Effects of changes in the shape of the intracellular action potential on the peak-to-peak ratio of single muscle fibre potentials

In situ recording of the intracellular action potential (IAP) of human muscle fibres is not yet feasible, and consequently, knowledge about certain IAP characteristics of these IAPs is still limited. The ratio between the amplitudes of the second and first phases (the so-called peak-to-peak ratio, PPR) of a single fibre action potential (SFAP) is known to be closely related to the IAP profile. The PPR of experimentally recorded SFAPs has been found to be largely independent of changes in the fibre-to-electrode (radial) distance. The main goal of this paper is to analyze the effect of changes in different aspects of the IAP spike on the relationship between PPR and radial distance. Based on this analysis, we hypothesize about the characteristics of IAPs obtained experimentally. It was found that the sensitivity of the SFAP PPR to changes in radial distance is essentially governed by the duration of the IAP spike. Assuming that, for mammals, the duration of the IAP rising phase lies within the range 0.2-0.4 ms, we tentatively suggest that the duration of the IAP spike should be over approximately 0.75 ms, with the shape of the spike strongly asymmetric. These IAP characteristics broadly coincide with those observed in mammal IAPs.     

Interval timing in genetically modified mice: a simple paradigm

We describe a behavioral screen for the quantitative study of interval timing and interval memory in mice. Mice learn to switch from a short-latency feeding station to a long-latency station when the short latency has passed without a feeding. The psychometric function is the cumulative distribution of switch latencies. Its median measures timing accuracy and its interquartile interval measures timing precision. Next, using this behavioral paradigm, we have examined mice with a gene knockout of the receptor for gastrin-releasing peptide that show enhanced (i.e. prolonged) freezing in fear conditioning. We have tested the hypothesis that the mutants freeze longer because they are more uncertain than wild types about when to expect the electric shock. The knockouts however show normal accuracy and precision in timing, so we have rejected this alternative hypothesis. Last, we conduct the pharmacological validation of our behavioral screen using d -amphetamine and methamphetamine. We suggest including the analysis of interval timing and temporal memory in tests of genetically modified mice for learning and memory and argue that our paradigm allows this to be done simply and efficiently.     

Interactions between TIME and PIN could play a role in the system that controls the duration of diapause development and synchronization with seasonal cycles in the silkworm Bombyx mori*

The significance of winter cold in the termination of diapause was investigated with regards to TIME and PIN in eggs of the silkworm Bombyx mori. TIME (time interval measuring enzyme) is an ATPase that can measure time intervals by exhibiting a transitory burst of activation of the enzyme in accordance with diapause development, which requires cold for resumption of embryonic development in the silkworm. The possible timer function of TIME comprises a built‐in mechanism in the protein structure. TIME is a metallo‐glycoprotein consisting of 156 amino acid residues with a unique sequence in the N‐terminal region to which a sugar chain is attached. PIN (peptidyl inhibitory needle) inhibits the ATPase activity of TIME. PIN is not a simple enzyme inhibitor, but holds the timer by forming a time‐regulatory complex with TIME. The carbohydrate moiety of TIME is essential for the assembly of a high‐affinity PIN‐binding site within the timer motif of the TIME structure. The binding interaction between TIME and PIN was much tighter (nearly 1000 times) at 25°C than that at 4°C, as measured by fluorescence polarization. Because the logEC₅₀ at 4°C was approximately 7 nmol/L, PIN must dissociate from TIME at the physiological concentration of TIME in eggs in the winter cold. Based on the results of our study, we propose that the dissociation of the TIME–PIN complex in the winter cold cues a series of conformational changes of TIME, ultimately reaching the active form of ATPase which in turn causes the completion of diapause development and initiates new developmental programs.     

Use of the EM algorithm to detect QTL affecting multiple-traits in an across half-sib family analysis

QTL detection experiments in livestock species commonly use the half-sib design. Each male is mated to a number of females, each female producing a limited number of progeny. Analysis consists of attempting to detect associations between phenotype and genotype measured on the progeny. When family sizes are limiting experimenters may wish to incorporate as much information as possible into a single analysis. However, combining information across sires is problematic because of incomplete linkage disequilibrium between the markers and the QTL in the population. This study describes formulæ for obtaining MLEs via the expectation maximization (EM) algorithm for use in a multiple-trait, multiple-family analysis. A model specifying a QTL with only two alleles, and a common within sire error variance is assumed. Compared to single-family analyses, power can be improved up to fourfold with multi-family analyses. The accuracy and precision of QTL location estimates are also substantially improved. With small family sizes, the multi-family, multi-trait analyses reduce substantially, but not totally remove, biases in QTL effect estimates. In situations where multiple QTL alleles are segregating the multi-family analysis will average out the effects of the different QTL alleles.     

Uncertainty Analysis of Pesticide Residues in Drinking Water Risk Assessment

Pesticide residues in drinking water can vary significantly from day to day. However, water quality monitoring performed under the Safe Drinking Water Act (SDWA) at most community water systems (CWSs) is typically limited to four data points per year over a few years. Due to this limited sampling, likely maximum residues may be underestimated in risk assessment. In this work, a statistical methodology is proposed to study two types of uncertainties in observed samples and their propagated effect in risk estimates. The methodology was demonstrated using data from 16 CWSs that have three independent databases of atrazine residue to estimate the uncertainty of risk in infants and children. The results showed that in 85% of the CWSs, chronic risks predicted with the proposed approach may be two- to four-folds higher than that predicted with the current approach, wheras intermediate risks may be two- to three-folds higher in 50% of the CWSs. In 12% of the CWSs, however, the proposed methodology showed a lower intermediate risk. A closed-form solution of propagated uncertainty was developed to demonstrate the number of years (seasons) of data and sampling frequency needed to reduce the uncertainty of risk estimates. In general, this methodology provided good insight into the importance of addressing uncertainty of observed water quality data and the need to predict likely maximum residues in risk assessment.     

Fire frequency and time‐since‐fire effects on the open‐forest and woodland flora of Girraween National Park,south‐east Queensland,Australia

Abstract The effects of recent fire frequency and time‐since‐fire on plant community composition and species abundance in open‐forest and woodland vegetation in Girraween National Park, south‐east Queensland, Australia, were examined. Cover‐abundance data were collected for shrub and vine species in at least 10 400‐m² plots in each of four study areas. Study areas were within one community type and had burnt most recently either 4 or 9 years previously. Variations in fire frequency allowed us to compare areas that had burnt at least three times in the previous 25 years with less frequently burnt areas, and also woodlands that had experienced a 28‐year interfire interval with more frequently burnt areas. Although species richness did not differ significantly with either time‐since‐fire or fire frequency, both these factors affected community composition, fire frequency being the more powerful. Moisture availability also influenced floristics. Of the 67 species found in five or more plots, six were significantly associated with time‐since‐fire, whereas 11 showed a significant difference between more and less frequently burnt plots in each of the two fire‐frequency variables. Most species, however, did not vary in cover‐abundance with the fire regime parameters examined. Even those species that showed a marked drop in cover‐abundance when exposed to a particular fire regime generally maintained some presence in the community. Five species with the capacity to resprout after fire were considered potentially at risk of local extinction under regimes of frequent fire, whereas two species were relatively uncommon in long‐unburnt areas. Variable fire regimes, which include interfire intervals of at least 15 years, could be necessary for the continuity of all species in the community.     

神经放电加周期分岔中由随机自共振引起一类新节律

当改变实验性神经起步点细胞外[Ca^2 ]时,放电节律表现出从周期1节律转换为周期4节律的加周期分岔序列。其中,周期n节律转换为周期n 1节律的过程中(n=1,2,3)存在一种新的具有交替特征的节律,该新节律为周期n簇与周期n 1簇放电的交替,并且周期n 1簇的时间间隔序列呈现出整数倍特征。确定性神经放电理论模型(chay模型)只能模拟周期n节律直接到周期n 1节律的加周期分岔序列;而随机chay模型可以模拟实验中的加周期分岔过程和新节律。进一步,新节律被确认是经随机自共振机制产生的。这不仅解释了实验现象,也将随机自共振的产生区间从以前认识到的Hopf分岔点附近扩大到加周期分岔点附近,同时扩大了噪声在神经放电和神经编码中起重要作用的参数区间。     

R法遗传参数估值置信区间的计算方法和重复估计次数的研究

探讨R法遗传参数估值置信区间的计算方法和重复估计次数(NORE)对参数估值的影响,利用4种模型通过模拟产生数据集。基础群中公、母畜数分别为200和2000头,BLUP育种值选择5个世代。利用多变量乘法迭代(MMI)法,结合先决条件的共扼梯度(PCG)法求解混合模型方程组估计方差组分。用经典方法、Box-Cox变换后的经典方法和自助法计算参数估值的均数、标准误和置信区间。结果表明,重复估计次数较多时,3种方法均可;重复估计次数较少时,建议使用自助法。简单模型下需要较少的重复估计,但对于复杂模型则需要较多的重复估计。随模型中随机效应数的增加,直接遗传力高估。随着PCG和MMI轮次的增大,参数估值表现出低估的趋势。     

Mean difference in live-weight per incremental difference in body condition score estimated in multiple sheep breeds and crossbreds

Body condition score (BCS) is a subjective assessment of the proportion of body fat an animal possesses and is independent of frame size. There is a growing awareness of the importance of mature animal live-weight given its contribution to the overall costs of production of a sector. Because of the known relationship between BCS and live-weight, strategies to reduce live-weight could contribute to the favouring of animals with lesser body condition. The objective of the present study was to estimate the average difference in live-weight per incremental change in BCS, measured subjectively on a scale of 1 to 5. The data used consisted of 19 033 BCS and live-weight observations recorded on the same day from 7556 ewes on commercial and research flocks; the breeds represented included purebred Belclare (540 ewes), Charollais (1484 ewes), Suffolk (885 ewes), Texel (1695 ewes), Vendeen (140 ewes), as well as, crossbreds (2812 ewes). All associations were quantified using linear mixed models with the dependent variable of live-weight; ewe parity was included as a random effect. The independent variables were BCS, breed (n=6), stage of the inter-lambing interval (n=6; pregnancy, lambing, pre-weaning, at weaning, post-weaning and mating) and parity (1, 2, 3, 4 and 5+). In addition, two-way interactions were used to investigate whether the association between BCS and live-weight differed by parity, a period of the inter-lambing interval or breed. The association between BCS and live-weight differed by parity, by a period of the inter-lambing interval and by breed. Across all data, a one-unit difference in BCS was associated with 4.82 (SE=0.08) kg live-weight, but this differed by parity from 4.23 kg in parity 1 ewes to 5.82 kg in parity 5+ ewes. The correlation between BCS and live-weight across all data was 0.48 (0.47 when adjusted for nuisance factors in the statistical model), but this varied from 0.48 to 0.53 by parity, from 0.36 to 0.63 by stage of the inter-lambing interval and from 0.41 to 0.62 by breed. Results demonstrate that consideration should be taken of differences in BCS when comparing ewes on live-weight as differences in BCS contribute quite substantially to differences in live-weight; moreover, adjustments for differences in BCS should consider the population stratum, especially breed.