Parasitic nematode ion channels: improving understanding of pharmacology and genetic composition

Parasitic nematode infections of humans, plants and animals are of major economic impact. These parasites cause losses of billions of dollars per year in crop damage and through livestock infection; the infections to humans are equally debilitating. Anthelmintics are the main chemotherapeutic agents used for treatment and prophylaxis of nematode infections because there is presently no effective vaccine on the market. Most of the anthelmintics presently used in treating nematode infections in humans were first developed for use in animals. In most cases, these anthelmintics have been used in humans without changing the properties of the drugs at all. However, resistance has been reported to the mainstay anthelmintics, namely AChR agonists (levamisole, pyrantel), benzimidazoles (albendazole) and macrocyclic lactones (ivermectin). There is therefore the urgent need to understand the genetics of the receptors targeted by these anthelmintics and the mechanisms of resistance, with the view to improving efficacy of the presently used drugs. In addition, there is the need to find alternative targets for developing new anthelmintics as well as fully studying the mechanism of action of any new anthelmintic. We have demonstrated the effects of the new novel-acting cyclooctadepsipeptide anthelmintic, emodepside, on the membrane potential and voltage-activated currents in the pig parasite Ascaris suum. Emodepside hyperpolarized the membrane in a slow, time-dependent manner without changing the input conductance. We show that the purported emodepside target receptors in C. elegans, SLO-1 and LAT-1 are expressed in the muscle flap of A. suum (Asu-slo-1 and Asu-lat-1). Emodepside potentiated the voltage-activated Ca2+-dependent K+ channel currents in a time- and voltage-dependent manner. We have demonstrated that emodepside effect on the K+ channel currents is inhibited by iberiotoxin, a selective SLO-1 channel inhibitor. The effects of emodepside on the membrane potential and K+ channel currents were modulated by NO and protein kinase activators/inhibitors. Last but not least, we demonstrate that diethylcarbamazine (DEC), a filarial anthelmintic, potentiates the effects of emodepside on the membrane potential and SLO-1-like currents. Our results clearly demonstrate effects of emodepside in a parasitic nematode and the modulation of emodepside effects by second messengers like protein kinases. We also show that a formulation of emodepside and DEC could be used for treating filarial parasites, slowing the development of resistance to emodepside. Finally, we show the cloning of four acetylcholine receptor subunit genes from another pig parasite, Oesophagostomum dentatum and the expression and characterization of these receptor subunits in Xenopus laevis oocytes. By employing the three ancillary factors of Haemonchus contortus, Hc-ric-3.1, Hc-unc-50 and Hc-unc-74, we have characterized four levamisole receptor subtypes of O. dentatum with different pharmacological properties. First, the receptor subtype we have termed Pyr-nAChR, was composed of Ode-unc-29 and Ode-unc-63 and responded to pyrantel as the most potent agonist. The second receptor subtype, Pyr/Tbd-nAChR, responded to pyrantel and tribendimidine as the most potent agonists and was composed of Ode-unc-29, Ode-unc-63 and Ode-unc-38. The third receptor subtype, nAChR, responded to ACh as the most potent agonist and was composed of Ode-unc-29, Ode-unc-63 and Ode-acr-8. The last receptor subtype, Lev-nAChR, responded to levamisole as the most potent agonist and was composed of Ode-unc-29, Ode-unc-63, Ode-acr-8 and Ode-unc-38. In the Lev-nAChR, derquantel distinguished receptor subtypes with pA2 values of 6.8 and 8.4 for levamisole and pyrantel, respectively. The calcium permeability (PCa/PNa) of three receptor subtypes differed. We measured PCa/PNa of 10.3, 0.38 and 0.38 for the Lev-nAChR, Pyr/Tbd-nAChR and nAChR subtypes, respectively. Unlike the receptors in Caenorhabditis elegans and Haemonchus contortus, all three ancillary factors were not absolutely required to reconstitute O. dentatum functional levamisole receptors. We reconstituted receptors with robust responses to the agonists when we sequentially removed these ancillary factors. However, removal of all three factors did not reconstitute any receptors, demonstrating the need for at least one of these ancillary factors. Our results demonstrate the plasticity in the levamisole receptors of O. dentatum and suggest that the subtypes may have different physiological roles and/or expressed in different tissues of the parasite

Development and application of path integral methods to study nuclear quantum effects in aqueous systems

Nuclear quantum effects have been shown to play a large role in defining the properties of chemical systems. However including these in computational simulations for example using path integral methods is far more computationally expensive than a classical simulation where these effects are ignored. This is because the number of individual force calculations is greatly increased when using a path integral method. This means that for some systems and system sizes it is difficult to computationally evaluate fully quantum properties. To address this, methods have been developed that can accelerate this simulations with minimal loss of accuracy, however the most popular methods all suffer from drawbacks which limits their application to certain types of system. This work presents a novel method for increasing the speed of path integral simulations that employs Kernel-Ridge Regression to enable fewer individual force calculations during the simulation while maintaining accuracy. The main advantage of this method lies in its ability to be applied to any system of interest with no conditions or prior assumptions about the potential energy surface. Results for this method are very positive when applied to two systems where quantum effects are prevalent, liquid water and para-hydrogen. In addition to this work, an investigation is carried out into the role of nuclear quantum effects in the free energies of hexagonal and cubic ice, as hexagonal is only more stable by _ 40 J mo

Sanctuary after asylum : addressing a gap in the political theory of refuge (Letter)

Published online: 1 December 2022This research note argues that political theorists of refuge ought to consider the experiences of refugees after they have received asylum in the Global North. Currently, much of the literature concerning the duties of states toward refugees implicitly adopts a blanket approach, rather than considering how varied identities may affect the remedies available to displaced people. Given the prevalence of racism, xenophobia, and homophobia in the Global North, and the growing norm of dissident persecution in foreign territory, protection is not guaranteed after either territorial or legal admission. This research note considers the case of LGBTQ refugees in order to demonstrate the analytical potential of more inclusive and diverse normative approaches. Taking the origin and extension of harm seriously requires a conceptualization of sanctuary after asylum that accurately reflects the experiences of the displaced. In doing so, questions arise regarding the nature and efficacy of territorial asylum

Sanctuary After Asylum: Addressing a Gap in The Political Theory of Refuge

This research note argues that political theorists of refuge ought to consider the experiences of refugees after they have received asylum in the Global North. Currently, much of the literature concerning the duties of states towards refugees implicitly adopts a blanket approach, rather than considering how varied identities may affect the remedies available to displaced people. Given the prevalence of racism, xenophobia, and homophobia in the Global North, and the growing norm of dissident persecution in foreign territory, protection is not guaranteed after either territorial or legal admission. This research note considers the case of LGBTQ refugees in order to demonstrate the analytical potential of more inclusive and diverse normative approaches. Taking the origin and extension of harm seriously requires a conceptualization of sanctuary after asylum that accurately reflects the experiences of the displaced. In doing so, questions arise regarding the nature and efficacy of territorial asylum

Functional Characterization of a Novel Family of Acetylcholine-Gated Chloride Channels in Schistosoma mansoni

Acetylcholine is the canonical excitatory neurotransmitter of the mammalian neuromuscular system. However, in the trematode parasite Schistosoma mansoni, cholinergic stimulation leads to muscle relaxation and a flaccid paralysis, suggesting an inhibitory mode of action. Information about the pharmacological mechanism of this inhibition is lacking. Here, we used a combination of techniques to assess the role of cholinergic receptors in schistosome motor function. The neuromuscular effects of acetylcholine are typically mediated by gated cation channels of the nicotinic receptor (nAChR) family. Bioinformatics analyses identified numerous nAChR subunits in the S. mansoni genome but, interestingly, nearly half of these subunits carried a motif normally associated with chloride-selectivity. These putative schistosome acetylcholine-gated chloride channels (SmACCs) are evolutionarily divergent from those of nematodes and form a unique clade within the larger family of nAChRs. Pharmacological and RNA interference (RNAi) behavioral screens were used to assess the role of the SmACCs in larval motor function. Treatment with antagonists produced the same effect as RNAi suppression of SmACCs; both led to a hypermotile phenotype consistent with abrogation of an inhibitory neuromuscular mediator. Antibodies were then generated against two of the SmACCs for use in immunolocalization studies. SmACC-1 and SmACC-2 localize to regions of the peripheral nervous system that innervate the body wall muscles, yet neither appears to be expressed directly on the musculature. One gene, SmACC-1, was expressed in HEK-293 cells and characterized using an iodide flux assay. The results indicate that SmACC-1 formed a functional homomeric chloride channel and was activated selectively by a panel of cholinergic agonists. The results described in this study identify a novel clade of nicotinic chloride channels that act as inhibitory modulators of schistosome neuromuscular function. Additionally, the iodide flux assay used to characterize SmACC-1 represents a new high-throughput tool for drug screening against these unique parasite ion channels

pyveg: A Python package for analysing the time evolution of patterned vegetation using Google Earth Engine

Periodic vegetation patterns (PVP) arise from the interplay between forces that drive the growth and mortality of plants. Inter-plant competition for resources, in particular water, can lead to the formation of PVP. Arid and semi-arid ecosystems may be under threat due to changing precipitation dynamics driven by macroscopic changes in climate. These regions display some noteable examples of PVP, for example the “tiger bush” patterns found in West Africa. The morphology of the periodic pattern has been suggested to be linked to the resilience of the ecosystem (Mander et al., 2017; Trichon et al., 2018). Using remote sensing techniques, vegetation patterns in these regions can be studied, and an analysis of the resilience of the ecosystem can be performed. The pyveg package implements functionality to download and process data from Google Earth Engine (GEE), and to subsequently perform a resilience analysis on the aquired data. PVP images are quantified using network centrality metrics. The results of the analysis can be used to search for typical early warning signals of an ecological collapse (Dakos et al., 2008). Google Earth Engine Editor scripts are also provided to help researchers discover locations of ecosystems which may be in decline. pyveg is being developed as part of a research project looking for evidence of early warning signals of ecosystem collapse using remote sensing data. pyveg allows such research to be carried out at scale, and hence can be an important tool in understanding changing arid and semi-arid ecosystem dynamics. An evolving list of PVP locations, obtained through both literature and manual searches, is included in the package at pyveg/coordinates.py. The structure of the package is outlined in Figure 1, and is discussed in more detail in the following sections

The role of nuclear quantum effects in the relative stability of hexagonal and cubic ice

At atmospheric pressure, hexagonal ice (Ih) is thermodynamically stable relative to cubic ice (Ic), although the magnitude and underlying physical origin of this stability difference are not well defined. Pure Ic crystals are not accessible experimentally, and hence computer simulations have often been used to interrogate the relative stabilities of Ih and Ic; however, these simulations are dominated by molecular interaction models that ignore the intramolecular flexibility of individual water molecules, do not describe intermolecular hydrogen-bonding with sufficient accuracy, or ignore the role of nuclear quantum effects (NQEs) such as zero-point energy. Here, we show that when comparing the relative stability of Ih and Ic using a flexible, anharmonic molecular interaction model, while also accurately accounting for NQEs, a new picture emerges: Ih is stabilized relative to Ic as a result of subtle differences in the intramolecular geometries and intermolecular interactions of water molecules which are modulated by NQEs. Our simulations hence suggest that NQEs are a major contributor to the stabilization of Ih under terrestrial conditions and thus contribute to the well-known hexagonal (sixfold) symmetry of ice crystals

Quantitatively monitoring the resilience of patterned vegetation in the Sahel

Patterning of vegetation in drylands is a consequence of localized feedback mechanisms. Such feedbacks also determine ecosystem resilience—i.e. the ability to recover from perturbation. Hence, the patterning of vegetation has been hypothesized to be an indicator of resilience, that is, spots are less resilient than labyrinths. Previous studies have made this qualitative link and used models to quantitatively explore it, but few have quantitatively analysed available data to test the hypothesis. Here we provide methods for quantitatively monitoring the resilience of patterned vegetation, applied to 40 sites in the Sahel (a mix of previously identified and new ones). We show that an existing quantification of vegetation patterns in terms of a feature vector metric can effectively distinguish gaps, labyrinths, spots, and a novel category of spot–labyrinths at their maximum extent, whereas NDVI does not. The feature vector pattern metric correlates with mean precipitation. We then explored two approaches to measuring resilience. First we treated the rainy season as a perturbation and examined the subsequent rate of decay of patterns and NDVI as possible measures of resilience. This showed faster decay rates—conventionally interpreted as greater resilience—associated with wetter, more vegetated sites. Second we detrended the seasonal cycle and examined temporal autocorrelation and variance of the residuals as possible measures of resilience. Autocorrelation and variance of our pattern metric increase with declining mean precipitation, consistent with loss of resilience. Thus, drier sites appear less resilient, but we find no significant correlation between the mean or maximum value of the pattern metric (and associated morphological pattern types) and either of our measures of resilience

Visual impairment among eye health workers in a tertiary eye centre in Ghana

Objective: To determine causes of visual impairment (VI) among staff of the Eye Centre at the Korle Bu Teaching Hospital.Design: This was a cross-sectional study.Setting: The Eye Centre, Korle Bu Teaching Hospital (KBTH), from October 2016 to March 2017 on all consenting members of staff.Participants: Eighty-four (79.3%) of 106 consenting staff members participated in this study.Data collection/Intervention: A detailed history (demographic, ocular, medical co-morbid conditions), ocular examination and relevant diagnostic investigations were conducted. Interventions initiated included treatment for glaucoma, dry eye and allergic conjunctivitis and spectacles prescription for refractive errors.Main outcomes: Prevalence of avoidable causes of VI (glaucoma, cataract, refractive errors). Secondary outcomes included prevalence of unavoidable causes of VI. Results Eighty-four (79.3%) members of staff participated in this study. Most of the participants were females, 54(64.3 %). Age ranged from 23 to 60 years with an average of 35.8±9.9 years (mean ± SD). Prevalence of VI was 9.5 % (8/84), all due to uncorrected refractive error. Other known causes of VI included open angle glaucoma in 12(14.3 %), macular scar of unknown cause, 1(1.2 %) and sutural cataract, 1(1.2 %) but were all visually insignificant.Conclusions: The prevalence of VI among the staff of the Eye Centre of the KBTH was 9.5 %, all due to refractive errors. Other known causes of avoidable visual impairment and blindness encountered were glaucoma (14.3 %), macular scar (1.2 %) and cataract (1.2 %), all asymptomatic. Routine eye screening should be part of periodic medical examination for employees

Bayesian population receptive field modelling

We introduce a probabilistic (Bayesian) framework and associated software toolbox for mapping population receptive fields (pRFs) based on fMRI data. This generic approach is intended to work with stimuli of any dimension and is demonstrated and validated in the context of 2D retinotopic mapping. The framework enables the experimenter to specify generative (encoding) models of fMRI timeseries, in which experimental manipulations enter a pRF model of neural activity, which in turns drives a nonlinear model of neurovascular coupling and Blood Oxygenation Level Dependent (BOLD) response. The neuronal and haemodynamic parameters are estimated together on a voxel-by-voxel or region-of-interest basis using a Bayesian estimation algorithm (variational Laplace). This offers several novel contributions to receptive field modelling. The variance / covariance of parameters are estimated, enabling receptive fields to be plotted while properly representing uncertainty about pRF size and location. Variability in the haemodynamic response across the brain is accounted for. Furthermore, the framework introduces formal hypothesis testing to pRF analysis, enabling competing models to be evaluated based on their model evidence (approximated by the variational free energy), which represents the optimal tradeoff between accuracy and complexity. Using simulations and empirical data, we found that parameters typically used to represent pRF size and neuronal scaling are strongly correlated, which should be taken into account when making inferences. We used the framework to compare the evidence for six variants of pRF model using 7T functional MRI data and we found a circular Difference of Gaussians (DoG) model to be the best explanation for our data overall. We hope this framework will prove useful for mapping stimulus spaces with any number of dimensions onto the anatomy of the brain.Comment: 30 pages, 10 figures. Code available at https://github.com/pzeidman/BayespR