Short-term and spike-timing-dependent plasticity facilitate the formation of modular neural networks

The brain has the phenomenal ability to reorganise itself by forming new connections among neurons and by pruning others. The so-called neural or brain plasticity facilitates the modification of brain structure and function over different time scales. Plasticity might occur due to external stimuli received from the environment, during recovery from brain injury, or due to modifications within the body and brain itself. In this paper, we study the combined effect of short-term (STP) and spike-timing-dependent plastic- ity (STDP) on the synaptic strength of excitatory coupled Hodgkin-Huxley neurons and show that plasticity can facilitate the formation of modular neural networks with complex topologies that resemble those of networks with preferential attachment properties. In particular, we use an STDP rule that alters the synaptic coupling intensity based on time intervals between spikes of postsynaptic and presynaptic neurons. Previous work has shown that STDP may induce the emergence of directed connections from high to low frequency spiking neurons. On the other hand, STP is attributed to the release of neurotransmitters in the synaptic cleft of neurons that alter its synaptic efficiency. Our results suggest that the combined effect of STP and STDP with long recovery times facilitates the formation of connections among neurons with similar spike frequencies only, a kind of preferential at- tachment. We then pursue this further and show that, when starting with all-to-all neural configurations, depending on the STP recovery time and dis- tribution of neural frequencies, modular neural networks can emerge as a direct result of the combined effect of STP and STDP

Genetic analysis of D-xylose metabolism by endophytic yeast strains of Rhodotorula graminis and Rhodotorula mucilaginosa

Two novel endophytic yeast strains, WP1 and PTD3, isolated from within the stems of poplar (Populus) trees, were genetically characterized with respect to their xylose metabolism genes. These two strains, belonging to the species Rhodotorula graminis and R. mucilaginosa, respectively, utilize both hexose and pentose sugars, including the common plant pentose sugar, D-xylose. The xylose reductase (XYL1) and xylitol dehydrogenase (XYL2) genes were cloned and characterized. The derived amino acid sequences of xylose reductase (XR) and xylose dehydrogenase (XDH) were 32%∼41% homologous to those of Pichia stipitis and Candida. spp., two species known to utilize xylose. The derived XR and XDH sequences of WP1 and PTD3 had higher homology (73% and 69% identity) with each other. WP1 and PTD3 were grown in single sugar and mixed sugar media to analyze the XYL1 and XYL2 gene regulation mechanisms. Our results revealed that for both strains, the gene expression is induced by D-xylose, and that in PTD3 the expression was not repressed by glucose in the presence of xylose

Lower Richness of Small Wild Mammal Species and Chagas Disease Risk

A new epidemiological scenario involving the oral transmission of Chagas disease, mainly in the Amazon basin, requires innovative control measures. Geospatial analyses of the Trypanosoma cruzi transmission cycle in the wild mammals have been scarce. We applied interpolation and map algebra methods to evaluate mammalian fauna variables related to small wild mammals and the T. cruzi infection pattern in dogs to identify hotspot areas of transmission. We also evaluated the use of dogs as sentinels of epidemiological risk of Chagas disease. Dogs (n = 649) were examined by two parasitological and three distinct serological assays. kDNA amplification was performed in patent infections, although the infection was mainly sub-patent in dogs. The distribution of T. cruzi infection in dogs was not homogeneous, ranging from 11–89% in different localities. The interpolation method and map algebra were employed to test the associations between the lower richness in mammal species and the risk of exposure of dogs to T. cruzi infection. Geospatial analysis indicated that the reduction of the mammal fauna (richness and abundance) was associated with higher parasitemia in small wild mammals and higher exposure of dogs to infection. A Generalized Linear Model (GLM) demonstrated that species richness and positive hemocultures in wild mammals were associated with T. cruzi infection in dogs. Domestic canine infection rates differed significantly between areas with and without Chagas disease outbreaks (Chi-squared test). Geospatial analysis by interpolation and map algebra methods proved to be a powerful tool in the evaluation of areas of T. cruzi transmission. Dog infection was shown to not only be an efficient indicator of reduction of wild mammalian fauna richness but to also act as a signal for the presence of small wild mammals with high parasitemia. The lower richness of small mammal species is discussed as a risk factor for the re-emergence of Chagas disease

Resource Quantity Affects Benthic Microbial Community Structure and Growth Efficiency in a Temperate Intertidal Mudflat

Estuaries cover <1% of marine habitats, but the carbon dioxide (CO2) effluxes from these net heterotrophic systems contribute significantly to the global carbon cycle. Anthropogenic eutrophication of estuarine waterways increases the supply of labile substrates to the underlying sediments. How such changes affect the form and functioning of the resident microbial communities remains unclear. We employed a carbon-13 pulse-chase experiment to investigate how a temperate estuarine benthic microbial community at 6.5°C responded to additions of marine diatom-derived organic carbon equivalent to 4.16, 41.60 and 416.00 mmol C m−2. The quantities of carbon mineralized and incorporated into bacterial biomass both increased significantly, albeit differentially, with resource supply. This resulted in bacterial growth efficiency increasing from 0.40±0.02 to 0.55±0.04 as substrates became more available. The proportions of diatom-derived carbon incorporated into individual microbial membrane fatty acids also varied with resource supply. Future increases in labile organic substrate supply have the potential to increase both the proportion of organic carbon being retained within the benthic compartment of estuaries and also the absolute quantity of CO2 outgassing from these environments

Uncharted waters: rare and unclassified cardiomyopathies characterized on cardiac magnetic resonance imaging

Cardiac magnetic resonance imaging (CMR) has undergone considerable technology advances in recent years, so that it is now entering into mainstream cardiac imaging practice. In particular, CMR is proving to be a valuable imaging tool in the detection, morphological assessment and functional assessment of cardiomyopathies. Although our understanding of this broad group of heart disorders continues to expand, it is an evolving group of entities, with the rarer cardiomyopathies remaining poorly understood or even unclassified. In this review, we describe the clinical and pathophysiological aspects of several of the rare/unclassified cardiomyopathies and their appearance on CMR

HIV-1 subtype C transmitted founders modulate dendritic cell inflammatory responses

Background Heterosexual transmission remains the main route of HIV-1 transmission and female genital tract (FGT) inflammation increases the risk of infection. However, the mechanism(s) by which inflammation facilitates infection is not fully understood. In rhesus macaques challenged with simian immunodeficiency virus, dendritic cell (DC) mediated recruitment of CD4+ T cells to the FGT was critical for infection. The aim of this study was to delineate the mechanisms underlying DC-mediated HIV infection by comparing chemokine and pro-inflammatory cytokine production in response to transmitted founder (TF) and chronic infection (CI) Envelope (Env) pseudotyped viruses (PSV). Results Monocyte-derived DCs (MDDCs) were stimulated with PSV and recombinant gp140 representing matched TF and CI pairs of four individuals and cytokine secretion measured by multiplex immuno-assay. We found that 4/9 Env induced robust MDDC inflammatory responses and of those, three were cloned from TFs. Overall, TF Env induced MDDCs from healthy donors to secrete higher concentrations of inflammatory cytokines and chemokines than those from CI, suggesting TF Env were better inducers of inflammation. Assessing the signalling pathway associated with inflammatory cytokines, we found that PSV of matched TF and CI variants and a gp140 clone activated ERK and JNK to similar levels. Recombinant soluble DC-SIGN inhibited cytokine release and activation of ERK by PSV, suggesting that Env-DC-SIGN binding was partly involved in MDDC stimulation. Therefore, Env clones might differentially stimulate MDDC immune responses via alternative, yet unidentified signalling pathways. Conclusion Overall, this could suggest that the genetics of the virus itself influences inflammatory responses during HIV infection. In the absence of pre-existing infections, induction of greater inflammatory response by TFs might favour virus survival within the healthy FGT by driving an influx of target cells to sites of infection while suppressing immune responses via IL-10

Testing a global standard for quantifying species recovery and assessing conservation impact

Recognizing the imperative to evaluate species recovery and conservation impact, in 2012 the International Union for Conservation of Nature (IUCN) called for development of a “Green List of Species” (now the IUCN Green Status of Species). A draft Green Status framework for assessing species’ progress toward recovery, published in 2018, proposed 2 separate but interlinked components: a standardized method (i.e., measurement against benchmarks of species’ viability, functionality, and preimpact distribution) to determine current species recovery status (herein species recovery score) and application of that method to estimate past and potential future impacts of conservation based on 4 metrics (conservation legacy, conservation dependence, conservation gain, and recovery potential). We tested the framework with 181 species representing diverse taxa, life histories, biomes, and IUCN Red List categories (extinction risk). Based on the observed distribution of species’ recovery scores, we propose the following species recovery categories: fully recovered, slightly depleted, moderately depleted, largely depleted, critically depleted, extinct in the wild, and indeterminate. Fifty-nine percent of tested species were considered largely or critically depleted. Although there was a negative relationship between extinction risk and species recovery score, variation was considerable. Some species in lower risk categories were assessed as farther from recovery than those at higher risk. This emphasizes that species recovery is conceptually different from extinction risk and reinforces the utility of the IUCN Green Status of Species to more fully understand species conservation status. Although extinction risk did not predict conservation legacy, conservation dependence, or conservation gain, it was positively correlated with recovery potential. Only 1.7% of tested species were categorized as zero across all 4 of these conservation impact metrics, indicating that conservation has, or will, play a role in improving or maintaining species status for the vast majority of these species. Based on our results, we devised an updated assessment framework that introduces the option of using a dynamic baseline to assess future impacts of conservation over the short term to avoid misleading results which were generated in a small number of cases, and redefines short term as 10 years to better align with conservation planning. These changes are reflected in the IUCN Green Status of Species Standard