Showing papers by "University of Konstanz published in 2000"

Guidelines for using human event-related potentials to study cognition: Recording standards and publication criteria

Abstract: Event-related potentials ~ERPs! recorded from the human scalp can provide important information about how the human brain normally processes information and about how this processing may go awry in neurological or psychiatric disorders. Scientists using or studying ERPs must strive to overcome the many technical problems that can occur in the recording and analysis of these potentials. The methods and the results of these ERP studies must be published in a way that allows other scientists to understand exactly what was done so that they can, if necessary, replicate the experiments. The data must then be analyzed and presented in a way that allows different studies to be compared readily. This paper presents guidelines for recording ERPs and criteria for publishing the results.

Are People Conditionally Cooperative? Evidence from a Public Goods Experiment

Abstract: We study the importance of conditional cooperation in a one-shot public goods game by using a variant of the strategy-method. We find that a third of the subjects can be classified as free riders, whereas 50 percent are conditional cooperators.

Myosin isoforms, muscle fiber types, and transitions.

Abstract: Skeletal muscle is an extremely heterogeneous tissue composed of a variety of fast and slow fiber types and subtypes. Moreover, muscle fibers are versatile entities capable of adjusting their phenotypic properties in response to altered functional demands. Major differences between muscle fiber types relate to their myosin complement, i.e., isoforms of myosin light and heavy chains. Myosin heavy chain (MHC) isoforms appear to represent the most appropriate markers for fiber type delineation. On this basis, pure fiber types are characterized by the expression of a single MHC isoform, whereas hybrid fiber type express two or more MHC isoforms. Hybrid fibers bridge the gap between the pure fiber types. The fiber population of skeletal muscles, thus, encompasses a continuum of pure and hybrid fiber types. Under certain conditions, changes can be induced in MHC isoform expression heading in the direction of either fast-to-slow or slow-to-fast. Increased neuromuscular activity, mechanical loading, and hypothyroidism are conditions that induce fast-to-slow transitions, whereas reduced neuromuscular activity, mechanical unloading, and hyperthyroidism cause transitions in the slow-to-fast direction.

Cellular compartmentation of cadmium and zinc in relation to other elements in the hyperaccumulator Arabidopsis halleri.

Abstract: The cellular compartmentation of elements was analysed in the Zn hyperaccumulator Arabidopsis halleri (L.) O'Kane & Al-Shehbaz (=Cardaminopsis halleri) using energy-dispersive X-ray microanalysis of frozen-hydrated tissues. Quantitative data were obtained using oxygen as an internal standard in the analyses of vacuoles, whereas a peak/background ratio method was used for quantification of elements in pollen and dehydrated trichomes. Arabidopsis halleri was found to hyperaccumulate not only Zn but also Cd in the shoot biomass. While large concentrations of Zn and Cd were found in the leaves and roots, flowers contained very little. In roots grown hydroponically, Zn and Cd accumulated in the cell wall of the rhizodermis (root epidermis), mainly due to precipitation of Zn/Cd phosphates. In leaves, the trichomes had by far the largest concentrations of Zn and Cd. Inside the trichomes there was a striking sub-cellular compartmentation, with almost all the Zn and Cd being accumulated in a narrow ring in the trichome base. This distribution pattern was very different from that for Ca and P. The epidermal cells other than trichomes were very small and contained lower concentrations of Zn and Cd than mesophyll cells. In particular, the concentrations of Cd and Zn in the mesophyll cells increased markedly in response to increasing Zn and Cd concentrations in the nutrient solution. This indicates that the mesophyll cells in the leaves of A. halleri are the major storage site for Zn and Cd, and play an important role in their hyperaccumulation.

Enhanced peroxynitrite formation is associated with vascular aging.

Abstract: Vascular aging is mainly characterized by endothelial dysfunction. We found decreased free nitric oxide (NO) levels in aged rat aortas, in conjunction with a sevenfold higher expression and activity of endothelial NO synthase (eNOS). This is shown to be a consequence of age-associated enhanced superoxide (·O2−) production with concomitant quenching of NO by the formation of peroxynitrite leading to nitrotyrosilation of mitochondrial manganese superoxide dismutase (MnSOD), a molecular footprint of increased peroxynitrite levels, which also increased with age. Thus, vascular aging appears to be initiated by augmented ·O2− release, trapping of vasorelaxant NO, and subsequent peroxynitrite formation, followed by the nitration and inhibition of MnSOD. Increased eNOS expression and activity is a compensatory, but eventually futile, mechanism to counter regulate the loss of NO. The ultrastructural distribution of 3-nitrotyrosyl suggests that mitochondrial dysfunction plays a major role in the vascular aging process.

Two-point microrheology of inhomogeneous soft materials.

Abstract: Many interesting and important materials such as polymers, gels, and biomaterials are viscoelastic; when responding to an external stress, they both store and dissipate energy. This behavior is quantified by the complex shear modulus, Gv, which provides insight into the material’s microscopic dynamics. Typically, Gv is measured by applying oscillatory strain to a sample and measuring the resulting stress. Recently a new method, called microrheology, has been developed which determines Gv from the thermal motion of microscopic tracer particles embedded in the material [1,2]. Microrheology offers significant potential advantages: it provides a local probe of Gv in miniscule sample volumes and can do so at very high frequencies. While microrheology provides an accurate measure of Gv for simple systems, its validity in common complex systems is far from certain. If the tracers locally modify the structure of the medium, or sample only pores in an inhomogeneous matrix, then bulk rheological properties will not be determined. Such subtle effects currently limit many interesting applications of microrheology. In this Letter, we introduce a new formalism, which we term “two-point microrheology,” based on measuring the cross-correlated thermal motion of pairs of tracer particles to determine Gv. This new technique overcomes the limitations of single-particle microrheology. It does not depend on the size or shape of the tracer particle; moreover it is independent of the coupling between the tracer and the medium. We demonstrate the validity of this approach with measurements on a highly inhomogeneous material, a solution of the polysaccharide guar. Two-point microrheology correctly reproduces results obtained with a mechanical rheometer, whereas single-particle microrheology gives erroneous results. We also compare ordinary and two-point microrheology of F-actin [2–4], a semiflexible biopolymer constituent of the cytoskeleton. Different results are obtained with the two techniques, suggesting that earlier interpretations of F-actin microrheology should be reexamined.

Onset of antiferromagnetism in heavy-fermion metals

Abstract: There are two main theoretical descriptions of antiferromagnets. The first arises from atomic physics, which predicts that atoms with unpaired electrons develop magnetic moments. In a solid, the coupling between moments on nearby ions then yields antiferromagnetic order at low temperatures1. The second description, based on the physics of electron fluids or ‘Fermi liquids’, states that Coulomb interactions can drive the fluid to adopt a more stable configuration by developing a spin density wave2,3. It is at present unknown which view is appropriate at a ‘quantum critical point’, where the antiferromagnetic transition temperature vanishes4,5,6,7. Here we report neutron scattering and bulk magnetometry measurements of the metal CeCu6-xAux, which allow us to discriminate between the two models. We find evidence for an atomically local contribution to the magnetic correlations which develops at the critical gold concentration (xc = 0.1 ), corresponding to a magnetic ordering temperature of zero. This contribution implies that a Fermi-liquid-destroying spin-localizing transition, unanticipated from the spin density wave description, coincides with the antiferromagnetic quantum critical point.

Statistical control of artifacts in dense array EEG/MEG studies

Abstract: With the advent of dense sensor arrays (64-256 channels) in electroencephalography and magnetoencephalography studies, the probability increases that some recording channels are contaminated by artifact. If all channels are required to be artifact free, the number of acceptable trials may be unacceptably low. Precise artifact screening is necessary for accurate spatial mapping, for current density measures, for source analysis, and for accurate temporal analysis based on single-trial methods. Precise screening presents a number of problems given the large datasets. We propose a procedure for statistical correction of artifacts in dense array studies (SCADS), which (1) detects individual channel artifacts using the recording reference, (2) detects global artifacts using the average reference, (3) replaces artifact-contaminated sensors with spherical interpolation statistically weighted on the basis of all sensors, and (4) computes the variance of the signal across trials to document the stability of the averaged waveform. Examples from 128-channel recordings and from numerical simulations illustrate the importance of careful artifact review in the avoidance of analysis errors.

Single-file diffusion of colloids in one-dimensional channels

Abstract: Single-file diffusion, prevalent in many processes, refers to the restricted motion of interacting particles in narrow micropores with the mutual passage excluded. A single-filing system was developed by confining colloidal spheres in one-dimensional circular channels of micrometer scale. Optical video microscopy study shows evidence that the particle self-diffusion is non-Fickian for long periods of time. In particular, the distribution of particle displacement is a Gaussian function.

Cyanobacterial toxins: removal during drinking water treatment, and human risk assessment.

Abstract: Cyanobacteria (blue-green algae) produce toxins that may present a hazard for drinking water safety. These toxins (microcystins, nodularins, saxitoxins, anatoxin-a, anatoxin-a(s), cylindrospermopsin) are structurally diverse and their effects range from liver damage, including liver cancer, to neurotoxicity. The occurrence of cyanobacteria and their toxins in water bodies used for the production of drinking water poses a technical challenge for water utility managers. With respect to their removal in water treatment procedures, of the more than 60 microcystin congeners, microcystin-LR (L, L-leucine; R, L-arginine) is the best studied cyanobacterial toxin, whereas information for the other toxins is largely lacking. In response to the growing concern about nonlethal acute and chronic effects of microcystins, the World Health Organization has recently set a new provisional guideline value for microcystin-LR of 1.0 microg/L drinking water. This will lead to further efforts by water suppliers to develop effective treatment procedures to remove these toxins. Of the water treatment procedures discussed in this review, chlorination, possibly micro-/ultrafiltration, but especially ozonation are the most effective in destroying cyanobacteria and in removing microcystins. However, these treatments may not be sufficient during bloom situations or when a high organic load is present, and toxin levels should therefore be monitored during the water treatment process. In order to perform an adequate human risk assessment of microcystin exposure via drinking water, the issue of water treatment byproducts will have to be addressed in the future.

Does the Governed Corporation Perform Better? Governance Structures and Corporate Performance in Germany

Abstract: Although there has been an intensive debate on the relative merits of different sys- tems of corporate governance, empirical evidence on the link between corporate governance and firm performance almost exclusively refers to the market-oriented Anglo-Saxon system. This paper therefore investigates the more network- or bank-oriented German system. In panel regressions for 361 German corporations over the time period 1991 to 1996, we find ownership concentration to affect profitability significantly negatively. However, this effect depends intricately on stock market exposure, the location of control rights, and the time horizon (short-run vs. long-run). We conclude from our results that (1) the presence of large shareholders does not necessarily enhance profitability, (2) ownership concentration seems to be sub-optimal for many German corporations, and, finally, (3) having financial institutions as largest shareholders of traded corporations improves corporate performance.

Life at the oxic-anoxic interface: microbial activities and adaptations.

Abstract: Molecular oxygen is one of the most important reactants in biogeochemical cycles. Due to its low solubility in water, the consumption of oxygen leads to the development of oxic–anoxic interfaces, which separate aerobic from anaerobic processes in virtually all environments, ranging in scale from oceanic sediments to the fecal pellets of a small soil invertebrate. Three case studies were selected to illustrate the basic situation and the specific characteristics of oxic–anoxic interfaces: sediments, the rhizosphere of aquatic plants, and the intestinal tract of insects. Each system is governed by the same general principles, but striking differences arise from, e.g., the nature of the major microbial activities and the mechanisms controlling metabolite fluxes. Also scale and dimensional differences as well as the consequences of temporal fluctuations are of fundamental importance. Recent developments in microbial ecology, which often combine traditional and modern approaches, have significantly furthered our understanding of the specific microniches and the metabolic and behavioral adaptations of microorganisms to life at the oxic–anoxic interface. New concepts help to define the targets of future studies: the spatial organization of microbial populations, their microenvironments and in situ activities, and the functional interactions within structured microbial communities.

Medial Frontal Cortex in Action Monitoring

Abstract: Effective behavior requires continuous action monitoring. Electrophysiological studies in both monkeys and humans have shown activity in the medial frontal cortex that reflects dynamic control and monitoring of behavioral acts. In humans, the centromedial frontal cortex shows an electrical response within 100 msec of an error, the error-related negativity (ERN). The ERN occurs only when subjects are aware of making an error, suggesting that a critical factor may be self-monitoring of the action process. In the present study, we examined late responses in a deadline reaction time task, in which the subject becomes increasingly aware of making an error as the response becomes increasingly late. We found evidence of response conflict before errors defined by late responses but not before errors defined by incorrect responses. The results also show a linear increase in the amplitude of the ERN with increasingly late responses. These data suggest that frontal networks provide dynamic representations that monitor and evaluate the unfolding action plan.

Does economics make citizens corrupt

Abstract: In this paper, we report on an experiment on corruption which investigates various determinants of corruptibility. We found that economics students are significantly more corrupt than others, which is due to self-selection rather than indoctrination. Moreover, our results vary with gender — male students of economics are most corrupt, male non-economists the least. Also, agents are no less corrupt if rewarded in addition to, and independently of a possible bribe. Our experiment isolates the influence of self-interest on cooperation from other influences such as risk attitude and expectations regarding the behavior of others.

Fragmentation of Landscape as a Cause for Genetic Subdivision in Bank Voles

Abstract: We studied the barrier effects of various roadways on the genetic subdivision of bank vole (Clethrionomys glareolus) populations. Allele frequencies, genetic variability, and genetic distances of natural populations were calculated based on polymorphism of seven microsatellite markers. We compared bank vole populations in control areas without such barriers with animals from both sides of a country road, a railway, and a highway. Using F and R statistics, we demonstrated significant population subdivision in bank vole populations separated by the highway, but not in populations on either side of the other roadways or in the control area. Correlations between geographic and genetic distances were revealed by an extended method based on a Mantel analysis. This allowed us to measure genetic barrier effects and express them as additional geographic distances. For instance, statistically significant differences in allele frequencies in all seven loci examined existed among populations in southern Germany and Switzerland, which are separated by the Rhine River and Lake Constance. The real geographic distance between bank vole populations in Konstanz and those in Lengwil, Switzerland, was 6 km. According to this analysis the genetic barrier effect of the Rhine could be defined as an additional distance of 7.7 km. This study shows for the first time that not only old geographic barriers but also more recent fragmentation of landscape by, for example, highways has an important effect on gene flow and the genetic substructuring of populations, which should be considered in future environmental impact assessments. Resumen: En este trabajo estudiamos los efectos de barrera de varias vias de comunicacion terrestre en la subdivision genetica en poblaciones de ratones de campo ( Clethrionomys glareolus). Las frecuencias de alelos, la variabilidad genetica y las distancias geneticas de poblaciones naturales fueron calculadas en base a polimorfismos de siete marcadores microsatelite. Comparamos las poblaciones de ratones de campo en areas de control sin las barreras mencionadas contra animales de ambos lados de una carretera rural, una via de ferrocarril y una autopista. Mediante el uso de estadisticas F y R, demostramos una subdivision poblacional significativa en poblaciones de ratones separados por la autopista, pero no entre poblaciones en ambos lados de las otras vias de comunicacion o en el area control. Un metodo extendido basado en un analisis Mantel revelo correlaciones entre las distancias geograficas y las distancias geneticas. Esto nos permitio medir los efectos de barreras geneticas y expresarlos como distancias geograficas adicionales. Por ejemplo, las diferencias estadisticamente significativas en las frecuencias de alelos en los siete locus examinados existieron en poblaciones al sur de Alemania y Suiza, las cuales estan separadas por el rio Rin y el lago Constance. La distancia geografica real entre las poblaciones de ratones en Constanz y aquellas en Lenwil, Suiza fue de 6 km. De acuerdo con este analisis el efecto de la barrera genetica del rio Rin podria ser definida como una distancia adicional de 7.7 km. Este estudio muestra por primera vez que no solo las barreras geograficas de antano sino tambien la fragmentacion mas reciente del paisaje como la ocasionada por autopistas, por ejemplo, tienen un efecto importante en el flujo de genes y la subestructuracion de poblaciones. Esto debe ser considerado en evaluaciones futuras de impacto ambiental.

Crystal structure of MalK, the ATPase subunit of the trehalose/maltose ABC transporter of the archaeon Thermococcus litoralis

Abstract: The members of the ABC transporter family transport a wide variety of molecules into or out of cells and cellular compartments. Apart from a translocation pore, each member possesses two similar nucleoside triphosphate-binding subunits or domains in order to couple the energy-providing reaction with transport. In the maltose transporter of several Gram-negative bacteria and the archaeon Thermo coccus litoralis, the nucleoside triphosphate-binding subunit contains a C-terminal regulatory domain. A dimer of the subunit is attached cytoplasmically to the translocation pore. Here we report the crystal structure of this dimer showing two bound pyrophosphate molecules at 1.9 A resolution. The dimer forms by association of the ATPase domains, with the two regulatory domains attached at opposite poles. Significant deviation from 2-fold symmetry is seen at the interface of the dimer and in the regions corresponding to those residues known to be in contact with the translocation pore. The structure and its relationship to function are discussed in the light of known mutations from the homologous Escherichia coli and Salmonella typhimurium proteins.

Optical microscopy using a single-molecule light source

Abstract: Rapid progress in science on nanoscopic scales has promoted increasing interest in techniques of ultrahigh-resolution optical microscopy. The diffraction limit can be surpassed by illuminating an object in the near field through a sub-wavelength aperture at the end of a sharp metallic probe1,2. Proposed modifications3,4 of this technique involve replacing the physical aperture by a nanoscopic active light source. Advances in the spatial5 and spectral6 detection of individual fluorescent molecules, using near-field and far-field methods7, suggest the possibility of using a single molecule8,9 as the illumination source. Here we present optical images taken with a single molecule as a point-like source of illumination, by combining fluorescence excitation spectroscopy10 with shear-force microscopy11. Our single-molecule probe has potential for achieving molecular resolution in optical microscopy; it should also facilitate controlled studies of nanometre-scale phenomena (such as resonant energy transfer) with improved lateral and axial spatial resolution.

Same Menu, Seperate Tables: The Institutionalist Turn in Political Science and the Study of European Integration

Abstract: Recent research on European integrationhas largely profited from the institutionalist turn inpolitical science. Theoretical progress has, however,been hampered by the diverse understandings of thisnew research tradition. This paper tries to tackle theconceptual diversity in a positive way. We firstanalyze the neo-institutionalist turn in politicalscience and European studies and then move on to adetailed analysis and comparison of the threecompeting approaches – sociological, historical, andrational choice institutionalism. Next, we will showthat the main differences are as much epistemologicalas theoretical. A convergence towards a unifyinginstitutionalist approach can thus only be possible ifsome sort of a methodological convergence takes place.We sketch how a synthesis between the competingschools might appear. `In my country there is a belief ...that the onlything separating us from the animals is mindlesssuperstitions and pointless rituals'. Quoted from Latka, `Taxi', in Tad Tuleja CuriousCustoms (New York: Harmony Books), p. xii. `Love and War are the same thing, and strategems andpolicy are as allowable in one as in the other'. Miguel de Cervantes, Don Quixote (reprint, NewYork: Modern Library, 1955, p. 580, quoted in Tim O'Brien1995. In the Lake of Woods. New York: Penguin, p. 193.)

Dynamic Criteria for Melting in Two Dimensions

Abstract: The two-dimensional (2D) melting transition is analyzed on the basis of the long-time behavior of a modified Lindemann parameter in 2D gamma(L)(t) and the bond-angular correlation function g(6)(t) Using video microscopy complete positional data are obtained over five decades in time for an ensemble of superparamagnetic colloidal particles confined to an air-water interface We find that each of the three phases (solid/hexatic/isotropic liquid) is uniquely characterized by the long-time behavior of gamma(L)(t), g(6)(t), and the non-Gaussian parameter of the relative neighbor-neighbor displacement

Bose-Einstein condensation with magnetic dipole-dipole forces

Abstract: Ground-state solutions in a dilute gas interacting via contact and magnetic dipole-dipole forces are investigated. To the best of our knowledge, it is the first example of studies of Bose-Einstein condensation in a system with realistic long-range interactions. We find that for the magnetic moment of, e.g., chromium $(6{\ensuremath{\mu}}_{B}),$ and a typical value of the scattering length, all solutions are stable and only differ in size from condensates without long-range interactions. By lowering the value of the scattering length we find a region of unstable solutions. In the neighborhood of this region, the ground-state wave functions show internal structures that we believe have not been seen before in condensates. Finally, we find an analytic estimate for the characteristic length appearing in these solutions.

The structure of L-amino acid oxidase reveals the substrate trajectory into an enantiomerically conserved active site

Abstract: The structure of l‐amino acid oxidase (LAAO) from Calloselasma rhodostoma has been determined to 2.0 A resolution in the presence of two ligands: citrate and o ‐aminobenzoate (AB). The protomer consists of three domains: an FAD‐binding domain, a substrate‐binding domain and a helical domain. The interface between the substrate‐binding and helical domains forms a 25 A long funnel, which provides access to the active site. Three AB molecules are visible within the funnel of the LAAO–AB complex; their orientations suggest the trajectory of the substrate to the active site. The innermost AB molecule makes hydrogen bond contacts with the active site residues, Arg90 and Gly464, and the aromatic portion of the ligand is situated in a hydrophobic pocket. These contacts are proposed to mimic those of the natural substrate. Comparison of LAAO with the structure of mammalian d‐amino acid oxidase reveals significant differences in their modes of substrate entry. Furthermore, a mirror‐symmetrical relationship between the two substrate‐binding sites is observed which facilitates enantiomeric selectivity while preserving a common arrangement of the atoms involved in catalysis.

Anaerobic naphthalene degradation by a sulfate-reducing enrichment culture.

Abstract: Anaerobic naphthalene degradation by a sulfate-reducing enrichment culture was studied by substrate utilization tests and identification of metabolites by gas chromatography-mass spectrometry. In substrate utilization tests, the culture was able to oxidize naphthalene, 2-methylnaphthalene, 1- and 2-naphthoic acids, phenylacetic acid, benzoic acid, cyclohexanecarboxylic acid, and cyclohex-1-ene-carboxylic acid with sulfate as the electron acceptor. Neither hydroxylated 1- or 2-naphthoic acid derivatives and 1- or 2-naphthol nor the monoaromatic compounds ortho-phthalic acid, 2-carboxy-1-phenylacetic acid, and salicylic acid were utilized by the culture within 100 days. 2-Naphthoic acid accumulated in all naphthalene-grown cultures. Reduced 2-naphthoic acid derivatives could be identified by comparison of mass spectra and coelution with commercial reference compounds such as 1,2,3,4-tetrahydro-2-naphthoic acid and chemically synthesized decahydro-2-naphthoic acid. 5,6,7,8-Tetrahydro-2-naphthoic acid and octahydro-2-naphthoic acid were tentatively identified by their mass spectra. The metabolites identified suggest a stepwise reduction of the aromatic ring system before ring cleavage. In degradation experiments with [1-13C]naphthalene or deuterated D8-naphthalene, all metabolites mentioned derived from the introduced labeled naphthalene. When a [13C]bicarbonate-buffered growth medium was used in conjunction with unlabeled naphthalene, 13C incorporation into the carboxylic group of 2-naphthoic acid was shown, indicating that activation of naphthalene by carboxylation was the initial degradation step. No ring fission products were identified.

Meteorological forcing of plankton dynamics in a large and deep continental European lake.

Abstract: The timing of various plankton successional events in Lake Constance was tightly coupled to a large- scale meteorological phenomenon, the North Atlantic Oscillation (NAO). A causal chain of meteorological, hydrological, and ecological processes connected the NAO as well as winter and early spring meteorological conditions to planktonic events in summer leading to a remarkable memory of climatic effects lasting over al- most half a year. The response of Daphnia to meteoro- logical forcing was most probably a direct effect of al- tered water temperatures on daphnid growth and was not mediated by changes in phytoplankton concentrations. High spring water temperatures during "high-NAO years" enabled high population growth rates, resulting in a high daphnid biomass as early as May. Hence, a critical Daphnia biomass to suppress phytoplankton was reached earlier in high-NAO years yielding an early and longer- lasting clear-water phase. Finally, an earlier summer de- cline of Daphnia produced in a negative relationship be- tween Daphnia biomass in July and the NAO. Meteoro- logical forcing of the seasonal plankton dynamics in Lake Constance included simple temporal shifts of pro- cesses and successional events, but also complex chang- es in the relative importance of different mechanisms. Since Daphnia plays an important role in plankton suc- cession, a thorough understanding of the regulation of its population dynamics provides the key for predictions of the response of freshwater planktonic food webs to glob- al climate change.

Kinetic parameters and intraindividual fluctuations of ochratoxin A plasma levels in humans

Abstract: The mycotoxin ochratoxin A (OTA) is a rodent carcinogen produced by species of the ubiquitous fungal genera Aspergillus and Penicillium. OTA is found in a variety of food items and as a consequence is also found in human plasma (average concentrations found in this study: 0.1–1 ng OTA/ml plasma). To improve the scientific basis for cancer risk assessment the toxicokinetic profile of OTA was studied in one human volunteer following ingestion of 395 ng 3H-labeled OTA (3.8 µCi). A two-compartment open model consisting of a central compartment was found to best describe the in vivo data. This two-compartment model consisted of a fast elimination and distribution phase (T1/2 about 20 h) followed by a slow elimination phase (renal clearance about 0.11 ml/min.) and a calculated plasma half-life of 35.55 days. This half-life was approximately eight times longer than that determined previously in rats. In addition, the intraindividual fluctuation of OTA plasma levels was investigated in eight individuals over a period of 2 months. The concentrations determined ranged between 0.2 and 0.9 ng OTA/ml plasma. The plasma levels in some individuals remained nearly constant over time, while others varied considerably (e.g. increase of 0.4 ng/ml within 3 days, decrease of 0.3 ng/ml within 5 days) during the observation period. This intraindividual fluctuation in OTA plasma levels, which may represent differences in OTA exposure and/or metabolism, as well as the large difference in plasma half-life in humans compared to rats must be taken into consideration when the results of rat cancer study data are extrapolated to humans for risk assessment purposes.

Origin of the antitropical distribution pattern in marine mussels (Mytilus spp.): routes and timing of transequatorial migration

Abstract: Many marine species, including mussels in the Mytilus edulis species group (i.e. M. edulis L., M. galloprovincialis Lamarck, and M. trossulus Gould), have an antitropical distribution pattern, with closely related taxa occurring in high latitudes of the northern and southern hemispheres but being absent from the tropics. We tested four hypotheses to explain the timing and route of transequatorial migration by species with antitropical distributions. These hypotheses yield different predictions for the phylogenetic relationship of southern hemisphere taxa relative to their northern counter-parts. The three Mytilus species were used to test these hypotheses since they exhibit a typical antitropical distribution and representative taxa occur in both the Pacific and Atlantic. Two types of mtDNA lineages were found among populations of mussels collected from the southern hemisphere between 1988 and 1996; over 90% of the mtDNA lineages formed a distinct subclade which, on average, had 1.4% divergence from haplotypes found exclusively in northern Atlantic populations of M. galloprovincialis. These data indicate that southern hemisphere mussels arose from a migration event from the northern hemisphere during the Pleistocene via an Atlantic route. The remainder of the southern hemisphere lineages (<10%) were very closely related to mtDNA haplotypes found in both M. edulis and M. galloprovincialis in the northern hemisphere, suggesting a second, more recent migration to the southern hemisphere. There was no evidence that southern hemisphere mussels arose from Pacific populations of mussels.