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 487 records · Page 27Linked to original sources
PubMed2006

Jack of all trades, master of some? On the role of phenotypic plasticity in plant invasions.

Invasion biologists often suggest that phenotypic plasticity plays an important role in successful plant invasions. Assuming that plasticity enhances ecological niche breadth and therefore confers a fitness advantage, recent studies have posed two main hypotheses: (1) invasive species are more plastic than non-invasive or native ones; (2) populations in the introduced range of an invasive species have evolved greater plasticity than populations in the native range. These two hypotheses largely reflect the disparate interests of ecologists and evolutionary biologists. Because these sciences are typically interested in different temporal and spatial scales, we describe what is required to assess phenotypic plasticity at different levels. We explore the inevitable tradeoffs of experiments conducted at the genotype vs. species level, outline components of experimental design required to identify plasticity at different levels, and review some examples from the recent literature. Moreover, we suggest that a successful invader may benefit from plasticity as either (1) a Jack-of-all-trades, better able to maintain fitness in unfavourable environments; (2) a Master-of-some, better able to increase fitness in favourable environments; or (3) a Jack-and-master that combines some level of both abilities. This new framework can be applied when testing both ecological or evolutionary oriented hypotheses, and therefore promises to bridge the gap between the two perspectives.

Adaptation, Physiological↗
PubMed2005

A comparison of phenotypic plasticity in the native dandelion Taraxacum ceratophorum and its invasive congener T. officinale.

We compared plastic responses to variation in the light environment for sympatric populations of native and exotic dandelion species, Taraxacum ceratophorum and Taraxacum officinale. Plasticity in leaf size, inflorescence height, reproductive phenology and dispersal-related traits were measured under experimentally altered light quality (red : far-red light ratio, R : FR) and light intensity (photosynthetically active radiation, PAR). To test whether differences in means and reaction norms of dispersal-related traits between species affected colonization potential, we created seed-dispersal models based on seed-fall rate and release height. Differences in plasticity between species were not systematic, but varied in direction and magnitude among traits. Taraxacum officinale produced larger leaves that exhibited greater plasticity in size under variable light intensity than T. ceratophorum. Plasticity in scape length at flowering occurred in relation to R : FR ratio in both species, but tended to be greater in T. ceratophorum. Seed-bearing scapes of T. officinale were taller and more canalized in height across light regimes than scapes of T. ceratophorum. Seeds of T. officinale were smaller than seeds of T. ceratophorum. Models predict greater dispersal in T. officinale within open and vegetated habitats. In contrast to the idea that plasticity promotes invasiveness, results suggest that the lack of plasticity in dispersal-related traits enhances the colonization potential of T. officinale.

Adaptation, Physiological↗
PubMedDate not supplied

Dose errors due to charge storage in electron irradiated plastic phantoms.

Commercial plastics used for radiation dosimetry are good electrical insulators . Used in electron beams, these insulators store charge and produce internal electric fields large enough to measurably alter the electron dose distribution in the plastic. The reading per monitor unit from a cylindrical ion chamber imbedded in a polymethylmethacrylate (PMMA) or polystyrene phantom will increase with accumulated electron dose, the increase being detectable after about 20 Gy of 6-MeV electrons. The magnitude of the effect also depends on the type of the plastic, the thickness of the plastic, the wall thickness of the detector, the diameter and depth of the hole in the plastic, the energy of the electron beam, and the dose rate used. Effects of charge buildup have been documented elsewhere for very low energy electrons at extremely high doses and dose rates. Here we draw attention to the charging effects in plastics at the dose levels encountered in therapy dosimetry where ion chamber or other dosimeter readings may easily increase by 5% to 10% and where a phantom, once charged, will also affect subsequent readings taken in 60Co beams and high-energy electron and x-ray beams for periods of several days to many months. It is recommended that conducting plastic phantoms replace PMMA and polystyrene phantoms in radiation dosimetry.

Electrons↗
PubMed2006

The relative contributions of developmental plasticity and adult acclimation to physiological variation in the tsetse fly, Glossina pallidipes (Diptera, Glossinidae).

Recent reviews of the adaptive hypotheses for animal responses to acclimation have highlighted the importance of distinguishing between developmental and adult (non-developmental) phenotypic plasticity. There has been little work, however, on separating the effects of developmental plasticity from adult acclimation on physiological traits. Therefore, we investigated the relative contributions of these two distinct forms of plasticity to the environmental physiology of adult tsetse flies by exposing developing pupae or adult flies to different temperatures and comparing their responses. We also exposed flies to different temperatures during development and re-exposed them as adults to the same temperatures, to investigate possible cumulative effects. Critical thermal maxima were relatively inflexible in response to acclimation temperatures (21, 25, 29 degrees C) with plasticity type accounting for the majority of the variation (49-67%, nested ANOVA). By contrast, acclimation had a larger effect on critical thermal minima with treatment temperature accounting for most of the variance (84-92%). Surprisingly little of the variance in desiccation rate could be explained by plasticity type (30-47%). The only significant effect of acclimation temperature on standard (resting) metabolic rate of adult flies was at 21 degrees C, resulting in treatment temperature, rather than plasticity type, accounting for the majority of the variance (30-76%). This study demonstrates that the stage at which acclimation takes place has significant, though often different, effects on several adult physiological traits in G. pallidipes, and therefore that it is not only important to consider the form of plasticity but also the direction of the response and its significance from a life-history perspective.

Acclimatization↗
PubMed2006

The evolutionary consequences of ecological interactions mediated through phenotypic plasticity.

Phenotypic plasticity describes the capacity of a genotype to exhibit a range of phenotypes in response to variation in the environment. Environmental variation encompasses both abiotic and biotic components of the environment, including interactions among organisms. The strength and outcome of many ecological interactions, ranging from antagonism to mutualism, are mediated through the phenotypically plastic responses of one or more players in the interaction. Herein, three broadly defined, non-mutually exclusive, evolutionary consequences of ecological interactions mediated through phenotypic plasticity are discussed. (1) The predictable plastic response of one partner can favor behaviors, physiological responses, and life history traits of an interacting partner that manipulate, circumvent, or ameliorate the response of that partner. (2) Phenotypic plasticity can generate substantial spatial and temporal variation within and among populations. Such phenotypic variation can depend on the density and identity of interacting players in an ecological community, and can ultimately affect the evolutionary outcome of ecological interactions. (3) Phenotypic plasticity affects the strength and direction of natural selection. Ecological interactions mediated through phenotypic plasticity are ubiquitous in nature, and the potential evolutionary consequences of these interactions illustrate the complexity inherent in understanding evolution in a community context.

Adaptation, Physiological↗
PubMed1975

The mechanism of plasticization of the abdominal cuticle in Rhodnius.

1. The mechanism of plasticization of the abdominal cuticle in Rhodnius larvae has been investigated, using the properties of loops of cuticle under varying test conditions as a model for the behaviour of the cuticle in vivo. 2. It is supposed that plasticization is effected by a change in the intracuticular environment. A number of model mechanisms for plasticization may be proposed, which suppose that the epidermis is capable of regulating (a) pH, (b) ionic strength,(c) Ca and/or Mg, (d) urea, within the cuticle. 3. Analyses of cuticle ash show that models(b) and (c) are not responsible for plasticization in vivo. The levels of inorganic ions within the unplasticized cuticle are not sufficiently high to allow plasticization upon their removal. 4. No evidence for model (d) has been found; urea does not occur in the cuticle in detectable quantities. 5. Exact measurements of the intracuticular pH have not been achieved but straining experiments strongly suggest that a change in pH occurs within the cuticle on plasticization. This pH change is probably large enough to account for the increased extensibility shown by plasticized cuticle.

Abdominal Muscles↗
PubMed2006

Enhanced long-term potentiation-like plasticity of the trigeminal blink reflex circuit in blepharospasm.

Benign essential blepharospasm (BEB) is a focal cranial dystonia affecting eye closure. Here, we tested the hypothesis that BEB is associated with abnormal plasticity of the neuronal circuits mediating reflex blinks. In patients with BEB and healthy age-matched controls, we used the conditioning protocol introduced by Mao and Evinger (2001) to induce long-term potentiation (LTP)-like plasticity in trigeminal wide dynamic range neurons of the blink reflex circuit. High-frequency trains of electrical stimuli were repeatedly given over the right supraorbital nerve (SO) and timed to coincide with the R2 response elicited by a preceding SO stimulus. High-frequency stimulation (HFS) resulted in a long-lasting and input-specific potentiation of the R2 response in both groups, yet the facilitation of the R2 response was markedly increased in patients relative to controls. Botulinum toxin (BTX) injections in both orbicularis oculi muscles normalized the previously enhanced LTP-like plasticity of the R2 response. The increased responsiveness to HFS provides first-time evidence that LTP-like plasticity is increased in the trigeminal reflex circuit of patients affected by BEB. The results also show that the enhanced modifiability is not fixed in BEB, because BTX injections can transiently restore normal LTP-like plasticity. We propose that an abnormal corneal input induced by excessive blinking exacerbates increased LTP-like plasticity in BEB. BTX treatment removes the latter and restores plasticity toward normal values. Our results support the concept that maladaptive reorganization contributes to the pathophysiology of focal dystonias.

Aged↗
PubMed1989

[Development of new type plastics air turbine handpiece for dental use].

The noise generated by the metal air turbine handpiece employed in dental practice is considerable and attended with predominant high frequency components. Therefore, investigation of the noise generation mechanism and development of a silent air turbine handpiece was only a matter of course. In addition, the metal air turbine hardpiece is comparatively heavy and its production cost is high. From this point of view as well, production of a light air turbine handpiece at low cost is also desirable. In order to overcome the objections to the metal air turbine handpiece, appropriate plastics materials were employed wherever possible. In this study, the number of revolutions, noise level, frequency analysis, start pressure and weight of newly produced plastics handpieces and metal handpieces were examined and compared. The following results were obtained: 1. The number of revolutions of single-nozzle type air turbine handpieces encased in plastics housings and fitted with metal turbine rotors was higher than that of all-metal air turbine handpieces. The noise level of the former tended to be lower. 2. The number of revolutions of multi-nozzle type air turbine handpieces encased in plastics housings and fitted with turbine rotors with plastics turbine blades was almost equal to that of similar metal handpieces, with the noise level tending to be lower. 3. In the case of handpieces fitted with turbine rotors with dynamic balance, the number of revolutions was high and the noise level was low. This indicated that dynamic balance was a factor affecting the number of revolutions and noise level. 4. Narrow band sound frequency analysis of single-nozzle type air turbine handpieces showed a sharp peak at the fundamental frequency which was the same as the number of revolutions multiplied by the number of rotor turbine blades. It is thought that the noise from air turbine handpieces was aerodynamic in origin, being generated by the periodical interruption of steady air flow by rotor turbine blades. 5. The start pressure of plastics handpieces was almost equal to that of metal handpieces. 6. The weight of plastics handpieces was 20%-50% of that of metal handpieces. The present results indicate that it is possible to produce a new type of light, silent and aesthetical air turbine handpiece.

Dental Cavity Preparation↗
PubMed1977

[Studies of the dental methacrylic resins. (V) Effects of molecular weight and temperature on the plasticity (author's transl)].

The plasticity, the douing time, and the working time, of the mixture of powder-liquid type methacrylic resin were measured under the various circumstances of the elapsed time and the certain temperature. Six polymethyl methacrylates, whose molecular weight was prepared by mean of gamma-ray irradiation, were used as the polymer of resin, again methyl methacrylate being used as the monomer of resin. The results obtained are as follows: (1) The plasticity is reduced with the increase of the molecular weight of the polymer. (2) The plasticity, generally, is reduced with the time elapsed, but its values appear at 10 min. and 5 min. elapsed at 16 degrees C and 23 degrees C respectively. (3) The plasticities of the mixtures of polymers with 6 X 10(4), 8 X 10(4), 20 X 10(4) and 34 X 10(4) molecular weights are increased with the increase of temperature. The plasticities of the mixtures of polymers with 60 X 10(4) and 74 X 10(4) molecular weights at 0 min. time elapsed, indicate their maximum value at 30 degrees C. At 5 min. time elapsed plasticities of all mixtures indicate their maximum value at 23 degrees C. Over 5 min. time elapsed, however, the plasticity is reduced with the increase of temperature. (4) The doughing time and the working time are reduced with the increase of molecular weight of the polymer and the temperature.

Acrylates↗
PubMed1988

The effect of the plasticizer di-2-ethylhexyl phthalate on the survival of stored RBCs.

Recent in vitro studies have shown that di-2-ethylhexyl-phthalate (DEHP) inhibits the deterioration of RBCs during refrigerated storage in containers that use this compound as a plasticizer. The experiments described in this report were designed to assess whether this in vitro protective effect of DEHP would result in a prolonged in vivo survival of RBCs infused into normal human recipients. Whole blood collected from ten normal donors was stored for 35 days in citrate-phosphate-dextrose-adenine (CPDA-1) anticoagulant contained in polyvinylchloride (PVC) bags plasticized with DEHP or a trimellitate compound that is known to have low leachability. Aliquots of RBCs from each container were then labeled with chromium-51 and were reinfused into the original donors. For blood stored in DEHP-plasticized PVC bags, 24% more red cells survived in vivo 24 hours after reinfusion than was observed when the blood had been stored in trimellitate-plasticized bags (P less than .001). Whole blood stored in glass bottles showed a similar improvement in in vivo survival when DEHP was added in weekly increments to mimic the accumulation of this plasticizer seen during storage in plastic containers. Survival of packed red cells stored in the presence of DEHP increased by 14% compared with storage in trimellitate-plasticized bags (P less than .05). In agreement with previous studies, hemolysis and microvesicle formation were also reduced in the presence of DEHP. These results suggest that proposed new storage systems lacking DEHP should be carefully evaluated to determine whether adequate post-transfusion survival of RBCs may be achieved.

Blood Preservation↗
PubMed1993

The selection of plastic materials for blood bags.

The procedures used in the preparation of blood components together with the processes used in the manufacture of multiple blood bag systems impose a unique combination of requirements that severely limits the selection of plastics. Plasticized PVC, the plastic used in the first blood bags introduced by Carl Walter over 40 years ago, remains the material of choice today. Blood bag material research has focused on two areas: (1) the development of containers with increased gas permeability for the storage of platelet concentrates; and (2) the reduction or elimination of plasticizer contamination of stored blood components. This research has led to the development of several second-generation containers that have improved the quality and extended the allowable storage period of platelet transfusion products. Plastics virtually free of extractives are available for the storage of platelets and plasma, but elimination of plasticizers from RBC products has not yet been achieved.

Blood Component Removal↗
PubMed1981

Migration of acetyl-tributylcitrate from plastic film into poultry products during microwave cooking.

Migration of the plasticizer acetyl-tributylcitrate from a plastic film into poultry meat and model food systems was studied. It was determined that this commonly used plasticizer migrated from the plastic film during microwave cooking by comparing the infrared spectra of the film used to cover the chicken to unused film. The peak at 1730 cm-1 was substantially reduced in the used film relative to a standard band at 2920 cm-1. Subsequent experimentation verified by chemical analysis that the compound was acetyl-tributylcitrate and that it migrated from the film into the chicken meat. Experiments using comminuted chicken meat and model food systems in a test cell indicated that the migration of the plasticizer was time related with a plateau being reached after cooking for 8 min. Studies with model food systems in the test cell indicated that the lipid portion of the system was responsible for migration and retention of acetyl-tributylcitrate in the sample. Increasing the lipid portion of the system tended to increase the amount of plasticizer found.

Animals↗
PubMed2001

Plasticity, hippocampal place cells, and cognitive maps.

Memory of even the briefest event can last a lifetime. Thus, learning and memory require neuronal mechanisms that allow rapid, yet persistent, changes to brain circuits. Hippocampal neuropsychology, synaptic and cellular electrophysiology, pharmacology, and molecular genetics converge and begin to reveal these mechanisms. Lesions of the hippocampus profoundly impair memory for recent events in humans and rodents. Circuits within the hippocampus are remarkably plastic, and this plasticity is mediated in part through changes in synaptic strength and revealed by long-term potentiation (LTP) and long-term depression (LTD). N-methyl D-aspartate (NMDA) receptors, a subtype of glutamate receptor, are crucial for inducing these plastic changes, and blocking these receptors reduces plasticity and impairs learning in tasks that require the hippocampus. Molecular genetic alterations that disrupt signaling mechanisms downstream of the NMDA receptor also prevent LTP induction and impair hippocampus-dependent learning. N-methyl D-aspartate receptor mechanisms have also been linked to information coding by hippocampal neurons. Hippocampal cells fire selectively in specific and restricted locations (place fields) as rodents move through open environments. Place fields form within minutes and persist for months. N-methyl D-aspartate receptor antagonists prevent the establishment of stable place fields. The same molecular genetic manipulations that interfere with hippocampal NMDA receptor function, prevent LTP induction, and impair spatial learning also disrupt the formation of stable hippocampal place fields. Finally, learning has been improved in mice with genetically modified NMDA receptors that enhance LTP induction. Thus, hippocampal cells "learn" to encode the salient features of experience through NMDA receptor-dependent synaptic plasticity mechanisms, and this rapid and persistent neuronal encoding is a crucial step toward the formation of long-term memory. Disruption of these plasticity mechanisms may underlie age-related memory deficits.

Amnesia↗
PubMed2004

The role of ECM molecules in activity-dependent synaptic development and plasticity.

Growth and guidance of neurites (axons and dendrites) during development is the prerequisite for the establishment of functional neural networks in the adult organism. In the adult, mechanisms similar to those used during development may regulate plastic changes that underlie important nervous system functions, such as memory and learning. There is now ever-increasing evidence that extracellular matrix (ECM)-associated factors are critically involved in the formation of neuronal connections during development, and their plastic changes in the adult. Here, we review the current literature on the role of ECM components in activity-dependent synaptic development and plasticity, with the major focus on the thrombospondin type I repeat (TSR) domain-containing proteins. We propose that ECM components may modulate neuronal development and plasticity by: 1) regulating cellular motility and morphology, thus contributing to structural alterations that are associated with the expression of synaptic plasticity, 2) coordinating transsynaptic signaling during plasticity via their cell surface receptors, and 3) defining the physical parameters of the extracellular space, thereby regulating diffusion of soluble signaling molecules in the extracellular space (ECS).

Animals↗
PubMed2003

Age-dependent alterations of long-term synaptic plasticity in thyroid-deficient rats.

Thyroid hormone deficiency during a critical period of development profoundly affects cognitive functions such as attention, learning, and memory, but the synaptic alterations underlying these deficits remain unexplored. The present study examines the effect of congenital hypothyroidism on long-term synaptic plasticity. This plasticity is believed to be essential for learning and memory and for activity-dependent regulation of synapse formation in the developing brain. We found that the neonatal expression of long-term potentiation (LTP), long-term depression (LTD), depotentiation, and de-depression in hippocampal slices from hypothyroid animals was similar to that of controls. To examine the postnatal development of these plasticities, we used slices from neonatal (2-3 weeks) and adult (7-8 weeks) rats. This work demonstrates that the ability to express all these forms of synaptic plasticity is reduced in an age-dependent manner in control rats. LTP and depotentiation are also downregulated in adult hypothyroid rats, but we have found that de-depression is not affected during maturation. In addition, these animals express LTD at ages at which controls fail to induce it. In contrast, input/output experiments have shown greater levels of basal synaptic efficacy in hypothyroid adults, and this effect is probably related to the higher probability of release observed by paired-pulse experiments. Nevertheless, these effects appear to be unrelated to the differences observed in long-term synaptic plasticity, as no correlation was found between basal synaptic efficacy and the degree of LTD and de-depression. Furthermore, the NMDA-receptor antagonist amino-phosphonopentanoic acid (APV) completely blocked LTD, which suggests a postsynaptic locus of this alteration. Because LTD has been associated with novelty acquisition, we suggest that the greater LTD observed in adult hypothyroid rats might be related to the hyperactivity of these animals. However, other possibilities such as a retarded maturation of synaptic plasticity must be taken into account.

Aging↗
PubMed1994

Ion-selective membranes with low plasticizer content: electroanalytical characterization and biocompatibility studies.

High molecular weight poly(vinyl chloride) and aliphatic polyurethane (Tecoflex)-based ion selective membranes, with normal and reduced amounts of plasticizer, as well as without plasticizer, were tested with respect to their analytical properties, their biocompatibility, and cellular responses. The analytical properties of the membranes did not change significantly within a wide range of polymer to plasticizer ratios. However, the membranes with reduced plasticizer content had better adhesive properties, less anion interference, extended life time, and better biocompatibility. Using the cage implant system, the results showed that an increase of plasticizer weight percent in Tecoflex membranes correlated positively with the increase in host inflammatory response up to 14 days of implantation. The results also demonstrated that both PVC and Tecoflex-based ion-selective membranes with the most common membrane composition (1:2 polymer to plasticizer ratio) exhibited a similar acute inflammatory response, but the PVC-based membrane elicited a reduced chronic inflammatory response when compared with the Tecoflex-based membrane.

Adhesiveness↗
PubMed2004

A new method for the evaluation of biodegradable plastic using coated cellulose paper.

A highly sensitive analytical method for evaluation of poly(L-lactide) (PLA), poly(epsilon-caprolactone) (PCL), poly(beta-hydroxybutyrate) (PHB), and poly(butylene succinate) (PBS) degradability was developed using coated cellulose paper, prepared by penetration and adhesion of these plastics into/onto the cellulose paper. Enzymatic degradability of the obtained plastic coated papers was evaluated using various commercial proteases and lipases. PLA coated paper was highly susceptible to subtilisin and mammalian enzymes, alpha-chymotrypsin, elastase and trypsin. To our knowledge, this is the first report on the degradation of PLA coated paper using subtilisin and mammalian enzymes. Almost all lipase preparations degraded PCL and PHB coated papers but not PBS coated paper. The biodegradability of plastic coated paper was greater than that of plastic powder. The penetration of plastic into cellulose paper by coating improved the plastic degradability, and can be regulated easily.

Biocompatible Materials↗
PubMed2002

Long-term consolidation and retention of learning-induced tuning plasticity in the auditory cortex of the guinea pig.

The major goal of this study was to determine whether classical conditioning produces long-term neural consolidation of frequency tuning plasticity in the auditory cortex. Local field potentials (LFPs) were obtained from chronically implanted adult male Hartley guinea pigs that were divided into conditioning (n = 4) and sensitization control (n = 3) groups. Tuning functions were determined in awake subjects for average LFPs (approximately 0.4 to 36.0 kHz, -20 to 80 dB) immediately before training as well as 1 h and 1, 3, 7, and 10 days after training; sensitization subjects did not have a 10-day retention test. Conditioning consisted of a single session of 30 to 45 trials of a 6-s tone (CS, 70 dB) that was not the best frequency (BF, peak of a tuning curve), followed by a brief leg shock (US) at CS offset. Sensitization control animals received the same density of CS and US presentations unpaired. Heart rate recordings showed that the conditioning group developed conditioned bradycardia, whereas the sensitization control group did not. Local field potentials in the conditioning group, but not in the sensitization group, developed tuning plasticity. The ratio of responses to the CS frequency versus the BF were increased 1 h after training, and this increase was retained for the 10-day period of the study. Both tuning plasticity and retention were observed across stimulus levels (10-80 dB). Most noteworthy, tuning plasticity exhibited consolidation (i.e., developed greater CS-specific effects across retention periods), attaining asymptote at 3 days. The findings indicate that LFPs in the auditory cortex have three cardinal features of behavioral memory: associative tuning plasticity, long-term retention, and long-term consolidation. Potential cellular and subcellular mechanisms of LFP tuning plasticity and long-term consolidation are discussed.

Animals↗