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Results for “systems drift”

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PubMed1995

Selective chemisorption and detoxification of aflatoxins by phyllosilicate clay.

Practical and effective strategies for the detoxification of aflatoxins are critically needed. We have shown that a phyllosilicate clay (HSCAS): i) tightly binds aflatoxins in aqueous solutions, including milk; ii) markedly decreases the bioavailability of radiolabeled aflatoxins; iii) greatly diminishes aflatoxicosis in young animals, i.e., rats, chickens, turkeys, lambs, and pigs; and iv) reduces the level of aflatoxin M1 in the milk from lactating dairy cattle and goats. In further studies, ligands with one or more of the functional groups in common with aflatoxin were reacted with HSCAS in vitro in an attempt to elucidate the specificity and mechanism of tight binding (or chemisorption). A chemisorption index (C alpha) was developed, allowing for direct comparison of various clay and zeolitic minerals with HSCAS. Chemisorption indices were determined by HPLC analysis of extracts of the supernatants and sorbed pellets (exhaustively extracted with methanol and chloroform). The beta-dicarbonyl system of aflatoxin was found to be essential for tight binding by HSCAS. Comparison of the chemisorption indices from various classes of compounds with spectral data (DRIFTS) indicated that the molecular mechanism of aflatoxin binding may involve the chelation of metal ions in HSCAS with the beta-dicarbonyl moiety in aflatoxin. Computer modeling was utilized to provide additional information. Preliminary evidence suggests that aflatoxin B1 may react at surfaces and within the interlayers of HSCAS particles. With knowledge of the mechanism involved, it has been possible to further enhance the propensity of HSCAS for aflatoxins.

Aflatoxins↗

PubMed1997

Recombinant expression and secretion of a natural splicing variant containing the ectodomain of porcine LH receptor in HC11 mammary epithelial cells.

Large-scale synthesis of active recombinant porcine luteinizing hormone/chorionic gonadotropin receptor (pLHR) is required for biophysical and structural studies. This study was undertaken to improve expression of the corresponding cDNA already obtained with a number of other systems, (i) by turning to cells from mammalian origin able to perform adequate glycosylation, (ii) by using an expression vector containing the acknowledged high-performance rabbit WAP gene upstream region together with transcription and translation stimulating sequences, and (iii) by expressing natural splicing variants. Selection of the transfected HC11 cells was performed in terms of pLHR expression using specific radioligand binding and immunoradiometric assays. Secretion of pLHR ectodomain into the culture medium of the HC11 clones was quantified, and reached 70 ng/ml, which represents the highest active amount ever produced. However, this level of expression was relatively low in comparison to that currently observed with bGH cDNA used as reporter gene. Additional investigations were performed in order to gain further insight into the limitation of the production of pLHR relative to bovine or human growth hormone using the same expression system. A high number of copies of cDNA in the genome of HC11 cells was found, provided that an antibiotic selection pressure was maintained to avoid drifting. The low mRNA levels detected for pLHR relative to hGH mRNAs correlate well with the relative protein production levels. They could arise from poor stability of mRNAs, a fact already observed for the natural receptor in gonadal cells. These results thus constitute a promising indicator for possible expression of pLHR in the milk of transgenic animals.

Animals↗

PubMed2000

Inbreeding depression due to mildly deleterious mutations in finite populations: size does matter.

We studied the effects of population size on the inbreeding depression and genetic load caused by deleterious mutations at a single locus. Analysis shows how the inbreeding depression decreases as population size becomes smaller and/or the rate of inbreeding increases. This pattern contrasts with that for the load, which increases as population size becomes smaller but decreases as inbreeding rate goes up. The depression and load both approach asymptotic limits when the population size becomes very large or very small. Numerical results show that the transition between the small and the large population regimes is quite rapid, and occurs largely over a range of population sizes that vary by a factor of 10. The effects of drift on inbreeding depression may bias some estimates of the genomic rate of deleterious mutation. These effects could also be important in the evolution of breeding systems in hermaphroditic organisms and in the conservation of endangered populations.

Genetics, Population↗

PubMed2005

Molecular evolution of the rice miR395 gene family.

MicroRNAs (miRNAs) are 20-22 nucleotide non-coding RNAs that play important roles in plant and animal development. They are usually processed from larger precursors that can form stem-loop structures. Among 20 miRNA families that are conserved between Arabidopsis and rice, the rice miR395 gene family was unique because it was organized into compact clusters that could be transcribed as one single transcript. We show here that in fact this family had four clusters of total 24 genes. Three of these clusters were segmental duplications. They contained miR395 genes of both 120 bp and 66 bp long. However, only the latter was repeatedly duplicated. The fourth cluster contained miR395 genes of two different sizes that could be the consequences of intergenic recombination of genes from the first three clusters. On each cluster, both 1-duplication and 2-duplication histories were observed based on the sequence similarity between miR395 genes, some of which were nearly identical suggesting a recent origin. This was supported by a miR395 locus survey among several species of the genus Oryza, where two clusters were only found in species with an AA genome, the genome of the cultivated rice. A comparative study of the genomic organization of Medicago truncatula miR395 gene family showed significant expansion of intergenic spaces indicating that the originally clustered genes were drifting away from each other. The diverse genomic organizations of a conserved microRNA gene family in different plant genomes indicated that this important negative gene regulation system has undergone dramatic tune-ups in plant genomes.

Base Sequence↗

PubMed1975

[Tolerance and immunogenicity of an attenuated live influenza virus vaccine in man (author's transl)].

The attenuated influenza-A-virus strain "Alice" (H3N2) - A Recombination from A2/England/72 and A/PR8 Mount Sinai/34 - was given intransally in drops (10(7,2) ID50 per dose), twice seven days apart. In a similar fashion, 25 healthy persons received placebos. Local antibodies were determined before and three weeks after the first vaccination from nasal irrigation fluid. The fluid was concentrated and adjusted to an IgA amount of 50 mg/l. Blood samples were obtained at similar intervals. Systemic antibody formation was comparable to that obtained with inactivated virus vaccine. There was good antibody formation against retrospective and prospective virus strains of the actual drift period. The conversion rate of antineuraminidase antibodies was comparable to that obtained with inactivated virus vaccine. The locally induced antibodies behaved predominantly in a strain-specific manner. However, there were also reactions with the virus strains Port Chalmers and Hong Kong. Live vaccine should in future be used in "drift" times, while inactivated virus vaccine should be used in shift periods (occurrence of new virus strains).

Administration, Intranasal↗

PubMed2001

Multiple current reversal in Brownian ratchets.

We address the problem of stationary transport of overdamped Brownian particles in a one-dimensional spatially periodic potential composed of N hills within one period. We show that in a system driven by both thermal equilibrium fluctuations and symmetric dichotomic fluctuations, a proper manipulation of the barrier heights and slopes of the potential leads to multiple drift velocity reversal. Under optimal conditions, the drift velocity as a function of temperature and intensity of dichotomic fluctuations possesses as many as N extrema of alternating signs. There exist N-1 values of a critical temperature which separate regimes of opposite directions of particle transport.

Journal Article↗

PubMed2004

Temporal changes in allele frequencies and low effective population size in greater prairie-chickens.

The number of greater prairie-chickens in Wisconsin has decreased by 91% since 1932. The current population of approximately 1500 birds exists primarily in four isolated management areas. In previous studies of the Wisconsin populations we documented low levels of genetic variation at microsatellite loci and the mitochondrial DNA control region. Here we investigate changes in genetic structure between the four management areas in Wisconsin over the last 50 years. We estimated the harmonic mean effective population size (Ne) over the last 50 years by comparing allele frequencies from the early 1950s with those from contemporary samples. Using a pseudo-likelihood approach that accounted for migration, estimates of Ne (15-32 prairie-chickens within each management area) were 10 times lower than census numbers from booming-ground counts. These low estimates of Ne are consistent with increased habitat fragmentation and an increase in genetic isolation between management areas over the last 50 years. The reduction of gene flow between areas has reduced Ne, increased genetic drift and, consequently, reduced genetic variation. These results have immediate consequences for the conservation of the prairie-chicken, and highlight the importance of how mating systems and limited dispersal may exacerbate the loss of genetic variation in fragmented populations.

Animals↗

PubMed2005

Properties of saccades in Duane retraction syndrome.

PURPOSE: To improve understanding of the binocular control of saccades by making high-resolution eye movement recordings in patients with unilateral Duane retraction syndrome (DRS) type I (marked by congenital absence of the sixth cranial nerve). METHODS: Binocular eye movements were recorded in four patients in binocular viewing conditions during a saccade task. RESULTS: Affected-side gaze showed normal saccades of the sound eye and undershooting saccades of the affected eye-evidence of intact interneurons, but deficient motoneurons, in the sixth-nerve nucleus on the affected side. Postsaccadic smooth onward drift followed undershooting saccades of the affected eye. Sound-side gaze, in the centripetal direction, showed relatively accurate saccades despite large offsets in initial position between the two eyes. In the centrifugal direction, there was a consistent undershoot of the affected eye. The sound eye showed unexpected overshoot. Postsaccadic drifts in opposite directions in the two eyes brought both eyes onto the target in an optimal time course. CONCLUSIONS: Studying the characteristics of the saccadic system in this oculomotor disorder gives new insight into binocular control of saccades and adaptation. In these patients, the oculomotor system was not capable of adapting the pulse command to the two eyes separately, even though DRS offers clear advantages of independent control. In contrast, independent adaptation of the saccadic step command was sent to the two eyes. This supports the idea that the rapid part of the saccadic command is common to both eyes.

Duane Retraction Syndrome↗

PubMed1981

An evaluation of the Hellige Transoxode (Servomed Oxymonitor SM 361 System): response to halothane and enflurane in vitro.

The effects of halothane (0.5-2%) and enflurane (1-4%) on two Transoxode transcutaneous oxygen (TcPO2) electrodes (Hellige Servomed Oxymonitor SM.361 system) were serially tested in atmospheres of nitrogen, air and 50% nitrous oxide in oxygen. Both TcPO2 electrodes reduced and "read" halothane but no enflurane. Calibration drift was significantly greater (p less than 0.05) after electrode exposure to halothane; 5.40 s.e.m. 1.37 kPa vs enflurane; -0.60 s.e.m. 0.93 kPa. Halothane has a direct effect in rendering the Transoxode inaccurate, which is probably clinically less important than the indirect cardiovascularly medicated influence of both halothane and enflurane on TcPO2 levels. A reduction in the electrode polarisation voltage is recommended to obviate the direct effect of halothane on Transoxode performance.

Air↗

PubMed2005

Emergency triage: comparing a novel computer triage program with standard triage.

BACKGROUND: Emergency department (ED) triage prioritizes patients based on urgency of care; however, little previous testing of triage tools in a live ED environment has been performed. OBJECTIVES: To determine the agreement between a computer decision tool and memory-based triage. METHODS: Consecutive patients presenting to a large, urban, tertiary care ED were assessed in the usual fashion and by a blinded study nurse using a computerized decision support tool. Triage score distribution and agreement between the two triage methods were reported. A random subset of patients was selected and reviewed by a blinded expert panel as a consensus standard. RESULTS: Over five weeks, 722 ED patients were assessed; complete data were available from 693 (96%) score pairs. Agreement between the two methods was poor (kappa = 0.202; 95% confidence interval [95% CI] = 0.150 to 0.254); however, agreement improved when using weighted kappa (0.360; 95% CI = 0.305 to 0.415) or "within one" level kappa (0.732; 95% CI = 0.644 to 0.821). When compared with the expert panel, the nurse triage scores showed lower agreement (0.263; 95% CI = 0.133 to 0.394) than the tool (kappa = 0.426; 95% CI = 0.289 to 0.564). There was a significant down-triaging of patients when patients were triaged without the computerized tool. Admission rates also differed between the triage systems. CONCLUSIONS: There was significant discrepancy by nurses using memory-based triage when compared with a computer tool. Triage decision support tools can mitigate this drift, which has administrative implications for EDs.

Canada↗

PubMed2001

Toxicity of pesticides to aquatic microorganisms: a review.

Microorganisms contribute significantly to primary production, nutrient cycling, and decomposition in estuarine eco-systems; therefore, detrimental effects of pesticides on microbial species may have subsequent impacts on higher trophic levels. Pesticides may affect estuarine microorganisms via spills, runoff, and drift. Both the structure and the function of microbial communities may be impaired by pesticide toxicity. Pesticides may also be metabolized or bioaccumulated by microorganisms. Mechanisms of toxicity vary, depending on the type of pesticide and the microbial species exposed. Herbicides are generally most toxic to phototrophic microorganisms, exhibiting toxicity by disrupting photosynthesis. Atrazine is the most widely used and most extensively studied herbicide. Toxic effects of organophosphate and organochlorine insecticides on microbial species have also been demonstrated, although their mechanisms of toxicity in such nontarget species remain unclear. There is a great deal of variability in the toxicity of even a single pesticide among microbial species. When attempting to predict the toxicity of pesticides in estuarine ecosystems, effects of pesticide mixtures and interactions with nutrients should be considered. The toxicity of pesticides to aquatic microorganisms, especially bacteria and protozoa, is an area of research requiring further study.

Animals↗

PubMedDate not supplied

Glucose sensor characteristics for miniaturized portable closed-loop insulin delivery: a step toward implantation.

An implantable glucose sensor must be free of baseline and sensitivity drift. To our knowledge, a drift-free glucose sensor with fast response time is not currently available. We are therefore proposing a miniature extracorporeal glucose sensor with access to the vascular system as a practical step toward implantation. This sensor could use existing technology to form the basis of a patient-wearable closed-loop system.

Blood Glucose↗

PubMed2000

Rhythmical eye-head-torso rotation alters fore-aft head stabilization during treadmill locomotion in humans.

A repetitive manoeuvre called torso rotation (TR) is known to temporarily reduce the gain of the horizontal vestibulo-ocular reflex by 10-15% in healthy humans. TR consists of a series of rhythmical rotations of the eyes, head and upper body executed continuously for 30 minutes while standing. Our aim was to investigate whether TR affects the ability to hold the head in a fixed fore-aft position relative to space while walking on a treadmill with eyes closed. Ten healthy subjects stood in a carefully standardized position on a stationary treadmill. The treadmill started unexpectedly and ran for 4 s at 29 cm/s. The test stimulus was a linear acceleration in the fore-aft direction at the moment of treadmill start-up. Linear head position (i.e., ability to stabilize the head) was measured during and following the stimulus. A mechanical system prevented head rotation. Two series of 60 trials were performed before TR (control 1 and control 2 series) and one after TR. Before TR, subjects drifted rearward at an average drift velocity +/- S.D. = 3.1 +/- 0.9 cm/s. This drift was reasonably stable over time within and between the two control series. After TR, head holding ability was further impaired, with subjects having more difficulty to stabilize their head after treadmill start-up. In the first 10 trials after the arrest of TR, the average drift velocity was significantly larger than before TR(6.1 +/- 1.5 cm/sec, p < 0.01). Recovery to control values followed a roughly exponential time course, with 67% recovery occurring in the first 3.4 minutes after TR. Our results indicate that TR impairs the ability to sense and/or respond to fore-aft linear accelerations of the head following treadmill start-up in the absence of vision.

Adult↗

PubMed1998

[Development of the LCY-3E intelligent intracranial pressure monitor].

The LCY-3E intelligent intracranial pressure (ICP) monitor uses a microcomputer system for measurement and control. The ICP is transmitted by an air capsule, and detected by an universal high precision transducer. The problem of zero point drift during continuous ICP measurement was successfully solved and the electric safety of the instrument was greatly improved.

Aerospace Medicine↗

PubMed2001

Intrasaccadic perception.

Mammalian vision has a lowpass frequency characteristic that filters out fast temporal oscillations. Thus, fast-drifting gratings cannot be detected with static eyes, but the same gratings can easily be detected by executing saccades. Because these gratings are invisible under fixation, they are useful for isolating and studying intrasaccadic perception, which is normally masked by presaccadic and postsaccadic perception. We have conducted a number of psychophysical studies using these stimuli, and here we report that intrasaccadic visual processing allows for motion perception, that gratings drifting in the direction of a saccade are perceived as having more contrast than the same gratings drifting in the opposite direction, and that intrasaccadic contrast perception has sufficient grain to allow psychophysical matching of the perceived contrast of gratings drifting in opposite directions. The conditions in which these phenomena occur disprove a recent hypothesis that intrasaccadic motion perception occurs for stimuli processed by the magnocellular system, and our results can be explained by assuming that the temporal lowpass characteristic that accounts for flicker fusion phenomena under vision with static eyes is also operative during saccades.

Contrast Sensitivity↗

PubMed1977

Modified magnetorheography. Measurement of cardiac output by a catheter and an externally applied high magnetic field.

This study is dealt with a design for measuring cardiac output using a catheter and an externally applied magnetic field with the most minimized trauma. Many trials have yielded the following results. When a high static magnetic field is applied externally to the body and a catheter carrying electrodes at the tip is inserted from the carotid artery cutdown, 2 sensing electrodes, across the lumen of the aortic arch, at a little larger electrode distance than the lumen can detect the greatest flow signal. Since the biggest noises in the signal are ECG, they can be cancelled to a great extent by the reversed deflection of the ECG which is detected with cancelling electrodes placed at the left chest surface point geometrically symmetrical to the ascending aorta with respect to the center of the heart. Clamping the flow signal to zero level during diastole leads to the remodulation of D-C level in the flow signal and to the reduction of zero drifts. The flow signal produced by giving known volume to the ascending aorta via a catheter can be used for the calibration of the flow measuring system.

Animals↗

PubMed2004

Plasticity and tuning by visual feedback of the stability of a neural integrator.

Persistent neural firing is of fundamental importance to working memory and other brain functions because it allows information to be held "online" following an input and to be integrated over time. Many models of persistent activity rely on some kind of positive feedback internal to the neural circuit concerned; however, too much feedback causes runaway firing (instability), and too little results in loss of persistence (leak). This parameter sensitivity leads to the hypothesis that the brain uses an error signal (external feedback) to tune the stability of persistent firing by adjusting the amount of internal feedback. We test this hypothesis by manipulating external visual feedback, a putative sensory error signal, in a model system for persistent firing, the goldfish oculomotor neural integrator. Over tens of minutes to hours, electronically controlled visual feedback consistent with a leaky or unstable integrator can drive the integrator progressively more unstable or leaky, respectively. Eye fixation time constants can be reduced >100-fold to <1 s. Normal visual feedback gradually retunes the integrator back to stability. Changes in the phase of the sinusoidal vestibulo-ocular response are consistent with integrator detuning, as are changes in ocular drift following eye position shifts compensating for brief passive head movements during fixations. Corresponding changes in persistent firing of integrator neurons are presented in the accompanying article. The presence, strength, and reversibility of the plasticity demonstrate that, in this system, external visual feedback plays a vital role in gradually tuning the stability of the neural integrator.

Animals↗

PubMed1978

Population structure and genetic heterogeneity in the Upper Markham Valley of New Guinea.

An analysis is presented of the standardized Wahlund's variances (f) in gene frequencies of the ABO, Rh and MNS blood group systems among 19 villages of the Atsera isolate of the upper Markham Valley, Papua New Guinea. In the past, there has been some disagreement over the relative importance of population structure and natural selection in the determination of these variances. The Lewontin-Krakauer test is presented as a means of resolving this disagreement. According to this test, selectively neutral variation in gene frequencies should generate essentially homogeneous values of f for all loci, a homogeneity which can be tested by comparing the value of (formula: see text) to a theoretical (formula: see text) expected when variations in (formula: see text) are due solely to sampling error. The observed value of (formula: see text) for the Atsera isolate is 2.9 x 10(-5), which is not significantly different from the expected values that range from 1.23 x 10(-5) to 2.46 x 10(-5) depending on the constant used in calculating (formula: see text). Therefore it appears that nonselective aspects of population structure such as genetic drift and intervillage migration are responsible for the recorded genetic variation in this isolate.

ABO Blood-Group System↗