Information filtering by synchronous spikes in a neural population

Information about time-dependent sensory stimuli is encoded by the spike trains of neurons. Here we consider a population of uncoupled but noisy neurons (each subject to some intrinsic noise) that are driven by a common broadband signal. We ask specifically how much information is encoded in the synchronous activity of the population and how this information transfer is distributed with respect to frequency bands. In order to obtain some insight into the mechanism of information filtering effects found previously in the literature, we develop a mathematical framework to calculate the coherence of the synchronous output with the common stimulus for populations of simple neuron models. Within this frame, the synchronous activity is treated as the product of filtered versions of the spike trains of a subset of neurons. We compare our results for the simple cases of (1) a Poisson neuron with a rate modulation and (2) an LIF neuron with intrinsic white current noise and a current stimulus. For the Poisson neuron, formulas are particularly simple but show only a low-pass behavior of the coherence of synchronous activity. For the LIF model, in contrast, the coherence function of the synchronous activity shows a clear peak at high frequencies, comparable to recent experimental findings. We uncover the mechanism for this shift in the maximum of the coherence and discuss some biological implications of our findings.     

Phylogenomics of the reproductive parasite Wolbachia pipientis wMel: a streamlined genome overrun by mobile genetic elements

The complete sequence of the 1,267,782 bp genome of Wolbachia pipientis wMel, an obligate intracellular bacteria of Drosophila melanogaster, has been determined. Wolbachia, which are found in a variety of invertebrate species, are of great interest due to their diverse interactions with different hosts, which range from many forms of reproductive parasitism to mutualistic symbioses. Analysis of the wMel genome, in particular phylogenomic comparisons with other intracellular bacteria, has revealed many insights into the biology and evolution of wMel and Wolbachia in general. For example, the wMel genome is unique among sequenced obligate intracellular species in both being highly streamlined and containing very high levels of repetitive DNA and mobile DNA elements. This observation, coupled with multiple evolutionary reconstructions, suggests that natural selection is somewhat inefficient in wMel, most likely owing to the occurrence of repeated population bottlenecks. Genome analysis predicts many metabolic differences with the closely related Rickettsia species, including the presence of intact glycolysis and purine synthesis, which may compensate for an inability to obtain ATP directly from its host, as Rickettsia can. Other discoveries include the apparent inability of wMel to synthesize lipopolysaccharide and the presence of the most genes encoding proteins with ankyrin repeat domains of any prokaryotic genome yet sequenced. Despite the ability of wMel to infect the germline of its host, we find no evidence for either recent lateral gene transfer between wMel and D. melanogaster or older transfers between Wolbachia and any host. Evolutionary analysis further supports the hypothesis that mitochondria share a common ancestor with the α-Proteobacteria, but shows little support for the grouping of mitochondria with species in the order Rickettsiales. With the availability of the complete genomes of both species and excellent genetic tools for the host, the wMel–D. melanogaster symbiosis is now an ideal system for studying the biology and evolution of Wolbachia infections.     

Signaling lymphocytic activation molecule (CDw150) is homophilic but self-associates with very low affinity

Signaling lymphocytic activating molecule ((SLAM) CDw150) is a glycoprotein that belongs to the CD2 subset of the immunoglobulin superfamily and is expressed on the surface of activated T- and B-cells. It has been proposed that SLAM is homophilic and required for bidirectional signaling during T- and B-cell activation. Previous work has suggested that the affinity of SLAM self-association might be unusually high, undermining the concept that protein interactions mediating transient cell-cell contacts, such as those involving leukocytes, have to be weak in order that such contacts are readily reversible. Using surface plasmon resonance-based methods and analytical ultracentrifugation (AUC), we confirm that SLAM is homophilic. However, we also establish a new theoretical treatment of surface plasmon resonance-derived homophilic binding data, which indicates that SLAM-SLAM interactions (solution K(d) approximately 200 micrometer) are in fact considerably weaker than most other well characterized protein-protein interactions at the cell surface (solution K(d) approximately 0.4-20 micrometer), a conclusion that is supported by the AUC analysis. Whereas further analysis of the AUC data imply that SLAM could form "head to head" dimers spanning adjacent cells, the very low affinity raises important questions regarding the physiological role and/or properties of such interactions.     

Psychosocial Factors of Antenatal Anxiety and Depression in Pakistan: Is Social Support a Mediator?

Introduction

Pregnancy is generally viewed as a time of fulfillment and joy; however, for many women it can be a stressful event. In South Asia it is associated with cultural stigmas revolving around gender discrimination, abnormal births and genetic abnormalities.

Methodology

This cross-sectional study was done at four teaching hospitals in Lahore from February, 2014 to June, 2014. A total of 500 pregnant women seen at hospital obstetrics and gynecology departments were interviewed with a questionnaire consisting of three sections: demographics, the Hospital Anxiety and Depression Scale (HADS) and the Social Provisions Scale (SPS). Pearson’s chi-squared test, bivariate correlations and multiple linear regression were used to analyze associations between the independent variables and scores on the HADS and SPS.

Results

Mean age among the 500 respondents was 27.41 years (5.65). Anxiety levels in participants were categorized as normal (145 women, 29%), borderline (110, 22%) or anxious (245, 49%). Depression levels were categorized as normal (218 women, 43.6%), borderline (123, 24.6%) or depressed (159, 31.8%). Inferential analysis revealed that higher HADS scores were significantly associated with lower scores on the SPS, rural background, history of harassment, abortion, cesarean delivery and unplanned pregnancies (P < .05). Social support (SPS score) mediated the relationship between the total number of children, gender of previous children and HADS score. Women with more daughters were significantly more likely to score higher on the HADS and lower on the SPS, whereas higher numbers of sons were associated with the opposite trends in the scores (P < .05).

Conclusion

Because of the predominantly patriarchal sociocultural context in Pakistan, the predictors of antenatal anxiety and depression may differ from those in developed countries. We therefore suggest that interventions designed and implemented to reduce antenatal anxiety and depression should take into account these unique factors.     

CD161 (human NKR-P1A) signaling in NK cells involves the activation of acid sphingomyelinase

NK and NKT cells play a major role in both innate immunity and in influencing the development of adaptive immune responses. CD161 (human NKR-P1A), a protein encoded in the NK gene complex, is a major phenotypic marker of both these cell types and is thought to be involved in the regulation of NK and NKT cell function. However, the mechanisms of action and signaling pathways of CD161 are poorly understood. To identify molecules able to interact with the cytoplasmic tail of human CD161 (NKR-P1A), we have conducted a yeast two-hybrid screen and identified acid sphingomyelinase as a novel intracellular signaling pathway linked to CD161. mAb-mediated cross-linking of CD161, in both transfectants and primary human NK cells, triggers the activation of acid, but not neutral sphingomyelinase. The sphingomyelinases represent the catabolic pathway for N-acyl-sphingosine (ceramide) generation, an emerging second messenger with key roles in the induction of apoptosis, proliferation, and differentiation. These data therefore define a novel signal transduction pathway for the CD161 (NKR-P1A) receptor and provide fresh insights into NK and NKT cell biology.     

New insights into the pathogenesis of glucocorticoid-induced avascular necrosis: microarray analysis of gene expression in a rat model

Introduction  

Avascular necrosis of the femoral head (ANFH) occurs variably after exposure to corticosteroids. Microvascular thrombosis is a common pathological finding. Since systemic thrombophilia is only weakly linked with ANFH, we propose that microvascular vessel pathology may be more related to local endothelial dysfunction and femoral head apoptosis. Corticosteroid effects on the endothelium and resultant apoptosis have been reported. We hypothesize that corticosteroids contribute to a differential gene expression in the femoral head in rats with early ANFH.