2,169 research outputs found
Mathematical modeling of the radial profile of basilar membrane vibrations in the inner ear
Motivated by recent experimental results we seek an explanation of asymmetry in the radial profile of basilar membrane vibrations in the inner ear. We study a sequence of one-dimensional beam models which take into account variations in the bending stiffness of the basilar membrane as well as the potential presence of structural hinges. Our results suggest that the main cause of asymmetry is likely to be differences between the boundary conditions at the two extremes of the basilar membrane's width. This has fundamental implications for more detailed numerical simulations of the entire cochle
The simulation of action disorganisation in complex activities of daily living
Action selection in everyday goal-directed tasks of moderate complexity is known to be subject to breakdown following extensive frontal brain injury. A model of action selection in such tasks is presented and used to explore three hypotheses concerning the origins of action disorganisation: that it is a consequence of reduced top-down excitation within a hierarchical action schema network coupled with increased bottom-up triggering of schemas from environmental sources, that it is a more general disturbance of schema activation modelled by excessive noise in the schema network, and that it results from a general disturbance of the triggering of schemas by object representations. Results suggest that the action disorganisation syndrome is best accounted for by a general disturbance to schema activation, while altering the balance between top-down and bottom-up activation provides an account of a related disorder - utilisation behaviour. It is further suggested that ideational apraxia (which may result from lesions to left temporoparietal areas and which has similar behavioural consequences to action disorganisation syndrome on tasks of moderate complexity) is a consequence of a generalised disturbance of the triggering of schemas by object representations. Several predictions regarding differences between action disorganisation syndrome and ideational apraxia that follow from this interpretation are detailed
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Effect of an acute bout of exercise on executive function and sleep in children with attention deficit hyperactivity disorder and autism spectrum disorder
Background and aims: The present study aimed to examine the effect of an acute bout of circuit-base exercise on executive function, visual perception and sleep parameters in neurodiverse children.
Methods: After familiarisation, 34 children (4 female) with ADHD and/or ASD completed two trials (30-min circuit-based exercise (E) or a rested control (C) trial) in a randomised, counterbalanced, crossover design. Participants completed cognitive function tests (Stroop test, Sternberg Paradigm and Visual Search Test) at baseline, immediately post-exercise, and the morning after exercise. Participants were provided with a wrist actigraph to wear overnight to determine sleep duration, wake after sleep onset, sleep efficiency, and sleep latency. Statistical analyses were conducted via ANCOVA, with diagnosis included as a covariate.
Results: Accuracy on the Stroop test (complex level) was better maintained following circuit-based exercise when compared with rest immediately post-exercise (E: 1.88% decreased accuracy; C: 4.73% decreased accuracy, p = 0.009), and on day two (E: 1.22% increased accuracy; C: 6.37% decreased accuracy; p 0.05).
Conclusion: Moderate intensity circuit-based exercise is an ecologically valid exercise modality that, acutely, improves executive function (compared to rest), which may alleviate the impaired executive function in children with ADHD and ASD
Defending the 'Negro Race': Lamine Senghor and Black Internationalism in Interwar France
This article examines the career of Lamine Senghor, a Senegalese veteran of the First World War, who emerged in the mid 1920s as the most influential black anti-colonial activist of the period. Senghor combined a communist-inspired critique of empire with an attempt to forge a transnational sense of black identity. Many of the questions facing Senghor remain relevant today: should the black community seek equality through its own independent pressure groups or through strategic alliances with mainstream political parties? And how does one engage with issues of racial (or religious) equality within the terms of the purportedly colour-blind and secular Republic
Characterisation of GLUT4 trafficking in HeLa cells: Comparable kinetics and orthologous trafficking mechanisms to 3T3-L1 adipocytes
Insulin-stimulated glucose transport is a characteristic property of adipocytes and
muscle cells and involves the regulated delivery of glucose transporter (GLUT4)-
containing vesicles from intracellular stores to the cell surface. Fusion of these
vesicles results in increased numbers of GLUT4 molecules at the cell surface. In an
attempt to overcome some of the limitations associated with both primary and
cultured adipocytes, we expressed an epitope- and GFP-tagged version of GLUT4
(HA–GLUT4–GFP) in HeLa cells. Here we report the characterisation of this system
compared to 3T3-L1 adipocytes. We show that insulin promotes translocation of
HA–GLUT4–GFP to the surface of both cell types with similar kinetics using
orthologous trafficking machinery. While the magnitude of the insulin-stimulated
translocation of GLUT4 is smaller than mouse 3T3-L1 adipocytes, HeLa cells offer a
useful, experimentally tractable, human model system. Here, we exemplify their
utility through a small-scale siRNA screen to identify GOSR1 and YKT6 as potential
novel regulators of GLUT4 trafficking in human cells
Disturbance and stress - different meanings in ecological dynamics?
There is an increasing frequency of papers
addressing disturbance and stress in ecology without
clear delimitation of their meaning. Some authors
use the terms disturbance and stress exclusively as
impacts, while others use them for the entire process,
including both causes and effects. In some studies, the
disturbance is considered as a result of a temporary
impact, which is positive for the ecosystem, while
stress is a negative, debilitating impact. By developing
and testing simple theoretical models, the authors
propose to differentiate disturbance and stress by
frequency. If the frequency of the event enables the
variable to reach a dynamic equilibrium which might
be exhibited without this event, then the event (plus its
responses) is a disturbance for the system. If frequency
prevents the variable’s return to similar pre-event
dynamics and drives or shifts it to a new trajectory,
then we are facing stress. The authors propose that
changes triggered by the given stimuli can be evaluated
on an absolute scale, therefore, direction of change of the variable must not be used to choose one
term or the other, i.e. to choose between stress and
disturbance
Somatic diversification of variable lymphocyte receptors in the agnathan sea lamprey
Although jawless vertebrates are apparently capable of adaptive immune responses, they have not been found to possess the recombinatorial antigen receptors shared by all jawed vertebrates. Our search for the phylogenetic roots of adaptive immunity in the lamprey has instead identified a new type of variable lymphocyte receptors (VLRs) composed of highly diverse leucine-rich repeats (LRR) sandwiched between amino- and carboxy-terminal LRRs. An invariant stalk region tethers the VLRs to the cell surface by means of a glycosyl-phosphatidyl-inositol anchor. To generate rearranged VLR genes of the diversity necessary for an anticipatory immune system, the single lamprey VLR locus contains a large bank of diverse LRR cassettes, available for insertion into an incomplete germline VLR gene. Individual lymphocytes express a uniquely rearranged VLR gene in monoallelic fashion. Different evolutionary strategies were thus used to generate highly diverse lymphocyte receptors through rearrangement of LRR modules in agnathans ( jawless fish) and of immunoglobulin gene segments in gnathostomes ( jawed vertebrates).Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/62870/1/nature02740.pd
Solution structure of a repeated unit of the ABA-1 nematode polyprotein allergen of ascaris reveals a novel fold and two discrete lipid-binding sites
Parasitic nematode worms cause serious health problems in humans and other animals. They can induce allergic-type immune responses, which can be harmful but may at the same time protect against the infections. Allergens are proteins that trigger allergic reactions and these parasites produce a type that is confined to nematodes, the nematode polyprotein allergens (NPAs). These are synthesized as large precursor proteins comprising repeating units of similar amino acid sequence that are subsequently cleaved into multiple copies of the allergen protein. NPAs bind small lipids such as fatty acids and retinol (Vitamin A) and probably transport these sensitive and insoluble compounds between the tissues of the worms. Nematodes cannot synthesize these lipids, so NPAs may also be crucial for extracting nutrients from their hosts. They may also be involved in altering immune responses by controlling the lipids by which the immune and inflammatory cells communicate. We describe the molecular structure of one unit of an NPA, the well-known ABA-1 allergen of Ascaris and find its structure to be of a type not previously found for lipid-binding proteins, and we describe the unusual sites where lipids bind within this structur
CD98hc facilitates B cell proliferation and adaptive humoral immunity.
The proliferation of antigen-specific lymphocytes and resulting clonal expansion are essential for adaptive immunity. We report here that B cell-specific deletion of the heavy chain of CD98 (CD98hc) resulted in lower antibody responses due to total suppression of B cell proliferation and subsequent plasma cell formation. Deletion of CD98hc did not impair early B cell activation but did inhibit later activation of the mitogen-activated protein kinase Erk1/2 and downregulation of the cell cycle inhibitor p27. Reconstitution of CD98hc-deficient B cells with CD98hc mutants showed that the integrin-binding domain of CD98hc was required for B cell proliferation but that the amino acid-transport function of CD98hc was dispensable for this. Thus, CD98hc supports integrin-dependent rapid proliferation of B cells. We propose that the advantage of adaptive immunity favored the appearance of CD98hc in vertebrates
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