Extent Of Plasticity Research Articles

Structure-mechanical property correlations in mechanochromic luminescent crystals of boron difluoride dibenzoylmethane derivatives.

The structure and mechanical properties of crystalline materials of three boron difluoride dibenzoylmethane (BF2dbm) derivatives were investigated to examine the correlation, if any, among mechanochromic luminescence (ML) behaviour, solid-state structure, and the mechanical behaviour of single crystals. Qualitative mechanical deformation tests show that the crystals of BF2dbm( (t) Bu)2 can be bent permanently, whereas those of BF2dbm(OMe)2 exhibit an inhomogeneous shearing mode of deformation, and finally BF2dbmOMe crystals are brittle. Quantitative mechanical analysis by nano-indentation on the major facets of the crystals shows that BF2dbm( (t) Bu)2 is soft and compliant with low values of elastic modulus, E, and hardness, H, confirming its superior suceptibility for plastic deformation, which is attributed to the presence of a multitude of slip systems in the crystal structure. In contrast, both BF2dbm(OMe)2 and BF2dbmOMe are considerably stiffer and harder with comparable E and H, which are rationalized through analysis of the structural attributes such as the intermolecular interactions, slip systems and their relative orientation with respect to the indentation direction. As expected from the qualitative mechanical behaviour, prominent ML was observed in BF2dbm( (t) Bu)2, whereas BF2dbm(OMe)2 exhibits only a moderate ML and BF2dbmOMe shows no detectable ML, all examined under identical conditions. These results confirm that the extent of ML in crystalline organic solid-state fluorophore materials can be correlated positively with the extent of plasticity (low recovery). In turn, they offer opportunities to design new and improved efficient ML materials using crystal engineering principles.

Role of phenotypic plasticity and population differentiation in adaptation to novel environmental conditions.

Species can adapt to new environmental conditions either through individual phenotypic plasticity, intraspecific genetic differentiation in adaptive traits, or both. Wild emmer wheat, Triticum dicoccoides, an annual grass with major distribution in Eastern Mediterranean region, is predicted to experience in the near future, as a result of global climate change, conditions more arid than in any part of the current species distribution. To understand the role of the above two means of adaptation, and the effect of population range position, we analyzed reaction norms, extent of plasticity, and phenotypic selection across two experimental environments of high and low water availability in two core and two peripheral populations of this species. We studied 12 quantitative traits, but focused primarily on the onset of reproduction and maternal investment, which are traits that are closely related to fitness and presumably involved in local adaptation in the studied species. We hypothesized that the population showing superior performance under novel environmental conditions will either be genetically differentiated in quantitative traits or exhibit higher phenotypic plasticity than the less successful populations. We found the core population K to be the most plastic in all three trait categories (phenology, reproductive traits, and fitness) and most successful among populations studied, in both experimental environments; at the same time, the core K population was clearly genetically differentiated from the two edge populations. Our results suggest that (1) two means of successful adaptation to new environmental conditions, phenotypic plasticity and adaptive genetic differentiation, are not mutually exclusive ways of achieving high adaptive ability; and (2) colonists from some core populations can be more successful in establishing beyond the current species range than colonists from the range extreme periphery with conditions seemingly closest to those in the new environment.

Sustained PI3K activation destabilized tTreg (BA15P.227)

Abstract Regulatory T cells (Treg) play a central role in immune homeostasis, whose dysfunction has been implicated in autoimmune disease pathogenesis. Two subsets Tregs have been defined in vivo: thymus derived tTregs and peripherally derived pTreg. The plasticity of Treg, especially the thymically derived tTreg remains considerable controversial. Since the conserved non-coding sequence 1(CNS1) of Foxp3 gene is only critical for the generation of induced pTreg cells, we generated a new BAC-transgenic mouse expressing a thy1.1 2A Cre fusion protein driven from the CNS1 deleted Foxp3 promoter (del CNS1 Foxp3-thy1.1-Cre). Characterization of these mice demonstrated the thy1.1 2A Cre fusion protein expressed exclusively in the Nrp1+Foxp3+ peripheral tTreg subset. Moreover, thy1.1 expression in the thymus was delayed compare with endogenous Foxp3. Stability of thy1.1+ Treg was tested by breeding the thy1.1 2A Cre Tg mouse line to a conditional YFP knock-in reporter mouse, termed ROSA26-stop-YFP. A subset range from 2% to 8% Cre mapped cells spontaneously lost Foxp3 expression in healthy animals, thus even the late developed tTreg cells have some extent of plasticity. Final, we found sustained PI3K activation by breeding with a conditional active PI3K Rosa26 knockin mouse, can significant destabilized late developed tTreg and generated pathogenic exFoxp3 cells in the homeostatic condition.

Plastic responses of Populus yunnanensis and Abies faxoniana to elevated atmospheric CO2 and warming

To examine whether deciduous and evergreen tree species differ in their performance and plastic responses to elevated atmospheric CO2 and temperature, we investigated growth, leaf area ratio (LAR), specific root length (SRL), nitrogen uptake efficiency (NUpE) and nitrogen use efficiency (NUE) of Populus yunnanensis and Abies faxoniana grown in environment-controlled chambers. Our results showed that temperature stimulated growth more than did CO2 in both species. The magnitude of temperature and CO2 effects varied between the species, as greater stimulation was detected in A. faxoniana than in P. yunnanensis. Greater responses of A. faxoniana were associated with higher LAR and higher NUE. However, NUpE did not differ between species and could not explain this advantage. On the other hand, the studied species did not differ in their mean overall plasticity (calculated for each species by averaging the indices of plasticity obtained for each of the 17 variables), which, however, was achieved in different ways. Across CO2 and temperature treatments, A. faxoniana exhibited greater plasticity in stomatal conductance, LAR, SRL and NUE, whereas P. yunnanensis exhibited greater plasticity in net photosynthesis rate, leaf respiration and root/shoot ratio. Our results suggested that plasticity of key traits, such as LAR, SRL and NUE, may have important implications for the superiority of A. faxoniana in the response to climate change. Our results highlight the importance of exploring the functional significance of traits rather than the extent of plasticity as potential determinants of interspecific differences in responses to climate change.

The effect of devulcanization level on mechanical properties of reclaimed rubber by thermal‐mechanical shearing devulcanization

AbstractGround tire rubber (GTR) with crosslinked structure has hardly any plasticity and processability, which makes its property very poor. Thermal‐mechanical shearing devulcanization method can effectively destroy the crosslinked structure and restore GTR a certain extent of plasticity and processability. This article investigated the characteristic and reprocessing performance of reclaimed rubber prepared through thermal‐mechanical shearing devulcanization. The relationship between the devulcanization level (indicated by gel fraction and crosslink density) and the mechanical property was analyzed by sufficient experiments. Fourier transform infrared spectroscopy and elemental analyzer studies revealed the chemical structure of GTR changed and many complex reactions occurred after devulcanization. The gel permeation chromatography indicated the specific changes of molecular weight and molecular weight distribution in devulcanization process. The differential scanning calorimetry revealed various vulcanized abilities and vulcanized structures of reclaimed rubber. The scanning electron microscope further confirmed the recovery of plasticity after devulcanization and the distinct vulcanized structures between revulcanizates. The determination of devulcanization level and mechanical properties verified that mechanical properties especially tensile strength reached to the optimum value only at an appropriate devulcanization level. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Paired stimulation between CA3 and CA1 alters excitability of CA3 in the rat hippocampus

It is generally accepted that the extent of plasticity is localized to the region around synapses and post-synaptic intracellular signaling cascades. We investigated the presence of long-range retrograde plasticity associated with excitability at pre-synaptic neurons (CA3) and regulated by the firing of post-synaptic neurons (CA1). We used acute hippocampus slices from transgenic rats expressing channelrhodopsin-2 (ChR2) in both CA1 and CA3 neurons. We employed a parallel photostimulation technique, which enabled robust and independent evocation of action potentials in either CA3 or CA1 neurons. Optically evoked CA3 firings were paired either with CA1 simultaneous firings or with CA1 suppression after the prolonged stimulation. Pre-synaptic excitability was monitored by measuring the optically-evoked firing rate (Opt-FR). We found that the Opt-FR of CA3 neurons was long-term up-regulated as a result of synchronous pre- and post-synaptic pairing stimulation, but down-regulated by the pre-synaptic stimulation during post-synaptic suppression. Both pairing-dependent up-regulation and down-regulation were retarded by NMDA receptor blocking or colchicine preincubation. This finding suggest that CA3 excitability is regulated by CA1 neuron activity at the time of CA3 firing.

Temperature‐humidity superposition in diffusion phenomena through polyamidic materials

AbstractIn this work, the diffusivity of three different migrants is investigated in water plasticized polyamides, while changing humidity at a steady temperature, and also in dry polyamides tested at different temperatures close to the glass transition point (Tg). The effect of hydration on the structure and the barrier properties of polyamides are investigated and the results reveal that the diffusion coefficient (D) can be described by a single Williams‐Landel‐Ferry type equation, expressing D as a function of the (T − Tg) parameter. This correlation is found valid regardless the cause of (T − Tg) variation that could be temperature increase or Tg reduction due to water induced plasticization. At the same time, the effect of specific interactions between the polyamidic matrix and the diffusing molecules is also investigated, indicating that such interactions are capable of delaying the diffusion process regardless the temperature increase or the extent of plasticization. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Critical periods, homeostasis and a role for MHC Class I molecules

Event Abstract Back to Event Critical periods, homeostasis and a role for MHC Class I molecules Carla J. Shatz1* 1 Stanford University, Bio-X, United States Connections in adult brain are highly precise, but they do not start out that way. Precision emerges during development as synaptic connections remodel, a process that requires neural activity (action potentials and synaptic transmission) and involves regression of some synapses and strengthening and stabilization of others. Neural activity also regulates neuronal genes. In an unbiased PCR-based differential screen, we made the completely unexpected discovery that MHC Class I genes are expressed in neurons and are upregulated by neural activity and visual experience (Corriveau et al, 1998; Goddard et al, 2007). To assess requirements for MHCI in the CNS, mutant mice that lack stable surface expression of all MHCI, or specific MHCI genes, were examined. Synapse regression in the developing visual system did not occur, and in adult hippocampus synaptic strengthening was greater than normal (Huh et al, 2000). These observations suggest that neuronal MHCI may normally function in synaptic plasticity. Receptors could interact with neuronal MHCI and carry out these activity-dependent synaptic processes. In a systematic search, mRNA for PirB, an innate immune receptor, was found highly expressed in neurons in many regions of mouse CNS. We generated mutant mice lacking PirB function and discovered that the extent of plasticity in visual cortex is increased (Syken et al., 2006), as is synaptic strengthening in the hippocampus. Thus, PirB, like MHCI, appears to function as a “brake” on synaptic plasticity in the CNS. Together, results imply that this family of molecules, thought previously to function only in the immune system, may also act at neuronal synapses to limit how much- or perhaps how quickly- synapse strength changes in response to new experience. These molecules may be crucial for controlling circuit excitability and stability in developing as well as adult brain, and changes in their function may contribute to developmental disorders such as Autism and Schizophrenia. Supported by NIH Grants EY02858, MH071666, and Mathers Charitable Foundation. Conference: EMBO workshop: Gaba Signalling and Brain Networks , Amsterdam, Netherlands, 30 Jun - 2 Jul, 2010. Presentation Type: Oral Presentation Topic: Talks Citation: Shatz CJ (2010). Critical periods, homeostasis and a role for MHC Class I molecules. Conference Abstract: EMBO workshop: Gaba Signalling and Brain Networks . doi: 10.3389/conf.fnins.2010.15.00051 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 25 Jun 2010; Published Online: 25 Jun 2010. * Correspondence: Carla J Shatz, Stanford University, Bio-X, Stanford, United States, cshatz@stanford.edu Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Carla J Shatz Google Carla J Shatz Google Scholar Carla J Shatz PubMed Carla J Shatz Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Ionic liquids as plasticizers/lubricants for polylactic acid

AbstractIn this study, two ionic liquids (IL) with different anions (decanoate, tetrafluoroborate) but with the same phosphonium‐based cation were evaluated as potential plasticizers and lubricants for polylactic acid (PLA). Both ILs at 5 wt% were well dispersible and partly miscible with PLA as evidenced by scanning electron microscopy, SEM, and glass transition temperature, Tg, characterization, as well as from solubility parameters calculations. However, phase separation in the PLA system containing the IL with tetrafluoroborate anions was observed 1 year after melt processing. The IL containing the tetrafluoroborate anion showed higher thermal stability compared with the IL containing decanoate as confirmed by thermogravimetric analysis. This was translated in corresponding behaviors of the PLA blends. The effects of the IL containing the tetrafluoroborate anion were more pronounced on lubrication as evidenced by lower values of coefficient of friction that could also be correlated with lower contact angle; this IL could then be considered as a more effective, overall, plasticizer than the IL containing the decanoate anion based on reduced flexural modulus and brittleness as well as Tg suppression results. The extent of plasticization, however, could also be related to the molecular weight reduction during melt processing that occurred in the presence of both ILs, but to different degrees. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers

Microgeographic life history variation in an alpine caddisfly: plasticity in response to seasonal time constraints

Summary1. Temporally constrained environments, such as habitats with short growth seasons or short hydroperiods, cause potentially strong selection on life histories. Depending on the predictability of these events and the extent of spatial and temporal heterogeneity, local populations could become adapted either via a fixed phenotype or via life history plasticity in response to these environmental cues.2. We used a common garden experiment to investigate microgeographic variation in life history responses to combined changes in photoperiod (ambient/late) and hydroperiod (constant/drying) time constraint cues in an alpine caddisfly (Trichoptera). We compared six populations (three permanent/three temporary streams) originating from a small, alpine floodplain and which spanned an expected gradient in growth period duration (GPD) with distance from glaciers.3. We made two main predictions in relation to locally varying selection pressures: (i) populations nearest glaciers (shorter GPD and strongest time constraints) should have the fastest development rates and (ii) populations from permanent streams should be less able to respond to drying hydroperiods than populations from temporary streams.4. All populations and both sexes accelerated development in response to late season photoperiod cues. However, only permanent stream populations showed an increase in development time with increasing GPD, suggesting that other factors were influencing populations in temporary streams.5. Permanent stream populations showed countergradient variation (genetic and environmental influences were in opposition) in development time, and under‐compensation of growth rates resulted in a converse Bergmann cline in body size (smaller body size along gradients of declining season length). The extent of plasticity in response to hydroperiod, and the combined effects of both time constraints, differed between populations and sexes, but were not consistent among populations.6. Taken together, our results suggest adaptive plasticity in response to season length. The lack of a predictable pattern in response to hydroperiod may be due to gene flow or weak selection. We conclude that spatially structured populations can strongly differ in phenotypic plasticity even at microgeographic scales.

Physiological variation and phenotypic plasticity: a response to`Plasticity in arthropod cryotypes' by Hawes and Bale

In a recent publication, Hawes and Bale provide an extended discussion of phenotypic plasticity in the context of low temperature responses of animals. They argue that phenotypic plasticity may be partitioned phylogenetically at several levels and go on to explore these levels, and cold hardiness strategies that they term cryotypes, which in their view constitute cryotypic plasticity. Here we argue that this attempt to partition plasticity is misleading, that the term 'genotypic plasticity' is potentially highly confusing and a misnomer for physiological variance, and that the term 'superplasticity' should not be used. We also show that a definition of strategies as cryotypes is not useful and that the hypothesis about the relationship between evolutionary derivation and extent of plasticity in freeze-avoiding vs freeze-tolerant species is not supported by current evidence.

Thermal treatment of dense polyimide membranes

AbstractA study has been conducted to clarify the relationship between polymer structure, annealing temperature, and the extent of plasticization by high‐pressure CO2 for two typical polyimide membranes; BTDA‐DAPI (poly(3,3′‐4,4′‐benzophenone tetracarboxylic–dianhydride diaminophenylindane) and 6FDA‐TMPDA (poly(2,2′‐bis(3,4′‐dicasrboxyphenyl) hexafluoropropane dianhydride–2,3,5,6‐tetramethyl‐1,4‐phenylenediamine). Both membrane materials are exposed to varying levels of thermal annealing at 200 and 250 °C. The effect of this heat treatment on free volume is examined using positron annihilation lifetime spectroscopy (PALS), whereas fluorescence spectroscopy is used to monitor changes in electronic structure. Results show that thermal annealing causes a reduction in both the size and number of free volume elements. A strong relationship is found between the fluorescence peak intensity for 6FDA‐TMPDA and both the membrane gas permeability and plasticization pressure. This correlation is most likely the result of the formation of charge transfer complexes, particularly at 250 °C. However, the formation of covalent crosslinks at these temperatures cannot be discounted. No fluorescence is observed for BTDI‐DAPI. Although thermal annealing has a significant effect on the extent of plasticization in both polymers, it is found that the rate of plasticization is unaffected by the annealing temperature. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1879–1890, 2008

Correlative deformation mechanisms in Ni xCo 1−xO/ZrO 2(CaO) directionally solidified eutectic composites with a confined metallic interphase

Ni x Co 1− x O/ZrO 2(CaO) directionally solidified eutectic composites have been previously shown to form Ni(Co) metallic interphases mediating Ni x Co 1− x O and ZrO 2(CaO) phases upon chemical reduction of the composite at high temperatures. Vickers and nanoindentation experiments indicate characteristics of toughening enhancement in the reduced composite due to plastic deformation of the confined metallic interphase. This paper reports on the effect of size scale and chemistry of the metallic interphase on the phenomenological aspects of deformation behavior and the extent of plasticity at different length scales in the reduced eutectic model system. Transmission electron microscopy observations clearly show that a size-dependent deformation mechanism operates within the metallic interphase. A decrease in the extent of strain energy absorption, dislocation activity and twinning propensity is observed within the ductile interphase with decreasing size scale. In addition, a transition is observed in the small-scale deformation mechanism of the metallic interphase with changes in the composition of the interphase.

Therapeutic Effect of an Implantable Peroneal Nerve Stimulator in Subjects With Chronic Stroke and Footdrop: A Randomized Controlled Trial

Footdrop, characterized by a person's inability to raise the foot at the ankle, is a common problem in patients with stroke. A randomized controlled trial was performed to determine the therapeutic effect of using a new implantable, 2-channel peroneal nerve stimulator for 6 months versus an ankle-foot orthosis (AFO). Twenty-nine patients with chronic stroke and footdrop participated in the study. The mean time from stroke was 7.3 years (SD=7.3), and all subjects were community ambulators. The study used a randomized controlled trial design. The functional electrical stimulation (FES) group received the implantable stimulation system for correction of their footdrop. The control group continued using their conventional walking device (ie, AFO, orthopedic shoes, or no walking device). All subjects were measured at baseline and at weeks 4, 8, 12, and 26 in the gait laboratory. The therapeutic effect of FES on the maximum value of the root mean square (RMSmax) of the tibialis anterior (TA) muscle with both flexed and extended knees and walking speed were selected as the primary outcome measures. The RMSmax of the peroneus longus (PL), gastrocnemius (GS), and soleus (SL) muscles with both flexed and extended knees and muscle activity of the TA muscle of the affected leg during the swing phase of gait were selected as secondary outcome measures. A significantly higher RMSmax of the TA muscle with extended knee was found after using FES. No change in walking speed was found when the stimulator was not switched on. A significantly increased RMSmax of the GS muscle with both flexed and extended knees was found after using FES. Functionally, no therapeutic effect of implantable peroneal nerve stimulation was found. However, the significantly increased voluntary muscle output of the TA and GS muscles after the use of FES suggests that there was a certain extent of plasticity in the subjects in this study.

Measuring the effect of environment on fatigue crack-wake plasticity in aluminum alloy 2024 using electron backscatter diffraction

Compact tension samples fatigue cracked within ultrahigh vacuum and humid air were examined using electron backscatter diffraction band contrast (i.e., pattern quality) maps obtained at the crack-wake. A protocol for relating changes in band contrast with the extent of plasticity (i.e., the cyclic plastic zone size, rcpz) as a function of environment, stress intensity range ΔK, and grain orientation is developed. Essentially, a Gaussian curve is fit to the band contrast plotted as function of distance from the crack-wake and the full width at half maximum is taken as a measure of rcpz. It is shown that the quadratic dependence between rcpz and ΔK predicted by conventional fracture mechanics theory is consistent with the observations, however, there are also strong grain-to-grain variations. Additionally, rcpz is sharply reduced in a humid environment most likely due to the combined effect of hydrogen on plasticity and decohesion.

Large scale analysis of genes contributing to the herbal preparation dependent hippocampal plasticity in postischemic rehabilitation

Herbal preparations can affect the expression of many genes involved in the ischemic process. These genes have been providing insights into the molecular basis of brain plasticity in stroke rehabilitation. However, the extent of plasticity has not been investigated using a chemogenomic approach. A herbal preparation (270 mg/kg) used to treat ischemic mice for 45 days after global ischemia resulted in a significant decrease in infarct volume and neurological score compared with that of vehicle. This effect was characterized by investigating chemical genomic profiles of the mouse hippocampus with a cDNA microarray containing 1176 known genes. Treatment with the herbal preparation reversed the expression of 46 genes out of 100 genes altered in untreated ischemic mouse hippocampus. These data indicated that more genes were upregulated (60.78%) than downregulated (30.61%), and only 46 genes (46%) appear to be prime targets for therapeutic intervention in ischemia. The altered genes can be classified into seven groups, including signal transduction (12 genes, 27%), oncogene (8 genes, 17%), and transcriptional regulation (7 genes, 15%). Such multiple plasticity of expression could be considered as the beneficial role of this herbal preparation in stroke rehabilitation. Changes in gene expression of nuclear factor of activated T cells, 14-3-3eta, and β-arrestin suggest a potential role for the immune system in this plasticity. Brain plasticity originates from a balance of up and downregulated genes (Yin and Yang), and reversal of gene expression in multiple pathways indicates that a complex signaling network may be constructed and investigated further.

Transcriptome changes associated with instructed learning in the barn owl auditory localization pathway

Owls reared wearing prismatic spectacles learn to make adaptive orienting movements. This instructed learning depends on re-calibration of the midbrain auditory space map, which in turn involves the formation of new synapses. Here we investigated whether these processes are associated with differential gene expression, using longSAGE. Newly fledged owls were reared for 8-36 days with prism or control lenses at which time the extent of learning was quantified by electrophysiological mapping. Transciptome profiles were obtained from the inferior colliculus (IC), the major site of synaptic plasticity, and the optic tectum (OT), which provides an instructive signal that controls the direction and extent of plasticity. Twenty-two differentially expressed sequence tags were identified in IC and 36 in OT, out of more than 35,000 unique tags. Of these, only four were regulated in both structures. These results indicate that regulation of two largely independent gene clusters is associated with synaptic remodeling (in IC) and generation of the instructive signal (in OT). Real-time PCR data confirmed the changes for two transcripts, ubiquitin/polyubiquitin and tyrosine 3-monooxgenase/tryotophan 5-monooxygenase activation protein, theta subunit (YWHAQ; also referred to as 14-3-3 protein). Ubiquitin was downregulated in IC, consistent with a model in which protein degradation pathways act as an inhibitory constraint on synaptogenesis. YWHAQ was up-regulated in OT, indicating a role in the synthesis or delivery of instructive information. In total, our results provide a path towards unraveling molecular cascades that link naturalistic experience with synaptic remodeling and, ultimately, with the expression of learned behavior.

Properties of long-term synaptic plasticity and metaplasticity in organotypic slice cultures of rat hippocampus

The aim of this study was to investigate whether synaptic plasticity and metaplasticity in slice cultures of the young rat hippocampus were comparable to previously reported synaptic plasticity and metaplasticity in acute adult hippocampal slices. This is relevant since differences do exist between the preparations as a result of age and the ex vivo maintenance. We prepared and maintained slice cultures from 5- to 6-day-old rats according to the porous membrane method. After 12-16 days in vitro, extracellular low-frequency stimulation (LFS) and high-frequency stimulation (HFS) protocols were applied to the Schaffer collaterals, and extracellular field potentials were recorded in area CA1. LFS and HFS induced long-term depression (LTD) and long-term potentiation (LTP), respectively. LTP could be reversed by LFS, as could LTD by HFS 60 min after induction. Plotting the amount of LTD and LTP versus stimulation protocol demonstrated frequency-dependence of the sign and extent of plasticity. Priming activation of group 1 metabotropic glutamate receptors (mGluRs) with DHPG facilitated subsequent LTP, revealing a metaplastic effect similar to that observed in acute slices. Immunohistochemistry for group 1 mGluR subtypes mGluR1alpha and mGluR5 showed both receptors to be present in these cultures. We conclude that synaptic plasticity and mGluR-mediated metaplasticity are largely comparable to those effects found in acute in vitro techniques.

Study of novel rosin-based biomaterials for pharmaceutical coating.

The film forming and coating properties of Glycerol ester of maleic rosin (GMR) and Pentaerythritol ester of maleic rosin (PMR) were investigated. The 2 rosin-based biomaterials were initially characterized in terms of their physicochemical properties, molecular weight (Mw), and glass transition temperature (Tg). Films were produced by solvent evaporation technique on a mercury substrate. Dibutyl sebacate plasticized and nonplasticized films were characterized by mechanical (tensile zzzz strength, percentage elongation, and Young's modulus), water vapor transmission (WVT), and moisture absorption parameters. Plasticization was found to increase film elongation and decrease the Young's modulus, making the films more flexible and thereby reducing the brittleness. Poor rates of WVT and percentage moisture absorption were demonstrated by various film formulations. Diclofenac sodium-layered pellets coated with GMR and PMR film formulations showed sustained drug release for up to 10 hours. The release rate was influenced by the extent of plasticization and coating level. The results obtained in the study demonstrate the utility of novel rosin-based biomaterials for pharmaceutical coating and sustained-release drug delivery systems.

Interface adhesion: effects of plasticity and segregation

The adhesion at interfaces between dissimilar materials is strongly affected by both segregation and the extent of plasticity in the adjoining material, particularly when one of these is a metal (or thermoplastic). It will be shown that these interfaces when clean, are generally strong and tough, such that failure occurs in one of the adjoining materials, rather than at the interface. However, segregrants and contaminants often embrittle and weaken the interface, especially in combination with ambient moisture. The embrittlement is obviated either by alloying with elements that “getter” the contaminants or by using an “adhesion layer” that has essentially the same effect: Cr and Ti are particularly effective gettering elements. Models that relate these effects to fundamental material parameters through non-dimensional indices are described. They comprise linkages between atomistic and continuum, enabled by implementation of a plasticity length scale, within the context of a crack growth simulation routine. Comparison with the experimental results is conducted, leading to suggestions for development of a predictive scheme.