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PubMedDate not supplied

Biodegradable films of partly branched poly(l-lactide)-co-poly(epsilon-caprolactone) copolymer: modulation of phase morphology, plasticization properties and thermal depolymerization.

We report on the modulation of phase morphology, plasticization properties, and thermal stability of films of partly branched poly(l-lactide)-co-poly(epsilon-caprolactone) copolymer (PLLA-co-PCL) with additions of low molecular weight compounds, namely, triethyl citrate ester, diethyl phthalate, diepoxy polyether (poly(propylene glycol) diglycidyl ether), and with epoxidized soybean oil (ESO). The PLLA-co-PCL/polyether films showed significant stability against thermal depolymerization, high film flexibility, and good plasticizing properties, probably due to cross-linking and chain branching formation between diepoxy groups with both the end carboxyl and hydroxyl groups of the PLLA copolymer (initially present or generated during the degradation process) to produce primary ester and ether bonds, respectively. Diethyl phthalate and triethyl citrate ester were found to be efficient plasticizers for PLLA copolymer in terms of glass transition and mechanical properties, but the more water-soluble plasticizer triethyl citrate induced a dramatic loss in the molecular weight of the copolymer. Although ESO cannot play the role of a plasticizer, it substantially stabilizes and retards thermal depolymerization of the PLLA copolymer matrix, possibly because of a reaction between epoxy groups with the end carboxyl and hydroxyl groups of the PLLA copolymer. The presence of ESO in PLLA-co-PCL/ESO/triethyl citrate blends enhanced the compatibility and miscibility of the plasticizer with the PLLA copolymer matrix, considerably improved the mechanical properties (elongation at break), and substantially stabilized the copolymer against thermal depolymerization. It seems likely that the epoxy groups interact not only with the end hydroxyl and carboxyl group of the copolymer but as well with the hydroxyl group of triethyl citrate plasticizer to produce a new ether bond (C-O-C) as the cross-linking unit. On the other hand, for PLLA-co-PCL/ESO/polyether blends, (80/10/10) epoxidized oil distorts the compactness of the blend by diminishing the proposed entanglements between carboxyl, hydroxyl, and diepoxy groups of polyether and reduces the high elongation properties otherwise observed in the PLLA-co-PCL/polyether films. The multicomponent approach toward modulating poly(l-lactide)-co-poly(epsilon-caprolactone) copolymer films using epoxy compounds and plasticizers and the insight into the nature of various PLLA matrixes presented here offer advantages to a broad engineering of PLLA copolymer films having desirable physical properties and multiphase behavior for efficient uses in future technical applications.

Biodegradation, Environmental↗
PubMed2003

Photocatalytic degradation of polystyrene plastic under fluorescent light.

Plastic is used widely all over the world, due to the fact that it is low cost, is easily processable, and has lightweight properties. However, the hazard of discarding waste plastic, so-called "white pollution", is becoming more and more severe. In this paper, solid-phase photocatalytic degradation of polystyrene (PS) plastic, one of the most common commercial plastics, over copper phthalocyanine (CuPc) sensitized TiO2 photocatalyst (TiO2/CuPc) has been investigated under fluorescent light irradiation in the air. UV-vis spectra show that TiO2/CuPc extends its photoresponse range to visible light, contrasting to only UV light absorption of pure TiO2. The PS photodegradation experiments exhibit that higher PS weight loss rate, lower PS average molecular weight, less amount of volatile organic compounds, and more CO2 can be obtained in the system of PS-(TiO2/CuPc), in comparison with the PS-TiO2 system. Therefore, PS photodegradation over TiO2 CuPc composite is more complete and efficient than over pure TiO2, suggesting the potential application of dye-sensitized TiO2 catalyst in the thorough photodegradation of PS plastic under fluorescent light. During the photodegradation of PS plastic, the reactive oxygen species generated on TiO2 or TiO2/CuPc particle surfaces play important roles in chain scission. The present study demonstrates that the combination of polymer plastic with dye-sensitized TiO2 catalyst in the form of thin film is a practical and useful way to photodegrade plastic contaminants in the sunlight.

Catalysis↗
PubMed1997

The phenotypic plasticity of wing size in Drosophila melanogaster: the cellular basis of its genetic variation.

The reaction norms in Drosophila melanogaster of thorax length, wing length and cell size were determined for 28 isofemale lines from three populations to investigate the role of cell size in determining the response of body size to temperature during the preimaginal stages. Both overall level and plasticity of the reaction norms of thorax length and wing length are highly correlated, leading to a relatively constant wing-thorax ratio between lines. Genetic differences in overall level of wing size reaction norms are mainly caused by differences in cell number. The response of wing size to temperature consists of changes in cell size and, to a lesser extent, cell number. The cellular basis of genetic differences in plasticity shows a transition point at an intermediate level. In steeper reaction norms, genetic differences in plasticity result from differences in the plasticity of cell size, whereas less steep reaction norms only differ in the plasticity of cell number. A significant partial correlation between wing length plasticity and cell size plasticity, correcting for thorax length plasticity, indicates a role of cell size in determining the wing-thorax ratio.

Animals↗
PubMed2002

Displacement of occluded plastic endoprostheses into the duodenum during percutaneous biliary drainage: description of an under-reported technique.

AIM: Percutaneous transhepatic biliary drainage (PTBD) is occasionally requested in patients with an occluded plastic stent in situ. We describe a technique for dislodging the stent into the duodenum during PTBD. MATERIALS AND METHODS: Twelve patients (M:F, 9:3 mean age 70 years) with plastic stents in the common bile duct (CBD) underwent PTBD. Eleven patients had malignant obstruction and one patient had Mirizzi's syndrome and a large duodenal diverticulum. PTBD was performed using right lobe access in nine patients and a left hepatic access in three patients. The level of biliary obstruction was at the lower CBD in five patients, mid-CBD in four patients and upper CBD in three patients. After standard percutaneous biliary access was established, an 8mm by 4 cm balloon catheter was gently inflated alongside the upper end of the plastic stent and advanced over a stiff guidewire, towards the duodenum, to dislodge the plastic stent. RESULTS: Plastic stents were successfully dislodged in all 11 patients with malignancy and metallic stents were deployed for palliation. In nine of 11 patients with malignant lesions the PTBD dislodgement of the plastic stent and insertion of a metallic stent was carried out as a single-step procedure. In two patients with biliary sepsis, a two-step procedure was necessary. In the patient with Mirizzi's syndrome the plastic stent could not be dislodged. No complications were observed. CONCLUSION: Plastic stents, inserted at ERCP, can be dislodged in the majority of cases at PTBD using a balloon catheter inserted alongside the failed stent without complication.

Aged↗
PubMed2000

Plasticity to light cues and resources in Arabidopsis thaliana: testing for adaptive value and costs.

Plants shaded by neighbors or overhead foliage experience both a reduction in the ratio of red to far red light (R:FR), a specific cue perceived by phytochrome, and reduced photosynthetically active radiation (PAR), an essential resource. We tested the adaptive value of plasticity to crowding and to the cue and resource components of foliage shade in the annual plant Arabidopsis thaliana by exposing 36 inbred families from four natural populations to four experimental treatments: (1) high density, full sun; (2) low density, full sun; (3) low density, neutral shade; and (4) low density, low R:FR-simulated foliage shade. Genotypic selection analysis within each treatment revealed strong environmental differences in selection on plastic life-history traits. We used specific contrasts to measure plasticity to density and foliage shade, to partition responses to foliage shade into phytochrome-mediated responses to the R:FR cue and responses to PAR, and to test whether plasticity was adaptive (i.e., in the same direction as selection in each environment). Contrary to expectation, we found no evidence for adaptive plasticity to density. However, we observed both adaptive and maladaptive responses to foliage shade. In general, phytochrome-mediated plasticity to the R:FR cue of foliage shade was adaptive and counteracted maladaptive growth responses to reduced PAR. These results support the prediction that active developmental responses to environmental cues are more likely to be adaptive than are passive resource-mediated responses. Multiple regression analysis detected a few costs of adaptive plasticity and adaptive homeostasis, but such costs were infrequent and their expression depended on the environment. Thus, costs of plasticity may occasionally constrain the evolution of adaptive responses to foliage shade in Arabidopsis, but this constraint may differ among environments and is far from ubiquitous.

Adaptation, Physiological↗
PubMed1990

Adhesion of an Amylolytic Arthrobacter sp. to Starch-Containing Plastic Films.

Cells of the amylolytic bacterium KB-1 (thought to be an Arthrobacter sp.) adhered ( approximately 70%) to the surface of plastic films composed of starch-poly (methylacrylate) graft copolymer (starch-PMA), but did not adhere (<10%) to films composed of polymethylacrylate (PMA), polyethylene (PE), carboxymethyl cellulose, or a mixture of PE plus poly (ethylene-coacrylic acid) (EAA), starch plus PE, or starch plus PE and EAA. About 30% of the cells adhered to gelatinized insoluble starch. Dithiothreitol (5 mM), EDTA (5 mM), and soluble starch (1%, wt/vol) had little effect on the adhesion of KB-1 cells to starch-PMA films. However, glutaraldehyde-fixed cells, azide-treated cells, and heat-killed cells did not bind to starch-PMA plastic, suggesting that the observed adhesion required cell viability. Culture supernatant from 5-day-old KB-1 cultures contained a proteolytic enzyme that inhibited cell adhesion to starch-PMA plastics. Trypsin-treated KB-1 cells also lost their ability to bind to starch-PMA plastic. When washed free of trypsin and suspended in fresh medium, trypsin-treated bacteria were able to recover adhesion activity in the absence, but not in the presence, of the protein synthesis inhibitor chloramphenicol. These results suggested that adhesion of KB-1 to starch-PMA plastic may be mediated by a cell surface protein. Although KB-1 bacteria bound to starch-PMA plastic, they did not appear to degrade starch in these films. Evidence of starch degradation was observed for starch-PE-EAA plastics, where <10% of the bacteria was bound, suggesting that cell adhesion may not be a prerequisite for degradation of some starch-containing plastics.

Journal Article↗
PubMed2006

Phenotypic plasticity, sexual selection and the evolution of colour patterns.

When a population comes to occupy a new environment, phenotypically plastic responses alter the distribution of phenotypes, and hence affect both the direction and the intensity of selection. Rates of evolution can be accelerated or retarded compared to what would happen in the absence of plasticity. Plastic responses in one trait result in novel selection pressures on other traits, and this can lead to evolution in completely different directions than predicted in the absence of plasticity. In this paper I use the concept of the adaptive surface in order to identify conditions under which the various different outcomes are expected. I then discuss differences between sexually and naturally selected traits. Sexually selected traits are often expected to be plastic in their expression, with individuals in high condition developing greater elaboration. As examples of sexually selected traits I review the evolution of colour patterns in birds with a view to assessing the magnitude of plastic responses in their development, and to ask how such responses may have influenced genetic evolution. The common colour pigments in birds are carotenoids and melanins. Both are used in social signaling, and consequently are expected to evolve to be phenotypically plastic indicators of an individual's quality. Perhaps partly because they are condition indicators, the quantity of carotenoids in the plumage can be strongly influenced by diet. Examples are described where alterations of carotenoids in the diet are thought to have altered the phenotype, driving genetic evolution in novel directions. Melanin patterns seem to be less affected by diet, but the intensity of melanization after moult is affected by social interactions during the moult and by raising birds in humid conditions. Hormonal manipulations can have dramatic effects on both the kinds of melanin produced (eumelanin or phaeomelanin) as well as the patterns they form. Differences between species in melanin patterns resemble differences produced by environmental manipulations, as well as those produced by simple modulations of parameters in computer simulations of pattern formation. While phenotypic plasticity is one way that genetic change in plumage patterns (and other traits) could be driven, there are others, including the appearance of major mutations and selection on standing variation whose distribution is not altered in the new environment. I consider some evidence for the different alternatives, and ask when they might lead to qualitatively different evolutionary outcomes.

Adaptation, Physiological↗
PubMed1999

Dynamic phenotypic plasticity for root growth in Polygonum: a comparative study.

Species differences in patterns of phenotypic plasticity may be an important aspect of adaptive diversity. Plasticity for functionally important root traits was studied in inbred field lineages of Polygonum persicaria and P. cespitosum (Polygonaceae). Replicate seedlings were grown in plexiglass rhizotrons under a range of constant and temporally variable moisture treatments. Plasticity was determined for final whole-plant biomass, root biomass allocation, and absolute and proportional root length. The dynamic aspect of root plasticity was examined by digitizing weekly tracings of the proportional deployment of each plant's root system to different vertical soil layers. Plants of both species expressed significant functionally adaptive phenotypic plasticity in the relative allocation, length, and vertical deployment of root systems in response to contrasting moisture conditions. Plasticity patterns in these closely related species were in general qualitatively similar, but for most traits differed in the magnitude and/or the timing of the plastic response. Dynamic changes in root deployment were more marked as well as faster in P. persicaria. Species differences in patterns of individual plasticity were generally consistent with the broader ecological distribution of P. persicaria in diverse as well as temporally variable moisture habitats.

Journal Article↗
PubMed1999

Palliative treatment of oesophageal carcinoma--efficacy of plastic versus self-expandable stents.

OBJECTIVES: A prospective randomised study of patients with irresectable oesophageal carcinoma treated with self-expandable covered metal Wallstent and plastic Procter Livingstone tubes was performed. The purpose was to compare the efficacy, cost effectiveness, ease of implantation, long-term patency and complications of the two different stents. METHODS: Data recorded included dysphagia score (0-4) the day before and after stent placement, location and length of stricture, procedural time and complications, and stent patency at 1 and 3 months' follow-up. A comparative costing of materials, theatre and anaesthetic time and hospital stay was undertaken. RESULTS: Forty patients were studied over 12 months (20 in each group). Strictures were located most commonly in the middle third of the oesophagus (75%), followed by the upper third (12.5%) and lower third (12.5%). Mean stricture length was 6 cm (2-12 cm); 10 patients (25%) had strictures 8 cm or longer. Five patients had tracheo-oesophageal fistulas (3 Wallstent; 2 Procter Livingstone tube). There was effective fistula sealing in all 3 Wallstent patients, and non-sealing in 1 of the Procter Livingstone patients. The mean pre-operative dysphagia score in both groups was 3, and immediately postoperatively the score was 0 in the Wallstent group and 2 in the plastic tube group. Initial stent placement was satisfactory in all Wallstent patients, with 2 patients requiring 2 stents each for adequate tumour coverage, and in 15 patients (75%) having plastic stents. Immediate complications were chest pain in 2 patients with Wallstents and oesophageal perforation in 2 patients (10%) with plastic stents. Wallstent patency at 1 and 3 months was 90% and 88%, respectively, and plastic stent patency was 66% and 50%. Four patients (10%), 2 in each group, died during the study from massive tumour load or metastatic disease. Comparative costing of the Wallstent versus the plastic tube stent was R4 123 versus R2 146 or a factor of 1.9. CONCLUSION: Palliation with the Wallstent is effective, with excellent 1- and 3-month patency. The Wallstent is superior to the conventional plastic stent in terms of ease of implantation, better long-term patency and fewer complications. It is particularly useful for the treatment of patients with fistulas and long strictures. Accurate placement is critical in order to prevent stent migration and tumour overgrowth. However, it costs almost twice as much to implant the Wallstent as it does to implant the plastic tube.

Carcinoma, Squamous Cell↗
PubMed1999

Corn protein-based thermoplastic resins: effect of some polar and amphiphilic plasticizers.

Homogeneous blends of corn gluten meal (CGM) and "polar" plasticizers (water, glycerol) or "amphiphilic" plasticizers [octanoic and palmitic acids, dibutyl tartrate and phthalate, and diacetyl tartaric acid ester of mono-diglycerides (DATEM)] were obtained by a hot-mixing procedure. The glass transition temperature (T(g)) of the blends was measured by modulated differential scanning calorimetry and dynamic mechanical thermal analysis, as a function of plasticizer type and content (0-30%, dwb). The plasticizing efficiency (i.e., decrease of T(g)) at equal molar content was found to be proportional to the molecular weight and inversely proportional to the percent of hydrophilic groups of the plasticizer. The migration rate of the plasticizers in the polymer was related to their physicochemical characteristics. It was assumed that polar substances interacted with readily accessible polar amino acids, whereas amphiphilic ones interacted with nonpolar zones, which are buried and accessible with difficulty. The temperature at which a thermoplastic resin of plasticized CGM could be formed was closely connected to the T(g) of the blend.

Flour↗
PubMed2004

Analysis of publications in three plastic surgery journals for the year 2002.

The goal of this study was to analyze the publications in the plastic surgery literature for the year 2002. Contents of these articles, authors' information (such as nationality affiliation of the first author), type of institution, presence of grant support, and previous presentation were analyzed. For inclusion in this study, the publications had to be original articles from the three most frequently read general plastic surgery journals: Annals of Plastic Surgery, British Journal of Plastic Surgery, and Plastic and Reconstructive Surgery. With this approach, 533 articles were included in the study. To give a cross-sectional analysis of the content of all articles, 11 distinct categories were created in which all the articles were subsummarized. The categories were based on anatomical regions and specific plastic surgical areas. A summary is given for each of the categories to provide an overview of the field in which most of the research in plastic surgery was taking place in 2002 and which topics were focused on. The authors found that only 7 percent of all articles had grant support, whereas 36 percent of articles were presented previously during a scientific meeting. Most of the articles came from university-based institutions (68 percent), followed by non-university-based institutions (29 percent) and private practice (3 percent). Regarding nationality affiliation, most of the articles came from the United States (n = 229) and Europe (n = 128); in Asia, Turkey (n = 39) and Japan (n = 36) were the countries with the most published articles.

Bibliometrics↗
PubMed2006

Differences in biopsy techniques of actinic keratoses by plastic surgeons and dermatologists: a histologically controlled pilot study.

OBJECTIVE: To compare differences in biopsy techniques of actinic keratoses between dermatologists and plastic surgeons. DESIGN: Blinded, comparative, retrospective study. SETTING: Dermatopathology laboratory at a major academic medical center with referral of outside cases. Intervention We reexamined the histopathologic slides of 405 actinic keratosis biopsy specimens obtained by plastic surgeons and dermatologists from January 1, 1992, through May 31, 2002. We were specifically interested in the type of biopsy technique (shave, punch, or excisional biopsy) used for the surgical management of actinic keratoses by both groups of physicians. We also recorded the clinical diagnoses rendered on the dermatopathology request form and compared them with the histopathologic diagnoses. RESULTS: Excisional biopsies were performed by plastic surgeons in 50.0% of the cases, compared with only 1.4% by dermatologists. In contrast, shave biopsies of actinic keratoses were performed by plastic surgeons in only 32.4% of the cases, compared with 89.4% by dermatologists. Only 1 (0.5%) of the 198 dermatopathology request forms submitted by the plastic surgeons mentioned actinic keratosis, compared with 82 (39.6%) of 207 histopathologic evaluation requests submitted by dermatologists. CONCLUSIONS: The predominance of excisional biopsies of actinic keratoses by plastic surgeons may be related to a different ability in the clinical recognition of actinic keratoses compared with that of dermatologists. The surgical approach of dermatologists to shave diagnostically uncertain cutaneous lesions is less invasive than that of plastic surgeons and is more likely to achieve a better cosmetic outcome.

Academic Medical Centers↗
PubMed1997

Age-related change in short-term synaptic plasticity intrinsic to excitatory striatal synapses.

Aging disrupts the expression of synaptic plasticity in many central nervous system (CNS) structures including the striatum. We found age differences in paired-pulse plasticity to persist at excitatory striatal synapses following block of gamma aminobutyric acid (GABA)A and GABA(B) receptors, a property that was independent of the number of afferents activated. High Mg2+/low Ca2+ artificial cerebral spinal fluid (ACSF) reduced release probability and consequently the size of the evoked excitatory post-synaptic potential (EPSP). High Mg2+/low Ca2+ ACSF also increased the expression of paired-pulse facilitation and eliminated the age difference seen previously in normal ACSF. These data suggest that age differences in paired-pulse plasticity reflect an alteration in release probability at excitatory striatal synapses. In support of this hypothesis, we found age differences in another presynaptic form of plasticity referred to as synaptic augmentation. Examination of the synaptic depression that developed during the conditioning tetanus also revealed an age-related increase in synaptic depression. These data indicate that age-related changes in facilitation may be due in part to a reduction in the readily releasable pool of synaptic vesicles. Dendritic structure (spine density and dendritic length) was correlated with short-term synaptic plasticity, but these relationships depended upon the variance associated with age (hierarchical regression). Post-hoc within-age group regressions demonstrated relationship between spine density and paired-pulse plasticity. No other age-specific correlations were found. These findings imply an age-dependent association between altered dendritic morphology and changes in synaptic plasticity.

Aging↗
PubMed2000

Functional state of corticostriatal synapses determines their expression of short- and long-term plasticity.

Relationships between presynaptic function and short- and long-term plasticity were investigated at adult corticostriatal synapses. Wide variability was observed in the expression of short- and long-term synaptic plasticity. Intracellular records from 47 cells produced 17 examples of LTD (<90% of control), 10 examples of no long-term change (between 90-110% of control), and 20 examples of LTP (>110% of control). Similar variation existed in paired-pulse and posttetanic plasticities. The variability expressed in all three forms of plasticity appears to be related, based on correlations found between the paired-pulse ratio (PPR) and tetanus-induced short- (3 min posttetanus) and long-term plasticities (16-20 min posttetanus). These data suggest that tetanus-induced changes in synaptic strength are related to the intrinsic, preconditioned behavior of synapses. Every cell showing paired-pulse depression also expressed LTD in response to high-frequency activation of its afferents. Those synapses showing paired-pulse potentiation tended to express LTP, although exceptions did exist. Similar relationships were found in a parallel analysis of population spikes. PPR also changed in association with the expression of posttetanic and long-term depression. Greater paired-pulse potentiation was observed in medial intracellular recordings, but no medial to lateral differences were seen in posttetanic plasticities. Field recordings also showed a medial bias toward paired-pulse and posttetanic potentiation, but not in long-term plasticity. Block of postsynaptic L-type Ca(2+) channels with nifedipine eliminated LTD expression, but overall no differences were found between nifedipine and control cells.

Action Potentials↗
PubMed1985

Plasticity of the central nervous system--a neurosurgeon's experience of cerebral compensation and decompensation.

Cerebral plasticity constitutes one of the most decisive factors in recovery and readaptation after cerebral lesions. In contrast to the considerable progress in current studies on normal neuronal plasticity including the idea of "l'homme neuronal", the concept of plasticity postulated by Albrecht Bethe in 1929 received little attention. The author, as a neurosurgeon, has tried to describe cranial morphological plasticity, morphological and functional plasticity in infantile encephalopathies and especially in hemiatrophic lesions. It is supposed that a true morphological substrate exists due to compensatory hyperplasia of the uninvolved hemisphere. Modern neurosurgical techniques have demonstrated that the functional plastic capacity is much larger than has been supposed, even in the elderly. Some aspects of the mechanisms of compensation and decompensation of cortical and subcortical structures as well as of the central regulation systems are discussed. The full extent of the amazing recovery and functional reorganization is reached by plastic capacity, personal motivation, adequate training and sufficient time. The contribution ends with an exposition of a personal philosophy concerning psycho-somatic dualism, the body-mind problem, the future of the human brain and the ethical outlook, based on the progressive biological evolution of the basal neocortex and the immanent functional development (H. Spatz).

Adaptation, Physiological↗
PubMed2001

Competitive anatomical and physiological plasticity: a neurotrophic bridge.

Understanding the mechanisms of competitive synaptic plasticity, both anatomical and physiological, is of central importance to developmental neuroscience. Neurotrophic factors (NTFs) are implicated at almost every level of synaptic plasticity, from rapid physiological effects to slower anatomical effects, in addition to being implicated in competitive plasticity. Previously, we have built and analysed a mathematical model of anatomical synaptic plasticity based on competition for neurotrophic support. Here, we extend our work to build a combined, anatomical and physiological model. We find that, in order to understand the mechanisms of competitive physiological plasticity, we must postulate a central role for the change in expression of NTF receptors (NTFRs) on afferent synaptic terminals. Only by supposing that the expression of NTFRs is governed by NTF uptake do we find that physiological plasticity is competitive in character. We perform a fixed point analysis that establishes when afferent segregation is possible as a function of the parameters in the model, and simulate the model numerically to shed further light on its properties. A very clear prediction emerges from our model: that, as the efficacy of a terminal that is destined to be retracted due to competitive interactions reduces to zero, the NTFRs on that terminal should be down-regulated. Furthermore, our model requires that this reduction in synaptic efficacy never occurs significantly before the down-regulation in NTFRs. Such a prediction should be testable, and renders our model capable of being invalidated, in contrast to many other models of synaptic competition, which merely impose rather than seek to illuminate the quintessential feature of developmental synaptic plasticity.

Computer Simulation↗
PubMed2006

Virally mediated knock-down of NR2 subunits ipsilateral to the deprived eye blocks ocular dominance plasticity.

NMDA receptors (NMDARs) are important in developmental plasticity in the visual cortex. The NR2A and NR2B subunits of this receptor develop with different time courses, suggesting that they play different roles in plasticity. To understand the role of the NR2B subunit, we knocked-down NR2B gene expression in visual cortex by injecting a recombinant adenovirus containing an antisense NR2B oligonucleotide. To assess knock-down, we injected the recombinant adenovirus into the right visual cortex of rats (p22) or mice (p30). Eight days later we perfused the animals and processed the visual cortex for NMDAR subunit immunoreactivity (IR). NR2B-IR was depleted dramatically in the neuropil near the injection. Depletion was more modest in the neuronal somata. Surprisingly, NR2A-IR was also reduced, but NR1-IR was not reduced. To assess the functional effects of depletion, we measured ocular dominance plasticity with monocular deprivation (MD). We compared mice receiving the NR2B antisense virus with mice receiving virus containing only the GFP sequence and mice receiving no injection. All injections were between p26 and p29 in the right cortex and bilateral recordings were performed 6-8 days later. Animals receiving the antisense virus lost plasticity if the right eye was deprived. If the left eye was deprived, the cortex was normally plastic bilaterally. Injection of control virus had no effect on plasticity. The data indicate that ocular dominance plasticity requires normal NMDARs in the hemisphere ipsilateral to the deprived eye but not in the hemisphere contralateral to the deprived eye.

Adenoviridae↗
PubMed1991

Lithium reduces ocular dominance plasticity in kitten visual cortex.

Activity-dependent processes within the visual pathway play a crucial role in the expression of ocular dominance plasticity in immature visual cortex. The necessity of non-retinal, modulatory afferents to the regulation of ocular dominance plasticity has been recognized. Among a few chemically defined signaling systems, the noradrenaline-activated beta-adrenoreceptors seem to have a prime role in this matter. The involvement of acetylcholine afferents was also proven. We looked for plausible molecular mechanisms which integrate the contribution of the two neuromodulator systems to ocular dominance plasticity. At the first step, based on the rich literature on psychotropic action of lithium and the recent advancement in understanding of its molecular mechanisms, we physiologically studied visual cortex of kittens which had been repeatedly injected with the lithium solution intraperitoneally or the cortex directly infused with it. We found (1) that ocular dominance plasticity was significantly reduced in lithium-injected kittens, (2) that the decrease was directly correlated with plasma concentrations of lithium (i.e. the higher the lithium concentration, the lower the plasticity), and (3) that the comparable decrease in the plasticity was obtained from kitten visual cortex which had been directly infused with the lithium solution. The present results suggest that lithium-sensitive processes, through most likely reduced production of second messengers, underlie the regulation of ocular dominance plasticity.

Animals↗