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At least 667 records · Page 37Linked to original sources
PubMed1982

Diffuse and local effects of light adaptation in photoreceptors of the honey bee drone.

Intracellular recordings from drone photoreceptors were made by means of glass microelectrodes in superfused retinae. Exposure of a small portion of a cell to white light decreased the amplitude of responses to a small stimulus subsequently applied at different sites of the photoreceptor cell, i.e. light adaptation occurred throughout the cell. After 7 min of darkness, the responses had completely recovered. When a violet light (404 nm) was used to adapt a small portion of the cell, the responses at the site of exposure to the adapting stimulus remained depressed for at least 30 min. Illumination at the site of the violet adapting stimulus with green light (585 nm) caused an immediate recovery of the amplitude of the response. These results can be explained by the existence of two processes responsible for light adaptation: one is localized and persistent and appears to be due to changes in concentration of rhodopsin. The other affects the whole cell, is spontaneously reversible and depends upon the ability of the light to produce a receptor potential but not on any lasting change in rhodopsin concentration.

Action Potentials↗
PubMed1989

A mechanism of peripheral spread or localization of inflammatory reactions--role of the localized ground substance adaptive phenomenon.

It is known that connective tissue-active peptides (CTAP) are released at sites of inflammation. Some of this material diffuses to immediately adjacent tissue and increases ground substance viscosity and fibroblast proliferation. This contributes to host protection against spread of infections and tumors. In a person with normal inflammatory reactivity, it should prevent spread of mediators and products of local inflammation. However, the host with an increased reactivity in sites of increased ground substance viscosity or who is highly reactive to dilution of tissue fluid would respond with more inflammation. A non-infectious, non-malignant process in a host with a highly reactive inflammatory or immune response could end up with peripheral spread. This could occur in any tissue but it occurs with great vigor in the skin. It could present as a peripheral extension of a local disease process, such as psoriasis, or the migration of cyclic lesions with clearing of the central area. There are over a dozen variants of peripherally spreading, ringed lesions described in the dermatologic literature. This includes erythema marginatum of rheumatic fever, erythema gyratum repens associated with cancer, and erythema annulare centrificum associated with allergic reactions to fungi. Many of the ringed dermatologic lesions have an immunologic component. They tend to be associated with inflammatory immune reactions at distant sites. Dermatologists have been gathering information on the ringed phenomenon at least since Hebra in 1854. The acute localized ground substance adaptive phenomenon is a broadly beneficial biologic response.(ABSTRACT TRUNCATED AT 250 WORDS)

Adaptation, Physiological↗
PubMed1989

[Degenerative, regenerative and adaptive reactions to local damage of the retina].

Retinal ganglion cells can respond to local lesions due to mechanical trauma or photocoagulation with degeneration, adaptation or regeneration. Animal experiments show that under natural conditions the kind of reaction is dependent on the age at onset and on the degree of destruction caused by the lesion. In early postnatal life directly severed cells undergo fast degeneration while indirectly affected cells show adaptive changes (dendritic reorganization in the neighborhood of retrogradely degenerated retinal areas). This kind of reaction is not observed in adulthood. In contrast, in the adult retina there is a greater resistance to lesion effects and surviving cells show signs of axonal regeneration. Such attempts at regeneration, however, do not lead to successful reentry of axons into the optic nerve. In addition, at the very borders of photocoagulator lesions we observe both in early postnatal and adult animals signs of dendritic plasticity (redistribution of dendrites away from the lesion and towards the normal retina). The dendritic changes are aimed at retaining function and at reducing lesion size. They are characterized by a redistribution of dendritic volume towards the intact retina. While spontaneous intraretinal axonal regeneration does not appear to be beneficial for the system, the dendritic phenomena can be interpreted as attempts to limit the actual damage.

Adaptation, Ocular↗
PubMed1983

[Spatial distribution and response interaction in the receptive fields of lateral geniculate body neurons in the cat].

A detailed comparison of responses of lateral geniculate neurons to local photic stimulation of central, antagonistic and disinhibiting zones of their receptive fields (RF) during local light adaptation of each zone was carried out in experiments on unanesthetized cats immobilized with d-tubocurarine. It was shown that most conditions of local adaptation of different RF zones activated neuronal on- and off-responses to stimulation of peripheral zones and depressed responses to flashes delivered to the central zone. Therefore under condition of local adaptation the geniculate neurons can produce intensive signals when photic stimulation switches on as well as switches off. The comparison of this fact with the known properties of on-off-channels allows suggesting that under condition of light adaptation the processing of large information volumes and more perfect performance of visual functions are connected with emergence of signals in different RF zones.

Adaptation, Physiological↗
PubMed1983

Spatial localization of bleaching adaptation in isolated vertebrate rod photoreceptors.

Bleaching of a large fraction of the rhodopsin in isolated rod outer segments results in an irreversible desensitization of the rod. This desensitization is referred to as bleaching adaptation. The logarithm of the sensitivity of the rod during bleaching adaptation has been found by a number of workers to be linearly related to the concentration of unbleached rhodopsin. We have measured the desensitization due to bleaching adaptation produced by a spatially confined stimulus and found that its effects are highly local. The space constant for the spread of desensitization was less than 4 microns. The small apparent spread of desensitization beyond the bleached regions probably can be accounted for by defocusing and light scatter. Thus, the involvement of a freely diffusible transmitter in bleaching adaptation does not appear to be required.

Adaptation, Physiological↗
PubMed2005

Adaptive smoothing via contextual and local discontinuities.

A novel adaptive smoothing approach is proposed for noise removal and feature preservation where two distinct measures are simultaneously adopted to detect discontinuities in an image. Inhomogeneity underlying an image is employed as a multiscale measure to detect contextual discontinuities for feature preservation and control of the smoothing speed, while local spatial gradient is used for detection of variable local discontinuities during smoothing. Unlike previous adaptive smoothing approaches, two discontinuity measures are combined in our algorithm for synergy in preserving nontrivial features, which leads to a constrained anisotropic diffusion process that inhomogeneity offers intrinsic constraints for selective smoothing. Thanks to the use of intrinsic constraints, our smoothing scheme is insensitive to termination times and the resultant images in a wide range of iterations are applicable to achieve nearly identical results for various early vision tasks. Our algorithm is formally analyzed and related to anisotropic diffusion. Comparative results indicate that our algorithm yields favorable smoothing results, and its application in extraction of hydrographic objects demonstrates its usefulness as a tool for early vision.

Algorithms↗
PubMed2004

Adaptive registration using local information measures.

Rapidly advancing registration methods increasingly employ warping transforms. High degrees of freedom (DOF) warpings can be specified by manually placing control points or instantiating a regular, dense grid of control points everywhere. The former approach is laborious and prone to operator bias, whereas the latter is computationally expensive. We propose to improve upon the latter approach by adaptively placing control points where they are needed. Local estimates of mutual information (MI) and entropy are used to identify local regions requiring additional DOF.

Abdomen↗
PubMed1988

Visual adaptation is highly localized in the cat's retina.

1. The aim of this study was to determine how the spatial pattern of steady light in a visual stimulus affects the state of adaptation of the retina. 2. Impulse rate was recorded from single X and Y ganglion cells in the cat's retina. The luminance of a narrow bar of light centred over the receptive field was modulated sinusoidally in time about a steady background, and a cell's contrast gain was measured as the ratio of impulse rate modulation to bar contrast. 3. The contrast gain of a cell was set by the background, a fixed luminance level about which luminance varied in the form of a grating; grating luminance varied sinusoidally with distance but did not vary in time. When the spatial frequency of the grating was low, contrast gain was increased by a grating with a trough centred over the receptive field, and decreased by a peak-centred grating. 4. As the spatial frequency of the grating increased, its effect on contrast gain disappeared. For cells around 10 deg from the central area, this change occurred at spatial frequencies close to 1 cycle deg-1. 5. For each cell the effect on contrast gain of the background's spatial frequency was compared with the spatial frequency response to a time-varying grating. It was found that the summation area for adapting light in both X and Y cells is very close in size to an X cell centre mechanism, and that the summation area for adapting light in Y cells is therefore considerably smaller than a Y cell centre. 6. From this and other evidence it was shown that sub-areas of the Y cell centre mechanism can be independently adapted. 7. A background grating with a trough centred over the receptive field raised contrast gain more at mid-range spatial frequencies than at low frequencies, producing a hump in the contrast gain versus frequency curve. A peak-centred grating reduced contrast gain more at mid-range frequencies than at low, producing a dip. 8. The dip in the contrast gain versus frequency curve for a peak-centred grating was always greater than the hump for a trough-centred grating. 9. These humps and dips were interpreted in terms of a model containing two antagonistic pathways. One pathway had a smaller summation area for adapting light than the other.(ABSTRACT TRUNCATED AT 400 WORDS)

Adaptation, Ocular↗
PubMed2006

Some observations on the adaptation of Eimeria tenella (local isolates) sporozoites on chicken embryos through chorioallantoic membrane.

Eimeria (E.) tenella (local isolate) sporozoites were adapted on the chorioallantoic membrane (CAM) of 10-12 days chicken embryos and completed its life cycle in 6-7 days at 39 degrees C and 70 per cent humidity. Only 23 embryos (4.6%) were found dead from 1-4 day post inoculation of sporozoites with mild lesions on CAM with no gametocytes but few sporozoites in chorioallantoic fluid (CAF). On 5-7 day post inoculation, 432 embryos (86.4%) were found dead with severe haemorrhages on CAM and CAF contained uncountable number of gametocytes. After seven days post inoculation, 45 embryos (9%) were found to be alive. Some oocysts were also detected in the CAF on 6-7 days post inoculation. In the histological sections of the CAM, there were abundant small dark colored rounded bodies of gametes; distributed extensively in tissues of CAM on 5-7 days post inoculation of sporozoites. In some cases, cluster of small mature and immature relatively large bodies were seen in increasing numbers on 5-6 days post inoculation.

Animals↗
PubMed1999

Adapt globally, act locally: the effect of selective sweeps on bacterial sequence diversity.

Previous studies have shown that genetic exchange in bacteria is too rare to prevent neutral sequence divergence between ecological populations. That is, despite genetic exchange, each population should diverge into its own DNA sequence-similarity cluster. In those studies, each selective sweep was limited to acting within a single ecological population. Here we postulate the existence of globally adaptive mutations, which may confer a selective advantage to all ecological populations constituting a metapopulation. Such adaptations cause global selective sweeps, which purge the divergence both within and between populations. We found that the effect of recurrent global selective sweeps on neutral sequence divergence is highly dependent on the mechanism of genetic exchange. Global selective sweeps can prevent populations from reaching high levels of neutral sequence divergence, but they cannot cause two populations to become identical in neutral sequence characters. The model supports the earlier conclusion that each ecological population of bacteria should form its own distinct DNA sequence-similarity cluster.

Adaptation, Physiological↗
PubMed1998

Local interaction fields and adaptive regularizers for surface reconstruction and image relaxation.

A set of novel local interaction fields associated with input point data and adaptive regularizers are introduced for some problems in image processing and early-middle vision. The local interaction field is used to take the place of the delta-error term in conventional approaches. It consists of two parts; one is the usual error term, the other is a window function whose shape, size and orientation can be adapted to local structures in specific applications. Unlike the usual delta-error term, local interaction fields favour local flatness and thus impose smoothing implicitly. Several adaptive regularizers are introduced to keep discontinuities while smoothing. In finding solutions, even the simplest gradient descent algorithm is efficient in many examples. The results are stable under varying parameters and quite robust against noise.

Image Processing, Computer-Assisted↗
PubMed2000

Monolayer anulus fibrosus cell cultures in a mechanically active environment: local culture condition adaptations and cell phenotype study.

Intervertebral disc cells can be cultured in vitro. Several culturing systems in a mechanically active environment have been developed to study the relationship between mechanical stimulations and biochemical events. The aim of this study was to assess the phenotype of rabbit intervertebral disc cells from the anulus fibrosus (AF) region cultured on flexible substrate before and after application of cyclic tensile stretch (CTS) and to control culture conditions during application of CTS. CTS was applied with a pressure-operated instrument, inducing the deformation of flexible-bottomed culture plates (Flexercell) at 20% and 5% stretch, at a frequency of 1 Hz, during 30 minutes to 24 hours. A significant decrease in culture medium volume and temperature was observed (52% and 2.1 degrees C at 20% stretch and 24 hours' application of CTS). These phenomena were inhibited by adding culture medium around culture wells and by a culture medium temperature control system. Like AF cells cultured in plastic wells, AF cells cultured on flexible substrate expressed collagen type II, but collagen type I mRNA was not detected. In both culture conditions, neosynthesized proteoglycans had the same aggregating properties. CTS at 20% stretch during 12 hours did not induce cell detachment from the substrate and did not modify aggregating properties of neosynthesized proteoglycans; AF cells continued to express collagen type II but not collagen type I mRNA. In conclusion, the Flexercell system appears to be appropriate for studying, at the cellular level, the metabolic responses to CTS.

Adaptation, Physiological↗
PubMed1998

Miranda as a multidomain adapter linking apically localized Inscuteable and basally localized Staufen and Prospero during asymmetric cell division in Drosophila.

Neuroblasts in the developing Drosophila CNS asymmetrically localize the cell fate determinants Numb and Prospero as well as prospero RNA to the basal cortex during mitosis. The localization of Prospero requires the function of inscuteable and miranda, whereas prospero RNA localization requires inscuteable and staufen function. We demonstrate that Miranda contains multiple functional domains: an amino-terminal asymmetric localization domain, which interacts with Inscuteable, a central Numb interaction domain, and a more carboxy-terminal Prospero interaction domain. We also show that Miranda and Staufen have similar subcellular localization patterns and interact in vitro. Furthermore, miranda function is required for the asymmetric localization of Staufen. Miranda localization is disrupted by the microfilament disrupting agent latrunculin A. Our results suggest that Miranda directs the basal cortical localization of multiple molecules, including Staufen and prospero RNA, in mitotic neuroblasts in an actin-dependent manner.

Actins↗
PubMedDate not supplied

Early adoption of human immunodeficiency virus quality improvement in Veterans Affairs medical centers: use of organizational surveys to measure readiness to change and adapt interventions to local priorities.

Potential delivery system responsiveness to quality improvement (QI) interventions is rarely assessed before implementation, although it might aid in interventional design. Preparing for a national initiative, we assessed Veterans Affairs (VA) human immunodeficiency virus (HIV) clinic organizational characteristics and attitudes toward QI interventions. Current QI activities and attitudes toward potential effectiveness of several techniques to improve antiretroviral and opportunistic infection prophylaxis therapy were assessed. These included computerized clinical reminders (CRs), group-based QI, expert advice, and facility and provider-level audit/feedback. Organizational characteristics were also examined. Respondents rated CRs and group-based QI (GBQI) interventions most highly. Western and complex facilities viewed CR and GBQI interventions more positively than less complex facilities or those in other regions, even controlling for organizational characteristics and perceived barriers to change. VA clinicians favored CR and GBQI over facility/ provider feedback. The persistence of regional variation should be further explored. Organizational surveys of attitudes toward potential QI interventions can assist in choosing interventions and targeting specific facilities.

Attitude of Health Personnel↗