3,387 research outputs found

    Aperiodic invariant continua for surface homeomorphisms

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    We prove that if a homeomorphism of a closed orientable surface S has no wandering points and leaves invariant a compact, connected set K which contains no periodic points, then either K=S and S is a torus, or KK is the intersection of a decreasing sequence of annuli. A version for non-orientable surfaces is given.Comment: 8 pages, to appear in Mathematische Zeitschrif

    Metabolic syndrome in polycystic ovary syndrome

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    Zespół metaboliczny (MS, metabolic syndrome) i zespół policystycznych jajników (PCOS, polycystic ovary syndrome) są często rozpoznawanymi zaburzeniami u kobiet. Częstość występowania zespołu metabolicznego u kobiet z PCOS zależy od zastosowanych kryteriów diagnostycznych. W prezentowanej pracy autorzy rozważają tezę, że przyczyną obu zaburzeń może być insulinooporność, będąca następstwem otyłości brzusznej. Ponadto dokonują przeglądu literatury dotyczącej występowania MS u kobiet z PCOS oraz omawiają wpływ wyboru określonych kryteriów diagnostycznych MS i PCOS na oszacowanie czêstoœci ich występowania.Both metabolic syndrome (MS) and polycystic ovary syndrome (PCOS) are common among women. The exact prevalence of MS in women with PCOS is dependent upon the diagnostic criteria used for each. However, the frequent co-occurrence of both MS and PCOS in women is suggestive of a common aetiology. In this short review article we argue that insulin resistance, as a consequence of abdominal obesity, may represent such a common aetiology. We also review the literature on the prevalence of MS in women with PCOS and consider the impact that the particular criteria used to diagnose both MS and PCOS may have had on these estimates of prevalence

    The random case of Conley's theorem

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    The well-known Conley's theorem states that the complement of chain recurrent set equals the union of all connecting orbits of the flow ϕ\phi on the compact metric space XX, i.e. XCR(ϕ)=[B(A)A]X-\mathcal{CR}(\phi)=\bigcup [B(A)-A], where CR(ϕ)\mathcal{CR}(\phi) denotes the chain recurrent set of ϕ\phi, AA stands for an attractor and B(A)B(A) is the basin determined by AA. In this paper we show that by appropriately selecting the definition of random attractor, in fact we define a random local attractor to be the ω\omega-limit set of some random pre-attractor surrounding it, and by considering appropriate measurability, in fact we also consider the universal σ\sigma-algebra Fu\mathcal F^u-measurability besides F\mathcal F-measurability, we are able to obtain the random case of Conley's theorem.Comment: 15 page

    Temporal reprogramming of calcium signalling via crosstalk of gonadotrophin receptors that associate as functionally asymmetric heteromers.

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    Signal crosstalk between distinct G protein-coupled receptors (GPCRs) is one mechanism that underlies pleiotropic signalling. Such crosstalk is also pertinent for GPCRs activated by gonadotrophic hormones; follicle-stimulating hormone (FSH) and luteinising hormone (LH), with specific relevance to female reproduction. Here, we demonstrate that gonadotrophin receptor crosstalk alters LH-induced Gαq/11-calcium profiles. LH-induced calcium signals in both heterologous and primary human granulosa cells were prolonged by FSHR coexpression via influx of extracellular calcium in a receptor specific manner. LHR/FSHR crosstalk involves Gαq/11 activation as a Gαq/11 inhibitor abolished calcium responses. Interestingly, the enhanced LH-mediated calcium signalling induced by FSHR co-expression was dependent on intracellular calcium store release and involved Gβγ. Biophysical analysis of receptor and Gαq interactions indicated that ligand-dependent association between LHR and Gαq was rearranged in the presence of FSHR, enabling FSHR to closely associate with Gαq following LHR activation. This suggests that crosstalk may occur via close associations as heteromers. Super-resolution imaging revealed that LHR and FSHR formed constitutive heteromers at the plasma membrane. Intriguingly, the ratio of LHR:FSHR in heterotetramers was specifically altered following LH treatment. We propose that functionally significant FSHR/LHR crosstalk reprograms LH-mediated calcium signalling at the interface of receptor-G protein via formation of asymmetric complexes

    Massive normalization of olfactory bulb output in mice with a 'monoclonal nose'

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    Perturbations in neural circuits can provide mechanistic understanding of the neural correlates of behavior. In M71 transgenic mice with a 'monoclonal nose', glomerular input patterns in the olfactory bulb are massively perturbed and olfactory behaviors are altered. To gain insights into how olfactory circuits can process such degraded inputs we characterized odor-evoked responses of olfactory bulb mitral cells and interneurons. Surprisingly, calcium imaging experiments reveal that mitral cell responses in M71 transgenic mice are largely normal, highlighting a remarkable capacity of olfactory circuits to normalize sensory input. In vivo whole cell recordings suggest that feedforward inhibition from olfactory bulb periglomerular cells can mediate this signal normalization. Together, our results identify inhibitory circuits in the olfactory bulb as a mechanistic basis for many of the behavioral phenotypes of mice with a 'monoclonal nose' and highlight how substantially degraded odor input can be transformed to yield meaningful olfactory bulb output

    Migration control: A distance compensation strategy in ants

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    ©The Author(s) 2016. This article is published with open access at Springerlink.com. Migratory behaviour forms an intrinsic part of the life histories of many organisms but is often a high-risk process. Consequently, varied strategies have evolved to negate such risks, but empirical data relating to their functioning are limited. In this study, we use the model system of the househunting ant Temnothorax albipennis to demonstrate a key strategy that can shorten migration exposure times in a group of social insects. Colonies of these ants frequently migrate to new nest sites, and due to the nature of their habitat, the distances over which they do so are variable, leading to fluctuating potential costs dependent on migration parameters. We show that colonies of this species facultatively alter the dynamics of a migration and so compensate for the distance over which a given migration occurs. Specifically, they achieve this by modulating the rate of ‘tandem running’, in which workers teach each other the route to a new nest site. Using this method, colonies are able to engage a larger number of individuals in the migration process when the distance to be traversed is greater, and furthermore, the system appears to be based on perceived encounter rate at the individual level. This form of decentralised control highlights the adaptive nature of a behaviour of ecological importance, and indicates that the key to its robustness lies in the use of simple rules. Additionally, our results suggest that such coordinated group reactions are central to achieving the high levels of ecological success seen in many eusocial organisms
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