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Asymptomatic surveillance testing together with COVID-19-related research can lead to positive SARS-CoV-2 tests resulting not from true infections, but non-infectious, non-hazardous by-products of research (amplicons). Amplicons can be widespread and persistent in lab environments and can be difficult to distinguish for true infections. We discuss prevention and mitigation strategies., Asymptomatic surveillance testing is a powerful approach for rapid detection of SARS-CoV-2, currently utilized by multiple research institutes as part of routine pandemic response protocols. In combination with the recent explosion in COVID-19 related research, many research labs are working with SARS-CoV-2 genetic material. This raises a critical issue: some positive test results are due to the detection of the non-infectious, non-hazardous genetic sequences used for research (amplicons) instead of true COVID-19 infections. By collecting positive test results from several of the universities associated with this study, we identified a cohort of individuals working with SARS-CoV-2 genetic material for non-diagnostic purposes. Follow-up PCR and antibody tests on a subset of 39 individuals showed that 36 of those were not true COVID-19 cases, but instead their positive test result likely arose from amplicon contamination. In research labs working with genetic materials derived from the virus, environmental testing indicated amplicon residue might be present on surfaces including on notebooks, keyboards, drinking glasses, and doorknobs. Removal of individuals from standard testing protocols, per CDC guidelines for positive cases, risks the spread of true infection if the individuals were to be truly infected during the recommended 90 days no-testing period after an initial positive test. On the basis of this risk, combined with unnecessary isolation, quarantine, and contact tracing, we argue that it is critical to minimize instances of amplicon contamination and develop protocols for handling suspected cases to propel research efforts and avoid diverting resources from patients with COVID-19. Although our results show how amplicon contamination in research environments can lead to false positives, they also demonstrate that it is important to perform follow-up tests of those asymptomatic individuals because some might be cases of true infection. Given that amplicon contamination has not been a problem in CLIA labs, we discuss potential prevention and mitigation strategies and emphasize the relevance of this study beyond this pandemic.

The two neuronal populations in the cortex, pyramidal neurons and interneurons, can be separated based on neurotransmitter identity, however, within this segregation a large degree of diversity exists. Investigations into the molecular diversity of neurons are impeded by the inability to isolate cell populations born at different times for gene expression analysis. Developing interneurons may be distinguished by the expression of Glutamic Acid Decarboxylase-67 (GAD67). Neuronal birthdating using nucleoside analogs is an effective means of identifying coetaneous interneurons. Using these two features, neurotransmitter identity and birthdating, we have developed a method to isolate migrating interneurons using fluorescent-activated cell sorting (FACS) for RNA extraction and gene expression analysis. We utilized 5-ethynyl-2'-deoxyuridine (EdU) to birthdate interneuron cohorts and the GAD67 knock-in GFP transgenic mice to identify interneurons. In combination, we achieved simultaneous detection of GFP and EdU signals during FACS sorting of coetaneous interneurons with minimum loss of RNA integrity. RNA quality was deemed to be satisfactory by quantitative polymerase chain reaction (qPCR) for the interneuron-specific transcript Gad67.

Understanding the biomechanical mechanisms by which the cerebral cortex folds is a fundamental problem in neuroscience. Current mathematical models of cortical folding do not include three dimensional geometry or measurement of cortical growth in developing brains extracted from experimental data. We present two biomechanical models of cortical folding which integrate 3D geometry and information taken from MRI scans of fetal sheep brains at a number of key developmental stages. The first model utilises diffusion tensor imaging (DTI) measurements of white matter fibre orientation in the fetal sheep brains as a cue to the tension forces that may regulate folding. In the second model, tangential cortical growth is modelled by osmotic expansion of the tissue and regulated by inhomogeneous white matter rigidity as a biomechanism of cortical folding. This is based on quantitative analysis of cortical growth and inhomogeneous white matter anisotropy measured from the MRI data. We demonstrate that structural and diffusion tensor MRI can be combined with finite element modelling and an explicit growth mechanism of the cortex to create biologically meaningful models of the cortical folding process common to higher order mammals.

Migration is a dynamic process in which a cell searches the environment and translates acquired information into somal advancement. In particular, interneuron migration during development is accomplished by two distinct processes: the extension of neurites tipped with growth cones; and nucleus translocation, termed nucleokinesis. The primary purpose of our study is to investigate neurite branching and nucleokinesis using high-resolution time-lapse confocal microscopy and computational modeling. We demonstrate that nucleokinesis is accurately modeled by a spring-dashpot system and that neurite branching is independent of the nucleokinesis event, and displays the dynamics of a stochastic birth-death process. This is in contrast to traditional biological descriptions, which suggest a closer relationship between the two migratory mechanisms. Our models are validated on independent data sets acquired using two different imaging protocols, and are shown to be robust to alterations in guidance cues and cellular migratory mechanisms, through treatment with brain-derived neurotrophic factor, neurotrophin-4, and blebbistatin. We postulate that the stochastic branch dynamics exhibited by interneurons undergoing guidance-directed migration permit efficient exploration of the environment.

SummaryDevelopment of appropriate dendritic arbors is crucial for neuronal information transfer. We show, using seizure-related gene 6 (sez-6) null mutant mice, that Sez-6 is required for normal dendritic arborization of cortical neurons. Deep-layer pyramidal neurons in the somatosensory cortex of sez-6 null mice exhibit an excess of short dendrites, and cultured cortical neurons lacking Sez-6 display excessive neurite branching. Overexpression of individual Sez-6 isoforms in knockout neurons reveals opposing actions of membrane-bound and secreted Sez-6 proteins, with membrane-bound Sez-6 exerting an antibranching effect under both basal and depolarizing conditions. Layer V pyramidal neurons in knockout brain slices show reduced excitatory postsynaptic responses and a reduced dendritic spine density, reflected by diminished punctate staining for postsynaptic density 95 (PSD-95). In behavioral tests, the sez-6 null mice display specific exploratory, motor, and cognitive deficits. In conclusion, cell-surface protein complexes involving Sez-6 help to sculpt the dendritic arbor, in turn enhancing synaptic connectivity.

The effects of either cation removal or ionic channel blockade were determined on the dose-response curve (DRC) to PCH (pigment-concentrating hormone) in Macrobrachium potiuna erythrophores. In sodium-, potassium- and calcium-free salines, the pigment-aggregating responses to PCH were depressed; in the former condition, maximal aggregation was not achieved and the slope of the regression curve determined from the DRC was significantly different from control. Tetrodotoxin, verapamil or tetraethylammonium (TEA) treatments also diminished the pigment-aggregating responses to PCH, and the slopes of the regression curves were different from control in the presence of 10 −6 M verapamil or 10 −6 M TEA. Interestingly, the DRC determined in the absence of both sodium and calcium ions was not significantly different from control. When verapamil was applied in sodium-free conditions, maximal aggregation was prevented. The erythrophore resting membrane potential ranged from −62 mV to −78 mV and did not vary during PCH-induced pigment aggregation as compared to the control. Our results suggest that transient modifications of potassium equilibrium potential may interfere with PCH signal transduction, revealing a more relevant role of potassium in the process, and that a sodium influx and an intracellular calcium mobilization are necessary to maintain a cytosolic balance between the ions for normality of PCH-induced responses.

The finite element program HOT CRISP developed at Cambridge University allows the two dimensional coupled heat conduction and consolidation analysis of soil barriers subjected to temperature gradients. The analysis uses an elasto-plastic soil model based on the critical state principles. This paper presents prediction of temperature and pore water pressure changes in kaolin clay and comparison with experimental data. The experiments undertaken involved triaxial samples subjected to temperature changes at the outer boundary by a temperature controlled water circulation system. Temperature sensors and miniature pore water pressure transducers were used for the monitoring of temperature and pore water pressures at two locations in the soil samples. Tests were performed both under undrained and drained conditions. The comparison of data between experiments and analyses showed very satisfactory results.

In finite element analysis of soil-structure interaction problems involving firm to stiff overconsolidated clay, there have been difficulties in modelling the stress-strain response of the soil. Non-linearity and anisotropy of the soil depend on the inherent anisotropy of its particle structure and the induced anisotropy of its stress history and current stress path. In CRISP modelling of the centrifuge test of an abutment wall and its backfill of sand on the surface of a firm to stiff overconsolidated kaolin, the clay foundation was divided into 6 broad zones in accordance with the stress history and stress path. Undrained movements of the abutment and its subsoil were closely modelled in two analyses; one with a non-linear elastic model and the other with the Schofield model with shear modulus G assigned to the foundation zone in accordance with the estimated strain level as well as stress history and stress path. In the prediction of consolidation movement, there is a difficulty in the current critical state soil model in CRISP. The fe solution incorrectly predicted that substantial horizontal movement would accompany settlement due to consolidation, whereas the centrifuge test showed mainly vertical movement. This is attributable to the pronounced anisotropy separately observed in element tests.

One method currently being considered for the disposal of high level radio-active waste is burial in the seabed. When a hot object is buried in soil, the temperature of the soil adjacent to the object is raised and there is transient heat flow away from the object. The rise in the temperature of the soil causes excess pore pressures to be generated and transient pore water diffusion also takes place. A finite element formulation of the coupled heat flow and consolidation problem is presented. The computer implementation of this formulation is found to compare favourably with analytical solutions based on the same physical principles.

1. In S. marmoratus melanophores, the DRC to norepinephrine (NE) was shifted to the right (30-fold) by yohimbine 10−6 M, but was not affected by labetalol. Methoxamine and phenylephrine were inactive, even in the presence of propranolol and yohimbine. 2. Clonidine was also inactive, but induced a dose-dependent pigment aggregation ( ed 50 = 1.75× 16 −6 M ), which was diminished (10-fold) by yohimbine 10−6 M, within Poecilia reticulata melanophores. 3. 4-Bromophenacyl bromide, neomycin sulphate, dibucaine, H-7 and lithium chloride did not affect the DRC to NE. Beta-glycerophosphate 10−2 M shifted to the right (10-fold) the DRC to NE. 4. The adrenoceptors mediating melanosome aggregation within S. marmoratus melanophores can not be denned by the classical alpha;-agonists, but their activation is unrelated to the DG/IP3 pathway. These peculiar adrenoceptors may be structurally and pharmacologically different from the two, alpha1 and alpha2, subtypes.

The results of finite element analyses of soils in simple shear devices, assuming that these soils can be modelled either as an elastic or an elastoplastic material, are presented. The results indicate that an elastic analysis produces larger levels of stress concentrations than an analysis using the modified Cam-clay model. The predicted stress-strain behavior of a very loose sand and speswhite kaolin using the modified Cam-clay model agrees very well with simple shear test results deduced from measurements made at the sample core of the top boundary of the samples for constant load tests. A satisfactory match of experimental and modified Cam-clay stress-strain results was not obtained for the constant height test. The simple shear devices (Norwegian Geotechnical Institute and Cambridge types) can be expected to give good quality results for monotonic loading from carefully prepared samples if measurements of stress and pore water pressures are made at the sample core on either the top or bottom or both horizontal boundaries of the sample.