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Selected AbstractsSimultaneous quantification of cell motility and protein-membrane-association using active contoursCYTOSKELETON, Issue 4 2002Dirk Dormann Abstract We present a new method for the quantification of dynamic changes in fluorescence intensities at the cell membrane of moving cells. It is based on an active contour method for cell-edge detection, which allows tracking of changes in cell shape and position. Fluorescence intensities at specific cortical subregions can be followed in space and time and correlated with cell motility. The translocation of two GFP tagged proteins (CRAC and GRP1) from the cytosol to the membrane in response to stimulation with the chemoattractant cAMP during chemotaxis of Dictyostelium cells and studies of the spatio-temporal dynamics of this process exemplify the method: We show that the translocation can be correlated with motility parameters and that quantitative differences in the rate of association and dissociation from the membrane can be observed for the two PH domain containing proteins. The analysis of periodic CRAC translocation to the leading edge of a cell responding to natural cAMP waves in a mound demonstrates the power of this approach. It is not only capable of tracking the outline of cells within aggregates in front of a noisy background, but furthermore allows the construction of spatio-temporal polar plots, capturing the dynamics of the protein distribution at the cell membrane within the cells' moving co-ordinate system. Compilation of data by means of normalised polar plots is suggested as a future tool, which promises the so-far impossible practicability of extensive statistical studies and automated comparison of complex spatio-temporal protein distribution patterns. Cell Motil. Cytoskeleton 52:221,230, 2002. © 2002 Wiley-Liss, Inc. [source] Optimal observability of sustained stochastic competitive inhibition oscillations at organellar volumesFEBS JOURNAL, Issue 1 2006Kevin L. Davis When molecules are present in small numbers, such as is frequently the case in cells, the usual assumptions leading to differential rate equations are invalid and it is necessary to use a stochastic description which takes into account the randomness of reactive encounters in solution. We display a very simple biochemical model, ordinary competitive inhibition with substrate inflow, which is only capable of damped oscillations in the deterministic mass-action rate equation limit, but which displays sustained oscillations in stochastic simulations. We define an observability parameter, which is essentially just the ratio of the amplitude of the oscillations to the mean value of the concentration. A maximum in the observability is seen as the volume is varied, a phenomenon we name system-size observability resonance by analogy with other types of stochastic resonance. For the parameters of this study, the maximum in the observability occurs at volumes similar to those of bacterial cells or of eukaryotic organelles. [source] Regulatory T cells and intestinal homeostasisIMMUNOLOGICAL REVIEWS, Issue 1 2005Janine L. Coombes Summary:, Murine models of inflammatory bowel disease (IBD) are useful tools for the study of the pathogenesis and regulation of intestinal inflammation. Colitis can be induced in immune-deficient mice following transfer of populations of T cells or following infection with Helicobacter hepaticus and other intestinal pathogens. In these situations, colitis occurs as a result of the absence of a specialized population of regulatory cells, as transfer of CD4+CD25+ T cells prevents disease. Importantly, from a clinical perspective, CD4+CD25+ T cells can also reverse an established colitis. CD4+CD25+ T cells proliferate both in the secondary lymphoid organs and at the site of inflammation, suggesting that regulation occurs both locally and systemically. CD4+CD25+ T cells are not only capable of regulating other T cells but are also capable of suppressing components of the innate immune system. Control of colitis is dependent on the presence of the immunosuppressive cytokines interleukin-10 and transforming growth factor-,, although their roles are divergent and complex. Regulatory T cells represent one of the host's mechanisms to prevent immune pathology during chronic immune stimulation. Enhancement of regulatory T-cell activity may be useful to control autoreactive T-cell responses and inhibit harmful inflammatory diseases such as asthma and IBD. [source] Improving TCP performance over networks with wireless components using ,probing devices'INTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 6 2002A. Lahanas Abstract TCP error control mechanism lacks the ability to detect with precision the nature of potential errors during communication. It is only capable of detecting the results of the errors, namely that segments are dropped. As a result, the protocol lacks the ability to implement an appropriate error recovery strategy cognizant of current network conditions and responsive to the distinctive error characteristics of the communication channel. TCP sender always calls for the sending window to shrink. We show that probing mechanisms could enhance the error detection capabilities of the protocol. TCP could then flexibly adjust its window in a manner that permits the available bandwidth to be exploited without violating the requirements of stability, efficiency and fairness that need to be guaranteed during congestion. Our experiments have three distinct goals: First, to demonstrate the potential contribution of probing mechanisms. A simple probing mechanism and an immediate recovery strategy are grafted into TCP-Tahoe and TCP-Reno. We show that, this way, standard TCP can improve its performance without requiring any further change. Second, to study the performance of adaptive strategies. An adaptive TCP with probing is used, that is responsive to the detected error conditions by alternating slow start, fast recovery and immediate recovery. An adaptive error recovery strategy can yield better performance. Third, to study the design limitations of the probing device itself. The aggressive or conservative nature of the probing mechanisms themselves can determine the aggressive or conservative behaviour of the protocol and exploit accordingly the energy/throughput trade-off. Copyright © 2002 John Wiley & Sons, Ltd. [source] A Flexible Software Architecture for Hybrid TrackingJOURNAL OF FIELD ROBOTICS (FORMERLY JOURNAL OF ROBOTIC SYSTEMS), Issue 2 2004Miguel Ribo Fusion of vision-based and inertial pose estimation has many high-potential applications in navigation, robotics, and augmented reality. Our research aims at the development of a fully mobile, completely self-contained tracking system, that is able to estimate sensor motion from known 3D scene structure. This requires a highly modular and scalable software architecture for algorithm design and testing. As the main contribution of this paper, we discuss the design of our hybrid tracker and emphasize important features: scalability, code reusability, and testing facilities. In addition, we present a mobile augmented reality application, and several first experiments with a fully mobile vision-inertial sensor head. Our hybrid tracking system is not only capable of real-time performance, but can also be used for offline analysis of tracker performance, comparison with ground truth, and evaluation of several pose estimation and information fusion algorithms. © 2004 Wiley Periodicals, Inc. [source] Potential implications of endogenous aldehydes in ,-amyloid misfolding, oligomerization and fibrillogenesisJOURNAL OF NEUROCHEMISTRY, Issue 5 2006Kun Chen Abstract Aldehydes are capable of inducing protein cross-linkage. An increase in aldehydes has been found in Alzheimer's disease. Formaldehyde and methylglyoxal are produced via deamination of, respectively, methylamine and aminoacetone catalyzed by semicarbazide-sensitive amine oxidase (SSAO, EC 1.4.3.6. The enzyme is located on the outer surface of the vasculature, where amyloidosis is often initiated. A high SSAO level has been identified as a risk factor for vascular disorders. Serum SSAO activity has been found to be increased in Alzheimer's patients. Malondialdehyde and 4-hydroxynonenal are derived from lipid peroxidation under oxidative stress, which is also associated with Alzheimer's disease. Aldehydes may potentially play roles in ,-amyloid aggregation related to the pathology of Alzheimer's disease. In the present study, thioflavin-T fluorometry, dynamic light scattering, circular dichroism spectroscopy and atomic force microscopy were employed to reveal the effect of endogenous aldehydes on ,-amyloid at different stages, i.e. ,-sheet formation, oligomerization and fibrillogenesis. Formaldehyde, methylglyoxal and malondialdehyde and, to a lesser extent, 4-hydroxynonenal are not only capable of enhancing the rate of formation of ,-amyloid ,-sheets, oligomers and protofibrils but also of increasing the size of the aggregates. The possible relevance to Alzheimer's disease of the effects of these aldehydes on ,-amyloid deposition is discussed. [source] Neurophysiological and biomechanical characterization of goat cervical facet joint capsulesJOURNAL OF ORTHOPAEDIC RESEARCH, Issue 4 2005Ying Lu Abstract Cervical facet joints have been implicated as a major source of pain after whiplash injury. We sought to identify facet joint capsule receptors in the cervical spine and quantify their responses to capsular deformation. The response of mechanosensitive afferents in C5,C6 facet joint capsules to craniocaudal stretch (0.5 mm/s) was examined in anaesthetized adult goats. Capsular afferents were characterized into Group III and IV based on their conduction velocity. Two-dimensional strains across the capsules during stretch were obtained by a stereoimaging technique and finite element modeling. 17 (53%) Group III and 14 (56%) Group IV afferents were identified with low strain thresholds of 0.107 ± 0.033 and 0.100 ± 0.046. A subpopulation of low-strain-threshold afferents had discharge rate saturation at the strains of 0.388 ± 0.121 (n = 9, Group III) and 0.341 ± 0.159 (n = 9, Group IV). Two (8%) Group IV units responded only to high strains (0.460 ± 0.170). 15 (47%) Group III and 9 (36%) Group IV units could not be excited even by noxious capsular stretch. Simple linear regressions were conducted with capsular load and principal strain as independent variables and neural response of low-strain-threshold afferents as the dependent variable. Correlation coefficients (R2) were 0.73 ± 0.11 with load, and 0.82 ± 0.12 with principal strain. The stiffness of the C5,C6 capsules was 16.8 ± 11.4 N/mm. Our results indicate that sensory receptors in cervical facet joint capsules are not only capable of signaling a graded physiological mechanical stimulus, but may also elieit pain sensation under excessive deformation. © 2005 Orthopaedic Research Society. Published by Elsevier Ltd. All rights reserved. [source] Recreational folk dance: A multicultural exercise component in healthy ageingAUSTRALIAN OCCUPATIONAL THERAPY JOURNAL, Issue 2 2000Margaret Connor Recreational international folk dance provides a gentle form of exercise for people of all age groups, and may be used by an occupational therapist to provide a different leisure option for older people. The older adult is often stereotypically perceived as being only capable of certain types of leisure activities, such as bowls, bingo and cards. In multicultural Australia, activities need to be more diverse. Recreational folk dance provides an activity that is socially engaging, physically challenging, creative, and culturally and mentally stimulating. Involvement in the activity has general exercise benefits, which contribute to a healthy lifestyle. The participants can be empowered by their increased participation in community life, due to the classes, but also because of the public performance aspect that is offered with this activity. Exposure to folk costumes, customs, and traditions, can increase awareness of other cultures. Recreational folk dance has a beneficial effect on interpersonal and intrapersonal aspects of self. The language of dance crosses many cultures. Gesture and movement can be conveyed without words, thus making folk dance a good ,non-language' based activity to be used in a multicultural population. [source] | ||||||||||||||||