4,448 research outputs found

    Glutamatergic Plasticity in Medial Prefrontal Cortex and Ventral Tegmental Area Following Extended-Access Cocaine Self-Administration

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    Glutamate signaling in prefrontal cortex and ventral tegmental area plays an important role in the molecular and behavioral plasticity associated with addiction to drugs of abuse. The current study investigated the expression and postsynaptic density redistribution of glutamate receptors and synaptic scaffolding proteins in dorsomedial and ventromedial prefrontal cortex and ventral tegmental area after cocaine self-administration. After 14 days of extended-access (6 h/day) cocaine self-administration, rats were exposed to one of three withdrawal regimen for 10 days. Animals either stayed in home cages (Home), returned to self-administration boxes with the levers withdrawn (Box), or underwent extinction training (Extinction). Extinction training was associated with significant glutamatergic plasticity. In dorsomedial prefrontal cortex of the Extinction group, there was an increase in postsynaptic density GluR1, PSD95, and actin proteins; while postsynaptic density mGluR5 protein decreased and there was no change in NMDAR1, Homer1b/c, or PICK1 proteins. These changes were not observed in ventromedial prefrontal cortex or ventral tegmental area. In ventral tegmental area, Extinction training reversed the decreased postsynaptic density NMDAR1 protein in the Home and Box withdrawal groups. These data suggest that extinction of drug seeking is associated with selective glutamatergic plasticity in prefrontal cortex and ventral tegmental area that include modulation of receptor trafficking to postsynaptic density

    Reallocation, Firm Turnover, and Efficiency: Selection on Productivity or Profitability?

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    There is considerable evidence that producer-level churning contributes substantially to aggregate (industry) productivity growth, as more productive businesses displace less productive ones. However, this research has been limited by the fact that producer-level prices are typically unobserved; thus within-industry price differences are embodied in productivity measures. If prices reflect idiosyncratic demand or market power shifts, high "productivity" businesses may not be particularly efficient, and the literature's findings might be better interpreted as evidence of entering businesses displacing less profitable, but not necessarily less productive, exiting businesses. In this paper, we investigate the nature of selection and productivity growth using data from industries where we observe producer-level quantities and prices separately. We show there are important differences between revenue and physical productivity. A key dissimilarity is that physical productivity is inversely correlated with plant-level prices while revenue productivity is positively correlated with prices. This implies that previous work linking (revenue-based) productivity to survival has confounded the separate and opposing effects of technical efficiency and demand on survival, understating the true impacts of both. We further show that young producers charge lower prices than incumbents, and as such the literature understates the productivity advantage of new producers and the contribution of entry to aggregate productivity growth.

    The Impact of State Physical Education Requirements on Youth Physical Activity and Overweight

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    To combat childhood overweight, which has risen dramatically in the past three decades, many medical and public health organizations have called for students to spend more time in physical education (PE) classes. This paper is the first to exploit state PE requirements as quasi-natural experiments in order to estimate the causal impact of PE on student activity and weight. We study nationwide data from the YRBSS for 1999, 2001, and 2003 merged with data on state minimum PE requirements from the 1994 and 2000 School Health Policies and Programs Study and the 2001 Shape of the Nation Report. We find that certain state regulations are effective in raising the number of minutes during which students are active in PE. Our results also indicate that additional PE time raises the number of days per week that students report having exercised or engaged in strength-building activities, but lowers the number of days in which students report light physical activity. PE time has no detectable impact on youth BMI or the probability that a student is overweight. We conclude that while raising PE requirements may make students more active by some (but not all) measures, there is not yet the scientific base to declare raising PE requirements an anti-obesity initiative.

    The Slow Growth of New Plants: Learning about Demand?

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    It is well known that new businesses are typically much smaller than their established industry competitors, and that this size gap closes slowly. We show that even in commodity-like product markets, these patterns do not reflect productivity gaps, but rather differences in demand-side fundamentals. We document and explore patterns in plants’ idiosyncratic demand levels by estimating a dynamic model of plant expansion in the presence of a demand accumulation process (e.g., building a customer base). We find active accumulation driven by plants’ past production decisions quantitatively dominates passive demand accumulation, and that within-firm spillovers affect demand levels but not growth.

    Atypical Work: Who Gets It, and Where Does It Lead? Some U.S. Evidence Using the NLSY79

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    Atypical work arrangements have long been criticized as offering more precarious and lower paid work than regular open-ended employment. In an important paper, Booth et al. (2002) were among the first to recognize that notwithstanding their potential deficiencies, such jobs also functioned as a stepping stone to permanent work. This conclusion proved prescient and has received increasing support in Europe. In the present note, we provide a parallel analysis to Booth et al. for the United States ‚Äď somewhat of a missing link in the evolving empirical literature ‚Äď and obtain not dissimilar similar findings for the category of temporary workers as do they for fixed-term contract workers.atypical work, temporary jobs, contracting/consulting work, regular open-ended employment, earnings development

    Design and Construction of a Programmable Electroporation system for Biological Applications

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    Studies into electroporation have grown rapidly in biotechnology and medicine in recent years. This paper presents the design and construction of a low cost programmable electroporation system for biological applications. The system consists of a control module, a pulse generation circuit and a high voltage switch using a power MOSFET. The programmable electroporation has been designed, developed and tested. Using a standard commercial electroporation cuvette, it is possible to generate electric fields of 100 to 1000V/cm with programmed pulse lengths of 10?sec to 20msec. The system was evaluated with Hela cells and propidium dye to evaluate transfection rates under a variety of electroporation conditions. Initial results showed that the electroporation system achieved a peak cell transfection efficiency of 48.74% at 600V/cm with pulse lengths of 10 ms

    Behavioural simulation of biological neuron systems using VHDL and VHDL-AMS

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    The investigation of neuron structures is an incredibly difficult and complex task that yields relatively low rewards in terms of information from biological forms (either animals or tissue). The structures and connectivity of even the simplest invertebrates are almost impossible to establish with standard laboratory techniques, and even when this is possible it is generally time consuming, complex and expensive. Recent work has shown how a simplified behavioural approach to modelling neurons can allow ‚Äúvirtual‚ÄĚ experiments to be carried out that map the behaviour of a simulated structure onto a hypothetical biological one, with correlation of behaviour rather than underlying connectivity. The problems with such approaches are numerous. The first is the difficulty of simulating realistic aggregates efficiently, the second is making sense of the results and finally, it would be helpful to have an implementation that could be synthesised to hardware for acceleration. In this paper we present a VHDL implementation of Neuron models that allow large aggregates to be simulated. The models are demonstrated using a system level VHDL and VHDL-AMS model of the C. Elegans locomotory system

    Minimum Wage Increases Under Straightened Circumstances

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    Do apparently large minimum wage increases in an environment of recession produce clearer evidence of disemployment effects than is typically observed in the new minimum wage literature? This paper augments the sparse literature on the most recent increases in the U.S. minimum wage, using three different data sets and the two main estimation strategies for handling geographically-disparate trends. The evidence is generally unsupportive of negative employment effects, still less of a 'recessionary multiplier.' Minimum wage workers seem to be concentrated in sectors of the economy for which the labor demand response to wage mandates is minimal.minimum wages, disemployment, earnings, low-wage sectors, geographically-disparate employment trends, recession

    Atypical Work: Who Gets It, and Where Does It Lead? Some U.S. Evidence Using the NLSY79

    Get PDF
    Atypical work arrangements have long been criticized as offering more precarious and lower paid work than regular open-ended employment. In an important paper published in this journal, Booth et al. (2002) were among the first to recognize that notwithstanding their potential deficiencies, such jobs also functioned as a stepping stone to permanent work. This conclusion proved prescient and has received increasing support in Europe. In the present note, we provide a parallel analysis to Booth et al. for the United States ‚Äď somewhat of a missing link in the evolving empirical literature ‚Äď and obtain not dissimilar similar findings for the category of temporary workers as do they for fixed-term contract workers.
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