Showing papers by "University of Freiburg published in 1989"

Three cytoplasmic loops of rhodopsin interact with transducin

Abstract: Rhodopsin is a member of an ancient class of receptors that transduce signals through their interaction with guanine nucleotide-binding proteins (G proteins). We have mapped the sites of interaction of rhodopsin with its G protein, which by analogy suggests how other members of this class of receptors may interact with their G proteins. Three regions of rhodopsin's cytoplasmic surface interact with the rod cell G protein transducin (Gt). These are (i) the second cytoplasmic loop, which connects rhodopsin helices III and IV, (ii) the third cytoplasmic loop, which connects rhodopsin helices V and VI, and (iii) a putative fourth cytoplasmic loop formed by amino acids 310-321, as the carboxyl-terminal sequence emerges from helix VII and anchors to the lipid bilayer via palmitoylcysteines 322 and 323. Evidence for these regions of interaction of rhodopsin and Gt comes from the ability of synthetic peptides comprising these regions to compete with metarhodopsin II for binding to Gt. A spectroscopic assay that measures the "extra MII" caused by Gt binding was used to measure the extent of binding of Gt in the presence of competing peptides. The three peptides corresponding to the second, third, and fourth cytoplasmic loops competed effectively with metarhodopsin II, exhibiting Kd values in the 2 microM range; 11 additional peptides comprising all remaining surface regions of rhodopsin failed to compete even at 200 microM. Any two peptides that were effective competitors showed a synergistic effect, having 15 times higher effectiveness when mixed than when assayed separately. A mathematical model was developed to describe this behavior.

Hemangioblastomas of the central nervous system. A 10-year study with special reference to von Hippel-Lindau syndrome.

Abstract: ✓ The findings of a 10-year study (1976 to 1986) conducted in southwest Germany on hemangioblastomas (HBL's) of the central nervous system (CNS) are presented. During that period, 47 HBL's were diagnosed and surgically removed in 44 patients, with a good postoperative survival rate and prognosis. The majority (83%) of these tumors were located in the cerebellum. By thorough clinical examination of the patients and careful evaluation of their family background, it was found that 23% of the HBL patients were afflicted with von Hippel-Lindau syndrome. In addition to the CNS tumors, 14 neoplastic or similar lesions were detected in other tissues. These included angiomatosis of the retinae, pheochromocytomas, pancreatic cysts, renal cysts, and renal carcinoma. The diagnosis of von Hippel-Lindau syndrome was thus established in seven families. The authors suggest the need for a screening program for patients with HBL of the CNS which is designed to confirm or exclude ocular or visceral lesions associated with v...

Flow-dependent coronary artery dilatation in humans.

Abstract: To determine the role of endothelium-mediated flow-dependent coronary dilatation in humans, we studied the coronary dilatation exerted by maximal pharmacologic increase of coronary flow in 14 patients with normal coronary arteries. Biplane views of the circumflex (Cx) and left anterior descending (LAD) coronary arteries were obtained before and 80 seconds after inducing a maximal increase in flow selectively in the Cx by injecting 7 mg papaverine through a 2F infusion catheter in the midportion of the Cx (n = 10). The diameter of the proximal Cx segment (exposed to increased flow but not to papaverine directly) increased with papaverine by 11.1 +/- 4% (range, 5.2-16.4%, p less than 0.001 vs. control), whereas the LAD diameter did not change. LAD and Cx diameters increased by 18.3% and 21.2% after nitroglycerin given into the left main artery, which showed the preserved capability of the LAD to dilate. In four patients with normal coronary arteries and six patients with coronary artery disease (CAD, non-flow-limiting stenosis), a similar protocol was applied with the LAD for the assessment of flow-dependent dilatation. Simultaneously, intracoronary blood flow velocity was measured by an intracoronary Doppler catheter. Papaverine-induced coronary flow reserve (peak/resting velocity ratio) in the LAD was 4 +/- 0.7 (range, 3.5-5) in normal arteries and was 3.5 +/- 0.6 (range, 2.7-4.4) in CAD.(ABSTRACT TRUNCATED AT 250 WORDS)

Amyloplasts are necessary for full gravitropic sensitivity in roots of Arabidopsis thaliana

Abstract: The observation that a starchless mutant (TC7) of Arabidopsis thaliana (L.) Heynh. is gravitropic (T. Caspar and B.G. Pickard, 1989, Planta 177, 185-197) raises questions about the hypothesis that starch and amyloplasts play a role in gravity perception. We compared the kinetics of gravitropism in this starchless mutant and the wild-type (WT). Wild-type roots are more responsive to gravity than TC7 roots as judged by several parameters: (1) Vertically grown TC7 roots were not as oriented with respect to the gravity vector as WT roots. (2) In the time course of curvature after gravistimulation, curvature in TC7 roots was delayed and reduced compared to WT roots. (3) TC7 roots curved less than WT roots following a single, short (induction) period of gravistimulation, and WT, but not TC7, roots curved in response to a 1-min period of horizontal exposure. (4) Wild-type roots curved much more than TC7 roots in response to intermittent stimulation (repeated short periods of horizontal exposure); WT roots curved in response to 10 s of stimulation or less, but TC7 roots required 2 min of stimulation to produce a curvature. The growth rates were equal for both genotypes. We conclude that WT roots are more sensitive to gravity than TC7 roots. Starch is not required for gravity perception in TC7 roots, but is necessary for full sensitivity; thus it is likely that amyloplasts function as statoliths in WT Arabidopsis roots. Furthermore, since centrifugation studies using low gravitational forces indicated that starchless plastids are relatively dense and are the most movable component in TC7 columella cells, the starchless plastids may also function as statoliths.

Complications of anterior cervical discectomy without fusion in 450 consecutive patients.

Abstract: The complications of anterior discectomy without fusion were analyzed on the basis of 450 consecutive cases treated surgically for degenerative disc disease. There was no death related to the procedure. The most common complication was a worsening of the pre-existing myelopathy. This occurred in 3.3%, including one case with severe medullary contusion. Wound infection developed in 1.6%. Additional radicular symptoms and wound haematoma, respectively, occurred in 1.3%; recurrent nerve palsy, Horner's syndrome, and respiratory insufficiency, respectively, in 1.1% of the cases. Epidural haematoma and instability of the cervical spine, respectively, occurred in 0.9%, nerve root lesion and aseptic spondylodiscitis, respectively, in 0.4%. There was one case each (0.2%) with a pharyngeal lesion, meningitis due to dural perforation, transient additional myelopathy, and epidural abscess. The results and the management of complications are discussed in relation to numerous previously published reports, including posterior procedures and anterior fusion techniques. Precise knowledge of all potential accidents and pitfalls related to the surgical procedure and of their aetiology may contribute to preventing failures. The rate of complications in this series has been reduced in the past years by better patient selection, by paying more attention to correct positioning of the patient during the operation, and by meticulous removal of all offending structures. Discectomy without interbody fusion is now considered to be a reasonably safe procedure with an acceptable operative morbidity and lack of mortality.

Contrasting peripheral short-term and long-term effects of converting enzyme inhibition in patients with congestive heart failure. A double-blind, placebo-controlled trial.

Abstract: To discover the underlying mechanisms involved in the beneficial long-term effects of angiotensin converting enzyme (ACE) inhibitors, we investigated the systemic and peripheral effects of short- and long-term ACE inhibition in patients with chronic heart failure After assessing the short-term effects and dose titration with cilazapril, a new long-acting ACE inhibitor, 21 patients were randomized to receive either placebo or the ACE inhibitor Seventeen patients completed the 3-month treatment Central hemodynamic output, femoral blood flow (measured by thermodilution), oxygen saturation, and lactate and norepinephrine levels were determined simultaneously in the femoral vein and radial artery during treatment and after a 3-month rest and during symptom-limited bicycle exercise Short-term ACE inhibition improved rest and exercise hemodynamic output, but it did not alter peak femoral blood flow, calculated leg oxygen consumption, or systemic oxygen uptake during exercise, despite significant reduction in femoral norepinephrine extraction and arterial angiotensin levels during exercise In contrast, long-term ACE inhibition further improved exercise cardiac output and increased leg blood flow (from 23 to 29 l/min, p less than 005), leg oxygen consumption (from 277 to 403 ml/min, p less than 005), and systemic oxygen uptake (from 1,133 to 1,453 ml/min, p less than 005), whereas these variables remained unchanged with placebo treatment (p less than 002 between groups) Moreover, a moderate but significant increase in femoral oxygen extraction occurred after long-term therapy (ACE inhibitor: from 76% to 83%, p less than 005; placebo: from 75% to 74%, NS; p less than 001 between groups) We conclude that long-term ACE inhibition is clinically beneficial in that it improves blood flow to skeletal muscle during exercise over time The long-term effects of ACE inhibition are, in part, probably related to peripheral (vascular) mechanisms, for example, by reversing the inability of peripheral vessels to dilate and by improving oxygen utilization

Interlimb coordination of leg-muscle activation during perturbation of stance in humans.

Abstract: 1. Electromyographic (EMG) responses were recorded in both legs, along with corresponding joint movements, after uni- and bilateral perturbations during stance on a treadmill with split belts. Displacements were directed forward, backward, or in opposing directions. They were induced by randomly timed ramp impulses at one of four different rates of treadmill acceleration. 2. Unilateral perturbations directed backward were followed by a bilateral gastrocnemius-EMG response, forward-directed perturbations by a bilateral tibialis anterior-EMG response. The amplitude of these responses was dependent on the rate of treadmill acceleration. Relative to the response of the displaced leg, the amplitude of the EMG response on the nondisplaced side was smaller when a gastrocnemius EMG response was induced, and about equal when the tibialis anterior muscle was activated. The onset latencies were shorter on the displaced side (displaced leg 75-96 ms, non-displaced leg 93-112 ms). 3. Bilateral perturbations in one direction were followed by larger EMG responses in both legs (in the gastrocnemius for backward-directed impulses, in the tibialis anterior for forward-directed impulses). For a given acceleration rate, their amplitude was about equal to the sum of the EMG amplitude of the displaced leg and that of the nondisplaced leg obtained during unilateral displacement. The inverse result was obtained when the legs were simultaneously displaced in opposite directions: EMG responses in both legs were significantly smaller than those obtained after unilateral displacement. 4. It is concluded that a unilateral displacement evokes reflex EMG responses in the synergistic muscles of both legs, which are graded according to the size of the proprioceptive input from the primarily displaced joint. During bilateral displacements, the activity induced by the respective contralateral leg is linearly summed or subtracted, depending on whether the legs are displaced in the same or in opposite directions. In view of the short latencies of these bilateral responses, it would seem that they are mediated by a spinal mechanism. 5. Distinct differences in the behavior of the antagonistic leg muscles were observed: 1) the coactivation of the contralateral leg muscle was significantly smaller when the gastrocnemius was stretched unilaterally, whereas it was about equal for the tibialis anterior; and 2) the gastrocnemius EMG responses were closely correlated with the displacement velocity, whereas the tibialis anterior response was more closely correlated with acceleration, i.e., the tibialis anterior response was more dynamic in nature.(ABSTRACT TRUNCATED AT 400 WORDS)

Bacterial growth blocked by a synthetic peptide based on the structure of a human proteinase inhibitor.

Abstract: Cysteine proteinases are important not only in the intracellular catabolism of peptides and proteins1 and in the processing of prohormones and proenzymes2,3, but also in the penetration of normal human tissue by malignant cells4 and possibly microorganisms5, including viruses. Cystatin C is a human cysteine proteinase inhibitor present in extracellular fluids6. We have synthesized peptide derivatives mimicking the proposed proteinase-binding centre of cystatin C7 and find that they irreversibly inhibit cysteine proteinases. Several bacteria produce proteinases, so we tested a tripeptide derivative (Z-LVG-CHN2) for in vitro anti-bacterial activity against a large number of bacterial strains belonging to thirteen different species. It was found to inhibit specifically the growth of all strains of group A streptococci. The susceptibility of these human pathogens to the peptide was compared with that to well-established anti-streptococcal antibiotics such as tetracy-cline and bacitracin. Moreover, the peptide was active in vivo against group A streptococci: mice injected with lethal doses of these bacteria were cured by a single injection of Z-LVG-CHN2. The cysteine proteinase produced by group A streptococci was isolated and found to be inhibited by Z-LVG-CHN2; moreover, excess proteinase relieved the growth inhibition caused by the peptide derivative, suggesting that the antibacterial activity of Z-LVG-CHN2 is due to inhibition of this cysteine proteinase. This strategy of blocking proteinases with peptide derivatives that mimic naturally occurring inhibitors could be useful in the construction of new agents against other microorganisms, including viruses.

Lipopolysaccharide-free conditions in primary astrocyte cultures allow growth and isolation of microglial cells.

Abstract: Primary rat astrocyte cultures were used to isolate a macrophage population that does not adhere to the confluent glial cells. The cells multiplied vigorously in coculture with astrocytes during the 14 d culture period, provided that functionally active lipopolysaccharide (LPS) was either absent or present in very low concentrations. Based on morphological, immunocytochemical, and pharmacological data, it was concluded that the isolated cells were microglia, the resident macrophages of the brain. The findings characterized them as a distinct cell population that shares features both of peritoneal macrophages and of astroglial cells. Like peritoneal macrophages, the isolated cells were able to phagocytize as shown by their ingestion of latex beads and uptake of L-leucyl methylester. Furthermore, they were immunocytochemically stainable by a specific monoclonal antibody (ED 1) against a macrophage-specific antigen (Dijkstra et al., 1985). They also synthesized prostaglandin E2 (PGE2) and secreted interleukin 1 (IL-1) upon stimulation with LPS. Upon stimulation with the ionophore A23187, PGD2, the predominant prostaglandin of the brain, was the major PG metabolite released by these cells. In contrast to peritoneal macrophages, microglial cells were able to multiply. Proliferation of microglial cells in coculture with astrocytes was suppressed when 2 ng LPS/ml or higher concentrations were added to astroglial culture media. These astrocyte cultures, which contained approximately 1% microglia, were used to investigate the influence of LPS on prostaglandin and IL-1 secretion in order to compare astroglial and microglial features. Increasing LPS concentrations induced increased PGE2 secretion, whereas PGD2 secretion was essentially unaffected by LPS. The critical influence of LPS contaminations in most of the commercially available animal sera used for astrocyte cultures on cellular composition in general and on metabolism of hormones and growth factors in particular is discussed.

Hypoxia stimulates release of endothelium-derived relaxant factor.

Abstract: It was tested whether hypoxia stimulates the release of endothelium-derived relaxant factor (EDRF). In paired segments (with and without endothelium) of either femoral artery (n = 49) or aorta (n = 42) from rabbits, selective luminal hypoxia (Po2 = 24 +/- 8 mmHg) was induced, whereas the Po2 at the adventitial side was kept above 300 mmHg. Hypoxia induced a dilation of 11 +/- 2% in aortic segments with endothelium, whereas the paired segments without endothelium dilated by only 1.2 +/- 0.2% (P less than 0.001). Similar results were obtained in femoral segments (11.8 +/- 1.5% dilation in segments with endothelium vs. 1.4 +/- 0.2% in segments without; P less than 0.001). Likewise in 19 out of 36 bioassay experiments, perfusate from endothelium-intact rabbit aortas or cultured bovine aortic endothelial cells exposed to hypoxia elicited dilation (10.7 +/- 3.2%) in the detector. The EDRF-inhibitors, hemoglobin (5 microM) and dithiothreitol (200 microM), significantly inhibited the hypoxia-induced dilation of intact segments as well as of assay segments perfused with effluent from hypoxic donors. These results suggest that hypoxia stimulates the release of EDRF from native and cultured endothelium. Low partial pressures of oxygen, such as those that exist in small arteries and arterioles, might therefore be a physiological stimulus for continuous release of EDRF.

The autonomic differentiation of emotions revisited: convergent and discriminant validation.

Abstract: The convergent and discriminant validity of three models of physiological emotion specificity were compared, Forty-two female students served as subjects in a 2 (Context of emotional inductions: real-life, imagery) × 3 (Emotion: fear, anger, control) + 1 (Happiness induced in real-life context) repeated measures design. The dependent measures included self-reports of emotion, Gottschalk-Gleser affect scores, back and forearm extensor EMG activity, body movements, heart period, respiration period, skin conductance, skin temperatures, pulse transit time, pulse volume amplitude, and blood volumes. Self-report data confirmed the generation of affective states in both contexts, as intended. Planned multivariate comparisons between physiological profiles established discriminant validity for fear and anger in the real-life context, whereas under imagery, emotion profiles were essentially equal. Convergent validity could not be substantiated. Implications for models of physiological specificity of emotion were discussed.

Kinetics, binding constant, and activation energy of the 48-kDa protein-rhodopsin complex by extra-metarhodopsin II.

Abstract: We have found that the 48-kDa protein (or S-antigen 48k) of the rod photoreceptor enhances the light-induced formation of the photoproduct metarhodopsin II (MII) from prephosphorylated rhodopsin. The effect is analogous to the known enhancement of MII (extra-MII) that results from selective interaction of MII with G-protein. We have determined some parameters of the MII-48k interaction by measuring the extra-MII absorption change induced by the 48-kDa protein. The amplitude saturation yields a dissociation constant for the MII-48k complex on the order of 50 nM. At the technical limit of these measurements, 13.7 degrees C and 12 microM 48-kDa protein, we find a rate of 2.3 s-1 for formation of the 48k-MII complex. Extrapolation of these values to cellular conditions yields an occupation time of phosphorylated MII by 48k less than 200 ms. This is short compared to estimated rates of phosphorylation. The temperature dependence of the MII-48k formation rate is very high (Q10 for 5 degrees C/15 degrees C = 9-10). The related Arrhenius activation energy (165 kJ mol-1) is correspondingly high and indicates a considerable transient chemical change during the binding process.

Beyond Steiner's Problem: A VLSI Oriented Generalization

Abstract: We consider a generalized version of Steiner's problem in graphs, motivated by the wire routing phase in physical VLSI design: given a connected, undirected distance graph with groups of required vertices and Steiner vertices, find a shortest connected subgraph containing at least one required vertex of each group We propose two efficient approximation algorithms computing different approximate solutions in time O(|E| + |V|log|V|) and in time O(g · (|E| + |V|log|V|)), respectively, where |E| is the number of edges in the given graph, |V| is the number of vertices, and g is the number of groups The latter algorithm propagates a set of wavefronts with different distances simultaneously through the graph; it is interesting in its own right

Cortisol response to a combined dexamethasone-human corticotrophin-releasing hormone challenge in patients with depression.

Abstract: We administered a combined dexamethasone-human corticotrophin-releasing hormone (hCRH) challenge test to 14 in-patients with a major depressive episode and to 14 age-matched controls. After pretreatment with 1.5 mg dexamethasone at 2300 h the day before, 100 mug hCRH was administered iv at 1500 h. Blood samples for cortisol determinations by radioimmunoassay were drawn at 1400 h, 1430 h and 1500 h before infusion of hCRH and thereafter every 15 min until 1700 h. Cortisol secretion after injection of hCRH assessed as area under the curve was significantly increased in patients with depression when compared to controls (14.5 +/- 4.3 ng x min x 1,000/ml vs 3.1 +/- 2.4 ng x min x 1,000/ml). Multiple regression analysis among patients revealed a significant impact of age and severity of depression upon hCRH-induced cortisol secretion, whereas in normal controls no significant influence of age on cortisol secretion after hCRH emerged. Our data show that in depressed patients hCRH evokes an escape from dexamethasone-induced suppression of the pituitary-adrenocortical activity, whereas it fails to do so among controls. This finding suggests that at the pituitary level the action of hCRH is enhanced by a factor that is less sensitive to dexamethasone suppression in depression. We postulate that this factor is vasopressin.

Cell biology and kinetics of Kupffer cells in the liver.

Abstract: Publisher Summary The study of Kupffer cells has developed rapidly and has been extended to problems concerning the origin, structure, and function of these cells in normal and pathological conditions This chapter provides an overview of the current morphological and biochemical data. Many of the major advances in Kupffer cells have resulted from the development of new methods, such as cell isolation, purification, and culture. Kupffer cells play a major role in the clearance of endotoxin from the blood, which induces the release of a number of mediators. Experimental virus infections provide the indications of the viral hepatitis development in human liver. The susceptibility of Kupffer cells to bacterial and viral infections is influenced by hormonal, immunological, nutritional, and genetic factors. The regulatory role of Kupffer cells in various hepatic disorders as well as in liver transplantation still requires further investigation. The chapter discusses the involvement of Kupffer cells and natural killer (NK) cells in the defense against tumor development and describes the way in which Kupffer cells coordinate their activities with liver-associated NK cells in tumor cell cytotoxicity. Since the descriptions of the isolation, purification, and culture of Kupffer cells from rat liver, the study of the function of these cells in vitro has made considerable progress.

Macula densa cells sense luminal NaCl concentration via furosemide sensitive Na+2Cl-K+ cotransport.

Abstract: The macula densa cells of the juxtaglomerular apparatus probably serve as the sensor cells for the signal which leads to the appropriate tubuloglomerular feedback response. The present study reports basolateral membrane voltage (PDbl) measurements in macula densa cells. We isolated and perfused in vitro thick ascending limb segments with the glomerulus, and therefore the macula densa cells, and the early distal tubule still attached. Macula densa cells were impaled with microelectrodes under visual control. PDbl was recorded in order to examine how these cells sense changes in luminal NaCl concentrations. The addition of furosemide, a specific inhibitor of the Na+2Cl-K+ cotransporter in the thick ascending limb, to the lumen of the perfused thick ascending limb hyperpolarized PDbl from -55 +/- 5 mV to -79 +/- 4 mV (n = 7). Reduction of NaCl in the lumen perfusate from 150 mmol/l to 30 mmol/l also hyperpolarized PDbl from -48 +/- 3 mV to -66 +/- 5 mV (n = 4). A Cl- concentration step in the bath from 150 mmol/l to 30 mmol/l resulted in a 24 +/- 4 mV (n = 4) depolarization of PDbl. This depolarization of PDbl was absent when furosemide was present during the Cl- concentration step. These data suggest that the macula densa cells sense changes in luminal NaCl concentration via coupled uptake of Na+ and Cl-.(ABSTRACT TRUNCATED AT 250 WORDS)

Computed tomography-osteoabsorptiometry for assessing the density distribution of subchondral bone as a measure of long-term mechanical adaptation in individual joints

Abstract: To estimate subchondral mineralisation patterns which represent the long-term loading history of individual joints, a method has been developed employing computed tomography (CT) which permits repeated examination of living joints. The method was tested on 5 knee, 3 sacroiliac, 3 ankle and 5 shoulder joints and then investigated with X-ray densitometry. A CT absorptiometric presentation and maps of the area distribution of the subchondral bone density areas were derived using an image analyser. Comparison of the results from both X-ray densitometry and CT-absorptiometry revealed almost identical pictures of distribution of the subchondral bone density. The method may be used to examine subchondral mineralisation as a measure of the mechanical adaptability of joints in the living subject.

A crystallographic study of the glutathione binding site of glutathione reductase at 0.3‐nm resolution

Abstract: The binding of glutathione, some related molecules and two redox compounds to crystals of glutathione reductase has been investigated by X-ray crystallography at 0.3-nm resolution. Models for several bound ligands have been built and subjected to crystallographic refinement. The results clearly show the residues involved in glutathione binding as well as the geometry of the disulfide exchange. Glutathione-I is bound in a V-shaped conformation, while glutathione-II is extended. The zwitterionic glutamyl end of glutathione-II appears to be the most tightly bound part of the substrate. All glutathione conjugates and derivatives studied show binding dominated by the interactions at this site. In the reduced enzyme, glutathione-I forms a mixed disulfide intermediate with Cys58. Other structural changes are observed on reduction of the enzyme, and it is demonstrated that the carboxamidomethylated enzyme is a good model for the reduced species. Lipoate, a weak substrate of the enzyme, assumes a defined binding site where its disulfide is available for being attacked by Cys58-Sγ. A second region with affinity for a number of compounds has been found in a large cavity at the dimer interface of the enzyme. No functional role of this site is known.

[The transjugular intrahepatic portosystemic stent-shunt. A new nonsurgical percutaneous method].

Abstract: In a 49-year-old male patient suffering from severe symptoms of end-stage portal hypertension and Child's stage C metabolic status, an intrahepatic stent-assisted portosystemic shunt was established for the first time exclusively by means of interventional radiology. Via transjugular access, a modified Brockenbrough needle was used to puncture the right branch of the portal vein via the right liver vein. As a target, a Dormia-basket was used that had previously been exposed in the right main portal branch. After successful puncture and balloon dilation of the artificial tract, two Palmaz stents were implanted to keep the tract permanently open. The portosystemic pressure gradient dropped from 38 to 18 mm Hg. The clinical status of the patient improved substantially during the following days. However, the patient died on day 11 after the procedure because of sudden onset of acute respiratory distress arising from acute nosocomial fungus and cytomegalovirus infection worsened by his primary immunoincompetence. Autopsy demonstrated a totally patent shunt without superficial thrombus. Microscopically, a thin endothelial layer on the inner shunt surface was found to be present.

A transcranial Doppler study of blood flow velocity in the middle cerebral arteries performed at rest and during mental activities.

Abstract: While changes in blood velocity in the middle cerebral artery relative to rest were assessed by transcranial Doppler sonography, 70 volunteers with no sign of cerebrovascular disease performed two (left and right middle cerebral artery) series of six cognitive tasks. The tasks are assumed to be processed predominantly by either the left (verbal and mathematical tests performed aloud) or the right hemisphere (dot/distance estimation, spatial perception, and face recognition performed silently). All tasks were shown to increase middle cerebral artery blood flow velocity on both sides, by 1.6-10.6%. After an initial maximum at approximately 8 seconds, velocity decreased then increased again. A steady state was reached after approximately 24-42 seconds. The initial minimum during the following rest phase was reached some seconds later, followed by a slow increase to the reference rest steady state. A difference according to side could be determined only during the three right-hemispheric tasks (right greater than left, 2.5-2.9%). Left-handedness/ambidexterity, familial sinistrality, and profession seemed to have no influence on the results. The middle cerebral artery blood flow velocity increase on both sides was higher in women than in men during the dot/distance estimation and was also higher bilaterally in older than in younger subjects during the dot/distance and the spatial perception tasks. Habituation in performing the tasks was an important factor associated with a decrease of blood flow velocity, especially in the right middle cerebral artery. The habituation more pronounced on the right side possibly reflects the role of the right hemisphere in attention and arousal. The absolute blood velocities at rest decreased bilaterally with age.

Nematic elastomers: The influence of external mechanical stress on the liquid-crystalline phase behavior

Abstract: The influence of external mechanical stress on the nematic-isotropic phase transformation of nematic elastomers was investigated. The experimental results of IR-dichroism measurements in the nematic phase and stress-optical measurements in the isotropic phase are in good agreement with the theoretical predicitions of the phenomenological Landau-de Gennes theory. This is for the first time that a significant influence of an external field on the nematic-isotropic phase transformation temperature and on the nematic order parameter S has been proved.