共查询到20条相似文献,搜索用时 15 毫秒
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KAMEMOTO FRED I.; KATO KENNETH N.; TUCKER LOIS E. 《Integrative and comparative biology》1966,6(2):213-219
The possible role of the neurosecretory system in regulationof salt and water has been studied in the annelids and crustaceans.In the earthworm, Lumbricus terrestris, a brain factor influences'the salt and osmotic concentration of the blood and coelomicfluid. Removal of the brain results in the increase of waterinflux with a decrease in the salt and osmotic concentrationsof the body fluids. The decreases in salt and osmotic concentrationscan be prevented by the implantation of the brain or the injectionof brain homogenates. In the freshwater crayfish, Procambarus clarkii, a factor, presumablysecreted in the brain and released in the eyestalk, seems tomaintain the normal permeability of the body surfaces to water.Eyestalk removal, which eliminates the release site, resultsin the increased influx of water with a decrease in the saltconcentration of the blood. A brain factor also seems to beinvolved in maintaining the sodium and osmotic concentrationsof the blood. In the semi-terrestrial grapsid crab, Metopograpsus messor,the thoracic ganglion, under the control of an eyestalk element,secretes a factor involved in increasing the permeability ofthe body surfaces to water. The removal of the eyestalks, theimplantation of the thoracic ganglion, or the injection of extractsof thoracic ganglia, results in changes in the osmotic concentrationof the blood tending toward that of the medium. In all threespecies studied, the neuroendocrine factors seem to be involvedprimarily in the regulation of the permeability of the bodysurfaces to water. 相似文献
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Geiser F 《Comparative biochemistry and physiology. Part A, Molecular & integrative physiology》2008,150(2):176-180
Endothermic thermoregulation in small, altricial mammals and birds develops at about one third to half of adult size. The small size and consequently high heat loss in these young should result in more pronounced energetic challenges than in adults. Thus, employing torpor (a controlled reduction of metabolic rate and body temperature) during development would allow them to save energy. Although torpor during development in endotherms is likely to occur in many species, it has been documented in only a few. In small, altricial birds (4 orders) and marsupials (1 order), which are poikilothermic at hatching/birth, the development of competent endothermic thermoregulation during cold exposure appears to be concurrent with the capability to display torpor (i.e. poikilothermy is followed by heterothermy), supporting the view that torpor is phylogenetically old and likely plesiomorphic. In contrast, in small, altricial placental mammals (2 orders), poikilothermy at birth is followed first by a homeothermic phase after endothermic thermoregulation is established; the ability to employ torpor develops later (i.e. poikilothermy-homeothermy-heterothermy). This suggests that in placentals torpor is a derived trait that evolved secondarily after a homeothermic phase in certain taxa perhaps as a response to energetic challenges. As mammals and birds arose from different reptilian lineages, endothermy likely evolved separately in the two classes, and given that the developmental sequence of torpor differs between marsupials and placentals, torpor seems to have evolved at least thrice. 相似文献
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Carl Neumann Stephen Cohen 《BioEssays : news and reviews in molecular, cellular and developmental biology》1997,19(8):721-729
Morphogen gradient theories have enjoyed considerable popularity since the beginning of this century, but conclusive evidence for a role of morphogens in controlling multicellular development has been elusive. Recently, work on three secreted signalling proteins, Activin in Xenopus, and Wingless and Dpp in Drosophila, has stongly suggested that these proteins function as morphogens. In order to define a factor as a morphogen, it is necessary to show firstly, that it has a direct effect on target cells and secondly, that it affects the development of target cells in a concentration-dependent manner. With these criteria in mind, the evidence available for a variety of proposed morphogens is discussed. While the evidence is not conclusive in most of the cases considered, there is a strong case in favour of the three proteins mentioned above, which suggests that morphogens are potentially of general importance in controlling the development of multicellular organisms. 相似文献
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Objective: It has recently been demonstrated that, in middle‐aged women, a wide hip circumference is a protective factor for a number of health endpoints in later years. The effect seems to be independent of both overweight and waist circumference. This paper aims to replicate this finding in another population‐based sample consisting of women and men. Research Methods and Procedures: This was a prospective observational study consisting of a random subset of adult Danes. A total of 2987 subjects born in 1922, 1932, 1942, or 1952 and 35, 45, 55, or 65 years of age (at examination in 1987 to 1988) participated in the Danish MONICA (MONItoring trends and determinants of CArdiovascular disease) project, with measurements of height, weight, and hip and waist circumference taken. Through personal identification numbers, incidence of coronary heart disease (CHD) and cardiovascular disease (CVD) until the end of 1998 and all causes of death until 2001 were retrieved from the National Registers of Hospital Discharge. There was an average of 10 years of follow‐up for incidence of CVD and CHD and 13 years of follow‐up for total mortality. Results: Large hip circumference, relative to body size and waist circumference, predicted less incidence of CVD, CHD, and total death in women. This was not the case in men; BMI and waist circumference were the strongest independent predictors. Discussion: A large hip circumference seems to have independent and positive effects on CVD and CHD morbidity and mortality in women, but no protective effect on cardiovascular health in men. However, a borderline significant protective effect on total mortality was observed. 相似文献
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Matthew J. Ravosa 《Journal of morphology》1996,229(2):171-190
Previous experimental and comparative studies among a wide variety of primate and nonprimate mammals provide a unique source of information for investigating the functional and phylogenetic significance of variation in the masticatory apparatus of Eocene primates. To provide a quantitative study of mandibular form and function in Eocene primates, the scaling of jaw dimensions and the development of symphyseal fusion was considered in a broad sample of North American and European Adapidae and Omomyidae. Statistical analyses indicate a significant size-related pattern of symphyseal fusion across Eocene primates, with larger taxa often having a greater degree of fusion than smaller species; this trend is also evident at the family level. As adapids are mostly larger than omomyids and these taxa show allometry of symphyseal fusion, this may explain why no omomyids evince complete fusion. Controlling for jaw size, species with greater symphyseal fusion tend to have more robust jaws than those with a lesser amount of fusion. Upon further examination, a primary reason why adapids have more robust mandibles than omomyids is associated with the presence of taxa with fused symphyses, and thus more robust jaws, in the adapid sample, whereas no omomyids have fused symphyses. In addition, there is little indication of a dietary effect, as measured by molar shear-crest development, on symphyseal fusion. Moreover, as there is no correlation between molar shear-crest development and skull size, this also points to the absence of a size-related pattern of dietary preference underlying the allometry of symphyseal fusion. Based on the interspecific and ontogenetic allometry of symphyseal ossification in Eocene primates, jaw-scaling patterns are used to further examine the functional determinants of fusion in this group. This study indicates that greater dorsoventral shear during mastication is a more likely factor than lateral transverse bending (“wishboning”) in the evolution of symphyseal fusion among “late-fusing” mammals like adapids and omomyids. Given that wishboning is an important functional determinant of symphyseal form in recent anthropoids, apparently the evolutionary development of marked wishboning occurs only in taxa that shift the timing of fusion to a growth stage preceding the onset of weaning (before adult masticatory patterns are fully developed) and perhaps first ossified the symphysis to counter elevated dorsoventral shear stress. As early anthropoids probably consisted of members varying interspecifically and ontogenetically in the degree of ossification, it is especially informative to analyze the adaptive setting in which anthropoid symphyseal fusion evolved from a similar primitive “prosimian” perspective. © 1996 Wiley-Liss, Inc. 相似文献
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Wisniewska-Jarosinska M Poplawski T Chojnacki CJ Pawlowska E Krupa R Szczepanska J Blasiak J 《Molecular biology reports》2011,38(7):4603-4611
Dental composite materials contain polymers of methacrylates, which, due to mechanical abrasion and enzymatic action of saliva,
may release their monomers into oral cavity and the pulp. Moreover, polymerization is always incomplete and leaves usually
considerable fraction of free monomers. Mechanisms of the genotoxicity of methacrylate monomers have been rarely explored.
As the polymerization of a monomer is catalyzed by a co-monomer, their combined action should be considered. In the present
work, we investigated cytotoxic and genotoxic effects of urethane dimethacrylate (UDMA), often used as a monomer, at 1 mM,
and triethylene glycol dimethacrylate (TEGDMA), a typical co-monomer, at 5 mM singly and in combination. Experiments were
conducted on Chinese hamster ovary cells. Cell viability, apoptosis and cell cycle were assessed by flow cytometry, whereas
DNA damage was evaluated by plasmid conformation test and comet assay. Both compounds decreased the viability of the cells,
but did not induce strand breaks in an isolated plasmid DNA. However, both substances, either singly or in combination, damaged
DNA in CHO cells as evaluated by comet assay. Both compounds induced apoptosis, but a combined action of them led to a decrease
in the number of apoptotic cells. The combined action of UDMA and TEGDMA in the disturbance of cell cycle was lesser compared
to the action of each compound individually. Individually, though UDMA and TEGDMA may induce cytotoxic and genotoxic, however,
a combination of both does not produce a significant increase in these effects. 相似文献
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The relative importance of transport by diffusion and convection in permeable tissues is investigated in three-dimensional structures. The transport of a solute takes place from a number of sources embedded in the tissue, to a number of sinks similarly embedded. An enhancement factor E is defined to be the ratio of the transport rate in the presence of a pressure difference between the sources and sinks, to the transport rate without a pressure difference. It is shown that E is a unique function of a parameter W, which characterizes the properties of the tissue and the pressure difference. This relation is independent of the number or the geometries of the sources and sinks.This relation is compared with experimental data obtained in a hollow fiber tissue culture device, with two sets of hollow fibers kept at different pressures. This relation is also used to estimate the importance of convection in vivo for a wide range of mammalian tissues and solute molecules. 相似文献
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We studied the competitive effects within and between two taxonomically distant freshwater herbivores, a snail and a mayfly,
common in Swedish lakes, Lymnaea peregra and Cloeon dipterum, respectively, and their effect on grazing in a laboratory experiment. The experimental set-up consisted of 2-l aquaria,
each containing a periphyton covered tile. Intra- and interspecific effects were tested by increasing the density of one species
at a time in four different treatments, (1) snails (intraspecific treatment), (2) mayflies (intraspecific treatment), (3)
mixed-snails (interspecific treatments, snails kept constant) and (4) mixed-mayflies (interspecific treatments, mayflies kept
constant). Intraspecific competition affected both snails and mayflies negatively, i.e. increasing mortality with increasing
con-specific density. Furthermore, there was a decrease in snail growth with increasing snail density. In the mixed-species
treatments both species changed their microhabitat use indicating interspecific competition. Despite this, we also found a
positive effect of mayfly density on snail growth, most likely due to indirect commensalism. No density-dependent effect of
grazing on periphyton was found, probably due to interference competition between grazers. However, there was a significant
difference in periphyton biomass, due to species composition of grazers. Irrespective of their densities, if they co-existed,
the two grazer species decreased the periphyton biomass significantly compared with both single-species treatments. We considered
this as a joint action of facilitation and interaction. Our results suggest that competition can be an important structuring
factor in macroinvertebrate communities and that species composition can be significant for ecosystem processes within lentic
environments. 相似文献
11.
Serotonin and thermoregulation: old and new views 总被引:3,自引:0,他引:3
R D Myers 《Journal de physiologie》1981,77(2-3):505-513
An overview is presented of the evidence favouring a pivotal role for serotoninergic neurons in the diencephalon's control system for body temperature. 1. Morphological investigations of the anterior hypothalamus reveal that 5-HT injected locally into this thermosensitive zone evokes a hyperthermia in virtually all species. Pharmacological blocking agents of serotoninergic receptors antagonize the 5-HT-induced rise in an animal's temperature. 2. Further, the destruction of serotoninergic neurons in the anterior hypothalamic pre-optic area of a rat or monkey severely impairs the heat production responses during cold stress. 3. In addition, the release of 5-HT from anterior hypothalamic tissue is enhanced significantly when the animal is exposed to a cold environmental temperature, and subsequently shivers, vasoconstricts and conserves heat. 4. New observations are described which show that 5-HT may elicit a fall in temperature as a result of the: (1) overloading of 5-HT receptor sites in the anterior hypothalamus; and/or (2) occupation by 5-HT of either noradrenergic or dopaminergic receptors, or both classes of catecholamine receptors which are believed to mediate the hypothalamic pathways for heat loss. 5. Finally, new data also implicate neuronal 5-HT, again only within the anterior hypothalamic pre-optic area, in the cellular mechanism which triggers a fever in response to a bacterial challenge. Thus, the serotoninergic neurons underlying the rostral hypothalamic temperature controller are responsible not only for the defense of an animal's body temperature during exposure to cold, but also for initiating the shift in the temperature "set-point" during a febrile episode. 相似文献
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Synchronous and Alternating Choruses in Insects and Anurans: Common Mechanisms and Diverse Functions 总被引:2,自引:0,他引:2
SYNOPSIS. Neighboring males in rhythmically calling insectsand anurans often chorus in a synchronizing or alternating fashion.Neuroethological investigations of chorusing species revealthat their rhythms are maintained by pacemakers and that a basicinteractive algorithm, common to many species, yields the collectivesynchrony or alternation observed. Traditionally, synchronyhas been viewed as a cooperative event. However, recent evidencesuggests that a collective synchronous display can also be anincidental outcome of signal "jamming" activities between neighboringmales competing to attract females. This arises when femalephonotaxis is influenced by a precedence effect in which thefirst of two or more closely synchronized calls is preferred.Under such circumstances, males are selected to adopt a timingmechanism averting following calls. If males happen to callat comparable rates, the adopted mechanism can yield synchronyas a by-product. Alternation, too, may be produced by a similarmechanism and also represent an epiphenomenon. That alternation,as opposed to synchrony, results may be a mere artefact of thespecies' solo calling rate, but perceptual constraints may selectspecifically for alternation in some species. 相似文献
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Genomics and microarray for detection and diagnostics 总被引:4,自引:0,他引:4
Khan AS 《Acta microbiologica et immunologica Hungarica》2004,51(4):463-467
Genomics provided biomedical scientists an inventory of all genes and sequences present in a living being. This provides an unique opportunity to the scientists to predict and study biological functions of these genes. The changes in the gene expression regulated by genomic sequences therefore reflect changes in the molecular processes working in a cell or tissue in response to external factors including exposure to toxic compounds and pathogens. Microarray offers a biotechnological revolution with the help of DNA chemistry, silicon chip technology and optics to be used to monitor gene expression for thousands of genes in one single experiment. Briefly, 20,000 to 100,000 unique DNA molecules get applied by a robot to the surface of silicon wafers (approximately the size of a microscope slide). Using a single microarray experiment, the expression level of 20,000 to 100,000 genes will be examined in one single experiment. Genomics and microarray have a significant role and impact on the design and development of modern detection and diagnostic tools in several different ways. Microarray tools are now used on regular basis for monitoring gene expression of large number of genes and also frequently applied to DNA sequence analysis, immunology, genotyping, and molecular diagnosing. For diagnostics, these tools can be used to distinguish and differentiate between different DNA fragments that differ by as little as a single nucleotide polymorphism (SNP). These microarrays can be divided based on the gene density spots that will be high density (>10,000 spots) per slide, medium (< 1000 > 100) and low density (< 100). High-density arrays have proven to be very useful in disease diagnosis especially in diagnosis and classification of different types of cancers. These microarray tools hold tremendous potential for pathogen detection, which will be comprised, of unique sets of genes (also referred to as "signatures") able to unambiguously identify the species and strain of pathogens of interest. 相似文献
15.
Studies of human constitution and mental features are traditionally among the main concepts of anthropological research. In
this research, we attempted to discover connections between morphological and constitutional features and self-esteem in children
and adolescents. Such a connection was discovered in some studied age groups. The obtained results could serve as a basis
for further studies in this field. 相似文献
16.
Folch A 《Journal of visualized experiments : JoVE》2007,(8):300
The ability to culture cells has revolutionized hypothesis testing in basic cell and molecular biology research. It has become a standard methodology in drug screening, toxicology, and clinical assays, and is increasingly used in regenerative medicine. However, the traditional cell culture methodology essentially consisting of the immersion of a large population of cells in a homogeneous fluid medium and on a homogeneous flat substrate has become increasingly limiting both from a fundamental and practical perspective. Microfabrication technologies have enabled researchers to design, with micrometer control, the biochemical composition and topology of the substrate, and the medium composition, as well as the neighboring cell type in the surrounding cellular microenvironment. Additionally, microtechnology is conceptually well-suited for the development of fast, low-cost in vitro systems that allow for high-throughput culturing and analysis of cells under large numbers of conditions. In this interview, Albert Folch explains these limitations, how they can be overcome with soft lithography and microfluidics, and describes some relevant examples of research in his lab and future directions. 相似文献
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Lee MP 《Biochimica et biophysica acta》2012,1819(7):739-742
Epigenetic information is characterized by its plasticity during development and differentiation as well as its stable transmission during mitotic cell divisions in somatic tissues. This duality contrasts to genetic information, which is essentially static and identical in every cell in an organism with only a few exceptions such as immunoglobulin genes in lymphocytes. Epigenetics is traditionally perceived as a means to regulate gene expression without a change in DNA sequence. This, however, does not exclude a potential role for genetic variations in providing differential backgrounds on which epigenetic modulations and their regulatory consequences are achieved. An effective approach to investigating the interplay between genetic variations and epigenetic variations is through allele-specific analysis of epigenetics and gene expression. Such studies have generated many new insights into functions of genetic variations, mechanisms of gene expression regulation, and the role of mutations and epigenetic alterations in human cancer. This article is part of a Special Issue entitled: Chromatin in time and space. 相似文献
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Luis A. Buatois M. Gabriela Mángano 《Lethaia: An International Journal of Palaeontology and Stratigraphy》2013,46(3):281-292
Ichnodiversity has been used as a proxy for environmental stress and stability in facies interpretations and to reconstruct evolutionary radiations and colonization histories in evolutionary palaeoecology. The three components of global diversity are exported from ecology and adapted for ichnology. Alpha ichnodiversity is used for palaeoenvironmental characterization, being assessed for individual facies. Beta ichnodiversity is commonly overlooked, although it may provide information about degree of similarity between ichnofaunas formed along environmental gradients. Gamma ichnodiversity may provide clues to detect ichnofossil provincialism. The concept of disparity may also prove to be significant in ichnological studies. Whereas ichnodiversity refers to ichnotaxonomic richness, ichnodisparity provides a measure of the variability of morphological plans in biogenic structures. Changes in global ichnodiversity do not necessarily parallel changes in ichnodisparity. For example, while the Cambrian explosion involved a dramatic increase in both, the Ordovician radiation essentially reflects an increase only in the former. Ichnodiversity and ichnodisparity should be used with caution because they are both affected by taphonomic processes. High diversity of superficial to shallow‐tier trace fossils may result from enhanced preservation due a poorly developed mixed layer, rather than a true reflection of ecosystem performance, as shown by underexploited infaunal ecospace after biotic crises (e.g. end‐Permian mass extinction). 相似文献
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Robert K. Colwell Anne Chao Nicholas J. Gotelli Shang-Yi Lin Chang Xuan Mao Robin L. Chazdon John T. Longino 《Journal of Plant Ecology》2012,5(1):3
Aims In ecology and conservation biology, the number of species counted in a biodiversity study is a key metric but is usually a biased underestimate of total species richness because many rare species are not detected. Moreover, comparing species richness among sites or samples is a statistical challenge because the observed number of species is sensitive to the number of individuals counted or the area sampled. For individual-based data, we treat a single, empirical sample of species abundances from an investigator-defined species assemblage or community as a reference point for two estimation objectives under two sampling models: estimating the expected number of species (and its unconditional variance) in a random sample of (i) a smaller number of individuals (multinomial model) or a smaller area sampled (Poisson model) and (ii) a larger number of individuals or a larger area sampled. For sample-based incidence (presence–absence) data, under a Bernoulli product model, we treat a single set of species incidence frequencies as the reference point to estimate richness for smaller and larger numbers of sampling units.Methods The first objective is a problem in interpolation that we address with classical rarefaction (multinomial model) and Coleman rarefaction (Poisson model) for individual-based data and with sample-based rarefaction (Bernoulli product model) for incidence frequencies. The second is a problem in extrapolation that we address with sampling-theoretic predictors for the number of species in a larger sample (multinomial model), a larger area (Poisson model) or a larger number of sampling units (Bernoulli product model), based on an estimate of asymptotic species richness. Although published methods exist for many of these objectives, we bring them together here with some new estimators under a unified statistical and notational framework. This novel integration of mathematically distinct approaches allowed us to link interpolated (rarefaction) curves and extrapolated curves to plot a unified species accumulation curve for empirical examples. We provide new, unconditional variance estimators for classical, individual-based rarefaction and for Coleman rarefaction, long missing from the toolkit of biodiversity measurement. We illustrate these methods with datasets for tropical beetles, tropical trees and tropical ants.Important findings Surprisingly, for all datasets we examined, the interpolation (rarefaction) curve and the extrapolation curve meet smoothly at the reference sample, yielding a single curve. Moreover, curves representing 95% confidence intervals for interpolated and extrapolated richness estimates also meet smoothly, allowing rigorous statistical comparison of samples not only for rarefaction but also for extrapolated richness values. The confidence intervals widen as the extrapolation moves further beyond the reference sample, but the method gives reasonable results for extrapolations up to about double or triple the original abundance or area of the reference sample. We found that the multinomial and Poisson models produced indistinguishable results, in units of estimated species, for all estimators and datasets. For sample-based abundance data, which allows the comparison of all three models, the Bernoulli product model generally yields lower richness estimates for rarefied data than either the multinomial or the Poisson models because of the ubiquity of non-random spatial distributions in nature. 相似文献
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Hey J 《BioEssays : news and reviews in molecular, cellular and developmental biology》2003,25(9):825-828
A new set of models has resurrected a role for chromosomal inversions in the formation of new species. Traditional models, which are generally considered to be unlikely in most cases, had imagined that inversions might aid speciation by directly causing low hybrid fitness. In contrast, the newer models focus on the effect that inversions have on local recombination rates. A test of these models found a strikingly high rate of amino-acid substitution within regions where humans and chimpanzees differ by inversions, suggesting perhaps that our ancestral species underwent a divergence process in which gene flow and inversions played a key role. However, it remains uncertain whether this interesting finding is actually consistent with the proposed model. 相似文献