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Search Results: 1 - 10 of 222841 matches for " Lisa C Foa "
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TRPM8 and Nav1.8 sodium channels are required for transthyretin-induced calcium influx in growth cones of small-diameter TrkA-positive sensory neurons
Robert J Gasperini, Xu Hou, Helena Parkington, Harry Coleman, David W Klaver, Adele J Vincent, Lisa C Foa, David H Small
Molecular Neurodegeneration , 2011, DOI: 10.1186/1750-1326-6-19
Abstract: Levels of intracellular cytosolic calcium were monitored in dorsal root ganglion (DRG) neurons isolated from embryonic rats using the calcium-sensitive fluorescent indicator Fluo4. An amyloidogenic mutant form of TTR, L55P, induced calcium influx into the growth cones of DRG neurons, whereas wild-type TTR had no significant effect. Atomic force microscopy and dynamic light scattering studies confirmed that the L55P TTR contained oligomeric species of TTR. The effect of L55P TTR was decreased by blockers of voltage-gated calcium channels (VGCC), as well as by blockers of Nav1.8 voltage-gated sodium channels and transient receptor potential M8 (TRPM8) channels. siRNA knockdown of TRPM8 channels using three different TRPM8 siRNAs strongly inhibited calcium influx in DRG growth cones.These data suggest that activation of TRPM8 channels triggers the activation of Nav1.8 channels which leads to calcium influx through VGCC. We suggest that TTR-induced calcium influx into DRG neurons may contribute to the pathophysiology of FAP. Furthermore, we speculate that similar mechanisms may mediate the toxic effects of other amyloidogenic proteins such as the β-amyloid protein of Alzheimer's disease.Protein misfolding is a common feature of many neurodegenerative diseases. In some of these diseases, such as the synucleinopathies and the tauopathies, cytoplasmic proteins aggregate to form intracellular deposits. However, in the amyloidoses, which include Alzheimer's disease (AD), prion diseases and the British and Danish familial dementias, proteinaceous aggregates are observed extracellularly [1-4]. There is increasing evidence that the mechanism of neurotoxicity in these amyloidoses is similar and that it is the conformation of the aggregated protein, rather than its specific amino acid sequence which results in altered membrane permeability to calcium [5]. Therefore, studies on the mechanism of neurotoxicity in one disease may provide insights into the mechanisms involved in other
Presenilins and the γ-secretase: still a complex problem
David H Small, David W Klaver, Lisa Foa
Molecular Brain , 2010, DOI: 10.1186/1756-6606-3-7
Abstract: Alzheimer's disease (AD) is the most common cause of dementia in the elderly. Typically 5-10% of the population over the age of 65 have dementia, and of these cases, a large percentage have AD [1]. AD is characterised by the presence of proteinaceous deposits in the brain [2]. The extracellular amyloid deposits, which are found in the neuropil (amyloid plaques) and in association with small-medium size cerebral blood vessels (cerebral amyloid angiopathy), are composed of a 4 kDa polypeptide known as the amyloid-β protein (Aβ) which is derived by proteolytic cleavage from a much larger amyloid-β precursor protein (APP) [3]. Aβ displays a spontaneous ability to aggregate into oligomers and larger fibrillar structures, and it is generally thought that the accumulation of oligomeric Aβ is chiefly responsible for the neurodegeneration that occurs in AD [4].For the generation of Aβ, APP is first cleaved on the N-terminal side of the Aβ sequence by the β-site APP cleaving enzyme-1 (BACE1), a transmembrane aspartyl protease [3]. The resulting 99-amino acid residue C-terminal fragment (C99) is then cleaved by the γ-secretase to yield Aβ and a C-terminal APP intracellular domain (AICD) fragment (Fig. 1). The function of the AICD fragment is unclear, although it is thought to have a role in intracellular signalling. For example, AICD may be involved in the regulation of gene transcription, synaptic plasticity and cytoskeletal dynamics [5].The major form of Aβ possesses 40 amino-acid residues (Aβ1-40). However, other minor species are also produced which vary in the C-terminal sequence. Production of a longer 42-residue species (Aβ1-42) is thought to be intimately associated with AD pathogenesis [6]. Aβ1-42 aggregates more readily than Aβ1-40, and increased production of Aβ1-42 may seed aggregation of Aβ1-40 or other Aβ species [4].Approximately 5% of all AD cases are autosomal dominant [7]. Soon after the complete APP sequence was cloned in 1987 [8], it became clear that at le
Homer regulates calcium signalling in growth cone turning
Robert Gasperini, Derek Choi-Lundberg, Michael JW Thompson, Camilla B Mitchell, Lisa Foa
Neural Development , 2009, DOI: 10.1186/1749-8104-4-29
Abstract: Homer1 knockdown reversed growth cone turning from attraction to repulsion in response to the calcium-dependent guidance cues brain derived neurotrophic factor and netrin-1. Conversely, Homer1 knockdown had no effect on repulsion to the calcium-independent guidance cue Semaphorin-3A. This reversal of attractive turning suggested a requirement for Homer1 in a molecular switch. Pharmacological experiments confirmed that the operational state of a calcium-calmodulin dependent protein kinase II/calcineurin phosphatase molecular switch was dependent on Homer1 expression. Calcium imaging of motile growth cones revealed that Homer1 is required for guidance-cue-induced rise of cytosolic calcium and the attenuation of spontaneous cytosolic calcium transients. Homer1 knockdown-induced calcium transients and turning were inhibited by antagonists of store-operated channels. In addition, immunocytochemistry revealed the close association of Homer1 with the store-operated proteins TRPC1 and STIM1 within dorsal root ganglia growth cones.These experiments provide evidence that Homer1 is an essential component of the calcium signalling repertoire within motile growth cones, regulating guidance-cue-induced calcium release and maintaining basal cytosolic calcium.Deciphering the cell signalling events that control growth cone navigation and, hence, axon guidance is crucial to our understanding of the development of functional neural circuitry. Cytosolic calcium ([Ca++]i) is a key signalling molecule that regulates growth cone motility [1,2]. The release of calcium from intracellular stores or influx via receptor-mediated or voltage-gated channels leads to discrete localised transients and/or global changes in [Ca++]i [3]. The frequency and magnitude of these [Ca++]i changes correlates with overall axon growth and extension as well as responses to soluble and contact-mediated guidance cues [2,4-6]. These changes in [Ca++]i can be of the order of milliseconds or quite persistent, lasting
(Anti-)Biography and Neo-Impressionism
Foa, Michelle
RIHA Journal , 2012,
Abstract: This article analyzes neo-impressionism in relation to the biographical model of art criticism and art history that became increasingly prevalent in France over the course of the 19th century. Examining the critical response to the neo-impressionists, as well as some of their pictures and writings, I argue for the centrality of questions of authorship, individuality, and subjectivity to the group and its reception. I identify a distinctly anti-biographical tendency in the movement, one that disquieted the critics and led them to try and re-inscribe biographical meaning back into the work of Georges Seurat. Indeed, though Seurat instituted a divide between his work and his life in a variety of ways, he also insisted throughout his career on his paternity over the neo-impressionist method. In all of these ways, the relationship between the self and art was a significant and problematic issue for the neo-impressionists and the critics around them.
Enhancing single-parameter quantum charge pumping in carbon-based devices
L. E. F. Foa Torres,H. L. Calvo,C. G. Rocha,G. Cuniberti
Physics , 2011, DOI: 10.1063/1.3630025
Abstract: We present a theoretical study of quantum charge pumping with a single ac gate applied to graphene nanoribbons and carbon nanotubes operating with low resistance contacts. By combining Floquet theory with Green's function formalism, we show that the pumped current can be tuned and enhanced by up to two orders of magnitude by an appropriate choice of device length, gate voltage intensity and driving frequency and amplitude. These results offer a promising alternative for enhancing the pumped currents in these carbon-based devices.
Multiterminal Conductance of a Floquet Topological Insulator
L. E. F. Foa Torres,P. M. Perez-Piskunow,C. A. Balseiro,G. Usaj
Physics , 2014, DOI: 10.1103/PhysRevLett.113.266801
Abstract: We report on simulations of the dc conductance and quantum Hall response of a Floquet topological insulator using Floquet scattering theory. Our results reveal that laser-induced edge states in graphene lead to quantum Hall plateaus once imperfect matching with the non-illuminated leads is lessened. But the magnitude of the Hall plateaus is not directly related to the number and chirality of all the edge states at a given energy as usual. Instead, the plateaus are dominated only by those edge states adding to the dc density of states. Therefore, the dc quantum Hall conductance of a Floquet topological insulator is not directly linked to topological invariants of the full the Floquet bands.
Irradiated graphene as a tunable Floquet topological insulator
Gonzalo Usaj,P. M. Perez-Piskunow,L. E. F. Foa Torres,C. A. Balseiro
Physics , 2014, DOI: 10.1103/PhysRevB.90.115423
Abstract: In the presence of a circularly polarized mid-infrared radiation graphene develops dynamical band gaps in its quasi-energy band structure and becomes a Floquet insulator. Here we analyze how topologically protected edge states arise inside these gaps in the presence of an edge. Our results show that the gap appearing at $\hbar\Omega/2$, where $\hbar \Omega$ is the photon energy, is bridged by two chiral edge states whose propagation direction is set by the direction of the polarization of the radiation field. Therefore, both the propagation direction and the energy window where the states appear can be controlled externally. We present both analytical and numerical calculations that fully characterize these states. This is complemented by simple topological arguments that account for them and by numerical calculations for the case of semi-infinite sample, thereby eliminating finite size effects.
Floquet chiral edge states in graphene
P. M. Perez-Piskunow,Gonzalo Usaj,C. A. Balseiro,L. E. F. Foa Torres
Physics , 2013, DOI: 10.1103/PhysRevB.89.121401
Abstract: We report on the emergence of laser-induced chiral edge states in graphene ribbons. Insights on the nature of these Floquet states is provided by an analytical solution which is complemented with numerical simulations of the transport properties. Guided by these results we show that graphene can be used for realizing non-equilibrium topological states with striking tunability: While the laser intensity can be used to control their velocity and decay length, changing the laser polarization switches their propagation direction.
Coherent versus sequential electron tunneling in quantum dots
L. E. F. Foa Torres,C. H. Lewenkopf,H. M. Pastawski
Physics , 2003, DOI: 10.1103/PhysRevLett.91.116801
Abstract: Manifestations of quantum coherence in the electronic conductance through nearly closed quantum dots in the Coulomb blockade regime are addressed. We show that quantum coherent tunneling processes explain some puzzling statistical features of the conductance peak-heights observed in recent experiments at low temperatures. We employ the constant interaction model and the random matrix theory to model the quantum dot electronic interactions and its single-particle statistical fluctuations, taking full account of the finite decay width of the quantum dot levels.
Aid to a Declining Matriarch in the Giant Otter (Pteronura brasiliensis)
Lisa C. Davenport
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0011385
Abstract: Scientists are increasingly revealing the commonalities between the intellectual, emotional and moral capacities of animals and humans. Providing assistance to elderly and ailing family members is a human trait rarely documented for wild animals, other than anecdotal accounts. Here I report observations of multiple forms of assistance to the declining matriarch of a habituated group of giant otters (Pteronura brasiliensis) in Manu National Park, Peru. The otter group had been observed annually for several years and all members were known individually. In 2007, the breeding female of the group failed to reproduce and appeared to be in physical decline. She begged from other family members 43 times over 41 contact hours and received food 11 times. Comparisons with 2004–2006 demonstrate that the family's behavior in 2007 constitutes a role-reversal, in which the majority of assistance and prey transfers accrued from young-to-old rather than from old-to-young. As in human societies, both non-adaptive and adaptive hypotheses could explain the family members' aid to their declining matriarch. I suggest that giant otter families may benefit from the knowledge and experience of an elderly matriarch and “grandparent helper,” consistent with the “Grandmother Hypothesis” of adaptive menopause in women.
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