Development and Validation of Dose-Response Relationship for Listeria monocytogenes

Listeria monocytogenes is a foodborne pathogen internationally and in the U.S. The objective of this work was to develop and validate a dose-response model for infection by this organism. Only animal data was available in the literature. The beta-Poisson dose response model provided good fit to the data, and one of the two data sets was found to be concordant with attack rates noted in human outbreaks. There are differences, however, between the dose-response relationship and endemic illness rates computed from market basket surveys of the prevalence of L. monocytogenes. Further work to elucidate the bases for this difference is necessary.     

The relationships between the structure of paddy levees and the plant species diversity in cultural landscapes on the west side of Lake Biwa,Shiga, Japan

Paddy levees form networks of narrow linear habitats and play various roles in cultural landscapes. Traditional landscapes on the west side of Lake Biwa consist of paddy field terraces and both stone and soil levees that have been maintained by paddy field management using local resources. Paddy levees in this study site are principally classified into five different types. Our study points out how differences in paddy levee structure as well as in management practices influence the plant species. Seventeen paddy levee transects were split into four habitat types based on their species components by TWINSPAN. Spatial characteristics and physical structures of paddy levees depended on natural conditions and human activities. The species–area curves of each levee type showed a clear distinction: the soil, stone and abandoned curves were steep, while the concrete and consolidated ones were gentle. The vegetation on consolidated levees was utterly different from the vegetation on traditional levee types from the aspect of species richness and species components. Soil type levees contained various woody plant species and included more diverse and indigenous plant species than abandoned type levees.     

The establishment of frequency dependent limits for electric and magnetic fields and evaluation of indirect effects

Summary The biophysical model described in this paper has been used as basis for the preparation of the German standards which determine and define limits of exposure to electric or magnetic fields below several MHz, including 50/60 Hz. The electric field strength within the tissue is considered decisive for the biological effect in the low frequency range. Threshold values of field strengths and current densities including biological effects are compared. It is possible to establish safe, dangerous and hazardous current density curves as a function of frequency. To define exposure limits, the field strength or current density causing injury should be reduced by a factor exceeding 100 in order to avoid well established biological effects. The electric and magnetic field strengths in the human environment are correlated with the corresponding electric current density induced in the human body. This enables safe, dangerous and hazardous levels of current density in the human body to be correlated with the external electric or magnetic field strength. Additionally to the direct field effects indirect effects must be considered. In the second part of this paper data on touch voltages and currents are summarized and evaluated with regard to their health risk. Furthermore, as an example for indirect effects the interference of electric and magnetic fields with pacemakers is considered.Review article by invitation of the editor     

Vertical planktonic structure in the central basin of Lake Baikal in summer 1999, with special reference to the microbial food web

Planktonic microbial interactions in the central basin of Lake Baikal were examined on a summer day in 1999. The subsurface maxima of bacterial abundance and chlorophyll concentration were recorded at the same depth, whereas the vertical distribution of heterotrophic nanoflagellates was the inverse of those of bacteria and picophytoplankton. Release of extracellular organic car-bon (EOC) from phytoplankton was estimated by the NaH¹⁴CO₃ method as 2.4µgCl^–1day^–1. Bacterial production (4.3µgCl^–1day^–1), estimated in a bottle incubation experiment using size-fractionated water samples, exceeded the EOC released. Thus, other supplying sources of organic matter are needed for the bacterial production. Grazing (2.6µgCl^–1day^–1) was also estimated in the experiment and accounted for 60% of the bacterial production. This is the first report on the microbial food web in the central basin of Lake Baikal.     

The low-light reduction in the quantum yield of photosynthesis: potential errors and biases when calculating the maximum quantum yield

Photosynthesis-irradiance (P-E) curves are widely used to describe photosynthetic efficiency and potential. Contemporary models assume maximal photosynthetic quantum yield () at low irradiances. But P-E observations made with both oxygen evolution and carbon uptake techniques show that this is not always the case. Using new and published data in conjunction with modeling exercises, we demonstrate that regardless of the mechanism there can be reductions in at low irradiances that are not readily observable using conventional P-E analyses. We also show that analytical errors, such as inaccurate estimation of dark oxygen consumption or carbon uptake, can markedly affect the structure of -E curves with negligible effect on P-E curve structure. Whether from respiration `corrections' or other mechanisms, these deviations in at low light levels from the maximum quantum yield of photosynthesis (_max) can lead to significant errors (> 50%) in the estimation of the linear portion of the P-E curve and ultimately _max. Non-linear models of P-E, such as the rectangular hyperbola, quadratic, exponential and hyperbolic tangent that are commonly used to estimate the initial slope () of the P-E curve assume that is maximal at low light levels and therefore can err in the estimation of _max when is reduced at low light levels. Using a diverse data set of 622 P-E curves with a total of 7623 points, we show that although model skills are high (r ² = 0.96 ± 0.05, 0.97 ± 0.04, 0.97 ± 0.04 and 0.97 ± 0.04, respectively), a large fraction of the model-predicted _max differ by greater than 10% from true _max values (91%, 50%, 82% and 46%, respectively). Data from these observations and modeling exercises lead us to suggest that _max be determined by directly estimating the true maximum of a -E curve rather than using the more conventional methodology employing the initial slope of the P-E curve.This revised version was published online in October 2005 with corrections to the Cover Date.     

The detection and characterization of bacteria-sized protists in “Protist-free” filtrates and their potential impact on experimental marine ecology

Nuclepore filters of 0.6–1.0m pore size have been used to prepare protist-free water for a number of studies in microbial ecology. This procedure has been called into question by a recent study claiming that a significant portion of bacterial loss in filtrates could be due to uncharacterized predators passing through 0.6m filters. We were unable to directly observe protists in 0.6m filtrates using phase contrast, epifluorescence, or transmission electron microscopy. Using the culture techniques of rice grain enrichment and most probable number, however, we were able to observe and quantify several species of bacterivorous nanoflagellates that developed not only in 0.6m, but also in 0.4m seawater filtrates. The ability of predacious nanoflagellates to squeeze through bacteria-sized pores questions studies of bacterial production and chemical cycling that have assumed protist-free filtrates.     

Abscission and thinning of young fruit and thier regulation by plant hormones and bioregulators

Natural abscission of young fruit and its regulation by plant hormones isconsidered and compared to the generally accepted model of senescencetriggered abscission of, for example, leaves or mature fruit. It isconcluded that abscission of young fruit cannot be explained by this model.Alternatively, it is suggested that the senescence triggered initial step inthe classical abscission model should be replaced by a correlativelytriggered step. Polar basipetal IAA transport with its autostimulation andautoinhibition components is the main regulating signal in this correlativeacting system and replaces ethylene as the initial driving force from thesenescence triggered model.Results supporting this model are presented and tested against existingresults from the literature. Finally, this hypothesis is tested as a possibleexplanation of the mode of action of some thinning chemicals orbioregulators. It is speculated how a thinning chemical should be designedto function in a more reliable way, at least as far as its interference with the endogenous hormone system is concerned.     

Polygonal inequalities as a key to neuronic equations

Neuronic or decision equations, first proposed as a mathematical model of neural activity, have shown, after their exact, compact solution was found, typical behaviours that make them natural tools for General Systems studies. It is shown here that their mathematical investigation is remarkably furthered by generalizing the triangular inequality to polygonal ones. These permit the immediate computation of the tensorial expansion of linearly separable boolean functions, and exhibit clearly the connection between their continuous and discontinuous aspects.     

Disease and illness Distinctions between professional and popular ideas of sickness

The dysfunctional consequences of the Cartesian dichotomy have been enhanced by the power of biomedical technology. Technical virtuosity reifies the mechanical model and widens the gap between what patients seek and doctors provide.Patients suffer illnesses; doctors diagnose and treat diseases. Illnesses are experiences of discontinuities in states of being and perceived role performances. Diseases, in the scientific paradigm of modern medicine, are abnormalities in the function and/or structure of body organs and systems. Traditional healers also redefine illness as disease: because they share symbols and metaphors consonant with lay beliefs, their healing rituals are more responsive to the psychosocial context of illness.Psychiatric disorders offer an illuminating perspective on the basic medical dilemma. The paradigms for psychiatric practice include multiple and ostensibly contradictory models: organic, psychodynamic, behavioural and social. This melange of concepts stems from the fact that the fundamental manifestations of psychosis are disordered behaviours. The psychotic patient remains a person; his self-concept and relationships with others are central to the therapeutic encounter, whatever pharmacological adjuncts are employed.The same truths hold for all patients. The social matrix determines when and how the patient seeks what kind of help, his compliance with the recommended regimen and, to a significant extent, the functional outcome. When physicians dismiss illness because ascertainable disease is absent, they fail to meet their socially assigned responsibility. It is essential to reintegrate scientific and social concepts of disease and illness as a basis for a functional system of medical research and care.Harvard Medical School     

Evidence for nucleus independent steps in control of repair of mitochondrial damage

Summary The induction of the cytoplasmic petite mutation by ultraviolet light in 21 UV-sensitive (rad) nuclear mutants of Saccharomyces cerevisiae was compared to that in the wild type. Six rad mutants showed an increased sensitivity and two were less sensitive than the wild type. Modifications in the dose-response paralleled that of UV-induced reversion in one nuclear locus (hi ₁) studied. In these eight mutants the repair of UV-induced mitochondrial lesions seems to be under nuclear control.A block in the repair steps controlled by eleven of the other rad genes studied did not interfere with the repair of mitochondrial damage. In strains carrying a mutation in any one of these genes the dose-response curve for petite induction could be superimposed on that of the wild type even though they differed from the wild type in respect of nuclear gene reversion. These steps of the mitochondrial repair pathway(s) are therefore likely to be controlled by a nuclear and/or a cytoplasmic genetic determinant whose product acts specifically on mitochondrial lesions or it may be that the products of these genes are not required in the process of induction of petites.     

Computational constraints that may have favoured the lamination of sensory cortex

At the transition from early reptilian ancestors to primordial mammals, the areas of sensory cortex that process topographic modalities acquire the laminar structure of isocortex. A prominent step in lamination is granulation, whereby the formerly unique principal layer of pyramidal cells is split by the insertion of a new layer of excitatory, but intrinsic, granule cells, layer IV. I consider the hypothesis that granulation, and the differentiation between supra- and infra-granular pyramidal layers, may be advantageous to support fine topography in their sensory maps. Fine topography implies a generic distinction between where information, explicitly mapped on the cortical sheet, and what information, represented in a distributed fashion as a distinct firing pattern across neurons. These patterns can be stored on recurrent collaterals in the cortex, and such memory can help substantially in the analysis of current sensory input. The simulation of a simplified network model demonstrates that a non-laminated patch of cortex must compromise between transmitting where information or retrieving what information. The simulation of a modified model including differentiation of a granular layer shows a modest but significant quantitative advantage, expressed as a less severe trade-off between what and where. The further connectivity differentiation between infra-granular and supra-granular pyramidal layers is shown to match the mix of what and where information optimal for their respective target structures.     

Pacemaker synaptic interactions: Modelled locking and paradoxical features

This communication describes a model for two pacemaker (i.e., regularly firing) nerve cells, such that one elicits IPSP's in the other. The assumptions involve essentially a linear dependence (delay function) of the postsynaptic interval lengthening (or delay) produced by the IPSP's on the position (or phase) with respect to the preceding spike of the latter's arrival. When the number of IPSP's in an interval increases, both the slope and intercept of the delay function increase, the former remaining under 2 and the latter unboundedly. Assumptions are more or less close to the actual biological reality, or are made for convenience. A recurrence equation for the phase can be calculated, as well as an expression for the locking phase (see below). Plots of postsynaptic vs presynaptic firing intensity averaged over steady conditions, e.g. of mean rates or intervals, are formed by a sequence of relatively broadparadoxical segments exhibiting positive slopes 1, 2, 1/2, 3, 1/3, ..., indicating that inhibited discharges are made more intense by those increases in inhibitory arrivals. These segments are separated by narrower intercalated segments where behavior is unclear except for a large overall negative slope, indicating that inhibited discharges are weakened markedly by other increases in inhibitory arrivals. Across the successive paradoxical segments that correspond to more and more intense presynaptic discharges (i.e., to higher rates or shorter intervals), postsynaptic intensities, though overlapping in part, become weaker and weaker. At the extremes, when the presynaptic discharge is very weak, or very intense, the postsynaptic cell tends to its natural undisturbed firing, or to not firing at all, respectively. The pre- and postsynaptic discharges inevitably achieve eventually an invariant relation, i.e., will lock at a constant phase, regardless of the phase of the first IPSP arrival. The characteristics of this behavior (e.g., the rate bounds of the paradoxical segments, or the magnitude of the locked phase) depend on such givens as presynaptic and postsynaptic pacemaker rates or intervals, and as the slope or intercept of the delay function.     

On the eigenvalue distribution of genetic and phenotypic dispersion matrices: Evidence for a nonrandom organization of quantitative character variation

A quantitative genetic model of random pleiotropy is introduced as reference model for detecting the kind and degree of organization in quantitative genetic variation. In this model the genetic dispersion matrix takes the form of G = BB ^T, where B is a general, real, Gaussian random matrix. The eigenvalue density of the corresponding ensemble of random matrices (_G) is considered. The first two moments are derived for variance-covariance matrices G as well as for correlation matrices R, and an approximate expression of the density function is given. The eigenvalue distribution of all empirical correlation matrices deviates from that of a random pleiotropy model by a very large leading eigenvalue associated with a size factor. However the frequency-distribution of the remaining eigenvalues shows only minor deviations in mammalian skeletal data. A prevalence of intermediate eigenvalues in insect data may be caused by the inclusion of many functionally unrelated characters. Hence two kinds of deviations from random organization have been found: a mammal like and an insect like organization. It is concluded that functionally related characters are on the average more tightly correlated than by chance (= mammal like organization), while functionally unrelated characters appear to be less correlated than by random pleiotropy (insect like organization).     

Significance of bacterial ectoenzymes in aquatic environments

The report presents studies on temporal and spatial variations of kinetics (Vmax and Km) of bacterial ectoenzyme activity (-glucosidase - Glc, leucine aminopeptidase - Leu-amp) in the naturally eutrophic Plusee. Glc and Leu-amp activity were positively correlated with the flux of polymeric materials (polysaccharides, proteins) in the lake. Glc activity was low when algal populations grew actively, but during the algal bloom breakdown Glc activity increased rapidly. Leu-amp displayed the highest rates of activity in the epilimnion and was tightly coupled to bacterial production. The synthesis of studied ectoenzymes was under control of a repression/derepression mechanism. The significance of ectoenzymes for the transformation and bacterial utilization of organic matter, and their role in the microbial loop in aquatic environments is discussed.     

Structure of triphosphoryl nucleotide bound at the active site of yeast hexokinase: 1H-nuclear magnetic resonance study

Conformation of a nonhydrolyzable adenosine triphosphate (ATP) analogue, adenylyl-(,-methylene)-diphosphonate (AMPPCP) bound at the active site of yeast hexokinase-PII was determined by proton two-dimensional transferred nuclear Overhauser effect spectroscopy (TRNOESY) and molecular dynamics simulations. The effect of the glucose-induced domain closure on the conformation of the nucleotide was evaluated by making measurements on two different complexes: PIIAMPPCPMg(II) and PIIGlcAMPPCPMg(II). TRNOE measurements were made at 500 MHz, 10°C, as a function of several mixing times varying in the range of 40 to 200 ms. Interproton distances derived from the analysis of NOE buildup curves were used as restraints in molecular dynamics simulations to determine the conformation of the enzyme bound nucleotide. The adenosine moiety was found to bind in high anti conformation with a glycosidic torsion angle = 48 ± 5 degrees in both complexes. However, significant differences in the conformations of the ribose and triphosphoryl chain of the nucleotide are observed between the two complexes. The phase angles of pseudorotation P in PIIAMPPCPMg(II) and PIIGlcAMPPCPMg(II) are 87 degrees and 77 degrees, describing a OE and OT₄ sugar pucker and the amplitudes of the sugar pucker () are 37 degrees and 61 degrees, respectively.     

Localization of Transforming Growth Factor β in Association with Neuromuscular Junctions in Adult Human Muscle

Transforming growth factors- 1, 2, and 3 are known for their regulatory function in embryogenesis, fibrogenesis, and tissue repair of different cell types. A trophic function of TGF- subclasses for motoneurons has been shown in vitro. TGF- 1 is a potent survival factor for cultured embryonic rat motoneurons. In addition, TGF- 1 stimulates proliferation of rat Schwann cells. Recently, TGF- 2 has been reported to be associated with the subsynaptic nuclei of mature rat neuromuscular junctions. In this study, we investigated the expression of TGF- 1, 2, and 3 at neuromuscular junctions in skeletal muscle of 11 adults without neuromuscular disease. On muscle biopsies, neuromuscular junctions were depicted by acetylcholine esterase reaction and acetylcholine receptor antibodies. TGF- 1, 2, and 3 were stained immunohistochemically with monoclonal antibodies. Some muscle fibers showed low levels of inhomogeneous immunoreactivity for both TGF- 1 and TGF- 3. Intense immunoreactivity of TGF- 1 and 3 was shown at the postsynaptic area of neuromuscular junctions. TGF- 2 was expressed in the same subcellular distribution, but less strongly. In conclusion, the colocalization of TGF- with neuromuscular junctions may suggest a significant function in neuromuscular communication.     

Ethnocentricity and the social construction of ‘mass hysteria’

This study provides a critical historical review and analysis of the variety of human expressions which have been erroneously labeled under the grandiose category mass hysteria. It is argued that Western science reductionist approaches to the classification of mass hysteria treat it as an entity to be discovered transculturally, and in their self-fulfilling search for universals systematically exclude what does not fit within the autonomous parameters of its Western-biased culture model, exemplifying what Kleinman (1977) terms a category fallacy. As a result of objectivist methodologies, the etiology of actions labeled as mass hysteria is typically viewed as deviant, irrational or abnormal behavior resulting from a malfunctioning proper social order. However, what constitutes the correct social order is a function of a researcher's historical sociocultural and/or scientific milieu. This study reviews the problem, advocating Geertz's (1973) culturally relativistic approach to understanding various cross-cultural behavior that is sensitive to and tolerant of the unique context and milieu of participants. Mass or epidemic hysteria is viewed as an invention of Western psychiatry and should be abandoned and replaced with the term collective exaggerated emotions. Instead of attempting to discover a neatly packaged, unitary external disease entity, the focus of a meaning-oriented approach emphasizes the deciphering of foreign realities, semantic networks and symbol systems.     

We Do Not Dream of the 3 R's: Implications for the Nature of Dreaming Mentation

This report examines the extent to which dream recall involves the 3 R's (reading, writing, and arithmetic). Two separate studies were done. In the first study, two scorers rated, on a blind basis, a total of 456 written dream reports, available from five previous studies. There was perfect agreement between the two scorers. They agreed that there were no instances of reading, no instances of writing, and one instance of probable calculating in the 456 dreams. The second study was a questionnaire survey. Complete responses were obtained from 240 frequent dreamers (who reported remembering a mean of seven dreams per week). The study examined in two ways the frequency of the 3 R's in their recalled dreams. First, in answer to direct questions as to how frequently they dreamt about each activity, roughly 90% of the respondents reported that they never or hardly ever dreamt about each of four activities: reading, writing, typing, and calculating. In answers to other questions, this group reported spending a mean of six hours per day engaged in these activities. Second, responses as to the relative prominence of six activities (walking, writing, talking with friends, reading, sexual activity, typing) in dreaming versus waking produced two clear groupings of activities. Walking, talking with friends, and sexual activity were each rated almost as prominent in dreaming as in waking whereas the second group consisting of writing, reading, and typing were rated as far more prominent in waking than in dreaming. The two activity groups differed at p < .0001. Thus, the 3 R's appear to occur very infrequently in dreams. These findings are placed in a theoretical frame which suggests that dreaming (compared to waking) deals very little with serial activities characterized by input—rapid-processing—output in which the neural nets function in a feed-forward mode. Rather, dreaming may be characterized by relatively broad or loose connection making in which the nets function more in an autoassociative mode.     

Lateral hydrodynamic effects of rotating filaments

On the basis of the filament rotation model that was elaborated for interpretations in cell motility, the lateral hydrodynamic effects of rotating filaments have been investigated by large-scale model experiments. Helices were rotated by small electric motors in a medium of high viscosity (honey or polyethyleneglycol). The observed effects, hitherto not investigated in detail by hydrodynamics, show some features that were attributed to the indefinable formative power or vital force of the past. The main effects generated by the rotating filaments are (1) flows and flow patterns with impact zones where flows collide, (2) regions of excessive pressure and negative pressure (corner effect) along a wall, (3) grooves and smoothly shaped ridges on a free fluid surface, and (4) rolling motions of freely hanging filaments. All effects and flow patterns depend on the appropriate distribution of rotating and counterrotating filaments. Each change of the rotational direction means a dramatic alteration. The application of the observed effects explains largely the function of the microtubule/microfilament hoops or helices during the cytokinesis of a plant cell. Interpretations or simulations are described for events as the formation of secondary wall thickenings, the orientation of their microfibrils, the motion of the preprophase band microtubules, the formation of the phragmosome, the migration, stationary position and shape of the preprophase nucleus, the girdle-, septum- and H-piece formation of cell walls in algae and some events of morphogenesis inMicrasterias. Further interpretations are related to the lateral flows and to invaginations of free cell membranes, to lateral filament motions, to the right-left problem, to the selfintertwining of filaments, to the rotation of a cell body by its flagellum, to the repulsion of chromatids during meiosis and to the tetragonal and hexagonal arrangement of filaments.Dedicated to Prof. DrLothar Geitler on the occasion of the 90th anniversary of his birthday.     

Changes in soil microbial community composition induced by cometabolism of toluene and trichloroethylene

The effects of trichloroethylene (TCE) on microbial community composition were analyzed by reverse sample genome probing. Soil enrichments were incubated in dessicators containing an organic phase of either 1 or 10% (w/w) toluene in vacuum pump oil, delivering constant equilibrium aqueous concentrations of 16 and 143mg/l, respectively. Increasing the equilibrium aqueous concentration of TCE from 0 to 10mg/l led to shifts in community composition at 16, but not at 143mg/l of toluene. In closed system co-degradation studies, TCE at an aqueous concentration of 1mg/1 was effectively degraded by toluene-degrading soil enrichments once the aqueous toluene concentration dropped below 25mg/l. Little TCE degradation was observed at higher toluene concentrations (50–250mg/l). The results indicate that TCE changes microbial community composition under conditions where it is being actively metabolized.