrier. Acute increases in arterial blood pressure beyond the autoregulatory capacity of cerebral blood vessels, application of hyperosmolar solutions, application of various inflammatory mediators known to be elevated during brain injury, and/or activation of blood-borne elements such as leukocytes can produce changes in permeability of the blood-brain barrier. The second messenger systems that account for increases in permeability of the blood-brain barrier during pathophysiologic conditions, however, remain poorly defined. This review will summarize studies that have examined factors that influence disruption of the blood-brain barrier, and will discuss the contribution of various cellular second messenger pathways in disruption of the blood-brain barrier during pathophysiologic conditions.

Role of extracellular matrix in experimental vasospasm. Inhibitory effect of antisense oligonucleotide on collagen induction

BACKGROUND AND PURPOSE

Although it has been suggested that collagen plays a role in the pathogenesis of cerebral vasospasm after subarachnoid hemorrhage, there has been no constructive research to prove it directly. In this study we stopped the transcription of the procollagen type I gene by introducing antisense oligonucleotides for its mRNA in a rat femoral artery model of vasospasm induced by blood and assayed the changes in the vasoconstrictive activity of the vessel and expression of the procollagen mRNA.

METHODS

We applied antisense, sense, or missense oligonucleotides, located at the carboxyl propeptide region for alpha 1(I) procollagen mRNA, onto the femoral artery in a rat femoral artery model of vasospasm. The diameter of the artery was measured by angiography. The transcription level of the procollagen gene in the arterial tissue was assayed by use of reverse transcription-polymerase chain reaction. Morphological change in the artery was observed with aldehyde-fuchsin-Masson-Goldner staining.

RESULTS

In the model, when the artery was exposed to antisense oligonucleotides in pluronic gel for 5 days to prevent arterial contraction, the contraction was inhibited at a significant level (76.0% +/- 5.6) when compared with that in control experiments using sense oligonucleotides (64.0% +/- 2.4), missense oligonucleotides (63.5% +/- 3.5), or gel alone (62.1% +/- 5.8). The application of antisense oligonucleotide resulted in a marked decrease in alpha 1(I) procollagen mRNA expression as determined by polymerase chain reaction, indicating that the collagen reduction by antisense oligonucleotides occurred at the transcription level. Histological staining suggested that collagen accumulation at the site in the artery where antisense oligonucleotide had been administered was indeed less than that in the control artery.

CONCLUSIONS

The results indicate that the induction of procollagen type 1 could cause pathogenesis of the arterial contraction induced by blood in a rat femoral vasospasm model.

Ultrastructural changes in the blood-brain barrier in rats after treatment with nimodipine and flunarizine. A comparison

The idea of using induced hypertension to treat the symptomatic ischaemia resulting from vasospasm after subarachnoidal hemorrhage, and the effect of this therapy on the blood-brain barrier, is checked in animal experiments. This therapy is combined with the application of nimodipine, which is recognised as the standard medication for prophylaxis of vasospasm. The effects of the induced hypertension combination with Nimodipine and in combination with another calcium antagonist, Flunarizine are compared. Seventy-four narcotised rats, one group with 22 animals treated with Nimodipine and 22 with placebo, and a second group 20 animals treated with Flunarizine and 10 with placebo, are evaluated. The blood pressure is raised to 150-180 mmHg by i.v. application of norfenephrine and measured continuously. The standard tracer, horseradish peroxidase, is applied as indicator for the blood-brain barrier function. 15 minutes later the experimental animals are exsanguinated by perfusion with saline, then perfused with Karnovsky's solution. After removal, the brains are stained for peroxidase to visualise extravasation of the horseradish peroxidase, and after evaluation of the results each brain is assigned to its experimental group. In the Nimodipine group, a significant accumulation (p < 0.001) of perivascular deposits of peroxidase reaction product were found, these were not found in the placebo group. The Flunarizine group does not differ from its placebo group in the number of extravasates, and thus, with respect to protein extravasation, appears better than the Nimodipine group. In electron micrographs of the extravasates one sees intact tight junctions and a neuroendothelial transport, and also vesicles, filled with horseradish peroxidase in the endothelium, the muscle cells, and the brain parenchyma, which arise from pinocytosis. The vesicles, which transport the high-molecular-weight protein, horseradish peroxidase, also transport other proteins and can, therefore, cause a brain edema. It follows from these morphological results that Nimodipine can disrupt the blood brain barrier function and can, therefore, also interfere with cerebral autoregulation, which depends on the resistance of vessels.

Protective effect of flunarizine on blood-brain barrier permeability alterations in acutely hypertensive rats

BACKGROUND AND PURPOSE

Increased cerebrovascular permeability to protein is a well-documented finding in acute and chronic hypertension. In this study, we examined the effect of pretreatment with a calcium entry blocker, flunarizine, on the increased cerebrovascular permeability to protein that develops in norepinephrine-induced acute hypertension.

METHODS

Protein transfer was assessed qualitatively with Evans blue dye and quantitatively with iodine-125-labeled serum albumin.

RESULTS

Brains of hypertensive rats showed increased permeability to both tracers. The number and size of the areas of Evans blue extravasation were smaller in the hypertensive groups pretreated with flunarizine intravenously. This was supported by the quantitative studies, which demonstrated a significant decrease in protein transfer in total brain of hypertensive rats pretreated with intravenous flunarizine, 1 mg/kg (p less than 0.005) and 2.5 mg/kg (p less than 0.001). Data from individual brain regions showed that pretreatment with flunarizine resulted in significant reduction of protein transfer in most brain regions.

CONCLUSIONS

These data support the hypothesis that calcium plays a role in increased cerebral endothelial permeability in hypertension.

Time- and pressure-dependent changes in blood-brain barrier permeability after temporary middle cerebral artery occlusion in rats

After 180 min of temporary middle cerebral artery occlusion in rats, the affect of phenylephrine-induced hypertension on blood-brain barrier permeability was assessed. One of the following blood-pressure regimens was maintained during either a 30- or 120-min period of reperfusion: (a) 30/Norm, 30 min of normotensive reperfusion was allowed; (b) 30/HTN, mean arterial blood pressure was increased by 35 mm Hg during 30 min of reperfusion; (c) 120/Norm, 120 min of normotensive reperfusion was allowed; or (d) 120/HTN, mean arterial blood pressure was increased by 35 mm Hg during 120 min of reperfusion. Evans blue (30 mg/kg) was given, and brains were analyzed for Evans blue by spectrophotometry. Evans blue (microgram/g brain tissue, mean +/- SD) was greater (P less than 0.05) in both hypertensive groups versus their time matched normotensive groups (30/HTN: 80 +/- 16 versus 18 +/- 6 in the 30/Norm group; 120/HTN: 17 +/- 6 versus 8 +/- 3 in the 120/Norm group). In addition, Evans blue was greater (P less than 0.05) in both 30-min groups versus their pressure matched 120-min groups (30/Norm: 18 +/- 6 versus 8 +/- 3 in the 120/Norm group; 30/HTN: 80 +/- 16 versus 17 +/- 6 in the 120/HTN group). The data are consistent with previous studies which have demonstrated an opening of the blood-brain barrier at the onset of reperfusion. In addition, the data support a hypothesis that changes in blood-brain barrier permeability are more sensitive to hypertension in the early period of reperfusion.

Hypervolemic-hemodilution and hypertension during temporary middle cerebral artery occlusion in rats: the effect on blood-brain barrier permeability

The effect of hypervolemic-hemodilution, with and without hypertension, on blood-brain barrier permeability was investigated in rats, after 180 minutes of middle cerebral artery occlusion (MCAo), and 60 minutes of reperfusion. One of the following conditions was maintained during MCAo: 1) Control--hematocrit and blood pressure were not manipulated; 2) Hypervolemic-Hemodilution/Normotension--the hematocrit was decreased to 30%; 3) Hypervolemic-Hemodilution/Hypertension--the hematocrit was decreased to 30% and mean arterial pressure increased by 30 mmHg with phenylphrine. In all groups, Evans Blue was administered, and its concentration determined by spectrophotometric assay. Evans Blue (micrograms (g-1 of brain tissue [mean +/- SD]) was greater in the Hypervolemic-Hemodilution/Hypertension group (71 +/- 20) versus the Control (13 +/- 9) and Hypervolemic-Hemodilution/Normotension (17 +/- 10) groups (p less than 0.05). No other differences were present. These results support the hypothesis that during MCAo, hypervolemic-hemodilution/hypertensive therapy effects an increase in blood-brain barrier permeability in the early period of reperfusion.

Etiology of the disruption in blood-arterial wall barrier following experimental subarachnoid hemorrhage

Aneurysmal subarachnoid hemorrhage is associated with a sudden rise in intracranial pressure, acute arterial hypertension, and subarachnoid blood. The role that each of these factors may play in the development of the acute barrier disruption of the major cerebral arteries following subarachnoid hemorrhage was investigated in 42 rabbits. Horseradish peroxidase was given intravenously to assess the integrity of the barrier by transmission electron microscopy. Permeation of the tracer into the vessel was noted only in animals with increased intracranial pressure. A sudden rise in intracranial pressure is suggested to trigger acute barrier disruption following subarachnoid hemorrhage.

Amitriptyline-induced morphological alterations of the rat blood-brain barrier

Amitriptyline is known to increase the permeability of the blood-brain barrier but the morphological basis of this increase has not been studied. As catecholamines can influence pinocytosis in dog peripheral blood vessels, the effect of amitriptyline on the pinocytotic activity of blood brain microvessels was studied. Amitriptyline, 34 mg.kg-1 i.p., was injected to rats and the parietal cortex of control and treated animals was prepared for ultrastructural study. Pinocytotic vesicles in endothelial cells were quantified. Amitriptyline significantly increased the density of pinocytotic vesicles in capillary endothelial cells. No other morphological changes occurred after amitriptyline treatment. We conclude that the increase in blood-brain barrier permeability due to amitriptyline may be ascribed at least in part to an increase of pinocytotic activity in brain capillary endothelial cells.

The effect of hypertension and its treatment on cerebral cell volume regulation during hypernatremic dehydration

Since hypertension may compromise the ability to withstand hypernatremic dehydration, we investigated the impact of two experimental models of hypertension and pharmacologic normalization of blood pressure on the tolerance to chronic hypernatremic dehydration. In DOCA-salt hypertensive animals and the spontaneously-hypertensive rat (SHR), there was increased mortality and cerebral cell shrinkage during hypernatremic dehydration, compared to control Sprague-Dawley or Wistar-Kyoto rats. These findings were paralleled by significant differences in the brain intracellular water compartment size (ml/100 g dry weight), i.e. 233 +/- 6, Sprague-Dawley vs 189 +/- 8, DOCA-salt, P less than 0.01; 246 +/- 3, Wistar-Kyoto vs 194 +/- 6, SHR, P less than 0.01. Normalization of the blood pressure in the SHR with captopril restored 48% of the cerebral cell volume regulatory capacity observed in normotensive Wistar-Kyoto rats. We conclude that sustained hypertension increases the risk of hypernatremic dehydration in select circumstances. Correction of the elevated blood pressure promotes partial recovery of normal cerebral cell volume regulation.

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

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

Effect of chronic hypertension on acute hypertensive disruption of the blood-brain barrier in rats

The effect of chronic hypertension on acute hypertensive disruption of the blood-brain barrier has been studied in only two models of hypertension, with inconsistent results. The purpose of this study was to reinvestigate whether chronic hypertension has a consistent effect on acute hypertensive disruption of the blood-brain barrier and to determine whether one of the previously studied models has an unusual response to chronic hypertension. We studied four rat models of chronic hypertension: spontaneously hypertensive rats (SHR), two-kidney, 1 clip Goldblatt rats (2K1C), rats treated with deoxycorticosterone acetate (DOCA) and NaCl, Dahl salt-sensitive rats fed a high salt diet, and two groups of normotensive controls: Wistar-Kyoto rats (WKY) and Dahl salt-sensitive rats fed a low salt diet. We caused acute hypertension in some rats with the use of bicuculline (1.2 mg/kg) and aortic occlusion. Rats without acute hypertension served as controls. Blood-brain barrier disruption was quantitated using the brain/blood ratio of 125I-labeled albumin. Acute hypertensive disruption was less in SHR, rats treated with DOCA-NaCl, and Dahl salt-sensitive rats fed a high salt diet, but not in 2K1C rats, as compared with normotensive controls. Acute hypertensive disruption was greater in Dahl salt-sensitive rats fed a low salt diet than in WKY. A series of control WKY, SHR, rats treated with DOCA-NaCl, 2K1C rats, and Dahl salt-sensitive rats fed low or high salt diets, but not subjected to acute hypertension, were also studied. Brain/blood 125I-albumin ratios were significantly less in these control rats not subjected to acute hypertension than in rats subjected to acute hypertension.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenaline-induced hypertension: morphological consequences of the blood-brain barrier disturbance

Acute hypertension may transiently open the blood-brain barrier (BBB). To determine whether such temporary exposure of the brain parenchyma to plasma constituents may lead to permanent morphological alterations, acute hypertension was induced by i.v. adrenaline in conscious rates given Evan's blue and horseradish peroxidase as tracers. The brain were perfused in situ 24 h later: 17 of 21 brains showed multifocal sites of extravasation of the tracers and of endogenous plasma albumin, fibrinogen and fibronectin identified by immunohistochemistry. The proteins spread locally in the parenchyma and were taken up by neurons. Within the leaking sites in the cortex, hippocampus, thalamus and basal ganglia some shrunken and grossly distorted acidophilic neurons were present. Focal areas of sponginess were observed in the subpial and subependymal zones. Thus, a transient opening of the BBB may lead to neuronal damage.

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.

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.

Brain phenobarbital uptake during prolonged status epilepticus

The brain uptake of phenobarbital during prolonged status epilepticus (3 h) was studied in paralyzed, ventilated sheep. The first 30 min of status epilepticus was characterized by systemic hypertension, increased CBF, increased peripheral vascular resistance, a fall in brain pH, and an elevation in brain lactate concentrations. Subsequently, hemodynamic factors normalized and brain acidosis persisted. Phenobarbital administered during the early phase of status epilepticus produced higher levels of brain phenobarbital concentration, which was greatest at the earliest sample time (5 min following infusion), compared to nonseizure controls. This elevation persisted for the first 3 h following the infusion. Phenobarbital administration during the established phase of status epilepticus, when systemic blood pressure, peripheral vascular resistance, and CBF had returned to preseizure values, resulted in attenuated brain phenobarbital uptake not different from controls for the first 30 min. These results are explained by disruption of the blood-brain barrier to phenobarbital during the early (hypertensive) phase of status epilepticus.

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.

Pharmacological modification of bradykinin induced breakdown of the blood-brain barrier

Internal carotid artery infusion of bradykinin caused extensive breakdown of the blood-brain barrier to protein as demonstrated by the extravasation of the marker, horseradish peroxidase, into vessel walls and the adjacent parenchyma. Pretreatment of the animals with indomethacin, trifluoperazine, or imidazole significantly reduced the quantity of abnormally permeable vessels as determined by light microscopy. By electron microscopy, it was determined that bradykinin caused an intense increase in the number of pinocytotic vesicles in the permeable segments, but no change in the interendothelial junctions. After imidazole pretreatment, although the extent of the permeability change was markedly reduced, the intensity of pinocytotic activity in the involved areas was not altered.

Focal brain edema associated with acute arterial hypertension

Acute arterial hypertension was studied in normal cats to determine its role in the formation of brain edema. Arterial hypertension was induced for 30 minutes by inflation of a balloon catheter situated in the descending aorta. Cerebral edema was evaluated by gross and microscopic observations, tissue water content by wet/dry weights, and blood-brain barrier (BBB) permeability by extravasation of horseradish peroxidase (HRP) and Evans blue dye. For 1 hour after the hypertensive insult, tissue pressure and regional cerebral blood flow (rCBF) were measured from the arterial boundary zone and from a non-boundary region, and intracranial pressure was recorded from the lateral ventricle as ventricular fluid pressure. Focal lesions with increased BBB permeability to Evans blue dye or HRP were usually located symmetrically in the cortex, corresponding to the occipitoparietal parts of the arterial boundary zones. The increase in water content was found only in areas of increased permeability. Tissue pressure increased simultaneously with the abrupt rise in blood pressure, and an increase in rCBF paralleled the elevation of blood pressure. Tissue pressure and rCBF returned to a steady state when blood pressure returned to normal. There were no differences in tissue pressure or rCBF between the arterial boundary zone and the non-boundary zone, even during arterial hypertension. In cerebral hemispheres examined 48 hours after the hypertensive challenge, brain edema had not continued to develop. The data indicate that acute arterial hypertension may produce focal brain edema with increased permeability of the BBB in the cortex of normal brain, particularly in the arterial boundary zones. The authors postulate that increased cerebral blood volume, high intraluminal pressure, and breakthrough of autoregulation play an important role in the formation of hypertensive brain edema.

Fundus lesions in malignant hypertension. IV. Focal intraretinal periarteriolar transudates

Experimental renovascular malignant arterial hypertension was produced in 57 rhesus monkeys by a modified Goldblatt's procedure and their eyes were studied by serial ophthalmoscopy, by stereoscopic color fundus photography, and by fluorescein fundus angiography over a period of months or years. A very common, and one of the earliest, lesions in hypertensive retinopathy was focal intraretinal periarteriolar transudates (FIPTs). In the past, FIPTs have been described erroneously as "cotton-wool spots." The two types of lesions differ very much in shape, size, color, location, fluorescein fundus angiographic pattern, resolution pattern, life cycle, and pathogenesis. FIPTs, on ophthalmoscopy, usually are pinpoint to pinhead size, round or oval, dull white in color, and situated in deeper layers of the retina and beside the major retinal arteries and their main branches. On fluorescein angiography, FIPTs show multiple punctate foci of fluorescein leakage from dilated precapillary retinal arterioles, and there is no focal retinal capillary obliteration. They usually last for two to three weeks, and on resolution leave no ophthalmoscopic, angiographic, or microvascular abnormality. Cotton-wool spots are seen in a variety of retinopathies; FIPTs, however, are a specific retinal lesion of malignant arterial hypertension only. They develop due to breakdown of blood-retinal barrier in pre-capillary retinal arterioles, due to dilatation of the arterioles from failure of autoregulation (caused by severe rise of blood pressure).

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.

Pharmacological modification of blood-brain barrier permeability following a cold lesion

The effect of desipramine, imidazole, thioridazine and trifluoperazine on blood-brain barrier (BBB) permeability after a 24 hour cold lesion was studied in rats. Changes in BBB permeability were determined using a quantitative horseradish peroxidase (HRP) assay. The four drugs tested did not alter the quantity of HRP in the cortex of control animals, or in the contralateral cortex of test animals. However, imidazole, desipramine and trifluoperazine significantly reduced the HRP extravasation in and around the cold lesion. Several mechanisms for this effect are suggested; one possible mechanism common to all these drugs is the reduction of increased vesicular transport in cortical vessels adjacent to the cold lesions.

Microvascular permeability in induced astrocytomas and peritumor neuropil of rat brain. A high-voltage electron microscope-protein tracer study

Brain tumors, benign and malignant, are characteristically more permeable to various types of tracer molecules than the neuropil in which they are embedded. Impermeability of brain neuropil capillaries is imparted by the blood-brain barrier, the anatomic basis of which is the network of interendothelial zonulae occludentes that seal capillary endothelial cells. To explore both the vascular elements of brain neoplasms and the route of tracer extravasation from them, as well as the possible effects of brain tumors on the permeability of peritumoral neuropil capillaries, brain tumors were induced in newborn Wistar rats by intracerebral (i.c.) injection of C-6 astrocytoma cells. The protein tracer horseradish peroxidase (HRP) was injected systemically into both normal and tumor-bearing rats to mark the pathway along which it flowed into the tumor parenchyma tissue spaces, and to signal any concomitant tracer loss from the tumor extracellular compartment or peritumoral brain capillaries, into the neuropil extracellular milieu. Electron-microscopic examination of thin plastic sections of tumor and peritumoral neuropil revealed massive extravasation of tracer into the tumor tissue spaces, but none was seen outside of the capillaries in the surrounding brain neuropil. Zonulae occludentes of both tumor capillary endothelium and brain capillary endothelium were devoid of tracer and judged tight (sealed). Tracer was seen in pinocytotic vesicles in the highly attenuated endothelium of tumor capillaries and also in cytoplasmic vesicles within the tumor cells. The peritumoral and contralateral neuropil capillary endothelium exhibited reaction product-filled pinocytotic vesicles and vesiculo-tubular conduits. Often, one end of a HRP-filled vesiculo-tubular channel appeared continuous with either the luminal or abluminal plasmalemma. High-voltage electron microscopy of these conduits often showed them to be continuous with both luminal and abluminal surfaces of the endothelium, thus forming a continuum across the capillary wall. In addition, these transendothelial channels, clearly constituted as chains of fused vesicles, were often seen in close proximity to, or fused with, dense bodies in the endothelial cytoplasm. In spite of the presence of HRP-filled structures in the peritumoral neuropil capillary endothelium of tumor-bearing rats, no evidence of tracer extravasation from these vessels was apparent. These results suggest that although peritumoral and contralateral neuropil capillaries possess the machinery for extravasation of tracer, likely as a response to the presence of the neoplasm, tracer is not lost but, instead, is degraded by endothelial enzymes.(ABSTRACT TRUNCATED AT 400 WORDS)

Formation of transendothelial channels in traumatic human brain edema

The formation of incomplete transendothelial channels is reported in four cases of traumatic human brain injury complicated with subdural or epidural hematoma or hygroma. Such structures were observed coexisting with increased transendothelial vacuolar and vesicular transport. They appeared in the following manners: as electron lucent corridors formed by deep invaginations of luminal endothelial plasma membranes, as chained spheroidal or elongated vacuoles connected with the luminal and abluminal endothelial membranes, as a result of a combined process of membrane fusion and fission, as a large protein containing vacuole or a micropinocytotic vesicle occupying the entire width of peripheral endothelial cytoplasm, as abluminal profiles of dilated basement membrane expansions, extending their course to the vicinity of endothelial luminal plasma membrane. The endothelial junctions appeared intact in most cases. The transendothelial channels apparently represent a transcytosis response to the traumatic brain injury. They may provide specific cytoplasmic corridors of facilitated transport for edema formation, which incorporate the intraluminal capillary content, ferry it across the peripheral zone of endothelial cytoplasm and empty it at the abluminal surface, into the surrounding basement membrane, from where it floods the intercellular spaces of neighbouring neuropile. The albuminal transendothelial channels, formed by the dilated basement membrane bifurcations, might be a reverse shuttle for endogeneous substances moving from parenchymal clefts to blood as a capillary mechanism of edema resolution.

Reversibility of blood-brain barrier dysfunction in acute hypertension induced by angiotensin

The reversibility of blood-brain barrier (BBB) dysfunction was examined in rats after acute experimental hypertension. A short-lasting (less than or equal to 4 min) acute hypertension was produced by intravenous injection of 20 micrograms/kg angiotensin. Evans blue, the barrier tracer, was administered intravenously either prior to or at intervals of 3, 10, 20, 30, and 60 min after the angiotensin injection. It was observed that the BBB dysfunction showed a peak 30 min after the angiotensin injection. Three of six animals that received Evans blue 60 min after angiotensin administration showed extravasation of the tracer on gross inspection. We concluded that BBB dysfunction may remain even 60 min after an acute hypertensive episode of short duration.

The protective influence of the locus ceruleus on the blood-brain barrier

The functions of the putative noradrenergic innervation of cerebral microvessels from the nucleus locus ceruleus remain ambiguous. Although most evidence indicates that such innervation does not have a major role in the control of cerebral blood flow, there are increasing indications that it modulates transport and permeability functions of the blood-brain barrier. In this study we investigated the effect of unilateral chemical lesioning of the locus ceruleus on the leakage of radioiodinated human serum albumin across the blood-brain barrier. Experiments were performed in awake and restrained rats under steady-state conditions and during drug-induced systemic arterial hypertension, and in anesthetized and paralyzed rats during bicuculline-induced seizures. Both hypertension and seizures are known to be associated with increased leakage of macromolecules across the blood-brain barrier. Albumin leakage into norepinephrine-depleted forebrain structures ipsilateral to the locus ceruleus lesion was compared with that of the contralateral side. There were no side-to-side differences in blood-brain barrier permeability to albumin under steady-state conditions, the stress of restraint, or angiotensin-induced hypertension, or after isoproterenol administration. Norepinephrine-induced hypertension and seizures, however, caused significant increases in albumin leakage into forebrain structures ipsilateral to the lesion. These results suggest that noradrenergic innervation of cerebral microvessels from the locus ceruleus helps preserve the integrity of the blood-brain barrier during pathophysiological states associated with hypertension and increased circulating catecholamines.

Pathophysiology of the opening of the blood-brain and blood-cerebrospinal fluid barriers in acute hypertension

Acute hypertension, produced by i.v. Aramine injection, opened the blood-brain and blood-cerebrospinal fluid (CSF) barriers to Evans blue-albumin. In rabbits the threshold for blood-brain barrier (B-BB) opening was approximately 160 mm Hg and for blood--CSF barrier opening 150 mm Hg. The blood-brain and blood-CSF barriers were not opened by blood pressure elevations less than 80 mm Hg. Multiple blue spots (1- to 10-mm diameter) which show Evans blue-albumin extravasation, were seen throughout the cerebral cortex, occasionally in the medulla-pons, and cerebellum. Diffuse extravasation was not seen and the extravasation was nearly symmetrical in the two hemispheres. The barrier permeability was increased when systemic blood pressure was elevated rapidly rather than gradually to the threshold level. Endothelial or epithelial cell destruction was never observed in light and electron microscopic studies. Arterial blood and CSF PCO2, PO2 and pH remained constant, which is indicative of the lack of significant metabolic effect caused by hypertension. Barrier opening in acute hypertension is postulated to be due primarily to the direct mechanical effect of increased intraluminal pressure in cerebral vessels, which may cause widening of the tight junctions between endothelial cells.

Acute responses to experimental blunt head trauma. Topography of cerebral cortical edema

Anesthetized cats subjected to impact followed by acceleration and rotation of the skull were sacrificed at 15 minutes or 6 hours after injury and were selected for study if unilateral cerebral contusion was present. Widespread areas of cerebral cortex were examined bilaterally for edema, using measurement of tissue density with an organic gradient, and for breakdown of the blood-brain barrier to plasma protein tagged with Evans blue dye. At both times tested, a halo of vasogenic edema (Evans blue stain plus decreased density) was present in the cortex surrounding areas of contusion. At 15 minutes after injury, animals with deep contusions also had a slight decrease in density without Evans blue staining, interpreted as cytotoxic edema, in some gyri neighboring the contusion. At 6 hours, cytotoxic edema was not evident, but some animals had vasogenic edema in the gyri adjoining the contusion. Most gyri contralateral to contused areas had neither Evans blue staining nor changes in tissue density. These findings suggest that, with the present head-injury model, acute changes in tissue density and vascular permeability occur in the cerebral cortex of hemispheres with contusion. These responses are related topographically to contusion sites, and change over the two times studied. The authors conclude that events in addition to spread of fluid from areas of contusion contribute to the edema of head injury, and that more than one form of edema can follow mechanical trauma to the brain.

Ultrastructural study of the effect of acute hypertension on the stria vascularis and spiral ligament

The effect of acute hypertension, induced in rats by intravenous injection of methoxamine chloride (Mexan), on the stria vascularis and spiral ligament was studied electronmicroscopically with the tracer method of horseradish peroxidase (HRP). Considerable extravasation of HRP occurred in the stria vascularis, due to the increased vesicular transport. The leaked HRP spread into intercellular spaces, but was prevented from spreading towards the endolymph by zonulae occludentes between marginal cells and towards the perilymph by zonulae occludentes between basal cells. The reaction product was occasionally found between basal cells. No leakage of HRP from capillaries was observed in the spiral ligament, although some labelled micropinocytotic vesicles were present in the endothelium. It is suggested that, under acute hypertensive conditions, areas of zonulae occludentes bordering the stria vascularis play an important role as a barrier to HRP, whereas capillaries in the spiral ligament themselves act as a barrier to it.

Effect of intracarotid etoposide on opening the blood-brain barrier

The effect of an intracarotid artery infusion of etoposide on blood-brain barrier (BBB) integrity was investigated in a rat model system. The external carotid arteries of Sprague-Dawley rats were catheterized in a retrograde manner. Etoposide in a dose range from 3.0 mg/kg to 22.5 mg/kg was infused into the internal carotid artery by this technique. BBB disruption was evaluated qualitatively by the appearance in the infused hemisphere of the systemically administered dye Evans blue and quantitatively by the ratio of counts of the technetium-labeled chelate of diethylenetriaminepentaacetic acid (99mTc-DTPA) in the infused to the noninfused hemisphere. Evidence of increased BBB permeability was seen at all doses of etoposide. Degree of BBB disruption increased with increasing doses of etoposide. The intracarotid infusion and subsequent BBB disruption were well tolerated. Further clinical trials employing the intracarotid administration of etoposide should be cognizant of the potential for BBB disruption.

The permeability to exogenous protein of the wall of the superior sagittal sinus of the cat

The permeability of the wall of the superior sagittal sinus of the cat has been studied using horseradish peroxidase (HRP) as an exogenously applied tracer. Cats were given intracisternal or intravascular injections of HRP before being perfused transcardially for examination of sinus tissues with the electron microscope. Tissues were processed with diaminobenzidine to reveal peroxidase activity. A diffusion barrier to the protein tracer was seen to occur at the level of the arachnoid mater. When injections of HRP were made into the cisterna magna, the protein was able to course through the subarachnoid space surrounding the sinus, and sequestration of the tracer was seen in deep cell layers of the arachnoid mater. However, a series of zonulae occludentes at more apical levels of the arachnoid prevented the tracer from penetrating intercellularly to the level of the dura mater. Conversely, when HRP was given intravascularly, the protein penetrated intercellular spaces of the dura mater and apical levels of the arachnoid mater, stopping at the level of the zonulae occludentes of the arachnoid. This barrier layer appears to be continuous with the arachnoid barrier layer which prevents diffusion of large molecules through the arachnoid mater over the brain convexities.

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.

Neurotoxicity of radiological contrast agents

The most important complications of intravascular administration of contrast agents include idiosyncratic (anaphylactoid) reactions, shock, congestive heart failure, cardiac arrhythmias, acute renal failure, and neurotoxic effects. The incidence of serious neurotoxic effects is low. Entry of contrast agents into the central nervous system normally is limited but may be increased by osmotic opening of the blood-brain barrier with cerebral arteriography or arch aortography. Most neurotoxic effects are thought to represent direct effects of the contrast agent on brain or spinal cord. Adverse effects with arteriography include seizures, transient cortical blindness, brain edema, and spinal cord injury. Most cases of focal brain deficit (other than cortical blindness) are attributed to embolism secondary to the catheter. Seizures may occur with intravenous administration, especially in patients with brain tumors or other processes disrupting the blood-brain barrier. The most important adverse effects observed with myelographic agents include acute and chronic meningeal reactions with iophendylate, and seizures and transient encephalopathy with metrizamide.

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.

Morphologic effect of dimethyl sulfoxide on the blood-brain barrier

Dimethyl sulfoxide (DMSO) opens the blood-brain barrier of mice to the enzymatic tracer horseradish peroxidase. A single injection of horseradish peroxidase in 10 to 15 percent DMSO into the tail vein along with 10 to 15 percent DMSO delivered intraperitoneally allowed horseradish peroxidase to fill the extracellular clefts throughout the brain within 2 hours. In the absence of DMSO, peroxidase failed to enter brain parenchyma except through the circumventricular organs. Opening of the blood-brain barrier by DMSO is reversible. Dimethyl sulfoxide stimulated the pinocytosis of horseradish peroxidase by the cerebral endothelium; the peroxidase was then directed to lysosomal dense bodies for degradation. Vesicular transport of horseradish peroxidase from the luminal to the abluminal wall of the endothelial cell was not observed. Dimethyl sulfoxide did not alter the morphology of endothelial cells or brain parenchyma.