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PubMed1997

Contrast adaptation and the spatial structure of natural images.

Natural images have a characteristic spatial structure, with amplitude spectra that decrease with frequency roughly as 1/f. We have examined how contrast (pattern-selective) adaptation to this structure influences the spatial sensitivity of the visual system. Contrast thresholds and suprathreshold contrast and frequency matches were measured after adaptation to random samples from an ensemble of images of outdoor scenes or of synthetic images formed by filtering the amplitude spectra of noise over a range of spectral slopes. Adaptation selectively reduced sensitivity at low-to-medium frequencies, biasing contrast sensitivity toward higher frequencies. The pattern of aftereffects was similar for different natural image ensembles but varied with large changes in the slope of the noise spectra. Our results suggest that adaptation to the spatial structure in natural scenes may exert strong and selective influences on perception that are important in characterizing the normal operating states of the visual system.

Adaptation, Physiological↗
PubMed1985

[Adaptation of breeding swine to high environmental temperatures and delimitation of tolerance ranges of thermically stressed swine populations].

Proceeding from the morphological and physiological specifics of pigs as to their adaptation to high ambient temperatures, the paper presents recent international findings on problems of the thermal tolerance of breeding pigs active in reproduction. The effect of humidity and air speed near the animals are summarized in attempting to delimitate tolerance levels for thermal stress to pigs, and conclusions are drawn for the amelioration of the climate.

Adaptation, Physiological↗
PubMedDate not supplied

Individualization of 5-fluorocytosine therapy.

Using a convenient and fast HPLC procedure we determined serum concentrations of the fungistatic agent 5-fluorocytosine (5-FC) in 375 samples from 60 patients treated with this drug. The mean trough concentration (n = 127) was 64.3 mg/l (range: 11.8-208.0 mg/l), the mean peak concentration (n = 122) was 99.9 mg/l (range: 25.6-263.8 mg/l), the mean nonpeak/nontrough concentration (n = 126) was 80.1 mg/l (range: 10.5-268.0 mg/l). Totally 134 (35.7%) samples were outside the therapeutic range (25-100 mg/l), 108 (28.8%) being too high, 26 (6.9%) being too low. Forty-four (73%) patients showed 5-FC serum concentrations outside the therapeutic range at least once during the treatment course. In a prospective study we performed 65 dosage predictions on 30 patients by use of a 3-point method previously developed for aminoglycoside dosage adaptation. The mean absolute prediction error of the dosage adaptation was +0.7 mg/l (range: -26.0 to +28.0 mg/l). The root mean square prediction error was 10.7 mg/l. The mean predicted concentration (65.3 mg/l) agreed very well with the mean measured concentration (64.6 mg/l). The frequency distribution of 5-FC serum concentrations indicates that 5-FC monitoring is important. The applied pharmacokinetic method allows individual adaptations of 5-FC dosage with a clinically acceptable prediction error.

Adolescent↗
PubMed1994

Adaptation, specificity and host-parasite coevolution in mites (Acari).

Parasitism by mites is widespread and involves all the classes of vertebrates, from fishes to mammals. Owing to their small size and their great plasticity, mites are able to adapt to a wide range of habitats. Most of the species are ectoparasites but endoparasitism, especially in the respiratory tract, is common in birds and mammals. The morphological modifications appearing during the process adaptation to parasitic life, especially in Myobiidae, are analysed. Two kinds of characters are particularly important: the constructive specialized characters, consisting of the production of new structures, especially attachment organs allowing the mite to attach to the skin and the hair of the host, and regressive characters. Regression of the external structures is the most important phenomenon appearing in the process of evolution of parasitic mites. The importance of the regression in the parasite is correlated with the degree of evolution of the host. Host and parasite have a parallel evolution, but they go in opposite directions. The author surmises that the regressive evolution is related to the immunological reactions of the host that tend to reject the parasite. To escape from this rejection the parasite tends to select the less antigenic and therefore the most regressed phenotype. Specificity is generally strict in permanent parasites. Coevolution of host and parasite is studied in the family Myobiidae which parasitizes marsupials, insectivores, bats and rodents. The concordance between the radiations of the mites and that of their hosts is very high.

Adaptation, Biological↗
PubMed1996

Regulation of sensitivity in vertebrate rod photoreceptors by calcium.

Over the past decade and a half, there have been great advances in our understanding of how light is transduced into electrical signals by the retinal rod and cone photoreceptors in vertebrates. One essential feature of these sensory neurons is their ability to adapt to background illumination, which allows them to function over a broad range of light intensities. This adaptation appears to arise mostly from negative feedback on phototransduction that is mediated by calcium ions. Recent work has suggested that this feedback is fairly complex, and involves several pathways directed at different components of phototransduction. From direct measurements of these feedback pathways in rods, it is possible to evaluate their relative contributions to the overall sensitivity of the cell. At the same time, these feedback mechanisms, as currently known, appear to be sufficient for explaining the change in sensitivity of rods during adaptation to light.

Animals↗
PubMed2003

Planning endovascular vein valve implantation: significance of vein size variability.

OBJECTIVE: Endovascular placement of prosthetic valves is currently in clinical trials as treatment for lower extremity venous hypertension caused by valvular insufficiency. Femoropopliteal vein sizing is a critical factor in treatment planning. A wide diameter range could influence selection of an endoprosthesis. Quantitative data describing intrasubject vein diameter variation are scant. We measured vein diameters with ultrasound imaging to assess minimum-maximum diameter range under forced conditions of venoconstriction and venodilatation. METHODS: Diameter of the common femoral vein (CFV), proximal femoral vein (PFV), mid-femoral vein (MFV), and distal femoral vein (DFV) in the thigh and the popliteal vein (PV) was measured in the morning under conditions of minimal venodilation and in the afternoon under conditions of stressed venodilatation that included activities of daily living and a 5-minute treadmill walk. Measurements were obtained twice on two different days in both extremities in 20 subjects with CEAP clinical classification C(0) (n = 10), C(3) (n = 7), C(4) (n = 1), or C(5) (n = 2). RESULTS: Average vein diameter increased, from 11.2 +/- 2.5 (SD) mm to 14.5 +/- 2.3 mm at the CFV, from 6.9 +/- 1.8 mm to 9.4 +/- 1.9 mm at the PFV, from 6.9 +/- 1.6 mm to 9.0 +/- 1.8 mm at the MFV, from 7.3 +/- 1.7 mm to 9.1 +/- 1.5 mm at the DFV, and from 8.4 +/- 1.4 mm to 9.7 +/- 1.8 mm at the PV (P <.001 for all differences). Maximum diameter change was 8.2 mm at the CFV, 7.0 mm at the PFV, 6.6 mm at the MFV, 6.0 mm at the DFV, and 5.1 mm at the PV. Dilatation of 4 mm or greater occurred in 43% of CFV, 15% of PFV, 11% of MFV, 3% of DFV, and 1% of PV. Minimum vein diameter was found at PFV in 41%, MFV in 34%, and DFV in 23% of morning measurements and at PFV in 21%, MFV in 38%, DFV in 28%, and PV in 16% of afternoon measurements. CONCLUSIONS: Femoropopliteal veins demonstrated a wide range of diameters, and significant diameter changes were detected in all vein segments. Variations in vein diameter must be evaluated in candidates for endovascular venous valve prostheses. Such devices must adapt to a wide range in vein diameter.

Adult↗
PubMed2004

Flagellar motors of marine bacteria Halomonas are driven by both protons and sodium ions.

Bacterial cells in aquatic environments are able to reach or stay near nutrient patches by using motility. Motility is usually attained by rotating flagellar motors that are energized by electrochemical potential of H+ or Na+. In this paper, the ion specificity for flagellar rotation of two marine isolates Halomonas spp. strains US172 and US201 was investigated. Both isolates require sodium for growth and possess a respiratory-driven primary sodium pump. They are motile because of lateral flagella regardless of the presence of sodium ions. Their swimming speed under various concentrations of sodium ions with and without carbonylcyanide m-chlorophenylhydrazone, a proton conductor, and with and without phenamil, a specific inhibitor for the sodium-driven flagellar motors, was examined. The effect of carbonylcyanide m-chlorophenylhydrazone on the transmembrane proton gradient was also determined. Our results showed that the flagellar motors of the Halomonas strains were energized by both H+ and Na+ in one cell. The bimodal nature of Halomonas spp. motility with respect to the driving energy source may reflect ecophysiological versatility to adapt to a wide range of salt conditions of the marine environment.

Adaptation, Biological↗
PubMed1998

[Characteristics of the leadership of health center coordinators in the autonomous community of Murcia].

OBJECTIVE: To describe the style and effectiveness (adaptability) of the leadership of coordinators of an autonomous community according to the model of leadership on the ground, analysing its relationship with the work environment. DESIGN: Observational crossover study. SETTING: All the functioning teams in this community. PARTICIPANTS: Medical and nursing coordinators. MEASUREMENTS AND MAIN RESULTS: Hersey and Blanchard's questionnaire on leadership on the ground was employed. This identifies 1) the predominant style (scoring for style 0-12). On the approach of the coordinator to personal relationships and/or task development, it identifies 4 points: direction, persuasion, participation, delegation. 2) Adaptability of the manager (ranging from +24 to -24), based on that the best choice between different options depends on the maturity of the group. To contrast work environment and leadership, a validated questionnaire, adapted to our milieu, was used. Overall reply rate (51 coordinators) was 89.4%. Analysis of styles was: persuasive 5.05 points (SD = 1.25), participatory 4.74 (SD 1.76), directive 1.2 (SD 1.11) and delegating 0.34 (SD 0.68). Adaptability scored 8.38 points (SD = 4.67), and was greater for the nursing coordinators (p < 0.002) without differences for type, place or teaching qualifications. The work environment, both overall and by dimensions, correlated with adaptability, although no relationship was found with leaders' styles. CONCLUSIONS: Leadership adaptability was quite high and greater in nursing. The most prevalent styles were the persuasive and the participatory, more efficacious in teams of average maturity. Theoretical effectiveness was positively related to a better work environment.

Cross-Over Studies↗
PubMed1988

The spectrum of Salmonella infection.

Salmonellae have demonstrated an extraordinary capacity to adapt to a wide range of ecologic niches and to the peculiarities of modern society, such as the mass production of food products. The vast majority of infections in the United States are caused by serotypes not specifically adapted to human or animal hosts, whereas the most frequent isolate in developing countries is S. typhi, which is highly adapted to human hosts. The number of isolates reported in the United States has been increasing steadily since 1975, largely a result of outbreaks associated with the mass production of food products, particularly poultry, which is frequently contaminated. Salmonella infection occurs when ingested organisms bypass gastric defenses, multiply within the intestinal lumen, penetrate the intestinal mucosa, and multiply within macrophages of the reticuloendothelial system. They may then disseminate via the systemic circulation. Several virulence factors have been identified. The wide range of pathologic and clinical manifestations are subdivided into four syndromes, each requiring a distinct diagnostic and therapeutic approach: (1) gastroenteritis, (2) enteric fever, (3) bacteremia with or without metastatic disease, and (4) asymptomatic carriage. Although any serotype can cause any of these syndromes, certain serotypes are associated with specific presentations. Serious complications of bacteremic infection include infections of the aorta, endocardium, bone, and meninges. Salmonella infection is particularly severe in patients who have AIDS, leukemia, lymphoma, immunodeficiency of other causes, inflammatory bowel disease, schistosomiasis, and macrophage dysfunction. Diagnosis is based on culture of the organism from appropriate sites. Several serologic tests have been developed that warrant further evaluation. Chloramphenicol, ampicillin, amoxicillin, and trimethoprimsulfamethoxazole have clearly established efficacy. Experience with third generation cephalosporins and quinolones is preliminary and fragmentary, but results suggest that they may prove to be efficacious in certain clinical circumstances. Antibiotic resistance has become a major problem in certain geographic areas. The three vaccines for S. typhi that are currently in use internationally provide only moderate protection for short periods of time.

Humans↗
PubMed2001

Adaptation in vertebrate photoreceptors.

When light is absorbed within the outer segment of a vertebrate photoreceptor, the conformation of the photopigment rhodopsin is altered to produce an activated photoproduct called metarhodopsin II or Rh(*). Rh(*) initiates a transduction cascade similar to that for metabotropic synaptic receptors and many hormones; the Rh(*) activates a heterotrimeric G protein, which in turn stimulates an effector enzyme, a cyclic nucleotide phosphodiesterase. The phosphodiesterase then hydrolyzes cGMP, and the decrease in the concentration of free cGMP reduces the probability of opening of channels in the outer segment plasma membrane, producing the electrical response of the cell. Photoreceptor transduction can be modulated by changes in the mean light level. This process, called light adaptation (or background adaptation), maintains the working range of the transduction cascade within a physiologically useful region of light intensities. There is increasing evidence that the second messenger responsible for the modulation of the transduction cascade during background adaptation is primarily, if not exclusively, Ca(2+), whose intracellular free concentration is decreased by illumination. The change in free Ca(2+) is believed to have a variety of effects on the transduction mechanism, including modulation of the rate of the guanylyl cyclase and rhodopsin kinase, alteration of the gain of the transduction cascade, and regulation of the affinity of the outer segment channels for cGMP. The sensitivity of the photoreceptor is also reduced by previous exposure to light bright enough to bleach a substantial fraction of the photopigment in the outer segment. This form of desensitization, called bleaching adaptation (the recovery from which is known as dark adaptation), seems largely to be due to an activation of the transduction cascade by some form of bleached pigment. The bleached pigment appears to activate the G protein transducin directly, although with a gain less than Rh(*). The resulting decrease in intracellular Ca(2+) then modulates the transduction cascade, by a mechanism very similar to the one responsible for altering sensitivity during background adaptation.

Adaptation, Ocular↗
PubMed1997

Evolutionary changes of nonlinear reaction norms according to thermal adaptation: a comparison of two Drosophila species.

While the adaptive significance of discontinuous reaction norms is generally accepted, the evolutionary interpretation of continuous response curves remains speculative, and the occurrence of internal constraints is often suggested as an explanation of experimental observations. In Drosophila melanogaster, various morphometrical traits exhibit convex reaction norms to growth temperature, with a maximum value within the developmental thermal range. We compared a cold-adapted species (D. subobscura) with a mid thermal range at 16 degrees C, to the warm-adapted D. melanogaster (mid thermal range at 22 degrees C) for three different morphometrical traits: wing and thorax length in both sexes and ovariole number in females. Maximum value temperatures were ordered in the same way for the three traits in both species: ovariole number > thorax length > wing length. Significant differences were also observed between the two species for the curvature parameter of the quadratic adjustment. The major observation was a significant lateral shift in the reaction norms: maximum values were observed at much lower temperatures in the cold-adapted species than in the warm-adapted one. The parallelism between mid thermal range variation and the position of the maximum value strongly suggests an adaptive displacement of the response curves. Natural selection may thus act not only on trait mean values but also on phenotypic plasticity and on the shape of reaction norms.

Animals↗
PubMed1994

A model of the role of adaptation and disadaptation in olfactory receptor neurons: implications for the coding of temporal and intensity patterns in odor signals.

Natural odors occur as turbulent plumes resulting in spatially and temporally variable odor signals at the chemoreceptor cells. Concentrations can fluctuate widely within discrete packets of odor and individual packets are very intermittent and unpredictable. Chemoreceptor cells display the temporally dynamic properties of adaptation and disadaptation, which serve to alter their responses to these fluctuating odor patterns. A computational model, modified from one previously published, was used to investigate the effect of adaptation and recovery of adaptation (disadaptation) on the spike output of model olfactory receptor cells under natural stimulus conditions. The response characteristics of model cells were based upon empirically determined dose-response, adaptation, disadaptation and flicker fusion properties of peripheral olfactory cells. The physiological properties of the model cell (adaptation and disadaptation rate and the dose-response relationship) could be modified independently, allowing assessment of the role of each in shaping the responses of the model cell. Complete adaptation and disadaptation time courses ranged from 500 ms (rapid cells) to 10 s (slow cells). The stimuli for the model cells were quantified odor plume recordings obtained under a variety of biologically relevant flow conditions. As expected, the rapidly adapting model cells displayed different response characteristics than the slowly adapting model cells to identical temporal odor profiles. Responses of the model cells depended upon their adaptation and disadaptation rates, and the frequency characteristics of the odor presentation. These results indicate that adaptation and disadaptation determine the range of concentration fluctuations over which a particular cell will respond. Thus, these properties function as an olfactory equivalent of a band-pass filter in electronics. This type of filtering has implications for the extraction of information from odor signals, such as the coding of temporal and intensity features.

Adaptation, Physiological↗
PubMed1998

Early developmental outcome after the Norwood procedure for hypoplastic left heart syndrome.

OBJECTIVE: To assess intellect and adaptive behavior in children with hypoplastic left heart syndrome (HLHS) who had undergone at least two surgical stages of the Norwood procedure. METHODS: Fourteen children with HLHS >3 years of age participated in the study. The patients underwent intelligence quotient (IQ) testing, and their parents were interviewed regarding their children's adaptive behavior. Results were compared with those of 10 family controls. Outcomes were studied for possible correlation with perioperative variables. RESULTS: Among the HLHS patients, the median scores for full scale IQ and adaptive behavior were 88 and 91, respectively (normal = 100 +/- 15). One child met criteria for mental retardation. Family controls scored generally higher than did HLHS patients, but only differences in adaptive behavior were statistically significant. A negative correlation was found between stage I circulatory arrest time and full scale IQ. CONCLUSIONS: Children with HLHS most often function in the low-normal range of intelligence and adaptive behavior. A prolonged circulatory arrest time may result in decreased intellectual function.

Adaptation, Psychological↗
PubMed1987

Mechanisms of halotolerance in microorganisms.

Microorganisms have the ability to adapt to a wide range of NaCl concentrations. In general the NaCl tolerance shown by microbes far exceeds the salt tolerance of any other organism, procryote or eukaryote. There are at least three mechanisms available for adaptation to different salt concentrations. The first would be a passive one in which the cytoplasmic ion content would always equal that in the medium. A second mechanism which is used by many organisms involves concentrating compatible solutes to create an osmotic balance between the cytoplasm and the external environment. The third mechanism involves changing the cell physiology to control the movement of water allowing the cell to exist with an ionically dilute cytoplasm. This article will review the major developments and discuss the implications of increasing knowledge about salt tolerance in microorganisms.

Bacteria↗
PubMed1996

Biomechanical studies of the remodeling of knee joint tendons and ligaments.

Living tissues and organs are dynamic and change their mechanical properties and structure in response to stress alteration as a phenomenon of functional adaptation and optimal operation. This phenomenon is called 'Tissue Remodeling', and Wolff's law on bone remodeling is widely known. Several recent studies have shown that fibrous connective tissues such as tendons and ligaments also have the ability of remodeling. However, relatively little is known about the stress and motion effects on tissue homeostasis in biological soft tissues. This article primarily deals with changes of the biomechanical properties of knee joint tendons and ligaments through a wide variety of treatment modalities, including stress deprivation, recovery after stress deprivation, and stress enhancement. The experimental results indicate that tendons and ligaments have an ability to adapt in response to the change of stress if the extent of stress alteration is within allowable ranges.

Adaptation, Physiological↗
PubMed2006

Determinants of range effects in face recognition.

The effects of test stimulus range on generalization gradients in humans were assessed for discriminations between faces that varied in brightness, faces that varied in orientation in the picture plane, and morphed faces. In Experiment 1, significant range effects, predicted by adaptation level theory, occurred when faces varied along the brightness or orientation dimension, but not for morphed faces. Changing the difficulty of discrimination of both training and test stimuli for Experiment 2 produced range effects in morphed faces. Experiment 3 explored training and testing stimulus factors as determinants of range effects in morphed faces. The results suggest that sufficiently biased testing ranges create shifts in response distributions (generalization gradients), and this may be amplified byusing relatively difficult discriminations between training stimuli.

Discrimination, Psychological↗
PubMed1996

Spatial and temporal properties of cat horizontal cells after prolonged dark adaptation.

We studied the change of spatial and temporal response properties for cat horizontal (H-) cells during prolonged dark adaptation. H-cell responses were recorded intracellularly in the optically intact, in vivo eye. Spatial and temporal properties were first measured for light-adapted H-cells, followed by a period of dark adaptation, after which the same measurements were repeated. During dark adaptation threshold sensitivity was measured at regular intervals. Stable, long lasting recordings allowed us to measure changes of sensitivity and receptive field characteristics for adaptation periods up to 45 min. Although cat H-cells showed no signs of dark suppression or light sensitization, they remained insensitive in the scotopic range, even after prolonged dark adaptation. Absolute thresholds were in the low mesopic range. The sensitization was brought about by a shift from cone to rod input, and by substantial increases of both spatial and temporal integration upon dark adaptation. The length constant in the light-adapted state was on average about 4 deg. After dark adaptation it was up to a factor of three larger, with a median ratio of 1.85. Response delays, latencies and durations for (equal amplitude) threshold flash responses substantially increased during dark adaptation.

Animals↗
PubMed1999

Ocular signs and symptoms and vitamin A status in patients with cystic fibrosis treated with daily vitamin A supplements.

BACKGROUND/AIMS: Patients with cystic fibrosis (CF) may have low plasma vitamin A levels from malabsorption, zinc deficiency, liver disease, or poor compliance with prescribed supplements. In view of the increasing number of adults with CF, many of whom drive cars, it is important to assess vitamin A status. In our centre an attempt has been made to achieve normal levels of fat soluble vitamins by annual estimation of plasma levels and appropriate oral supplementation. This study aimed to determine if this approach prevents vitamin A deficiency and the consequent problems with dark adaptation. METHODS: The study was conducted at the regional adult and paediatric cystic fibrosis unit and the patients were recruited from there. Dark adaptation studies were conducted at the department of ophthalmology, St James's University Hospital. All patients are regularly seen in the outpatient department by a CF specialist dietitian and have a comprehensive annual dietary assessment. 28 patients had the following investigations: serum retinol, plasma zinc, serum retinol binding protein, liver function tests, dark adaptation, contrast sensitivity, and anterior ocular surface status. 25 age and sex matched controls without CF or ocular pathology were also recruited for the dark adaptation study. RESULTS: None of the patients had vitamin A deficiency, the median value of serum retinol being 48 microg/dl, range 31-80 microg/dl (normal range 30-80 microg/dl). Dark adaptation was normal in all cases compared with the control group where the mean value was 3.4 log units of threshold luminance (95% confidence interval 2.4-4.0). None of the test group had a value of threshold luminance 2 SD above the mean value for the control group. Eight patients had reduced contrast sensitivity. The median value for serum zinc was 14.2 micromol/ l, range 13-81 micromol/l (normal range 8-23 micromol/l) and the median value for retinol binding protein was 36 mg/l, range 13-81 mg/l (normal range 35-58 mg/l). There was no correlation between dark adaptation and serum retinol, zinc, or retinol binding protein. Two patients had clinical evidence of dry eye. CONCLUSION: Regular estimates of plasma vitamin A together with appropriate supplementation and expert dietetic review can maintain normal dark adaptation in patients with cystic fibrosis. The occurrence of reduced contrast sensitivity function is well documented but remains an unexplained phenomenon and deserves further study.

Adolescent↗