bluuebunny/crossref_metadata_2025 huggingface dataset:
GT3 Synthesis in the Proximal Golgi Occurs in a Compartment Different from Those for GD3 and GM3 Synthesis
Authors: Rosales Fritz Víctor M. , Maxzúd Mariana K. , Maccioni Hugo J. F.
Published: July 2010

Abstract: Previous studies from this laboratory have shown that synthesis of GT3, the precursor of c series gangliosides, occurs in proximal Golgi compartments, as has been shown for the synthesis of GM3 and GD3, the precursors of a and b series gangliosides, respectively. In this work we studied whether the synthesis of GM3, GD3, and GT3 occurs in the same or in different compartments of the proximal Golgi. For this, we examined in retina cells (a) the effect of monensin, a sodium ionophore that affects mostly the trans Golgi and the trans Golgi network function, on the metabolic labeling of glycolipids from [3H]Gal by cultured cells from 7‐ and 10‐day chick embryos and (b) the labeling in vitro of endogenous glycolipids of Golgi membrane preparations from 7‐day embryos incubated with UDP‐[3H]Gal. In (a), 1 µM monensin produced a twofold accumulation of radioactive glucosylceramide and a decrease to ∼50 and 20% of total ganglioside labeling in 7‐ and 10‐day cells, respectively. At both ages, monensin produced a threefold accumulation of radioactive GM3 and an inhibition of >90% of GT3, GM1, GD1a, and GT1b synthesis. GD3 synthesis was inhibited ∼30 and 70%, respectively, in 7‐ and 10‐day cells. In (b), >80% of the [3H]Gal was incorporated into endogenous glucosylceramide to form radioactive lactosylceramide. About 90% of [3H]Gal‐labeled lactosylceramide was converted into GM3, and most of this in turn into GD3 when unlabeled CMP‐NeuAc was also present in the incubation system. Under the same conditions, however, <5% of labeled GD3 was converted into GT3. Golgi membranes incubated with CMP‐[3H]NeuAc incorporated ∼20% of [3H]NeuAc into endogenous GT3, and this percentage was not affected by 1 µM monensin. These results indicate that synthesis of GT3 is carried out in a compartment of the proximal Golgi different from those for lactosylceramide, GM3, and GD3 synthesis. Results from the experiments with monensin point to the cis/medial Golgi as the main compartment for coupled synthesis of lactosylceramide, GM3, and GD3 and to the trans Golgi as the main compartment for synthesis of GT3.
Endothelins Induce Fos Expression in Neurons and Glia in Organotypic Cultures of Rat Cerebellum
Authors: Sullivan A. M. , Morton A. J.
Published: July 2010

Abstract: Endothelins (ETs) and their receptors are present in high levels in the brain and have been proposed to act as neuromodulators or neurotransmitters. However, neither their role nor their precise mechanism of action in the brain is understood. In this study, c‐fos expression was used as a marker of neuronal activation in organotypic cultures of rat cerebellum. ETs induced Fos protein expression in both granule cells and glia but not in Purkinje cells. Granule cells and glia were both very sensitive to ETs, but different receptor subtypes appeared to be involved, because granule cells did not respond to ET‐3. However, they did respond to the ETB‐selective agonist BQ3020, suggesting the possible existence of a novel neuronal ETB‐like receptor. The induction of Fos in granule cells was independent of extracellular calcium ion concentration, but the ryanodine receptor antagonist dantrolene significantly inhibited the response to ETs, suggesting that the mobilisation of calcium ions from intracellular stores is important. These data support previous evidence that ETs act directly on neurones and show that the intracellular pathways after ET receptor activation are complex. It appears likely that ETs play an important neuromodulatory role in the cerebellum.
Actions of Neurotoxic β‐Amyloid on Calcium Homeostasis and Viability of PC12 Cells Are Blocked by Antioxidants but Not by Calcium Channel Antagonists
Authors: Zhou Yan , Gopalakrishnan Venkat , Richardson J. Steven
Published: July 2010

Abstract: The fragment of β‐amyloid comprised of amino acids 25–35 induces a rapid, concentration‐dependent increase in cytosolic free calcium levels in suspensions of PC12 neuronal cells. This action of β‐amyloid 25–35 is not altered by pretreatment with the calcium channel blockers nifedipine or cobalt, with the depleter of intracellular calcium stores cyclopiazonic acid, or with the phospholipase C inhibitor neomycin. However, the effects of β‐amyloid 25–35 on cytosolic free calcium are absent in calcium‐free buffer and are blocked by the antioxidant lazaroid U‐83836E and by vitamin E. β‐Amyloid 25–35 is also neurotoxic and produces a concentration‐dependent reduction in the viability of PC12 cells in culture. The neurotoxic action of β‐amyloid is blocked by U‐83836E and vitamin E but not by nifedipine or cobalt. These data indicate that both the disruption of calcium homeostasis and the reduction of cell viability produced by β‐amyloid in PC12 cells are mediated by free radical‐based processes.
Exposure of Astrocytes to Thrombin Reduces Levels of the Metabotropic Glutamate Receptor mGluR5
Authors: Miller Stephan , Sehati Nouzhan , Romano Carmelo , Cotman Carl W.
Published: July 2010

Abstract: Thrombin is one of the first regulatory molecules present at sites of CNS trauma or injury. Exposure of neuronal and glial cells to thrombin produces potent morphological as well as cytoprotective and cytotoxic effects, but little is known about how this important modulator affects neurotransmitter signaling. In astrocyte cultures that have been morphologically differentiated by exposure to transforming growth factor‐α, addition of thrombin induced a retraction of astrocytic processes and suppressed the stimulation of phosphoinositide hydrolysis by the selective metabotropic glutamate receptor (mGluR) agonist 1‐aminocyclopentane‐1S,3R‐dicarboxylic acid. In addition to the suppression of phosphoinositide hydrolysis, thrombin treatment produced a corresponding reduction in level of mGluR5 mRNA as demonstrated with ribonuclease protection assay and reduced content of mGluR5 receptor protein as seen with western blotting. In contrast, thrombin exposure up‐regulated astrocyte β‐actin mRNA levels. A synthetic hexapeptide with a sequence corresponding to the amino‐terminus of the thrombin receptor's tethered ligand also mimicked the ability of thrombin to suppress mGluR5 levels and to increase β‐actin mRNA content, suggesting that these effects of thrombin are mediated by proteolytically activated cell surface thrombin receptors. Thrombin's suppressive effect on mGluR5 was resistant to pretreatment with pertussis toxin or various protein kinase and protein phosphatase inhibitors. However, the serine/threonine protein kinase inhibitor H‐7 did prevent thrombin‐induced reversal of astrocyte stellation and induction of β‐actin mRNA levels, indicating that these effects of thrombin involve a signaling pathway distinct from the one that mediates the suppressive effects of thrombin on mGluR5.
Initial Processing of Human Proenkephalin in Bovine Chromaffin Cells
Authors: Liu Fang , Housley Paul R. , Wilson Steven P.
Published: July 2010

Abstract: The opioid peptide precursor preproenkephalin (PPE) contains seven enkephalin sequences and is synthesized by epinephrine‐producing adrenal chromaffin cells and various peripheral and central neurons. After removal of its signal peptide. PPE undergoes processing at dibasic amino acid sites to yield its final opioid products—Met‐enkephalin, Leu‐enkephalin, and various larger, enkephalin‐containing peptides. Processing of PPE was examined in bovine chromaffin cells using a plasmid containing the human PPE (hPPE) cDNA under the control of the cytomegalovirus immediate early enhancer/promoter. Following transfection of this hPPE‐containing plasmid into bovine chromaffin cells, several proenkephalin‐immunoreactive bands were observed on western blots with monoclonal antibodies that recognize human, but not bovine, proenkephalin sequences. The pattern of hPPE‐derived peptides observed was similar to that of bovine PPE processing products. A series of recombinant plasmids containing mutations in the hPPE sequence at putative processing sites was then constructed. Conversion of Lys‐Lys and Lys‐Arg sequences to Lys‐Gln and of Arg‐Arg to Arg‐Gln altered initial hPPE processing at only three of the putative processing sites. When hPPE cDNA containing mutations at all of these initially processed sites was expressed, one or more alternative processing sites were revealed. These data suggest the importance of structural features in addition to the dibasic sequences that limit the processing of proenkephalin.
Adenosine A1 Receptors in Cultured Cerebellar Granule Cells: Role of Endogenous Adenosine
Authors: Sanz Juana M. , Vendite Deusa , Fernández Mercedes , Andrés Antonio , Ros Manuel
Published: July 2010

Abstract: Adenosine A1 receptors as well as other components of the adenylate cyclase system have been studied in cultured cerebellar granule cells. No significant changes in adenosine A1 receptor number, assayed by radioligand binding in intact cells, were detected from 2 days in vitro (DIV) until 7 DIV. Nevertheless, a decline in this parameter was detected at 9 DIV. The steady‐state levels of α‐Gs and α‐Gi, detected by immunoblotting, showed similar profiles, increasing from 2 to 5 DIV and decreasing afterward. Forskolin‐stimulated adenylate cyclase levels also showed an increase until 5 DIV, decreasing at 7 and 9 DIV. The adenosine A1 receptor analogue cyclopentyladenosine (CPA) was able to inhibit cyclic AMP accumulation at 2, 5, and 7 DIV but failed to do so at 9 DIV. This inhibition was prevented by the specific adenosine A1 receptor antagonist 8‐cyclopentyl‐1,3‐dipropylxanthine. The presence of adenosine deaminase in the culture increased adenosine A1 receptor number during the period studied and induced recovery of the inhibitory effect of CPA, lost after 7 DIV. These data suggest that functional expression of adenosine A1 receptors and the other components of the adenylate cyclase system is subjected to regulation during the maturation of cultured cerebellar granule cells and demonstrates a key role for endogenous adenosine in the process.
High Level Expression of the NMDAR1 Glutamate Receptor Subunit in Electroporated COS Cells
Authors: Ishmael Jane E. , Franklin Paul H. , Murray Thomas F. , Leid Mark
Published: July 2010

Abstract: The rat N‐methyl‐d‐aspartate (NMDA) glutamate receptor subunit NR1‐1a was transiently expressed in COS cells using the technique of electroporation, which was fivefold more efficient than the calcium phosphate precipitation method of transfection. The glycine site antagonist 5,7‐[3H]dichlorokynurenic acid labeled a single high‐affinity site (KD = 29.6 ± 6 nM; Bmax = 19.4 ± 1.6 pmol/mg of protein) in membranes derived from COS cells electroporated with NR1‐1a. In contrast to previous reports using transiently transfected human embryonic kidney 293 cells, binding of the noncompetitive antagonist (+)‐5‐[3H]methyl‐10,11‐dihydro‐5H‐dibenzo[a,d]‐cyclohepten‐5,10‐imine ([3H]MK‐801) was not detected in NR1‐1a‐transfected COS cells. Although immunofluorescent labeling of electroporated COS cells demonstrated that the NR1‐1a protein appears to be associated with the cell membrane, neither NMDA nor glutamate effected an increase in intracellular calcium concentration in fura‐2‐loaded cells, suggesting that homomeric NR1‐1a receptors do not act as functional ligand‐gated ion channels. Therefore, COS cells appear to differ from Xenopus oocytes with respect to the transient expression of functional homomeric NR1 receptors. Although expression of NR1‐1a is sufficient to reconstitute a glycine binding site with wild‐type affinity for antagonists in COS cells, recombinant homomeric NR1‐1a receptors do not display properties that are characteristic of native NMDA receptors, such as permeability to Ca2+ and channel occupancy by MK‐801, when expressed in this mammalian cell line.
Effect of Long‐Term Treatment with Selective Monoamine Oxidase A and B Inhibitors on Dopamine Release from Rat Striatum In Vivo
Authors: Lamensdorf Itschak , Youdim Moussa B. H. , Finberg John P. M.
Published: July 2010

Abstract: Acute inhibition of monoamine oxidase B (MAO‐B) in the rat does not affect striatal dopamine (DA) metabolism, but chronic MAO‐B inhibition with deprenyl has been reported to increase the release of striatal DA, as shown using in vitro techniques. To see whether chronic MAO‐B inhibition also causes an increase in DA release in vivo, rats were treated for 21 days with either deprenyl (0.25 mg/kg), TVP‐1012 [R(+)‐N‐propargyl‐1‐aminoindan mesylate; 0.05 mg/kg), an irreversible inhibitor of MAO‐B that is not metabolized to amphetamines, clorgyline (0.2 mg/kg), or saline (all doses once daily by subcutaneous injection). Concentric 4‐mm‐long microdialysis probes were implanted in the left striatum under pentobarbital/chloral hydrate anesthesia on day 21, and microdialysate DA, 3,4‐dihydroxyacetic acid (DOPAC), and 4‐hydroxy‐3‐methoxyphenyl acetic acid (HVA) were determined in the conscious animals on day 22. Baseline levels of DA were as follows: control, 0.34 ± 0.04 (n = 13); deprenyl, 0.88 ± 0.10 (n = 8, p < 0.01); TVP‐1012, 0.94 ± 0.20 (n = 7, p < 0.01); clorgyline, 0.90 ± 0.12 (n = 7, p < 0.01) pmol/20 min. Levels of DOPAC and HVA were reduced only in the clorgyline‐treated group. The incremental release of DA induced by depolarizing concentration of K+ (100 mM bolus of KCl in perfusate) was significantly greater in clorgyline‐ and deprenyl‐treated rats and elevated (nonsignificantly) in TVP‐1012‐treated rats. Chronic treatment with the MAO‐B inhibitors reduced striatal MAO‐B activity by 90%, with 15% (TVP‐1012) or 40% (deprenyl) inhibition of MAO‐A. Clorgyline inhibited MAO‐A by 95%, with 30% inhibition of MAO‐B. A single dose of deprenyl (0.25 mg/kg, 24 h before microdialysis) had no significant effect on striatal efflux of DA. The results show that DA metabolism was reduced only by clorgyline, whereas neuronal release of DA was enhanced by both MAO‐A and MAO‐B inhibitors on chronic administration. The enhanced DA release by chronic MAO‐B inhibition does not appear to be dependent on production of amphetamine‐like metabolites of the inhibitor. Possible mechanisms for the release‐enhancing effect of the MAO‐B inhibitors include elevation in levels of endogenous β‐phenylethylamine, or an inhibition of DA reuptake, which develops only on chronic administration, because both deprenyl and TVP‐1012 have only very weak effects on amine uptake in acute experiments.
Preferential Vulnerability of Nucleus Accumbens Dopamine Binding Sites to Low‐Level Lead Exposure: Time Course of Effects and Interactions with Chronic Dopamine Agonist Treatments
Authors: Pokora M. J. , Richfield E. K. , Cory‐Slechta D. A.
Published: July 2010

Abstract: This study examined the hypotheses that low‐level lead (Pb) exposure would increase dopamine (DA) binding sites, would do so preferentially in nucleus accumbens, and that such effects would be modified by concurrent DA agonist treatment. D1‐like and D2‐like binding sites and the dopamine transporter (DT) were measured autoradiographically in caudate‐putamen and nucleus accumbens of rats exposed from weaning to 0, 50, or 150 ppm Pb acetate drinking solutions with or without concurrent chronic intermittent intraperitoneal injections of the D1‐like agonist SKF 82958 or the DA agonist apomorphine after 2 weeks (no injections), 8 months, or 12 months of Pb exposure. Pb selectively decreased DA binding in nucleus accumbens. Decreases in D2‐like and DT sites were sustained across the 12‐month exposure, whereas D1‐like sites evidenced recovery at 12 months. Chronic intermittent DA agonist treatments reversed these effects of Pb in nucleus accumbens, restoring receptor and DT binding levels to normal, despite decreasing binding sites of non‐Pb‐treated rats. These studies implicate increased DA availability as a mechanism of Pb‐induced DA system changes. They also raise the possibility that Pb exposure could serve as a predisposing factor in neurodegenerative diseases associated with DA system dysfunction or could alter the course of DA‐based therapeutic treatments.
Nitric Oxide Synthase Type II mRNA Stability Is Translation‐ and Transcription‐Dependent
Authors: Park Song Kyu , Murphy Sean
Published: July 2010

Abstract: Nitric oxide synthase (NOS) type II is induced in many cell types in response to cytokines or endotoxin. The duration of type II NOS mRNA expression in astroglial cells and macrophages in vitro is brief, even in the continuous presence of inducers, and their removal dramatically accelerates mRNA decay. Addition of cycloheximide, in the presence or absence of actinomycin D, protected the mRNA from degradation. Whereas type II NOS mRNA was partially stabilized by actinomycin D, manganese superoxide dismutase mRNA was almost completely stabilized. This suggests that type II NOS mRNA stability is regulated via transcription‐ as well as translation‐dependent processes and that the effect of actinomycin D is mRNA specific.
Attenuation of β‐Amyloid Neurotoxicity In Vitro by Potassium‐Induced Depolarization
Authors: Pike Christian J. , Balázs Robert , Cotman Carl W.
Published: July 2010

Abstract: The cell death of cultured neurons triggered by β‐amyloid peptides has been theorized to model, at least in part, the neurodegeneration associated with Alzheimer's disease. To investigate potential strategies to interrupt β‐amyloid neurotoxicity in vitro, we examined the effects of potassium‐induced membrane depolarization; a treatment previously demonstrated to reduce development‐related apoptosis in cultured neurons. We report here that cultured rat hippocampal neurons pretreated for several hours with 30 mM KCI exhibit significantly reduced vulnerability to aggregated β‐amyloid peptides. The potassium‐mediated neuroprotection was mimicked by activation of voltage‐sensitive calcium channels using S(−)‐Bay K 8644 and was attenuated by R(+)‐Bay K 8644, a blocker of voltage‐dependent calcium channels, and KN‐62, an inhibitor of calcium/calmodulin‐dependent protein kinase II. The protein synthesis inhibitor cycloheximide also attenuated β‐amyloid neurotoxicity. Addition of cycloheximide following 30 mM KCI significantly increased protection offered by membrane depolarization, whereas cycloheximide addition during membrane depolarization blocked the protective effect. These data suggest that one cellular pathway that can inhibit neuronal death induced by β‐amyloid involves calcium influx through voltage‐sensitive channels followed by stimulation of calcium/calmodulin‐dependent protein kinase activity and synthesis of new protein(s).
The C Terminal Tail of the Histamine H2 Receptor Contains Positive and Negative Signals Important for Signal Transduction and Receptor Down‐Regulation
Authors: Smit M. J. , Timmerman H. , Blauw J. , Beukers M. W. , Roovers E. , Jacobs E. H. , Hoffmann M. , Leurs R.
Published: July 2010

Abstract: To examine the role of the C terminal tail in H2 receptor regulation, three cDNAs, encoding truncated histamine H2 receptor mutants (H2T295, H2T307, and H2T341), were constructed and stably transfected in Chinese hamster ovary (CHO) cells. The amino acids before position 307 appear to be necessary for proper receptor transport or folding, as no detectable H2 receptor binding of the H2T295 was observed after transfection. Truncation of the C terminal tail by 51 amino acids (H2T307) did not affect the binding properties of H2 antagonists and histamine or histamine‐induced signaling. Yet, removal of 17 amino acids generated a mutant receptor (H2T341), which was able to form a ternary complex but was unable to fully activate the Gs protein on histamine exposure. Agonist‐induced but not the cyclic AMP‐dependent H2 receptor down‐regulation was more profound for the H2T307 receptor, indicating that different structural elements of the H2 receptor protein are involved in the cyclic AMP‐dependent and independent pathways of H2 receptor down‐regulation. Taken together, in this study we identified regions in the C terminal tail of the H2 receptor that act as positive and/or negative signals in H2 receptor signaling and down‐regulation.
Differential Compartmentalization of mRNAs in Squid Giant Axon
Authors: Chun Jong‐Tai , Gioio Anthony E. , Crispino Marianna , Giuditta Antonio , Kaplan Barry B.
Published: July 2010

Abstract: Previously, we reported that the squid giant axon contains a heterogeneous population of mRNAs that includes β‐actin, β‐tubulin, kinesin, neurofilament proteins, and enolase. To define the absolute levels and relative distribution of these mRNAs, we have used competitive reverse transcription‐PCR to quantify the levels of five mRNAs present in the giant axon and giant fiber lobe (GFL), the location of the parental cell soma. In the GFL, the number of transcripts for these mRNAs varied over a fourfold range, with β‐tubulin being the most abundant mRNA species (1.25 × 109 molecules per GFL). Based on transcript number, the rank order of mRNA levels in the GFL was β‐tubulin > β‐actin > kinesin > enolase > microtubule‐associated protein (MAP) H1. In contrast, kinesin mRNA was most abundant in the axon (4.1 × 107 molecules per axon) with individual mRNA levels varying 15‐fold. The rank order of mRNA levels in the axon was kinesin > β‐tubulin > MAP H1 > β‐actin > enolase. The relative abundance of the mRNA species in the axon did not correlate with the size of the transcript, nor was it directly related to their corresponding levels in the GFL. Taken together, these findings confirm that significant amounts of mRNA are present in the giant axon and suggest that specific mRNAs are differentially transported into the axonal domain.
Dual Effects of Anandamide on NMDA Receptor‐Mediated Responses and Neurotransmission
Authors: Hampson Aidan J. , Bornheim Lester M. , Scanziani Massimo , Yost C. Spencer , Gray Andrew T. , Hansen Bonnie M. , Leonoudakis Dmitri J. , Bickler Philip E.
Published: July 2010

Abstract: Anandamide is an endogenous ligand of cannabinoid receptors that induces pharmacological responses in animals similar to those of cannabinoids such as Δ9‐tetrahydrocannabinol (THC). Typical pharmacological effects of cannabinoids include disruption of pain, memory formation, and motor coordination, systems that all depend on NMDA receptor mediated neurotransmission. We investigated whether anandamide can influence NMDA receptor activity by examining NMDA‐induced calcium flux (ΔCa2+NMDA) in rat brain slices. The presence of anandamide reduced ΔCa2+NMDA and the inhibition was disrupted by cannabinoid receptor antagonist, pertussis toxin treatment, and agatoxin (a calcium channel inhibitor). Whereas these treatments prevented anandamide inhibiting ΔCa2+NMDA, they also revealed another, underlying mechanism by which anandamide influences ΔCa2+NMDA. In the presence of cannabinoid receptor antagonist, anandamide potentiated ΔCa2+NMDA in cortical, cerebellar, and hippocampal slices. Anandamide (but not THC) also augmented NMDA‐stimulated currents in Xenopus oocytes expressing cloned NMDA receptors, suggesting a capacity to directly modulate NMDA receptor activity. In a similar manner, anandamide enhanced neurotransmission across NMDA receptor‐dependent synapses in hippocampus in a manner that was not mimicked by THC and was unaffected by cannabinoid receptor antagonist. These data demonstrate that anandamide can modulate NMDA receptor activity in addition to its role as a cannabinoid receptor ligand.
Nicotine as an Antiepileptic Agent in ADNFLE: An N‐of‐One Study
Authors: Willoughby John O. , Pope Kenneth J. , Eaton Vaughn
Published: July 2010

Summary:  Purpose: To test nicotine patch treatment for a patient with a defined mutation for autosomal dominant nocturnal frontal lobe epilepsy (ADNFLE) whose seizures were refractory to standard antiepileptic therapy.

Methods: Open and double‐blind trials of nicotine patches in an “n‐of‐one” study. The double‐blind trial comprised periods during which either placebo or nicotine patches were each used for three periods of 2 weeks, randomized in a double‐blind manner.

Results: In an open study, nicotine patches reduced seizures from 1.65 ± 2.36 to 0.01 ± 0.0 seizures per day (p < 0.0001). In a double‐blinded placebo‐controlled phase, the average frequency of seizures on nicotine versus placebo was 0 ± 0 versus 0.56 ± 1.14 seizures per day (p < 0.0001).

Conclusions: Nicotine patches may be of benefit to some individuals with ADNFLE.
Classification of two and three dimensional Lie superbialgebras
Authors: Eghbali A. , Rezaei-Aghdam A. , Heidarpour F.
Published: July 2010

Using adjoint representation of Lie superalgebras, we obtain the matrix form of super-Jacobi and mixed super-Jacobi identities of Lie superbialgebras. By direct calculations of these identities, and use of automorphism supergroups of two and three dimensional Lie superalgebras, we obtain and classify all two and three dimensional Lie superbialgebras.
Catalytic effect and nucleation stability of Au on GaAs(111)B surface
Authors: Shu Haibo , Chen Xiaoshuang , Lu Wei
Published: July 2010

We perform comprehensive first-principles calculations to study the catalytic effect and nucleation stability of Au on GaAs(111)B surface during the initial growth of Au-assisted III-V nanowires (NWs). The atomic structures and energetics of GaAs(111)B surface with the deposited Au atoms are systematically discussed for various possible surface configurations. With the deposition of Au, the As trimer on GaAs(111)B-(2×2) surface undergoes a desorption process. The surface phase diagrams as functions of temperature and As2 pressure reveal that the As-trimer desorption on the (2×2) surface with Au adatom occurs beyond 540–650 K, while the desorption without Au adatom does beyond 800–970 K. The result shows the catalytic effect of Au on the desorption of As trimer. The calculated surface formation energies indicate that the on-surface adsorption of Au on GaAs(111)B surface is unstable, and the Au adatoms prefer to be incorporated on GaAs(111)B surface with a (3×3) phase during the initial deposition of Au. The simulated scanning tunneling microscopy image for the (3×3) surface with the incorporating Au atom is in good agreement with the experimental observation. Nevertheless, the added Au adatoms tend to form Au droplets on the surface when the Au coverage is further increased. It is expected that our calculations can contribute to the understanding of Au wetting experiments and the initial growth of Au-assisted III-V NWs.
Bioconvection in a suspension of isotropically scattering phototactic algae
Authors: Ghorai S. , Panda M. K. , Hill N. A.
Published: July 2010

Phototaxis is a directed swimming response toward a light source sensed by micro-organisms. Positive phototaxis represents swimming toward the source of light intensity and negative phototaxis is the swimming away from it. In this paper we develop a new model for phototaxis that incorporates the effects of absorption and scattering by the micro-organisms. This model is then used to analyze the linear stability of a suspension of phototactic algae illuminated by a collimated radiation at the top. A comprehensive numerical study of the linear stability is presented with particular emphasis on the scattering effect. As a result of scattering, for some parameter values, the micro-organisms accumulate in two horizontal layers at different depths in the basic equilibrium state. Examples of oscillatory instabilities are also found.
Calculation of IR frequencies and intensities in electrical and mechanical anharmonicity approximations: Application to small water clusters
Authors: Bégué D. , Baraille I. , Garrain P. A. , Dargelos A. , Tassaing T.
Published: July 2010

We present a method for automatic computation of infrared (IR) intensities using parallel variational multiple window configuration interaction wave functions (P_VMWCI2 algorithm). Inclusion of both mechanical and electrical anharmonic effects permits fundamental vibrational frequencies, including combinations and overtones, to be assigned. We use these developments to interpret the near-IR (NIR) and mid-IR (MIR) spectra of individual water clusters (H2O)n (n=1–4). Cyclic and linear systems are studied to provide equivalent reference theoretical data to investigate the structure of water as a function of density using NIR and MIR experimental spectra. Various density functional theory methods for generating the potential energy surface have been compared to reference results obtained at the CCSD(T) level [X. Huang et al., J. Chem. Phys. 128, 034312 (2008)]. For cyclic clusters, the IR intensities and frequencies obtained using B1LYP/cc-pVTZ are found to be in very good agreement with the available experimental values and of the same orders of magnitude as the reference theoretical values. These data are completed by the vibrational study of linear systems.
Use of second generation coated conductors for efficient shielding of dc magnetic fields
Authors: Fagnard J. F. , Dirickx M. , Levin G. A. , Barnes P. N. , Vanderheyden B. , Vanderbemden P.
Published: July 2010

This paper reports the results of an experimental investigation of the performance of two types of magnetic screens assembled from YBa2Cu3O7−δ (YBCO) coated conductors. Since effective screening of the axial dc magnetic field requires the unimpeded flow of an azimuthal persistent current, we demonstrate a configuration of a screening shell made out of standard YBCO coated conductor capable to accomplish that. The screen allows the persistent current to flow in the predominantly azimuthal direction at a temperature of 77 K. The persistent screen, incorporating a single layer of superconducting film, can attenuate an external magnetic field of up to 5 mT by more than an order of magnitude. For comparison purposes, another type of screen which incorporates low critical temperature quasipersistent joints was also built. The shielding technique we describe here appears to be especially promising for the realization of large scale high-Tc superconducting screens.
How to use a nanowire to measure vibrational frequencies: Device simulator results
Authors: Horsfield A. P. , Tong Lianheng , Soh Yeong-Ah , Warburton P. A.
Published: July 2010

Here we present a theoretical investigation of double well nanowire device that will be studied experimentally over a range of temperatures. Our nanowires are made from InAs with three InP barriers between which lie two InAs quantum wells. These wells have associated with them sharp electronic states between which electrons can tunnel. In the absence of a bias, resonant transmission of electrons is possible; but on applying a bias the levels in neighboring wells acquire different energies, thereby frustrating transmission. If the offset in energy is matched by the frequency of a phonon within the device that couples to the electrons in the wells then there will be a rise in current. We present here the results of simple device simulator calculations, on the basis of which the dimensions of an optimized device are determined.
Production of ozone and nitrogen oxides by laser filamentation
Authors: Petit Yannick , Henin Stefano , Kasparian Jérôme , Wolf Jean-Pierre
Published: July 2010

We have experimentally measured that laser filaments in air generate up to 1014, 3×1012, and 3×1013 molecules of O3, NO, and NO2, respectively. The corresponding local concentrations in the filament active volume are 1016, 3×1014, and 3×1015 cm−3, and allows efficient oxidative chemistry of nitrogen, resulting in concentrations of HNO3 in the parts per million range. The latter forming binary clusters with water, our results provide a plausible pathway for the efficient nucleation recently observed in laser filaments.
Nanostructures in p-GaAs with improved tunability
Authors: Csontos M. , Komijani Y. , Shorubalko I. , Ensslin K. , Reuter D. , Wieck A. D.
Published: July 2010

A nanofabrication technique is presented which enables the fabrication of highly tunable devices on p-type, C-doped GaAs/AlGaAs heterostructures containing shallow two-dimensional hole systems. The high tunability of these structures is provided by the complementary electrostatic effects of intrinsic in-plane gates and evaporated metallic top-gates. Quantum point contacts fabricated with this technique were tested by electrical conductance spectroscopy.
Design, Synthesis, and Cytotoxicity of Indolizinoquinoxaline-5,12-dione Derivatives, Novel DNA Topoisomerase IB Inhibitors
Authors: Shen De-Qing , Wu Ning , Li Yan-Ping , Wu Zu-Ping , Zhang Hong-Bin , Huang Zhi-Shu , Gu Lian-Quan , An Lin-Kun
Published: July 2010

A series of new indolizinoquinoxaline-5,12-dione derivatives were designed and synthesized via a heterocyclization reaction of 6,7-dichloroquinoxaline-5,8-dione with active methylene reagents and pyridine derivatives. The synthesized compounds exhibited significant activity to inhibit the growth of four human tumour cell lines, including lung adenocarcinoma cell, large-cell lung carcinoma cell, breast carcinoma cell, and ardriamycin-resistant breast carcinoma cell at micromolar range. These compounds were also investigated for their inhibition to DNA topoisomerase IB activity. The results indicated that the indolizinoquinoxaline-5,12-dione structure might be a potential pharmacophore in anti-cancer drug design.
Pitfalls in the Photoelectron Spectroscopic Investigations of Benzyne. Photoelectron Spectrum of Cyclopentadienylideneketene
Authors: Chrostowska Anna , Pfister-Guillouzo Genevieve , Gracian Françoise , Wentrup Curt
Published: July 2010

The 9.24 eV ionization energy often quoted in photoelectron spectroscopic investigations of benzyne is not due to benzyne 1 but to benzene, C6H6. The 8.9 eV ionization is not due to benzyne either but to cyclopentadienylideneketene 12 when a 10.2 eV band is also present, or to biphenylene 5 when a 7.6 eV band is simultaneously present. Cyclopentadienylideneketene 12 has been generated by flash vacuum thermolysis of four different precursors, which permit a linking of infrared, mass, and photoelectron spectroscopic observations.
Matrix Isolation and Electronic Structure of Di- and Tridehydrobenzenes
Authors: Winkler Michael , Sander Wolfram
Published: July 2010

Within the past four decades, matrix isolation spectroscopy has emerged as the method of choice for obtaining direct structural information on benzynes and related dehydroaromatics. In combination with quantum chemical computations, detailed insight into the structure and reactivity of di-, tri-, and tetradehydrobenzenes has been obtained. This Review focuses on rather recent developments in aryne chemistry with a special emphasis on the matrix isolation of tridehydrobenzenes and related systems.
Thermochemical Properties of the Benzynes
Authors: Wenthold Paul G.
Published: July 2010

The thermochemical properties of the benzynes have been the subject of investigation for nearly 50 years. This work provides an overview and assessment of all the experimental thermochemical properties that have been reported for the benzynes, or can be derived from reported thermochemical data. These properties include enthalpies of formation and thermochemical values that correspond to formation and dissociation of the benzynes by neutral and ionic processes. Thermochemical values are provided for both the ground-state singlet and the excited-state triplet states of the benzynes. The starting point for all the thermochemical consideration of the benzynes are the enthalpies of formation, which, in this work, are recommend to be 107.3 ± 3.5, 121.9 ± 3.1, and 138.0 ± 1.0 kcal mol–1 for ortho-, meta-, and para-benzyne, respectively (1 kcal mol–1 = 4.184 kJ mol–1). Whereas the paper predominantly focuses on the experimentally determined values, it also provides a comparison with theoretical studies that have examined the absolute thermochemical properties of the benzynes.
Aryne Complexes of Zerovalent Metals of the Nickel Triad
Authors: Bennett Martin A.
Published: July 2010

The chemistry of dihapto-aryne complexes of the zerovalent Group 10 metals of general formula [M(η2-aryne)L2] (M = Ni, Pd, Pt; L = various tertiary phosphines) is reviewed, with emphasis on the highly reactive nickel(0) compounds (aryne = benzyne, C6H4; 4,5-difluorobenzyne, 4,5-C6H2F2; 2,3-naphthalyne, 2,3-C10H6; L2 = 2 PEt3, 2 PiPr3, 2 PCy3, dcpe). These can be generated by alkali metal reduction of the appropriate (2-halogenoaryl)nickel(ii) halide precursors, such as [NiX(2-XC6H4)L2], which in turn are accessible by oxidative addition of the 1,2-dihaloarene to nickel(0) precursors such as [Ni(1,5-COD)2]. The X-ray structure of [Ni(η2-C6H4)(dcpe)] shows that this compound is a typical 16-electron Ni(0) (3d10) species in which benzyne acts as a 2π-electron donor. Several unusual organonickel compounds derived from [Ni(η2-4,5-C6H2F2)(PEt3)2] have been isolated recently, including [Ni2(μ-η2:η2-4,5-C6H2F2)(PEt3)4], in which a 4π-electron donor 4,5-difluorobenzyne is located at right-angles to a pair of nickel atoms. Free benzyne can be intercepted by both [Ni(η2-C2H4)(dcpe)] and [Pt(η2-C2H4)(PPh3)2], but the resulting benzyne complexes rapidly insert benzyne to give the appropriate η1:η1-2,2′-biphenylyl complexes. [Pt(η2-C6H4)(PPh3)2] also undergoes rapid ortho-metallation to give [PtPh(2-C6H4PPh2)(PPh3)]. However, a trapping reaction has been used to make the first 1,4-benzdiyne complex, [{Ni(dcpe)2}2(μ-η2:η2-1,4-C6H2)] by treatment of the 4-fluorobenzyne complex [Ni(η2-4-FC6H3)(dcpe)] with LiTMP. The use of alkali metals in the preparation of the η2-benzyne complexes is avoided in a more recently developed procedure, which starts from (2-bromophenyl)boronic acid, and is based on Suzuki–Miyaura coupling. This procedure has made accessible for the first time an aryne complex of palladium(0), [Pd(η2-C6H4)(PCy3)2], and the labile nickel(0) complex [Ni(η2-C6H4)(PPh3)2]. The aryne-nickel(0) complexes Ni(η2-aryne)L2 (L2 = 2 PEt3, dcpe) undergo sequential insertions into the aryne-metal bond with unsaturated molecules, such as CO, C2F4, substituted alkynes, substituted diynes, alkynylphosphines, and alkynyl thioethers, often with considerable regioselectivity. After the reductive elimination of two nickel-carbon σ-bonds, a variety of interesting polycyclic compounds can be obtained.
Substantial nitrogen acquisition by arbuscular mycorrhizal fungi from organic material has implications for N cycling
Authors: Hodge Angela , Fitter Alastair H.
Published: July 2010

Arbuscular mycorrhizal (AM) fungi are obligate biotrophs that acquire carbon (C) solely from host plants. AM fungi can proliferate hyphae in, and acquire nitrogen (N) from, organic matter. Although they can transfer some of that N to plants, we tested the hypothesis that organic matter is an important N source for the AM fungi themselves. We grew pairs of plants with and without the AM fungus
Glomus hoi
in microcosms that allowed only the fungus access to a
15
N/
13
C-labeled organic patch; in some cases, one plant was shaded to reduce C supply to the fungus. The fungal hyphae proliferated vigorously in the patch, irrespective of shading, and increased plant growth and N content; ∼3% of plant N came from the patch. The extraradical mycelium of the fungus was N-rich (3–5% N) and up to 31% of fungal N came from the patch, confirming the hypothesis. The fungus acquired N as decomposition products, because hyphae were not
13
C-enriched. In a second experiment, hyphae of both
G. hoi
and
Glomus mosseae
that exploited an organic material patch were also better able to colonize a new host plant, demonstrating a fungal growth response. These findings show that AM fungi can obtain substantial amounts of N from decomposing organic materials and can enhance their fitness as a result. The large biomass and high N demand of AM fungi means that they represent a global N pool equivalent in magnitude to fine roots and play a substantial and hitherto overlooked role in the nitrogen cycle.
Induction of Liver Steatosis and Lipid Droplet Formation in ATF6α-Knockout Mice Burdened with Pharmacological Endoplasmic Reticulum Stress
Authors: Yamamoto Keisuke , Takahara Kazuna , Oyadomari Seiichi , Okada Tetsuya , Sato Takashi , Harada Akihiro , Mori Kazutoshi
Published: July 2010

Accumulation of unfolded proteins in the endoplasmic reticulum (ER) activates homeostatic responses collectively termed the unfolded protein response. Among the three principal signaling pathways operating in mammals, activating transcription factor (ATF)6α plays a pivotal role in transcriptional induction of ER-localized molecular chaperones and folding enzymes as well as components of ER-associated degradation, and thereby mouse embryonic fibroblasts deficient in ATF6α are sensitive to ER stress. However, ATF6α-knockout mice show no apparent phenotype under normal growing conditions. In this report, we burdened mice with intraperitoneal injection of the ER stress-inducing reagent tunicamycin and found that wild-type mice were able to recover from the insult, whereas ATF6α-knockout mice exhibited liver dysfunction and steatosis. Thus, ATF6α-knockout mice accumulated neutral lipids in the liver such as triacylglycerol and cholesterol, which was ascribable to blockage of β-oxidation of fatty acids caused by decreased mRNA levels of the enzymes involved in the process, suppression of very-low-density lipoprotein formation due to destabilized apolipoprotein B-100, and stimulation of lipid droplet formation resulting from transcriptional induction of adipose differentiation-related protein. Accordingly, the hepatocytes of tunicamycin-injected knockout mice were filled with many lipid droplets. These results establish links among ER stress, lipid metabolism, and steatosis.
Bridging the gulf between correlated random walks and Lévy walks: autocorrelation as a source of Lévy walk movement patterns
Authors: Reynolds Andy M.
Published: July 2010

For many years, the dominant conceptual framework for describing non-oriented animal movement patterns has been the correlated random walk (CRW) model in which an individual's trajectory through space is represented by a sequence of distinct, independent randomly oriented ‘moves’. It has long been recognized that the transformation of an animal's continuous movement path into a broken line is necessarily arbitrary and that probability distributions of move lengths and turning angles are model artefacts. Continuous-time analogues of CRWs that overcome this inherent shortcoming have appeared in the literature and are gaining prominence. In these models, velocities evolve as a Markovian process and have exponential autocorrelation. Integration of the velocity process gives the position process. Here, through a simple scaling argument and through an exact analytical analysis, it is shown that autocorrelation inevitably leads to Lévy walk (LW) movement patterns on timescales less than the autocorrelation timescale. This is significant because over recent years there has been an accumulation of evidence from a variety of experimental and theoretical studies that many organisms have movement patterns that can be approximated by LWs, and there is now intense debate about the relative merits of CRWs and LWs as representations of non-orientated animal movement patterns.
Heterogeneity in susceptible–infected–removed (SIR) epidemics on lattices
Authors: Neri Franco M. , Pérez-Reche Francisco J. , Taraskin Sergei N. , Gilligan Christopher A.
Published: July 2010

The percolation paradigm is widely used in spatially explicit epidemic models where disease spreads between neighbouring hosts. It has been successful in identifying epidemic thresholds for invasion, separating non-invasive regimes, where the disease never invades the system, from invasive regimes where the probability of invasion is positive. However, its power is mainly limited to homogeneous systems. When heterogeneity (environmental stochasticity) is introduced, the value of the epidemic threshold is, in general, not predictable without numerical simulations. Here, we analyse the role of heterogeneity in a stochastic susceptible–infected–removed epidemic model on a two-dimensional lattice. In the homogeneous case, equivalent to bond percolation, the probability of invasion is controlled by a single parameter, the transmissibility of the pathogen between neighbouring hosts. In the heterogeneous model, the transmissibility becomes a random variable drawn from a probability distribution. We investigate how heterogeneity in transmissibility influences the value of the invasion threshold, and find that the resilience of the system to invasion can be suitably described by two control parameters, the mean and variance of the transmissibility. We analyse a two-dimensional phase diagram, where the threshold is represented by a phase boundary separating an invasive regime in the high-mean, low-variance region from a non-invasive regime in the low-mean, high-variance region of the parameter space. We thus show that the percolation paradigm can be extended to the heterogeneous case. Our results have practical implications for the analysis of disease control strategies in realistic heterogeneous epidemic systems.
Technological innovation in industry and the role of the Royal Society
Authors: Snowden Christopher M.
Published: July 2010

This paper examines the interplay between industrial and academic research and explores how innovation stimulated by the Royal Society has influenced technological development in business and industry over the past 50 years. The trend for universities to foster the creation of spin-out companies has grown significantly over the past 20 years, while universities and government simultaneously appreciated the potential value of intellectual property and increasingly formalized interaction between industry and academia. Before this the flow of ideas, discoveries and technology from universities to industry relied largely on individuals. Examples of how academics, industrialists and Fellows of the Royal Society have influenced and contributed to industrial research and the world's technology base are explored. The paper examines the supportive role played by the Royal Society through research grants, innovation awards and distinguished Research Fellowships such as the Industry Fellowships Scheme. The most recent initiative to support scientific and technological ventures shows a new direction for the Royal Society in contributing to innovation through its Enterprise Fund.
A role in running UK science?
Authors: Collins Peter
Published: July 2010

The election of a new President of the Royal Society in 1945 was enlivened by a petition, signed by 20% of the Fellowship, promoting a vision of the Society as playing a strong role in managing UK science. One of the signatories was Howard Florey. During the final year of Cyril Hinshelwood's presidency in 1960, and throughout Florey's subsequent presidency, the Society fought hard for a share of the action as publicly funded science, managed by Government-appointed bodies, grew at a sustained 15% per annum. The implementation of the Trend report in 1965 closed out the main options: the Government wanted control, and the Society, in the end, wanted its independence. It found other ways to make an impact on UK science.