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Biomedical subjects

T Bär

Publications and source records attributed to T Bär.

At least 19 recordsLinked to original sources
PubMed2001

In situ dynamic study of hydrogen oxidation on rhodium.

The reaction of hydrogen/oxygen gas mixtures with rhodium single crystals was studied using video-FIM (Field Ion Microscopy) at temperatures between 350 and 550 K and up to 2 x 10(-2) Pa total pressure. Imaging at 500 K in a hydrogen rich gas mixture (H2:O2 = 9) revealed considerable morphological changes of the (0 0 1)-oriented field emitter tip, i.e. the growth of low-index at the expense of high-index planes and strong crystal coarsening. Decreasing the hydrogen partial pressure led to chemical and structural changes of the Rh sample. Starting on the [1 1 0] planes a surface oxide formed, which spread anisotropically across the surface until it finally covered the whole visible surface area. The transformation was reversible upon increasing the hydrogen pressure back to its initial value. However, a hysteresis behavior was observed, i.e. a larger hydrogen partial pressure was found to be necessary to re-establish the initial patterns of a reactive Oad/Had layer. By varying the temperature from 400 to 500 K a phase diagram was established for the Oad/Had system. Increasing the electric field proved to shift the phase diagram towards higher H2 pressures. At 550K self-sustained kinetic oscillations with a cycle time of approximately 40s could be observed.

Journal Article↗
PubMed1998

Patient treatment insistence and medication craving in long-term low-dosage benzodiazepine prescriptions.

BACKGROUND: Long-term low-dosage dependence on benzodiazepines in traditionally explained by withdrawal symptoms. Previous research has not given much attention to reports that suggest that many patients oppose stopping benzodiazepines long before withdrawal symptoms have developed. This study investigates the scope of and factors associated with this pre-withdrawal treatment insistence. METHODS: Patients receiving long-term low-dosage benzodiazepines in primary care were asked to take a drug-holiday of at least 3 weeks. Sociodemographic, medication, morbidity and attitudinal variables were assessed in addition to the GPs' perceptions of their patients. RESULTS: Two-thirds of the patients rejected the drug-holiday proposal. Patients who refused a drug-holiday were less educated and were using a higher percentage of long-acting benzodiazepines than patients who accepted the drug-holiday proposal. Those who refused were seen by their GPs as being more complaining, harder to satisfy and less co-operative. CONCLUSIONS: These results provide evidence for drug-seeking or craving behaviour of patients who receive low-dosage benzodiazepine prescriptions. A major problem in benzodiazepine withdrawal occurs before the withdrawal programme has even begun. These data show that benzodiazepine low-dosage dependence should be considered a real form of dependence.

Aged↗
PubMed1997

cis-4-Methylsphingosine decreases sphingolipid biosynthesis by specifically interfering with serine palmitoyltransferase activity in primary cultured neurons.

The effect of six different structurally modified sphingosine analogues on biosynthesis of sphingolipids was studied in primary cultured murine cerebellar neurons. Treatment of cells with cis-4-methylsphingosine at micromolar levels resulted in a markedly decreased sphingolipid biosynthesis, whereas the other compounds examined, trans-4-methylsphingosine, cis-5-methylsphingosine, trans-5-methylsphingosine, cis-sphingosine, and 1-deoxysphingosine, inhibited sphingolipid biosynthesis less efficiently. The inhibition of sphingolipid biosynthesis by the various compounds was paralleled by a decrease of serine palmitoyltransferase activity in situ. For cis-4-methylsphingosine the inhibitory effect on serine palmitoyltransferase activity was shown to be concentration- and time-dependent. Half-maximal reduction of enzyme activity occurred after 24 h of treatment with 10 microM of the compound. The activity of other enzymes of sphingolipid biosynthesis as well as phospholipid and protein biosynthesis was not affected. Analysis of the sphingoid moiety of cellular sphingolipids suggests that the sphingosine analogues listed above were subject to degradation rather than being utilized as precursors for sphingolipid biosynthesis by cultured neurons. Except of 1-deoxysphingosine, the other five sphingosine analogues were shown to be substrates for sphingosine kinase in vitro. After 24 h of treatment of primary cerebellar neurons with the various sphingosine analogues the relative percentage of the respective intracellular 1-phosphate derivatives paralleled exactly the inhibitory effect on serine palmitoyltransferase activity observed when cells were treated with the unphosphorylated compounds. In contrast to the respective 1-phosphate derivatives of the other methyl-branched sphingosine analogues examined, cis-4-methylsphingosine 1-phosphate showed an intracellular accumulation suggesting a delayed turnover rate in cultured murine neurons for this compound. These results suggest that the inhibitory effect of the sphingosine analogues on serine palmitoyltransferase is mediated by their respective 1-phosphate derivatives and that the pronounced effect of cis-4-methylsphingosine is caused by a high intracellular concentration of cis-4-methylsphingosine 1-phosphate. cis-4-Methylsphingosine, in addition, caused drastic changes in cell morphology of primary cerebellar neurons, which were not observed when these cells were treated with one of the other sphingosine analogues examined.

Acyltransferases↗
PubMed1997

[The osteosynthesis implant and early postoperative infection: healing with or without removal of the material?].

This prospective study served as a quality control of a revision concept for case of post-traumatic infection following open reduction and internal fixation in fracture treatment. It is based on clinical and microbiological criteria and has two aims: (1) eradication of the infection and avoidance of development of chronic osteitis; (2) maintenance of internal fixation, if possible. Thirty-four patients were recruited in this study. Surgical revisions were performed according to a consistent concept (debridement, irrigation, local chemotherapy, drainage) in defined time intervals (2 days). The operation site had to be bacteriologically clean after four revisions. Otherwise, the implant had to be removed. Both aims were reached in 11 cases: management of infection with maintenance of internal fixation. In 23 cases the implant material had to be removed. Nevertheless the infection was eliminated in all these patients without exception. The following risk factors for mandatory implant removal were evaluated: diabetes, arteriosclerosis, alcoholism, nicotine. This revision concept helps in the management of acute postoperative osteitis following ORIF in fracture treatment and in avoiding the development of chronic osteitis.

Adolescent↗
PubMed1997

Determination of psilocin and 4-hydroxyindole-3-acetic acid in plasma by HPLC-ECD and pharmacokinetic profiles of oral and intravenous psilocybin in man.

In order to investigate the pharmacokinetic properties of psilocybin (PY), the main psychoactive compound of Psilocybe mushrooms, high performance liquid chromatographic procedures with column-switching coupled with electrochemical detection (HPLC-ECD) for reliable quantitative determination of the PY metabolites psilocin (PI) and 4-hydroxyindole-3-acetic acid (4HIAA) in human plasma were established. Sample work-up includes protection of the highly unstable phenolic analytes with ascorbic acid, freeze-drying and in-vitro microdialysis. The data of two controlled clinical studies with healthy volunteers are presented. The subjects (N = 6 for both studies) received single oral PY doses of 0.224 +/- 0.02 mg/kg b.wt. (10-20 mg) and intravenous doses of 1 mg PY, respectively. Peak plasma levels of PI after oral administration of PY were measured after 105 +/- 37 min showing an average concentration of 8.2 +/- 2.8 ng PI/ml plasma. 4HIAA peak concentrations of 150 +/- 61 ng/ml plasma were found 113 +/- 41 min after ingestion of PY. After intravenous administration, a mean PI maximum plasma concentration of 12.9 +/- 5.6 ng/ml plasma was found 1.9 +/- 1.0 min after injection. The maximum plasma levels appearing within a very short period indicate a rapid dephosphorylation of PY also when administered systemically. 4HIAA was not detected after 1 mg of intravenous PY. Estimates for the absolute bioavailability of PI after oral administration of PY were 52.7 +/- 20% (N = 3).

Administration, Oral↗
PubMed1996

Differential effects of synthetic sphingosine derivatives on melanoma cell motility, growth, adhesion and invasion in vitro.

Cancer cell surface glycosphingolipids are considered to play a critical role in tumor growth and metastasis. However, the implications of glycoconjugates in the control of cell motility, which is considered to be involved in tumor invasion, are not fully understood. In this study, the effects of a series of synthetic sphingosine derivatives, obtained by the chemical transformation of azidosphingosines, on directional migration of K1735-M2 melanoma cells grown on type I collagen-coated surfaces were investigated. Following the application of 60 microM (2R, 3S, 4E)-2, 3-epimino-4-octadecen-3-ol (S4) the migration rate was 94 +/- 10 microns/day, compared with 377 +/- 22 microns/day in the control experiment. Six other analogues were not as potent. S4 also considerably down-modulated melanoma single cell motility. Inhibition of motile activity was associated with changes in the actin filament organization as well as with changes in the number and distribution of vinculin plaques. Moreover, the compound reduced the attachment abilities of melanoma cells to basement membrane Matrigel. Tumor cell invasion, however, was less affected and proliferation remained unimpaired after treatment with S4. These data suggest at least one intracellular mode of action of this particular synthetic sphingosine derivative by modulation of cytoskeletal organization. Melanoma cell motility and growth may be controlled independently via glycosphingolipids.

Actins↗
PubMed1987

Arterial supply of the choriocapillaris of anuran amphibians (Rana temporaria, Rana esculenta). Scanning electron-microscopic (SEM) study of microcorrosion casts.

The pattern of the vascular supply to the choroid of the frog eye was studied in toto with the use of the injection-replication-SEM technique. The choroid of anuran amphibians is composed mainly of the choriocapillaris. In both species studied (Rana temporaria, Rana esculenta), an independent arterial supply to the choriocapillaris supplemented that from the ciliary arteries. This additional vascular route arises from the optic artery, a separate branch of the arteria infundibularis superficialis. The optic artery, accompanied by its vein within the vascular sheath of the optic nerve, joins the rich arterial capillary network of the choriocapillaris and supplies the posterior pole of the ocular bulb. The superficial capillary network displays a dense collar around the entrance of the optic nerve into the eye and is composed of a circular meshwork of small capillaries, several layers deep. More peripherally, however, it becomes a single layered. This capillary network, as a whole, establishes numerous connections with the adjacent choriocapillaris at the posterior pole of the ocular bulb. In anuran amphibians the complex arrangement of both arterial systems supporting the choriocapillaris may be regarded as a more complete equivalent of the short posterior ciliary arteries of mammals.

Animals↗
PubMed1987

The superficial vascular hyaloid system in the eye of the frogs, Rana temporaria and Rana esculenta. Scanning electron-microscopic study of vascular corrosion casts.

The angioarchitecture of the superficial vascular hyaloid system (membrana vasculosa retinae) of the frog eye was studied by means of scanning electron microscopy of vascular corrosion casts. The terminal vessels form a single-layered sheath intimately adjacent to the vitreal side of the avascular retina. The hyaloid system is subdivided by the ventral venous trunk into three central areas: the dorsal, the temporo-ventral, and the naso-ventral area. Toward the ora serrata, the hyaloid system is bordered by an arterial ring, and by nasal and temporal venous branches forming more or less complete hemicircles. A vascular zone composed of several tongue-like sectors establishes an interconnection between the peripheral vascular rings and the central areas of the fundus. The arterial blood is supplied from the arterial ring. The drainage of the hyaloid system is provided via two routes: (1) the Y-shaped ventral trunk collects blood from the central areas, (2) the two peripheral venous branches drain the tongue-like sectors. The vessels within the dorsal area follow preferentially a dorso-ventral meridional direction. This densely capillarized territory corresponds in localization to the area centralis retinae. The ultrastructure of microvessels of the hyaloid system is characterized by features typical for capillaries of the central nervous system.

Animals↗
PubMed1986

Postnatal development of the vascular pattern in the rat telencephalic pia-arachnoid. A SEM study.

The postnatal changes in arrangement of the vascular system of the pia-arachnoid of rats are described based on scanning electron microscopy of microcorrosion casts and transmission electron microscopy. At birth, the distal arteries and veins are embedded in a dense plexiform network of immature capillaries. Arteries and veins are interconnected by many small capillary anastomoses. The trunks are located above the pial plexus. The underlying plexiform vessels provide the matrix for the formation of additional collateral and precortical segments during further development. During the first postnatal week, the distal pial arteries and veins become visible as separate channels and emerge from the subjacent capillary plexus. The pattern of anastomosing arterial rings is now clearly visible. The pial arterial tree can be subdivided into conductive, collateral, and precortical distributive segments, according to Jokelainen et al. (1982). Subsequently, passive expansion of the vascular system takes place during the period of rapid brain growth. In young adults the majority of the formerly closed arterial rings are interrupted, possibly by regression of single collateral arterial segments (Fig. 6). The dense venous capillary plexus of the pia is maintained during the first eight days in spite of marked brain growth. The process of reduction of this capillary plexus starts at the arterial side and proceeds from proximal to distal segments of the veins during the second and third week. The capillary segments, which provide anastomosis between arterial and venous vessels, disappear at the same time as the regression of the dense venous capillary network.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

Postnatal development of gamma-GT activity in rat brain microvessels corresponds to capillary growth and differentiation.

It has been demonstrated histochemically that endothelial cells of the cerebral capillaries show a high activity in gamma-glutamyl transpeptidase (gamma-GT), an enzyme which takes part in the transfer of large neutral amino acids across the blood-brain barrier. Reports of the disappearance of enzyme activity in endothelial cells (EC) grown in culture suggest that the presence of astroglial cells (AG) is required for the expression of gamma-GT in these cells. The present study deals with the developmental changes in gamma-GT activity in capillaries of rat cerebral cortex during ontogenesis (i.e. on days 2, 7, 11, 14, 21 and 60 after birth). gamma-GT activity is determined by measuring the enzyme kinetics of the histochemical reaction on isolated brain capillaries using a flying spot microscope densitometer. Enzyme activity is expressed as an increase in relative optical density (at 500 nm) in arbitrary units/min/micron 2 during the 2 min immediately after initiating incubation and corresponds to the gamma-GT active area (in micron 2) of the capillary segment. During early postnatal development, a biphasic change of gamma-GT activity in capillaries of rat cerebral cortex is observed. The first phase (i.e. the postnatal period between the 2nd and 12th day) is characterized by a significant decrease in gamma-GT activity, which coincides with the onset of the rapid mitotic proliferation of cortical endothelial cells. During the second phase (i.e. the postnatal period between the 12th and 21st day), a fast increase in the gamma-GT activity can be measured. Then enzyme activity reaches the adult level between the 21st and 60th postnatal day.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗
PubMed1984

Local cytochrome oxidase activity in the cerebral cortex of the rat, histochemically detected with the DAB-method: a micro-densitometric and electron microscope study.

For demonstration of the local cytochrome oxidase activity, coronal sections through the frontal cortex of four Sprague-Dawley rats were incubated with DAB medium after Seligman et al. (1968). The pattern of distribution of the DAB reaction product (DAB-RP) was measured at a wavelength of 460 nm. Cryostat sections were scanned with a microdensitometer. The cytochrome reaction product was accumulated in the laminae I and IV. A comparative morphometric study of mitochondrial profiles in ultra-thin sections through equivalent cortical regions showed an approximately similar distribution in percentage of areal density of the mitochondria labeled by DAB-RP. On average 30% of the mitochondrial profiles were labeled with DAB-RP which was localized in the intracristate spaces and the outer mitochondrial compartment. The marked mitochondria mainly occurred in dendrites. Furthermore, the mean and median value of the size distribution of marked mitochondrial profiles was shifted to greater values when compared with non-marked ones.

3,3'-Diaminobenzidine↗
PubMed1984

"Seamless" endothelial cells of blood capillaries.

The distribution and number of seamless endothelial cells (SE) were studied in various organs and tissues of rats, rabbits and humans (1) by light microscopy after silver impregnation of the endothelial cell boundaries, (2) by electron microscopy, and (3) in three-dimensional reconstructions of duodenal villi and renal glomeruli. Since SE are situated mostly at branching points, the number of SE is roughly correlated to the number of branchings in the capillary system concerned. SE make up about 50% of all endothelial cells in the renal glomerulum and duodenal villi, and about 30% in the cerebral cortex. However, they rarely occur in bradytrophic tissues. SE have been found exclusively in net capillaries (true capillaries). They seem to be absent in most arterio-venous capillaries (capillary parts of thoroughfare channels), in the capillaries of endocrine glands, as well as in the sinusoidal systems of heart muscle, liver, spleen and bone marrow. It is concluded that SE are developed when tube formation is confined to a single endothelial cell. SE are intercalated most frequently in those capillaries that develop lastly in the terminal vascular bed. The seamless segments are canalized by fusion of intraendothelial vacuoles with pre-existing vascular walls. The existence of SE, confirming the dual structural design of capillary systems, may be used as a detector for net capillaries.

Adipose Tissue↗
PubMed1984

Identification of pericytes in the central nervous system by silver staining of the basal lamina.

Vibratome sections obtained from perfusion-fixed rat brains were stained by means of silver impregnation and physical development according to Gallyas (1970). Small pieces of the cerebral cortex were postfixed with buffered osmium tetroxide solution and processed for electron microscopy to examine the localization of the silver deposit at the cellular level. The cell surfaces of pericytes and smooth muscle cells were completely outlined by silver grains. Endothelial cells and perivascular astrocytes, however, showed an asymmetric distribution of the silver deposit, i.e., the deposit was restricted to the abluminal endothelial surface and to the astrocytic membrane adjacent to the vessel wall, respectively. The method allowed a clear-cut distinction between perikarya of endothelial cells and pericytes as well as glial cells in perivascular position, even at the light-microscopic level.

Animals↗
PubMed1983

Patterns of vascularization in the developing cerebral cortex.

The vascular system of the cerebral cortex can be adapted to changing metabolic requirements which occur during development. Apart from a purely nutritive function the intracerebral vessels influence embryonal gliogenesis and migration of neuroblasts. The internal vascularization of the cerebral cortex starts during embryonic development and continues until the postnatal period. The formation of new penetrating vascular trunks and intracortical capillary branching is terminated before global brain growth reaches a plateau. The information necessary to develop a vascular system designed for functional needs later in development may already be expressed in the basic fetal pattern. The formation of such a system is probably not under direct metabolic control. The cellular composition of the capillary tube changes with the developmental stage and the actual growth rate of the endothelial cells. In the cerebral cortex the maximal growth rate of capillaries proceeds in a regional- and lamina-specific manner according to a defined ontogenetic time-scale. The importance of a local factor in the regulation of vascular growth is strengthened by this observation. The vascular system of the cerebral cortex is evaluated using morphometry and reconstructions of serial sections at different stages of postnatal development. This study aims to provide a morphological basis which may help to define cellular mechanisms associated with vascular patterning during brain development.

Animals↗
PubMed1982

[Ultrastructural aspects of amniotic-fluid cells B. "vital cells" (author's transl)].

It has been shown, that apart from the mass of non-vital squamous epithelial cells, there also exist vital cells in the amniotic fluid. In this study, two types of amniotic fluid cells, which upon examination based on morphological characteristics gave rise to conclusions concerning their vitality, are presented, described and correlated with morphologically similar cells with known origin. Probably one type of these amniotic fluid cells are macrophages or Hofbauer-cells and the other types could be amnion-cells.

Amniotic Fluid↗
PubMed1981

["Ultrastructural aspects of amniotic-fluid cells". A. Non-vital cells. I. Periderm-cells (author's transl)].

The surface layer of fetal epidermis in early pregnancy, the Periderm, is progressingly replaced by the final keratinization process during fifth to sixth month of gestation. Then the peridermal cells are shed into the amniotic fluid. It is still controversial, whether complete peridermal cells or just their globular protrusions are separated. Formation of mikrovilli and invaginations of plasma membrane, the numerous smaller and larger vacuoles and the cytoplasmatic meshwork of fine filaments without production of keratohyaline, are characteristics of peridermal cells, and are described in detail by electron microscopical investigations on cells suspended in the amniotic fluid, which are most likely of peridermal origin.

Amniotic Fluid↗
PubMed1981

["Ultrastructural aspects of amniotic-Fluid Cells". A. Non-vital cells. II. Keratinocytes (author's transl)].

The ultrastructural morphology of epidermal keratinocytes, which at the end of pregnancy and after shedding of vernix represent the majority of amniotic fluid cell population, is analysed by electron microscopy. Special attention is focused on the morphological characteristics of epidermal keratinization according the changes of the cell's ultrastructure during this process: The transformation of the cytoplasma into keratin, the formation of the typical cell membrane of the keratinized squamous cells, and the findings concerning the intercellular space, especially of the zones of intercellular contact - desmosomes - and their changes.

Amniotic Fluid↗