Baseline training history and effects of methamphetamine on performance of pigeons on an interval-bisection task

Length of baseline training influences how methamphetamine disrupts temporal performance under a peak interval schedule. Acute methamphetamine produces overestimation of time following relatively brief training, but following extended training, methamphetamine produces more general loss of stimulus control. The current study extends the study of training length on the effects of methamphetamine to an interval-bisection procedure. Six pigeons responded under a psychophysical choice procedure in which responses to one key color were correct after presentation of four shorter sample durations and responses to another key color were correct after presentation of four longer sample durations. One group of three pigeons received briefer baseline training (45 sessions), while another group received more extended training (223 sessions) prior to methamphetamine administration. There was no evidence of overestimation of time or generalized loss of stimulus control in either group. Sensitivity (precision of timing) was higher in the group with more extensive training and was disrupted by methamphetamine.     

Bottom-up effects of host-plant species diversity and top-down effects of ants interactively increase plant performance

While plant diversity is well known to increase primary productivity, whether these bottom-up effects are enhanced by reciprocal top-down effects from the third trophic level is unknown. We studied whether pine tree species diversity, aphid-tending ants and their interaction determined plant performance and arthropod community structure. Plant diversity had a positive effect on aphids, but only in the presence of mutualistic ants, leading to a threefold greater number of both groups in the tri-specific cultures than in monocultures. Plant diversity increased ant abundance not only by increasing aphid number, but also by increasing ant recruitment per aphid. The positive effect of diversity on ants in turn cascaded down to increase plant performance; diversity increased plant growth (but not biomass), and this effect was stronger in the presence of ants. Consequently, bottom-up effects of diversity within the same genus and guild of plants, and top-down effects from the third trophic level (predatory ants), interactively increased plant performance.     

Menstrual cycle effects on performance of mental arithmetic task

The purpose of this research was to identify the relationship between task performance and menstrual cycle. The difference of performance on menstrual cycle phase was investigated. The task was the mental arithmetic task which involved the non-sequential and higher order cognitive processes. The duration of the experiment was twenty minutes. Two-way analysis of variance by repeated-measures design was used to examine the differences in task performance between phases and temporal variations. Results showed that there was a significant difference in correct input time during temporal variations though there was no significant difference between phases. Moreover, the relationships between phases and intra-individual variations in task performance were examined using coefficient of variance (CV). CVs were plotted in three dimensions to examine the relationships between intra-individual variations and phases. Based on CVs, the subjects who showed differences were classified into two groups: those with a small difference in three phases and those with a difference every phase. The phase which indicated large CV changed with individuals.     

Minimal models of top-down control of phytoplankton

1. A set of models describing the dynamics of top-down control of phytoplankton by Daphnia in lakes is reviewed. The basis of these models is a simple and well-known model that has been used, among other things, to demonstrate the paradox of enrichment.
2. We discuss minimal extensions that allow this model to mimic the effects of spatial heterogeneity, planktivory, seasonality and inedible algae.
3. These models generate hypotheses about mechanisms that may cause patterns observed in the field such as:

4. We discuss the way in which such very simple models may contribute to the building of theories about plankton dynamics in the field, and the caveats of interpreting wrongly the message from models.     

Habitat structure alters top-down control in litter communities

The question whether top-down or bottom-up forces dominate trophic relationships, energy flow, and abundances within food webs has fuelled much ecological research with particular focus on soil litter ecosystems. Because litter simultaneously provides habitat structure and a basal resource, disentangling direct trophic and indirect non-trophic effects on different trophic levels remains challenging. Here, we focussed on short-term per capita interaction strengths of generalist predators (centipedes) on their microbi-detritivore prey (springtails) and addressed how the habitat structuring effects of the leaf litter modifies this interaction. We performed a series of laboratory functional response experiments where four levels of habitat structure were constructed by adding different amounts of leaf litter to the experimental arenas. We found that increased leaf litter reduced the consumption rate of the predator. We interpreted this as a dilution effect of the augmented habitat size provided by the increasing leaf litter surface available to the species. Dilution of the prey population decreased encounter rates, whereas the capture success was not affected. Interestingly, our results imply that top-down control by centipedes decreased with increasing resource supply for the microbi-detritivore prey (i.e. the leaf litter that simultaneously provides habitat structure). Therefore, effective top-down control of predators on microbi-detritvore populations seems unlikely in litter-rich ecosystems due to the non-trophic, habitat-structuring effect of the basal litter resource.     

Limbic irritability and chaotic neural response during conflicting stroop task in the patients with unipolar depression

According to recent findings activation of anterior cingulate cortex (ACC) is related to detecting cognitive conflict. This conflict related activation elicits autonomic responses which can be assessed by psychophysiological measures such as heart rate variability calculated as beat to beat R-R intervals (RRI). Recent findings in neuroscience also suggest that cognitive conflict is related to specific nonlinear chaotic changes of the signal generated by neural systems. The present study used Stroop word-color test as an experimental approach to psychophysiological study of cognitive conflict in connection with RRI measurement, psychometric measurement of limbic irritability (LSCL-33), depression (BDI-II) and calculation of largest Lyapunov exponents in nonlinear data analysis of RRI time series. Significant correlation 0.61 between largest Lyapunov exponents and LSCL-33 found in this study indicate that a defect of neural inhibition during conflicting Stroop task is closely related to limbic irritability. Because limbic irritability is probably closely related to epileptiform abnormalities in the temporolimbic structures, this result might represent useful instrument for indication of anticonvulsant treatment in depressive patients who are resistant to antidepressant medication.     

S-phase and M-phase timing are under independent circadian control in the dinoflagellate Lingulodinium

In many phytoplankton species, cell division (mitosis) usually occurs at defined times of day. This timing is also observed under constant conditions, indicating that it is regulated by a circadian clock rather than by a simple response to the light-dark cycle. For those algae with cell cycles longer than a day, the clock opens a window of opportunity for mitosis at a particular time of day through which cells in an appropriate phase of the cell cycle can pass. Although the timing of mitosis is generally studied due to ease of measurement, for some phytoplankton the timing of S-phase is also circadian. This thus raises the possibility that mitosis is not directly gated by the clock but occurs instead at a defined interval (a constant G2 length) following a circadian controlled S-phase. To determine if the clock exercises independent control over the timing of both S- and M-phase, we measured the timing of both S- and M-phase in cultures of the dinoflagellate Lingulodinium grown under a variety of different photoperiods. We interpret the phase angles of both rhythms, in particular those resulting in a change in the length of G2, as an indication that the clock independently regulates the timing of S-phase and mitosis.     

Searching for "the top" in top-down control

Although numerous theoretical models implicate the prefrontal cortex (PFC) as a source of top-down control signals, empirical support is limited. In this review, we highlight direct evidence for this view of PFC function and discuss several lines of other supportive findings. Most evidence to-date is only suggestive due to methodological challenges in tracking the spatiotemporal dynamics of cortical networks. However, we discuss several promising approaches that could further our understanding of the role of the PFC in goal-directed behavior.     

The beneficial effects of rosuvastatin are independent of zinc supplementation in patients with atherosclerosis

BackgroundStatins have multiple antiatherosclerotic effects, but can reduce blood plasma concentrations of minerals, including zinc. As zinc possesses antiinflammatory and antioxidant effects, low zinc status can promote injuries or inadequate tissue repair in endothelial cells. Metallothionein (MT) expression might modulate responses induced by statins in patients with atherosclerosis. However, research regarding mineral status and the use of statins is scarce. This study evaluated the effects of zinc supplementation on zinc status and expression of the zinc-dependent MT1F and MT2A genes in patients with atherosclerosis treated with rosuvastatin.MethodsA double-blind, randomized clinical trial was performed with 54 participants treated with 10 mg rosuvastatin for 4 months with or without zinc supplementation (30 mg/day). Diet, lipid profile, high-sensitivity reactive protein C (hs-CRP), plasma and erythrocyte zinc concentrations, erythrocyte superoxide dismutase (SOD) activity, and MT1F and MT2A genes expression were analyzed before and after intervention.ResultsRosuvastatin therapy was effective in reducing low- and non-high-density lipoprotein, total cholesterol, triglycerides, and hs-CRP levels, independent of zinc supplementation. Additionally, zinc treatment had no effect on SOD enzyme activity (P = 0.201), plasma (P > 0.671) and erythrocyte (P > 0.123) zinc concentrations, or the pattern of MT1F and MT2A genes expression (P = 0.088 and P = 0.229, respectively).ConclusionsThe effectiveness of rosuvastatin treatment is independent of the effects of zinc supplementation. Moreover, rosuvastatin treatment did not have a significant impact on zinc status or MT1F and MT2A genes expression in patients with atherosclerosis.     

Radiation-induced bystander effects in malignant trophoblast cells are independent from gap junctional communication

It is controversially discussed that irradiation induces bystander effects via gap junction channels and/or diffusible cellular factors such as nitric oxide or cytokines excreted from the cells into the environment. But up to now the molecular mechanism leading to a bystander response is not well understood. To discriminate between both mechanisms of bystander response, (i) mediated by gap junctional communication and/or (ii) mediated by diffusible molecules, we used non-communicating Jeg3 malignant trophoblast cells transfected with inducible gap junction proteins, connexin43 and connexin26, respectively, based on the Tet-On system. We co-cultivated X-ray irradiated and non-irradiated bystander Jeg3 cells for 4 h, separated both cell populations by flow cytometry and evaluated the expression of activated p53 by Western blot analysis. The experimental design was proven with communicating versus non-communicating Jeg3 cells. Interestingly, our results revealed a bystander effect which was independent from gap junctional communication properties and the connexin isoform expressed. Therefore, it seems more likely that the bystander effect is not mediated via gap junction channels but rather by paracrine mechanisms via excreted molecules in Jeg3 cells.     

Pollinators as mediators of top-down effects on plants

This paper explores the idea that predators may disrupt plant–pollinator relationships and consequently inhibit reproduction in flowering plants. Amidst growing evidence that predators influence plant–pollinator interactions, I suggest that such pollinator‐mediated indirect effects may be a common feature of terrestrial communities, with implications for research into top‐down effects and pollination ecology. Experimental evidence of such an effect from a riparian system in northern California is provided, where crab spiders decreased seed production in inflorescences of the invasive plant Leucanthemum vulgare by reducing the frequency and duration of floral visits by pollinating insects.     

The anti-inflammatory effects of soluble epoxide hydrolase inhibitors are independent of leukocyte recruitment

Excess leukocyte recruitment to the lung plays a central role in the development or exacerbation of several lung inflammatory diseases including chronic obstructive pulmonary disease. Epoxyeicosatrienoic acids (EETs) are cytochrome P-450 metabolites of arachidonic acid reported to have multiple biological functions, including blocking of leukocyte recruitment to inflamed endothelium in cell culture through reduction of adhesion molecule expression. Inhibition of the EET regulatory enzyme, soluble epoxide hydrolase (sEH) also has been reported to have anti-inflammatory effects in vivo including reduced leukocyte recruitment to the lung. We tested the hypothesis that the in vivo anti-inflammatory effects of sEH inhibitors act through the same mechanisms as the in vitro anti-inflammatory effects of EETs in a rat model of acute inflammation following exposure to tobacco smoke. Contrary to previously published data, we found that sEH inhibition did not reduce tobacco smoke-induced leukocyte recruitment to the lung. Furthermore, sEH inhibition did not reduce tobacco smoke-induced adhesion molecule expression in the lung vasculature. Similarly, concentrations of EETs greater than or equal to their reported effective dose did not reduce TNFα induced expression of the adhesion molecules. These results suggest that the anti-inflammatory effects of sEH inhibitors are independent of leukocyte recruitment and EETs do not reduce the adhesion molecules responsible for leukocyte recruitment in vitro. This demonstrates that the widely held belief that sEH inhibition prevents leukocyte recruitment via EET prevention of adhesion molecule expression is not consistently reproducible.     

Energetic conditions promoting top-down control of prey by predators

Humans remove large amounts of biomass from natural ecosystems, and large bodied high trophic level animals are especially sensitive and vulnerable to exploitation. The effects of removing top-predators on food webs are often difficult to predict because of limited information on species interaction strengths. Here we used a three species predator-prey model to explore relationships between energetic properties of trophodynamic linkages and interaction strengths to provide heuristic rules that indicate observable energetic conditions that are most likely to lead to stable and strong top-down control of prey by predator species. We found that strong top-down interaction strengths resulted from low levels of energy flow from prey to predators. Strong interactions are more stable when they are a consequence of low per capita predation and when predators are subsidized by recruitment. Diet composition also affects stability, but the relationship depends on the form of the functional response. Our results imply that for generalist satiating predators, strong top-down control on prey is most likely for prey items that occupy a small portion of the diet and when density dependent recruitment is moderately high.     

Disentangling the effects of predator hunting mode and habitat domain on the top-down control of insect herbivores

1.?Polyphagous predatory invertebrates play a key role in the top-down control of insect herbivores. However, predicting predation risk for herbivores is not a simple function of predator species richness. Predation risk may be reduced or enhanced depending on the functional characteristics predator species. We predict that where predator species spatially overlap this will reduce predation risk for herbivores by allowing negative inter-specific interaction between predators to occur. Where increased predation risk occurs, we also predict that this will have a cascading effect through the food chain reducing plant growth. 2.?We used a substitutive replicated block design to identify the effect of similarity and dissimilarity in predator hunting mode (e.g. 'sit and wait', 'sit and pursue', and 'active') and habitat domain (e.g. canopy or ground) on the top-down control of planthoppers in grasslands. Predators included within the mesocosms were randomly selected from a pool of 17 local species. 3.?Predation risk was reduced where predators shared the same habitat domain, independent of whether they shared hunting modes. Where predators shared the same habitat domains, there was some evidence that this had a cascading negative effect on the re-growth of grass biomass. Where predator habitat domains did not overlap, there were substitutable effects on predation risk to planthoppers. Predation risk for planthoppers was affected by taxonomic identity of predator species, i.e. whether they were beetles, spiders or true bugs. 4.?Our results indicated that in multi-predator systems, the risk of predation is typically reduced. Consideration of functional characteristics of individual species, in particular aspects of habitat domain and hunting mode, are crucial in predicting the effects of multi-predator systems on the top-down control of herbivores.     

The importance of picophytoplankton and its top-down control in marine environments

Phytoplankton are classfied into three groups based on size: microphytoplankton (＞20 μm),nanophytoplankton (2-20 μm),and picophytoplankton(＜2 μm) (Sieburth et al.1978)[1].Picophytoplanktonare composed of three groups:Prochlorococcus,Synechococcus,and picophytoeukaryotes.The former two are unicellular cyanobacteria.     

Nonadditive effects of consumption in an intertidal macroinvertebrate community are independent of food availability but driven by complementarity effects

Suboptimal environmental conditions are ubiquitous in nature and commonly drive the outcome of biological interactions in community processes. Despite the importance of biological interactions for community processes, knowledge on how species interactions are affected by a limiting resource, for example, low food availability, remains limited. Here, we tested whether variation in food supply causes nonadditive consumption patterns, using the macroinvertebrate community of intertidal sandy beaches as a model system. We quantified isotopically labeled diatom consumption by three macroinvertebrate species (Bathyporeia pilosa, Haustorius arenarius, and Scolelepis squamata) kept in mesocosms in either monoculture or a three‐species community at a range of diatom densities. Our results show that B. pilosa was the most successful competitor in terms of consumption at both high and low diatom density, while H. arenarius and especially S. squamata consumed less in a community than in their respective monocultures. Nonadditive effects on consumption in this macroinvertebrate community were present and larger than mere additive effects, and similar across diatom densities. The underlying species interactions, however, did change with diatom density. Complementarity effects related to niche‐partitioning were the main driver of the net diversity effect on consumption, with a slightly increasing contribution of selection effects related to competition with decreasing diatom density. For the first time, we showed that nonadditive effects of consumption are independent of food availability in a macroinvertebrate community. This suggests that, in communities with functionally different, and thus complementary, species, nonadditive effects can arise even when food availability is low. Hence, at a range of environmental conditions, species interactions hold important potential to alter ecosystem functioning.