Models and Hypotheses

Complex linear appearing structures and networks (e.g. blood vessels, leaf veins, nerves) are formed reproducibly during the development of nearly every organism, but the molecular mechanism leading to such patterns is still unknown. A model is proposed in which a few simple coupled biochemical reactions are able to generate such structures. Among undifferentiated cells, a local peak of differentiation-inducing substance (activator) is formed by autocatalysis and lateral inhibition. The activator peak triggers the differentiation of the cell at that location. Due to changes in metabolism, the differentiated cell repels the activator peak and drives it to a neighbouring cell which then also differentiates. The repulsion between the activator peak and the already differentiated cells forces the activator peak to move ahead of the tip of the extending filament. Long filaments of differentiated cells may be formed, which can split, branch laterally, reconnect with each other and grow towards specific target cells. Partial differential equations describing the mutual interaction of the substances involved were presented and solved with a computer. The resulting patterns show self-regulating properties and other features found in the leaf vascular system, the pattern of tracheae in insect epidermis, and other biological networks.     

Models and muddles

The first model in marine ecology was that of the biocoenosis by Moebius (1883), conceived as a self-contained box limited by a finite food resource. This box was almost immediately broken bown by Dean (1893) and demonstrated to be a bit of a muddle, but the concept and the general term has persisted. Today, the construction of elaborate diagrams and mystico-mathematical representations of assumed relationships powered by selected values is a favorite pastime of many ecologists and environmental engineers. When taken with a grain of salt (preferably benzoate of soda), such models may stimulate further thought. Fisheries biologists have had some success with single species or paucispecific models, but complex models require simplification and selection of data unrepresentative of nature. A model which is simply an elaborate mathematical summary of a textbook does not tell us much more than we allready know, and its formulation involves a questionable diversion of funds.     

Requirements on Models and Models of Active Transport of Ions in Biomembranes

Requirements on models of the active transport of ions in biomembranes have been formulated. The basic requirements include an explicit dependence of the resting potential and intracellular concentrations of ions on the difference of ATP-ADP chemical potentials, a consideration of the reversibility of the ionic pump operation, a correlation between theoretical and experimental data on the resting potential and intracellular concentrations of ions for different types of cells, the pump efficiency approaching 100%, and a tendency of the resting potential to the Donnan potential if the active transport is blocked. A model satisfying the aforementioned requirements has been proposed by the authors as an example.     

Mouse Models of Osteoarthritis: A Summary of Models and Outcomes Assessment

Osteoarthritis (OA) is a multidimensional health problem and a common chronic disease. It has a substantial impact on patient quality of life and is a common cause of pain and mobility issues in older adults. The functional limitations, lack of curative treatments, and cost to society all demonstrate the need for translational and clinical research. The use of OA models in mice is important for achieving a better understanding of the disease. Models with clinical relevance are needed to achieve 2 main goals: to assess the impact of the OA disease (pain and function) and to study the efficacy of potential treatments. However, few OA models include practical strategies for functional assessment of the mice. OA signs in mice incorporate complex interrelations between pain and dysfunction. The current review provides a comprehensive compilation of mouse models of OA and animal evaluations that include static and dynamic clinical assessment of the mice, merging evaluation of pain and function by using automatic and noninvasive techniques. These new techniques allow simultaneous recording of spontaneous activity from thousands of home cages and also monitor environment conditions. Technologies such as videography and computational approaches can also be used to improve pain assessment in rodents but these new tools must first be validated experimentally. An example of a new tool is the digital ventilated cage, which is an automated home-cage monitor that records spontaneous activity in the cages.

Osteoarthritis (OA) is a multidimensional health problem and a common chronic disease.³⁶ Functional limitations, the absence of curative treatments, and the considerable cost to society result in a substantial impact on quality of life.⁷⁶ Historically, OA has been described as whole joint and whole peri-articular diseases and as a systemic comorbidity.^9,111 OA consists of a disruption of articular joint cartilage homeostasis leading to a catabolic pathway characterized by chondrocyte degeneration and destruction of the extracellular matrix (ECM). Low-grade chronic systemic inflammation is also actively involved in the process.^42,92 In clinical practice, mechanical pain, often accompanied by a functional decline, is the main reason for consultations. Recommendations to patients provide guidance for OA management.^{22, 33,49,86} Evidence-based consensus has led to a variety of pharmacologic and nonpharmacologic modalities that are intended to guide health care providers in managing symptomatic patients. Animal-based research is of tremendous importance for the study of early diagnosis and treatment, which are crucial to prevent the disease progression and provide better care to patients.The purpose of animal-based OA research is 2-fold: to assess the impact of the OA disease (pain and function) and to study the efficacy of a potential treatment.^18,67 OA model species include large animals such as the horse, goat, sheep, and dog, whose size and anatomy are expected to better reflect human joint conditions. However, small animals such as guinea pig, rabbit, mouse, and rat represent 77% of the species used.^1,87 In recent years, mice have become the most commonly used model for studying OA. Mice have several advantageous characteristics: a short development and life span, easy and low-cost breeding and maintenance, easy handling, small joints that allow histologic analysis of the whole joint,³² and the availability of genetically modified lines.¹⁰⁸ Standardized housing, genetically defined strains and SPF animals reduce the genetic and interindividual acquired variability. Mice are considered the best vertebrate model in terms of monitoring and controlling environmental conditions.^7,14,15,87 Mouse skeletal maturation is reached at 10 wk, which theoretically constitutes the minimal age at which mice should be entered into an OA study.^64,87,102 However, many studies violate this limit by testing mice at 8 wk of age.Available models for OA include the following (32,111 physical activity and exercise induced OA; noninvasive mechanical loading (repetitive mild loading and single-impact injury); and surgically induced (meniscectomy models or anterior cruciate ligament transection). The specific model used would be based on the goal of the study.⁷ For example, OA pathophysiology, OA progression, and OA therapies studies could use spontaneous, genetic, surgical, or noninvasive models. In addition, pain studies could use chemical models. Lastly, post-traumatic studies would use surgical or noninvasive models; the most frequently used method is currently destabilization of the medial meniscus,³² which involves transection of the medial meniscotibial ligament, thereby destabilizing the joint and causing instability-driven OA. An important caveat for mouse models is that the mouse and human knee differ in terms of joint size, joint biomechanics, and histologic characteristics (layers, cellularity),^32,64 and joint differences could confound clinical translation.¹⁰ Table 1. Mouse models of osteoarthritis.

Multinomial Distribution and Ascertainment Models

In this paper general ascertainment models are studied relaxing the strong assumption of complete dominance. Probabilitis of ascertaiment for both the complete and incomplete models depending on family size and register size for two types of affected individuals are derived.     

新生血管生成模型及应用

新生血管生成包括血管发生和微血管生成。微血管生成也称血管新生,在胚胎发育、正常生理和病理生理过程中均发挥重要作用。近年来研究发现,肿瘤、糖尿病视网膜病变和风湿性关节炎等疾病的发生发展均与新生血管生成有关,而抑制血管生成已成为治疗这些疾病的有效策略。建立新生血管生成模型对研究该类疾病的分子机制和研发相关的治疗药物有极其重要的价值。为此,我们简要综述近年来新生血管生成模型及其应用进展。     

Models of race and cline

Computer models have been constructed to depict in the form of two-dimensional maps the effect of local selection on gene frequencies, particularly where partial barriers to gene flow are present at some points in an area. It was found that small amounts of uniform gene flow between foci of contrasting selection tend to produce evenly spaced isogenes, giving a “clinal” pattern. The interposition of partial barriers causes isogenes to become closer together in the region of the barriers and to become parallel to the barriers. A corollary result is that in the region of the barriers the isogene systems for different genes tend to become parallel to one another even though the exact foci of active selection for the genes do not coincide. This resembles a “racial” rather than “clinal” trait distribution. It was further observed that if a focus of active selection was peripheral in position (i.e., far from a genetic barrier) a clinal pattern extended across the area it affected between it and the barrier. If such a focus lies close to the barrier, the area it affects becomes rather uniform in gene frequency, with the “hinterland” approximating the gene frequency of the focus of active selection. On the basis of these models interpretation of the distribution of cold-adapted Mongoloid traits, and of the distribution of skin color across Europe and Africa, are suggested.     

Spatial Uncertainty and Ecological Models

Applied ecological models that are used to understand and manage natural systems often rely on spatial data as input. Spatial uncertainty in these data can propagate into model predictions. Uncertainty analysis, sensitivity analysis, error analysis, error budget analysis, spatial decision analysis, and hypothesis testing using neutral models are all techniques designed to explore the relationship between variation in model inputs and variation in model predictions. Although similar methods can be used to answer them, these approaches address different questions. These approaches differ in (a) whether the focus is forward or backward (forward to evaluate the magnitude of variation in model predictions propagated or backward to rank input parameters by their influence); (b) whether the question involves model robustness to large variations in spatial pattern or to small deviations from a reference map; and (c) whether processes that generate input uncertainty (for example, cartographic error) are of interest. In this commentary, we propose a taxonomy of approaches, all of which clarify the relationship between spatial uncertainty and the predictions of ecological models. We describe existing techniques and indicate a few areas where research is needed.     

Which Models Are Appropriate for Six Subtropical Forests: Species-Area and Species-Abundance Models

The species-area relationship is one of the most important topic in the study of species diversity, conservation biology and landscape ecology. The species-area relationship curves describe the increase of species number with increasing area, and have been modeled by various equations. In this paper, we used detailed data from six 1-ha subtropical forest communities to fit three species-area relationship models. The coefficient of determination and F ratio of ANOVA showed all the three models fitted well to the species-area relationship data in the subtropical communities, with the logarithm model performing better than the other two models. We also used the three species-abundance distributions, namely the lognormal, logcauchy and logseries model, to fit them to the species-abundance data of six communities. In this case, the logcauchy model had the better fit based on the coefficient of determination. Our research reveals that the rare species always exist in the six communities, corroborating the neutral theory of Hubbell. Furthermore, we explained why all species-abundance figures appeared to be left-side truncated. This was due to subtropical forests have high diversity, and their large species number includes many rare species.     

眼镜蛇伤模型造模探讨及多项指标的动态观察

目的 探讨眼镜蛇伤模型的造模方法并观察模型多项指标的动态变化。方法 用中华眼镜蛇毒于家兔左小腿作皮下注射制作眼镜蛇伤模型,并分别于注蛇毒前1天,注蛇毒后6h,24h和7天从家兔耳缘静脉采血作血液和生化等多项指标的检查。结果 与生理盐水组相比,眼镜蛇毒组的家兔在注毒后数小时至24h可出现炎症反应和急性弥漫性血管内凝血(DIC),心功能及水盐代谢亦受到一些影响。结论 利用家兔可制作出眼镜蛇伤模型。     

Hidden Markov Models and Animal Behaviour

This paper proposes the use of hidden Markov time series models for the analysis of the behaviour sequences of one or more animals under observation. These models have advantages over the Markov chain models commonly used for behaviour sequences, as they can allow for time-trend or expansion to several subjects without sacrificing parsimony. Furthermore, they provide an alternative to higher-order Markov chain models if a first-order Markov chain is unsatisfactory as a model. To illustrate the use of such models, we fit multivariate and univariate hidden Markov models allowing for time-trend to data from an experiment investigating the effects of feeding on the locomotory behaviour of locusts (Locusta migratoria).     

度量误差模型及其应用

本文介绍度量误差模型的基本概念和参数估计的基本结果以及与通常回归之间的关系．并讨论了这个模型在生物学中应用的可能性．     

Hans Ussing, Experiments and Models

The article describes work and impact of Hans H. Ussing, a founder of epithelial physiology. Emphasis is on Ussing's model of epithelial transport, which showed early how a complex function can arise from a few basic principles. The KJU-model was developed 1958 for the amphibian epidermis and later applied and adapted to many epithelia, but especially to those that express amiloride-sensitive sodium channels in their apical membrane. Some of the subsequent research dealing with such channels and their cellular environment is briefly reviewed. The ideas of Hans Ussing were and are an inspiration to many of us, who continue to work in the way Ussing has taught us.