Biomedical subjects
Publications and source records attributed to K G Go.
A survey is given on the history of the discovery of the blood-brain barrier, of its functions and of its clinical importance. Also attempts to circumvent or disrupt the barrier with the aim of introducing therapeutic or diagnostic agents into the brain tissue have been reported. Finally the possible negative effects of lasting barrier defects in transplanted foetal tissue are mentioned.
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.
Although generally benign, meningiomas may be associated with extensive peritumoral brain edema, as visualized on computed tomographic (CT) scans. An analysis of 38 meningiomas indicated that severity of edema on CT scans positively correlated with tumor size and also with evidence of disruption of the cortical layer, which initially separates the tumor from the white matter, in which edema tends to accumulate. The various histological subtypes also seemed to be distinct in their tendency to induce edema, with the transitional and meningotheliomatous subtypes associated with the more severe grades of edema. There was no correlation between grade of edema and location of the tumor. Contact of the edematous area or the tumor itself with the ventricle, which is relevant to the possibility of drainage of edema fluid into the ventricle, seemed to occur in cases of the more severe grades of edema rather than in cases showing slight or no edema.
T1 and T2 relaxation times were determined in vitro at 21 MHz (0.5 T) for a variety of spinal and paraspinal tissues. Intensity formulas for spin echo and inversion recovery sequences were derived and used to calculate the intensities of these tissues as they would appear in magnetic resonance images. The intensity was calculated as a function of various repetition, echo, and inversion times. It is shown that the combination of acquiring in vitro relaxation time values and calculating intensity as a function of pulse timings is useful to predict the parameter setting for optimal contrast between certain tissues without applying series of magnetic resonance images.
Although CT scanning has considerably improved diagnostic accuracy, problems remain in establishing a precise preoperative diagnosis in cases of intracranial lesions especially when a cyst is present. Five cases of cystic lesions are presented to illustrate these problems. The CT features of cystic lesions as well as the pathophysiological processes that lead to their formation are discussed. The pertinent literature on this topic is reviewed.
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The morphological similarity of the lining of arachnoid cysts to subdural neurothelium and the mesothelium of arachnoid granulations suggested that the latter tissues might be the origin of arachnoid cysts. Transport Na+-K+-adenosine triphosphatase was shown by enzyme ultracytochemistry to be an indication of secretory activity in the lining of arachnoid cysts and in the endothelial lining of arachnoid granulations. This secretory activity suggests the existence of a biochemical mechanism for cerebrospinal fluid absorption at these granulations separate from the mechanisms already demonstrated.
When relaxation parameters of tissues are known, selection of adequate instrumental parameters in magnetic resonance imaging is possible. The signal strength of various tissues is defined by proton density, T1 and T2. The calculation of this signal strength is given. The advantages of multiple echoes and the reason why they are used, are mentioned.
NMR spectroscopical measurements of relaxation times were conducted on muscle, intestine, fatty tissue and cerebral cortex and white matter of the rat at various time intervals following removal of the tissue. It appeared that most tissues can be stored at 4 degrees C up to 24 hours without noticeable effects on NMR relaxation parameters. Exceptions are the T2 of muscle and the T1 and T2 of intestine, which tended to change in the first hour after biopsy. Relaxation parameters change considerably after fixation of the tissues. Therefore the effects of fixation have to be taken into account when carrying out NMR measurements on fixed tissues.
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Proton spin longitudinal (T1) and transverse (T2) relaxation and proton density studies were carried out on human fatty tissue and bovine white matter, both in the native state and after immersion in D2O. It is concluded that nuclear magnetic resonance signals from fatty tissue result mainly from methyl and methylene protons of hydrocarbons. No contribution from lipid protons could be detected for white matter, although it contains a high percentage of lipids. Imaging experiments, resulting in T1, T2, and proton density maps, support the results obtained with spectroscopic relaxation studies.
Morphological and enzyme ultracytochemical evidence is presented to support the contention that the walls of arachnoid cysts secrete fluid. Clinical evidence has already suggested this phenomenon, including intracranial pressure elevation and expansion in some cases, and the observation that arachnoid cysts constitute closed compartments with a fluid content that cannot be derived from other cerebrospinal fluid-containing spaces. Ultrastructurally, the cyst lining showed a similarity to subdural neurothelium and the neurothelial lining of arachnoid granulations in such morphological features as intercellular clefts with sinusoid dilatations, desmosomal intercellular junctions (upon which tonofilaments may be abutting), pinocytotic vesicles, multivesicular bodies, lysosomal structures, and the presence of a basal lamina. Some of these features, together with the presence of microvilli on the luminal surface, are consistent with fluid secretion. Moreover, enzyme cytochemistry demonstrated (Na+ + K+)-ATPase in the plasma membranes lining the cavity, either directly (the apical membranes), or via the intercellular clefts (the basolateral membranes), and, with alkaline phosphatase occupying the opposite plasma membranes, this structural organization indicates fluid transport toward the lumen. It may be surmised that arachnoid cysts derive from subdural neurothelium differentiating towards arachnoid villus mesothelium.
Nuclear magnetic resonance tomography is an imaging method based on the magnetic resonance behavior of protons, as they occur predominantly in tissue water or in fatty acids. This behavior, as characterized by the relaxation times T1 and T2, is determined by the chemical and physical environment of the protons. The relaxation properties of the tissue can be accentuated by selection of the appropriate pulse sequence. Interpretation of the images requires an understanding of the principles of the technique with which the relaxation times are expressed in the images, and acquaintance with the composition of the tissue in terms of relaxation properties (as in computerized tomography, tissue composition is expressed as attenuation coefficients).
The present report describes SEM observations on a variety of subjects, such as the walls of cerebral ventricles under pathological circumstances (hydrocephalus) as well as the surface morphology of abnormal cavities like arachnoid cysts and subdural hematomas. In the human specimens with hydrocephalus the changes consisted of degeneration of ependymal cilia, progressing to denudation of the ependyma while rupture of the ependymal layer was also seen. In experimental animals where the hydrocephalus was induced by agents (presumably irritant to the tissue), the presence of reactive supraependymal cells was observed next to the manifestations of ependymal degeneration. With the SEM the wall of arachnoid cysts showed numerous microvilli of stubby appearance with interspersed projections of diverse shape in the individual cases. SEM may aid in the diagnosis of arachnoid cysts, particularly in differentiating them from traumatic leptomeningeal cysts.
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Explore the source record for details and available documents.
Explore the source record for details and available documents.
By external detection, the influence of arterial blood pressure (BP), osmolarity, and cold-induced blood-brain barrier damage was assessed on the extraction of water labeled with oxygen 15 during single-capillary transit in the rat. There was an inverse relation between arterial BP and extraction that was attributable to the influence of arterial BP on cerebral blood flow (CBF) and the relation between CBF and extraction. Neither arterial BP nor osmolarity of the injected bolus had any direct effect on extraction of water 15O, signifying that the diffusional exchange component (determined by blood flow) of extraction greatly surpasses the convection flow contribution by hydrostatic or osmotic forces. Damage to the blood-brain barrier did not change its permeability to water.