K. G. Go

CEREBRAL CATION SHIFTS IN HYPOXIC ISCHEMIC BRAIN-DAMAGE ARE PREVENTED BY THE SODIUM-CHANNEL BLOCKER TETRODOTOXIN

We investigated the effect of the sodium channel blocker, tetrodotoxin, in two animal models of brain pathology. In the first, an acute model, we recorded the interstitial brain potential in the striatum of rats after cardiac arrest. The time of deflection of this potential, an indication of changes in cerebral cation concentrations, was determined in control rats, and in rats pretreated with intrastriatal tetrodotoxin. In control rats a deflection of the brain potential was noted 2 min after cardiac arrest; tetrodotoxin pretreatment delayed this deflection to about 5 min. The second, a survival model, was based on the Levine preparation in rats. A combination of ischemia and hypoxia produced unilateral, cerebral infarcts, which were characterized by a decrease of brain [K+], and by increases of [Ca2+] and [Na+] and thus of the Na+:K+ ratio. Data on the cation shifts, determined by chemical assay methods, were complemented by those of more conventional methods of assessment of brain damage, such as the determination of survival, of Evans blue staining, and of brain water content. Cation shifts could be prevented locally by tetrodotoxin. In conclusion, the drug can, at least partially, prevent the detrimental effects of an ischemic insult. In addition, our results showed that protective effects observed in the acute model may sometimes offer an indication of the effects to be expected in the survival model. Furthermore, the effect of tetrodotoxin on the brain potentials in the acute model showed that its protective action in the survival model may be brought about by delaying cell depolarization and by shortening the actual duration of the depolarized state. We conclude that Na+ influx and, consequently, neurotransmission may play a crucial role in the development of cerebral damage.

The mechanisms of blood-brain barrier impairment by hyperosmolar perfusion

SummaryProtein tracer flux from brain microvessels has been studied at intervals of 10 s and 5, 15 and 60 min following hyperosmolar perfusion injury of the blood-brain barrier with 0.6 ml of a 4 M urea solution. In one group of Wistar rats 75 mg horseradish peroxidase (HRP) was given intravenously 10 min before killing as an exogenous protein tracer. In another group endogenous IgG was used as tracer; to enhance serum levels and to facilitate demonstration, the rats were immunized with HRP beforehand, resulting in high titer serum antibodies of IgG class. After perfusion fixation and tracer demonstration in Vibratome sections the localization of the tracer was studied in 1 μm Epon sections and unstained ultrathin sections. The incidence of tracer presence was estimated with quantitative and statistical methods.The results indicate that in this experimental model of blood-brain barrier damage protein tracer extravasation only occurs during the first minutes and thus may be a rapidly reversible phenomenon. The signs of endothelial activation include increased numbers of vesicles and channel-like structures. As the ratio of vesicles with and without tracer remains fairly constant, increased vesicle formation seems to occur randomly in activated endothelial cells and thus does not represent a tracer outflow mechanism by itself. Any qualitative sign of endothelial activation and protein tracer uptake may occur with or without tracer passage into the surrounding brain, actual tracer extravasation thus appearing to be an overflow mechanism in endothelial cells that can be estimated only with quantitative methods. Protein tracer extravasation may occur by random uptake in vesicular or channel-like structures or by cytoplasmic pooling in endothelial cells or cell segments; tracer extravasation through interendothelial junctional areas is not substantiated by our results. Removal of extravasated tracer may occur at least in part by local tracer backflow into the lumina of larger vessles. And finally, the differences in extravasation pathways between HRP and IgG appear to be significant, demonstrating that more than one pathway may be involved and that the predominance of a pathway may at least in part be tracer dependent.

THE PATHOGENESIS OF CEREBRAL GLIOMATOUS CYSTS

In this study, the authors have examined the mechanism of the formation of tumor cysts. Cyst fluid samples were obtained during surgery and by percutaneous aspiration from 22 patients with cystic cerebral gliomas. The concentration of protein was measured in the cyst fluid and blood plasma. Analysis of brain tumor cyst fluids revealed that plasma proteins constituted a major fraction (92%) of cyst fluid proteins; moreover, the protein fractions occurred in concentrations (relative to the plasma concentrations) that were around 50-fold of those in cerebrospinal fluid. This strongly indicates blood-brain barrier disruption. Evidence from computed tomographic and magnetic resonance imaging scans as well as from electron microscopy of tumor cyst walls suggests the transition of spongy edematous tissue in or around tumors into the contents of associated cysts. Pathophysiologically, blood-brain barrier breakdown is inherent to the occurrence of vasogenic brain edema. It is therefore plausible that the development of cysts is related to peritumoral vasogenic edema.

Changes of ventricular ependyma and choroid plexus in experimental hydrocephalus, as observed by scanning electron microscopy

SummaryHydrocephalus was induced in rats by the injection of silicone oil or kaolin suspension into the cisterna magna. One to 5 weeks later the walls of the lateral ventricles were studied with the scanning electron microscope after killing the animals by perfusion fixation. In contrast to controls, the hydrocephalic animals killed 1 or 2 weeks after injection showed degeneration of ependymal cilia and infestation of the ependymal and choroid plexus surface with reactive cells, which presumably may be identified as Kolmer phagocytic cells by their ultrastructural features as studied by the transmission electron microscope. A coating of debris on the surface of the choroid plexus in the hydrocephalic animals possibly bears upon the ciliary degeneration with consequent deficiency of the clearing effect of ciliary movement. In the longer surviving hydrocephalic animals regeneration of cilia seemed to have occurred.

Morphology and origin of arachnoid cysts scanning and transmission electron microscopy of three cases

SummaryThree surgically removed primary arachnoidal cysts were studied with scanning electron microscopy (SEM) and two of the cases with transmission electron microscopy (TEM). The cells lining the cyst cavity had microvilli at the surface, true cilia were absent. In the cytoplasm multivesicular bodies, many pinocytotic vesicles, some large vacuoles and strands of tonofilaments were prominent features. The cells were interconnected by desmosome-like junctions and were interconnected by desmosome-like junctions and were separated from the surrounding tissue by a distinct but sometimes incomplete basal membrane.Based on these findings it is concluded that arachnoid cysts are derived from the outer arachnoid cells (subdural neurothelium), the formation of the cysts being attributable to secretory capacity of the subdural neurothelium.

Protective effect of fasting upon cerebral hypoxic-ischemic injury

This study was designed to determine the effect of fasting upon cerebral hypoxic-ischemic injury. In the first part of the study the effect of fasting was determined for survival, brain tissue water and kation contents, and blood-brain barrier intregrity. In the second part of the study the administration of the substratesβ-hydroxybutyrate (BHB) and glucose has been evaluated regarding their influence upon the effect of fasting. The study used the Levine-Klein model of unilateral carotid occlusion and hypoxia because it mimics clinical situations of ischemia with hypoxia. The data show that fasting did protect rats from developing brain infarction following hypoxia-ischemia. Hypoglycemia seems to be involved in the mitigation of ischemic blood-brain barrier disruption. The plasma glucose level seems to be not the only factor involved in the genesis of the tissue kation changes. Starvation-induced ketosis probably does not play a role in the protection mechanism.

The Starling Hypothesis of Capillary Fluid Exchange in Relation to Brain Edema

The study of edema fluid colloid osmotic pressure (COP) in cold-induced brain edema has confirmed the high level of edema fluid COP, which approaches, and in some instances even exceeds, plasma COP, thereby upsetting the balance of transcapillary fluid exchange in favor of retention of edema fluid in brain tissue. The findings also suggest that plasma COP and the systemic factors affecting it are important in the dynamics of the protein exudation, and that cellular injury plays a role in determining the ultimate composition of the extracellular edema fluid.

CIRCULATORY FACTORS INFLUENCING EXUDATION IN COLD-INDUCED CEREBRAL EDEMA

Abstract In cats with cold-induced cerebral edema, the influence of the arterial blood pressure on the volume of edematous tissue was studied. A low blood pressure was associated with a small amount of edema, but a high blood pressure did not always result in a large volume of exudate. This was attributed to a variable degree of vasomotor paralysis in the cortical lesion, allowing a varying extent of propagation of the arterial blood pressure into the capillary bed. Vasomotor autoregulation was studied in cats in which elevations of arterial blood pressure were induced. After the cold injury these elevations of arterial blood pressure resulted in greater but varying increments of cortical vein wedge pressure, measured in the vein draining the cortical lesion. The results indicated impairment—although to a varying extent—of vasomotor regulation in the cold lesion.

Prediction of specific damage or infarction from the measurement of tissue impedance following repetitive brain ischaemia in the rat.

The development of irreversible brain damage during repetitive periods of hypoxia and normoxia was studied in anaesthetized rats with unilateral occlusion of the carotid artery (modified Levine model). Rats were exposed to 10 min hypoxia and normoxia until severe damage developed. As indices of damage, whole striatal tissue impedance (reflecting cellular water uptake), sodium/ potassium contents (due to exchange with blood), Evans Blue staining (blood‐brain barrier [BBB] integrity) and silver staining (increased in irreversibly damaged neurons) were used. A substantial decrease in blood pressure was observed during the hypoxic periods possibly producing severe ischaemia. Irreversibly increased impedance, massive changes in silver staining, accumulation of whole tissue Na and loss of K occurred only after a minimum of two periods of hypoxia, but there was no disruption of the BBB. Microscopic examination of tissue sections revealed that cell death was selective with reversible impedance changes, but became massive and non‐specific after irreversible increase of the impedance. The development of brain infarcts could, however, not be predicted from measurements of physiological parameters in the blood. We suggest that the development of cerebral infarction during repetitive periods of hypoxia may serve as a model for the development of brain damage in a variety of clinical conditions. Furthermore, the present model allows the screening of potential therapeutic measuring of the prevention and treatment of both infarction and selective cell death.

CATION SHIFTS AND EXCITOTOXINS IN ALZHEIMER AND HUNTINGTON DISEASE AND EXPERIMENTAL BRAIN-DAMAGE

Publisher Summary This chapter reviews the significance of cation shifts as an index to cell death and discusses the results obtained by the examination of post-mortem brain material of humans showing that cation shifts are highly related to the dysfunction of amino acid neurotransmitters. The integrity of the brain is highly dependent on the availability of oxygen and glucose. In contrast to non-neuronal tissue, the cells of the central nervous tissue die within a few minutes in the absence of appropriate nutrients. Although the energy metabolism in vitro has dropped to about 50% of that in vivo , brain slices can only survive for a few hours even if sufficient oxygen and glucose are available. In tissue culture, brain cells can be kept alive for several weeks, but in this preparation, a lack of nutrients produces rapid cell death. Comparable to in vitro condition, short-term hypoxia in vivo will induce irreversible degeneration. The possible role of excitatory amino acids (glutamate and the related compound, kainate) and the influx of cations in experimental animals and human neurodegenerative diseases are discussed in the chapter. In experimental designs, changes in cations during cell death were detected by the measurement of their tissue levels, by the autoradiography of Ca, or by the recording of interstitial electrical potentials.