bluuebunny/crossref_metadata_2025 huggingface dataset:
Hypoxia induces a complex response of globin expression in zebrafish(Danio rerio)
Authors: Roesner Anja , Hankeln Thomas , Burmester Thorsten
Published: May 2006

Unlike most mammals, many fish species live and survive in environments with low or changing levels of oxygen. Respiratory proteins like hemoglobin or myoglobin bind or store oxygen, thus enhancing its availability to the respiratory chain in the mitochondria. Here we investigate by means of quantitative real-time PCR the changes of hemoglobin, myoglobin, neuroglobin,cytoglobin and globin X mRNA in zebrafish (Danio rerio) exposed to mild (PO2=∼8.6 kPa) or severe(PO2=∼4.1 kPa) hypoxia. Neuroglobin and myoglobin protein levels were investigated by western blotting. Whereas mild hypoxia caused only minor changes of mRNA levels, strong hypoxia enhanced mRNA levels of the control genes (lactate dehydrogenase A and phosphoglycerate kinase 1). Surprisingly, levels of hemoglobin α and β mRNA were significantly reduced under severe hypoxia. Myoglobin mRNA and protein in heart mildly increased, in line with its proposed oxygen supply function. Likewise,neuroglobin mRNA and protein significantly increased in brain (up to 5.7-fold at the protein level), but not in eye. This observation, firstly, suggests physiological differences of zebrafish eye and brain under hypoxia, and secondly, indicates an important role of neuroglobin in oxidative metabolism,probably oxygen supply within neurons. There was little change in the expression of the two cytoglobin genes. Globin X mRNA significantly decreased under hypoxia, pointing to a functional linkage to oxygen-dependent metabolism.
The regenerative nidi of the locust midgut as a model to study epithelial cell differentiation from stem cells
Authors: Illa-Bochaca Irineu , Montuenga Luis M.
Published: May 2006

A better knowledge of the regulatory mechanisms involved in stem cell proliferation and/or differentiation could reveal new methods for the treatment of some diseases. Most previous studies in the field of stem cell biology have been carried out on cultured isolated cells. In the case of adult tissue stem cells, mesenchymal bone marrow derived cells have been most widely studied, while the undifferentiated stem cells present in the epithelial tissues are less known. In order to advance further our understanding of epithelial tissue stem cells, new in vivo models are required. The present study focuses on the dynamics of a new and simple model of intestinal epithelial regeneration found in the midgut of the migratory locust, Locusta migratoria (Linnaeus 1758). The locust midgut consists of three cell types: columnar cells, endocrine cells and undifferentiated regenerative clustered cells. The undifferentiated epithelial midgut cells give rise to two other cell types and are located in a nest of regenerative cells known as regenerative niche. We have performed single and continuous bromodeoxyuridine (BrdU) administration experiments to study regeneration niches and their cellular dynamics. Immunocytochemistry and immunofluorescence techniques were used to detect the incorporation of BrdU into regenerative niches and the presence of FMRFamide-like immunoreactivity, as a marker for endocrine cell differentiation. Some isolated label retaining cells (LRC) were observed at the niche base 10-15 days after the final BrdU administration. We propose that these cells are the stem cells of this epithelial tissue. We also calculated the length of the cell cycle phases for a subpopulation of transit amplifying cells within the regenerative niche: G1, 2.5±0.5 h; S,5.5±0.5 h; G2, 0.75±0.25 h; M, 2.5±0.5 h. These amplifying cells will give rise to the columnar epithelial non-endocrine lineage. The differentiation of an endocrine cell from a niche stem cell occurs less frequently and thus leads to a lower proportion of endocrine cells as compared with epithelial columnar digestive cells (up to three endocrine cells per niche). Endocrine cell commitment seems to occur very early in the differentiation process within the niche, as double-labelled BrdU and FMRF endocrine cells have never been found. The only exception is the endocrine cells located in the ampullar region of the midgut, some of which show double immunostaining after long-term chronic BrdU injection. In summary, we have characterized a new and simple animal model of epithelial stem cell regeneration that may be useful for understanding the complex biological process that drives tissue renewal from undifferentiated and uncommitted progenitor cells.
Involvement of ryanodine-operated channels intert-butylhydroperoxide-evoked Ca2+ mobilisation in pancreatic acinar cells
Authors: Martínez-Burgos María A. , Granados María P. , González Antonio , Rosado Juan A. , Yago María D. , Salido Ginés M. , Martínez-Victoria Emilio , Mañas Mariano , Pariente José A.
Published: May 2006

Reactive oxygen species and related oxidative damage have been implicated in the initiation of acute pancreatitis, a disease characterised in its earliest stages by disruption of intracellular Ca2+ homeostasis. The present study was carried out in order to establish the effect of the organic pro-oxidant, tert-butylhydroperoxide (tBHP), on the mobilisation of intracellular Ca2+ stores in isolated rat pancreatic acinar cells and the mechanisms underlying this effect. Cytosolic free Ca2+ concentrations ([Ca2+]c) were monitored using a digital microspectrofluorimetric system in fura-2 loaded cells. In the presence of normal extracellular Ca2+ concentrations([Ca2+]o), perfusion of pancreatic acinar cells with 1 mmol l-1tBHP caused a slow sustained increase in[Ca2+]c. This increase was also observed in a nominally Ca2+-free medium, indicating a release of Ca2+ from intracellular stores. Pretreatment of cells with tBHP abolished the typical Ca2+ response of both the physiological agonist CCK-8 (1 nmol l-1) and thapsigargin (TPS, 1 μmol l-1), an inhibitor of the SERCA pump, in the absence of extracellular Ca2+. Similar results were observed with carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP, 0.5 μmol l-1),a mitochondrial uncoupler. In addition, depletion of either agonist-sensitive Ca2+ pools by CCK-8 or TPS or mitochondrial Ca2+ pools by FCCP were unable to prevent the tBHP-induced Ca2+release. By contrast, simultaneous administration of TPS and FCCP clearly abolished the tBHP-induced Ca2+ release. These results show that tBHP releases Ca2+ from agonist-sensitive intracellular stores and from mitochondria. On the other hand, simultaneous application of FCCP and of 2-aminoethoxydiphenylborane (2-APB), a blocker of IP3-mediated Ca2+release, was unable to suppress the increase in [Ca2+]c induced by tBHP, while the application of 50 μmol l-1 of ryanodine (which is able to block the ryanodine channels) inhibits tBHP-evoked Ca2+mobilisation. These findings indicate that tBHP releases Ca2+ from non-mitochondrial Ca2+ pools through ryanodine channels.
Evidence that blue petrel,Halobaena caerulea,fledglings can detect and orient to dimethyl sulfide
Authors: Bonadonna F. , Caro S. , Jouventin P. , Nevitt G. A.
Published: May 2006

Procellariiform seabirds (the petrels, albatrosses and shearwaters) are recognized for their acute sense of smell. These pelagic seabirds forage over thousands of miles of ocean to find patchily distributed prey resources. Over the past decade, much headway has been made in unravelling the variety of olfactory foraging strategies that Antarctic species employ, and it is becoming clearer that olfaction plays a key role in foraging, particularly for burrow nesting species. Now we are beginning to explore how these behaviours develop in chicks. Procellariiform chicks fledge and survive the open seas without aid or instruction from a parent, but how they are able to accomplish this task is unknown. Here we explore whether chicks leave the nest pre-tuned to olfactory cues necessary for foraging. In this study, we tested the hypothesis that blue petrel chicks (Halobaena caerulea) are able to detect and orient to a foraging cue (dimethyl sulphide, DMS) used by adults without ever having experienced this odour at sea. We first established that chicks could detect DMS at a biologically relevant concentration that they will later naturally encounter at sea (<10 pmol l-1). We then performed preference tests in a Y-maze on a group of birds 1-6 days before they fledged. Sixteen out of 20 fledglings preferred DMS (e.g. DMS+propylene glycol) to a `control' odour (propylene glycol alone). Our results suggest that chicks can detect and may already recognize DMS as an orientation cue even before they leave the nest to forage for the first time.
Nutrient regulation in relation to diet breadth: a comparison ofHeliothissister species and a hybrid
Authors: Lee Kwang Pum , Behmer, Spencer T. , Simpson, Stephen J.
Published: May 2006

We examined the nutritional correlates of diet breadth in insect herbivores by comparing patterns of diet selection, nutrient balancing, post-ingestive utilization and development in two sister species of caterpillar and a hybrid between them. One species, Heliothis virescens (HV) has a broad host range, feeding on plants in at least 14 families. The other, Heliothis subflexa (HS), is a specialist on plants in the genus Physalis(Solanaceae). Experiments using synthetic foods showed that when the caterpillars were allowed to mix their diet, the generalist self-selected a higher-protein diet whereas the specialist ate almost equal amounts of protein and carbohydrate, which accords with differences between the two species in the nutrient content of their natural diets. When confined to nutritionally imbalanced diets, the generalist showed a propensity to over-eat high protein:carbohydrate (P:C) diets to a greater degree than did the specialist and maintained higher rates of development. The generalist did not, however,over-eat low P:C diets to the same degree as the specialist. The hybrid selected a diet composition that was indistinguishable to that of its generalist father (HV), while its response to imbalanced diets was closely similar to that of the specialist mother (HS). The generalist converted ingested nutrient to growth with lower efficiency than did the specialist and the hybrid. Our findings imply that different behavioural and physiological traits linked to nutrient regulation are under genetic control and are explicable in terms of the different life-histories, feeding ecologies and presumed levels of nutritional heterogeneity in the environments of the two insects.
Hydrodynamic consequences of flexural stiffness and buoyancy for seaweeds: a study using physical models
Authors: Stewart Hannah Louise
Published: May 2006

An upright posture in the water column may expose benthic marine organisms to faster flow higher in the water column than near the substratum,potentially increasing rates of mass exchange while also exposing the organisms to higher hydrodynamic forces. Benthic organisms maintain upright postures in the water column by one of two mechanisms, stiffness or buoyancy. Turbinaria ornata is a tropical macroalga that uses either buoyancy or flexural stiffness (EI), depending on its flow habitat. This study used physical models of T. ornata to compare the effect of different magnitudes of these two mechanisms on relative water velocity and hydrodynamic forces in both unidirectional and wavy flow. Models of the alga were constructed to span and exceed natural levels of T. ornata's EI and buoyancy. Models with high EI and high buoyancy maintained upright postures in both unidirectional flow and waves, and experienced higher forces than models with low EI and moderate or low buoyancy that deflected in the direction of water motion. In waves, buoyant models that were deflected by high velocity rebounded back into upright positions when the flow slowed. Non-buoyant, flexible models were also pushed over by flow but lacked the ability to rebound upright, which led to decreased force in unidirectional flow, but high force in waves.
The human gluteus maximus and its role in running
Authors: Lieberman Daniel E. , Raichlen David A. , Pontzer Herman , Bramble Dennis M. , Cutright-Smith Elizabeth
Published: May 2006

The human gluteus maximus is a distinctive muscle in terms of size, anatomy and function compared to apes and other non-human primates. Here we employ electromyographic and kinematic analyses of human subjects to test the hypothesis that the human gluteus maximus plays a more important role in running than walking. The results indicate that the gluteus maximus is mostly quiescent with low levels of activity during level and uphill walking, but increases substantially in activity and alters its timing with respect to speed during running. The major functions of the gluteus maximus during running are to control flexion of the trunk on the stance-side and to decelerate the swing leg; contractions of the stance-side gluteus maximus may also help to control flexion of the hip and to extend the thigh. Evidence for when the gluteus maximus became enlarged in human evolution is equivocal, but the muscle's minimal functional role during walking supports the hypothesis that enlargement of the gluteus maximus was likely important in the evolution of hominid running capabilities.
In vivocranial suture function and suture morphology in the extant fishPolypterus: implications for inferring skull function in living and fossil fish
Authors: Markey Molly J. , Main Russell P. , Marshall, Charles R.
Published: May 2006

This study describes the mechanical role that cranial sutures play in fish during feeding. The long-term goal of our work is to establish relationships between suture form and function, so that functional inferences can be made from suture morphology in fossil taxa. To this end, strain gauges were surgically implanted across selected sutures in the skull roof of four individuals of Polypterus endlicherii. After surgery, bone and suture strains during feeding were recorded along with high-speed video of the feeding events. Each trial was designated as a suction feeding or biting on prey trial, and neurocranial elevation, hyoid position and gape were quantified to aid in interpreting the strain data. The strains due to suction feeding are different from those observed during biting. Suction feeding results in a fairly stereotyped strain pattern, with the interfrontal and frontoparietal sutures experiencing tension, while the interparietal suture is compressed. Biting causes much more variable strain patterns. However, both suction and biting result in compression in the back of the skull, and tension between the frontals. Peak strains, and the time at which they occur in the feeding cycle, were compared between suction and biting. In general, peak suture strains are higher during suction than during biting, but not all of these differences are significant. Peak suture and bone strains occur at or near maximum gape during both suction and biting, suggesting that these strains are caused by muscle contraction involved in mouth opening and closing. Micro-computed tomography (microCT) scans of the experimental specimens indicate that the interfrontal and frontoparietal sutures, typically loaded in tension, are less interdigitated in cross section than the interparietal suture, which experiences compression. This is consistent with published correlations of suture form and function in mammals, where interdigitated sutures indicate compression and lack of interdigitation is associated with tension.
Designing a Family of Development-Intensive Products
Authors: Krishnan V. , Zhu W.
Published: May 2006

Faced with fragmented markets, saturated and demanding customers, and global competition, firms increasingly must design and offer a line of innovative, quality-differentiated products to target customers with differing willingness to pay (WTP). In this context, designing a special class of products that we term development-intensive products (DIPs)—for which the fixed costs of development far outweigh the unit-variable costs—presents some unique managerial challenges. Examples of such development-intensive offerings abound in a number of industries, including the pharmaceutical, information, and entertainment sectors of the economy. Our contributions in this paper are threefold: (a) to show that managerial insights from the traditional approach to product-line design developed for unit-variable cost-intensive products do not carry over to DIPs, (b) to present new mechanisms and managerial guidelines for designing a family of products for which development costs cannot be ignored, and (c) to illustrate the insights with an extended industry example. We find that the design approach based on degrading (or subtracting value from) a high-end product to obtain a subsumed low-end edition, shown in the literature to be an effective approach for designing unit cost-intensive products, can be inappropriate for DIPs. This limitation of value subtraction has implications for the number of variants and the sequence in which they are developed. As an alternative to a subsumed product-design strategy, we propose and examine the overlapped product-design approach, in which a low-end product is not completely subsumed within its high-end counterpart, but differentiated on additional vertical quality dimensions. Our results both explain the recent challenges of firms with subsumed low-end products and guide them in designing a product line to successfully address emerging low-end market segments.
A Bargaining Model for a First-Time Interaction Under Asymmetric Beliefs of Supply Reliability
Authors: Gurnani Haresh , Shi Mengze
Published: May 2006

We consider the case of a first-time interaction between a buyer and a supplier who is unreliable in delivery. The supplier declares her estimate of the ability to meet the order obligations, but the buyer may have a different estimate, which may be higher or lower than the supplier’s estimate. We derive the Nash bargaining solution and discuss the role of using a down-payment or nondelivery penalty in the contract. For the case of buyer overtrust, the down-payment contract maximizes channel profits when the supplier’s estimate is public information. If the supplier’s estimate is private information, a nonsymmetric contract is shown to be efficient and incentive compatible. For the case of buyer undertrust, the contract structure is quite different as both players choose not to include down-payments in the contract. When delivery estimates are public information, a nondelivery penalty contract is able to maximize channel profits if the buyer uses the supplier’s estimate in making the ordering decision. If estimates are private information, channel profits are maximized only if the true estimates of both players are not far part. We also discuss the effect of different risk profiles on the nature of the bargaining solution. In three extensions of the model, we consider the following variants of the basic problem. First, we analyze the effect of early versus late negotiation on the bargaining solution. Then, we study the case of endogenous supply reliability, and finally, for the case of repeated interactions, we discuss the impact of updating delivery estimates on the order quantity and negotiated prices of future orders.
Exploring Decision Makers’ Use of Price Information in a Speculative Market
Authors: Johnson Johnnie E. V. , Jones Owen , Tang Leilei
Published: May 2006

We explore the extent to which the decisions of participants in a speculative market effectively account for information contained in prices and price movements. The horse race betting market is an ideal environment to explore these issues. A conditional logit model is constructed to determine winning probabilities based on bookmakers’ closing prices and the time-indexed movement of prices to the market close. We incorporate a technique for extracting predictors from price (odds) curves using orthogonal polynomials. The results indicate that closing prices do not fully incorporate market price information, particularly information that is less readily discernable by market participants.
Static Mean-Variance Analysis with Uncertain Time Horizon
Authors: Martellini Lionel , Urošević Branko
Published: May 2006

We generalize Markowitz analysis to the situations involving an uncertain exit time. Our approach preserves the form of the original problem in that an investor minimizes portfolio variance for a given level of the expected return. However, inputs are now given by the generalized expressions for mean and variance-covariance matrix involving moments of the random exit time in addition to the conditional moments of asset returns. Although efficient frontiers in the generalized and the standard Markowitz case may coincide under certain conditions, we demonstrate that, by means of an example, in general that is not true. In particular, portfolios efficient in the standard Markowitz sense can be inefficient in the generalized sense and vice versa. As a result, an investor facing an uncertain time horizon and investing as if her time of exit is certain would in general make suboptimal portfolio allocation decisions. Numerical simulations show that a significant efficiency loss can be induced by an improper use of standard mean-variance analysis when time horizon is uncertain.
Competitive Advertising Strategies and Market-Size Dynamics: A Research Note on Theory and Evidence
Authors: Nguyen Dung , Shi Lei
Published: May 2006

This paper analyzes competing firms’ advertising strategies in markets characterized by dynamic market sizes. For new product innovations, a large literature has been developed on the basis of the celebrated Bass diffusion process, which captures what we call market-size dynamics. However, in spite of the significant literature incorporating competitiveness into the Bass model, few if any analytical results have been obtained, especially those with normative implications. On the other hand, important theoretical and empirical insights have recently been obtained using the famous Lanchester warfare model of competition, in which market-share dynamics are governed by advertising activities for mature products whose market sizes are typically fixed or stable. Our paper seeks to address the issue of optimal advertising strategies incorporating both market-share dynamics and market-size dynamics. In doing so, we seek to take advantage of the theoretical and normative insights currently available in the Lanchester formulation for mature products to obtain normative, analytical results on competitive advertising strategies for new product innovations whose markets evolve around the Bass process. We first obtain analytical solutions to the problem at hand and offer theoretical implications for competitive advertising on the Bass diffusion model. The model’s parameters are then estimated using a set of data on sales and advertising expenditures of Polaroid Corp. and Eastman Kodak Co. in instant photography during the 1976–1985 period; optimal trajectories for the firms’ advertising spending are then calculated, and other marketing and managerial implications of optimal advertising strategies are explored.
Procuring Fast Delivery: Sole Sourcing with Information Asymmetry
Authors: Cachon Gérard P. , Zhang Fuqiang
Published: May 2006

This paper studies a queuing model in which a buyer sources a good or service from a single supplier chosen from a pool of suppliers. The buyer seeks to minimize the sum of her procurement and operating costs, the latter of which depends on the supplier’s lead time. The selected supplier can regulate his lead time, but faster lead times are costly. Although the buyer selects the supplier to source from (possibly via an auction) and dictates the contractual terms, the buyer’s bargaining power is limited by asymmetric information: The buyer only has an estimate of the suppliers’ costs, while the suppliers know their costs precisely. We identify a procurement mechanism that minimizes the buyer’s total cost (procurement plus operating). This mechanism is not simple: It is a numerically derived nonlinear menu of contracts. Therefore, we study several simpler mechanisms: e.g., one that charges a late fee and one that specifies a fixed lead-time requirement (no menus, no nonlinear functions). We find that simple mechanisms are nearly optimal (generally within 1% of optimal) because asymmetric information conveys significant protection to the supplier, i.e., the supplier is able to retain most of the benefit of having a lower cost. Renegotiation is another concern with the optimal mechanism: Because it does not minimize the supply chain’s cost, the firms can be both better off if they throw away the contract and start over. Interestingly, we find that the potential gain from renegotiation is relatively small with either the optimal or our simple mechanisms. We conclude that our simple mechanisms are quite attractive along all relevant dimensions: buyer’s performance, supply chain performance, simplicity, and robustness to renegotiation.
Technological Development and the Boundaries of the Firm: A Knowledge-Based Examination in Semiconductor Manufacturing
Authors: Macher Jeffrey T.
Published: May 2006

This paper examines how the knowledge-based view (KBV) can be applied to firm boundary decisions and the performance implications of those decisions. At the center of the paper is a theoretical and empirical examination of how firms most efficiently organize to solve different types of problems related to technological development, using the semiconductor industry as the empirical setting. Measures that capture important dimensions of performance support the proposition that organization affects performance in problem solving related to knowledge development. Integrated firms realize performance advantages when problem solving in technological development is ill structured and complex, while the same is true for specialized firms when problem solving in technological development is well structured and simple. Performance differences also arise from the presence of scale economies and scope economies.
Supply Chain Choice on the Internet
Authors: Netessine Serguei , Rudi Nils
Published: May 2006

Internet companies extensively use the practice of drop-shipping, where the wholesaler stocks and owns the inventory and ships products directly to customers at retailers’ request. Under the drop-shipping arrangement, the supply chain benefits from risk pooling because the inventory for multiple retailers is stocked at the same location, the wholesaler’s. Another more traditional channel alternative on the Internet is one in which retailers stock and own the inventory. These two supply chain structures, which predominate on the Internet, result in different inventory risk allocation, stocking decisions, and profits for channel members. Moreover, the two channel alternatives can be combined into a dual strategy whereby the retailer uses local inventory as a primary source and relies on drop-shipping as a backup. We model the dual strategy as a noncooperative game among the retailers and the wholesaler, analyze it, and obtain insights into the structural properties of the equilibrium solution to facilitate development of recommendations for practicing managers. Finally, we characterize situations in which each of three channels is preferable by specifying appropriate ranges of critical parameters, including demand variability, the number of retailers in the channel, wholesale prices, and transportation costs.
Identifying Sources of Heterogeneity for Empirically Deriving Strategic Types: A Constrained Finite-Mixture Structural-Equation Methodology
Authors: DeSarbo Wayne S. , Di Benedetto C. Anthony , Jedidi Kamel , Song Michael
Published: May 2006

The resource-based view (RBV) of the firm suggests that strategic deployment of capabilities allows strategic business units (SBUs) to exploit distinctive competencies and create sustainable competitive advantage. Following the RBV, we propose a new predictive methodology for deriving typologies of SBUs that accommodates heterogeneity among SBUs with respect to their strategic capabilities, how effectively they are employed, and performance. Statistically, we devise a constrained finite-mixture structural-equation procedure that simultaneously accounts for firm capabilities, performance outcomes, and the relationships between them. The procedure allows for a comprehensive modeling and grouping of entities, and simultaneously provides a diagnosis of the sources of heterogeneity via the flexibility of estimating a series of nested models. Managerially, our proposed methodology is grounded in the strategic type and RBV literature and can capture the effects of environmental and industry-specific factors. Using data obtained from 216 SBUs in the United States for illustration, the results show that our derived four mixed-type solution dominates the four-group, Prospectors-Analyzers-Defenders-Reactors classification as well as a number of other nested model solutions in terms of objective statistical fit criteria for this data set, suggesting a more contingency-driven strategic stance adopted by these SBUs. We conclude with a discussion of the theoretical and managerial benefits of an improved methodology for empirically deriving strategic typologies.
Sensitive and Quantitative Measurement of Gene Expression Directly from a Small Amount of Whole Blood
Authors: Zheng Zhi , Luo Yuling , McMaster Gary K
Published: May 2006

Background: Accurate and precise quantification of mRNA in whole blood is made difficult by gene expression changes during blood processing, and by variations and biases introduced by sample preparations. We sought to develop a quantitative whole-blood mRNA assay that eliminates blood purification, RNA isolation, reverse transcription, and target amplification while providing high-quality data in an easy assay format.

Methods: We performed single- and multiplex gene expression analysis with multiple hybridization probes to capture mRNA directly from blood lysate and used branched DNA to amplify the signal. The 96-well plate singleplex assay uses chemiluminescence detection, and the multiplex assay combines Luminex-encoded beads with fluorescent detection.

Results: The single- and multiplex assays could quantitatively measure as few as 6000 and 24 000 mRNA target molecules (0.01 and 0.04 amoles), respectively, in up to 25 μL of whole blood. Both formats had CVs <10% and dynamic ranges of 3–4 logs. Assay sensitivities allowed quantitative measurement of gene expression in the minority of cells in whole blood. The signals from whole-blood lysate correlated well with signals from purified RNA of the same sample, and absolute mRNA quantification results from the assay were similar to those obtained by quantitative reverse transcription-PCR. Both single- and multiplex assay formats were compatible with common anticoagulants and PAXgene-treated samples; however, PAXgene preparations induced expression of known antiapoptotic genes in whole blood.

Conclusions: Both the singleplex and the multiplex branched DNA assays can quantitatively measure mRNA expression directly from small volumes of whole blood. The assay offers an alternative to current technologies that depend on RNA isolation and is amenable to high-throughput gene expression analysis of whole blood.
Somatosensory Coding of Roughness: The Effect of Texture Adaptation in Direct and Indirect Touch
Authors: Hollins Mark , Lorenz Florian , Harper Daniel
Published: May 2006

To examine somatosensory mechanisms contributing to the perception of roughness, subjects examined surfaces with rigorously specified spatial textures under conditions of direct moving contact between the fingertip and the surface (direct touch) and contact through a rigid probe (indirect touch). Subjects were trained to scan the surfaces along a consistent path and with a speed of 2.7 cm/s. With each mode of touch, periods of prolonged inspection of a single adapting surface were followed by shorter periods in which the roughness of multiple test surfaces was reported. Adaptation caused a drop in perceived roughness under conditions of indirect touch, reflecting the reduced sensitivity of vibrotactile mechanisms that are the main recipients of textural information transmitted through the probe. During direct touch, adaptation had no significant effect on the perception of textures with spatial period >200 μm, which are spatially encoded. The results have an important implication for the physiological basis of the spatial code, which is believed to involve somatosensory cortical neurons with highly structured receptive fields: these cortical populations appear to be less susceptible to adaptation than otherwise similar neuronal populations in the visual system.
The Impact of Astrocytic Gap Junctional Coupling on Potassium Buffering in the Hippocampus
Authors: Wallraff Anke , Köhling Rüdiger , Heinemann Uwe , Theis Martin , Willecke Klaus , Steinhäuser Christian
Published: May 2006

Astrocytic gap junctions have been suggested to contribute to spatial buffering of potassium in the brain. Direct evidence has been difficult to gather because of the lack of astrocyte-specific gap junction blockers. We obtained mice with coupling-deficient astrocytes by crossing conditional connexin43-deficient mice with connexin30−/−mice. Similar to wild-type astrocytes, genetically uncoupled hippocampal astrocytes displayed negative resting membrane potentials, time- and voltage-independent whole-cell currents, and typical astrocyte morphologies. Astrocyte densities were also unchanged. Using potassium-selective microelectrodes, we assessed changes in potassium buffering in hippocampal slices of mice with coupling-deficient astrocytes. We demonstrate that astrocytic gap junctions accelerate potassium clearance, limit potassium accumulation during synchronized neuronal firing, and aid in radial potassium relocation in the stratum lacunosum moleculare. Furthermore, slices of mice with coupling-deficient astrocytes displayed a reduced threshold for the generation of epileptiform events. However, it was evident that radial relocation of potassium in the stratum radiatum was not dependent on gap junctional coupling. We suggest that the perpendicular array of individual astrocytes in the stratum radiatum makes these cells ideally suited for spatial buffering of potassium released by pyramidal cells, independent of gap junctions. In general, a surprisingly large capacity for K+clearance was conserved in mice with coupling-deficient astrocytes, indicating that gap junction-dependent processes only partially account for K+buffering in the hippocampus.
Spatiotemporal Tuning of Rapid Interactions between Visual-Motion Analysis and Reaching Movement
Authors: Gomi Hiroaki , Abekawa Naotoshi , Nishida Shin’ya
Published: May 2006

In addition to the goal-directed preplanned control, which strongly governs reaching movements, another type of control mechanism is suggested by recent findings that arm movements are rapidly entrained by surrounding visual motion. It remains, however, controversial whether this rapid manual response is generated in a goal-oriented manner similarly to preplanned control or is reflexively and directly induced by visual motion. To investigate the sensorimotor process underlying rapid manual responses induced by large-field visual motion, we examined the effects of contrast and spatiotemporal frequency of the visual-motion stimulus. The manual response amplitude increased steeply with image contrast up to 10% and leveled off thereafter. Regardless of the spatial frequency, the response amplitude increased almost proportionally to the logarithm of stimulus speed until the temporal frequency reached 15–20 Hz and then fell off. The maximum response was obtained at the lowest spatial frequency we examined (0.05 cycles/°). These stimulus specificities are surprisingly similar to those of the reflexive ocular-following response induced by visual motion, although there is no direct motor entrainment from the ocular to manual responses. In addition, the spatiotemporal tuning is clearly different from that of perceptual effects caused by visual motion. These comparisons suggest that the rapid manual response is generated by a reflexive sensorimotor mechanism. This mechanism shares a distinctive visual-motion processing stage with the reflexive control for other motor systems yet is distinct from visual-motion perception.
Neurophysiology of Implicit Timing in Serial Choice Reaction-Time Performance
Authors: Praamstra Peter , Kourtis Dimitrios , Fei Kwok Hoi , Oostenveld Robert
Published: May 2006

Neural representations of time for the judgment of temporal durations are reflected in electroencephalographic (EEG) slow brain potentials, as established in time production and perception tasks. Here, we investigated whether anticipatory processes in reaction-time procedures are governed by similar mechanisms of interval timing. We used a choice reaction task with two different, temporally regular stimulus presentation regimes, both with occasional deviant interstimulus intervals. Temporal preparation was shown in the form of adjustments in time course of slow brain potentials, such that they reached their maximum amplitude just before a new trial, independent of the duration of the interstimulus interval. Preparation was focused on a brief time window, demonstrated by a drop in amplitude of slow potentials as the standard interval had elapsed in deviant interstimulus intervals. Implicit timing influencing perceptual processing was shown in reduced visual-evoked responses to delayed stimuli after a deviant interstimulus interval and in a reduction of EEG α power over the visual cortex at the time when the standard interval had elapsed. In contrast to explicit timing tasks, the slow brain potential manifestations of implicit timing originated in the lateral instead of the medial premotor cortex. Together, the results show that temporal regularities set up a narrow time window of motor and sensory attention, demonstrating the operation of interval timing in reaction time performance. The divergence in slow brain potential distribution between implicit and explicit timing tasks suggests that interval timing for different behaviors relies on qualitatively similar mechanisms implemented in distinct cortical substrates.
Ischemic Insults Direct Glutamate Receptor Subunit 2-Lacking AMPA Receptors to Synaptic Sites
Authors: Liu Baosong , Liao Mingxia , Mielke John G. , Ning Ke , Chen Yonghong , Li Lei , El-Hayek Youssef H. , Gomez Everlyne , Zukin R. Suzanne , Fehlings Michael G. , Wan Qi
Published: May 2006

Regulated AMPA receptor (AMPAR) trafficking at excitatory synapses is a mechanism critical to activity-dependent alterations in synaptic efficacy. The role of regulated AMPAR trafficking in insult-induced synaptic remodeling and/or cell death is, however, as yet unclear. Here we show that brief oxygen–glucose deprivation (OGD), anin vitromodel of brain ischemia, promotes redistribution of AMPARs at synapses of hippocampal neurons, leading to a switch in AMPAR subunit composition. Ischemic insults promote internalization of glutamate receptor subunit 2 (GluR2)-containing AMPARs from synaptic sites via clathrin-dependent endocytosis and facilitate delivery of GluR2-lacking AMPARs to synaptic sites via solubleN-ethylmaleimide-sensitive factor attachment protein receptor-dependent exocytosis, evident at early times after insult. The OGD-induced switch in receptor subunit composition requires PKC activation, dissociation of GluR2 from AMPA receptor-binding protein, and association with protein interacting with C kinase-1. We further show that AMPARs at synapses of insulted neurons exhibit functional properties of GluR2-lacking AMPARs. AMPAR-mediated miniature EPSCs exhibit increased amplitudes and enhanced sensitivity to subunit-specific blockers of GluR2-lacking AMPARs, evident at 24 h after ischemia. The OGD-induced alterations in synaptic AMPA currents require clathrin-mediated receptor endocytosis and PKC activation. Thus, ischemic insults promote targeting of GluR2-lacking AMPARs to synapses of hippocampal neurons, mechanisms that may be relevant to ischemia-induced synaptic remodeling and/or neuronal death.
Deglycosylated Anti-Amyloid-β Antibodies Eliminate Cognitive Deficits and Reduce Parenchymal Amyloid with Minimal Vascular Consequences in Aged Amyloid Precursor Protein Transgenic Mice
Authors: Wilcock Donna M. , Alamed Jennifer , Gottschall Paul E. , Grimm Jan , Rosenthal Arnon , Pons Jaume , Ronan Victoria , Symmonds Keisha , Gordon Marcia N. , Morgan Dave
Published: May 2006

Systemic administration of anti-amyloid-β (Aβ) antibodies results in reduced parenchymal amyloid but increased vascular amyloid and microhemorrhage in amyloid precursor protein (APP) transgenic mice. Here, we evaluate the effects of reducing effector interactions of the antibody via deglycosylation. Mice aged 20 months were treated weekly for 4 months and tested behaviorally before they were killed. APP transgenic mice receiving either anti-Aβ (2H6) or deglycosylated anti-Aβ (de-2H6) showed significant improvement in radial arm water maze performance compared with mice receiving a control antibody. Both groups receiving anti-Aβ antibodies showed significant reductions in total Aβ immunochemistry and Congo red. Significantly fewer vascular amyloid deposits and microhemorrhages were observed in mice administered the de-2H6 antibody compared with those receiving unmodified 2H6 antibody. Deglycosylated anti-Aβ antibodies may be preferable to unmodified IgG because they retain the cognition-enhancing and amyloid-reducing properties of anti-Aβ immunotherapy, while greatly attenuating the increased vascular amyloid deposition and microhemorrhage observed with unmodified IgG.
Involvement of Protein Kinase A in Patterning of the Mouse Somatosensory Cortex
Authors: Watson Ruth F. , Abdel-Majid Raja M. , Barnett Mark W. , Willis Brandon S. , Katsnelson Alla , Gillingwater Thomas H. , McKnight G. Stanley , Kind Peter C. , Neumann Paul E.
Published: May 2006

Patterning of the mouse somatosensory cortex is unusually evident because of the presence of a “barrel field.” Presynaptic serotonin and postsynaptic glutamate receptors regulate barrel formation, but little is known of the intracellular signaling pathways through which they act. To determine whether protein kinase A (PKA) plays a role in the development of the barrel field, we examined five viable PKA subunit-specific knock-out (KO) mouse lines for barrel field abnormalities. Barrels are present in these mice, but those lacking the RIIβ subunit display significantly reduced contrast between the cell densities of barrel hollows and sides compared with wild-type animals. Thalamocortical afferent segregation in the posterior medial barrel subfield appeared normal, suggesting a postsynaptic site of gene action for the RIIβ protein. Immunoelectron microscopy confirmed that RIIβ was selectively localized to dendrites and dendritic spines. Mice lacking RIIβ show reduced glutamate receptor A (GluRA) subunit insertion into the postsynaptic density in postnatal day 7 somatosensory cortex; however, GluRA KO mice developed normal barrels. Our results clearly demonstrate a role for postsynaptic PKA signaling pathways in barrel differentiation. They also demonstrate a clear dissociation between the regulation of GluRA trafficking by PKA and its role in barrel formation. Finally, although a role for PKA downstream of cAMP cannot be ruled out, these data suggest that PKA may not be the principle downstream target because none of the mutants showed a barrelless phenotype similar to that observed in adenylate cyclase type 1 KO mice. These results give insight into activity-dependent mechanisms that regulate barrel formation.
The Cytokine Interleukin-6 Is Sufficient But Not Necessary to Mimic the Peripheral Conditioning Lesion Effect on Axonal Growth
Authors: Cao Zixuan , Gao Ying , Bryson J. Barney , Hou Jianwei , Chaudhry Nagarathnamma , Siddiq Mustafa , Martinez Jennifer , Spencer Tim , Carmel Jason , Hart Ronald B. , Filbin Marie T.
Published: May 2006

Lesioning the peripheral branch of a dorsal root ganglion (DRG) neuron before injury of the central branch of the same neuron enables spontaneous regeneration of these spinal axons. This effect is cAMP and transcription dependent. Here, we show that the cytokine interleukin-6 (IL-6) is upregulated in DRG neurons after either a conditioning lesion or treatment with dibutyryl-cAMP. In culture, IL-6 allows neurons to grow in the presence of inhibitors of regeneration present in myelin. Importantly, intrathecal delivery of IL-6 to DRG neurons blocks inhibition by myelin bothin vitroandin vivo, effectively mimicking the conditioning lesion. Blocking IL-6 signaling has no effect on the ability of cAMP to overcome myelin inhibitors. Consistent with this, IL-6-deficient mice respond to a conditioning lesion as effectively as wild-type mice. We conclude that IL-6 can mimic both the cAMP effect and the conditioning lesion effect but is not an essential component of either response.
ASIC1a-Specific Modulation of Acid-Sensing Ion Channels in Mouse Cortical Neurons by Redox Reagents
Authors: Chu Xiang-Ping , Close Natasha , Saugstad Julie A. , Xiong Zhi-Gang
Published: May 2006

Acid-sensing ion channel (ASIC)-1a, the major ASIC subunit with Ca2+permeability, is highly expressed in the neurons of CNS. Activation of these channels with resultant intracellular Ca2+accumulation plays a critical role in normal synaptic plasticity, learning/memory, and in acidosis-mediated glutamate receptor-independent neuronal injury. Here we demonstrate that the activities of ASICs in CNS neurons are tightly regulated by the redox state of the channels and that the modulation is ASIC1a subunit dependent. In cultured mouse cortical neurons, application of the reducing agents dramatically potentiated, whereas the oxidizing agents inhibited the ASIC currents. However, in neurons from the ASIC1 knock-out mice, neither oxidizing agents nor reducing reagents had any effect on the acid-activated current. In Chinese Hamster Ovary cells, redox-modifying agents only affected the current mediated by homomeric ASIC1a, but not homomeric ASIC1b, ASIC2a, or ASIC3. In current-clamp recordings and Ca2+-imaging experiments, the reducing agents increased but the oxidizing agents decreased acid-induced membrane depolarization and the intracellular Ca2+accumulation. Site-directed mutagenesis studies identified involvement of cysteine 61 and lysine 133, located in the extracellular domain of the ASIC1a subunit, in the modulation of ASICs by oxidizing and reducing agents, respectively. Our results suggest that redox state of the ASIC1a subunit is an important factor in determining the overall physiological function and the pathological role of ASICs in the CNS.
Genes Associated with Adult Axon Regeneration Promoted by Olfactory Ensheathing Cells: A New Role for Matrix Metalloproteinase 2
Authors: Pastrana Erika , Moreno-Flores Maria Teresa , Gurzov Esteban N. , Avila Jesus , Wandosell Francisco , Diaz-Nido Javier
Published: May 2006

The molecular mechanisms used by olfactory ensheathing cells (OECs) to promote repair in the damaged adult mammalian CNS remain unknown. Thus, we used microarrays to analyze three OEC populations with different capacities to promote axonal regeneration in cultured rat retinal neurons. Gene expression in “long-term cultured OECs” that do not stimulate adult axonal outgrowth was compared with that of “primary olfactory ensheathing cells” and the immortalized OEC cell line TEG3. In this way, we identified a number of candidate genes that might play a role in promoting adult axonal regeneration. Among these genes, it was striking that both the matrix metalloproteinase 2 (MMP2) and an inhibitor of this protease were represented. The disruption of MMP2 activity in TEG3 cells impaired their capacity to trigger axon regeneration in cultured adult retinal neurons. Furthermore, the MMP2 protein was detected in grafts of OECs that elicited robust axonal regeneration in the injured spinal cord of adult ratsin vivo. These data suggest that MMP2 does indeed participate in adult axonal regeneration induced by OECs.