Showing papers by "University of Zurich published in 1991"

The soft tissue barrier at implants and teeth

Abstract: In the present animal experiment, analyses and comparisons were made between the structure and composition of clinically healthy supraalveolar soft tissues adjacent to implants and teeth. 5 beagle dogs were used. The right mandibular premolar region was selected in each dog for placement of titanium implants, while the left mandibular premolar region served as control. Extractions of the mandibular premolars were preformed, healing allowed, following which titanium fixtures were installed in the edentolous premolar region. Abutment connection was carried out 3 months later. After another 2 months of healing, plaque control was initiated and maintained for 8 weeks. At the end of the plaque control period, clinical examinations were performed and biopsies harvested from the implant site and the contralateral premolar tooth region. Following fixation and decalcification, all tissue samples were embedded in EPON and examined by histometric and morphometric means. The result from the analyses demonstrated that the periimplant mucosa which formed at titanium implants following abutment connection had many features in common with gingival tissue at teeth. Thus, like the gingiva, the peri-implant mucosa established a cuff-like barrier which adhered to the surface of the titanium abutment. Further, both the gingiva and the peri-implant mucosa had a well-keratinized oral epithelium which was continuous with a junctional epithelium that faced the enamel or the titanium surface. In the periimplant mucosa, the collagen fibers appeared to commence at the marginal bone and were parallel with the abutment surface. All gingival and periimplant units examined were free from infiltrates of inflammatory cells. It was suggested that under the conditions of study, both types of soft tissues, gingiva and periimplant mucosa, have a proper potential to prevent subgingival plaque formation.

Declining Amphibian Populations: The Problem of Separating Human Impacts from Natural Fluctuations

Abstract: Reports of declining amphibian populations in many parts of the world are numerous, but supporting long-term census data are generally unavailable. Census data from 1979 to 1990 for three salamander species and one frog species at a breeding pond in South Carolina showed fluctuations of substantial magnitude in both the size of breeding populations and in recruitment of juveniles. Breeding population sizes exhibited no overall trend in three species and increased in the fourth. Recent droughts account satisfactorily for an increase in recruitment failures. These data illustrate that to distinguish between natural population fluctuations and declines with anthropogenic causes may require long-term studies.

Alpha B-crystallin is a small heat shock protein.

Abstract: Sequence similarity between alpha B-crystallin and small heat shock proteins (HSPs) has prompted us to investigate whether alpha B-crystallin expression is induced by heat shock. Indeed, accumulation of alpha B-crystallin was detected immunologically in NIH 3T3 cells after incubation at elevated temperatures and after addition of Cd2+ or sodium arsenite to these cells. Two-dimensional gel electrophoresis revealed identity between alpha B-crystallin from eye lenses and from heat-treated fibroblasts. The promoter of the alpha B-crystallin gene was fused to the bacterial chloramphenicol acetyltransferase gene and was shown to confer heat inducibility on this reporter gene in transient transfection assays. A perfect heat shock element within the promoter region is likely to mediate this response. Small HSPs and alpha B-crystallin were shown to share the following two physical properties: (i) they form supramolecular structures with sedimentation values around 17 S and (ii) they are associated with the nucleus at high temperatures and are localized in the cytoplasm under normal conditions. We conclude that alpha B-crystallin has to be considered a member of the class of small HSPs.

Functional expression cloning and characterization of the hepatocyte Na+/bile acid cotransport system.

Abstract: Liver parenchymal cells continuously extract high amounts of bile acids from portal blood plasma. This uptake process is mediated by a Na+/bile acid cotransport system. A cDNA encoding the rat liver bile acid uptake system has been isolated by expression cloning in Xenopus laevis oocytes. The cloned transporter is strictly sodium-dependent and can be inhibited by various non-bile-acid organic compounds. Sequence analysis of the cDNA revealed an open reading frame of 1086 nucleotides coding for a protein of 362 amino acids (calculated molecular mass 39 kDa) with five possible N-linked glycosylation sites and seven putative transmembrane domains. Translation experiments in vitro and in oocytes indicate that the transporter is indeed glycosylated and that its polypeptide backbone has an apparent molecular mass of 33-35 kDa. Northern blot analysis with the cloned probe revealed crossreactivity with mRNA species from rat kidney and intestine as well as from liver tissues of mouse, guinea pig, rabbit, and man.

Sleep deprivation in rats: effects on EEG power spectra, vigilance states, and cortical temperature.

Abstract: Vigilance states, electroencephalogram (EEG) power spectra (0.25-25.0 Hz), and cortical temperature (TCRT) of 10 rats were obtained during a baseline day, a 24-h sleep deprivation (SD) period, and 2 days of recovery (recoveries 1 and 2). EEG power density in waking gradually increased in most frequencies during the SD period. Non-rapid-eye-movement (NREM) sleep was enhanced on both recovery days, and rapid-eye-movement sleep was enhanced only on recovery 1. In the initial 4 h of recovery 1, EEG slow-wave activity (SWA; mean power density 0.75-4.0 Hz) in NREM sleep was elevated relative to baseline, and the number of brief awakenings (nBA) was reduced. In the dark period of recovery 1 and the light period of recovery 2, SWA was below baseline, and nBA was increased. During the entire recovery period, SWA and nBA, both expressed as deviation from baseline values, were negatively correlated. During the SD period, TCRT was above baseline, and in the initial 16 h of recovery 1 it was below baseline. Whereas TCRT was negatively correlated with NREM sleep, no significant correlation was found between TCRT and SWA within NREM sleep. It is concluded that SD causes a short-lasting intensification of sleep, as indicated by the enhanced SWA and the reduced nBA, and a long-lasting increase in sleep duration. The different time courses of SWA and TCRT suggest that variations in NREM sleep intensity are not directly related to changes in TCRT.

The Effects of Leopard Predation On Grouping Patterns in Forest Chimpanzees

Abstract: [During a 5-year period, 29 interactions between chimpanzees and leopards have been observed or inferred in the tropical rainforest of the Tai National Park, Cote d'Ivoire. Chimpanzees chased away leopards in 9 cases, rescued alarm calling chimpanzees in 11 cases (in 4 of these footprints or growls of leopards were noted), 9 times leopards attacked chimpanzees, injuring 6 of them and killing 4. Two of the latters were most certainly eaten by the leopard later. Predation by leopards is estimated to be the first cause of mortality in the Tai chimpanzees and individual chimpanzees may experience a risk of predatory attack of 0.30 per year and a mortality risk of 0.055 per year. Tai chimpanzees adapt specifically their grouping patterns to food availability and to predation: with abundant food and low predation, party size increases and mixed parties are more frequent, whereas with the same food condition but with high predation, party size decreased and all-male party types increase. Comparisons with data on grouping patterns from Gombe and Mahale chimpanzees living in more open habitats support the hypothesis that this species adapts itself to leopard predation which is known to be lower in savanna habitats. The grouping patterns of the bonobo in Lomako forest seem more similar to Tai than to Gombe or Mahale chimpanzees, suggesting an analogous adaptation to high predation pressure., During a 5-year period, 29 interactions between chimpanzees and leopards have been observed or inferred in the tropical rainforest of the Tai National Park, Cote d'Ivoire. Chimpanzees chased away leopards in 9 cases, rescued alarm calling chimpanzees in 11 cases (in 4 of these footprints or growls of leopards were noted), 9 times leopards attacked chimpanzees, injuring 6 of them and killing 4. Two of the latters were most certainly eaten by the leopard later. Predation by leopards is estimated to be the first cause of mortality in the Tai chimpanzees and individual chimpanzees may experience a risk of predatory attack of 0.30 per year and a mortality risk of 0.055 per year. Tai chimpanzees adapt specifically their grouping patterns to food availability and to predation: with abundant food and low predation, party size increases and mixed parties are more frequent, whereas with the same food condition but with high predation, party size decreased and all-male party types increase. Comparisons with data on grouping patterns from Gombe and Mahale chimpanzees living in more open habitats support the hypothesis that this species adapts itself to leopard predation which is known to be lower in savanna habitats. The grouping patterns of the bonobo in Lomako forest seem more similar to Tai than to Gombe or Mahale chimpanzees, suggesting an analogous adaptation to high predation pressure.]

Range perception through apparent image speed in freely flying honeybees.

Abstract: When negotiating a narrow gap, honeybees tend to fly through the middle of the gap, balancing the distances to the boundary on either side. To investigate the basis of this “centering response,” bees were trained to fly through a tunnel on their way to a feeding site and back, while their flight trajectories were filmed from above. The wall on either side carried a visual pattern. When the patterns were stationary vertical gratings, bees tended to fly through the middle of the tunnel, i.e. along its longitudinal axis. However, when one of the gratings was in motion, bees flying in the same direction as the moving grating tended to fly closer to while bees flying in the opposite direction tended to fly closer to the stationary grating. This demonstrates, directly and unequivocally, that flying bees estimate the distances of surfaces in terms of the apparent motion of their images. A series of further experiments revealed that the distance to the gratings is gauged in terms of their apparent angular speeds, and that the visual system of the bee is capable of measuring angular speed largely independently of the spatial period, intensity profile, or contrast of the grating. Thus, the motion-sensitive mechanisms mediating range perception appear to be qualitatively different from those that mediate the well-known optomotor response in insects, or those involved in motion detection and ocular tracking in man.

HIV-associated disease of the nervous system: review of nomenclature and proposal for neuropathology-based terminology.

Abstract: Herbert Budka 1, Clayton A. Wiley 2, Paul Kleihues 3, Juan Artigas 4, Arthur K. Asbury 5, Eun-Sook Cho 6, David R. Cornblath 7, Mauro C. Dal Canto 8, Umberto DeGirolami 9, Dennis Dickson 10, Leon G. Epstein 11, Margaret M. Esiri 12, Felice Giangaspero 13, Georg Gosztonyi 14, Francoise Gray 15, John W. Griffin 7, Dominique Henin 16, Yuzo lwasaki 17, Robert S. Janssen '8, Richard T. Johnson 7, Peter L. Lantos 19, William D. Lyman 10, Justin C. McArthur 7, Kazuo Nagashima 20, Nancy Peress 21, Carol K. Petito 22, Richard W. Price 23, Roy H. Rhodes Z4, Marc Rosenblum 25, Gerard Said 26, Francesco Scaravilli 27, Leroy R. Sharer 6, Harry V. Vinters 28

A 'unified theory' of prion propagation.

Abstract: There is now very persuasive evidence that the transmissible agent for spongiform encephalopathies such as scrapie, consists of a modified form of the normal host protein PrPc, devoid of any nucleic acid. On the other hand, because there are many different strains of scrapie agent with distinct phenotypes which can be propagated in animals homozygous for the PrPc gene, it has been suggested that a nucleic acid must be a component of the agent. Can the two views be reconciled?

Neurite outgrowth on immobilized axonin-1 is mediated by a heterophilic interaction with L1(G4).

Abstract: Axonin-1 is an axon-associated cell adhesion molecule with dualistic expression, one form being glycophosphatidylinositol-anchored to the axonal membrane, the other secreted from axons in a soluble form. When presented as a substratum for neuronal cultures it strongly promotes neurite outgrowth from chicken embryonic dorsal root ganglia neurons. In this study, the axon-associated cell adhesion molecule G4, which is identical with Ng-CAM and 8D9, and homologous or closely related to L1 of the mouse and NILE of the rat, was investigated with respect to a receptor function for axonin-1. Using fluorescent microspheres with covalently coupled axonin-1 or L1(G4) at their surface we showed that these proteins bind to each other. Within the sensitivity of this microsphere assay, no interaction of axonin-1 with itself could be detected. Axonin-1-coated microspheres also bound to the neurites of cultured dorsal root ganglia neurons. This interaction was exclusively mediated by L1(G4), as indicated by complete binding suppression by monovalent anti-L1(G4) antibodies. The interaction between neuritic L1(G4) and immobilized axonin-1 was found to mediate the promotion of neurite growth on axonin-1, as evidenced by the virtually complete arrest of neurite outgrowth in the presence of anti-L1(G4) antibodies. Convincing evidence has recently been presented that neurite growth on L1(8D9) is mediated by the homophilic binding of neuritic L1(G4) (1989. Neuron. 2: 1597-1603). Thus, both L1(G4)- and axonin-1-expressing axons may serve as "substrate pathways" for the guidance of following axons expressing L1(G4) into their target area. Conceivably, differences in the concentration of axonin-1 and L1(G4), and/or modulatory influences on their specific binding parameters in leading pathways and following axons could represent elements in the control of axonal pathway selection.

A central role of perforin in cytolysis

Abstract: Studies on the gene structure, on the transcript, and on perforin protein are reviewed, including intracellular trafficking. Perforin transcription is tightly regulated and specific for CTL and NK. Two independent pathways for perforin induction exist, only one of them being IL-2 independent. Perforin expression in vitro and in vivo correlates with the functional expression of cytotoxicity in viral infection, transplant and tumor rejection, and in autoimmunity. Perforin together with granzymes is localized in cytolytic granules. However, the trafficking of those two proteins is quite different. Since the properties of perforin containing granules encompass the characteristics of secretory granules and of lyzosomes, the term granulosomes is used to describe this unique organelle. Evidence is reviewed to refute the concept that the homologous restriction factors of complement also restrict the lysis of homologous cells by perforin.

Lower receptor avidity required for thymic clonal deletion than for effector T-cell function.

Abstract: CLONAL deletion in the thymus plays a major part in T-cell tolerance to self antigens1–3. But the mechanism of negative selection, its fine specificity and the threshold of affinity and avidity remains unknown. We have now examined these aspects of negative selection with mice expressing a transgenic T-cell receptor with specificity for lymphocytic choriomeningitis virus (LCMV) glycoprotein in association with the class I H–2Db molecule. These mice were rendered tolerant to LCMV by neonatal infection with mutant LCMVs hearing point mutations in the T-cell epitope recognized by the transgenic T-cell receptor (ref. 4). Variant LCMVs were also tested for their ability to elicit antiviral responses in transgenic mice in vivo and in vitro. Comparison in vivo revealed that a low-avidity receptor interaction, which was unable to induce effector T cells in the periphery, was still sufficient for clonal deletion in the thymus.

Clonal deletion of V beta 14-bearing T cells in mice transgenic for mammary tumour virus.

Abstract: Autoreactive T lymphocytes are clonally deleted during maturation in the thymus. Deletion of T cells expressing particular receptor V beta elements is controlled by poorly defined autosomal dominant genes. A gene has now been identified by expression of transgenes in mice which causes deletion of V beta 14+ T cells. The gene lies in the open reading frame of the long terminal repeat of the mouse mammary tumour virus.

Molecular, cytogenetic, and clinical investigations of Prader-Willi syndrome patients.

Abstract: Thirty-seven patients presenting features of the Prader-Willi syndrome (PWS) have been examined using cytogenetic and molecular techniques. Clinical evaluation showed that 29 of these patients fulfilled diagnostic criteria for PWS. A deletion of the 15q11.2-q12 region could be identified molecularly in 21 of these cases, including several cases where the cytogenetics results were inconclusive. One clinically typical patient is deleted at only two of five loci normally included in a PWS deletion. A patient carrying a de novo 13;X translocation was not deleted for the molecular markers tested but was clinically considered to be "atypical" PWS. In addition, five cases of maternal heterodisomy and two of isodisomy for 15q11-q13 were observed. All of the eight patients who did not fulfill clinical diagnosis of PWS showed normal maternal and paternal inheritance of chromosome 15 markers; however, one of these carried a ring-15 chromosome. A comparison of clinical features between deletion patients and disomy patients shows no significant differences between the two groups. The parental ages at birth of disomic patients were significantly higher than those for deletion patients. As all typical PWS cases showed either a deletion or disomy of 15q11.2-q12, molecular examination should provide a reliable diagnostic tool. As the disomy patients do not show either any additional or more severe features than typical deletion patients do, it is likely that there is only one imprinted region on chromosome 15 (within 15q11.2-q12).

Cloning and expression of cDNA for a Na/Pi cotransport system of kidney cortex.

Abstract: A cDNA library from rabbit kidney cortex was screened for expression of Na-dependent transport of phosphate (Pi) using Xenopus laevis oocytes as an expression system. A single clone was eventually isolated (designated NaPi-1) that stimulated expression of Na/Pi cotransport approximately 700-fold compared to total mRNA. The predicted sequence of the Na/Pi cotransporter consists of 465 amino acids (relative molecular mass, 51,797); hydropathy profile predictions suggest six (possibly eight) membrane-spanning segments. In vitro translation of NaPi-1/complementary RNA in the presence of pancreatic microsomes indicated NaPi-1 to be a glycosylated protein; four potential N-glycosylation sites are present in the amino acid sequence. Northern blot analysis demonstrated the presence of NaPi-1/mRNA in kidney cortex and liver; no hybridization signal was obtained with mRNA from other tissues (including small intestine). Kinetic analysis of Na/Pi cotransport expressed by NaPi-1/complementary RNA demonstrated characteristics (sodium interaction) similar to those observed in cortical apical membranes. The alignment of 5 amino acid residues (Gly342/Ala381-Xaa-Xaa-Xaa-Xaa-Leu386-Xaa-Xaa-Xaa-P ro390- Arg391) is consistent with a motif proposed for Na-dependent transport systems. We conclude that we have cloned a cDNA for a Na/Pi cotransport system present in rabbit kidney cortex.

Contrasting properties of monkey somatosensory and motor cortex neurons activated during the control of force in precision grip

Abstract: 1. Single cell activity was investigated in the precentral motor (MI) and postcentral somatosensory (SI) cortex of the monkey to compare the neuronal activity related to the control of isometric force in the precision grip and to assess the participation of SI in motor control. 2. Three monkeys (Macaca fascicularis) were trained in a visual step-tracking paradigm to generate and precisely maintain force on a transducer held between thumb and index finger. Great care was taken to have the monkeys use only their fingers without moving the wrist or proximal joints. In two monkeys electromyographic (EMG) activity was checked in 23 muscles over several sessions. 3. Five similar classes of task-related firing patterns were found in both SI and MI cortical hand and finger representations, but their relative proportions differed. The majority of the SI neurons were phasically or phasic-tonically active (61%), whereas in MI the neurons that decreased their firing rate with force were most frequent (42%). 4. The timing of activity changes related to the onset of force increase from low to higher levels strongly differed in the two neuronal populations. In SI, only 14% of the task-related neurons increased or decreased their firing rate before the onset of force increase, in contrast to 56% in MI. Only 3% of the SI neurons showed changes before the earliest EMG activation. 5. In both SI and MI neurons with tonic and phasic-tonic, increasing or decreasing discharge patterns disclosed a relationship between neuronal activity and static force. Distinction was made between neurons modulating their activity in a monotonic way and those that were active only at one force level and had a kind of recruitment or deactivation threshold. The latter ones were more frequent in MI than in SI, and in the neuron population with decreasing firing patterns. For the neurons with increases in activity, statistically significant linear correlations between firing rate and force were found more frequently in MI than in SI, where the proportion of nonsignificant correlations was relatively high (35% vs. 15% in MI). In SI the indexes of force sensitivity, calculated from the slopes of the regression lines, covered a wider range than in MI; and their distribution was bimodal, with one mean of 30 Hz/N and the other of 155 Hz/N. In contrast, the mean rate-force slope in MI was 69 Hz/N.(ABSTRACT TRUNCATED AT 400 WORDS)