Automatic segmentation of surface EMG images: Improving the estimation of neuromuscular activity

Surface electromyograms (EMGs) recorded with a couple of electrodes are meant to comprise representative information of the whole muscle activation. Nonetheless, regional variations in neuromuscular activity seem to occur in numerous conditions, from standing to passive muscle stretching. In this study, we show how local activation of skeletal muscles can be automatically tracked from EMGs acquired with a bi-dimensional grid of surface electrodes (a grid of 8 rows and 15 columns was used). Grayscale images were created from simulated and experimental EMGs, filtered and segmented into clusters of activity with the watershed algorithm. The number of electrodes on each cluster and the mean level of neuromuscular activity were used to assess the accuracy of the segmentation of simulated signals. Regardless of the noise level, thickness of fat tissue and acquisition configuration (monopolar or single differential), the segmentation accuracy was above 60%. Accuracy values peaked close to 95% when pixels with intensity below ～70% of maximal EMG amplitude in each segmented cluster were excluded. When simulating opposite variations in the activity of two adjacent muscles, watershed segmentation produced clusters of activity consistently centered on each simulated portion of active muscle and with mean amplitude close to the simulated value. Finally, the segmentation algorithm was used to track spatial variations in the activity, within and between medial and lateral gastrocnemius muscles, during isometric plantar flexion contraction and in quiet standing position. In both cases, the regionalization of neuromuscular activity occurred and was consistently identified with the segmentation method.     

Probing the Role of CXC Motif in Chemokine CXCL8 for High Affinity Binding and Activation of CXCR1 and CXCR2 Receptors

All chemokines share a common structural scaffold that mediate a remarkable variety of functions from immune surveillance to organogenesis. Chemokines are classified as CXC or CC on the basis of conserved cysteines, and the two subclasses bind distinct sets of GPCR class of receptors and also have markedly different quaternary structures, suggesting that the CXC/CC motif plays a prominent role in both structure and function. For both classes, receptor activation involves interactions between chemokine N-loop and receptor N-domain residues (Site-I), and between chemokine N-terminal and receptor extracellular/transmembrane residues (Site-II). We engineered a CC variant (labeled as CC-CXCL8) of the chemokine CXCL8 by deleting residue X (CXC → CC), and found its structure is essentially similar to WT. In stark contrast, CC-CXCL8 bound poorly to its cognate receptors CXCR1 and CXCR2 (K_i > 1 μm). Further, CC-CXCL8 failed to mobilize Ca²⁺ in CXCR2-expressing HL-60 cells or recruit neutrophils in a mouse lung model. However, most interestingly, CC-CXCL8 mobilizes Ca²⁺ in neutrophils and in CXCR1-expressing HL-60 cells. Compared with the WT, CC-CXCL8 binds CXCR1 N-domain with only ∼5-fold lower affinity indicating that the weak binding to intact CXCR1 must be due to its weak binding at Site-II. Nevertheless, this level of binding is sufficient for receptor activation indicating that affinity and activity are separable functions. We propose that the CXC motif functions as a conformational switch that couples Site-I and Site-II interactions for both receptors, and that this coupling is critical for high affinity binding but differentially regulates activation.     

Rapid generation of rotavirus-specific human monoclonal antibodies from small-intestinal mucosa

The gut mucosal surface is efficiently protected by Abs, and this site represents one of the richest compartments of Ab-secreting cells in the body. A simple and effective method to generate Ag-specific human monoclonal Abs (hmAbs) from such cells is lacking. In this paper, we describe a method to generate hmAbs from single Ag-specific IgA- or IgM-secreting cells of the intestinal mucosa. We found that CD138-positive plasma cells from the duodenum expressed surface IgA or IgM. Using eGFP-labeled virus-like particles, we harnessed the surface Ig expression to detect rotavirus-specific plasma cells at low frequency (0.03-0.35%) in 9 of 10 adult subjects. Single cells were isolated by FACS, and as they were viable, further testing of secreted Abs by ELISPOT and ELISA indicated a highly specific selection procedure. Ab genes from single cells of three donors were cloned, sequenced, and expressed as recombinant hmAbs. Of 26 cloned H chain Ab genes, 22 were IgA and 4 were IgM. The genes were highly mutated, and there was an overrepresentation of the VH4 family. Of 10 expressed hmAbs, 8 were rotavirus-reactive (6 with K(d) < 1 × 10(-10)). Importantly, our method allows generation of hmAbs from cells implicated in the protection of mucosal surfaces, and it can potentially be used in passive vaccination efforts and for discovery of epitopes directly relevant to human immunity.     

Effects of wing polyphenism, aphid genotype and host plant chemistry on energy metabolism of the grain aphid, Sitobion avenae

Wing dimorphism has been proposed as a strategy to face trade-offs between flight capability and fecundity. In aphids, individuals with functional wings have slower development and lower fecundity compared with wingless individuals. However, differential maintenance costs between winged and wingless aphids have not been deeply investigated. In the current study, we studied the combined effect of wing dimorphism with the effects of aphid genotypes and of wheat hosts having different levels of chemical defences (hydroxamic acids, Hx) on adult body mass and standard metabolic rates (SMR) of winged and wingless morphs of the grain aphid, Sitobion avenae. We found that wingless aphids had higher body mass than winged aphids and that body mass also increased towards host with high Hx levels. Furthermore, winged aphids showed a plastic SMR in terms of Hx levels, whereas wingless aphids displayed a rigid reaction norm (significant interaction between morph condition and wheat host). These findings suggest that winged aphids have reduced adult size compared to wingless aphids, likely due to costs associated to the development of flight structure in early-life stages. These costs contrast with the absence of detectable metabolic costs related to fuelling and maintenance of the flight apparatus in adults.     

Long-term trends of epilimnetic and hypolimnetic bacteria and organic carbon in a deep holo-oligomictic lake

We analysed the long-term dynamics (1980–2007) of hypolimnetic and epilimnetic bacterial abundances and organic carbon concentrations, both dissolved (DOC) and particulate (POC), in the deep holo-oligomictic Lake Maggiore, included in the Southern Alpine Lakes Long-Term Ecological Research (LTER) site. During the 28 years of investigation, bacterial abundance and POC concentrations did not decrease with declining phosphorus concentrations, while DOC concentrations showed a pronounced decrease in the epi- and hypolimnion. We used the annual mean total lake heat content and total annual precipitation as climate-related variables, and in-lake total phosphorus as a proxy for trophic state. The model (forward stepwise regression, FSR) showed that reduced anthropogenic pressure was more significant than climate change in driving the trend in DOC concentrations. Bacterial dynamics in the hypolimnion mirrored the fluctuations observed in the epilimnion, but average cell abundance was three times lower. The FSR model indicates that bacterial number variability was dependent on POC in the epilimnion and DOC in the hypolimnion. In the hypolimnion, cell biovolumes for rod and coccal morphotypes were significantly larger than in the epilimnion.     

Morphological and molecular analysis of centropagids from the high Andean plateau (Copepoda: Calanoidea)

In small metazoan invertebrates classical taxonomic analyses can be ambiguous due to the limited number of morphological characters available. This difficulty can yield incorrect estimates of species richness or taxa distribution. The Boeckella genus has been described as the dominant taxon of zooplankton assemblages in the Andean biogeographical region. In this genus, taxonomic classification and delimitation of boundaries between species has long been problematic and controversial. Among South American centropagids Boeckella gracilipes has been regarded as one of the most broadly distributed species, its presence having been reported from Ecuador to Tierra del Fuego. However, in the high Andean plateau some centropagid populations identified as Boeckella gracilipes have also been considered as B. gracilipes titicacae or even identified as a different species, namely Boeckella titicacae. In an attempt to resolve the taxonomic status of the Centropagidae family from the high Andean plateau, we combined traditional and multivariate morphological analyses (integral approach) with the molecular phylogenetic approach. The results obtained allow us to conclude that centropagids collected from the high Andean plateau actually represent a different species, B. titicacae, not B. gracilipes. The phylogenetic reconstruction of the South American Centropagidae family indicated that B. gracilipes represents a sister taxon to B. titicacae. The present study stresses the usefulness of integrating alfa-taxonomy with morphometric and molecular approaches in order to resolve species boundaries, to determine geographical distributions and to investigate evolutionary processes.     

Human mortality seasonality in Castile-León, Spain, between 1980 and 1998: the influence of temperature, pressure and humidity

This study was carried out in the region of Castile and Leon, Spain, from 1980 to 1998 and analyzes the relationship between the number of monthly deaths caused by cardiovascular, respiratory and digestive diseases and three meteorological variables: temperature, pressure and humidity. One of the innovations in this study is the application of principal component analysis in a way that differs from its usual application: one single series representing the whole region was constructed for each meteorological variable from the series of eight weather stations. Annual and seasonal mortality trends were also studied. Cardiovascular diseases are the leading cause of death in Castile and Leon. The mortality related to cardiovascular, respiratory and digestive systems shows a statistically significant rising trend across the study period (an annual increase of 6, 16 and 4‰, respectively). The pressure at which mortality is lowest is approximately the same for all causes of death (about 915 hPa), but temperature values vary greatly (16.8–19.7°C for the mean, 10.9–18.1°C for the minimum, and 24.1–27.2°C for the maximum temperature). The most comfortable temperatures for patients with cardiovascular diseases (16.8°C) are apparently lower than those for patients with respiratory diseases (18.1°C), which are, in turn, lower than in the case of diseases of the digestive system (19.7°C). Finally, the optimal humidity for patients with respiratory diseases is the lowest (24%) among the diseases, and the highest (51%) corresponds to diseases of the digestive system, while the optimal relative humidity for the cardiovascular system is 45%.     

Effect of sexual segregation on host-parasite interaction: Model simulation for abomasal parasite dynamics in alpine ibex (Capraibex)

We investigated whether sexual segregation might affect parasite transmission and host dynamics, hypothesising that if males are the more heavily infected sex and more responsible for the transmission of parasite infections, female avoidance of males and the space they occupy could reduce infection rates. A mathematical model, simulating the interaction between abomasal parasites and a hypothetical alpine ibex (Capraibex) host population composed of its two sexes, was developed to predict the effect of different degrees of sexual segregation on parasite intensity and on host abundance. The results showed that when females tended to be segregated from males, and males were distributed randomly across space, the impact of parasites was the lowest, resulting in the highest host abundance, with each sex having the lowest parasite intensity. The predicted condition that minimises the impact of parasites in our model was the one closest to that observed in nature where females actively seek out the more segregated sites while males are less selective in their ranging behaviour. The overlapping of field observation with the predicted optimal strategy lends support to our idea that there might be a connection between parasite transmission and sexual segregation. Our simulations provide the biological boundaries of host-parasite interaction needed to determine a parasite-mediated effect on sexual segregation and a formalised null hypothesis against which to test future field experiments.