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PubMed2000

The role of plasticization in starch granule assembly.

There is a growing interest in the nonfood usage of starch-based products. This interest is predominantly motivated by the ability to produce thermoplastic materials, known as thermoplastic starch (TPS), which can be manufactured using technology already developed for the production of synthetic plastics yet which are fully biodegradable. With the strength and flexibility of TPS materials being highly dependent upon the presence of nonaqueous plasticizing solvents, the nature of the interaction between starch and plasticizer is of obvious interest. As well as interest in the industrial applications of starch, the general nature of plasticization and structure formation within native starch granules is of fundamental interest. This paper presents results from a small and wide angle scattering and calorimetric investigation of model starch-plasticizer systems. Issues relevant to TPS production are addressed, and a model of lamellar assembly within starch granules facilitated by the plasticizing effect of low molecular weight solvents is proposed.

Calorimetry, Differential Scanning↗
PubMedDate not supplied

Material properties of plasticized hardwood xylans for potential application as oxygen barrier films.

Free films based on glucuronoxylan isolated from aspen wood were prepared by casting from aqueous solutions and drying in a controlled environment. Addition of xylitol or sorbitol facilitated film formation and thus examination of the material properties of these films. The mechanical properties of the films were evaluated using tensile testing and dynamic mechanical analysis in a controlled ambient relative humidity. The strain at break increased, and the stress at break and Young's modulus of the films decreased with increasing amounts of xylitol and sorbitol due to plasticization. At high amount of plasticizer, it was found that films with xylitol gave lower extensibility. Wide-angle X-ray scattering analysis showed that xylitol crystallized in a distinct phase, which we believe contributes to the more brittle behavior of these films. The effect of the plasticizers on the glass transition temperature was determined using dynamic mechanical analysis and differential scanning calorimetry. An increased amount of plasticizer shifted the glass transition to lower temperatures. The effect of moisture on the properties of plasticized films was investigated using water vapor sorption isotherms and by humidity scans in dynamic mechanical analysis. Sorption isotherms showed a transition from type II to type III when adding plasticizer. The films showed low oxygen permeability and thus have a potential application in food packaging.

Biocompatible Materials↗
PubMed2001

Solubility and moisture sorption isotherms of whey-protein-based edible films as influenced by lipid and plasticizer incorporation.

Plasticized whey-protein and whey-protein emulsion films were produced using sorbitol and glycerol as plasticizers and butterfat and candelilla wax as lipids. Protein, plasticizer, and lipid ratios were optimized to obtain acceptable free-standing flexible films. Water solubility (20 degrees C, 24 h) and moisture sorption isotherms (0.18-0.90 a(w), 25 degrees C) of the films were determined. The experimental moisture sorption isotherm values were fitted using the Guggenheim-Anderson-DeBoer (GAB) model. Solubility and equilibrium moisture contents (EMC) of the films were influenced by plasticizer and lipid incorporation. EMCs of all films increased rapidly at a(w) > or = 0.65. Incorporation of lipids reduced solubilities and EMCs of sorbitol- and glycerol-plasticized films. The effects of plasticizer and lipid type on GAB constants were also determined.

Adsorption↗
PubMed2002

Biodegradation of plasticizers by Rhodococcus rhodochrous.

Rhodococcus rhodochrous was grown in the presence of one of three plasticizers: bis 2-ethylhexyl adipate (BEHA), dioctyl phthalate (DOP) or dioctyl terephthalate (DOTP). None of the plasticizers were degraded unless another carbon source, such as hexadecane, was also present. When R. rhodochrous was grown with hexadecane as a co-substrate, BEHA was completely degraded and the DOP was degraded slightly. About half of the DOTP was degraded, if hexadecane were present. In all of these growth studies, the toxicity of the media, which was assessed using the Microtox assay, increased as the organism degraded the plasticizer. In each case, there was an accumulation of one or two intermediates in the growth medium as the toxicity increased. One of these was identified as 2-ethylhexanoic acid and it was observed for all three plasticizers. Its concentration increased until degradation of the plasticizers had stopped and it was always present at the end of the fermentation. The other intermediate was identified as 2-ethylhexanol and this was only observed for growth in the presence of BEHA. The alcohol was observed early in the growth studies with BEHA and had disappeared by the end of the experiment. Both the 2-ethylhexanol and 2-ethylhexanoic acid were shown to be toxic and their presence explained the increase of toxicity as the fermentations proceeded. The appearance of these intermediates was consistent with similar degradation mechanisms for all three plasticizers involving hydrolysis of the ester bonds followed by oxidation of the released alcohol.

Alkanes↗
PubMed2003

Stress and plasticity in the limbic system.

The adult nervous system is not static, but instead can change, can be reshaped by experience. Such plasticity has been demonstrated from the most reductive to the most integrated levels, and understanding the bases of this plasticity is a major challenge. It is apparent that stress can alter plasticity in the nervous system, particularly in the limbic system. This paper reviews that subject, concentrating on: a) the ability of severe and/or prolonged stress to impair hippocampal-dependent explicit learning and the plasticity that underlies it; b) the ability of mild and transient stress to facilitate such plasticity; c) the ability of a range of stressors to enhance implicit fear conditioning, and to enhance the amygdaloid plasticity that underlies it.

Amygdala↗
PubMedDate not supplied

Assembly, plasticity and selective vulnerability to disease of mouse neuromuscular junctions.

Although physiological differences among neuromuscular junctions (NMJs) have long been known, NMJs have usually been considered as one type of synapse, restricting their potential value as model systems to investigate mechanisms controlling synapse assembly and plasticity. Here we discuss recent evidence that skeletal muscles in the mouse can be subdivided into two previously unrecognized subtypes, designated FaSyn and DeSyn muscles. These muscles differ in the pattern of neuromuscular synaptogenesis during embryonic development. Differences between classes are intrinsic to the muscles, and manifest in the absence of innervation or agrin. The distinct rates of synaptogenesis in the periphery may influence processes of circuit maturation through retrograde signals. While NMJs on FaSyn and DeSyn muscles exhibit a comparable anatomical organization in postnatal mice, treatments that challenge synaptic stability result in nerve sprouting, NMJ remodeling, and ectopic synaptogenesis selectively on DeSyn muscles. This anatomical plasticity of NMJs diminishes greatly between 2 and 6 months postnatally. NMJs lacking this plasticity are lost selectively and very early on in mouse models of motoneuron disease, suggesting that disease-associated motoneuron dysfunction may fail to initiate maintenance processes at "non-plastic" NMJs. Transgenic mice overexpressing growth-promoting proteins in motoneurons exhibit greatly enhanced stimulus-induced sprouting restricted to DeSyn muscles, supporting the notion that anatomical plasticity at the NMJ is primarily controlled by processes in the postsynaptic muscle. The discovery that entire muscles in the mouse differ substantially in the anatomical plasticity of their synapses establishes NMJs as a uniquely advantageous experimental system to investigate mechanisms controlling synaptic rearrangements at defined synapses in vivo.

Animals↗
PubMed1996

Induction of receptive field plasticity in the auditory cortex of the guinea pig during instrumental avoidance conditioning.

Classical tone conditioning shifts frequency tuning in the auditory cortex to favor processing of the conditioned stimulus (CS) frequency versus other frequencies. This receptive field (RF) plasticity is associative, highly specific, rapidly acquired, and indefinitely retained-all important characteristics of memory. The investigators determined whether RF plasticity also develops during instrumental learning. RFs were obtained before and up to 24 hr after 1 session of successful 1-tone avoidance conditioning in guinea pigs. Long-term RF plasticity developed in all subjects (N = 6). Two-tone discrimination training also produced RF plasticity, like classical conditioning. Because avoidance responses prevent full elicitation of fear by the CS, long-term RF plasticity does not require the continual evocation of fear, suggesting that neural substrates of fear expression are not essential to RF plasticity.

Animals↗
PubMed1995

Production of polyhydroxyalkanoates, a family of biodegradable plastics and elastomers, in bacteria and plants.

In response to problems associated with plastic waste and its effect on the environment, there has been considerable interest in the development and production of biodegradable plastics. Polyhydroxyalkanoates (PHAs) are polyesters that accumulate as inclusions in a wide variety of bacteria. These bacterial polymers have properties ranging from stiff and brittle plastics to rubber-like materials. Because of their inherent biodegradability, PHAs are regarded as an attractive source of nonpolluting plastics and elastomers that can be used for specialty and commodity products. The possibility of producing PHAs in large scale and at a cost comparable to synthetic plastics has arisen from the demonstration of PHA accumulation in transgenic Arabidopsis plants expressing the bacterial PHA biosynthetic genes. Synergism between knowledge of the enzymes and genes contributing to PHA synthesis in bacteria and engineering of plant metabolic pathways will be necessary for the development of crop plants that produce biodegradable plastics.

Acids, Acyclic↗
PubMed2005

RIM function in short- and long-term synaptic plasticity.

RIM1alpha (Rab3-interacting molecule 1alpha) is a large multidomain protein that is localized to presynaptic active zones [Wang, Okamoto, Schmitz, Hofmann and Südhof (1997) Nature (London) 388, 593-598] and is the founding member of the RIM protein family that also includes RIM2alpha, 2beta, 2gamma, 3gamma and 4gamma [Wang and Südhof (2003) Genomics 81, 126-137]. In presynaptic nerve termini, RIM1alpha interacts with a series of presynaptic proteins, including the synaptic vesicle GTPase Rab3 and the active zone proteins Munc13, liprins and ELKS (a protein rich in glutamate, leucine, lysine and serine). Mouse KOs (knockouts) revealed that, in different types of synapses, RIM1alpha is essential for different forms of synaptic plasticity. In CA1-region Schaffer-collateral excitatory synapses and in GABAergic synapses (where GABA is gamma-aminobutyric acid), RIM1alpha is required for maintaining normal neurotransmitter release and short-term synaptic plasticity. In contrast, in excitatory CA3-region mossy fibre synapses and cerebellar parallel fibre synapses, RIM1alpha is necessary for presynaptic long-term, but not short-term, synaptic plasticity. In these synapses, the function of RIM1alpha in presynaptic long-term plasticity depends, at least in part, on phosphorylation of RIM1alpha at a single site, suggesting that RIM1alpha constitutes a 'phosphoswitch' that determines synaptic strength. However, in spite of the progress in understanding RIM1alpha function, the mechanisms by which RIM1alpha acts remain unknown. For example, how does phosphorylation regulate RIM1alpha, what is the relationship of the function of RIM1alpha in basic release to synaptic plasticity and what is the physiological significance of different forms of RIM-dependent plasticity? Moreover, the roles of other RIM isoforms are unclear. Addressing these important questions will contribute to our view of how neurotransmitter release is regulated at the presynaptic active zone.

Animals↗
PubMed2002

Shear bond strengths of plastic brackets with a mechanical base.

This study compares the shear bond strengths of plastic brackets with a mechanical base and metal brackets using two different adhesives, and examines the modes of failure using a scanning electron microscope (SEM). Forty extracted human premolars were selected for bonding. Two types of brackets: metal and plastic-Spirit MB, and two orthodontic adhesives: System 1 + and Enlight, were used. After bonding, all samples were put into a 37 degrees C distilled water bath for 24 hours before shear bond strengths were tested. The bond strengths of the plastic brackets were significantly lower than those of the metal brackets (P < .0001). There was a statistically significant difference in bond strengths between System 1 + and Enlight for plastic brackets (P < .05), but not for metal brackets. The modes of failure predominantly occurred at the enamel/adhesive interface in the metal bracket-System 1 + group, within the adhesive in the metal bracket-Enlight and plastic bracket-System 1 + groups, and at the bracket/adhesive interface in the plastic bracket-Enlight group.

Bicuspid↗
PubMed2002

Acute cholinergic rescue of synaptic plasticity in the neurodegenerating cortex of anti-nerve-growth-factor mice.

Deficits in cholinergic systems innervating cerebral cortex are associated with cognitive impairment during senescence and in age-related neurodegenerative pathologies. However, little is known about the role of cholinergic pathways in modulating cortical plasticity. Basal forebrain cholinergic neurons are a major target for nerve-growth factor (NGF). In order to investigate the relationship between cholinergic innervation and cortical synaptic plasticity, we exploited a transgenic mouse model in which the activity of NGF in the adult nervous system is neutralized by the expression of blocking antibodies to NGF itself (anti-NGF mice) [Ruberti, F. et al. (2000). J. Neurosci. 20, 2589-2601]. In 6-month-old anti-NGF mice, we show that the reduction in cholinergic innervation of the cortex is associated with different forms of synaptic plasticity impairment. A local, acute increase in the availability of acetylcholine rescues these synaptic plasticity deficits, thus indicating that a cholinergic system mediates the impairment of cortical plasticity at this early stage of the neurodegenerative process triggered by NGF neutralization. Our results represent an important step in unveiling the pivotal role of cholinergic transmission in modulating adult cortical plasticity.

Acetylcholine↗
PubMedDate not supplied

Extended storage of platelets in a new plastic container. II. In vivo response to infusion of platelets stored for 5 days.

A new blood container material (PL 1240 plastic) made of polyvinyl chloride containing a tri(2-ethylhexyl) trimellitate plasticizer was evaluated in three laboratories. When platelet concentrates (50-60 ml) were stored on a variety of agitators for 7 days at 22 +/- 2 degrees C, poststorage pH (mean +/- SD) ranged from 7.29 +/- 0.05 (6 rpm elliptical rotator) to 6.87 +/- 0.8 (70 cycles per minute flatbed agitator). The platelet counts ranged from 1.51 +/- 0.12 to 0.95 +/- 0.36 X 10(6) per microliter. Morphology scores and hypotonic shock response values of platelets stored 7 days in PL 1240 plastic containers were better than those noted following 3-day storage of control platelets in PL 146 plastic containers. The percent discharge of lactic dehydrogenase from platelets stored 7 days in PL 1240 plastic containers for 3 days (p less than 0.05). Mean platelet recoveries of 44 +/- 15 percent (n = 11; 111Indium) and 39 +/- 8 percent (n = 29; 51Chromium) were seen when autologous platelets were infused following 5-day storage in PL 1240 plastic bags. Platelet half-lives of 3.6 +/- 0.4 (n = 9) 4.1 +/- 0.4 (n = 20) days were reported in the two laboratories which used 51Cr labeling, while survival values of 7.0 +/- 1.0, 2.8 +/- 0.8, and 5.4 +/- 1.9 days were seen when data from the 111Indium studies (n = 11) were analyzed using linear, exponential, and multiple hit programs, respectively. Platelets stored for 5 days also were administered to 13 thrombocytopenic oncology patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood Platelets↗
PubMed1998

PLink, plastic surgery and the Internet.

The Internet is a fast growing, global computer network that is easy to access at a low cost. This form of communication allows rapid electronic exchange of information such as text, pictures, animations, video and sound. This offers physicians an opportunity to enhance the quality of patient care, research and communication with colleagues. Patients who previously had limited access to information concerning diseases and treatment options are now able to find medical information on the Internet. The quality of information found on the Internet varies widely, from the most up-to-date protocols, produced by leading physicians and surgeons, to out of date or inaccurate recommendations. Faced with an enormous quantity of information of variable quality, guidelines certified by recognised medical organisations are essential to provide websites with valuable information. This so-called "safe house principle" creates reliable places on the Internet ("safe houses") that are generally accepted and trusted for containing valid information. We have created such a "safe house" on plastic surgical topics for the Netherlands Society for Plastic Surgery called "PLink" (the Plastic Surgery link). Its goals are: 1. to provide a well-organised list of existing plastic surgery Internet resources; 2. to improve communication; and 3. to provide original information on plastic surgical subjects for patients and physicians. Professionals always review the content. Since July 1996 our files have been accessed over 1.3 million times in 17 months, with the visit rate increasing from 1470 in July 1996 to 4200 in March 1997 and remaining stable since then. This indicates that there is a growing need for high quality information on plastic surgery on the Internet.

Communication↗
PubMed2001

[Presentation of plastic surgery on the internet: experiences with the home page of a department].

Plastic surgeons are increasingly taking advantage of information opportunities offered by the internet. Between October 1998 and March 1999, 87 individuals returned by e-mail a feed-back form included in the homepage of the Division of Plastic Surgery, Department of Surgery, Karl-Franzens University School of Medicine, Graz, Austria. Most of the responses originated from Austria or other European countries; 10% were from overseas. The most frequent reason for visiting our homepage was to gain information on scientific activities in our department (43 visitors), followed by interest in plastic surgical procedures on the part of patients or referring physicians (35 visitors). Other reasons were interest in educational matters, positions, and general interest in plastic surgery. Our results show that physicians, medical students, and laypersons are increasingly inclined to seek information on plastic surgery via the internet. This in turn should encourage plastic surgery services to present themselves in the World Wide Web.

Austria↗
PubMed1998

Improved endoscopic stenting for malignant dysphagia using Tygon plastic prostheses.

BACKGROUND AND STUDY AIMS: Endoscopic palliative treatment of malignant esophageal stenosis using conventional plastic stents has been reported to be associated with a considerable risk of perforation. Stenoses with a distance of less than 2cm from the upper esophageal sphincter (UES) have generally been excluded from treatment. Using self-expandable metal stents, procedure-related complications are rare. However, the rates of late complications necessitating retreatment appear to be as high as those of plastic stents. This study describes our stent placement technique and our results using a modified Tygon plastic stent. PATIENTS AND METHODS: Over a two-year period, 71 consecutive patients with incurable malignant esophageal stenosis were prospectively studied. Tygon plastic stents of diameter 9-14 mm were individually tailored according to length and location of the stenosis. Prior to stenting, stepwise bougienage was performed, if necessary over several sessions. After endoscopic placement of a guide wire, the stent was inserted over a bougie without fluoroscopic monitoring. RESULTS: A total of 71 patients (54 men and 17 women, median age 69, range 34-93), were treated with Tygon plastic stents (14 mm: 19 patients; 12 mm: 50 patients; 9 mm: 2 patients). Median length of the strictures and of the stents were 7 (range 2-18) and 10 (range 6-25) cm, respectively. Four patients had an associated esophago-respiratory fistula. After a median of 2 (range 1-5) bougienage sessions, stent insertion was technically successful in all patients. Forty-one stents were placed across the cardia, 13 were positioned 0.5-1 cm below the UES. Three patients had to undergo retreatment within 24 hours because of pain or stent migration and the stents were repositioned or exchanged. No procedure-related perforation, hemorrhage or respiratory problems were observed. During a median follow-up of 63 (range 2-388) days, 82% of the patients died. Improvement or stabilization of dysphagia allowing for oral nutrition could be achieved in 89%. Dislocation occurred in eight patients, bolus obstruction in five patients and tumor overgrowth in four patients. Three of the four fistulas could be covered by the stent. In one patient with a fistula located at the level of the UES, a stent was placed but migrated after 5 days. Overall, 27 patients (38%) required reinterventions, mainly for dysphagia or nutritional problems. CONCLUSIONS: In our experience, Tygon plastic stents with a diameter of 9-14 mm can be safely placed after stepwise, less extensive bougienage. Effective palliation is possible even for lesions located close to the UES. Perforation can be avoided. Reintervention rates seem to be comparable to those seen with self-expanding metal stents.

Aged↗
PubMed2004

Amygdala stimulation modulates hippocampal synaptic plasticity.

Experience-dependent synaptic plasticity is a fundamental feature of neural networks involved in the encoding of information, and the capability of synapses to express plasticity is itself activity-dependent. Here, we introduce a "low-frequency burst stimulation" protocol, which can readily induce both long-term potentiation (LTP) and long-term depression (LTD) at in vivo medial perforant path-dentate gyrus synapses. By varying stimulation parameters, we were able to build a stimulus-response map of synaptic plasticity as a LTP-LTD continuum. The response curve displayed a bidirectional shift toward LTP and LTD, depending on the degree and timing of neural activity of the basolateral amygdala. The range of this plastic modulation was also modified by past activity of the basolateral amygdala, suggesting that the amygdala can arrange its ability to regulate the dentate plastic responses. The effects of the BLA activation were replicated by stimulation of the lateral perforant path and, hence, BLA stimulation may recruit the lateral entorhinal cortex. These results represent a high-order dimension of heterosynaptic modulations of hippocampal synaptic plasticity.

Amygdala↗
PubMed1988

Neural plasticity without postsynaptic action potentials: less-active inputs become dominant when kitten visual cortical cells are pharmacologically inhibited.

Models of synaptic plasticity in the nervous system have conventionally assumed a mechanism in which spike activity of a postsynaptic cell enhances the efficacy of recently active presynaptic inputs. Making use of the prompt and dramatic response of the visual cortex to occlusion of vision in one eye during the critical period, we tested the role of postsynaptic activity in ocular dominance plasticity. To do so, we selectively blocked cortical cell discharges with a continuous intracortical infusion of the inhibitory neurotransmitter agonist muscimol during a period of monocular deprivation. This drug inhibits cortical cell discharges with no apparent effect on the activity of their presynaptic geniculocortical inputs. Recording from single cortical cells after they had recovered from the muscimol-induced blockade, we found a consistent shift in the responsiveness of the visual cortex in favor of the less-active, closed eye, while the normal shift in favor of the more-active, open eye was evident in regions not affected by the treatment. Such an inhibition-coupled expression of plasticity in favor of the less-active, closed eye cannot be explained by a nonspecific disruption of cortical function. We interpret these results to indicate (i) that the postsynaptic cell is crucially involved in plasticity of the visual cortex, (ii) that the direction of cortical plasticity depends on postsynaptic membrane conductance or polarization, and (iii) that plasticity can occur in the absence of postsynaptic spike activity.

Action Potentials↗
PubMed1993

Storage of a sensory pattern by anti-Hebbian synaptic plasticity in an electric fish.

Synaptic plasticity occurs in several regions of the vertebrate brain and is believed to mediate the storage of behaviorally significant information during learning. Synaptic plasticity is well demonstrated in most cases, but the behavioral meaning of the relevant neural signals and the behavioral role of the plasticity are uncertain. In this paper we describe a case of synaptic plasticity which involves identifiable sensory and motor signals and which appears to mediate the storage of an image of past sensory input. Corollary discharge signals associated with the motor command that drives the electric organ are prominent in the electrosensory lobe of mormyrid electric fish. Some of these corollary discharge signals elicit a negative image or representation of the electrosensory input pattern that has followed recent motor commands. When the temporal and spatial pattern of sensory input changes, the corollary discharge effect also changes in a corresponding manner. The cellular mechanisms by which the corollary discharge-evoked representation is stored were investigated by intracellular recording from cells of the electrosensory lobe and pairing intracellular current pulses with the corollary discharge signal. The results indicate that the representation of recent sensory input is stored by means of anti-Hebbian plasticity at the synapses between corollary discharge-conveying fibers and cells of the electrosensory lobe. The results also suggest that dendritic spikes and plasticity at inhibitory synapses are involved in the phenomenon.

Animals↗