Clustering vertical ground reaction force curves produced during countermovement jumps

The aim of this study is to assess and compare the performance of commonly used hierarchical, partitional (k-means) and Gaussian model-based (Expectation–Maximization algorithm) clustering techniques to appropriately identify subgroup patterns within vertical ground reaction force data, using a continuous waveform analysis. In addition, we also compared the performance across each technique using normalized and non-normalization input scores. Both generated and real data (one hundred and twenty two vertical jumps) were analyzed. The performance of each cluster technique was measured by assessing the ability to explain variances in jump height using a stepwise regression analysis. Only k-means (normalized scores; 82%) and hierarchical clustering (normalized scores; 85%) were able to extend the ability to describe variances in jump height beyond that achieved using the group analysis (i.e. one cluster; 78%). Further, our findings strongly indicate the need to normalize the input data (similarity measure) when clustering. In contrast to the group analysis, the subgroup analysis was able to identify cluster specific phases of variance, which improved the ability to explain variances in jump height, due to the identification of cluster specific predictor variables. Our findings therefore highlight the benefit of performing a subgroup analysis and may explain, at least in part, the contrasting findings between previous studies that used a single group level of analysis.     

The Brain Ages Optimally to Model Its Environment: Evidence from Sensory Learning over the Adult Lifespan

The aging brain shows a progressive loss of neuropil, which is accompanied by subtle changes in neuronal plasticity, sensory learning and memory. Neurophysiologically, aging attenuates evoked responses—including the mismatch negativity (MMN). This is accompanied by a shift in cortical responsivity from sensory (posterior) regions to executive (anterior) regions, which has been interpreted as a compensatory response for cognitive decline. Theoretical neurobiology offers a simpler explanation for all of these effects—from a Bayesian perspective, as the brain is progressively optimized to model its world, its complexity will decrease. A corollary of this complexity reduction is an attenuation of Bayesian updating or sensory learning. Here we confirmed this hypothesis using magnetoencephalographic recordings of the mismatch negativity elicited in a large cohort of human subjects, in their third to ninth decade. Employing dynamic causal modeling to assay the synaptic mechanisms underlying these non-invasive recordings, we found a selective age-related attenuation of synaptic connectivity changes that underpin rapid sensory learning. In contrast, baseline synaptic connectivity strengths were consistently strong over the decades. Our findings suggest that the lifetime accrual of sensory experience optimizes functional brain architectures to enable efficient and generalizable predictions of the world.     

Worse Renal Disease in Postmenopausal F2[Dahl S x R]-Intercross Rats: Detection of Novel QTLs Affecting Hypertensive Kidney Disease

The prevalence of hypertension increases after menopause with 75% of postmenopausal women developing hypertension in the United States, along with hypertensive end organ diseases. While human and animal model studies have indicated a protective role for estrogen against cardiovascular disease and glomerulosclerosis, clinical studies of hormone replacement therapy in postmenopausal women have shown polar results with some improvement in hypertension but worsening of hypertensive kidney disease, or no effect at all. These observations suggest that the pathogenesis of postmenopausal hypertension and its target organ complications is more complex than projected, and that loss of endogenous estrogens induces epigenetic changes that alter genetic susceptibility to end-organ complications per se resulting in pathogenetic mechanisms beyond correction by hormone replacement. We studied postmenopausal-induced changes in renal disease and performed a total genome scan for quantitative trait loci (QTLs) affecting kidney disease in postmenopausal 16m-old F2[Dahl S x R]-intercross female rats. We used glomerular injury score (GIS) as quantitative trait. We compared QTLs amongst premenopausal, ovariectomized and postmenopausal F2[Dahl S x R]-intercross rats using identical phenotype characterization. Postmenopausal F2[Dahl S x R]-intercross rats exhibited increased hypertensive glomerulosclerosis (P<0.01) and equivalent levels of kidney disease when compared to premenopausal and ovariectomized F2[Dahl S x R]-intercross rats respectively. We detected three significant to highly significant GIS-QTLs (GIS-pm1 on chromosome 4, LOD 3.54; GIS-pm2 on chromosome 3, LOD 2.72; GIS-pm3 on chromosome 5, LOD 2.37) and two suggestive GIS-QTLs (GIS-pm4 on chromosome 2, LOD 1.70; GIS-pm5 on chromosome 7, LOD 1.28), all of which were unique to this postmenopausal population. Detection of increased renal disease phenotype in postmenopausal and ovariectomized subjects suggests a protective role of ovarian hormones. Furthermore, the detection of distinct GIS-QTLs in postmenopausal intercross female rats suggests that distinct genetic mechanisms underlie hypertensive glomerulosclerosis in premenopausal and postmenopausal states.     

Alteration of the structural attributes of a compact clay loam soil by growth of a perennial grass crop

Soil aggregate stability, organic matter content, pH, bulk density, strength, and macropore attributes were assessed in order to evaluate the influence of grass root growth in a field sward. The amount of grass grown was varied by varying the quantity of applied nitrogen fertilizer: following one year with a uniform application rate, nitrogen fertilizer was applied over the subsequent three years to a compact soil at zero (N0), moderate (N1) and high (N2) rates. Differences in herbage production were evident in the three years of the contrasting nitrogen treatments. An index of soil aggregate stability increased in response to the increased grass growth promoted by heavier applications of nitrogen, but both bulk density and vane shear strength were unchanged. Binary images of the soil solid and pore space showed that for each treatment the largest volume of macropores occurred close to the surface, particularly in N0 where there was more pore space than in either N1 or N2. Analysis of the pore structure attributes of the binary images revealed further differences between treatments, in particular, at 40–80 mm depth, the soil in treatment N0 had fewer and smaller pores, and greater distance between pores, than the soil in the N1 and N2 treatments. The larger macropore volume in N1 and N2 constituted a major portion of the air-filled porosity when the soil was relatively wet. It was concluded that the root growth in the intensively cropped grassland was conducive to maintenance of a relatively stable and porous soil structure. An attendant increase in soil acidity close to the soil surface was a disadvantage of the larger nitrogen inputs.     

Effect of gamma radiation on sodium channels in different conformations in neuroblastoma cells

We studied the dose-response relationship between gamma radiation and batrachotoxin-stimulated sodium influx in neuroblastoma cells in tissue culture. We also tested the hypothesis that changes in sodium channel conformation may alter the radiosensitivity of the channel. We found that gamma radiation inhibited toxin-stimulated 22Na uptake at doses beyond a threshold of 200-300 Gy. No effects were seen following doses below 100 Gy. This inhibition of sodium permeability was seen when the cells were irradiated with sodium channels in the closed or inactivated, nonconducting states. However, when the channels were in the toxin-opened, conducting state, gamma radiation had no effect at doses up to 2000 Gy. Our results support earlier electrophysiological studies that showed that high doses of ionizing radiation are required to produce a measurable decrease in sodium permeability. In addition, our data suggest that by changing the sodium channel conformation, batrachotoxin appears to alter radiosensitive chemical bonds in the gating or ion-conducting portion of the channel.     

Pulmonary Thromboembolism Presenting as Asthma

When a patient presents with wheezing, pulmonary embolism is not usually considered as a possible cause. However, undoubtedly bronchoconstriction can be caused by pulmonary emboli and occasionally wheezing may be so obvious as to suggest a diagnosis of bronchial asthma. Eleven cases are reported in which wheezing was attributable to recurrent pulmonary emboli and one in which it was a clamant feature after a single embolic incident.     

Sodium ionic and gating currents in mammalian cells

Ionic and gating currents from voltage-gated sodium channels were recorded in mouse neuroblastoma cells using the path-clamp technique. Displacement currents were measured from whole-cell recordings. The gating charge displaced during step depolarizations increased with the applied membrane potential and reached saturating levels above 20 mV Prolonged large depolarizations produced partial immobilization of the gating charge, and only about one third of the displaced charge was quickly reversed upon return to negative holding potentials. The activation and inactivation properties of macroscopic sodium currents were characterized by voltage-clamp analysis of large outside-out patches and the single-channel conductance was estimated from nonstationary noise analysis. The general properties of the sodium channels in mouse neuroblastoma cells are very similar to those previously reported for various preparations of invertebrate and vertebrate nerve cells. Offprint requests to: O. Moran     

Bias in manta tow surveys of Acanthaster planci

To investigate the biases associated with manta tow surveys of Acanthaster planci, counts obtained by manta-towed observers were compared with counts made on SCUBA swims under a limited range of conditions. Five 10 m wide strip transects on different parts of two reefs and with different densities of A. planci were surveyed. On average, 22.7% of starfish counted on SCUBA searches were counted on manta tows over the same transect (SD=12.0%, n=69). This proportion is termed sightability. As sightability decreases with increasing transect width, we estimate that, on average, less than 5% of the A. planci present are counted on routine manta tows which are conducted over transect of undefined width. Multiple regression analysis was used to determine which of 33 variables explained most of the variation in sightability in 10 m wide transects. The most influential variables were the proportion of cryptic starfish and an index of the degree of reef complexity. A regression equation designed to improve estimates of the abundance of A. planci on routine manta tows was developed. However, as it explained only 39% of the variation in sightability, this equation is of limited value in stabilising the negative bias associated with manta tow counts. In view of the variability of this bias, the manta tow technique is not suitable for estimating absolute densities of A. planci. Manta tow surveys are appropriate for identifying gross relative differences between densities of A. planci, and thus for determining broad-scale patterns of abundance. As such, they are a cost-effective method of estimating the geographical extent of A. planci outbreaks.