Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “PLASTICS”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,441 records · Page 80Linked to original sources
PubMed1996

The consequences of phenotypic plasticity in cyclically varying environments: a genetic algorithm study.

By "phenotypic plasticity" we refer to the capacity of a genotype to exhibit different phenotypes, whether in the same or in different environments. We have previously demonstrated that phenotypic plasticity can improve the degree of adaptation achieved via natural selection (Behera & Nanjundiah, 1995). That result was obtained from a genetic algorithm model of haploid genotypes (idealized as one-dimensional strings of genes) evolving in a fixed environment. Here, the dynamics of evolution is examined under conditions of a cyclically varying environment. We find that the rate of evolution, as well as the extent of adaptation (as measured by mean population fitness) is lowered because of environmental cycling. The decrease in adaptation caused by a varying environment can, however, be partly or wholly compensated by an increase in the degree of plasticity that a genotype is capable of. Also, the reduction of population fitness caused by a variable environment can be partially offset by decreasing the total number of genetic loci. We conjecture that an increase in genome size may have been among the factors responsible for the evolution of phenotypic plasticity.

Adaptation, Physiological↗
PubMed2000

Undermining the Baldwin expediting effect: does phenotypic plasticity accelerate evolution?

The claim that phenotypic plasticity speeds up evolution towards a target phenotype is a recent incarnation of the Baldwin effect. To differentiate this theory from earlier interpretations of Baldwin's ideas, we name it the Baldwin expediting effect. Models that demonstrate this effect assume an extreme fitness scenario which bestows high fitness upon a single optimal phenotype and treats all other phenotypes as equal. In two modeling frameworks, we demonstrate that the effects of plasticity on the rate of evolution are highly dependent on the fitness function and population starting conditions. We argue that phenotypic plasticity does not universally facilitate evolution. Furthermore, in cases where the Baldwin expediting effect occurs, it is not necessarily correlated with increased fitness and therefore is not sufficient to explain the evolutionary success of plasticity.

Biological Evolution↗
PubMed1981

Intracellular studies on cortical synaptic plasticity. Conditioning effect of antidromic activation on test-EPSPs.

1. An intracellular study on pyramidal tract (PT) neurons in the cat's motor cortex was carried out to examine whether their antidromic activation would be able to induce plastic changes in the efficacy of the synapses situated on their membrane. 2. The experimental paradigm was based on the principles of classical conditioning. It included habituation, pseudoconditioning, conditioning and extinction procedures. The antidromic spike was regarded as an unconditioned stimulus while excitatory postsynaptic potentials (EPSPs) evoked by thalamic (n. ventralis lateralis), callosal and somatosensory afferents served as conditioned stimuli. Stimulus pairs were given, consisting of EPSPs and antidromic spikes with various time intervals, and the stimulus sequences were at a 0.2--1.0/s frequency. 3. Reversible, short-term (3--28 min) enhancement of synaptic excitability was observed in 27% of the PT cells after conditioning with 60--150 stimulus pairs. 4. EPSP-spike and spike-EPSP sequences were equally effective, but plastic changes were induced only by stimulus pairs with less than 100 ms interstimulus intervals. 5. Facilitated EPSP states were frequently accompanied by changes in membrane potential, membrane resistance and firing activity. 6. In repeated conditioning series, the temporal parameters of conditioning changes, the number of stimuli necessary for full development of facilitation, and some membrane parameters showed marked alterations. 7. Conditioned plastic changes in synaptic efficacy showed analogies with associative learning: (a) they were specific to the pairing procedure, because randomized presentation of EPSPs and antidromic spikes never produced synaptic facilitation; (b) unpaired spike trains used as unconditioned stimuli (of 10--200/s frequency and 1--20 s duration) caused only a minor degree of facilitation as compared with EPSP-spike pairings; (c) changes in synaptic efficacy were subject to extinction. 8. The present findings indicate that the plastic changes in synaptic transmission may be localized to the postsynaptic membrane of the conditioned PT cells.

Action Potentials↗
PubMed2003

Bone marrow-derived stem cells and "plasticity".

Studies describing plasticity of somatic stem cells have become a focus of interest because clinical applications in the treatment of degenerative diseases would be at hand. In particular, bone marrow-derived cells and their potential to contribute to skeletal and cardiac muscle, liver, neurons and epithelium have recently been studied extensively. Nevertheless, results of these studies have not always been consistent with each other, and yet it remains to be resolved whether plasticity of adult stem cells truly exists. This review will discuss the role of bone marrow-derived stem cells in the field of experimental and clinical plasticity studies. Observations compatible with the concept of stem cell plasticity will be weighed against limitations of the experimental systems employed.

Adult↗
PubMed2002

Plastic particle migration during intravenous infusion assisted by a peristaltic finger pump in an animal model.

The contamination of intravenously administered fluid with foreign material has always been of major concern, but the in-vivo impact of silicone embolisation from administration of fluid via a peristaltic finger pump (PFP) has not previously been assessed. To determine whether silicone particles enter the lungs and to review the histological response, 10 rabbits received an IV infusion of 0.9% saline at 10 ml/kg per hour over a 72-h period, via an IVAC 591 PFP. The lungs were analysed for silicone particles with scanning electron microscopy (SEM) and energy-dispersive X-ray analysis (EDXA). These results were compared with a control group of non-infused animals. Silicone particles were found in 8 of 10 animals in the experimental group and in 2 of 9 control animals, indicating that silicone particles are dislodged during pump-assisted IV infusions. The difference between the control and infused animals was statistically significant using Fisher's exact test (P = 0.023). However, silicone plastic particles in control animals suggest that there is also environmental exposure to silicone in addition to those particles that come from a therapeutic source. The additional finding of elemental silicon (which is one of the constituents of silicone plastic) in both infused and control animals in which silicone plastic was not found indicates that not all elemental silicon in animals reflects the presence of silicone plastic. The clinical significance of each of these two findings is yet to be determined.

Animals↗
PubMed2004

Effects of behavioral and morphological plasticity on risk of predation in a Neotropical tadpole.

Predator-induced phenotypic plasticity is widespread among aquatic animals, however the relative contributions of behavioral and morphological shifts to reducing risk of predation remain uncertain. We tested the phenotypic plasticity of a Neotropical tadpole ( Rana palmipes) in response to chemical cues from predatory Belostoma water bugs, and how phenotype affects risk of predation. Behavior, morphology, and pigmentation all were plastic, resulting in a predator-induced phenotype with lower activity, deeper tail fin and muscle, and darker pigmentation. Tadpoles in the predator cue treatment also grew more rapidly, possibly as a result of the nutrient subsidy from feeding the caged predator. For comparison to phenotypes induced in the experiment, we quantified the phenotype of tadpoles from a natural pool. Wild-caught tadpoles did not match either experimentally induced phenotype; their morphology was more similar to that produced in the control treatment, but their low swimming activity was similar to that induced by predator cues. Exposure of tadpoles from both experimental treatments and the natural pool to a free-ranging predator confirmed that predator-induced phenotypic plasticity reduces risk of predation. Risk of predation was comparable among wild-caught and predator-induced tadpoles, indicating that behavioral shifts can substantially alleviate risk in tadpoles that lack the typical suite of predator-induced morphological traits. The morphology observed in wild-caught tadpoles is associated with rapid growth and high competition in other tadpole species, suggesting that tadpoles may profitably combine a morphology suited to competition for food with behaviors that minimize risk of predation.

Analysis of Variance↗
PubMed2004

Ecotypic differentiation and phenotypic plasticity in reproductive traits of Armadillidium vulgare (Isopoda: Oniscidea).

Armadillidium vulgare differed in growth and survivorship on two field sites. Growth rates were higher at a site with consistently higher quality food than at the other site where less high-quality food was produced and which was less predictably accessible. Survivorship was higher at the second site where temperature fluctuations were consistently smaller. Individuals from the two populations were kept for 6 months under the same food and temperature conditions and patterns of resource allocation to reproductive traits analysed. Members of the population from the site with good growth conditions had significantly higher reproductive allocation, by 13.5%, and larger broods, by 9.1%, than those from the site with poor growth conditions. Contrary to theoretical predictions, they also had significantly larger offspring, by 7.5% dry mass. Larger offspring survived better than small ones. This differential survivorship, by 20% for a 3.4% difference in live mass, was much more pronounced under conditions of moisture stress and under fluctuating temperature regimes. Larger offspring would therefore be at a selective advantage on the site with more severe temperature fluctuations. Phenotypic plasticity in reproductive traits in response to experimental changes in food quality, temperature and crowding were monitored. Reproductive allocation was increased by 20.8% under conditions of higher food quality, by 14.7% at higher temperatures, and by 12.5% under less crowded conditions. Brood size, but not offspring dry mass, increased when food quality increased. When crowding increased by 25.0%, the size of broods remained the same but the dry mass of individual offspring decreased by 11.2%. Members of the population from the site with more variable access to high-quality food showed more plasticity in reproductive traits in response to changes in food supply than members of the population from the site with the more predictable food supply. Members of the population from the site with more stable temperatures showed less plasticity to temperature changes than members of the population from the site with greater temperature fluctuations. It is concluded that the observed microevolutionary processes and phenotypic plasticity have adaptative value as responses to spatial and temporal heterogeneity in environmental conditions.

Adaptation, Physiological↗
PubMed2005

Balancing food availability and hydrodynamic constraint: phenotypic plasticity and growth in Simulium noelleri blackfly larvae.

Organisms through phenotypic plasticity can cope with multiple changed environmental conditions. Theory predicts that animals in streams and rivers should be able to balance demands of the needs to obtain food efficiently and to adjust response to hydrodynamic variability. This study examined effects of variations in food availability and current velocity on the feeding structure and growth rate of Simulium noelleri blackfly larvae. The larvae developed larger labral fans and more rays under slow current and low food regimes than in fast current and high food conditions. In both fast and slow current regimes, growth rates were higher and development periods to the final-instar stage were shorter in high food treatments. The estimated flux rates of food particles through labral fans under high food treatments for both fast and slow current regimes were higher than those under low food treatments. Although both food and current velocity appeared to have selected for flexibility of feeding structure and growth rate, food availability was a more important factor for phenotypic and developmental plasticity than current velocity. The results indicate a strong link between environmental changes in food availability and current velocity, phenotypic plasticity, and growth rate of S. noelleri. This study suggests that plasticity of ecomorphs with macroevolutionary significance may play a role in the early evolutionary stages of blackfly larvae.

Adaptation, Physiological↗
PubMed2007

Self-expanding Polyflex plastic stents in esophageal disease: various indications, complications, and outcomes.

BACKGROUND: Esophageal stenting has become an important technique in the treatment of different clinical problems such as malignant or benign stenosis, anastomotic leaks after surgery, or fistulas. In this study we present our experience with the self-expanding Polyflex plastic stent in various indications, arising complications, and patient's outcomes. METHODS: Over a three-year period, 35 patients underwent self-expanding Polyflex plastic stent placement for esophageal stenosis (n = 23) with 22 malignant, and for perforations, fistulas, or anastomotic leaks after surgery (n = 12). The short-term efficacy and long-term outcomes were analyzed. RESULTS: In patients with stenosis, implantation was performed without any complications in 91% (21/23). In one patient perforation occurred while passing the stenosis; in another patient the stent dislocated during the insertion procedure. Dysphagia score improved from 3.0 to 1.0 after stenting. In all patients with perforations, fistulas, or anastomotic leaks (n = 12), stents were placed successfully without any complication. Complete sealing of the mucosal defect was proven by radiography in 92% (n = 11) and healing was seen in 42% (n = 5). If indicated, stent removal was performed without any complications. Stent migration (n = 13; 37%) was the most common long-term complication. CONCLUSIONS: The placement of self-expanding Polyflex plastic stents is a highly sufficient and cost-effective treatment for malignant and benign esophageal disorders. Because the long-term results were highly favorable, self-expanding plastic stent placement could be used as the initial treatment for various conditions.

Adolescent↗
PubMed1979

Analysis of short-term plasticity at the perforant path-granule cell synapse.

Short-term plasticity was investigated at the perforant path-granule cell synapse in the hippocampal slice preparation. A successive decrement in the amplitude of the extracellular EPSP was obtained at all stimulus frequencies above 0.05 Hz. This effect of repetitive stimulation has previously been shown to fulfill the requirements for habituation processes. If each stimulus within an habituation train was followed by a second identical test stimulus the response to the test stimulus was larger than that to the paired conditioning stimulus. This short-term plasticity has been called paired pulse potentiation. The test response potentiated only with respect to the paired conditioning response and not with respect to previous test responses. Neither form of plasticity appeared to result from changes in the amplitude of the afferent fiber volley. Both habituation and paired pulse potentiation result from an interaction of at least three changes in the efficacy of transmission after a conditioning stimulus: (1) an initial depression, (2) an intermediate relative potentiation and (3) a late depression which decays slowly. Paired pulse potentiation could be demonstrated only if the interpair interval corresponded to the period of maximal late depression and the interstimulus interval to the period of relative potentiation. The amplitudes of intermediate relative potentiation and late depression (and inhibition of transmission by 2-amino-4-phosphonobutyric acid (APB)) were inversely related to the control response amplitude. This relationship likely derives from nonlinear stimulation of postsynaptic ionic currents at higher stimulus intensities. In contrast, the initial depression increased with response amplitude. This is consistent with a mechanism dependent on the postsynaptic membrane potential, such as refractoriness to succeeding stimuli. When the response amplitudes in the presence and absence of 2.5 mM APB were equalized by adjusting the stimulus intensity, no difference was found in the magnitude of either form of plasticity. Since APB probably inhibits transmission at this site through competitive antagonism at the postsynaptic receptor, this observation suggests that habituation and paired pulse potentiation are generated presynaptically.

Action Potentials↗
PubMed1990

Studies on the distribution of abnormal cells in cytological smears. VII. Cervical brush versus plastic and wooden spatulas.

A model system of exfoliated normal human cervicovaginal squamous cells, exfoliated rodent tumor cells, and acellular, viscous, mucuslike material was used to investigate cell deposition on smear preparations made with three different instruments: plastic spatulas, wooden spatulas, and brush-tipped collectors. The total number of exfoliated cells and the total number of tumor cells present within the randomly distributed holes were then recorded for 41 smear preparations. For smears done with the brush, a total of 47,146 exfoliated cells were recorded; with wooden spatulas, 4517 cells; and with plastic spatulas, 7648 cells. When the brush was used, 6905 tumor cells were recorded. When wooden or plastic spatulas were applied, 563 and 1132 tumor cells were found, respectively. Thus, the brush yielded 12.2 and 6.1 times more tumor cells than plastic and wooden spatulas, respectively.

Cervix Uteri↗
PubMed1989

Plastic particle and tar pollution on beaches of Kuwait.

Twelve beaches on the northwestern Arabian Gulf coast of Kuwait were surveyed for the occurrence of plastic particles, tar balls and tar lumps. Particles were found on all beaches and were abundant on four: Suleibkhat, Fintas, Fahaheel and New Al Khiran. Most particles were composed of low-density polyethylene, but a few were of high-density polyethylene, polypropylene and polystyrene. Many were weathered and had traces of tar. Tar lumps and balls were present on all beaches, but were not as abundant as was expected, considering the heavy volume of oil tanker traffic in this region of the Arabian Gulf. Tar appeared to be less abundant than it was in 1979. With at least 33 plastics factories operating on the coast of Kuwait, it is possible that plastic particles occur more abundantly than has been observed in this study. The high winds and concurrent wave activity, which often vary in strength and direction but regularly occur here, probably play an important role in dispersing plastic particles which are washed up on to these beaches, making it difficult to accurately measure their abundance.

Journal Article↗
PubMed1994

Measurements of the electron dose distribution near inhomogeneities using a plastic scintillation detector.

PURPOSE: Accurate measurement of the electron dose distribution near an inhomogeneity is difficult with traditional dosimeters which themselves perturb the electron field. We tested the performance of a new high resolution, water-equivalent plastic scintillation detector which has ideal properties for this application. METHODS AND MATERIALS: A plastic scintillation detector with a 1 mm diameter, 3 mm long cylindrical sensitive volume was used to measure the dose distributions behind standard benchmark inhomogeneities in water phantoms. The plastic scintillator material is more water equivalent than polystyrene in terms of its mass collision stopping power and mass scattering power. Measurements were performed for beams of electrons having initial energies of 6 and 18 MeV at depths from 0.2-4.2 cm behind the inhomogeneities. RESULTS: The detector reveals hot and cold spots behind heterogeneities at resolutions equivalent to typical film digitizer spot sizes. Plots of the dose distributions behind air, aluminum, lead, and formulations for cortical and inner bone-equivalent materials are presented. CONCLUSION: The plastic scintillation detector is suited for measuring the electron dose distribution near an inhomogeneity.

Electrodes↗
PubMed1994

Storage of saline-adenine-glucose-mannitol suspended red cells in diethylhexyl phtalate and butyryl-n-trihexyl-citrate plasticized polyvinyl chloride containers. An in vitro comparative study.

Units of whole blood collected into butyryl-n-trihexyl-citrate (BTHC) and diethylhexyl phtalate (DEHP) plasticized polyvinylchloride (PVC) blood storage containers and processed by means of an 'Optipress', which allows automated removal of the buffy coat, were compared. Units collected into standard PVC containers processed by the traditional method (no buffy coat removal) were used as a control group. The red cell concentrates were suspended in saline-adenine-glucose-mannitol (SAGM) and stored 42 days at 2-6 degrees C. Comparison of the buffy coat depleted red cell concentrates showed that red cell energy and oxygen delivery capacity, as evidenced by ATP and 2,3-DPG values, were slightly better preserved in the BTHC plasticized container, compared to the DEHP container. The red cell membrane, however, was slightly less well preserved, (the hemolysis at day 42 with BTHC ww 0.39%; with DEHP, 0.20%) in this container. The higher ATP levels might lead to a better in vivo recovery of stored red cells. In vivo studies comparing both plastic containers, therefore are indicated in order to determine if these differences have practical significance. A longer holding time of the whole blood at room temperature before processing reduced the hemolysis (42 days stored RCC as 0.26%). Slightly more fibrinopeptide A (FPA) generation and marginally lower pH and 2,3-DPG values were observed in this situation. This finding suggests an effect of higher plasticizer levels on the red cell membrane.

Adenine↗
PubMed2005

Stem cell plasticity.

The central dogma in stem cell biology has been that cells isolated from a particular tissue can renew and differentiate into lineages of the tissue it resides in. Several studies have challenged this idea by demonstrating that tissue specific cell have considerable plasticity and can cross-lineage restriction boundary and give rise to cell types of other lineages. However, the lack of a clear definition for plasticity has led to confusion with several reports failing to demonstrate that a single cell can indeed differentiate into multiple lineages at significant levels. Further, differences between results obtained in different labs has cast doubt on some results and several studies still await independent confirmation. In this review, we critically evaluate studies that report stem cell plasticity using three rigid criteria to define stem cell plasticity; differentiation of a single cell into multiple cell lineages, functionality of differentiated cells in vitro and in vivo, robust and persistent engraft of transplanted cells.

Adult↗
PubMed2004

Phenotypic plasticity in Scenedesmus incrassatulus (Chlorophyceae) in response to heavy metals stress.

The microalgae genus Scenedesmus is commonly found in freshwater bodies, wastewater facilities and water polluted with heavy metals. Phenotypic plasticity in Scenedesmus has been documented in response to a wide variety of conditions; however, heavy metals have not been comprehensively documented as phenotypic plasticity inducers. In this study, we report the phenotypic plasticity of Scenedesmus incrassatulus (a non-spiny, four-cell coenobium forming species) in response to EC(50) value of copper, cadmium and hexavalent chromium. S. incrassatulus was grown in batch cultures in the presence of each metal. Chlorophyll-a content, cell size, parameters derived from the schematic energy-flux model for photosystem II, and morphotype expressions were recorded. Divalent cation metals induced unicellular forms, and hexavalent chromium produced out-of-shape coenobia corresponding to various stages of autospore formation. The changes induced by divalent metals were interpreted as phenotypic plasticity, because they were always associated to population doublings and were reversible when toxicant pressure was removed (only for Cu). Copper was the best inductor of unicellular forms and also affected significantly all the photosynthetic parameters measured. The developed morphotypes could confer ecological advantages to S. incrassatulus in metal stressed environments.

Animals↗
PubMed2004

The Helicobacter pylori plasticity region locus jhp0947-jhp0949 is associated with duodenal ulcer disease and interleukin-12 production in monocyte cells.

Colonization with Helicobacter pylori always results in chronic gastritis, which is controlled by infiltration of mononuclear cells and the subsequent release of cytokines like interleukin (IL)-12. To identify H. pylori factors involved in inducing cytokine production in mononuclear cells, a random H. pylori mutant library was screened for the inability to induce IL-12 production in monocyte THP-1 cells. Of the 231 random mutants screened, one mutant (M1) showed a consistent twofold decrease in the amount of IL-12 induction compared to the parental strain 1061 (P <0.01). Further characterization of mutant M1 revealed that the kanamycin resistance cassette had integrated in the jhp0945 gene, which is situated in an H. pylori strain-specific plasticity region. Three reference strains possessing this plasticity region induced significantly higher amounts of IL-12 when compared to the H. pylori 26695 reference strain, which does not possess this plasticity region. The role in disease outcome of jhp0945 as well as the neighbouring plasticity region genes jhp0947 and jhp049 was assessed in a Dutch population cohort. Firstly, the presence of jhp0947 was completely linked with that of jhp0949 and was roughly associated with jhp0945 (P=0.072), but not with the cag pathogenicity island (PAI) (P=0.464). The presence of the jhp0947 and jhp0949 genes, but not of jhp0945, was significantly associated with duodenal ulcer disease when compared to gastritis (P=0.027). Therefore, the jhp0947-jhp0949 locus may be a novel putative H. pylori marker for disease outcome independent of the cag PAI.

Cells, Cultured↗
PubMed2005

An elastic-plastic hybrid adhesion model for contacting rough surfaces in the presence of molecularly thin lubricant.

The study of adhesion has received considerable attention in recent years, partly due to advances in the design and fabrication of micro/nano devices. Many adhesion investigations are centered on single-spherical-contact models, which include the classic Johnson-Kendall-Roberts (JKR), improved Derjaguin-Muller-Toporov (IDMT), and Maugis-Dugdale (MD) models. Based on the IDMT single-asperity model, adhesive rough surface contact models have also been developed, which are valid for elastic and elastic-plastic contact conditions. A limitation of the IDMT-based models is that they are only valid for application cases with low adhesion parameter values. In this research, a contacting rough surface adhesion model was developed by combining an extended Maugis-Dugdale (EMD) model (which is only valid for elastic contacts) with an IDMT-based elastic-plastic adhesion model. The proposed model, termed the elastic-plastic hybrid adhesion model, is valid for the entire adhesion parameter range and also for elastic-plastic contacts. The proposed model gives results similar to the EMD rough surface model when the contact is primarily elastic. Moreover, the proposed model was compared to an IDMT-based model (ISBL model) and both gave similar results for contacts with low adhesion parameter values. With high adhesion parameter values, the ISBL model fails, whereas the proposed model correctly predicts higher adhesion. Last, based on the stiffness of the external force, the instability for adhesive rough surfaces in contact was also discussed, and it was postulated that a high peak value of the external force stiffness directly relates to the unstable contact process.

Journal Article↗