Attentional resolution and the locus of visual awareness

Visual spatial resolution is limited by factors ranging from optics to neuronal filters in the visual cortex, but it is not known to what extent it is also limited by the resolving power of attention. To investigate this, we studied adaptation to lines of specific orientation, a process that occurs in primary visual cortex. When a single grating is presented in the periphery of the visual field, human observers are aware of its orientation, but when it is flanked by other similar gratings ('crowding'), its orientation becomes impossible to discern. Nevertheless, we show that orientation-specific adaptation is not affected by crowding, implying that spatial resolution is limited by an attentional filter acting beyond the primary visual cortex. Consistent with this, we find that attentional resolution is greater in the lower than in the upper visual field, whereas there is no corresponding asymmetry in the primary visual cortex. We suggest that the attentional filter acts in one or more higher visual cortical areas to restrict the availability of visual information to conscious awareness.

Evolution and transmission of stable CTL escape mutations in HIV infection

Increasing evidence indicates that potent anti-HIV-1 activity is mediated by cytotoxic T lymphocytes (CTLs); however, the effects of this immune pressure on viral transmission and evolution have not been determined. Here we investigate mother-child transmission in the setting of human leukocyte antigen (HLA)-B27 expression, selected for analysis because it is associated with prolonged immune containment in adult infection. In adults, mutations in a dominant and highly conserved B27-restricted Gag CTL epitope lead to loss of recognition and disease progression. In mothers expressing HLA-B27 who transmit HIV-1 perinatally, we document transmission of viruses encoding CTL escape variants in this dominant Gag epitope that no longer bind to B27. Their infected infants target an otherwise subdominant B27-restricted epitope and fail to contain HIV replication. These CTL escape variants remain stable without reversion in the absence of the evolutionary pressure that originally selected the mutation. These data suggest that CTL escape mutations in epitopes associated with suppression of viraemia will accumulate as the epidemic progresses, and therefore have important implications for vaccine design.

A graphene-based fluorescent nanoprobe for silver(I) ions detection by using graphene oxide and a silver-specific oligonucleotide

A fluorescence sensor for Ag(I) ions is developed based on the target-induced conformational change of a silver-specific cytosine-rich oligonucleotide (SSO) and the interactions between the fluorogenic SSO probe and graphene oxide.

Mechanism of active transcriptional repression by the retinoblastoma protein

The retinoblastoma tumour-suppressor protein (Rb) belongs to a family that share a motif known as the pocket. The pocket was originally identified as the region of Rb required for binding to oncoproteins from DNA tumour viruses, which disrupt the binding of Rb to the E2F family of cell-cycle transcription factors (referred to collectively here as E2F). Rb switches E2F sites from positive to negative elements, suggesting that Rb-E2F is an active complex that blocks transcription. Here we report that Rb is selectively recruited to promoters through E2F, where it in turn inactivates surrounding transcription factors by blocking their interaction with the basal transcription complex. We suggest that this repressor activity is essential for inhibiting promoters that contain enhancers in addition to E2F sites.

A particle swarm optimizer with passive congregation

This paper presents a particle swarm optimizer (PSO) with passive congregation to improve the performance of standard PSO (SPSO). Passive congregation is an important biological force preserving swarm integrity. By introducing passive congregation to PSO, information can be transferred among individuals of the swarm. A particle swarm optimizer with passive congregation (PSOPC) is tested with a set of 10 benchmark functions with 30 dimensions and compared to a global version of SPSO (GSPSO), a local version of SPSO (LSPSO), and PSO with a constriction factor (CPSO), respectively. Experimental results indicate that the PSO with passive congregation improves the search performance on the benchmark functions significantly.

Integrated mechanism for functional mitral regurgitation: leaflet restriction versus coapting force: in vitro studies

BACKGROUND

Functional mitral regurgitation in patients with ischemic or dilated ventricles has been related to competing factors: altered tension on the leaflets due to displacement of their papillary muscle and annular attachments, which restricts leaflet closure, versus global ventricular dysfunction with reduced transmitral pressure to close the leaflets. In vivo, however, geometric changes accompany dysfunction, making it difficult to study these factors independently. Functional mitral regurgitation also paradoxically decreases in midsystole, despite peak transmitral driving pressure, suggesting a change in the force balance acting to create a regurgitant orifice, with rising transmitral pressure counteracting forces that restrict leaflet closure. In vivo, this mechanism cannot be tested independently of annular contraction that could also reduce midsystolic regurgitation.

METHODS AND RESULTS

An in vitro model was developed that allows independent variation of papillary muscle position, annular size, and transmitral pressure, with direct regurgitant flow rate measurement, to test the hypothesis that functional mitral regurgitation reflects an altered balance of forces acting on the leaflets. Hemodynamic and echocardiographic measurements of excised porcine valves were made under physiological pressures and flows. Apical and posterolateral papillary muscle displacement caused decreased leaflet mobility and apical leaflet tethering or tenting with regurgitation, as seen clinically. It reproduced the clinically observed midsystolic decrease in regurgitant flow and orifice area as transmitral pressure increased. Tethering delayed valve closure, increased the early systolic regurgitant volume before complete coaptation, and decreased the duration of coaptation. Annular dilatation increased regurgitation for any papillary muscle position, creating clinically important regurgitation; conversely, increased transmitral pressure decreased regurgitant orifice area for any geometric configuration.

CONCLUSIONS

The clinically observed tented-leaflet configuration and dynamic regurgitant orifice area variation can be reproduced in vitro by altering the three-dimensional relationship of the annular and papillary muscle attachments of the valve so as to increase leaflet tension. Increased transmitral pressure acting to close the leaflets decreases the regurgitant orifice area. These results are consistent with a mechanism in which an altered balance of tethering versus coapting forces acting on the leaflets creates the regurgitant orifice.

Substantial differences in specificity of HIV-specific cytotoxic T cells in acute and chronic HIV infection

Cytotoxic T lymphocytes (CTLs) play a vital part in controlling viral replication during human viral infections. Most studies in human infections have focused on CTL specificities in chronic infection and few data exist regarding the specificity of the initial CTL response induced in acute infection. In this study, HIV-1 infection in persons expressing human histocompatibility leukocyte antigen (HLA)-A*0201 was used as a means of addressing this issue. In chronic infection, the dominant HLA-A*0201-restricted CTL response is directed towards the epitope SLYNTVATL ("SL9") in p17 Gag (residues 77-85). This epitope is targeted by 75% of HLA-A*0201-positive adults, and the magnitude of this A*0201-SL9 response shows a strong negative association with viral load in progressive infection. Despite using the highly sensitive peptide-major histocompatibility complex tetramer and intracellular cytokine assays, responses to the SL9 epitope were not detectable in any of 11 HLA-A*0201-positive subjects with acute HIV-1 infection (P = 2 x 10(-6)), even when assays were repeated using the SL9 peptide variant that was encoded by their autologous virus. In contrast, multiple responses (median 3) to other epitopes were evident in 7 of the 11 A*0201-positive subjects. Longitudinal study of two subjects confirmed that the A*0201-SL9 response emerged later than other CTL responses, and after viral set point had been reached. Together, these data show that the CTL responses that are present and that even may dominate in chronic infection may differ substantially from those that constitute the initial antiviral CTL response. This finding is an important consideration in vaccine design and in the evaluation of vaccine candidates.

Injectable biodegradable polymer composites based on poly(propylene fumarate) crosslinked with poly(ethylene glycol)-dimethacrylate

New injectable, in situ crosslinkable biodegradable polymer composites were investigated consisting of poly(propylene fumarate) (PPF), poly(ethylene glycol)-dimethacrylate (PEG-DMA), and beta-tricalcium phosphate (beta-TCP). We examined the effects of the PEG-DMA/PPF double-bond ratio and beta-TCP content on the crosslinking characteristics of the composites including the maximum crosslinking temperature and the gel point, as well as the properties of the crosslinked composites such as the compressive strength and modulus, and the water-holding capacity. The maximum crosslinking temperature was constant averaging 39.7 degrees C for the composite formulations tested. The gel points varied from 8.0 +/- 1.0 to 12.6 +/- 2.5 min and were not affected by the relative amounts of PEG-DMA. The compressive strength at yield of PEG-DMA/PPF composites without beta-TCP increased from 5.9 +/- 1.0 to 11.2 +/- 2.2 MPa as the double-bond ratio of PEG-DMA/PPF increased from 0.38 to 1.88. An increase in compressive modulus was also observed from 30.2 +/- 3.5 to 58.4 +/- 6.2 MPa for the same range of the PEG-DMA/PPF double-bond ratio. Also, the addition of beta-TCP (33 wt%) enhanced the mechanical properties of all composites. The equilibrium water content of networks without beta-TCP increased from 21.7 +/- 0.2 to 30.6 +/- 0.2% for a double-bond ratio of PEG-DMA/PPF ranging from 0.38 to 1.88. However, the mechanical properties of the swollen composites under compression were smaller than the dry ones. These data demonstrate the feasibility of fabricating injectable biodegradable polymer composites with engineered mechanical properties for orthopedic tissue engineering.

Protein kinase C inhibitors induce apoptosis in human malignant glioma cell lines

Previous work has demonstrated the importance of the protein kinase C (PKC) system in regulating glioma growth, and has led to clinical trials utilizing PKC inhibitors as adjuncts in the therapy of patients harboring malignant gliomas. This study was performed to explore the possibility that inhibition of PKC in gliomas was triggering an apoptosis signal. Glioma cell lines were treated with PKC inhibitors staurosporine (10 nM), and tamoxifen (10 microM). DNA from cells treated with each of these drugs exhibited a 'ladder' pattern of oligonucleosome-sized fragments characteristic of apoptosis, thus suggesting that in glioma cells, these drugs may be cytocidal in action.

Membrane translocation of mitochondrially coded Cox2p: distinct requirements for export of N and C termini and dependence on the conserved protein Oxa1p

To study in vivo the export of mitochondrially synthesized protein from the matrix to the intermembrane space, we have fused a synthetic mitochondrial gene, ARG8m, to the Saccharomyces cerevisiae COX2 gene in mitochondrial DNA. The Arg8mp moiety was translocated through the inner membrane when fused to the Cox2p C terminus by a mechanism dependent on topogenic information at least partially contained within the exported Cox2p C-terminal tail. The pre-Cox2p leader peptide did not signal translocation. Export of the Cox2p C-terminal tail, but not the N-terminal tail, was dependent on the inner membrane potential. The mitochondrial export system does not closely resemble the bacterial Sec translocase. However, normal translocation of both exported domains of Cox2p was defective in cells lacking the widely conserved inner membrane protein Oxa1p.

Nickel-catalyzed allylic defluorinative alkylation of trifluoromethyl alkenes with reductive decarboxylation of redox-active esters

Herein, we report a nickel-catalyzed allylic defluorinative alkylation of trifluoromethyl alkenes through reductive decarboxylation of redox-active esters. The present reaction enables the preparation of functionalized gem-difluoroalkenes with the formation of sterically hindered C(sp3)-C(sp3) bonds under very mild reaction conditions, while tolerating many sensitive functional groups and requiring minimal substrate protection. Therefore, this method provides an efficient and convenient approach for late-stage modification of biologically interesting molecules.

Human mast cell tryptase: a stimulus of microvascular leakage and mast cell activation

We have investigated the potential of tryptase to stimulate an increase in microvascular permeability following injection into the skin of guinea pigs. Tryptase was isolated from high salt extracts of human lung tissue by octyl-agarose and heparin-agarose chromatography. Injection of purified tryptase (2.5 ng-2.5 microg/site) into the skin of guinea pigs which had been injected intravenously with Evans blue dye provoked a dose-dependent increase in microvascular permeability. The skin reactions elicited by tryptase were apparent up to 80 min following injection, while histamine-induced microvascular leakage resolved completely by 40 min. Heat-inactivation of tryptase, or preincubating the proteinase with certain proteinase inhibitors, significantly reduced the extent of microvascular leakage, suggesting dependency on an intact catalytic site. No evidence was found for a synergistic or antagonistic interaction between tryptase (2.5 ng-2.5 microg/site) and histamine (1-10 microg/site) when these mast cell products were injected together. Addition of heparin to tryptase (10:1; w/w) prior to injection was without effect on tryptase-induced microvascular leakage. Pretreatment of guinea pigs with a combination of the histamine H1 receptor antagonist pyrilamine and the histamine H2 receptor antagonist cimetidine (both 10 mg/kg), partially abolished tryptase-induced microvascular leakage as well as attenuating the reaction to histamine. Reasoning that the microvascular leakage induced by tryptase is likely to involve the release of histamine, we investigated the ability of tryptase to stimulate histamine release from dispersed guinea-pig skin and lung cells in vitro. Tryptase was found to induce concentration-dependent histamine release from both sources of tissue. Mast cell activation stimulated by tryptase in vitro was inhibited by heat treating the enzyme or by addition of proteinase inhibitors, suggesting a requirement for an intact catalytic site. Histamine release was inhibited also by preincubating cells with the metabolic inhibitors antimycin A and 2-deoxy-D-glucose indicating that the mechanism was energy-requiring and non-cytotoxic. We conclude that human mast cell tryptase may be a potent stimulus of microvascular leakage. The activation of mast cells by this proteinase may represent an amplification process in allergic inflammation.

Reassortment and insertion-deletion are strategies for the evolution of influenza B viruses in nature

The evolution of influenza B viruses is poorly understood. Reassortment of influenza B viruses in nature as a means of genetic variation has not been considered to be a major contributor to their evolution. However, the current practice of assigning evolutionary relationships by antigenic analysis of the hemagglutinin of influenza B viruses would fail to detect reassortants. In this study, influenza B viruses isolated within the past 10 years from sites in the United States and China were studied by nucleotide sequencing of the hemagglutinin and neuraminidase genes and construction of phylogenetic trees to assess evolutionary relationships. A group of viruses represented by B/Houston/1/92 possess a hemagglutinin derived from a B/Yamagata/16/88-like strain and a neuraminidase derived from a B/Victoria/2/87-like strain. A second reassortment event between the hemagglutinin of a B/Yamagata/16/88-like virus closely related to the B/Beijing/184/93 strain and the neuraminidase of a B/Victoria/2/87-like strain is represented by a single virus, B/Memphis/3/93. The neuraminidase of the reassortant viruses is most closely related to that of B/Victoria/2/87-like viruses currently circulating in Nanchang, China. A pattern of insertions and deletions in the hemagglutinin and the neuraminidase of different strains of influenza B viruses is observed. Reassortment plays a role in the evolution of influenza B viruses and may necessitate a change in the methods used to assess and identify new influenza viruses.

Graphene oxide-facilitated electron transfer of metalloproteins at electrode surfaces

Graphene is a particularly useful nanomaterial that has shown great promise in nanoelectronics. Because of the ultrahigh electron mobility of graphene and its unique surface properties such as one-atom thickness and irreversible protein adsorption at surfaces, graphene-based materials might serve as an ideal platform for accommodating proteins and facilitating protein electron transfer. In this work, we demonstrate that graphene oxide (GO) supports the efficient electrical wiring the redox centers of several heme-containing metalloproteins (cytochrome c, myoglobin, and horseradish peroxidase) to the electrode. Importantly, proteins retain their structural intactness and biological activity upon forming mixtures with GO. These important features imply the promising applications of GO/protein complexes in the development of biosensors and biofuel cells.

Graphene-based high-efficiency surface-enhanced Raman scattering-active platform for sensitive and multiplex DNA detection

We have developed a surface-enhanced Raman scattering (SERS)-active substrate based on gold nanoparticle-decorated chemical vapor deposition (CVD)-growth graphene and used it for multiplexing detection of DNA. Due to the combination of gold nanoparticles and graphene, the Raman signals of dye were dramatically enhanced by this novel substrate. With the gold nanoparticles, DNA capture probes could be easily assembled on the surface of graphene films which have a drawback to directly immobilize DNA. This platform exhibits extraordinarily high sensitivity and excellent specificity for DNA detection. A detection limit as low as 10 pM is obtained. Importantly, two different DNA targets could be detected simultaneously on the same substrate just using one light source.

Human mast cell chymase induces the accumulation of neutrophils, eosinophils and other inflammatory cells in vivo

The roles of chymase in acute allergic responses are not clear, despite the relative abundance of this serine proteinase in the secretory granules of human mast cells. We have isolated chymase to high purity from human skin tissue by heparin-agarose affinity chromatography and Sephacryl S-200 gel filtration procedures, and have investigated the ability of human mast cell chymase to stimulate cell accumulation following injection into laboratory animals. Injection of chymase provoked marked neutrophilia and eosinophilia in the skin of Dunkin Hartley guinea-pigs. Compared with saline injected control animals, there were some 60 fold more neutrophils and 12 fold more eosinophils present at the injection site. Following injection of chymase into the peritoneum of BALB/c mice, there were up to 700 fold more neutrophils. 21 fold more eosinophils, 19 fold more lymphocytes and 7 fold more macrophages recovered than from saline injected controls at 16 h. Doses of chymase as low as 5 ng (1.7 x 10(-13) mole) stimulated an inflammatory infiltrate, and significant neutrophilia was elicited within 3 h. The chymase induced cell accumulation in both the guinea-pig and mouse models was dependent on an intact catalytic site, being reduced by co-injection of proteinase inhibitors or heat inactivation of the enzyme. Co-injection of histamine or heparin significantly reduced the chymase induced neutrophil accumulation, whereas neither histamine nor heparin by themselves had any effect on the accumulation of nucleated cells. No synergistic or antagonist interactions between chymase and tryptase were observed when these two major mast cell proteinases were co-injected into the mouse peritoneum. Our findings suggest that chymase may provide an potent stimulus for inflammatory cell recruitment following mast cell activation.

Lovastatin induces growth inhibition and apoptosis in human malignant glioma cells

The competitive HMG-CoA reductase inhibitor lovastatin has been shown to suppress growth and induce morphological changes in a variety of non-glioma tumor cell lines. This study assesses the effects of this agent on the growth and survival of the human malignant glioma cell lines A172 and U87-MG. The response to the drug was investigated using a cell proliferation assay which revealed significant dose-dependent growth inhibition. Treatment with as little as 100 nM lovastatin over a period of 72 hours led to DNA degradation into nucleosome-sized fragments characteristic of apoptosis. Our data suggest that HMG-CoA reductase inhibitors such as lovastatin merit further investigation as potential therapeutic agents for the treatment of malignant gliomas.

Dendritic computation of direction selectivity by retinal ganglion cells

Direction-selective ganglion cells (DSGCs) in the retina respond strongly when stimulated by image motion in a preferred direction but are only weakly excited by image motion in the opposite null direction. Such coding represents an early manifestation of complex information processing in the visual system, but the cellular locus and the synaptic mechanisms have yet to be elucidated. We recorded the synaptic activity of DSGCs using strategies to observe the asymmetric inhibitory inputs that underlie the generation of direction selectivity. The critical nonlinear interactions between the excitatory and inhibitory inputs took place postsynaptically within the dendrites of the DSGCs.

Retinal direction selectivity after targeted laser ablation of starburst amacrine cells

Directionally selective retinal ganglion cells respond strongly when a stimulus moves in their preferred direction, but respond little or not at all when it moves in the opposite direction. This selectivity represents a classic paradigm of computation by neural microcircuits, but its cellular mechanism remains obscure. The directionally selective ganglion cells receive many synapses from a type of amacrine cell termed 'starburst' because of its regularly spaced, evenly radiating dendrites. Starburst amacrine cells have a synaptic asymmetry that has been proposed as the source of the directional response in the ganglion cells. Here we report experiments that make this unlikely, and offer an alternative concept of the function of starburst cells. We labelled starburst cells in living retinas, then killed them by targeted laser ablation while recording from individual directionally selective ganglion cells. Ablating starburst cells revealed no asymmetric contribution to the ganglion cell response. Instead of being direction discriminators, the starburst cells appear to potentiate generically the responses of ganglion cells to moving stimuli. The origin of direction selectivity probably lies with another type of amacrine cell.

The role of recombinant factor VIIa (FVIIa) in fibrin structure in the absence of FVIII/FIX

Patients with hemophilia have an impaired thrombin generation and therefore form loose fibrin hemostatic plugs that are easily dissolved by fibrinolysis. This prevents maintained hemostasis in these patients, resulting in a severe bleeding disorder. Recombinant (F)VIIa has been shown to enhance thrombin generation on already thrombin-activated platelets in the absence of FVIII and FIX. An efficacy rate of 80-90% has been found in hemophilia patients with inhibitors against FVIII or FIX both in association with major surgery and in the treatment of serious bleedings. In a model measuring fibrin clot permeability in a platelet-containing system described by Blombäck et al. (1994) this was demonstrated to be dependent on the concentration of FVIII and FIX. The addition of rFVIIa in concentrations of 1.9, 4.8 and 9.6 microg mL(-1) normalized fibrin clot permeability. The concentration of 1.9 microg mL(-1) of rFVIIa normalized clot permeability in this system and the higher concentrations of rFVIIa added only slightly to the effect. No further decrease in clot permeability was found when rFVIIa in a concentration of 1.9 microg mL(-1) was added to a sample with a normal concentration (100%) of FVIII or FIX. Higher concentrations of rFVIIa added to the plasma containing 100% of FVIII or FIX induced only a slight further decrease of fibrin permeability constant, arguing against any unwanted effect of extra rFVIIa on clot permeability in the case of a normal hemostasis. Furthermore, the fibrin network was studied with 3D microscopy and the loose network found in the absence of FVIII or FIX increased in density with increasing FVIII or FIX concentrations. The addition of rFVIIa to FVIII- or FIX-deficient systems altered the network structure, making the fibers thinner and more tightly packed.