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At least 649 records · Page 36Linked to original sources
PubMed1980

Tandem fusion, centric fusion, and chromosomal evolution in the cotton rats, genus Sigmodon.

G-banded and C-banded karyotypes of three closely related and morphologically similar species of cotton rats, Sigmodon hispidus (2n=52; 52 autosomal arms), S. mascotensis (2n=28; 28 autosomal arms), and S. arizonae (2n=22,24; 38 autosomal arms) are presented and compared. Despite the enormous difference between the higher diploid number of hispidus and the lower diploid numbers of mascotensis and arizonae, a great deal of G-band homology is retained. If the karyotype of hispidus is considered ancestral in the group, then chromosome evolution toward lower diploid numbers has proceeded through the fixation of a large number of both tandem and centric fusions. Centromeric heterochromatin has not, however, persisted as intetstitial C-band material on the tandem fusion products. The karyotypes of mascotensis and arizonae share several tandem fusion products of hispidus chromosomes indicating a common origin of the former two species from an ancestor of intermediate diploid number. Chromosome evolution from the ancestral hispidus-like karyotype to the karyotype of the common ancestor of arizonae and mascotensis proceeded almost exclusively by tandem fusion. This orthokaryotypic trend continued in the evolution of the karyotype of modern mascotensis. In the line leading from the arizonae-mascotensis ancestor to modern arizonae a trend of centric fusion predominated.

Animals↗
PubMed1981

[Histologic evolution of acute alcoholic hepatitis].

Although acute alcoholic hepatitis is a frequent disease with distinct histologic diagnosis, the prognostic factors of its evolution are largely unknown. The present report analyzes the data of 18 patients with acute alcoholic liver disease submitted to two liver biopsies with a mean interval of 35 months. The results demonstrate a favorable histologic evolution in six of seven patients that abandoned alcohol ingestion, and an evolution to chronic liver disease in the remaining case. Out of six patients with continuous alcohol ingestion the evolution was unfavorable in five, while one case evolved to healing. Centrilobular fibrosis disappeared in the six cases that discontinued alcohol ingestion and who had favorable evolution, and it persisted in four of the six patients that continued drinking. The results suggest that centrilobular fibrosis is not always an unfavorable prognostic marker, and that the evolution of acute alcoholic hepatitis is not exclusively dependent on the continuation of alcohol abuse.

Acute Disease↗
PubMed1994

Results of endonasal laser-assisted dacryocystorhinostomy.

BACKGROUND: Endonasal laser-assisted dacryocystorhinostomy has been a subject of much interest since its introduction in 1990, offering the potential advantages of decreased postoperative morbidity and the lack of a cutaneous scar. In this study, the authors report the results of 46 endonasal laser-assisted dacryocystorhinostomy procedures performed on 42 patients between February 1991 and July 1992. METHODS: The medical records of all patients undergoing endonasal laser-assisted dacryocystorhinostomy procedures were reviewed retrospectively in detail. Patients undergoing laser-assisted external dacryocystorhinostomies or conjunctivo-dacryocystorhinostomies and those with follow-up periods less than 4 months were not included in the study. RESULTS: A total of 46 endonasal laser-assisted dacryocystorhinostomy procedures were performed. Of these, 32 were successful and 14 failed after a single attempt, yielding a success rate of 70% (32/46). Of the 14 patients with failed procedures, 6 underwent a second endonasal laser-assisted dacryocystorhinostomy. Of these, five were successful. The success rate calculated on the basis of one or two attempts was 80% (37/46). CONCLUSIONS: The science and technology of endonasal laser-assisted dacryocystorhinostomy is undergoing a continuous process of evolution as a number of modifications are introduced, including better patient selection, more complete tissue removal at the osteotomy site, and the adjunctive use of mitomycin C. As this process continues, it is likely that the success rates in this modality will improve, making it an increasingly attractive alternative to external dacryocystorhinostomy.

Dacryocystorhinostomy↗
PubMed1999

Human teeth exposed to argon laser irradiation: determination of power-time-temperature working conditions.

OBJECTIVE: This study was conducted to establish the operating parameters of the argon laser without thermal damage to the pulp tissue for clinical applications. SUMMARY BACKGROUND DATA: Previous studies have mainly compared the temperature modifications of the pulp chamber in a very limited situation, where a complete view of the thermal history cannot be obtained nor even extrapolated to new applications. METHODS: We used samples of molar and premolar tooth where a class V cavity was prepared and illuminated with an argon laser at different power levels, fixing the exposition area for all cases. Situations including open cavity and teeth restoration were analyzed. High-precision thermistors were placed in four different positions, one of which was inside the pulp chamber. The temperature evolution was monitored continuously by an interfaced computer during all laser exposure. Special attention was paid to the intrapulpal temperature variation because it is considered the most vulnerable thermal region. The temperature time evolution allowed the determination of the operating conditions (power-time-temperature variation) in which the use of the argon laser causes no pulpal damage. As a function of temperature variation, we divided the whole parameter space (power-time-temperature) into zones and the optimum zone of operation was determined. CONCLUSIONS: We created a diagram called power-time-temperature (PTT) where zones of temperature increased under laser irradiation allow the verification of which condition is safe for clinical laser application. The results have a broad use when this type of analysis is applicable.

Argon↗
PubMed1994

The evolutionary origin of development: cycles, patterning, privilege and continuity.

A scenario for the evolution of a simple spherical multicellular organism from a single eukaryotic cell is proposed. Its evolution is based on environmentally induced alterations in the cell cycle, which then, by the Baldwin effect, become autonomous. Further patterning of this primitive organism--a Blastaea, could again involve environmentally induced signals like contact with the substratum, which could then become autonomous, by, perhaps, cytoplasmic localization and asymmetric cell division. Generating differences between cells based on positional information is probably very primitive, and is well conserved; its relation to asymmetric cell division is still unclear. Differentiation of new cell types can arise from non equivalence and gene duplication. Periodicity also evolved very early on. The origin of gastrulation may be related to mechanisms of feeding. The embryo may be evolutionarily privileged and this may facilitate the evolution of novel forms. Larvae are secondarily derived and direct development is the primitive condition as required by the continuity principle.

Animals↗
PubMed2003

Eucaryotic genome evolution through the spontaneous duplication of large chromosomal segments.

There is growing evidence that duplications have played a major role in eucaryotic genome evolution. Sequencing data revealed the presence of large duplicated regions in the genomes of many eucaryotic organisms, and comparative studies have suggested that duplication of large DNA segments has been a continuing process during evolution. However, little experimental data have been produced regarding this issue. Using a gene dosage assay for growth recovery in Saccharomyces cerevisiae, we demonstrate that a majority of the revertant strains (58%) resulted from the spontaneous duplication of large DNA segments, either intra- or interchromosomally, ranging from 41 to 655 kb in size. These events result in the concomitant duplication of dozens of genes and in some cases in the formation of chimeric open reading frames at the junction of the duplicated blocks. The types of sequences at the breakpoints as well as their superposition with the replication map suggest that spontaneous large segmental duplications result from replication accidents. Aneuploidization events or suppressor mutations that do not involve large-scale rearrangements accounted for the rest of the reversion events (in 26 and 16% of the strains, respectively).

Base Sequence↗
PubMed2004

Gene network polymorphism is the raw material of natural selection: the selfish gene network hypothesis.

Population genetics, the mathematical theory of modern evolutionary biology, defines evolution as the alteration of the frequency of distinct gene variants (alleles) differing in fitness over the time. The major problem with this view is that in gene and protein sequences we can find little evidence concerning the molecular basis of phenotypic variance, especially those that would confer adaptive benefit to the bearers. Some novel data, however, suggest that a large amount of genetic variation exists in the regulatory region of genes within populations. In addition, comparison of homologous DNA sequences of various species shows that evolution appears to depend more strongly on gene expression than on the genes themselves. Furthermore, it has been demonstrated in several systems that genes form functional networks, whose products exhibit interrelated expression profiles. Finally, it has been found that regulatory circuits of development behave as evolutionary units. These data demonstrate that our view of evolution calls for a new synthesis. In this article I propose a novel concept, termed the selfish gene network hypothesis, which is based on an overall consideration of the above findings. The major statements of this hypothesis are as follows. (1) Instead of individual genes, gene networks (GNs) are responsible for the determination of traits and behaviors. (2) The primary source of microevolution is the intraspecific polymorphism in GNs and not the allelic variation in either the coding or the regulatory sequences of individual genes. (3) GN polymorphism is generated by the variation in the regulatory regions of the component genes and not by the variance in their coding sequences. (4) Evolution proceeds through continuous restructuring of the composition of GNs rather than fixing of specific alleles or GN variants.

Alleles↗
PubMed2005

Image analysis of X-ray microtomograms of soft materials during convective drying: 3D measurements.

Drying dewatered sludge leads to a complex three-dimensional porous structure. Moreover, this operation is dependent on the way the material is processed. In this study, textural changes of sludge extrudates submitted to convective drying are followed by a 3D image analysis of reconstructed X-ray microtomograms. To achieve this goal, two different wastewater sludges collected in wastewater treatment plant after the thickening step and dewatered in the laboratory are used. It is showed that the evolution of the 3D-crack ratio vs. the residual water content evolves following a hyperbolic law. The 3D opening crack size distribution reveals two different types of pore development, i.e. a continuous pore size evolution for one sludge and the sudden appearance of cracks for the other sludge.

Journal Article↗
PubMed1992

The continuity of gerontological themes.

Based on the premise that scientists should periodically examine the history of their ideas and methodologies, this article focuses on the issue of continuity in the evolution of scientific knowledge about aging. Taking a twenty-five-year perspective, selected research questions and priorities in the biomedical, behavioral, and social domains of aging are used to exemplify the continuity of the gerontological knowledge base. This article concludes that there is considerable evidence of continuity, despite the strong influences of changing cohorts of people and external forces that have shaped new ideas and research questions in gerontology.

Aging↗
PubMed1999

The continuous Prisoner's dilemma: II. Linear reactive strategies with noise.

We present a general model for the Continuous Prisoner's Dilemma and study the effect of errors. We find that cooperative strategies that can resist invasion by defectors are optimistic (make high initial offers), generous (always offer more cooperation than the partner did in the previous round) and uncompromising (offer full cooperation only if the partner does). A necessary condition for the emergence of cooperation in the continuous Prisoner's Dilemma with noise is b (1-p)>c, where b and c denote, respectively, the benefit and cost of cooperation, while p is the error rate. This relation can be reformulated as an error threshold: cooperation can only emerge if the probability of making a mistake is below a critical value. We note, however, that cooperation in the continuous Prisoner's Dilemma with noise does not seem to be evolutionarily stable: while it is possible to find cooperative strategies that resist invasion by defectors, such cooperators are generally invaded by more cooperative strategies which eventually yield to defectors. Thus, the long-term evolution of the continuous Prisoner's Dilemma is either characterized by unending cycles or by stable polymorphisms of cooperators and defectors.

Biological Evolution↗
PubMed1977

Oxygen Concentration in Isolated Chloroplasts during Photosynthesis.

The O(2) concentration in intact and osmotically disrupted isolated spinach (Spinacia oleracea, L.) chloroplasts during photosynthesis was estimated. The chloroplasts were allowed to reduce 3-phosphoglycerate, CO(2), or ferricyanide in light until the rate of O(2) production was linear. When the light was turned off O(2) evolution from the chloroplasts continued for a few seconds. This prolonged O(2) evolution is due to an O(2) surplus inside the chloroplasts which equilibrates with that in the medium. From this surplus the O(2) concentration inside the chloroplasts at the moment when the light had been switched off was calculated. In all experiments the O(2) concentration inside the photosynthesizing chloroplasts was higher than that outside, but was dependent upon the O(2) concentration of the chloroplast medium. At low external O(2) concentration (30 mum) the ratio of the internal to the external O(2) concentration was about 5, whereas at concentrations corresponding to those in airsaturated water this ratio was close to 1. With osmotically broken chloroplasts this ratio was 1.2 at 30 mum O(2) and almost 1 from 150 mum onward. When the O(2) surplus found in broken chloroplasts during photosynthesis was related to the volume of the thylakoids, a ratio of about 2.3 was observed.

Journal Article↗
PubMed2001

The Dynamics of Marangoni-Driven Local Film Drainage between Two Drops.

A study of Marangoni-driven local continuous film drainage between two drops induced by an initially nonuniform interfacial distribution of insoluble surfactant is reported. Using the lubrication approximation, a coupled system of fourth-order nonlinear partial differential equations was derived to describe the spatio-temporal evolution of the continuous film thickness and surfactant interfacial concentration. Numerical solutions of these governing equations were obtained using the Numerical Method of Lines with appropriate initial and boundary conditions. A full parametric study was undertaken to explore the effect of the viscosity ratio, background surfactant concentration, the surface Péclet number, and van der Waals interaction forces on the dynamics of the draining film for the case where surfactant is present in trace amounts. Marangoni stresses were found to cause large deformations in the liquid film: Thickening of the film at the surfactant leading edge was accompanied by rapid and severe thinning far upstream. Under certain conditions, this severe thinning leads directly to film rupture due to the influence of van der Waals forces. Time scales for rupture, promoted by Marangoni-driven local film drainage were compared with those associated with the dimpling effect, which accompanies the approach of two drops, and implications of the results of this study on drop coalescence are discussed. Copyright 2001 Academic Press.

Journal Article↗
PubMed1976

Deficiency in renomedullary prostaglandin synthesis related to the evolution of essential hypertension.

Continued PG synthesis in the early stages of essential hypertension might reflect an activation of the renal antihypertensive function in respect to neurogenic and/or hormonal pression stimuli, subsequently a deficiency of renal PG synthesis related to irreversible changes with the kidney would lead to the prepoderance of a pressure mechanism, resulting to a further increase of blood pressure.

Adult↗
PubMed2004

Assessing the likelihood of recurrence during RNA evolution in vitro.

Recurrence is the possibility of resulting in the same endpoint multiple times when a living system is allowed to evolve repeatedly starting from a given initial point. This concept is of concern to both evolutionary theoreticians and molecular biologists who use nucleic acid selection techniques to mimic biotic and computorial processes in the test tube. Using the continuous in vitro evolution methodology, many replicate experimental evolutionary lineages with populations of catalytic RNA were performed to gain insight into the parameters that could affect recurrence. The likelihood that the same genotype will result in parallel trials of an evolution experiment in vitro depends on several factors, including the phenotype under selection, the size and composition of the initial diverse pool of nucleic acids used in the experiment, the degree of mutation possible during the experiment, the shape of the fitness landscape through which the population evolves, and the strategies used to invoke selection and to search the landscape, among others. By considering these factors, it can be predicted that recurrence is more likely when a small, wild-type-based starting pool is used with efficient selection and search strategies involving little online mutagenesis within a rugged adaptive landscape with a strong local optimum. The recurrence experiments performed here on the 150-nucleotide ligase ribozyme demonstrate that it repeatedly jumps from one peak in a fitness landscape to another, apparently hurdling a deep fitness valley. These predictions can and should be tested by additional multiple replicates of actual evolution experiments in the laboratory.

Base Sequence↗
PubMed2006

History of endovascular surgery: personal accounts of the evolution.

Endovascular therapy has continuously evolved since it was first described in 1904. It was first used as a technique to inject particles to follow the flow into vascular lesions, and from the mid-seventies on, microballoons were developed to reach targets in the arterial vascular tree. Arteriovenous malformations were approached with catheters, the tip mounted by calibrated leak balloons. The embolizing material injected was cyanoacrylate labeled with Lipiodol (Lafayette Pharmacal, Lafayette, IN), a technique that is similar to what we use today. Flow-guided microballoons placed and detached in brain aneurysms eventually became unstable, making reperfusion and rupture possible. With the introduction of guidewire-supported microcatheters, controlled navigation in the endovascular tree became possible, allowing the injection of particles, liquid embolizing agents, or free coils. In 1991, detachable coils became available and brought new therapeutic concepts. Having learned that detachable coils could not be used to treat aneurysms, which were difficult to treat surgically, the neurosurgical community accepted this new technology primarily for patients in poor condition following aneurysmal subarachnoid hemorrhage. Increased experience led to better clinical results, and Guglielmi detachable coiling therapy began to be accepted also for patients with posterior circulation aneurysms. Recent controlled trials and new technologies improving the endovascular feasibility have raised the acceptance of endovascular therapy for brain aneurysms. The elegance of the endovascular approach was an important argument for this technology from its inception, but in early years, restricted endovascular efficacy limited the efficiency of embolizations. Increasing experience and exploding new technologies have made endovascular techniques not only safer but also as effective as microsurgery. The number of vascular pathologies where microsurgery is the only option is decreasing, and training in vascular neurosurgery may become the privilege of specialized centers in the future.

Catheterization↗