The Experts below are selected from a list of 15861 Experts worldwide ranked by ideXlab platform
Victor W M Van Hinsbergh - One of the best experts on this subject based on the ideXlab platform.
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polarized vascular endothelial growth factor secretion by human retinal pigment epithelium and localization of vascular endothelial growth factor receptors on the inner choriocapillaris evidence for a Trophic paracrine relation
American Journal of Pathology, 1999Co-Authors: H G T Blaauwgeers, G M Holtkamp, Hugo Rutten, A N Witmer, Pieter Koolwijk, Taina A Partanen, Kari Alitalo, Marielle E Kroon, Aize Kijlstra, Victor W M Van HinsberghAbstract:The retinal pigment epithelium (RPE) maintains the choriocapillaris (CC) in the normal eye and is involved in the pathogenesis of choroidal neovascularization in age-related macular degeneration. Vascular endothelial growth factor-A (VEGF) is produced by differentiated human RPE cells in vitro and in vivo and may be involved in paracrine signaling between the RPE and the CC. We investigated whether there is a polarized secretion of VEGF by RPE cells in vitro. Also, the localization of VEGF receptors in the human retina was investigated. We observed that highly differentiated human RPE cells, cultured on transwell filters in normoxic conditions, produced two- to sevenfold more VEGF toward their basolateral side as compared to the apical side. In hypoxic conditions, VEGF-A secretion increased to the basal side only, resulting in a three- to 10-fold higher basolateral secretion. By immunohistochemistry in 30 human eyes and in two cynomolgus monkey eyes, KDR (VEGFR-2) and flt-4 (VEGFR-3) were preferentially localized at the side of the CC endothelium facing the RPE cell layer, whereas flt-1 (VEGFR-1) was found on the inner CC and on other choroidal vessels. Our results indicate that RPE secretes VEGF toward its basal side where its receptor KDR is located on the adjacent CC endothelium, suggesting a role of VEGF in a paracrine relation, possibly in cooperation with flt-4 and its ligand. This can explain the known Trophic Function of the RPE in the maintenance of the CC and its fenestrated permeable phenotype and points to a role for VEGF in normal eye Functioning. Up-regulated basolateral VEGF secretion by RPE in hypoxia or loss of polarity of VEGF production may play a role in the pathogenesis of choroidal neovascularization.
Roger Arditi - One of the best experts on this subject based on the ideXlab platform.
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Predator interference emerging from trophotaxis in predator-prey systems: An individual-based approach
Ecological Complexity, 2008Co-Authors: Yuri Tyutyunov, L. I. Titova, Roger ArditiAbstract:An individual-based model describing predator–prey interactions within a closed rectangular habitat was developed to study how different assumptions about the individual movements lead to the emergence at the population level of various kinds of prey- and predator-dependence in the spatially aggregated Trophic Function. In addition to random walk, both species are capable of directional movement, i.e., the model accounts for the predator prey-taxis and evasion of predators by prey individuals. The taxis stimulus of each species is the odour of the other species, which is distributed continuously in space. Spatial behaviour of individuals is determined by the specific response to the odour gradient and the tendency to maintain the taxis velocity. In order to facilitate the assessment of the Trophic Function, the model allows removing the effect of demographic density variations on the predator ration, keeping population sizes constant. Analyzing the dependence of the Trophic Function with the average predator density, we found that, depending on the intensity of taxis, the predator population exhibits various degrees of interference, from very low to very high values. In particular, a moderate taxis generates distinct levels of interference including the ratio-dependent case. The letter maximizes the average consumption rate. A new generalized Function containing ratio-dependence and prey-dependence as special cases, at high and low population abundances, is suggested. This Trophic Function fits the simulated data better than the Hassell–Varley–Holling expression does.
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The Role of Prey Taxis in Biological Control: A Spatial Theoretical Model
American Naturalist, 2003Co-Authors: Natalia Sapoukhina, Yuri Tyutyunov, Roger ArditiAbstract:We study a reaction-diffusion-advection model for the dynamics of populations under biological control. A control agent is assumed to be a predator species that has the ability to perceive the heterogeneity of pest distribution. The advection term represents the predator density movement according to a basic prey taxis assumption: acceleration of predators is proportional to the prey density gradient. The prey population reproduces logistically, and the local population interactions follow the Holling Type II Trophic Function. On the scale of the population, our spatially explicit approach subdivides the predation process into random movement represented by diffusion, directed movement described by prey taxis, local prey encounters, and consumption modeled by the Trophic Function. Thus, our model allows studying the effects of large-scale predator spatial activity on population dynamics. We show under which conditions spatial patterns are generated by prey taxis and how this affects the predator ability to maintain the pest population below some economic threshold. In particular, intermediate taxis activity can stabilize predator-pest populations at a very low level of pest density, ensuring successful biological control. However, very intensive prey taxis destroys the stability, leading to chaotic dynamics with pronounced outbreaks of pest density.
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The Role of Prey Taxis in Biological Control: A Spatial Theoretical Model
The American Naturalist, 2003Co-Authors: Natalia Sapoukhina, Yuri Tyutyunov, Roger ArditiAbstract:Abstract: We study a reaction‐diffusion‐advection model for the dynamics of populations under biological control. A control agent is assumed to be a predator species that has the ability to perceive the heterogeneity of pest distribution. The advection term represents the predator density movement according to a basic prey taxis assumption: acceleration of predators is proportional to the prey density gradient. The prey population reproduces logistically, and the local population interactions follow the Holling Type II Trophic Function. On the scale of the population, our spatially explicit approach subdivides the predation process into random movement represented by diffusion, directed movement described by prey taxis, local prey encounters, and consumption modeled by the Trophic Function. Thus, our model allows studying the effects of large‐scale predator spatial activity on population dynamics. We show under which conditions spatial patterns are generated by prey taxis and how this affects the predator...
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Explicit model for searching behavior of predator
Zhurnal obshchei biologii, 2002Co-Authors: Tiutiunov Iuv, Sapukhina Niu, Inna Senina, Roger ArditiAbstract:The authors present an approach for explicit modeling of spatio-temporal dynamics of predator-prey community. This approach is based on a reaction-diffusion-adjection PD (prey dependent) system. Local kinetics of population is determined by logistic reproduction Function of prey, constant natural mortality of predator and Holling type 2 Trophic Function. Searching behavior of predator is described by the advective term in predator balance equation assuming the predator acceleration to be proportional to the prey density gradient. The model was studied with zero-flux boundary conditions. The influence of predator searching activity on the community dynamics, in particular, on the emergence of spatial heterogeneity, has been investigated by linear analysis and numerical simulations. It has been shown how searching activity may effect the persistence of species, stabilizing predator-prey interactions at very low level of pest density. It has been demonstrated that obtaining of such dynamic regimes does not require the use of complex Trophic Functions.
M.-e. Halatsch - One of the best experts on this subject based on the ideXlab platform.
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Glioblastoma treatment using perphenazine to block the subventricular zone’s tumor Trophic Functions
Journal of Neuro-Oncology, 2014Co-Authors: R. E. Kast, B. M. Ellingson, C. Marosi, M.-e. HalatschAbstract:We present here a potential new treatment adjunct for glioblastoma. Building on murine studies, a series of papers appeared recently showing that therapeutic irradiation of the ipsilateral subventricular zone (SVZ) retards growth of more peripherally growing cortical glioblastomas in humans, suggesting a tumor Trophic Function for the SVZ. Further studies showed that SVZ cells migrate out towards a peripheral glioblastoma. Dopamine signaling through D3 subtype receptor indirectly drives this centrifugal migration in humans. Since psychiatry has several drugs with good D3 blocking attributes, such as fluphenazine, or perphenazine, we suggest that adding one of these D3 blocking drugs to current standard treatment of resection followed by temozolomide and irradiation might prolong survival by depriving glioblastoma of the Trophic Functions previously subserved by dopaminergic signaling on SVZ cells.
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Glioblastoma treatment using perphenazine to block the subventricular zone's tumor Trophic Functions.
Journal of Neuro-Oncology, 2013Co-Authors: R. E. Kast, B. M. Ellingson, C. Marosi, M.-e. HalatschAbstract:We present here a potential new treatment adjunct for glioblastoma. Building on murine studies, a series of papers appeared recently showing that therapeutic irradiation of the ipsilateral subventricular zone (SVZ) retards growth of more peripherally growing cortical glioblastomas in humans, suggesting a tumor Trophic Function for the SVZ. Further studies showed that SVZ cells migrate out towards a peripheral glioblastoma. Dopamine signaling through D3 subtype receptor indirectly drives this centrifugal migration in humans. Since psychiatry has several drugs with good D3 blocking attributes, such as fluphenazine, or perphenazine, we suggest that adding one of these D3 blocking drugs to current standard treatment of resection followed by temozolomide and irradiation might prolong survival by depriving glioblastoma of the Trophic Functions previously subserved by dopaminergic signaling on SVZ cells.
H G T Blaauwgeers - One of the best experts on this subject based on the ideXlab platform.
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polarized vascular endothelial growth factor secretion by human retinal pigment epithelium and localization of vascular endothelial growth factor receptors on the inner choriocapillaris evidence for a Trophic paracrine relation
American Journal of Pathology, 1999Co-Authors: H G T Blaauwgeers, G M Holtkamp, Hugo Rutten, A N Witmer, Pieter Koolwijk, Taina A Partanen, Kari Alitalo, Marielle E Kroon, Aize Kijlstra, Victor W M Van HinsberghAbstract:The retinal pigment epithelium (RPE) maintains the choriocapillaris (CC) in the normal eye and is involved in the pathogenesis of choroidal neovascularization in age-related macular degeneration. Vascular endothelial growth factor-A (VEGF) is produced by differentiated human RPE cells in vitro and in vivo and may be involved in paracrine signaling between the RPE and the CC. We investigated whether there is a polarized secretion of VEGF by RPE cells in vitro. Also, the localization of VEGF receptors in the human retina was investigated. We observed that highly differentiated human RPE cells, cultured on transwell filters in normoxic conditions, produced two- to sevenfold more VEGF toward their basolateral side as compared to the apical side. In hypoxic conditions, VEGF-A secretion increased to the basal side only, resulting in a three- to 10-fold higher basolateral secretion. By immunohistochemistry in 30 human eyes and in two cynomolgus monkey eyes, KDR (VEGFR-2) and flt-4 (VEGFR-3) were preferentially localized at the side of the CC endothelium facing the RPE cell layer, whereas flt-1 (VEGFR-1) was found on the inner CC and on other choroidal vessels. Our results indicate that RPE secretes VEGF toward its basal side where its receptor KDR is located on the adjacent CC endothelium, suggesting a role of VEGF in a paracrine relation, possibly in cooperation with flt-4 and its ligand. This can explain the known Trophic Function of the RPE in the maintenance of the CC and its fenestrated permeable phenotype and points to a role for VEGF in normal eye Functioning. Up-regulated basolateral VEGF secretion by RPE in hypoxia or loss of polarity of VEGF production may play a role in the pathogenesis of choroidal neovascularization.
G M Holtkamp - One of the best experts on this subject based on the ideXlab platform.
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polarized vascular endothelial growth factor secretion by human retinal pigment epithelium and localization of vascular endothelial growth factor receptors on the inner choriocapillaris evidence for a Trophic paracrine relation
American Journal of Pathology, 1999Co-Authors: H G T Blaauwgeers, G M Holtkamp, Hugo Rutten, A N Witmer, Pieter Koolwijk, Taina A Partanen, Kari Alitalo, Marielle E Kroon, Aize Kijlstra, Victor W M Van HinsberghAbstract:The retinal pigment epithelium (RPE) maintains the choriocapillaris (CC) in the normal eye and is involved in the pathogenesis of choroidal neovascularization in age-related macular degeneration. Vascular endothelial growth factor-A (VEGF) is produced by differentiated human RPE cells in vitro and in vivo and may be involved in paracrine signaling between the RPE and the CC. We investigated whether there is a polarized secretion of VEGF by RPE cells in vitro. Also, the localization of VEGF receptors in the human retina was investigated. We observed that highly differentiated human RPE cells, cultured on transwell filters in normoxic conditions, produced two- to sevenfold more VEGF toward their basolateral side as compared to the apical side. In hypoxic conditions, VEGF-A secretion increased to the basal side only, resulting in a three- to 10-fold higher basolateral secretion. By immunohistochemistry in 30 human eyes and in two cynomolgus monkey eyes, KDR (VEGFR-2) and flt-4 (VEGFR-3) were preferentially localized at the side of the CC endothelium facing the RPE cell layer, whereas flt-1 (VEGFR-1) was found on the inner CC and on other choroidal vessels. Our results indicate that RPE secretes VEGF toward its basal side where its receptor KDR is located on the adjacent CC endothelium, suggesting a role of VEGF in a paracrine relation, possibly in cooperation with flt-4 and its ligand. This can explain the known Trophic Function of the RPE in the maintenance of the CC and its fenestrated permeable phenotype and points to a role for VEGF in normal eye Functioning. Up-regulated basolateral VEGF secretion by RPE in hypoxia or loss of polarity of VEGF production may play a role in the pathogenesis of choroidal neovascularization.
