Lamina-specific AMPA receptor dynamics following visual deprivation in vivo.

Regulation of AMPA receptor (AMPAR) expression is central to synaptic plasticity and brain function, but how these changes occur in vivo remains elusive. Here, we developed a method to longitudinally monitor the expression of synaptic AMPARs across multiple cortical layers in awake mice using two-photon imaging. We observed that baseline AMPAR expression in individual spines is highly dynamic with more dynamics in primary visual cortex (V1) layer 2/3 (L2/3) neurons than V1 L5 neurons. Visual deprivation through binocular enucleation induces a synapse-specific and depth-dependent change of synaptic AMPARs in V1 L2/3 neurons, wherein deep synapses are potentiated more than superficial synapses. The increase is specific to L2/3 neurons and absent on apical dendrites of L5 neurons, and is dependent on expression of the AMPAR-binding protein GRIP1. Our study demonstrates that specific neuronal connections, across cortical layers and even within individual neurons, respond uniquely to changes in sensory experience

Depletion potentials in highly size-asymmetric binary hard-sphere mixtures: Comparison of accurate simulation results with theory

We report a detailed study, using state-of-the-art simulation and theoretical methods, of the depletion potential between a pair of big hard spheres immersed in a reservoir of much smaller hard spheres, the size disparity being measured by the ratio of diameters q=\sigma_s/\sigma_b. Small particles are treated grand canonically, their influence being parameterized in terms of their packing fraction in the reservoir, \eta_s^r. Two specialized Monte Carlo simulation schemes --the geometrical cluster algorithm, and staged particle insertion-- are deployed to obtain accurate depletion potentials for a number of combinations of q\leq 0.1 and \eta_s^r. After applying corrections for simulation finite-size effects, the depletion potentials are compared with the prediction of new density functional theory (DFT) calculations based on the insertion trick using the Rosenfeld functional and several subsequent modifications. While agreement between the DFT and simulation is generally good, significant discrepancies are evident at the largest reservoir packing fraction accessible to our simulation methods, namely \eta_s^r=0.35. These discrepancies are, however, small compared to those between simulation and the much poorer predictions of the Derjaguin approximation at this \eta_s^r. The recently proposed morphometric approximation performs better than Derjaguin but is somewhat poorer than DFT for the size ratios and small sphere packing fractions that we consider. The effective potentials from simulation, DFT and the morphometric approximation were used to compute the second virial coefficient B_2 as a function of \eta_s^r. Comparison of the results enables an assessment of the extent to which DFT can be expected to correctly predict the propensity towards fluid fluid phase separation in additive binary hard sphere mixtures with q\leq 0.1.Comment: 16 pages, 9 figures, revised treatment of morphometric approximation and reordered some materia

Policy Formulation Versus Policy Implementation Under the Magnuson-Stevens Fishery Conservation and Management Act: Insight from the North Pacific Crab Rationalization

The Magnuson-Stevens Fishery Conservation and Management Act (MSA) governs management of fisheries located three to 200 miles off the coast of the United States. The MSA is unique in administrative law in that it devolves policy formulation to eight Regional Fishery Management Councils rather than to a federal agency. That agency, the National Marine Fisheries Service (NMFS), is relegated primarily to developing regulations that implement the councils’ policies. NMFS can review the councils’ policies only to ensure that they are consistent with existing laws. NMFS has no authority to revise policy to suit its own preferences, or to write regulations that undercut council policy intent, except when conflicts with other applicable laws arise. The MSA’s legislative history reveals NMFS routinely undercuts this special administrative process through the regulations it writes. We review a recent example in which NMFS attempted to undermine the North Pacific Fishery Management Council’s crab rationalization policy through the regulation-writing process. We offer a simple solution to help avoid future abuse of administrative authority. This solution may have utility in other areas of administrative law in which authority to formulate policy is separated from the power to implement it

Vitamin D Status of Infants in Northeastern Rural Bangladesh: Preliminary Observations and a Review of Potential Determinants

Vitamin D deficiency is a global public-health concern, even in tropical regions where the risk of deficiency was previously assumed to be low due to cutaneous vitamin D synthesis stimulated by exposure to sun. Poor vitamin D status, indicated by low serum concentrations of 25-hydroxyvitamin D [25(OH)D], has been observed in South Asian populations. However, limited information is available on the vitamin D status of young infants in this region. Therefore, to gain preliminary insights into the vitamin D status of infants in rural Bangladesh, 25(OH)D was assessed in a group of community-sampled control participants in a pneumonia case-control study in rural Sylhet, Bangladesh (25°N) during the winter dry season (January-February). Among 29 infants aged 1-6 months, the mean 25(OH)D was 36.7 nmol/L [95% confidence interval (CI) 30.2-43.2]. The proportion of infants with vitamin D deficiency defined by 25(OH)D <25 nmol/L was 28% (95% CI 10-45), 59% (95% CI 40-78) had 25(OH)D<40 nmol/L, and all were below 80 nmol/L. From one to six months, there was a positive correlation between age and 25(OH)D (Spearman=0.65; p=0.0001). Within a larger group of 74 infants and toddlers aged 1-17 months (cases and controls recruited for the pneumonia study), young age was the only significant risk factor for vitamin D deficiency [25(OH)D <25 nmol/L]. Since conservative maternal clothing practices (i.e. veiling) and low frequency of intake of foods from animal source (other than fish) were common among the mothers of the participants, determinants of low maternal-infant 25(OH)D in Bangladesh deserve more detailed consideration in future studies. In conclusion, the vitamin D status in young infants in rural Sylhet, Bangladesh, was poorer than might be expected based on geographic considerations. The causes and consequences of low 25(OH)D in infancy and early childhood in this setting remain to be established

L'hybridation d'arbres aléatoires d'exploration et de basin hopping conduit à une exploration plus efficace des paysages énergétiques

The number of local minima of the PEL of molecular systems generally growsexponentially with the number of degrees of freedom, so that a crucial property of PEL explorationalgorithms is their ability to identify local minima which are low lying and diverse.In this work, we present a new exploration algorithm, retaining the ability of basin hopping (BH) toidentify local minima, and that of transition based rapidly growing random trees (T-RRT) to fosterthe exploration of yet unexplored regions. This ability is obtained by interleaving calls to theextension procedures of BH and T-RRT, and we show tuning the balance between these two typesof calls allows the algorithm to focus on low lying regions. Computational efficiency is obtainedusing state-of-the art data structures, in particular for searching approximate nearest neighbors inmetric spaces.We present results for the BLN69, a protein model whose conformational space has dimension 207and whose PEL has been studied exhaustively. On this system, we show that the propensity ofour algorithm to explore low lying regions of the landscape significantly outperforms those of BHand T-RRT

Decoherence of electron spin qubits in Si-based quantum computers

Direct phonon spin-lattice relaxation of an electron qubit bound by a donor impurity or quantum dot in SiGe heterostructures is investigated. The aim is to evaluate the importance of decoherence from this mechanism in several important solid-state quantum computer designs operating at low temperatures. We calculate the relaxation rate $1/T_1$ as a function of [100] uniaxial strain, temperature, magnetic field, and silicon/germanium content for Si:P bound electrons. The quantum dot potential is much smoother, leading to smaller splittings of the valley degeneracies. We have estimated these splittings in order to obtain upper bounds for the relaxation rate. In general, we find that the relaxation rate is strongly decreased by uniaxial compressive strain in a SiGe-Si-SiGe quantum well, making this strain an important positive design feature. Ge in high concentrations (particularly over 85%) increases the rate, making Si-rich materials preferable. We conclude that SiGe bound electron qubits must meet certain conditions to minimize decoherence but that spin-phonon relaxation does not rule out the solid-state implementation of error-tolerant quantum computing.Comment: 8 figures. To appear in PRB-July 2002. Revisions include: some references added/corrected, several typos fixed, a few things clarified. Nothing dramati

The Anatomy of the Facial Vein: Implications for Plastic, Reconstructive, and Aesthetic Procedures

Background: Anatomical knowledge of the facial vasculature is crucial for successful plastic, reconstructive, and minimally invasive procedures of the face. Whereas the majority of previous investigations focused on facial arteries, the precise course, variability, and relationship with adjacent structures of the facial vein have been widely neglected. Methods: Seventy-two fresh frozen human cephalic cadavers (32 male and 40 female cadavers;mean age, 75.2 +/- 10.9 years;mean body mass index, 24.2 +/- 6.6 kg/m(2);99 percent Caucasian ethnicity) were investigated by means of layer-by-layer anatomical dissection. In addition, 10 cephalic specimens were investigated using contrast agent-enhanced computed tomographic imaging. Results: The facial vein displayed a constant course in relation to the adjacent anatomical structures. The vein was identified posterior to the facial artery, anterior to the parotid duct, and deep to the zygomaticus major muscle. The angular vein formed the lateral boundary of the deep medial cheek fat and the premaxillary space, and the medial boundary of the deep lateral cheek fat and the suborbicularis oculi fat. The mean distance of the inferior and superior labial veins, of the deep facial vein, and of the angular vein from the inferior orbital margin was 51.6 +/- 3.1, 42.6 +/- 2.3, 27.4 +/- 3.0, and 4.2 +/- 0.7 mm, respectively. Conclusions: This work provides detailed information on the course of the facial vein in relation to neighboring structures. The presented clinically relevant anatomical observations and descriptions of landmarks will serve as helpful information for plastic, reconstructive, and aesthetic surgeons