Blood-brain barrier opening to horseradish peroxidase in acute arterial hypertension

Endothelial tight junctions and their regulatory signaling pathways in vascular homeostasis and disease

Endothelial tight junctions (TJs) regulate the transport of water, ions, and molecules through the paracellular pathway, serving as an important barrier in blood vessels and maintaining vascular homeostasis. In endothelial cells (ECs), TJs are highly dynamic structures that respond to multiple external stimuli and pathological conditions. Alterations in the expression, distribution, and structure of endothelial TJs may lead to many related vascular diseases and pathologies. In this review, we provide an overview of the assessment methods used to evaluate endothelial TJ barrier function both in vitro and in vivo and describe the composition of endothelial TJs in diverse vascular systems and ECs. More importantly, the direct phosphorylation and dephosphorylation of TJ proteins by intracellular kinases and phosphatases, as well as the signaling pathways involved in the regulation of TJs, including and the protein kinase C (PKC), PKA, PKG, Ras homolog gene family member A (RhoA), mitogen-activated protein kinase (MAPK), phosphatidylinositol 3-kinase (PI3K)/Akt, and Wnt/β-catenin pathways, are discussed. With great advances in this area, targeting endothelial TJs may provide novel treatment for TJ-related vascular pathologies.

Role of Hyperintense Acute Reperfusion Marker for Classifying the Stroke Etiology

Purpose

The hyperintense acute reperfusion marker (HARM) is a delayed enhancement of the subarachnoid or subpial space observed on post-contrast fluid-attenuated inversion recovery (FLAIR) images and is associated with permeability changes to the blood–brain barrier in acute stroke. We investigated the relationship between HARM and stroke etiology based on the Trial of ORG 10172 in Acute Stroke Treatment (TOAST) classification. In addition, we evaluated the relationship between HARM and stroke locations with respect to vascular territories and anatomic compartments.

Materials and methods

We recruited 264 consecutive patients (109 women; mean age 68.63 years) who were diagnosed with acute ischemic stroke and underwent brain magnetic resonance imaging (MRI) including post-contrast FLAIR and DWI within 7 days of symptom onset from May 2015 to March 2016 for this retrospective study. Post-contrast FLAIR images were obtained 5 min after gadolinium administration. The mean time interval between the onset of stroke symptoms and MRI acquisition in total included patients was 18 h and 7 min (median 12 h and 57 min, range 2–127 h). We analyzed the overall incidence and distribution patterns of HARM in acute ischemic stroke cases and compared the relative incidence and distribution patterns of HARM between the subgroups of stroke etiology based on conventional TOAST classification. We obtained odds ratio (OR) of HARM in different stroke locations based on vascular territories and anatomical compartments. This study was approved by our institutional review board.

Results

Among the 264 patients, 67 (25.38%) patients were HARM positive and 197 (74.62%) patients were HARM negative. There was significant difference in HARM incidence among the stroke subgroups (p < 0.001). Small vessel occlusion (SVO) was associated with the HARM-negative group (p < 0.001), while large artery atherosclerosis (LAA) and cardioembolism (CE) were associated with the HARM-positive group (p = 0.001). Also, regional pattern of HARM on the same vascular territory as the acute infarction was dominantly demonstrated regardless of stroke etiology. The OR for HARM from middle cerebral artery (MCA) infarction was 1.868 [95% confidence interval (CI): 1.025–3.401]. The OR for HARM from cortical infarction was 9.475 (95% CI: 4.754–18.883) compared to other anatomic compartments.

Conclusion

The presence of the HARM was significantly associated with embolic infarctions including LAA and CE. Conversely, SVO was exclusively associated with the absence of the HARM. Second, MCA and cortical infarction showed a more pronounced HARM compared to infarctions at other vascular territories and anatomic compartments. According to the results in the current study, we speculate that the presence of HARM on post-contrast FLAIR images was associated with specific stroke causes especially in embolic causes.

Cell-specific blood-brain barrier regulation in health and disease: a focus on hypoxia

The blood-brain barrier (BBB) is a complex vascular structure consisting of microvascular endothelial cells that line the vessel wall, astrocyte end-feet, pericytes, as well as the basal lamina. BBB cells act in concert to maintain the characteristic impermeable and low paracellular flux of the brain vascular network, thus ensuring a homeostatic neuronal environment. Alterations in BBB stability that occur during injury have dire consequences on disease progression and it is clear that BBB cell-specific responses, positive or negative, must make a significant contribution to injury outcome. Reduced oxygenation, or hypoxia, is a characteristic of many brain diseases that significantly increases barrier permeability. Recent data suggest that hypoxia-inducible factor (HIF-1), the master regulator of the hypoxic response, probably mediates many hypoxic effects either directly or indirectly via its target genes. This review discusses current knowledge of physiological cell-specific regulation of barrier function, their responses to hypoxia as well as consequences of hypoxic- and HIF-1-mediated mechanisms on barrier integrity during select brain diseases. In the final sections, the potential of current advances in targeting HIF-1 as a therapeutic strategy will be overviewed.

Biphasic opening of the blood-brain barrier following transient focal ischemia: effects of hypothermia

OBJECTIVE

Tracer constants (Ki) for blood-to-brain diffusion of sucrose were measured in the rat to profile the time course of blood-brain barrier injury after temporary focal ischemia, and to determine the influence of post-ischemic hypothermia.

METHODS

Spontaneously hypertensive rats were subjected to transient (2 hours) clip occlusion of the right middle cerebral artery. Reperfusion times ranged from 1.5 min to 46 hours, and i.v. 3H-sucrose was circulated for 30 min prior to each time point (1 h, 4 h, 22 h, and 46 h; n = 5-7 per time point). Ki was calculated from the ratio of parenchymal tracer uptake and the time-integrated plasma concentration. Additional groups of rats (n = 7-8) were maintained either normothermic (37.5 degrees C) or hypothermic (32.5 degrees C or 28.5 degrees C) for the first 6 hours of reperfusion, and Ki was measured at 46 hours.

RESULTS

Rats injected after 1.5-2 min exhibited a 10-fold increase in Ki for cortical regions supplied by the right middle cerebral artery (p < 0.01). This barrier opening had closed within 1 to 4 hours post-reperfusion. By 22 hours, the blood-brain barrier had re-opened, with further opening 22 and 46 hours (p < 0.01), resulting in edema. Whole body hypothermia (28 degrees C-29 degrees C) during the first six hours of reperfusion prevented opening, reducing Ki by over 50% (p < 0.05).

CONCLUSIONS

Transient middle cerebral artery occlusion evokes a marked biphasic opening of the cortical blood-brain barrier, the second phase of which causes vasogenic edema. Hypothermic treatment reduced infarct volume and the late opening of the blood-brain barrier. This opening of the blood-brain barrier may enhance delivery of low permeability neuroprotective agents.

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.

Cerebral oedema after subarachnoid haemorrhage. Pathogenetic significance of vasopressin

The authors report the frequency, characteristic clinical symptoms, laboratory alterations and diagnostic criteria of the syndrome of inappropriate secretion of antidiuretic hormone (SIADH) after subarachnoid haemorrhage. The data on 290 patients with subarachnoid haemorrhage (SAH) during a period of years at the Division of Neurosurgery, University Medical School, Szeged, are analysed. Twenty-seven (9.3%) patients developed SIADH. Thirteen (4.5%) patients had severe and 14 (4.8%) had mild SIADH. The problems of the treatment are discussed in detail and the different therapeutic methods are listed: NaCl infusion, water withdrawal and administration of Dilantin, diuretics, mineralocorticosteroids, lithium and demeclocycline. The undesirable side-effects observed accompanying various therapeutic regimen are analysed. The introduction of V2 antagonists into clinical practice appears to be a most perspective procedure. For study of the pathogenesis of SIADH following SAH, the possibility of treatment with V2 antagonists on an experimental model of SAH in rat was created. A significant water retention and increases in brain water and sodium content were observed in rats with SAH. Plasma AVP levels were also elevated after SAH. AVP plays an important role in the development of antidiuresis following water loading and disturbance of the brain water and electrolyte balance after SAH. Water retention and the higher brain water and sodium accumulation could be totally prevented by administration of a V2 antagonist. These results demonstrate that cerebral oedema generated by artificial cerebral bleeding in rats is significantly reduced following the administration of a highly specific V2 antagonist, suggesting a new approach to the treatment of SIADH.

Contraction of human brain endothelial cells induced by thrombogenic and fibrinolytic factors. An in vitro cell culture model

BACKGROUND AND PURPOSE

Vasogenic brain edema is a frequent complication of ischemic stroke. The mechanism of the blood-brain barrier opening that underlies the edema formation is poorly understood. In the present study we examined the response of endothelial cells cultured from adult human brain to thrombogenic and fibrinolytic factors that possibly accumulate in the occluded vascular segments in ischemic stroke.

METHODS

The changes in the morphology of cultured human brain microvascular endothelial cells were observed by phase-contrast light microscopy and quantified with computerized morphometry.

RESULTS

Active proteases (eg, thrombin, plasmin, urokinase) as well as heparin and protamine, but not fibrinogen and antithrombin III, produced significant changes in endothelial cell morphology. Two shape patterns of contraction were observed: protamine treatment resulted in rounded cells with a decrease in both cell perimeter and area, whereas all other agents induced spiderlike cell morphology with increased perimeter and reduced area. The rate of contraction was dose dependent, and at comparable enzyme concentrations plasmin produced faster contraction than thrombin. The observed changes were reversed 3 hours after abrogating the treatment.

CONCLUSIONS

In an in vitro model we have demonstrated that factors involved in thrombus formation and dissolution induce endothelial cell contraction, which could affect focally the permeability of the blood-brain barrier by opening paracellular avenues between endothelial cells in vivo. Thus, the genesis of brain edema in thromboembolic stroke or occasionally during fibrinolytic therapy can be attributed in part to the contact of these factors with the microvascular endothelium.

Ultrastructural evidence for neurogenically mediated changes in blood vessels of the rat dura mater and tongue following antidromic trigeminal stimulation

We investigated the effects of unilateral electrical trigeminal ganglion stimulation (0.1 or 1.0 mA, 5 Hz, 5 ms, 5 min) on the morphology of blood vessels within the rat dura mater and tongue using light and transmission electron microscopy. Stimulation at both intensities caused changes which were confined to the ipsilateral post-capillary venules except in the tongue where arterioles were affected as well. Changes were more marked after 1.0 mA. Dramatic increases in the numbers of endothelial pinocytotic vesicles were found along the luminal and abluminal surfaces ipsilateral to the stimulation. Tight junctions remained largely intact, except that injected ferritin particles were occasionally trapped inside these junctions. Cytoplasmic microvilli and endothelial blebs were sometimes present as well. Approximately 80% of the examined dural post-capillary venules showed one or more of these endothelial changes. Horseradish peroxidase injected intravenously 5 min prior to stimulation was detected in the extracellular space surrounding dural blood vessels and within pinocytotic vesicles. Ferritin injected similarly, was also localized in post-capillary venule walls, interstitial spaces, intraendothelial vesicles and in vacuoles. Platelet accumulation and aggregation were present in approximately 10% of post-capillary venules in dura and tongue. These changes were associated with mast cell secretion, but neither vascular nor mast cell activation was observed in adult rats in whom C-fibers were destroyed during the neonatal period with capsaicin. The present observations provide morphological evidence which supports findings from previously reported albumin tracer studies suggesting enhanced transport and endothelial activation following electrical stimulation of small caliber afferent fibers.

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.

Brain kininogen following experimental brain injury: evidence for a secondary event

Previous studies have shown that following experimental brain injury cerebral arterioles dilate and display endothelial lesions and reduced responsiveness to hypocapnia. These abnormalities are caused by cyclo-oxygenase-dependent free radical generation. There is evidence that the kallikrein-kinin system may in part stimulate the cyclooxygenase-dependent damage since bradykinin is a powerful stimulator of prostaglandin formation and it has recently been shown that a specific kinin receptor blocker decreases the arteriolar abnormalities caused by injury. In order to further examine the hypothesis that the kallikrein-kinin system is important in inducing damage, rat brain tissue was examined for kininogen, the precursor of kinins, at 10 minutes and 1, 3, 6, 15, 24, 48, and 72 hours after injury. A fluid-percussion brain injury device was attached over the right cerebral cortex of rats and a 1.6-atmosphere pressure injury was administered. The kininogen content was determined by a radioimmunoassay procedure in tissues which were free of intravascular blood. After injury, bleeding was confined mainly to the right hemisphere. The kininogen content in the right hemisphere was significantly elevated by one hour after injury, continued to rise until 15 hours after injury, then was significantly decreased by 2 days after injury. In the left hemisphere, kininogen was significantly elevated at 1 hour postinjury, returned toward control levels over the 3- to 6-hour period after injury, then was again elevated at 15 hours after injury. These studies also show that brain water and cerebrovascular permeability were greater at 15 hours postinjury than at earlier time points. The data further support a role for the kallikrein-kinin system in brain injury and, when considered with the results of other studies, suggest that a secondary event is occurring in the 12- to 24-hour period after neural injury. The authors hypothesize that this secondary event is related to endothelial and vascular repair and may be important for the return of normal cerebrovascular function.

Ultrastructural study of micro-blood vessels in human brain tumors and peritumoral tissue

Ultrastructural and tracer studies have demonstrated that vasogenic edema, a serious complication of brain tumor is the result of increased permeability of tumor vessels. However, not much information is available on the alterations in the vessels in the peritumoral areas. Therefore, we studied the ultrastructural changes in the tumor micro-blood vessels (MBVs) in 20 cases of glioma and compared these with the changes in the peritumoral MBVs in 10 of these cases. The tumor MBVs showed remarkable structural changes, viz, increase in pinocytotic vesicles, large vacuoles and microvilli in the endothelial cells, varying degrees of endothelial attenuation and fenestration, an occasional partially or completely opened-up junction and some pale and edematous endothelial cells, which can adequately explain their increased permeability. The peritumoral MBVs also showed evidence of increased permeability in the form of increased pinocytotic vesicles, large vacuoles and microvilli associated with pale and edematous cytoplasm of some endothelial cells. Thickened multilayered basement membrane, absence of ensheathment of capillary basement membrane by astrocytic cell processes and widened perivascular space were observed in both tumoral and peritumoral MBVs. An interesting observation was that in the peritumoral MBVs, the pinocytotic vesicles were most conspicuously seen on the abluminal side of the endothelial cells often fused with the abluminal plasma membrane. Although a static study like this cannot indicate any definite direction of movement of fluid, we feel that the occurrence of reverse pinocytosis is a distinct possibility in the peritumoral MBVs and that it may be an important means of resorption of edema fluid.

Effect of intracisternal thromboxane A2 analogue on cerebral artery permeability

Thromboxane, a highly vasoactive substance, is found in the cerebrospinal fluid of patients and experimental animals following subarachnoid haemorrhage. A stable synthetic analogue of thromboxane A2 was administered intracisternally in rabbits. This resulted in an increase in endothelial permeability of the major cerebral arteries to Evans Blue dye and horseradish peroxidase. Thromboxane may be involved in the pathogenesis of cerebral vasospasm and may be related to the contrast enhancement of the arteries in the basal cisterns on CT scans of patients who are prone to develop arterial narrowing.

Ultrastructural features of a brain injury model in cat. I. Vascular and neuroglial changes and the prevention of astroglial swelling by a fluorenyl (aryloxy) alkanoic acid derivative (L-644,711)

We present qualitative and quantitative ultrastructural observations on the changes induced in neuroglia and blood vessels of gray matter of cat brain by an experimental acceleration-deceleration injury which, when used alone, causes negligible morbidity and mortality, but, when combined with systemic hypoxia, leads to coma and delayed death in approximately 50% of experimental subjects. An increase in the proportion of neuropil occupied by astrocytic cytoplasm is detectable qualitatively in layer Vb of pericruciate cortex 20 min after injury without hypoxia, and is maximal (22%, as measured morphometrically, vs 11.4% in controls) 40 min afterward. Near-normal values (14.1%) are obtained 100 min following the insult. If trauma is succeeded 40 min later by a 60-min period of hypoxia, there is prolongation of astrocytic edema and other neuroglial accompaniments of the traumatic lesion, such as aggregation of nuclear nucleoprotein granules and, in astrocytes, fusion of rosette ribosomes and enlargement of mitochondria. A decrease in luminal area occurs in capillaries 40 min after trauma applied alone. Hypoxia without trauma leads to a significant increase in capillary luminal area, which, however, is abolished when trauma precedes the hypoxic interlude. Intravenous injection of a non-diuretic, fluorenyl derivative (L-644,711) of (aryloxy)alkanoic acid loop diuretics, completely prevents the astrocytic swelling ordinarily present 40 min after acceleration-deceleration injury. Also, L-644,711 improves mortality and morbidity scores in cats subjected to trauma with hypoxia. We suggest that astroglial swelling may be a critical step in the evolving pathology of this head injury model and its prevention, as by L-644,711 administration, may have relevance to the treatment of cerebral edema in human head injury and other clinical disorders accompanied by astrocytic swelling.

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.

Plasticity of the brain in respect of functional restoration after subarachnoid haemorrhage

Subarachnoid haemorrhage caused by aneurysmal rupture constitutes a great impact on the brain and on the intracranial content as a whole, with emphasis on the subarachnoid spaces and arteries. The rupture is followed by a wide range of pathological alterations in the neural function and an outcome varying from neglected signs subsiding in a few days to immediate death. Two main factors seem to influence the different events after subarachnoid bleeding. One is the rupture itself which can be extremely variable in severity and in its immediate as well as late consequences. The other is the ability of all parts of the intracranial content to recover. In order to understand either of both the other should also be looked at and both have to be dealt with if we are to treat patients with an aneurysmal rupture properly. For this reason a grading of rupture will be given in respect of some characteristic events in the light of neural restoration. Clearing of CSF, resolution of brain oedema, restoration of impaired CBF, absorption of cisternal and parenchymal haematoma are all of importance. The majority of lesions which developed after the rupture are not fatal or irreversible and even the neural tissue destroyed by the impact or late ischaemia can be functionally replaced. Possible methods of treatment for attaining this functional restoration will be discussed.

The blood-brain barrier to horseradish peroxidase at the onset of bicuculline-induced seizures in hypothalamus, pallidum, hippocampus, and other selected regions of the rabbit

Rabbits were subjected to bicuculline-induced generalized seizures of 15-min duration to elucidate the mechanism by which the macromolecule horseradish peroxidase (HRP) traverses the blood-brain barrier (BBB) in specific brain areas. Transendothelial pinocytosis at the level of arterioles was the main route of passage. In addition, in thalamus and hippocampus pinocytotic vesicles were observed in capillaries. In thalamus, hypothalamus and septum vesicles in the endothelium of venules were also present. Repeatedly, pinocytotic vesicles were ejecting their content into the interendothelial clefts, so that the presence of HRP reaction product between adjacent tight junctions cannot be considered a conclusive evidence for their opening. The HRP, which had reached the neuropil due to the seizure-evoked BBB opening, accumulated in the interstitial spaces and penetrated the synaptic cleft. Uptake of the tracer in vesicular form into presynaptic boutons, presumably excitatory ones as diagnosed by their ultrastructural features, was observed in all brain regions. The uptake was rare in septum, periaqueductal gray, hypothalamus, and cerebellar cortex; frequent in pallidum, hippocampus, and medulla oblongata; and very intense in thalamus. Uptake in postsynaptic dendrites was present mostly in the vicinity of boutons. Incorporation into glial processes was rare and confined to perivascular astrocytes. It is suggested, that HRP traverses the BBB by regionally selective, transmitter-controlled pinocytotic transport and that the neuronal uptake of the foreign protein is at least partially dependent on the involvement of synapses of particular brain regions in the paroxysmal activity during the generalized seizures.

Pathophysiological aspects of blood-brain barrier permeability in epileptic seizures

Blood-brain barrier (BBB) permeability to macromolecules was assessed during seizures induced by pentylenetetrazole, bicuculline, methoxypyridoxine, methionine sulfoximine, and kainic acid. It was observed that each convulsant induced a specific pattern of regional BBB opening. This was, however, only the case when systemic blood pressure (BP) rose with seizure onset. The analysis of regional cerebral blood flow revealed that a high increase in flow in rabbits with BP rise is related to the normal flow at rest in the single brain region, but not to BBB permeability. In rabbits without BP increase, regional flow increase was low but well modulated and is possibly a better indicator for neuronal activity. The ultrastructural analysis showed that macromolecular transport over the cerebrovascular endothelium is by pinocytosis, an neurotransmitter controlled process. It is suggested that seizure-induced regional BBB opening is determined by two factors: release of neurotransmitters due to the process of auto-regulation during peripheral pressure increase, and change in local neurotransmitter milieu due to the action of the convulsant and/or the seizure activity.

The pathogenetic and prognostic significance of blood-brain barrier damage at the acute stage of aneurysmal subarachnoid haemorrhage. Clinical and experimental studies

In a retrospective study, pathological tissue enhancement was found in nearly two fifths of patients with acute SAH on contrast-enhanced cranial computed tomography. By means of absorption measurements with the region of interest technique over the basal ganglia, it was proved indirectly that pathological tissue enhancement should be brought about not only by hyperaemia, i.e., a blood volume increase, but also by extravasation of the contrast material, i.e., blood-brain barrier (BBB) disruption. A similar conclusion was drawn from the retrospective isotope brain scintigraphy study. It was further established that, although the pathological contrast enhancement was most obvious in the cortex, and particularly in the neighbourhood of the subarachnoid spaces, the phenomenon is probably widespread throughout the brain. Patients with abnormal enhancement are likely to be in less favourable clinical grades, have a high incidence of marked or diffuse spasm, have a poorer outcome independent of surgical or conservative treatment, and develop cerebral infarction more frequently. Systemic arterial hypertension was associated with an increased incidence of abnormal enhancement. Pathological tissue contrast enhancement or isotope accumulation in the first few days of SAH may serve as prognostic signs indicative of the late development of vasospasm and ischaemia. As ischaemic disruption of the capillary system is not prominent in the initial days following any stroke, vasoactive substances arising from the breakdown of the blood clot should play important part in the BBB damage in the acute stage of SAH. The "cortical SAH" model developed in the animal experiments ensured a constant subarachnoid blood volume with minimal local brain damage. The intracranial pressure and mean arterial blood pressure did not change significantly, and perfusion defects did not arise. Thus, this model proved suitable for studying the influence on the BBB of vasoactive blood breakdown products (responsible for arterial spasm) without the accompanying effects of pathological conditions such as raised intracranial pressure, systemic hypertension, non-reflow phenomena, which also disrupt the BBB. Measurements on the water, electrolyte, albumin contents of brain tissue, as well as the immunohistochemical localization of albumin, clearly indicated that the brain oedema developing at the acute stage of experimental SAH could be classified as having a primary vasogenic component in addition to the cytotoxic component. This increased capillary permeability was found to be brought about by opening of tight junctions and pinocytosis in the endothelial cells. The pathological capillary permeabilit

Adrenergic-induced enhancement of brain barrier system permeability to small nonelectrolytes: choroid plexus versus cerebral capillaries

Acute hypertension induced by adrenergic agents opens up the blood-CSF barrier (choroid plexus) to nonelectrolyte and protein tracers. Sprague-Dawley adult rats anesthetized with ketamine were given an intravenous bolus of either epinephrine (10 micrograms/kg), phenylephrine (100 micrograms/kg), isoproterenol (10 micrograms/kg), or D,L-amphetamine (2 mg/kg). Tracers were injected simultaneously with test agents, and the animals killed 10 min later. Epinephrine raised MABP by 57 mm Hg, to a peak pressure of 160 mm Hg; and it increased the volume of distribution (Vd) of urea, mannitol, and 125I-bovine serum albumin in CSF by 1.5-, 2.7-, and 30-fold, respectively. There was enhanced uptake by lateral and fourth ventricle choroid plexuses, cerebral cortex, cerebellum, medulla, and thalamus. Phenylephrine also elevated MABP to 160 mm Hg, but it increased permeation of tracers into CSF (and several brain regions) to a lesser extent than epinephrine, attributable to protective vasoconstriction associated with alpha-agonist activity. Ratio analysis of Vd data provides evidence that augmented permeation of nonelectrolyte tracers in acute hypertension occurs predominantly by diffusion rather than vesicular transport. It is postulated that elevated MABP distends the central cores of choroid plexus villi and cerebral capillaries, with resultant stretching and opening of tight junctions in both barrier systems; with less hindrance to diffusion, urea and mannitol are cleared at rates closer to free diffusion. Neither isoproterenol (decreased MABP by 40 mm Hg) nor amphetamine (did not alter MABP) significantly opened the choroid plexus or blood-brain barrier to tracers.

Tracer study on a paracellular route in experimental hydrocephalus

Considering the possibility of a paracellular pathway for edema resolution, we studied the intracerebral movement of proteins and ionic lanthanum in rats with experimental hydrocephalus. Hydrocephalus was induced by injection of kaolin suspension into the cisterna magna. After induction of hydrocephalus, horseradish peroxidase (HRP), microperoxidase (MP), or lanthanum chloride (LaCl3) were perfused into the ventricle system. HRP and MP were localized mainly in the intercellular spaces between ependymal cells, glial cells, and in perivascular spaces and were restricted by endothelial tight junctions. Ionic lanthanum (La3+), however, penetrated these tight junctions and moved between the blood and CSF cavities by paracellular pathways. These findings indicate that in obstructive hydrocephalus, the tight junctions may constitute part of a paracellular pathway for the transendothelial movement of small solutes, although they prevent the movement of larger molecules.

Increased susceptibility to osmotic disruption of the blood-brain barrier in chronic hypertension

We examined the effects of chronic hypertension and acute reduction of arterial pressure on the susceptibility of the blood-brain barrier (BBB) to disruption. The BBB was disrupted with an intracarotid injection of 1.6 M arabinose in spontaneously hypertensive rats (SHR), stroke-prone SHR (SHRSP), and normotensive Wistar-Kyoto (WKY) rats. Permeability of the BBB was determined from the ratio of 125I-albumin in brain to 125I-albumin in blood. When the BBB was intact, permeability was less than 0.4%. After hypertonic arabinose, permeability of the BBB was greater (mean +/- SE) in SHRSP (17.6% +/- 1.6%) and in SHR (21.1% +/- 3.1%) than in WKY (10.3% +/- 2.4%) (p less than 0.05). When arterial pressure of SHRSP was reduced acutely with nitroprusside before arabinose, the BBB permeability to albumin was not reduced (21.5% +/- 1.5%). In other rats, we examined survival after osmotic disruption. In SHRSP, 14 of 15 rats died within 1 day after osmotic disruption with marked cerebral edema. In WKY, four of 15 rats died (p less than 0.05 vs SHRSP). When arterial pressure of SHRSP was reduced before arabinose, mortality was reduced to six of 15 (p less than 0.05 vs untreated SHRSP). We conclude that the BBB in SHRSP has enhanced vulnerability that is detrimental to survival. Reduction of arterial pressure improves survival in SHRSP without affecting BBB permeability to albumin.(ABSTRACT TRUNCATED AT 250 WORDS)

Morphology of endoneurial blood vessels of frog sciatic nerve during vascular perfusion

In order to determine if increased injection pressures can alter the permeability and ultrastructure of blood vessels of the frog blood-nerve barrier, these vessels were examined following perfusion of the iliac artery at rates of 0.21 or 0.82 ml/min. At either perfusion rate, endoneurial blood vessel profiles were clearly evident and the surface area of these vessels amounted to 60% of the surface area of the perineurium. In all vessels a large number of vesicles were present within the endothelial cells. Many were attached by necks to one or the other plasma membrane, but no transcellular channels were evident. At the higher flow rate no changes in vesicles or junctions were seen, but blebs and blisters were evident at the luminal membranes of the endoneurial endothelium. When microperoxidase was perfused at 0.82 ml/min, reaction product frequently flooded the endothelial cells, was found as clumps on the cell surface, and was distributed within the endoneurial space. These changes represent the only ultrastructural evidence of endothelial cell damage and altered permeability in response to increased rate of perfusion.

Increased capillary permeability of the stria vascularis to HRP, induced by experimental acute hypotension in rats

Acute hypotension was produced in rats by using two experimental techniques: intravenous infusion of a ganglion-blocking agent (Arfonad), and venesection of a femoral vein. Horseradish peroxidase (HRP) was injected intravenously after each procedure, and subsequently observed in the inner ear by light and electron microscopy. In both experimental models, a large amount of tracer spread into the intercellular spaces, but it was halted by tight junctions bordering the stria vascularis. The endothelium exhibited a high distribution density of labelled vesicles, which suggested increased vesicular transport. There was no extravasation of HRP from capillaries in the spiral ligament in spite of the presence of some labelled pinocytotic vesicles. The present study was concerned with the discovery of enhanced capillary permeability of the stria vascularis under acute hypotension, as in the case of acute hypertension (Sakagami et al., 1984).

The vasculature of experimental brain tumours. Part 4. The quantification of vascular permeability

In order to quantify changes in vessel permeability seen previously in experimental astrocytomas produced in rats by an intracerebral injection of cultured neoplastic glial cells, the flux of mannitol across the vascular endothelium from the blood into the normal brain or tumour tissue was measured using a specially devised technique by which a steady level of radioactively labelled mannitol can be achieved rapidly and maintained in the bloodstream. This is done by a continuous injection given at a rate which is adjusted by a predetermined programme so as to replace the tracer at the rate at which it has been found to leave the circulation in previous experiments. In separate experiments on both tumour-bearing and control rats steady levels of the tracer were maintained in the circulation for progressively longer times of up to 30 min. The kinetic parameters of the process gave estimates for the apparent transfer constant of mannitol across the vascular endothelium and of the size of the extravascular extracellular mannitol space in the tumours. The apparent transfer constant for the movement of mannitol across the blood-brain barrier was increased more than a hundred-fold in the region of the tumour compared to the values for the brain of control rats or that of tumour-bearing rats remote from the tumour site. The extracellular extravascular space within the tumour was estimated to be 22%, somewhat larger than accepted normal values.

Effect of 2450 MHz microwave energy on the blood-brain barrier to hydrophilic molecules. B. Effect on the permeability to HRP

Alteration of blood-brain barrier (BBB) permeability by 2450 MHz CW microwaves was assessed semi-quantitatively after intravenous injection of horseradish peroxidase (HRP) and exposure of conscious, unrestrained rats to incident power densities of 0, 20 or 65 mW/cm2 for 30, 90 or 180 min. Additional rats were exposed to ambient heat (42 +/- 2 degrees C) for 30 or 90 min. None of the brain regions studied, with the exception of the normally leaky pineal gland, showed extracellular HRP leakage attributable to microwave or thermally-induced breakdown of the blood-brain barrier. The mean ratio of HRP-labeled microvessel endothelium/total number of microvessels counted was determined for each brain region. Mean values for the cortex, hypothalamus, cerebellum and medulla of microwave-exposed and heated rats were consistently below those of corresponding sham levels. This decrease appeared to correlate inversely with power density and duration of exposure. Statistically significant deviation (P less than 0.05) from sham mean values occurred in the cortex, hypothalamus, cerebellum and medulla of animals made hyperthermic with ambient heat or exposure to microwaves at 65 mW/cm2 (specific absorption rate approximately equal to 13.0 W/kg) for 30 or 90 min. Additionally, electron microscopic evaluation of ultrathin sections taken from each of the 4 brain regions revealed no significant extravasation of HRP indicative of microwave or ambient heat-induced disruption of the blood-brain barrier.

Effect of 2450 MHz microwave energy on the blood-brain barrier to hydrophilic molecules. D. Brain temperature and blood-brain barrier permeability to hydrophilic tracers

Measurement of temperature within the cerebral cortex, hypothalamus, cerebellum and medulla of rats sham-, heat- or microwave-exposed revealed the presence of a thermal gradient within the brain. In all groups, cerebral cortex and the cerebellum were cooler than the deeper hypothalamus and medulla. Exposure to 2450 MHz CW microwaves or ambient heat (42 +/- 2 degrees C) resulted in measurable elevation of regional brain temperature, but without alteration of temperature gradients normally observed within the brain. Exposure to 20 mW/cm2 (SAR approximately equal to 4 W/kg) for 30, 90 or 180 min induced a small, but significantly (U = 0, P less than 0.05) increased temperature of the colon, and in each region of the brain studied. Exposure to an incident power density of 65 mW/cm2 (SAR approximately equal to 13.0 W/kg) for 30 or 90 min or to ambient heat (42 +/- 2 degrees C) for 90 min resulted in a substantially greater thermal response as indicated by higher colonic and brain temperatures. Comparison of regional brain temperature with individual colonic temperatures is expressed as delta T = t degrees Cbrain--t degrees Ccolon. In general delta T values for ambient heat or microwave-exposed rats did not differ significantly from those of sham-exposed animals. Exposure to microwaves or ambient heat did not alter the general relationships between regional brain and colonic temperatures, i.e., cortical and cerebellar temperatures were always below and hypothalamic and medullary temperatures always above corresponding colonic temperatures. The plotted temperature data (brain vs colonic temperature) indicate a linear relationship between brain and colonic temperatures. Levels of sodium fluorescein (NAFl), horseradish peroxidase (HRP) and [14C]sucrose (described in preceding papers) within the brain show a high correlation (P less than 0.05) with brain temperature. Suppression of blood-brain barrier permeability to hydrophilic tracers was most pronounced at brain temperatures exceeding approximately 40 degrees C and is demonstrated to be temperature dependent.

Penetration of some compounds through blood-brain and blood-testis barriers in chronically hypertensive rats

Acute hypertension impairs the function of biological barriers, e.g. that of blood-brain barrier. We tested the hypothesis that chronic hypertension might influence the penetration of compounds through blood-brain and blood-testis barriers. With this in mind, the penetration of relatively small radioactive compounds (14C-2-methyl-4-chlorophenoxyacetic acid = 14C-MPA, 14C-sucrose and 14C-antipyrine, 5 microCi/kg intravenously) into the brain, liquor space and testis was compared in male normotensive (Wistar and chronically hypertensive SH rats (11-22 months old). In chronic hypertension after 14C-MCPA and 14C-sucrose administration the penetration of radioactivity into the brain, cerebrospinal fluid and testis had significantly decreased or showed evidence of decrease, while after 14C-antipyrine administration the penetration remained unchanged. Penetration of Evans blue-albumin complex into the brain was studied by giving intravenous injection of Evans blue (5% solution) which is firmly bound to serum albumin. Extravasation of dye-protein complex into the brain showed no difference between Wistar and SH rats. The results suggest that chronic hypertension does not increase the penetration of compounds into the brain and testis but rather, reduces it.

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.

The blood-brain barrier following experimental subarachnoid hemorrhage. Part 1: Response to insult caused by arterial hypertension

In three groups of cats, the authors studied the effect of subarachnoid hemorrhage (SAH) on the permeability of the blood-brain barrier (BBB) to the penetration of Evans blue-protein complex. One group received arterial hypertension alone, one group SAH alone, and one group SAH followed by arterial hypertension. Animals subjected to arterial hypertension alone showed areas of BBB breakdown. However, when cats were rendered hypertensive after SAH, there were no demonstrable BBB lesions. The SAH was produced by intracisternal injection of whole blood and hypertension by the intravenous injection of metaraminol. The preservation of the BBB after SAH is discussed. Vasospasm is considered as a possible hemodynamic variable responsible for the protection of the BBB from hypertensive damage. The need for a new model is proposed to further investigate the state of the BBB after SAH.

Ultrastructural characteristics of endothelial permeability in chronic hypertension

This study examined characteristics of paracellular and pinocytotic permeability pathways across the middle cerebral artery endothelium of 12- to 16- month-old spontaneously hypertensive rats (SHR). Interendothelial junctions in SHR, like those of age-matched Wistar-Kyoto controls, were impermeable to lanthanum and horseradish peroxidase (HRP) tracers. Freeze-fracture preparations revealed that interendothelial junctions of chronically hypertensive rats are characterized by a twofold increase over controls in the number of tight junctional strands and the mean apical-basal depth. It is believed that this tight junctional hypertrophy may function to increase adhesive forces between neighboring endothelial cells, and may play a role inthe prevention of hypertension-induced paracellular permeability increases. Morphological and tracer studies of pinocytotic pathways indicated that, it the middle cerebral artery, endothelial vesicular transport activity is not increased during chronic hypertension. No evidence was found to indicate the presence of transendothelial permeability channels across control or hypertensive arterial endothelium. Thus, increased transendothelial permeability, commonly observed in acute hypertension, does not appear to occur during chronic hypertension, at least in the middle cerebral artery. Our findings suggest that the arterial endothelium may undergo structural (tight junctional) adaptation in response to prolonged hypertension.

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.

Does ethanol damage the blood--brain barrier?

The permeability of the blood--brain barrier has been measured using a technique which is independent of blood flow and is sufficiently accurate to monitor the penetration of weakly permeant substances. The permeability of the blood--brain barrier to [14C]sucrose has been measured in rats anaesthetised with either urethane or pentobarbitone (Nembutal). The values obtained from urethane-anaesthetised untreated rats were slightly lower, thus demonstrating the suitability of urethane as an anaesthetic for blood--brain barrier experiments. The permeability of the barrier has been measured in rats which had been drinking 7.5% ethanol for 6 months, or had been administered an anaesthetic dose of ethanol, or both. No statistically significant difference was found between the permeability measurements in rats subjected to any of these treatments. Positive controls in which 0.3 ml of a 30% ethanol solution was injected into the internal carotid artery demonstrated the sensitivity of the employed technique. Thus it was found that the blood--brain barrier does not weaken with respect to sucrose when the blood ethanol concentration reaches an anaesthetic level.

The vasculature of experimental brain tumours. Part 2. A quantitative assessment of morphological abnormalities

Two groups of the morphological abnormalities of brain tumour vasculature described in the previous paper (Deane and Lantos 1981) were quantified. First, blood vessel density, endothelial hyperplasia and endothelial cytology, 3 general features of the vasculature, were assessed, giving a score according to the Microscopic Angiogenesis Grading System (Brem et al. 1972). This not only gives information about the vascular supply of tumours but also often provides a reliable index of malignancy. The system was also adapted for electron microscopy. Secondly, 3 specific features of the endothelial lining were estimated: cytoplasmic vesicle content, fenestrations and abnormal endothelial intercellular junctions, which are thought to represent possible mechanisms of increased trans-endothelial transport. It was found that cytoplasmic vesicle content was 3--6-fold greater in tumour blood vessels than in capillaries from normal brain, and may therefore play an important role in cerebral oedema. However, fenestrations and abnormal endothelial junctions were infrequently seen, and were unevenly distributed.

The permeability of the blood-brain barrier in acute hypertension. Comparison of an endogenous and exogenous protein tracer

Experimental acute hypertension in male Wistar rats was produced by metaraminol infusion to systemic blood pressure levels of 190-210 mm Hg. After 20 sec or 30 min the animals were killed by perfusion fixation with 8% formaldehyde perfusion. The barrier passage of exogenous HRP (75 mg i.v.) given 10 min before killing (5 rats) and the passage of endogenous anti-HRP antibodies of the IgG class (8 rats, produced by antigenic stimulation beforehand) were compared electron microscopically by semiquantitation of tracer location in unstained ultrathin sections. Five rats served as controls. The number of tracer-filled vesicles was consistently lower in anti-HRP rats than in HRP rats: not only during acute hypertension but also in the controls. The penetration of both tracers into the basement membrane and brain parenchyma, however, was comparable. Anti-HRP was more prominent in the endothelial cytoplasm. Vesicular transport and penetration through the plasma membrane with diffuse cytoplasmic passage tend to be the most likely transport mechanisms, the former for HRP and the latter for the antibody.