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 451 records · Page 25Linked to original sources
PubMed2004

Influence of blood collection in plastic vs. glass evacuated serum-separator tubes on hormone and tumour marker levels.

Introduction of preanalytical automation in our laboratory required the use of plastic blood collection tubes. Because of possible interference caused by adsorption of components to the plastic wall and because there is virtually no literature on this subject, we investigated the influence of collection of serum in plastic tubes on the results of nearly all our immunoassays for hormones and tumour markers. Blood from healthy volunteers was collected simultaneously in glass and plastic tubes, or sera prepared from blood collected in glass tubes were brought into the plastic tubes under investigation. Hormone and tumour marker levels were measured in the pairs thus obtained. Results were analysed using paired t-tests or Wilcoxon signed rank tests. We found small but statistically significant differences (p<0.05) between glass and plastic for free triiodothyronine, progesterone, prolactin, prostate-specific antigen and pregnancy-associated plasma protein-A. Non-significant trends (0.05<p<0.15) were seen with alpha-foetoprotein, androstenedione, BR (an assay for carbohydrate antigen 15.3), human chorionic gonadotropin and testosterone. Passing and Bablok regression analysis, however, revealed no clinically relevant differences (slopes ranged from 0.89 for progesterone to 1.07 for pregnancy-associated plasma protein-A, while intercepts were all small). We concluded that a switch to plastic blood collection tubes could occur without any implications for the interpretation of results.

Biomarkers, Tumor↗
PubMed2006

Cortical plasticity and motor activity studied with transcranial magnetic stimulation.

For decades cortical representations of the parts of the body have been considered to be unchangeable. This view has changed radically during the past 20 years using new tools designed to study plasticity in the adult human brain. Transcranial magnetic stimulation (TMS) is a valuable non-invasive technique for exploring the ability of the motor cortex to change during motor skill acquisition. Results obtained with TMS in neurological patients as well as in normal subjects demonstrate that cortical plasticity is a necessity for correct adaptation to the continuously changing environment. Topographical reorganization of the motor cortex depends on the types of movements performed by the subjects. During simple training, the cortical representation is enlarged, and it returns to its initial size when the task is overlearned. These transient modifications characterize simple motor training. Motor skills in which coordination of distal and proximal muscles, precision of the task and spatio-temporal constraints are associated, has a different impact on cortical reorganization. We propose that years of practice of a complex motor skill induces a new cortical topography that must be interpreted as structural plasticity which provides the capacity to execute a plastic behaviour instead of a stereotypical movement. We review the neuronal mechanisms underlying plasticity in different types of movement. We stress new emerging notions, such as overlap of cortical maps, and system dynamics at single neuron and network levels, to explain the reorganization of movement representations that encode motor skill. Dendritic arborizations as functional computing elements, newly generated neurons in adult brain, and plastic architectures of cortical networks operating as distributed functional modules are new hypotheses for structural plasticity.

Adaptation, Physiological↗
PubMed2005

Dissociating barrel development and lesion-induced plasticity in the mouse somatosensory cortex.

In the mouse somatosensory cortex, thalamocortical axons (TCAs) corresponding to individual whiskers cluster into restricted barrel domains during the first days of life. If whiskers are lesioned before that time, the cortical space devoted to the afferents from the damaged whisker shrinks and becomes occupied by thalamocortical afferents from neighboring unlesioned whiskers. This plasticity ends by postnatal day 3 (P3) to P4 when barrels emerge. To test whether TCA development and lesion-induced plasticity are linked, we used monoamine oxidase A knock-out (MAOA-KO) mice in which normal TCA development is halted by an excess of serotonin. Normal TCA development can be restored when serotonin levels are lowered by parachlorophenylalanine (PCPA). By varying the time of PCPA administration, we found that barrel development can be reinitiated until P11, although the emergence of TCA clusters becomes gradually slower and less complete. In mice in which barrels emerge 3 d later than the normal schedule, at P6 instead of P3, we examined lesion-induced plasticity. We find a progressive decline of the lesion-induced plasticity and a closure at P3, similar to normal mice, showing that this plasticity is not influenced by an excess of serotonin levels. Thus, in MAOA-KO mice, the emergence of barrel patterning can be delayed without a concomitant delay in lesion-induced plasticity, and the cortical space devoted to one whisker representation cannot be modified by the periphery once patterning is imprinted in the subcortical relays. We conclude that the closure of the lesion-induced plasticity period in the barrelfield is probably not determined at the cortical level.

Animals↗
PubMed2003

Origins and biological accumulation of small plastic particles in fur seals from Macquarie Island.

One hundred and sixty four plastic particles (mean length 4.1 mm) recovered from the scats of fur seals (Arctocephalus spp.) on Macquarie Island were examined. Electron micrographs of 41 of the plastic particles showed that none could be identified as plastic pellet feedstock from their shapes. Commonly, such pellets are cylindrical and spherical. Instead, all the 164 plastic particles from the seal scats were angular particles of 7 colors (feedstock particles are normally opaque or white) and could be classified into 2 categories: i) fragmented along crystal lines and likely to be the result of UV breakdown; and ii) worn by abrasion (where striations were clearly visible) into irregular shapes with rounded corners. White, brown, green, yellow and blue were the most common colors. In composition, they came from 5 polymer groups; polyethylene 93%, polypropylene 4%, poly(1-Cl-1-butenylene) polychloroprene 2%, melamine-urea (phenol) (formaldehyde) resin 0.5%, and cellulose (rope fiber) 0.5%. The larger groups are buoyant with a specific gravity less than that of seawater. These small plastic particles are formed from the breakdown of larger particles (fragments). Their origin seems to be from the breakdown of user plastics washed ashore and ground down on cobbled beaches. Certainly most particles (70%) had attained their final form by active abrasion. It is hypothesized that the plastic particles were washed out to sea and then selected by size and consumed by individuals of a pelagic fish species, Electrona subaspera, who in turn were consumed by the fur seals. Thus, the particles were accumulated both by the fish and the seals in the usual process of their feeding.

Animals↗
PubMedDate not supplied

Plasticizers and their effects on microencapsulation process by spray-drying in an aqueous system.

Microencapsulated theophylline particles were prepared by an aqueous spray-drying process using hydroxypropylmethylcellulose. The effect of different plasticizers, triethylcitrate, polyethylene glycol, propylene glycol, glycerin and citric acid, was investigated. Triethylcitrate, a water-insoluble plasticizer, produced a porous honeycomb-like microcapsule wall resulting in rapid drug release. The presence of the plasticizers also influenced crystallization of the drug. The formation of a solid drug dispersion was observed with the addition of citric acid or glycerin. Changes in the pH of liquid feed caused by the plasticizer had an effect on the product dissolution profile, but this was not a major factor. Formation of pores due to leaching of plasticizers during dissolution enhanced drug release. Flow property measurements indicated that the plasticizers also affect the cohesiveness of the spray-dried products. Compared to the microcapsules formed without any plasticizers, propylene glycol, glycerin and citric acid appeared to be beneficial to the microcapsule wall formation, with microcapsules containing citric acid having the slowest drug release.

Crystallization↗
PubMedDate not supplied

Citric acid as a plasticizer for spray-dried microcapsules.

An aqueous spray-drying process was used to coat theophylline particles with a cellulose polymer, sodium carboxymethylcellulose (NaCMC) or hydroxypropylmethylcellulose (HPMC). Effect of a plasticizer, citric acid, was studied. Strength of cast films have a direct relationship to the dissolution T50% values of the respective spray-dried products. With varying plasticizer concentrations, changes in interaction between plasticizer and polymer, and in size of crystallized drug crystals, were observed with HPMC films. The plasticizer content also affected the films of NaCMC by bringing about a change in the form and arrangement of the drug. X-ray diffraction analyses of the different spray-dried products revealed a possibility of the predominance of different crystal forms. Spherical spray-dried microcapsules of NaCMC were formed with a 20-30% w/w plasticizer content. With HPMC, as plasticizer concentration was increased there was a corresponding increase in mean size of the spray-dried products. In terms of drug release and formation of spherical particles, a plasticizer concentration of 30% w/w was found to be suitable for both HPMC and NaCMC.

Capsules↗
PubMed2002

Factors affecting lead leaching from microwavable plastic ware made with lead-containing pigments.

Although food contact polymers do not normally contain lead, it is suspected that lead may be leached from some microwavable plastic ware items made in Thailand with lead-containing pigments. The purpose of this study was to examine relationships with regard to lead leached from microwavable plastic ware. Four factors were studied: pH, heat level, extraction time, and number of repeated extractions. A total of 243 samples of microwavable plastic ware items locally manufactured in Thailand were used. This study used three pH values (3.5, 4.5, and 6.5) and three heat levels (levels 3, 6, and 9 [170, 500, and 850 W, respectively]). Acetic acid was used both as the extracting agent and for adjusting the pH. Samples were collected at each level at 1, 3, and 5 min, and the amount of leached lead was measured with an atomic adsorption spectrometer. The results of this study show that pH, heat, and extraction time affected the amount of lead leaching from microwavable plastic ware. The amount of lead leaching increased with decreasing pH but increased with increasing heat level and extraction time. On the basis of these three factors, the results of this study indicate that the pH of the extractant (r = -0.592, P < 0.01), the heat level of extraction (r = 0.293, P < 0.01), the extraction time (r = 0.226, P < 0.01), and the number of extractions (r = -0.153, P < 0.01) are related to lead leaching from microwavable plastic ware. The relationship between the pH of the extractant, the heat level of extraction, and the extraction time significantly moderated lead leaching from microwavable plastic ware (R2 = 0.511, P < 0.001). For all factors, the amount of lead leaching was lower than the permissible level of 1 mg/liter specified by the Minister of Public Health. In conclusion, a combination of high acid, prolonged heating, and extraction time accelerated the amount of lead leaching from microwavable plastic ware, but the incidence of lead leaching was negligible.

Acetic Acid↗
PubMed2000

[Fifty years of plastic surgery in the Netherlands. V. History].

For many centuries plastic surgical operations have been practised incidentally by general surgeons. Both World Wars combined with a multidisciplinary approach have been instrumental to the development of plastic surgery as a specialty. The Great War experience of maxillofacial surgery was for some surgeons in Europe a reason to dedicate their lives solely towards plastic surgery. A prominent Dutch surgeon in this field was J.F.S. Esser. With his systematic study and clinical application of arterial flaps in plastic surgery he proved to be far ahead of his time. Plastic surgery as such was established in the Netherlands after World War II in 1950 by the triumvirate Koch, Raadsveld and Honig. In the beginning, plastic surgery was strongly British influenced, while now, 50 years later, European cooperation on harmonization of the training in plastic surgery of a good quality is in progress.

History, 20th Century↗
PubMed2000

Abnormal synaptic plasticity and impaired spatial cognition in mice transgenic for exon 1 of the human Huntington's disease mutation.

Huntington's disease (HD) is an autosomal dominant progressive and fatal neurodegenerative brain disorder caused by an expanded CAG/polyglutamine repeat in the coding region of the gene. Presymptomatic Huntington's disease patients often exhibit cognitive deficits before the onset of classical symptoms. To investigate the possibility that changes in synaptic plasticity might underlie cognitive impairment in HD, we examined hippocampal synaptic plasticity and spatial cognition in a transgenic mouse (R6/2 line) expressing exon 1 of the human Huntington's disease gene containing an expanded CAG repeat. This mouse exhibits a progressive and fatal neurological phenotype that resembles Huntington's disease. We report that R6/2 mice show marked alterations in synaptic plasticity at both CA1 and dentate granule cell synapses, and impaired spatial cognitive performance in the Morris water maze. The changes in hippocampal plasticity were age dependent, appearing at CA1 synapses several weeks before they were observed in the dentate gyrus. Deficits in synaptic plasticity at CA1 synapses occurred before an overt phenotype. This suggests that altered synaptic plasticity contributes to the pre-symptomatic changes in cognition reported in human carriers of the Huntington' disease gene. The temporal and regional changes in synaptic plasticity within the hippocampus mirror the appearance of neuronal intranuclear inclusions, suggesting a relationship between polyglutamine aggregation and dysfunction.

Action Potentials↗
PubMed2000

Synaptic plasticity in the human dentate gyrus.

Activity-dependent plasticity is a fundamental feature of most CNS synapses and is thought to be a synaptic correlate of memory in rodents. In humans, NMDA receptors have been linked to verbal memory processes, but it is unclear whether NMDA receptor-dependent synaptic plasticity can be recruited for information storage in the human CNS. Here we have for the first time analyzed different forms of synaptic plasticity in human hippocampus. In human subjects who show a morphologically intact hippocampus that is not the primary seizure focus, NMDA receptor-dependent long-term potentiation (LTP) and forskolin-induced long-lasting potentiation are readily induced at the perforant path-dentate gyrus synapse. In this group, long-term potentiation could be partially depotentiated by low-frequency stimulation. Because patients with a hippocampal seizure focus showed a marked reduction in verbal memory performance in previous studies, we asked whether synaptic plasticity is similarly affected by the presence of a hippocampal primary seizure focus. We found that the amount of potentiation induced by high-frequency stimulation or perfusion of forskolin is dramatically reduced in this patient group. In addition, low-frequency stimulation is not effective in inducing synaptic depression. In summary, we show that activity-dependent synaptic plasticity with properties similar to the rodent is available for information storage in the human hippocampus. Because both verbal memory processes and synaptic plasticity are impaired by a hippocampal seizure focus, we suggest that impaired synaptic plasticity may contribute to deficient declarative memory in human temporal lobe epilepsy.

1-Methyl-3-isobutylxanthine↗
PubMed2001

Body image, psychosocial functioning, and personality: how different are adolescents and young adults applying for plastic surgery?

This study addressed three questions: (1) Do adolescents undergoing plastic surgery have a realistic view of their body? (2) How urgent is the psychosocial need of adolescents to undergo plastic surgery? (3) Which relations exist between bodily attitudes and psychosocial functioning and personality? From 1995 to 1997, 184 plastic surgical patients aged 12 to 22, and a comparison group of 684 adolescents and young adults from the general population aged 12 to 22 years, and their parents, were interviewed and completed questionnaires and standardised rating scales. Adolescents accepted for plastic surgery had realistic appearance attitudes and were psychologically healthy overall. Patients were equally satisfied with their overall appearance as the comparison group, but more dissatisfied with the specific body parts concerned for operation, especially when undergoing corrective operations. Patients had measurable appearance-related psychosocial problems. Patient boys reported less self-confidence on social areas than all other groups. There were very few patient-comparison group differences in correlations between bodily and psychosocial variables, indicating that bodily attitudes and satisfaction are not differentially related to psychosocial functioning and self-perception in patients than in peers. We concluded that adolescents accepted for plastic surgery have considerable appearance-related psychosocial problems, patients in the corrective group reporting more so than in the reconstructive group. Plastic surgeons may assume that these adolescents in general have a realistic attitude towards their appearance. are psychologically healthy, and are mainly dissatisfied about the body parts concerned for operation. corrective patients more so than reconstructive patients. Introverted patients may need more attention from plastic surgeons during the psychosocial assessment.

Adaptation, Psychological↗
PubMed2000

Ca2+/calmodulin signaling in NMDA-induced synaptic plasticity.

Repeated experiences induce a synaptic plasticity in neurons that can be very long lasting. The neurotransmitter, glutamate, acting through N-methyl-D-aspartate (NMDA) receptors is integrally involved in eliciting persistent changes in synaptic function resulting in learning and memory. The permeability of NMDA receptors to Ca2+ implies the close involvement of Ca2+ and the Ca2+-binding protein, calmodulin, in NMDA-induced synaptic plasticity. A notable example of NMDA-induced synaptic plasticity is long-term potentiation in the hippocampal CA1 region. The involvement of Ca2+ and calmodulin in the induction and expression of LTP has been intensively investigated and documented. Less well studied are neurochemical adaptations in another example of NMDA-induced synaptic plasticity, stimulant-induced behavioral sensitization. Although amphetamine and cocaine increase synaptic monoamines, glutamate is involved in the induction and expression of the sensitization. Activating NMDA receptors in dopamine midbrain cell bodies is required for inducing stimulant sensitization, implying a role for Ca2+ in this plasticity. The purpose of this review is to examine the role of Ca2+ and calmodulin in two examples of NMDA-based plasticity, LTP, and stimulant-induced behavioral sensitization. There are similarities in the neuroadaptations, although the role of Ca2+ and calmodulin has not been thoroughly investigated in the stimulant-induced plasticity.

Animals↗
PubMed2002

Lesion-induced thalamocortical axonal plasticity in the S1 cortex is independent of NMDA receptor function in excitatory cortical neurons.

Neural activity plays an important role in refinement and plasticity of synaptic connections in developing vertebrate sensory systems. The rodent whisker-barrel pathway is an excellent model system to investigate the role of activity in formation of patterned neural connections and their plasticity. When whiskers on the snout or the sensory nerves innervating them are damaged during a critical period in development, whisker-specific patterns are altered along the trigeminal pathway, including the primary somatosensory (S1) cortex. In this context, NMDA receptor (NMDAR)-mediated activity has been implicated in patterning and plasticity of somatosensory maps. Using CxNR1KO mice, in which NMDAR1 (NR1), the essential NMDAR subunit gene, is disrupted only in excitatory cortical neurons, we showed that NMDAR-mediated activity is essential for whisker-specific patterning of barrel cells in layer IV of the S1 cortex. In CxNR1KO mice, thalamocortical axons (TCAs) representing the large whiskers segregate into rudimentary patches, but barrels as cellular modules do not develop. In this study, we examined lesion-induced TCA plasticity in CxNR1KO mice. TCA patterns underwent normal structural plasticity when their peripheral inputs were altered after whisker lesions during the critical period. The extent of the lesion-induced morphological plasticity and the duration of the critical period were quantitatively indistinguishable between CxNR1KO and control mice. We conclude that TCA plasticity in the neocortex is independent of postsynaptic NMDAR activity in excitatory cortical neurons, and that non-NMDAR-mediated cortical activity and/or subcortical mechanisms must be operational in this process.

Animals↗
PubMed1996

Receptive-field plasticity in the adult auditory cortex induced by Hebbian covariance.

The goal of this experiment was to evaluate the role of cellular interactions postulated by the Hebbian, or covariance, hypothesis in the induction of receptive-field (RF) plasticity in the adult auditory cortex (ACx). This was accomplished by determining whether a "covariance treatment" (see below) was sufficient to induce RF plasticity without behavioral experiences that normally induce such plasticity. During the covariance treatment (conducted in urethane-anesthetized adult guinea pigs), one tone was paired with excitatory juxtacellular current, applied to a single postsynaptic cell in the primary ACx. Excitatory current increased postsynaptic discharge, thereby increasing covariance between activity of the postsynaptic cell and its afferents that were activated by the tone. In alternation, within the same cell a second, different tone was paired with inhibitory juxtacellular current, decreasing covariance between the postsynaptic cell and afferents activated by the second tone. After treatment, responses to tones associated with increased covariance strengthened significantly relative to tones associated with decreased covariance, as predicted by the Hebbian hypothesis. This occurred in 7 of 22 (32%) cells undergoing 120 pairing trials, but in only 4 of 38 (11%) cells undergoing 60 trials. Fewer than 5% of cells showed significant effects opposite those predicted by the hypothesis. Significant plasticity lasted > or = 15 min. Probability of plasticity was significantly higher when the cortical electroencephalogram was nonsynchronized during treatment (5/9 cells) than when synchronized (2/13 cells). These findings support the role of presynaptic-postsynaptic covariance processes in the induction of adult neocortical RF plasticity and suggest that factors associated with cortical state "gate" such plasticity.

Acoustic Stimulation↗
PubMed1996

[Neuronal plasticity].

The term 'brain plasticity' means the brain capacity to diminish the effects of the lesions through structural functional changes. A great part of the pathological processes of the nervous system affecting the corticospinal and the subcorticospinal tracts, the cerebellar, spinal, visual, language and other systems show neuronal plasticity, spontaneously in some cases and after suitable rehabilitation in others. The clinical manifestations of neuronal plasticity are observed especially after prenatal, neonatal or childhood cerebral damage. During the adulthood, the brain has less capacity of neuronal plasticity, although plastic changes may be found at any age. Apart the clinic, the neuronal plasticity can be studied through electrophysiology, MR, positron emission tomography (PET), transcranial magnetic stimulation (TME), and obviously by histology, this latter especially in experimental studies. In pediatric Neurology, the concept of brain plasticity is frequently used to explain the favourable clinic evolution in a lot of cases with severe brain injury.

Age Factors↗
PubMed1998

Absence of plasticity of the frequency map in dorsal cochlear nucleus of adult cats after unilateral partial cochlear lesions.

In adult animals, lesions to parts of the auditory receptor organ, the cochlea, can produce plasticity of the topographic (cochleotopic) frequency map in primary auditory cortex and a restricted or patchy plasticity in the auditory midbrain. This effect is similar to the plasticity of topographic maps of the sensory surface seen in visual and somatosensory cortices after restricted damage to the appropriate receptor surface in these sensory systems. There is dispute about the extent to which subcortical effects contribute to cortical plasticity. Here, we have examined whether topographic map plasticity similar to that seen in the auditory cortex and the midbrain is observed in the adult auditory brainstem. When partial cochlear lesions were produced in the same manner as those that were produced in the cortex and midbrain studies, we found no plasticity of the frequency map in the dorsal cochlear nucleus (DCN). Small regions of the DCN that were deprived of their normal, most sensitive frequency (characteristic frequency; CF) input by the cochlear lesion appeared to have acquired new CFs at frequencies at or near the edge of the cochlear lesion. However, examination of thresholds at the new CFs established that the changes simply reflected the residue of prelesion input to those sites: The patterns of CF thresholds were very well predicted by simple calculations of the patterns that were expected from such residual input. The results of this study suggest that the DCN does not exhibit the type of plasticity that has been found in the auditory cortex and midbrain; therefore, it does not account for the changes in responsiveness observed in the higher level structures under similar experimental conditions.

Age Factors↗
PubMed2003

Stem cell plasticity, cell fusion, and transdifferentiation.

One of the most contentious issues in biology today concerns the existence of stem cell plasticity. The term "plasticity" refers to the capacity of tissue-derived stem cells to exhibit a phenotypic potential that extends beyond the differentiated cell phenotypes of their resident tissue. Although evidence of stem cell plasticity has been reported by multiple laboratories, other scientists have not found the data persuasive and have remained skeptical about these new findings. This review will provide an overview of the stem cell plasticity controversy. We will examine many of the major objections that have been made to challenge the stem cell plasticity data. This controversy will be placed in the context of the traditional view of stem cell potential and cell phenotypic diversification. What the implications of cell plasticity are, and how its existence may modulate our present understanding of stem cell biology, will be explored. In addition, we will examine a topic that is usually not included within a discussion of stem cell biology--the direct conversion of one differentiated cell type into another. We believe that these observations on the transdifferentiation of differentiated cells have direct bearing on the issue of stem cell plasticity, and may provide insights into how cell phenotypic diversification is realized in the adult and into the origin of cell phenotypes during evolution.

Animals↗
PubMed1991

PVC as pharmaceutical packaging material. A literature survey with special emphasis on plasticized PVC bags.

In this report the state of the art with respect to PVC as pharmaceutical packaging material is described. A general introduction into the applications of PVC is followed by a description of its production process. The metabolic effects of the monomer of PVC, vinyl chloride and of the most commonly used plasticizer diethylhexylphthalate are mentioned. Special attention is given to the pharmaceutical properties of plasticized PVC bags in comparison to other plastics and the environmental aspects of waste PVC disposal. Although there are emotional and political queries regarding the future use of PVC as a (pharmaceutical) packaging material, we conclude that there is no scientific justification for a total or partial ban of PVC. PVC will remain a fact of life as a cheap, versatile, high-performance and well-investigated plastic material for medical and pharmaceutical applications, to be replaced by newer plastics only for certain well-defined indications where the requirements of the plastic to be used are so specific that it will economically and technically be justified to use another polymer. Community and hospital pharmacists have to be prepared for a role in intake of waste plastic disposables, probably against deposit money, in order to fulfil the logistics needed for recycling.

Drug Packaging↗