Extravasation Of Horseradish Peroxidase Research Articles

Selective Vulnerability to Transcellular Pathway of Blood-Brain Barrier in Chronic Stage of the Kainate Model of Temporal Lobe Epilepsy in Rats

1. Abstract 1.1. Background: The blood-brain barrier (BBB) integrity is severely affected in many epilepsy syndromes including temporal lobe epilepsy (TLE). 1.2. Aim: In the present study, we investigated the effects of acute and chronic seizures induced by kainic acid (KA) on the transport pathways of BBB in rats. 1.3. Methods: Electroencephalography (EEG) was recorded to evaluate seizure activity. Immunohistochemistry for claudin-5, a tight junction protein, caveolin-1, and the glial fibrillary acidic protein (GFAP), a marker of astrocyte activation, was performed. Electron microscopy was used to ultrastructurally assess the presence and route of extravasation of horseradish peroxidase (HRP), a permeability marker, in barrier type of brain capillary endothelial cells. 1.4. Results: The immunoreactivity of claudin-5 and caveolin-1 in hippocampus increased by both acute and chronic seizures (p 1.5. Conclusion: This study provides immunohistochemical and ultrastructural evidence of BBB disruption through a selective vulnerability of the transcellular transport via an increase in caveolar vesicles in the endothelial cells brain capillaries rather than activation of paracellular pathway in the KA-induced rat model of TLE. 2. Keywords: Blood-Brain Barrier; Caveolin-1; Claudin-5; Electron Microscopy; Kainic Acid; Temporal Lobe Epilepsy

Morphological and Immunophenotypic Microglial Changes in the Denervated Fascia Dentata of Adult Rats: Correlation with Blood–Brain Barrier Damage and Astroglial Reactions

The reactions of microglial and astroglial cells to anterograde axonal degeneration were studied in the fascia dentata of adult rats from 1 to 42 days after removal of the entorhinal perforant path projection. The observations focused on the kinetics of glial activation in terms of induction of immunomolecules on the glial cells and the possible correlation between these changes and lesion-induced extravasation of plasma constituents. Normal and activated microglial cells were identified by immunohistochemical visualization of the constitutively expressed complement type 3 receptor (CR3/CD11b). Activated microglial cells were stained immunohistochemically for the inducible major histocompatibility complex (MHC) antigen class I and class II and the leukocyte common antigen (LCA/CD45). Astroglial cells were identified by immunohistochemical staining for glial fibrillary acidic protein (GFAP). Blood–brain barrier (BBB) conditions were primarily evaluated by immunohistochemical staining for extravasated Immunoglobulin G (IgG), but also by intravenously injected horseradish peroxidase (HRP) and Evans Blue. Twenty-four hours after entorhinal cortex ablation, microglial cells in the perforant path terminal zones displayed an increase in CR3 immunoreactivity, changes of morphology and an induced expression of MHC antigen class I. At the same time there was a hitherto undescribed leakage of IgG through the BBB (albeit without detectable extravasation of HRP and Evans Blue). One day later microglial cells also expressed LCA, but MHC antigen class II was not induced under these degenerative conditions. The activation of microglial cells occurred prior to a noticeable hypertrophy of astroglial cells and increase in GFAP immunoreactivity, as this first became evident on Postlesional Day 2. From the results we conclude (1) that perforant path axonal degeneration induces an endothelial transcytosis of blood-borne IgG by mechanisms which cannot be envisioned by conventional HRP tracer methods and (2) that the early activation of both microglial cells and astroglial cells is likely to be initiated and later influenced by both axonal degeneration and extravasated plasma constituents. The demonstration of an early induction of immunomolecules on activated microglial cells and extravasation of blood borne molecules might moreover form the basis for a correspondingly early intervention aiming to regulate microglial immunomolecule, cytokine, and growth factor gene expression in the affected areas.

Blood-spinal cord barrier function and morphometry after single doses of X-rays in rat spinal cord

The effects of irradiation on blood-spinal cord barrier (BSCB) function and ultrastructure were evaluated using a rat spinal cord model. Rats received a single dose of 25 Gy to the cervical spinal cord (C2-T2). At various times following irradiation and before the onset of paralysis, BSCB function was assessed using horseradish peroxidase (HRP) as a vascular tracer, and barrier-related structural changes in the capillaries were evaluated using morphometric techniques. Focal extravasation of HRP was seen at 93 days after irradiation, and extensive extravasation was apparent by 114 days in white matter, but not in gray matter. At 93 days, pathologic changes apparent by light microscopy were very minor in the white matter of the irradiated segment. By 107 days, myelin beading, Wallerian degeneration, edema, and histiocytes were apparent in white matter, and these features became increasingly prominent over the following weeks. No noteworthy changes were seen in gray matter at these times. Electron microscopic examination showed that, during the first 93 days following irradiation, more than half of the endothelial cells in white matter had disappeared (p < 0.05). In terms of the putative vascular pores, no abnormalities in endothelial junctions (the presumed small pore) were found, but there was an increase in the density of endothelial vesicles (a putative form of the large pore) in irradiated white matter (p < 0.001), but not in gray matter. Pericytes, thought to act as a second line of defence in the blood-brain barrier, increased in size but not in number in the irradiated white matter of the spinal cord. We suggest that radiation damage to endothelial cells, which form the BSCB prior to the onset of neurological deficit, may play an important role in the pathogenesis of white matter necrosis.

The development of the blood-brain barrier in the chick. Studies with Evans blue and horseradish peroxidase

The development of the blood-brain barrier was microscopically examined in the optic tectum of the chick. The permeability of neural vessels to Evans blue and horseradish peroxidase decreases progressively during the period of incubation. Diffusion is massive on the 6th and 10th days of incubation and is reduced on the 14th day; on the 18th-21st day of incubation the vascular walls still allow Evans blue to diffuse but prevent extravasation of horseradish peroxidase completely. In one month old chickens the nervous substrate is free of both tracers.

Effect of whole-body hyperthermia on the development of peritumoral brain oedema.

The effect of whole-body hyperthermia on the development of peritumoral brain oedema and intracranial pressure was studied in cats with intracerebral transplanted tumour. Whole-body hyperthermia was achieved by means of extracorporeal circulation. The temperature within the brain tumour tissue was increased to 41.8 +/- 0.15 degrees C (mean +/- SD) for 2 h. Measurements of brain water content revealed that hyperthermia worsened the degree of peritumoral brain oedema. Microscopical observation demonstrated that extravasation of horseradish peroxidase, indicating disruption of the blood-brain barrier in the oedematous region, was more severe in animals exposed to hyperthermia than in non-treated animals. Intracranial pressure significantly increased from 13.5 +/- 5.26 mmHg to 25.8 +/- 6.16 mmHg (p < 0.05) during hyperthermia, although it was controlled at 20.7 +/- 2.60 mmHg by continuous infusion of glycerol. The results suggest that whole-body hyperthermia acting on a brain-bearing tumour caused an increase in intracranial pressure due to worsening of the degree of peritumoral vasogenic type of brain oedema. We emphasize that whole-body hyperthermia may be performed with careful monitoring of intracranial pressure for patients who have brain tumour.

Acute effects of human recombinant tumor necrosis factor-? on the cerebral vasculature of the rat in both normal brain and in an experimental glioma model

The effects of intravenous (IV) infusion of human recombinant tumor necrosis factor-alpha (rTNF-alpha, Cetus) on normal brain and malignant glioma in rats were examined. Twelve Fischer 344 rats were given either a single injection of 10(6) U rTNF-alpha or injections of 5 x 10(5) U rTNF-alpha for three days. One day post-rTNF-alpha injection(s), rats were injected IV with horseradish peroxidase (HRP) to determine blood-brain barrier (BBB) breakdown and, one hour later, were perfused with an aldehyde fixative and processed for histologic examination. Treatment of normal rats with rTNF-alpha by either dosage or schedule caused no remarkable histopathologic changes in the brain and no alteration in BBB integrity. Human glioma models were produced by intracerebal inoculation of 10(4) syngeneic RT-2 glioma cells into the right parietal lobe of 30 rats. Animals received single IV injections of 10(6) U human rTNF-alpha or its excipient (TNF-E) as above on day 3, 7, or 10 post-tumor inoculation or multiple injections of 5 x 10(5) U rTNF-alpha beginning on day 7, 10, or 12 post-tumor inoculation. With a single IV injection of either rTNF-alpha or its excipient, 3-day models showed a similar pattern of HRP extravasation limited to the extracellular space of the tumor inoculation site. In 7-day models treated with a single IV injection of rTNF-alpha or TNF-E, HRP extravasated throughout the tumor, but did not exceed peritumoral margins. In 10-day models treated with a single injection of TNF-E, HRP was found only in the tumor and immediate peritumoral regions while rTNF-alpha-treated rats showed more extensive areas of BBB breakdown with HRP evident throughout the entire right hemisphere and extending via the corpus callosum into the contralateral hemisphere. Pericapillary halos were also evident around the small blood vessels within the edematous areas of the corpus callosum. Within tumors, hemorrhagic necrosis and adherence of neutrophils to vessels was observed only in animals treated with rTNF-alpha at 10 days post-tumor inoculation. Multiple IV injections of rTNF-alpha in 7 and 10-day models triggered widespread hemorrhagic necrosis, neutrophil adherence and infiltration in the tumor. There was also extravasation and diffusion of HRP from the site of glioma into the contralateral hemisphere. Twelve-day models treated with multiple rTNF-alpha injections, in addition, showed irregular luminal surfaces and gaps between adjacent endothelial cells of tumor vasculature.(ABSTRACT TRUNCATED AT 400 WORDS)

Blood-brain barrier alteration after microwave-induced hyperthermia is purely a thermal effect: I. Temperature and power measurements

The effect of microwave-induced hyperthermia on the blood-brain barrier was studied in 21 Sprague-Dawley rats. Under sodium pentobarbital anesthesia, animals were place in a stereotactic frame, and an interstitial microwave antenna operating at 2450 MHz was inserted in a bony groove drilled parallel to the sagittal suture. Some antennae were equipped with an external cooling jacket. Temperature measurements were made lateral to the antenna by fluoroptical thermometry, and power was calculated from the time-temperature profile. Five minutes prior to termination of microwave irradiation, horseradish peroxidase (1 mg/20 g body weight) was injected intravenously. Extravasation of horseradish peroxidase was observed in brain tissue heated above 44.3°C for 30 minutes and at 42.5°C for 60 minutes. Microwave irradiation failed to open the blood-brain barrier when brain temperatures were sustained below 40.3°C by the cooling system. Extravasation of blood-borne peroxidase occurred at sites of maximal temperature elevation, even when these did not coincide with the site of maximum power density. The data suggest that microwave-induced hyperthermia is an effective means for opening the blood-brain barrier and that the mechanism is not related to the nonthermal effect of microwaves.

Oxidant damage and deterioration of the blood-brain barrier in optic neuritis: A correlative study in the guinea pig by MRI and TEM

Optic neuritis, a demyelinating autoimmune disease, is usually the initial site of multiple sclerosis (MS). Experimental allergic encephalomyelitis (EAE), the experimental model for MS, is induced by injecting spinal cord emulsion in complete Freund’s Adjuvant into susceptible animals; clinical symptoms of ataxia and hind quarter paralysis develop 8 to 14 days later. Damage to the bloodbrain barrier (BBB) and free radical derived oxidants, including hydrogen peroxide (H2O2), have been implicated in the pathology of EAE and other inflammatory diseases. Cytochemical localization of H2O2 in the optic nerve head of animals with EAE corresponds to areas of extravasation of horseradish peroxidase (HRP) at later stages of EAE. Damage to the BBB is monitored clinically in human cases of MS by magnetic resonance imaging (MRI) of gadolinium-DTPA (Gd-DTPA), contrast agent, leakage. Preliminary studies of EAE with MRI at 4 days post antigen sensitization showed leakage of Gd-DTPA in the optic nerve; light and electron microscopy (TEM) of sections from the same nerve showed substantial inflammation from the optic nerve head to the optic chiasm.

Experimental analysis of the spinal cord compressed by spinal metastasis.

The purpose of the present study of experimental spinal metastasis, developed in rats by inoculation of tumor cells through the spinous process, was to find the factor that causes the initial damage to the cord in this disorder. In the early stage of paralysis, the degenerated posterior funiculus originated from a small hemorrhagic area in the posterior column of the involved cord. Using the scanning electron microscope, the hemorrhage was found to be from the intrinsic vein, resulting from the disturbance of venous drainage in the compressed portion. In the early stage of compression, extravasation of horseradish peroxidase was observed in the white matter, but histologic degeneration was not. A hemorrhage existed wherever degeneration of the funiculus was observed. Therefore, the trigger to induce the initial damage on the cord in spinal metastasis was not likely to be vasogenic edema, but instead the intrinsic venous hemorrhage.

Antioxidant enzymes reduce loss of blood-brain barrier integrity in experimental optic neuritis.

We studied the effect of antioxidant enzymes on the loss of integrity of the blood-brain barrier in the optic nerves of strain-13 guinea pigs with chronic experimental allergic encephalomyelitis, a demyelinating disorder with neurologic and histopathologic characteristics similar to multiple sclerosis. Animals with experimental allergic encephalomyelitis received daily intraperitoneal injections of either preservative-free saline (group 1), catalase (group 2), or glutathione peroxidase (group 3) for 2.2 months after the onset of appendicular paralysis. Following intravascular administration, extravascular leakage of horseradish peroxidase was histopathologically graded as mild, moderate, or severe within the optic nerve head and myelinated retrolaminar nerve. Severe extravasation of horseradish peroxidase was exclusive to group 1, in addition to moderate and mild leakage. In groups 2 and 3, leakage of horseradish peroxidase was infrequent, and when detected, it was graded as mild. Detoxification of hydrogen peroxide with catalase and glutathione peroxidase substantially reduced horseradish peroxidase leakage in experimental optic neuritis, suggesting a role for hydrogen peroxide and its reactive by-products in the pathogenesis of increased vascular permeability of the blood-brain barrier in experimental allergic encephalomyelitis.

Histopathological and blood-brain barrier changes in rats induced by an intracerebral injection of human recombinant interleukin 2.

Adoptive immunotherapy utilizing human recombinant interleukin 2 (rIL-2) in conjunction with lymphokine-activated killer cells has shown some efficacy in the treatment of various types of cancers, particularly renal carcinoma and melanoma. Intravenous administration of rIL-2, with or without lymphokine-activated killer cells, produces a variety of serious side effects and approximately one-third of the patients experience a decrease in neurological status. Our previous investigations in animals have indicated that a single intravenous injection of rIL-2 can compromise the integrity of the blood-brain barrier (BBB). The present study examined the histopathological effect and BBB changes in rats which occur after a single intracerebral injection of rIL-2, its excipient, or saline into the parietal lobe. Animals were killed at various intervals up to 8 days (1 hour after intravenous injection of horseradish peroxidase), and the brain tissue was sectioned and processed for light microscopy. All animals showed increased cerebrovascular permeability for horseradish peroxidase due to traumatic BBB disruption at 4, 12, and 24 hours after injection. Extravasation of horseradish peroxidase persisted at 3 and 8 days only in animals injected with rIL-2. Injections of rIL-2 led to an increased leukocytic infiltration into the injection site, perivascular cuffing, and localized edema by 24 hours, which continued to increase over the 8-day study period. These results suggest that a single injection of human rIL-2 into the brain of rats induces an influx of leukocytes into the brain and may contribute to the cellular events that perpetuate a trauma-induced compromise in the integrity of the BBB.

A new model of concussive brain injury in the cat produced by extradural fluid volume loading: II. Physiological and neuropathological observations

This study examined physiological and histopathological changes in the cat produced by a new experimental fluid injury device. Spontaneously breathing (N = 14) and artificially ventilated (N = 45) cats were subjected to systemically varied magnitudes of fluid percussion brain injury. Within certain injury ranges, increasing magnitudes of fluid percussion injury produced increasing durations of apnea, as well as greater transient increases in mean arterial blood pressure, intracranial pressure and cerebral perfusion pressure. Acute increases in intracranial pressure may have been related to cerebral vasodilatation produced by the systemic hypertension following brain injury. Injuries associated with pressure transients greater than 10 atm ms produced concussive responses, including irreversible apnea in spontaneously breathing cats and temporary pupillary dilatation, increases in heart rate and mean arterial blood pressure in artificially ventilated cats. Injuries greater than 39 atm ms frequently produced histopathological and physiological indices of significant irreversible brain damage, including fixed and dilated pupils, systemic cardiovascular hypotension and deteriorating blood gases. Injury magnitudes less than 20 atm ms did not produce macroscopic evidence of histopathology, intermediate injury ranges produced increasing evidence of subarachnoid and petechial hemorrhage while injury levels greater than 40 atm ms frequently produced significant histopathology including massive hematomas. Injury greater than 10 atm ms resulted in opening of the blood-brain barrier, as assessed by extravasation of horseradish peroxidase. Injury greater than 19 atm ms produced suppression of EEG amplitudes which did not recover for up to 40 minutes after injury. These data provide detailed information on the physiological and histopathological consequences of fluid percussion injury in the cat and indicate that this modified fluid percussion apparatus can produce graded levels of brain injury similar to those previously reported for fluid percussion injury.

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.

E. coli peritonitis and bacteremia cause increased blood-brain barrier permeability

Impaired mental status is a poorly understood manifestation of sepsis and may be associated with altered permeability of the blood-brain barrier. To examine the possibility that sepsis affects permeability of the blood-brain barrier, rats were infected with a peritoneal implant consisting of sterilized feces, barium sulfate, and 10 8 colony forming units (CFU) of Echerichia coli. Using this model, reproducible episodes of peritonitis with bacteremia resulted. Rats were sacrificed hourly after 5 min circulation of 100 mg horseradish peroxidase. Animals were perfused-fixed and the brains removed. Representative coronal sections were stained for peroxidase reaction product and cerebral blood vessels were examined microscopically for evidence of HRP staining and extravasation. The number of stained cerebral vessels from infected rats was increased at all times compared to uninfected control rats. Extravasation of horseradish peroxidase within neuropil was significantly higher in hours 1, 4 and 5 as compared to controls. The lack of significant increase in hours 2 and 3 may suggest transient closing or repair of the tight junctions. We conclude that peritonitis and bacteremia are associated with increased permeability of the blood-brain barrier.

Blood-brain barrier impairment by low pH buffer perfusion via the internal carotid artery in rat.

Krebs-Ringer bicarbonate buffer (KRB) adjusted by lactic acid to low pH levels (6.6, 6.2, 6.0, 5.8, 5.5) was perfused via the internal carotid artery as a bolus into rat brain hemispheres. In one group of animals, the fluid phase tracer horseradish peroxidase (HRP) was perfused immediately following the low pH treatment. In the other group of animals, the brain hemispheres were fixed and the endothelial cells were stained with colloidal iron (CI) at pH 1.8. Widespread extravasation of HRP was detected indicating blood-brain barrier (BBB) opening to this tracer in hemispheres perfused with KRB at pH 6.2, 6.0, 5.8, or 5.5. HRP was seen in pools of endothelial tight junctions. Endothelial cell injury reflected by swelling and influx of HRP into the cytoplasm was occasionally encountered. CI evenly decorated the negatively charged surface of endothelial cells in the control brains, in contrast to markedly diminished iron binding capacity of endothelial cells in low pH-treated hemispheres. Our results suggest that the ionic milieu influences the negatively charged cell surface sialoglycoproteins and glycolipids, which are integral parts of the BBB system.

Opening of the blood-brain barrier in Anolis carolinensis. A high voltage electron microscope protein tracer study.

The tight junctions between endothelial cells of capillaries in the forebrain of Anolis carolinensis are a common component of the structural basis for the blood-brain barrier in this reptile. The complexity of these junctions, which is apparent in platinum replicas of freeze-fractured brain capillaries, is unchanged by treatments designed to render the blood-brain barrier of these lizards leaky to horseradish peroxidase. An alternative route for extravasation of horseradish peroxidase, following injection of chameleons with 2.7 mg of D-glucose to render their brain capillaries leaky, is a system of transient cytoplasmic vesicles and vesiculo-tubular channels whose lumina may be open to the luminal or abluminal surface (or both) of the capillary endothelial cell. High voltage electron microscopy (HVEM) of 0.25 and 0.5 micron thick plastic sections of experimental brain capillary endothelium confirmed the existence of vesiculo-tubular conduits. These channels display a sigmoid morphology and are situated in the cytoplasm at angles oblique to the luminal and abluminal surfaces of the endothelium. Occasionally, the channels spanned the entire endothelial wall of the capillary, and in such cases, appeared to connect the lumen with the brain extracellular compartment. HVEM images (including stereo pairs) of the vesiculo-tubular channels show them to have a scalloped, irregular profile consistent with their proposed formation by fusion of pinocytotic vesicles. Also, HVEM examinations of experimental capillaries from peroxidase-treated lizards reveal massive quantities of dense reaction product in cytoplasmic vesicles and vesiculo-tubular membrane compartments of the endothelium, and the complex pleomorphism exhibited by these structures. Observations made in the present study suggest that as a consequence of severe hyperglycaemia, transendothelial channels form in the brain capillaries by fusion of pinocytotic vesicles generated by accelerated pinocytosis at the luminal surface of the endothelium, and subsequently serve as open routes for massive floods of tracer into the central nervous system.

Increased cerebrovascular permeability to protein during systemic kainic acid seizures.

Cerebrovascular permeability to protein (CVP-p) was assessed during limbic seizures by injecting unrestrained rats intraperitoneally with kainic acid followed by intravenous horseradish peroxidase (HRP); animals survived approximately 1 h after seizure onset. Brains were processed for the blue HRP reaction product followed by light microscopic examination of sequential sagittal sections. In all cases kainate-induced seizures caused increased CVP-p within the thalamus, temporal hippocampal formation, and neocortex. Somewhat less frequently other limbic structures and the striatum were HRP-positive. A lamina-specific extravasation occurred in the dorsal hippocampus; reaction product occupied the mossy fiber zone of field CA3, a likely focus of kainate action. Extravasation of HRP also occurred within, or juxtaposed to, certain myelinated fiber bundles. Brains from animals treated as blanks (kainate but no HRP) were devoid of peroxidase activity, and in nonseizing animals HRP gained access only to circumventricular organs. Although regions of increased CVP-p partially covary with areas of increased electrical activity and glucose metabolism, neuronal activation occurs over a much greater volume of brain tissue than does CVP-p. A close relationship may exist between these circumscribed areas of protein extravasation and seizure foci. Both vasogenic and cytotoxic edema appear to be simultaneously present during kainate seizures.

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).

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.

Ultrastructural Study of the Effect of Acute Hypertension on the Stria Vascularis and Spiral Ligament

The effects of acute hyper- and hypotension on the stria vascularis and spiral ligament of the rat were studied electron microscopically with the horseradish peroxidase (HRP) tracer method. Acute hypertension was induced by i.v. infusion of methoxamine chloride (Mexan), and acute hypotension by i.v. infusion of a ganglion-blocker (Arfonad) and by venesection. In both acute hyper- and hypotensive experiments, a large amount of leaked HRP spread into the intercellular spaces until it was stopped by tight junctions bordering the stria vascularis. The stria capillary endothelium displayed a dense distribution of labelled vesicles, which suggests increased vesicular transport. There was no extravasation of HRP from capillaries in the spiral ligament, despite the presence of some labelled pinocytotic vesicles. The present paper deals with the discovery of enhanced capillary permeability of the stria vasuclaris under acute hyper- and hypotension, and makes comparison between acute hyper- and hypotension in order...