bluuebunny/crossref_metadata_2025 huggingface dataset:
Earnings Mobility of Rural versus Urban Workers in Canada
Authors: Vera‐Toscano Esperanza , Weersink Alfons , Phimister Euan
Published: July 2005

The policy choice to enhance household income for poor, working families depends on the dynamics of individual earnings and their direct, albeit imperfect, link to household income levels. This paper assesses the factors affecting the dynamics of low pay for rural versus nonrural individuals in Canada. Approximately one‐quarter of the rural workers sampled in Statistics Canada's SLID data receive a wage less than two‐thirds of the median wage for the period and the percentage is increasing over time. In contrast, an average of 17% of workers in urban areas receives wages below this threshold. The low pay in rural areas is also “longer lasting,” either because the probability of an upward wage move is less, because the probability of moving out of the labor force is less, or because the probability of moving down from high pay is greater. Thus, direct mechanisms such as a minimum wage are likely to be more effective in rural areas. The higher probability of a move downward (either to low pay or out of the labor force) may be associated with greater seasonal work in rural areas. Hence, policy to address rural low pay may need to take seasonality into account more than in urban labor markets.
Social Welfare and the Selection of the Optimum Hog Slaughter Weight in Quebec
Authors: Goldsmith Peter D. , Pomar Candido , Tao Zhisong , Rivest Joel
Published: July 2005

What is the optimum slaughter weight? It depends from whose perspective. A dynamic systems model is built to analyze the welfare impact of alternative animal genetics, feeding program, feed quality and slaughter weight on producers, processors and the environment. The unique systems approach analyzes eight possible welfare rules and a corresponding harm function to assess animal performance within a multistakeholder context. The model results show there are significant tradeoff problems among producers, processors and the environment. The model highlights how the definition of animal performance needs to be revisited, as it has different meaning to different stakeholders in society. While performance historically was synonymous with production efficiency, with new social and political concerns, this interpretation is not universal. The model demonstrates greater complexities by broadening the set of affected parties.
Economic Returns to Feed Barley Yield‐increasing and Disease Resistance Research at the Alberta Field Crop Development Centre
Authors: Nagy Joseph G.
Published: July 2005

The Alberta Field Crop Development Centre (FCDC) at Lacombe has carried out an extensive research and development program on feed barley since 1973. Prior to 2002, FCDC released 11 hulled and six hull‐less barley varieties that have been adopted by farmers. The primary objective of this study is to estimate an economic rate of return to the FCDC barley research and development program from 1973 to 2001. A secondary objective is to include benefits arising from research that improved feed barley disease resistance in new cultivars in addition to benefits from purely higher‐yielding cultivar research. The analysis uses an ex post economic surplus methodology. Benefits are identified and empirically investigated for three separate FCDC feed barley research thrusts:

• benefits arising from FCDC research that developed new, higher‐yielding feed barley cultivars that give a yield advantage

• benefits arising from FCDC research that improved feed barley disease resistance in new cultivars that result in yield loss avoidance from disease

• benefits arising from FCDC research that developed new feed barley cultivars that yield higher silage production.

Of the total benefits from research on feed grain varieties, 52% can be attributed to yield advantage research and 48% to yield loss avoidance research. The overall internal rate of return with base elasticity parameters is estimated at 27%, ranging between 23% and 31%, depending on the assumptions made about the yield advantage and base variety. The IRR was sensitive to changes in supply elasticities and ranges from 20% (∈= 1.5) to 54% (∈= 0.1).
Household Composition and Brazilian Food Purchases: An Expenditure System Approach
Authors: Agüero Jorge M. , Gould Brian W.
Published: July 2005

The use of household level data for food demand analysis requires the researcher to address issues such as purchase censoring and the impacts of household age/gender composition on such demand. This analysis adopts an estimation approach to modeling censored food expenditures. The major methodological contribution of this analysis is our incorporation of an endogenous equivalence scale measure within the expenditure system. Our empirical application is concerned with Brazilian household food expenditures. We use the estimated adult equivalence scales to evaluate a measure of household welfare represented by per‐adult equivalent food expenditures. We find a significant shift of the distribution of per capita food distributions when comparing member count versus adult equivalent‐based per capita distributions.
Quantifying the Contribution of Plant Breeders’Rights and Transgenic Varieties to Canola Yields: Evidence from Manitoba
Authors: Carew Richard , Devadoss Stephen
Published: July 2005

Canola yield functions that account for plant breeders’rights, changes in technology, measures of varietal diversity and environmental conditions are estimated for the province of Manitoba for the period 1995–2001. Various measures are employed to estimate the effect of plant breeders’rights (PBR) on canola yields. Panel data models, which allow for differences in behavior over cross‐sectional units at the same point in time as well as differences in behavior over time for a given cross‐sectional unit, are used for the analysis. The performance of canola yield response functions are superior with random effects models. The adoption of transgenic varieties and varieties qualifying for PBR are positively associated with increasing yields. The policy implication of this study is that a greater commitment of public funds to fundamental research may be necessary to complement the applied research that private companies are undertaking in producing finished varieties.
Testing for Processor Market Power in the Markets for Cattle and Hogs in Canada
Authors: Quagrainie Kwamena , Unterschultz James , Veeman Michele , Jeffrey Scott
Published: July 2005

Deviations of livestock input prices from processor marginal value product are usually interpreted as an indication of the application of market power by the meat packing industry. However, market power depends on economic conditions that can influence the behavior of meat packers in the market for cattle and hogs. An industry‐level translog profit function is applied to data on the Canadian finished cattle and hog markets and industry‐wide oligopsony market power functions are estimated. The estimates suggest beef packers exercised a small but sustained amount of market power in the Canadian finished cattle market from 1978 to 1997. This is not the case in the market for hogs, which was competitive from 1960 to 1997. Application of market power in packers’purchases of farm animals decreased with increases in the utilization of domestic supply of slaughter animals and with increased levels of livestock exports. Livestock productivity increases appear to have significantly enhanced oligopsony power in packers’purchases of farm animals. The analysis suggests that beef processors may exert market power when cattle prices are relatively higher.
Information, Incentives and Institutions in the Agri‐food Sector
Authors: Hobbs Jill E.
Published: July 2005

This paper examines the factors driving changes in the agri‐food sector with respect to food safety, quality assurances, technological change and the environment. External shocks change the nature, size and distribution of transaction costs, leading to institutional adaptation. Asymmetric and incomplete information provides the underlying theme of the paper, which draws on transaction cost economics to provide insights into the role of incentive mechanisms and institutions for the delivery of credible quality signals to consumers.
Research in the Canadian Food Marketing Supply Chain System Post‐1986
Authors: Hawkins Murray H. , Copeland James
Published: July 2005

Economists have taken over the world. That's been a very negative factor because we have gone completely out of balance. I would hope that another trend, one that is broader, more humanistic and open to human beings rather than simply interested in maximizing shareholder value, will redress the balance. (Mintzberg 2002)
Improving Market Selection for Fed Beef Cattle: The Value of Real‐Time Ultrasound and Relations Data
Authors: Walburger Allan M. , Crews D. H.
Published: July 2005

The introduction of value‐based marketing has provided the industry with the means to price cattle based on their desired attributes and has provided an alternative marketing channel for producers to select. Gains can be made by selecting animals that will be “in the grid” for value‐based marketing channels while screening out animals that won't and sending them to dressed‐value or live‐weight marketing channels. This study estimates the gains from using real‐time ultrasound (RTU) as well as information on graded animal relations (i.e., animals that have the same parentage slaughtered and graded in previous years) to predict carcass quality and yield grades prior to slaughter. These predictions are used in an optimization model designed to select the marketing channel for individual animals that will maximize returns. The optimal marketing strategy from this study involves a mix of live‐weight, dressed‐weight and grid sales methods rather than marketing all of the animals together. The results suggest that increases in returns in the range of $0.61–27.26 per head from using relations data, $9.04‐16.75 per head from using RTU measures and $11.27‐27.93 per head from using both to selectively market beef animals. These estimates do not account for the gains that could be obtained from using RTU to improve market timing, i.e., to time when the animal will grade best.
Incidence of the 1996 Canada–U.S. Softwood Lumber Agreement and the Optimal Export Tax
Authors: Kinnucan Henry W. , Zhang Daowei
Published: July 2005

Our partial‐equilibrium analysis suggests 63% of the Canada‐U.S. Softwood Lumber Agreement's export tax is absorbed by Canadian consumers. Still, sufficient surplus was extracted from U.S. consumers for the agreement to be in Canada's national interest. In fact, the agreement was suboptimal from a Canadian perspective in that a higher tax rate would have raised national welfare, at least in the short run. Although the agreement decreased U.S. welfare, the net loss for the combined U.S. and Canadian economies is modest, about 5% of the bilateral softwood lumber trade value according to our baseline estimates. This suggests the agreement's tariff rate quota scheme is a reasonably efficient mechanism for redistributing economic surplus from U.S. consumers to producers. Still, a better policy may be to enlarge the softwood lumber market via a research and promotion program funded by a modest (say, 5%) tax on Canadian exports.
Transparency and Bidding Competition in International Wheat Trade
Authors: Wilson William W. , Dahl Bruce L.
Published: July 2005

One of the trade policy issues identified by U.S. interests, including grower groups, traders and policy makers, is price transparency. This has been a point of contention between the United States and Canada as well as other exporting countries with state trading enterprises (STEs). The transparency problem generally refers to the inability to observe terms of trade (including price, quality, credit, etc.)offered by STEs, and the potential strategic advantage this provides in bidding competition. A game theory model of import tendering is developed in this paper to examine the effects of information asymmetry among rivals. Several stylized examples are used to illustrate aspects of competition and to analyze effects on bidding strategies. Results indicate that:

Less uncertainty among rivals reduces equilibrium bids and prices.

Tenders with less transparency have the effect of increasing prices to buyers and payoffs to sellers.

Increases in the number of rivals have the effect of reducing bids and mitigating the informational advantages of STEs.

In all cases, less transparent sellers have an advantage in bidding relative to more transparent sellers. That advantage in our stylized case is in the area of $1–2/t. However, the advantage is reduced when there are many transparent rivals and in the case where transparent players act as agents for an STE.
Measurement and Testing for Equality of Foreign Price and Consumer Price Index Transmission in Russia
Authors: Arnade Carlos , Osborne Stefan
Published: July 2005

This paper tests for segmentation of retail meat markets in Russia before and after the financial crisis of 1998. Using monthly prices of pork and beef in 80 regions of Russia from 1994 to 1999, we measure the short‐run response of regional prices to changes in foreign prices and domestic inflation. We find that changes in both foreign prices and domestic inflation have distinct impacts on the prices of these commodities in different Russian cities, indicating that the markets are segmented in the short run. An analysis of the effect of the financial crisis shows that the response to the crisis was mixed, with some regions showing more evidence of segmentation than others.
Does the Exchange Rate Matter to Agricultural Bilateral Trade between Canada and the U.S.?
Authors: Kim Mina , Cho Gue Dae , Koo Won W.
Published: July 2005

This study examines the effects of the Canada–U.S. exchange rate on bilateral trade of agricultural goods between the two countries and on U.S. farm income. Special attention is given to agricultural trade between the two countries under the Canada–U.S. Free Trade Agreement (CUSTA). This study utilizes two time series models: the vector error correction model (VECM) and the vector moving average model (VMA) with quarterly time series data from 1983 to 2000. It is found that the exchange rate has a significant impact on U.S. agricultural trade with Canada, but the impact on U.S. agricultural price and income is insignificant. The exchange rate between the two currencies is found to be weakly exogenous in the U.S. agricultural sector, which answers a fundamental question about the role of the exchange rate in Canada–U.S. bilateral trade for agricultural products. In addition, the results point to a significant, though minimal, effect on bilateral trade due to CUSTA.
The Impact of Organizational Form on Producer Contracting Decisions
Authors: Zeuli Kimberly A. , King Robert P.
Published: July 2005

A variable that has not yet been considered in the contracting literature is the impact of agribusiness organizational form on the producer's contracting decision. Contracts with cooperatives are more complicated decisions for producers than a standard marketing contract with noncooperatives because of the requisite membership capital investment in the firm. Contracting with cooperatives requires producers to make a dual supply and investment decision. Individual membership equity holdings in all agricultural cooperatives are increasing, but they are generally most substantial in the value‐added, new‐generation cooperatives. Portfolio theory is used to analyze the producer's decision to contract with three alternatively structured value‐added processing organizations in an uncertain environment: a traditional cooperative, a new‐generation cooperative and an investor‐oriented firm. In the cooperative cases, the contract requires both supply and equity investment.
Quality Measurement and Contract Design: Lessons from the North American Sugarbeet Industry
Authors: Hueth Brent , Melkonyan Tigran
Published: July 2005

This paper examines contracts used in the North American sugarbeet industry. Though quite similar in many respects, the contracts we study vary across processing firms in the set of quality measures used to condition contract payments to growers. This is somewhat surprising, given the homogeneous nature of the processors' finished product (refined sugar). It seems unlikely that processors differ significantly in how they value the various attributes of a sugarbeet, and such a difference is perhaps the most natural reason to expect variation in the structure of quality incentives across processors. Previous attempts to explain the observed variation in sugarbeet contracts have focused on differences in organizational form across firms. In this paper, we provide an alternative explanation that relies on variation across production regions in growers' ability to control the relevant measures of sugarbeet quality.
Demand for Domestic and Imported Table Wine in British Columbia: A Source‐differentiated Almost Ideal Demand System Approach
Authors: Carew R. , Florkowski W. J. , He S.
Published: July 2005

The premium quality wine market in British Columbia has grown substantively over the past decade. However, few empirical studies exist to quantify how consumers have responded to these wines. This paper employs a source‐differentiated almost ideal demand system (AIDS) model with time‐varying parameters to estimate the demand for premium quality wines using scanner sales data from the British Columbia wine market. The empirical findings reveal that consumers' response to foreign‐produced wines differs from that for wine produced locally. It is evident that the expenditure elasticities for British Columbia, European and Rest‐of‐the‐World white wines are larger than those for red wines. The high expenditure elasticities associated with British Columbia white wines may suggest that these wines are associated with higher quality. We reject the hypotheses of block separability and product aggregation. There is no evidence of structural change from the tests employed in this paper.
Do Agricultural Commodity Prices Respond to Bans against Bioengineered Crops?
Authors: Parcell Joe L. , Kalaitzandonakes Nicholas G.
Published: July 2005

Bans against bioengineered food ingredients by major food companies have been broadly reported and have been often taken to signal demand shifts away from commodities in favor of identity‐preserved non‐bioengineered crops. Yet, the impacts of such bans have not been quantified and, indeed, the market size for non‐bioengineered crops remains unknown. We tested whether either the Chicago Board of Trade soybean futures prices (commodity) or the Tokyo Grain Exchange non‐GMO soybean futures prices (identity preserved market) responded to firm bans of bioengineered food ingredients. Neither the Chicago Board of Trade soybean futures prices nor the Tokyo Grain Exchange non‐GMO soybean futures prices respond to bans.
Evaluating the Effect of Conservation Policies on Agricultural Land Use: A Site‐specific Modeling Approach
Authors: Tanaka Katsuya , Wu JunJie
Published: July 2005

This study evaluates quantitatively the effect of three policies (payments for cropland retirement, fertilizer use taxes and payments for crop rotations) on agricultural land use in the upper Mississippi River basin. This is done by estimating two logit models of land use decisions using data from the 1982, 1987,1992 and 1997 Natural Resource Inventories. The models predict farmers' crop choice, crop rotation and participation in the Conservation Reserve Program (CRP) at more than 48,000 Natural Resource Inventories sites under each of the three policies. Results suggest that an increase in the CRP rental rates would significantly increase the CRP acreage, but most of the acreage increase would come initially from less fertilizer‐intensive crops. In contrast, a fertilizer use tax would significantly reduce acreage planted to more fertilizer‐intensive crops, and thus would likely be cost effective for reducing agricultural chemical use and pollution. Although an incentive payment for a corn‐soybean rotation would raise acreage of this rotation and reduce the acreage of continuous corn, the acreage response is in general quite inelastic.

Cette étude évalue quantitativement les effets rovoqués par les trois politiques (paiements pour le retrait des terres cultivables, taxes sur l'utilisation d'engrais et paiements pour l'alternance des cultures) sur les terres agricoles du bassin supérieur du Mississipi. Ceci est obtenu en évaluant deux modéles logit des décisions sur l'utilisation des terres provenant des données des «Natural Resource Inventories» de 1982, 1987, 1992 et 1997. Les modéles prédisent le choix des cultures des agriculteurs, l'alternance des cultures et la participation du «Conservation Reserve Program (CRP)» dans plus de 48 000 Natural Resource Inventories dans le cadre de chacune des trois politiques. Les résultats suggérent qu'une augmentation des taux de location du CRP accroisse de maniére significative la surface de CRP, mais la majeure partie de cet accroissement de surface provenaient initialement de cultures moins intensives sans engrais. Cependant, l'utilisation d'une taxe sur l'utilisation d'engrais pouvait réduire de maniére significative la surface plantée avec des récoltes intensives utilisant plus d'engrais, et ainsi ce serait sans doute plus économique pour réduire la pollution et l'utilisation de produits chimiques en agriculture. Bien que des paiements incitatifs à l'alternance maïs‐soja réduisent la surface d'une culture continue de maïs et augmentaient la surface de l'alternance maïs‐soja, les résultats aux transformations des surfaces des terres seraient tout à fait rigides.
Design and Costs of a Measurement Protocol for Trades in Soil Carbon Credits
Authors: Mooney Siân , Antle John , Capalbo Susan , Paustian Keith
Published: July 2005

Previous work has demonstrated that in the absence of transaction costs, contracts that pay producers per carbon (C) credit are more efficient than those that tie payments to changes in management practices. In this paper we develop a measurement protocol to support contracts for C credits and estimate its implementation costs using an empirical example. We find that the costs of implementing a measurement protocol for soil C credits depend on: the price of credits; the regional heterogeneity in C values as well as assumed error and confidence intervals. We find that the upper estimate of measurement costs associated with a contract that pays producers per C credit can be as little as 3% of the value of a credit. These contract measurement costs are less than the efficiency gains from implementing a per‐credit contract.

Des travaux antérieurs montrent que si la transaction ne coûte rien, les ententes prévoyant la rémuné ration des agriculteurs par cré dit carbone (C) sont plus efficaces que celles oè les paiements sont lié s à l'adaptation des pratiques culturales. Dans leur article, les auteurs proposent une mé thode de calculpour de telles ententes et estiment ce que coûterait son implantation au moyen d'un exemple empirique. On constate que, pour les cré dits C du sol, le coût de mise en æuvre dépend du prix des cré dits, de l'hé térogénéité régionale de la valeur des crédits ainsi que dxe l'erreur présumée et des intervalles de confiance. On se rend compte que la plus haute estimation du coût des ententes rémunérant les agriculteurs enfonction des crédits C ne dépasse pas trois pour cent de la valeur du crédit. De tels coûts sont inférieurs aux gains de productivité résultant de l'adoption d'une entente articulée sur les crédits C.
Nitrogen Fertilizer Demand from Danish Crop Farms: Regulatory Implications of Heterogeneity
Authors: Hansen Lars Gårn
Published: July 2005

This paper estimates nitrogen fertilizer demand elasticities for Danish crop farms using the dual profit function approach on micro panel data. The model includes several farm‐specific parameters, allowing us to estimate the mean demand elasticity and test for homogeneity of elasticities across panel farms. The mean own‐price elasticity for nitrogen is −0.45, and there is a significant standard deviation from this mean for individual farms of 0.24.

Heterogeneity of demand elasticities implies that regulating fertilizer application through mandated uniform percentage reductions, as is currently used in Danish nitrogen regulation, increases abatement costs relative to tax regulation. Somewhat surprisingly, this causes the abatement costs of quota regulation to be only 8% larger than with tax regulation. Simulation results indicate that the primary threat to the efficiency of uniform reduction schemes comes from inaccurate estimation of baselines rather than from heterogeneity of elasticities.

L'auteur estime les élasticités de la demande d'engrais azotés pour l'agriculture danoise en appliquant la fonction du double profit aux données issues de microgroupes de consultation. Le modèle inclut plusieurs paramètres spécifiques à l'agriculture, ce qui permet d'estimer l'élasticité moyenne de la demande et de vérifier l'homogénéité des élasticités pour les agriculteurs consultés. On constate qu'il existe une élasticité‐prix moyenne de −0,45 pour l'azote et que cette moyenne présente un écart‐type significatif de 0,24 par exploitation agricole.

Les élasticités hétérogènes de la demande supposent que si on régule les engrais azotés par une réduction uniforme du volume employé en pour cent, ainsi que l'exige présentment le règlement danois, on accroît le coût des mesures de lutte, comparativement à ce qui se produit avec les mesures fiscales. Il est un peu surprenant de voir que la régulation par quota n'augmente le coût des mesures de lutte que de 8%, par rapport aux mesures fiscales. Les résultats de la simulation révèlent que l'efficacité des programmes de réduction uniforme est surtout menacée par une estimation inexacte des valeurs de base et non par l'hétérogénéité des élasticités.
Measuring Real Capital Input in OECD Agriculture
Authors: Ball V. Eldon , Butault Jean‐Pierre , Mesonada Carlos San Juan
Published: July 2005

This paper provides a farm sector comparison of levels of capital input for 17 OECD countries. The estimates of capital input are derived by representing capital stock as a weighted sum of past investments. The weights correspond to the relative efficiencies of capital goods of different ages, so that the weighted components of capital stock have the same efficiency. We convert estimates of capital stock into estimates of capital services by means of capital rental prices. Comparisons of levels of capital input among countries require data on relative prices of capital input. We obtain relative price levels for capital input among countries via relative investment goods prices, taking into account the flow of capital input per unit of capital stock in each country.

Cet article se propose de comparer le niveau du capital dans Vagriculture de 17pays de l'OCDE. Les estimations du niveau de capital sont déduites en calculant un stock de capital comme une somme pondérée des investissements passés. Les poids utilisés correspondent a Vefficacite relative des biens capitaux à différents âges, de telle sorte que les différentes composantes du stock du capital ait la même efficacité. Le stock de capital est déduit une estimation des services de capital en utilisant un taux de rentabilité. Cette comparaison des niveaux de capital entre pays nécessite des données sur les prix relatifs du capital. Ces prix dépendent des prix relatifs des biens capitaux mais aussi des flux de service générés dans chaque pays par une unité de capital.
The Effect of Quality‐Environmental Investment on Horticultural Firms' Competitiveness
Authors: Galdeano‐Gómez Emilio , Céspedes‐Lorente José
Published: July 2005

The aim of this paper is to analyze the impact that environment‐friendly and management‐quality improvements have on the firm's competitiveness (profitability and market share) within the fresh fruit and vegetable sector. Andalusian farming/marketing entities (producer organizations) serve as a reference for our analysis. For these entities, there are subsidy programs aimed at developing quality and environmental practices. Such programs are a top priority for the CAP's Common Market Organizations. An analysis of a simultaneous equations model is suggested, considering the distinguishing effect of quality‐environmental investment and the possible endogeneity problems among the variables. The results show a positive correlation between the application of the aforementioned activities and the competitiveness of the horticultural firms.

L'objectif de ce travail c'est d'analyser l'impact des pratiques de production favorables à l'environnement ainsi que de la gestion de la qualité (rentabilité et part du marché) par rapport aux secteurs des fruits et légumes frais. Les organismes de commercialisation agricole d'Andalousie (organ‐ismes de production) représentent un point de référence pour notre analyse. Ces organismes bénéficient de programs d'aide au développement de la qualité et des pratiques favorables à l'environnement. Ces pro‐grammes constituent une priorité majeure pour les Organisations du Marché Commun dans le cadre des Politiques Agricoles Communes (PAC). Nous proposons ici une analyse d'un modèle aux équations simul‐tanées considérant l'effet caractéristique d'un investissement de qualité de l'environnement ainsi que les possibles problèmes à caractère endogène parmi les variables. Le résultat met en évidence une corrélation positive entre l'application des activités précédemment citées et la compétitivité des entreprises horticoles.
Exocytic responses of single leukaemic human cytotoxic T lymphocytes stimulated by agents that bypass the T cell receptor
Authors: Pores‐Fernando Arun T. , Bauer Roslyn A. , Wurth Georjeana A. , Zweifach Adam
Published: July 2005

Cytotoxic T lymphocytes kill targets via secretion of lytic agents including perforin and granzymes. Recently, new methods have been developed to monitor cytotoxic T lymphocyte degranulation. These include detecting the appearance of lysosome‐associated membrane protein on the cell's surface, and monitoring decreases in cellular perforin content. We have combined these methods with microscopy and flow cytometry to provide the first analysis of how single cytotoxic T cells degranulate. We used TALL‐104 human leukaemic cytotoxic T cells as a model system, and stimulated them with thapsigargin and PMA, soluble agents that mimic the two major signalling pathways activated by T cell receptor cross‐linking. Our results indicate that essentially every TALL‐104 cell responds to maximal stimulation by releasing about half of its lytic granule complement. This reflects complete release of the contents of half the cell's granules, rather than partial release of the contents of all of the granules. Sub‐maximal stimulation reduces both the fraction of cells that respond and the magnitude of single cell responses. We find that individual cells respond to maximal stimulation with a variable latency, and provide evidence that, once it starts, degranulation is a slow process taking tens of minutes.
Electrophysiological and molecular identification of voltage‐gated sodium channels in murine vascular myocytes
Authors: Saleh Sohag , Yeung Shuk Yin M. , Prestwich Sally , Pucovský Vladimír , Greenwood Iain
Published: July 2005

A voltage‐gated Na+ current was characterised in freshly dissociated mouse portal vein (PV) smooth muscle myocytes. The current was found superimposed upon the relatively slow L‐type Ca2+ current and was resistant to conventional Ca2+ channel blockers but was abolished by external Na+ replacement and tetrodotoxin (TTX, 1 μm). The molecular identity of the channel responsible for this conductance was determined by RT‐PCR where only the transcripts for Na+ channel genes SCN7a, 8a and 9a were detected. The presence of the protein counterparts to the SCN8a and 9a genes (NaV1.6 and NaV1.7, respectively) on the individual smooth muscle myocytes were confirmed in immunocytochemistry, which showed diffuse staining around a predominantly plasmalemmal location. TTX inhibited the action potential in individual myocytes generated in the current clamp mode but isometric tissue tension experiments revealed that TTX (1 and 5 μm) had no effect on the inherent mouse PV rhythmicity. However, the Na+ channel opener veratridine (10 and 50 μm) significantly increased the length of contraction and the interval between contractions. This effect was not influenced by pre‐incubation with atropine, prazosin and propranolol, but was reversed by TTX (1 μm) and completely abolished by nicardipine (1 μm). Furthermore, preincubation with the reverse‐mode Na+–Ca2+ exchange blocker KB‐R7943 (10 μm) also inhibited the veratridine response. We have established for the first time the molecular identity of the voltage‐gated Na+ channel in freshly dispersed smooth muscle cells and have shown that these channels can modulate contractility through a novel mechanism of action possibly involving reverse mode Na+–Ca2+ exchange.
Integration of K+and Cl–currents regulate steady‐state and dynamic membrane potentials in cultured rat microglia
Authors: Newell Evan W. , Schlichter Lyanne C.
Published: July 2005

The role of ion channels and membrane potential (Vm) in non‐excitable cells has recently come under increased scrutiny. Microglia, the brain's resident immune cells, express voltage‐gated Kv1.3 channels, a Kir2.1‐like inward rectifier, a swelling‐activated Cl–current and several other channels. We previously showed that Kv1.3 and Cl–currents are needed for microglial cell proliferation and that Kv1.3 is important for the respiratory burst. Although their mechanisms of action are unknown, one general role for these channels is to maintain a negativeVm. An impediment to measuringVmin non‐excitable cells is that many have a very high electrical resistance, which makes them extremely susceptible to leak‐induced depolarization. Using non‐invasiveVm‐sensitive dyes, we show for the first time that the membrane resistance of microglial cells is several gigaohms; much higher than the seal resistance during patch‐clamp recordings. Surprisingly, we observed that small current injections can evoke largeVmoscillations in some microglial cells, and that injection of sinusoidal currents of varying frequency exposes a strong intrinsic electrical resonance in the 5‐ to 20‐Hz frequency range in all microglial cells tested. Using a dynamic current clamp that we developed to actively compensate for the damage done by the patch‐clamp electrode, we found that theVmoscillations and resonance were more prevalent and larger. Both types of electrical behaviour required Kv1.3 channels, as they were eliminated by the Kv1.3 blocker, agitoxin‐2. To further determine how the ion currents integrate in these cells, voltage‐clamp recordings from microglial cells displaying these behaviours were used to analyse the biophysical properties of the Kv1.3, Kir and Cl–currents. A mathematical model that incorporated only these three currents reproduced the observedVmoscillations and electrical resonance. Thus, the electrical behaviour of this ‘non‐excitable’ cell type is much more complex than previously suspected, and might reflect a more common oversight in high resistance cells.
TASK‐like K+channels mediate effects of 5‐HT and extracellular pH in rat dorsal vagal neuronesin vitro
Authors: Hopwood Sarah E. , Trapp Stefan
Published: July 2005

Dorsal vagal neurones (DVN) receive serotonergic projections from the medullary raphé nuclei, suggesting that 5‐HT modulates vagal activity. A previous study has shown that 5‐HT excites DVN in part by inhibition of a K+current via postsynaptic 5‐HT2Areceptors. As mRNA for the two‐pore‐domain K+channels TASK‐1 (KCNK3) and TASK‐3 (KCNK9) has been found in DVN, we investigated the possibility that 5‐HT exerts its effects via inhibition of these K+channels using whole‐cell patch‐clamp techniques. In current clamp, 5‐HT (20 μm) elicited a depolarization by 5.1 ± 1.5 mV and an increase in firing rate. In voltage clamp, 5‐HT reduced the standing outward current (ISO) at −20 mV by 106 ± 17 pA, inhibiting a conductance (reversal, −95 ± 4 mV) which displayed Goldman‐Hodgkin‐Katz outward rectification, supportive of a TASK‐like K+current. Since TASK channels are modulated by extracellular pH (pHo), we next investigated the pH sensitivity ofISOin Hepes‐buffered ACSF. At pHo7.3, DVN exhibited anISOof 147 ± 15 pA at −20 mV. Acidification to pHo6.3 reducedISOto 85 ± 13 pA, whereas raising pHoto 8.5 increasedISOto 216 ± 26 pA. At pHo7.3,ISOwas inhibited by BaCl2(IC50465 μm), but unaffected by ZnCl2(100 μm). 5‐HT (10 μm) reducedISOby 114 ± 17 pA at pHo7.3, but at pHo6.3 the 5‐HT‐induced inhibition ofISOwas significantly smaller. The present data suggest that the excitatory effects of 5‐HT on DVN are mediated in part by inhibition of a TASK‐like, pH‐sensitive K+conductance. The pharmacological profile of this conductance excludes TASK‐3 homomers, but rather implicates TASK‐1‐containing channels.
β‐Scorpion toxin effects suggest electrostatic interactions in domain II of voltage‐dependent sodium channels
Authors: Mantegazza Massimo , Cestèle Sandrine
Published: July 2005

β‐Scorpion toxins specifically modulate the voltage dependence of sodium channel activation by acting through a voltage‐sensor trapping model. We used mutagenesis, functional analysis and the action of β‐toxin as tools to investigate the existence and role in channel activation of molecular interactions between the charged residues of the S2, S3 and S4 segments in domain II of sodium channels. Mutating to arginine the acidic residues of the S2 and S3 transmembrane segments in domain II, or making charge‐reversal mutation of the two outermost gating charges of the IIS4 voltage sensor, shifts the voltage dependence of channel activation to more positive potentials and enhances the effect of β‐scorpion toxin. Thus, mutations of acidic residues in IIS2 and IIS3 segments are able to promote voltage‐sensor trapping in a way that is similar to the mutations of the arginines in the IIS4 segment. In order to disclose the network of interactions among acidic and basic residues we performed functional analysis of charge‐inversion double mutants: our data suggest that the first arginine of the voltage sensor S4 in domain II (R850) interacts specifically with E805, D814 and E821 in the S2 and S3 segments, whereas the second arginine (R853) only interacts with D827 in the S3 segment. Our results suggest that the S2, S3 and S4 segments in domain II form a voltage‐sensing structure, and that molecular interactions between the charged residues of this structure modulate the availability of the IIS4 voltage sensor for trapping by β‐toxins. They also provide unique insights into the molecular events that occur during channel activation, as well as into the structure of the channel.
Glucose‐induced electrical activity in rat pancreatic β‐cells: dependence on intracellular chloride concentration
Authors: Best L.
Published: July 2005

A rise in glucose concentration depolarizes the β‐cell membrane potential leading to electrical activity and insulin release. It is generally believed that closure of KATP channels underlies the depolarizing action of glucose, though work from several laboratories has indicated the existence of an additional anionic mechanism. It has been proposed that glucose activates a volume‐regulated anion channel, generating an inward current due to Cl− efflux. This mechanism requires that intracellular [Cl−] is maintained above its electrochemical equilibrium. This hypothesis was tested in rat β‐cells by varying [Cl−] in the patch pipette solution using the Cl−‐permeable antibiotic amphotericin B to allow Cl− equilibration with the cell interior. Under such conditions, a depolarization and electrical activity could be evoked by 16 mm glucose with pipette solutions containing 80 or 150 mm Cl−. At 40 or 20 mm Cl−, a subthreshold depolarization was usually observed, whilst further reduction to 12 or 6 mm abolished depolarization, in some cases leading to a glucose‐induced hyperpolarization. With a pipette solution containing gramicidin, which forms Cl−‐impermeable pores, glucose induced a depolarization and electrical activity irrespective of [Cl−] in the pipette solution. Under the latter conditions, glucose‐induced electrical activity was prevented by bumetanide, an inhibitor of the Na+–K+–2Cl− co‐transporter. This inhibition could be overcome by the use of amphotericin B with a high [Cl−] pipette solution. These findings suggest that the maintenance of high intracellular [Cl−] in the β‐cell is an important determinant in glucose‐induced depolarization, and support the hypothesis that β‐cell stimulation by glucose involves activation of the volume‐regulated anion channel and generation of an inward Cl− current.
Erectile dysfunction in mice lacking the large‐conductance calcium‐activated potassium (BK) channel
Authors: Werner Matthias E. , Zvara Peter , Meredith Andrea L. , Aldrich Richard W. , Nelson Mark T.
Published: July 2005

Penile erection is dependent on the nitric oxide (NO)/cGMP‐dependent protein kinase I (PKGI) pathway. One important target of PKGI in smooth muscle is the large‐conductance, calcium‐activated potassium (BK) channel, which upon activation hyperpolarizes the smooth muscle cell membrane, causing relaxation. Relaxation of arterial and corpus cavernosum smooth muscle (CCSM) is necessary to increase blood flow into the corpora cavernosa that leads to penile tumescence. We investigated the functional role of BK channels in the corpus cavernosum utilizing a knock‐out mouse lacking the Slo gene (Slo−/−) responsible for the pore‐forming subunit of the BK channel. Whole‐cell currents were recorded from isolated CCSM cells of Slo+/+ and Slo−/− mice. Iberiotoxin‐sensitive voltage‐ and [Ca2+]‐activated K+ currents, the latter activated by local transient calcium releases (calcium sparks), were present in Slo+/+ CCSM cells, but absent in Slo−/− cells. CCSM strips from Slo−/− mice demonstrated a four‐fold increase in phasic contractions, in the presence of phenylephrine. Nerve‐evoked relaxations of precontracted strips were reduced by 50%, both in strips from Slo−/− mice and by blocking BK channels with iberiotoxin in the Slo+/+ strips. Consistent with the in vitro results, in vivo intracavernous pressure exhibited pronounced oscillations in Slo−/− mice, but not in Slo+/+ mice. Furthermore, intracavernous pressure increases to nerve stimulation, in vivo, were reduced by 22% in Slo−/−mice. These results indicate that the BK channel has an important role in erectile function, and loss of the BK channel leads to erectile dysfunction.
Ultrafast X-ray Diffraction of Transient Molecular Structures in Solution
Authors: Ihee H. , Lorenc M. , Kim T. K. , Kong Q. Y. , Cammarata M. , Lee J. H. , Bratos S. , Wulff M.
Published: July 2005

We report direct structural evidence of the bridged radical (CH
2
ICH
2
·) in a polar solution, obtained using time-resolved liquid-phase x-ray diffraction. This transient intermediate has long been hypothesized to explain stereo-chemical control in many association and/or dissociation reactions involving haloalkanes. Ultrashort optical pulses were used to dissociate an iodine atom from the haloethane molecule (C
2
H
4
I
2
) dissolved in methanol, and the diffraction of picosecond x-ray pulses from a synchrotron supports the following structural dynamics, with ∼0.01 angstrom spatial resolution and ∼100 picosecond time resolution: The loss of one iodine atom from C
2
H
4
I
2
leads to the C-I-C triangular geometry of CH
2
ICH
2
·. This transient C
2
H
4
I then binds to an iodine atom to form a new species, the C
2
H
4
I-I isomer, which eventually decays into C
2
H
4
+ I
2
. Solvent dynamics were also extracted from the data, revealing a change in the solvent cage geometry, heating, and thermal expansion.
Genome-Wide RNAi Screen for Host Factors Required for Intracellular Bacterial Infection
Authors: Agaisse Hervé , Burrack Laura S. , Philips Jennifer A. , Rubin Eric J. , Perrimon Norbert , Higgins Darren E.
Published: July 2005

Most studies of host-pathogen interactions have focused on pathogen-specific virulence determinants. Here, we report a genome-wide RNA interference screen to identify host factors required for intracellular bacterial pathogenesis. Using
Drosophila
cells and the cytosolic pathogen
Listeria monocytogenes
, we identified 305 double-stranded RNAs targeting a wide range of cellular functions that altered
L. monocytogenes
infection. Comparison to a similar screen with
Mycobacterium fortuitum
, a vacuolar pathogen, identified host factors that may play a general role in intracellular pathogenesis and factors that specifically affect access to the cytosol by
L. monocytogenes
.
AUTISM: A Window Onto the Development of the Social and the Analytic Brain
Authors: Baron-Cohen Simon , Belmonte Matthew K.
Published: July 2005

Although the neurobiological understanding of autism has been increasing exponentially, the diagnosis of autism spectrum conditions still rests entirely on behavioral criteria. Autism is therefore most productively approached using a combination of biological and psychological theory. The triad of behavioral abnormalities in social function, communication, and restricted and repetitive behaviors and interests can be explained psychologically by an impaired capacity for empathizing, or modeling the mental states governing the behavior of people, along with a superior capacity for systemizing, or inferring the rules governing the behavior of objects. This empathizing-systemizing theory explains other psychological models such as impairments of executive function or central coherence, and may have a neurobiological basis in abnormally low activity of brain regions subserving social cognition, along with abnormally high activity of regions subserving lower-level, perceptual processing—a pattern that may result from a skewed balance of local versus long-range functional connectivity.
DENDRITIC COMPUTATION
Authors: London Michael , Häusser Michael
Published: July 2005

One of the central questions in neuroscience is how particular tasks, or computations, are implemented by neural networks to generate behavior. The prevailing view has been that information processing in neural networks results primarily from the properties of synapses and the connectivity of neurons within the network, with the intrinsic excitability of single neurons playing a lesser role. As a consequence, the contribution of single neurons to computation in the brain has long been underestimated. Here we review recent work showing that neuronal dendrites exhibit a range of linear and nonlinear mechanisms that allow them to implement elementary computations. We discuss why these dendritic properties may be essential for the computations performed by the neuron and the network and provide theoretical and experimental examples to support this view.
MOLECULAR GRADIENTS AND DEVELOPMENT OF RETINOTOPIC MAPS
Authors: McLaughlin Todd , O'Leary Dennis D.M.
Published: July 2005

Gradients of axon guidance molecules have long been postulated to control the development of the organization of neural connections into topographic maps. We review progress in identifying molecules required for mapping and the mechanisms by which they act, focusing on the visual system, the predominant model for map development. The Eph family of receptor tyrosine kinases and their ligands, the ephrins, remain the only molecules that meet all criteria for graded topographic guidance molecules, although others fulfill some criteria. Recent reports further define their modes of action and new roles for them, including EphB/ephrin-B control of dorsal-ventral mapping, bidirectional signaling of EphAs/ephrin-As, bifunctional action of ephrins as attractants or repellents in a context-dependent manner, and complex interactions between multiple guidance molecules. In addition, spontaneous patterned neural activity has recently been shown to be required for map refinement during a brief critical period. We speculate on additional activities required for map development and suggest a synthesis of molecular and cellular mechanisms within the context of the complexities of map development.