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At least 1,171 records · Page 65Linked to original sources
PubMed2002

Metallic stents and plastic endoprostheses in percutaneous treatment of biliary obstruction.

BACKGROUND: In the light of the clinical controversy whether metallic stents or plastic endoprostheses should be used in the percutaneous treatment of biliary obstruction we retrospectively evaluated our experience with both drainage-systems. METHODS: 71 patients (mean age 68 +/- 12 years) underwent a total of 81 interventions and received either plastic endoprostheses (11.5 or 12 French diameter; N = 57/81) or metallic stents (N = 24/81). RESULTS: Drainage insertion was technically successful in all of the 71 patients. There was no procedure-related mortality, but a 30-day mortality of 15 % (N = 11). Overall, 27 complications occurred in 81 interventions with a statistically significant higher complication-rate in plastic endoprostheses (39 %; N = 21/54) compared to metallic stents (22 %; N = 6/27). The average patency of the drainage-systems was 166 +/- 341 days (range 1-2,705 days) and did not differ significantly between the drainage-subtypes. Incidence of complications and a further increase in serum bilirubin following intervention was associated with a higher drainage occlusion-rate and reduced survival, irrespective of the drainage-system used. CONCLUSIONS: Percutaneous transhepatic treatment of biliary obstructions with internal drainages is a reliable therapy. The overall complication-rate of metallic stents was lower compared to plastic endoprostheses; however, no significant differences were found with respect to drainage patency or success-rate.

Adult↗
PubMed2005

[Quality of surgical continuing education in plastic surgery in Germany].

PURPOSE: Medical profession lost continuously attractiveness due to various reasons (insufficient training, irregular working time, decreasing income) in the last years. This does notably apply to surgical disciplines. In a survey should be clarified to what extent this dissatisfaction may be the case for residents and young specialists in plastic surgery. MATERIAL AND METHODS: A questionnaire was sent to all associated members of the "Vereinigung der Deutschen Plastischen Chirurgen (VDPC)" and was published in the communication journal of the VDPC. The questionnaire was sent back by 91 surgical residents or newly specialists (about 19 % of all). RESULTS: A well structured residency program existed for 47 %. 40 % of the residents were satisfied with the teaching assistance by their clinical teachers in the OR, whereas the fewest surgical procedures were done in the field of aesthetic surgery (n = 7). At least once per year it was possible for 80 % to take part in seminars or congresses. Therefore 45 % had to take holyday. For 44 % no financial support was paid. As perspective 30 % aim a career advancement in their hospitals and 18 % aim a private practice as plastic surgeon. CONCLUSION: To some extent training structures in plastic surgery are not well established. An urgent challenge should be to develop improvements in the continuing education in plastic surgery. This includes an increase in internal training, an organised rotation of residents between different hospitals, and structured mentoring of the residents.

Germany↗
PubMed2006

[Apoptosis and its role in plastic surgery].

Apoptosis and cell proliferation are the main mechanisms of cell homeostasis. The pathogenesis of approximately 70 % of all diseases results from an imbalance between these two counterparts. Therefore, research on apoptosis is a main target in biological and clinical fields. Many signalling pathways and proteins involved in their regulation have been characterized. In order to evaluate the relevance of apoptosis in plastic surgery, the literature was reviewed for its impact on ischemia and reperfusion concerning flap surgery as well as wound healing and angiogenesis. Furthermore, the relevance of apoptosis in ageing, allotransplantation and tumors was investigated. In all subsections of plastic surgery, a high impact was identified. More studies on the influence and regulation of apoptosis can bring further understanding on the disease patterns of plastic surgery and other specialties as well as the development of new therapeutic options. Research focusing on apoptosis is therefore an essential means for the advancement of and future trends in plastic surgery.

Aging↗
PubMed1982

[In vitro and in vivo images of puncture devices in real time ultrasound. 2. Plastic instruments].

The article reports on a systematic sonographic examination of plastic puncture instruments in a water-bath and in an animal model. The plastic instruments used showed visualization of the lumen in a horizontal (longitudinal) cross-section. In an oblique longitudinal cross-section of an instrument filled homogeneously with water, only one echo generated at the tip of the instrument could be demonstrated. It was possible to achieve contrast enhancement of the plastic instrument by roughening its exterior or interior surfaces, by insufflation of air bubbles or by inhomogenization, using various plastic-cum-metal constructions. The effects produced in the water-bath were found to be similar to those observed in vivo.

Angioplasty, Balloon↗
PubMed1981

Creep and flexibility measurements on plastic frames for tissue heart valves.

Measurements on plastic flexible frames for heart valves have shown that the design influences the creep potential of any one plastic material. This has been shown for both in vitro accelerated fatigue tests and after clinical implantation of more than 10 years. The flexibility of the plastic, a polypropylene, was not affected either by fatigue testing, shelf storage or clinical implantation. The possibility of 30 years freedom from creep for a flexible plastic frame for a tissue heart valve has been examined.

Heart Valve Prosthesis↗
PubMed1997

[Massive foreign body reaction after intraocular penetration of hot, liquid plastic].

PATIENT: A 32-year-old male had an injury of his right eye by hot liquid plastic (Ultradur R). Intraoperatively, the eye was found broadly penetrated and filled up by more than 50% with ragged pieces of plastic. Computed tomography three days after wound closure revealed remaining foreign body material. As function was totally lost no further operation was considered. Seven weeks after the trauma, the eye was enucleated because of a painful phthisis. Histology showed numerous giant cells. CONCLUSIONS: Hot liquid plastic may perforate the eye and fill it up to a great extent. Due to intraocular cooling, pieces with sharp edges may develop, thus producing further (mechanical) tissue damage. Intraocular plastic is able to induce a massive foreign body reaction. It may be detected easily by computed tomography.

Adult↗
PubMed2006

Cooperation of spike timing-dependent and heterosynaptic plasticities in neural networks: a Fokker-Planck approach.

It is believed that both Hebbian and homeostatic mechanisms are essential in neural learning. While Hebbian plasticity selectively modifies synaptic connectivity according to activity experienced, homeostatic plasticity constrains this change so that neural activity is always within reasonable physiological limits. Recent experiments reveal spike timing-dependent plasticity (STDP) as a new type of Hebbian learning with high time precision and heterosynaptic plasticity (HSP) as a new homeostatic mechanism acting directly on synapses. Here, we study the effect of STDP and HSP on randomly connected neural networks. Despite the reported successes of STDP to account for neural activities at the single-cell level, we find that, surprisingly, at the network level, networks trained using STDP alone cannot seem to generate realistic neural activities. For instance, STDP would stipulate that past sensory experience be maintained forever if it is no longer activated. To overcome this difficulty, motivated by the fact that HSP can induce strong competition between sensory experiences, we propose a biophysically plausible learning rule by combining STDP and HSP. Based on the Fokker-Planck theory and extensive numerical computations, we demonstrate that HSP and STDP operated on different time scales can complement each other, resulting in more realistic network activities. Our finding may provide fresh insight into the learning mechanism of the brain.

Action Potentials↗
PubMed2005

Graded bidirectional synaptic plasticity is composed of switch-like unitary events.

Biological information storage events are often rapid transitions between discrete states. In neural systems, the initiation of bidirectional plasticity by all-or-none events may help confer robustness on memory storage. Here, we report that at CA3-CA1 hippocampal synapses, individual potentiation and depression plasticity events are discrete and heterogeneous in nature. Individual synapses began from extreme high and low strength states. Unitary plasticity events were all-or-none and drove synaptic strength between extremes in <1 min. Under naïve conditions, approximately three-fourths of synapses began in a low-strength state. The timing of these unitary events can account for the time course of macroscopic synaptic plasticity.

Animals↗
PubMed2006

Operant matching is a generic outcome of synaptic plasticity based on the covariance between reward and neural activity.

The probability of choosing an alternative in a long sequence of repeated choices is proportional to the total reward derived from that alternative, a phenomenon known as Herrnstein's matching law. This behavior is remarkably conserved across species and experimental conditions, but its underlying neural mechanisms still are unknown. Here, we propose a neural explanation of this empirical law of behavior. We hypothesize that there are forms of synaptic plasticity driven by the covariance between reward and neural activity and prove mathematically that matching is a generic outcome of such plasticity. Two hypothetical types of synaptic plasticity, embedded in decision-making neural network models, are shown to yield matching behavior in numerical simulations, in accord with our general theorem. We show how this class of models can be tested experimentally by making reward not only contingent on the choices of the subject but also directly contingent on fluctuations in neural activity. Maximization is shown to be a generic outcome of synaptic plasticity driven by the sum of the covariances between reward and all past neural activities.

Animals↗
PubMed2002

Glial protein S100B modulates long-term neuronal synaptic plasticity.

Glial cells are traditionally regarded as elements for structural support and ionic homeostasis, but have recently attracted attention as putative integral elements of the machinery involved in synaptic transmission and plasticity. Here, we demonstrate that calcium-binding protein S100B, which is synthesized in considerable amounts in astrocytes (a major glial cell subtype), modulates long-term synaptic plasticity. Mutant mice devoid of S100B developed normally and had no detectable abnormalities in the cytoarchitecture of the brain. These mutant mice, however, had strengthened synaptic plasticity as identified by enhanced long-term potentiation (LTP) in the hippocampal CA1 region. Perfusion of hippocampal slices with recombinant S100B proteins reversed the levels of LTP in the mutant slices to those of the wild-type slices, indicating that S100B might act extracellularly. In addition to enhanced LTP, mutant mice had enhanced spatial memory in the Morris water maze test and enhanced fear memory in the contextual fear conditioning. The results indicate that S100B is a glial modulator of neuronal synaptic plasticity and strengthen the notion that glial-neuronal interaction is important for information processing in the brain.

Animals↗
PubMed2001

An analysis of neural receptive field plasticity by point process adaptive filtering.

Neural receptive fields are plastic: with experience, neurons in many brain regions change their spiking responses to relevant stimuli. Analysis of receptive field plasticity from experimental measurements is crucial for understanding how neural systems adapt their representations of relevant biological information. Current analysis methods using histogram estimates of spike rate functions in nonoverlapping temporal windows do not track the evolution of receptive field plasticity on a fine time scale. Adaptive signal processing is an established engineering paradigm for estimating time-varying system parameters from experimental measurements. We present an adaptive filter algorithm for tracking neural receptive field plasticity based on point process models of spike train activity. We derive an instantaneous steepest descent algorithm by using as the criterion function the instantaneous log likelihood of a point process spike train model. We apply the point process adaptive filter algorithm in a study of spatial (place) receptive field properties of simulated and actual spike train data from rat CA1 hippocampal neurons. A stability analysis of the algorithm is sketched in the. The adaptive algorithm can update the place field parameter estimates on a millisecond time scale. It reliably tracked the migration, changes in scale, and changes in maximum firing rate characteristic of hippocampal place fields in a rat running on a linear track. Point process adaptive filtering offers an analytic method for studying the dynamics of neural receptive fields.

Adaptation, Physiological↗
PubMed1993

Long-term retention of learning-induced receptive-field plasticity in the auditory cortex.

Brief learning experience (classical conditioning) induces frequency-specific receptive-field (RF) plasticity in the auditory cortex, characterized as increased response to the frequency of the conditioned stimulus and decreased responses to most other frequencies, including the pretraining best frequency. This experiment asked (i) whether learning-induced RF plasticity, established in the waking state, can be expressed under general anesthesia and if so (ii) whether it exhibits long-term retention. Pure-tone-frequency RFs were obtained from adult guinea pigs under general anesthesia (sodium pentobarbital or ketamine) before and repeatedly after (1 hr-8 weeks) a 20- to 30-trial session of pairing a non-best-frequency tone with mild footshock. Conditioned-stimulus-specific RF plasticity was expressed under both types of anesthesia and included shifts of the pretraining best frequency toward or even to the frequency of the conditioned stimulus. Moreover, this RF plasticity exhibits long-term retention, being evident 1-8 weeks after training. This satisfies a criterion for the long-term storage of information in the auditory cortex.

Acoustic Stimulation↗
PubMed1998

Glucocorticoid receptor and protein/RNA synthesis-dependent mechanisms underlie the control of synaptic plasticity by stress.

Learning and memory are exquisitely sensitive to behavioral stress, but the underlying mechanisms are still poorly understood. Because activity-dependent persistent changes in synaptic strength are believed to mediate memory processes in brain areas such as the hippocampus we have examined the means by which stress affects synaptic plasticity in the CA1 region of the hippocampus of anesthetized rats. Inescapable behavioral stress (placement on an elevated platform for 30 min) switched the direction of plasticity, favoring low frequency stimulation-induced decreases in synaptic transmission (long-term depression, LTD), and opposing the induction of long-term potentiation by high frequency stimulation. We have discovered that glucocorticoid receptor activation mediates these effects of stress on LTD and long-term potentiation in a protein synthesis-dependent manner because they were prevented by the glucocorticoid receptor antagonist RU 38486 and the protein synthesis inhibitor emetine. Consistent with this, the ability of exogenously applied corticosterone in non-stressed rats to mimic the effects of stress on synaptic plasticity was also blocked by these agents. The enablement of low frequency stimulation-induced LTD by both stress and exogenous corticosterone was also blocked by the transcription inhibitor actinomycin D. Thus, naturally occurring synaptic plasticity is liable to be reversed in stressful situations via glucocorticoid receptor activation and mechanisms dependent on the synthesis of new protein and RNA. This indicates that the modulation of hippocampus-mediated learning by acute inescapable stress requires glucocorticoid receptor-dependent initiation of transcription and translation.

Animals↗
PubMed2004

In vivo and in vitro characterization of novel neuronal plasticity factors identified following spinal cord injury.

Following spinal cord injury, there are numerous changes in gene expression that appear to contribute to either neurodegeneration or reparative processes. We utilized high density oligonucleotide microarrays to examine temporal gene profile changes after spinal cord injury in rats with the goal of identifying novel factors involved in neural plasticity. By comparing mRNA changes that were coordinately regulated over time with genes previously implicated in nerve regeneration or plasticity, we found a gene cluster whose members are involved in cell adhesion processes, synaptic plasticity, and/or cytoskeleton remodeling. This group, which included the small GTPase Rab13 and actin-binding protein Coronin 1b, showed significantly increased mRNA expression from 7-28 days after trauma. Overexpression in vitro using PC-12, neuroblastoma, and DRG neurons demonstrated that these genes enhance neurite outgrowth. Moreover, RNAi gene silencing for Coronin 1b or Rab13 in NGF-treated PC-12 cells markedly reduced neurite outgrowth. Coronin 1b and Rab13 proteins were expressed in cultured DRG neurons at the cortical cytoskeleton, and at growth cones along with the pro-plasticity/regeneration protein GAP-43. Finally, Coronin 1b and Rab13 were induced in the injured spinal cord, where they were also co-expressed with GAP-43 in neurons and axons. Modulation of these proteins may provide novel targets for facilitating restorative processes after spinal cord injury.

Animals↗
PubMed2003

Estimated daily intake of plasticizers in 1-week duplicate diet samples following regulation of DEHP-containing PVC gloves in Japan.

Duplicate hospital diet samples obtained over 1 week in 2001 were analysed to estimate the daily intake of plasticizers and the results were compared with those obtained in 1999. The plasticizers quantified in this study were: dibutyl phthalate, butylbenzyl phthalate (BBP), di(2-ethylhexyl) phthalate (DEHP), diisononyl phthalate (DINP), di(2-ethylhexyl) adipate (DEHA), diisononyl adipate (DINA) and O-acetyl tributyl citrate (ATBC). Dipropyl, dipentyl, dihexyl and dicyclohexyl phthalate were also analysed but not detected. The analytical procedure for this follow-up study was essentially the same as in the previous one. Detection limits were 0.1-15.6 ng g(-1) for each plasticizer. One-week duplicate diet samples provided by three hospitals in three remote prefectures of Japan were analysed as individual meals. DEHP was detected at 6-675 ng g(-1) in 62 of 63 meals, significantly lower levels compared with those detected in 1999. Levels of DEHA and DINP also decreased. The mean intake of plasticizers estimated from all samples was 160 microg DEHP day(-1), 12.5 microg DEHA day(-1), 4.7 microg DINP day(-1) and 3.4 microg BBP day(-1). Levels of DINA were relatively high in meals from one hospital: in those meals, the average daily intake was 1338 microg day(-1). Those of ATBC were also higher in meals from another hospital: the average daily intake was 1228 microg day(-1). The sources of DINA and ATBC can be cling-film or sausage packaging.

Adipates↗
PubMedDate not supplied

Additive migration from various plastics with different processing or properties into test fat HB 307.

The migration of the antioxidant n-octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)-propionate from various plastics into the test fat HB 307 was investigated. Plastics from the following classes were included: high-impact polystyrene (HIPS), polypropylene (PP), high- and low-density polyethylene (HDPE and LDPE), and were found to have distinctly different properties--in particular, different densities, melt flow indices and structural characteristics. Each plastic was processed into test specimens such as pressed and extruded sheets, injection-moulded cups, deep-drawn tubs and blown bottles. The migration out of these specimens was investigated under identical test conditions. The results confirm that the amounts of additive migrating from the different classes of plastics into test fat HB 307 in general decrease in the order LDPE greater than HDPE greater than PP greater than HIPS. Moreover, it seems to be of great importance that the respective amounts of additive migrating from the injection-moulded cups, deep-drawn tubs and blown bottles into test fat were significantly lower in all cases than those from the corresponding pressed or extruded sheets. Presumably, this effect is mainly caused by orientation of the polymer molecules in the injection-moulded, deep-drawn or blown products. It is concluded that the migration of the antioxidant decreases with increasing density of the polymer and that the melt flow index (molecular weight) has hardly any influence. Migration from HIPS into fat increases with the content of impact modifier. In the case of the polyethylenes, the influence of processing on the migration rate decreases with decreasing density of the polymer.

Antioxidants↗
PubMedDate not supplied

Migration from food contact plastics. Part I. Establishment and aims of the PIRA project.

In the European Community regulatory approaches adopted by individual Member States to the control of food contact plastics differ markedly and, as a result, the European Commission has identified a need for harmonized legislation in this sector. The Commission requested its Scientific Committee for Food to advise on the toxicity of monomers and other starting substances used in the production of such plastics and the Committee's report has recently been published. It is apparent that, although some monomers have been studied in depth, for many little or no information was available to the Committee on either the levels migrating into food or their likely toxic effects. The Committee has requested that such information be provided within 3 years. Following discussions between the UK Ministry of Agriculture, Fisheries and Food, PIRA and companies involved in either the manufacture or use of food contact plastics, a Project has been established at PIRA to develop sensitive analytical procedures for the relevant UK-required monomers and to provide the required migration data. As a second part to this project the methodology for determining overall migration is being examined with a view to resolving existing experimental difficulties. The first analytical methods to be developed in the project are those for the determination or terephthalic acid and isophthalic acid. Residual levels of these monomers in plastics and the quantities migrating into food simulants and food have been shown to be very low.

Food↗
PubMedDate not supplied

An improved olive oil overall migration test for plastics using Karl Fischer titration.

Karl Fischer titration has been used to eliminate the need to humidity-condition food contact plastics under test for overall migration into olive oil. The water content of the oil is measured before and after the migration test. This direct measure of the loss (or uptake) of water by the test plastic is then used in calculations of the overall migration. The use of Karl Fischer titration gives faster analysis with reduced labour input. The time savings varied from a few days to several weeks depending on the type of plastic. Karl Fischer titration is particularly useful in the high temperature testing of polar plastics where incomplete humidity conditioning can lead to erroneous results. The technique should be equally valuable when employing sunflower oil or the triglyceride HB307 in place of olive oil.

Dietary Fats, Unsaturated↗