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At least 703 records · Page 39Linked to original sources
PubMed1997

Influence of picrotoxin and strychnine on the spectral sensitivity of the turtle ERG b- and d-wave: I. Dark adaptation.

The ERG ON- (b-wave) and OFF-response (d-wave) to differently coloured stimuli was studied using a wide range of stimulus intensities in dark adapted turtle retina. The intensity-response curve of the b-wave showed saturation but that of the d-wave, decline in the high-intensity stimulus range. The curves of the relative spectral sensitivity of the ERG ON- and OFF-response were similar and showed a maximum in the longwave part of the spectrum. GABAergic blockade by 50 mumol L-1 picrotoxin caused an increase of the sensitivity, contrast sensitivity and the amplitude range of both ON- and OFF-responses without narrowing of the response dynamic range. In the range of lower stimulus intensities the ON-responses to blue stimuli and the OFF-responses to red stimuli were affected to a greater extent. An increased ERG b- and d-wave sensitivity was also observed during glycinergic blockade by 50 mumol L-1 strychnine. In the low intensity stimulus range the effect was maximal on the ON-response to blue stimuli and on the OFF-responses to 570 nm stimuli. It was concluded that the GABA- and glycinergic systems in the retina equalize rather than make different the relative spectral sensitivities of the ON- and OFF-responses.

Animals↗
PubMed2003

Spectral sensitivity of the pupillary system.

BACKGROUND: The spectral sensitivity of the pupillary mechanism is reported to be greater in the blue part of the visible spectrum compared to the sensitivity of the visual system as defined by V(lambda) for a two-degree field. This means that blue light gives rise to smaller pupils compared to those that occur with light of other colours of the same luminance. This has been interpreted as indicating that there may be a rod input to pupil response even at photopic levels of illumination. An alternative explanation is that the smaller pupil size for blue light is an artefact arising from the use of the CIE V(lambda) function which is based on the spectral sensitivity of the eye to a two-degree field. In most investigations of pupil response, the adapting luminous field is much larger than two degrees. METHOD: The size of the static pupil was measured using an entoptic method when the eye was adapted to a large 'Ganzfeld' field of wavelengths of 624, 580, 521, 467 and 429 nm and luminances ranging from mesopic to photopic. RESULTS: The pupil is smaller for light of shorter wavelengths compared to that for light of longer wavelengths of the same luminance. This effect disappears at photopic luminances when luminance is calculated using the V(10 degrees ) (lambda) function instead of the V(2 degrees ) (lambda) function but is still evident at mesopic levels. When pupil size is plotted against equivalent luminance for a 10-degree field V(10 degrees ) (lambda, L(eq)) pupil size is independent of wavelength. CONCLUSION: The apparent enhanced sensitivity of the pupil to blue light at photopic levels is an artefact arising from the inappropriate use of the V(2 degrees ) (lambda) for the measurement of luminance when the adapting field in pupil response measurements is a large field. Pupil size is a simple linear function of the log of equivalent luminance calculated for large fields for adapting luminances from photopic to mesopic and is independent of the wavelength of the adapting field for the whole range of adapting luminances.

Adaptation, Physiological↗
PubMed1991

EEG data compression with source coding techniques.

A data compression algorithm for the EEG, derived from the adaptive pulse code modulation scheme, is described where the consecutively computed differences are coded by passing them through a quantizer possessing only a few levels; the range of these levels is adapted to local signal statistics. Three different versions of the algorithm with data reduction up to 75% are presented. The system was validated using several multichannel-routine EEG recordings with both visual evaluation and computation of signal-to-noise ratios.

Algorithms↗
PubMed2003

A molecular phylogeny of the neotropical butterfly genus Anartia (Lepidoptera: Nymphalidae).

While Anartia butterflies have served as model organisms for research on the genetics of speciation, no phylogeny has been published to describe interspecific relationships. Here, we present a molecular phylogenetic analysis of Anartia species relationships, using both mitochondrial and nuclear genes. Analyses of both data sets confirm earlier predictions of sister species pairings based primarily on genital morphology. Yet both the mitochondrial and nuclear gene phylogenies demonstrate that Anartia jatrophae is not sister to all other Anartia species, but rather that it is sister to the Anartia fatima-Anartia amathea lineage. Traditional biogeographic explanations for speciation across the genus relied on A. jatrophae being sister to its congeners. These explanations invoked allopatric divergence of sister species pairs and multiple sympatric speciation events to explain why A. jatrophae flies alongside all its congeners. The molecular phylogenies are more consistent with lineage divergence due to vicariance, and range expansion of A. jatrophae to explain its sympatry with congeners. Further interpretations of the tree topologies also suggest how morphological evolution and eco-geographic adaptation may have set species range boundaries.

Animals↗
PubMedDate not supplied

[T- and B-components of immunity in acute altitude sickness].

Immunological aspects of the adaptation process were investigated in 57 male test subjects that stayed for 30 days at an altitude of 3600 m above sea level (Eastern Pamir Mountain Range). The uneventful development of adaptation was accompanied by a short-term decrease in the number and activity of T-lymphocytes. An acute mountain disease led to a distinct deficiency of T-cell immunity which still persisted on test day 30. Besides, the content of zero cells in circulating blood was increased and the blast-transformation reaction of lymphocytes to concanavalin A was inhibited. Prior to the ascent the test subjects who were susceptible to the acute mountain disease showed a lower content of T-lymphocytes and a higher content of zero cells in circulating blood.

Acclimatization↗
PubMed2025

Harnessing Landscape Genomics to Evaluate Genomic Vulnerability and Future Climate Resilience in an East Asia Perennial.

In this era of rapid climate change, understanding the adaptive potential of organisms is imperative for buffering biodiversity loss. Genomic forecasting provides invaluable insights into population vulnerability and adaptive potential under diverse climatic conditions, thereby facilitating management interventions and bolstering shaping species-specific germplasm conservation strategies. We primarily employed landscape genomics approaches, leveraging single-nucleotide polymorphisms obtained through whole-genome resequencing of 201 individuals across 43 Rheum palmatum complex populations, to pinpoint adaptive variation and its significance in the context of future climates, delineate seed zones, and establish guidelines for ex situ germplasm conservation. The species complex exhibited strong signatures of local adaptation and differential genomic vulnerabilities across its distribution range, with eastern lineage populations facing significant maladaptation risks under future climate scenarios. Using diverse datasets of putatively adaptive loci and climate change scenarios, we delineated three distinct seed zones within the species' range, estimated varying sample sizes per zone to capture most adaptive diversity, and predicted shifts in seed zone centroids ranging from 48.3 to 359.3 km from historical distributions to mitigate climate change impacts. Collectively, our findings underscore the importance of integrating genomic and environmental data to forecast the adaptive trajectory of an East Asian perennial under anticipated climate changes, guide seed zone delineation for germplasm conservation and enhance population resilience. These results provide a blueprint for designing targeted conservation strategies and restoration plans in other imperilled species.

Climate Change↗
PubMed2006

Precise adaptation in bacterial chemotaxis through "assistance neighborhoods".

The chemotaxis network in Escherichia coli is remarkable for its sensitivity to small relative changes in the concentrations of multiple chemical signals over a broad range of ambient concentrations. Key to this sensitivity is an adaptation system that relies on methylation and demethylation (or deamidation) of specific modification sites of the chemoreceptors by the enzymes CheR and CheB, respectively. It was recently discovered that these enzymes can access five to seven receptors when tethered to a particular receptor. We show that these "assistance neighborhoods" are necessary for precise adaptation in a model for signaling by clusters of chemoreceptors. In agreement with experiment, model clusters composed of receptors of different types exhibit high sensitivity and precise adaptation over a wide range of chemical concentrations and the response of adapted clusters to addition/removal of attractant scales with free-energy change. We predict two limits of precise adaptation at large attractant concentrations: Either receptors reach full methylation and turn off, or receptors become saturated and cease to respond to attractant but retain their adapted activity.

Adaptation, Physiological↗
PubMed1987

Macromolecular crowding increases binding of DNA polymerase to DNA: an adaptive effect.

Macromolecular crowding extends the range of ionic conditions supporting high DNA polymerase reaction rates. Reactions tested were nick-translation and gap-filling by DNA polymerase I of Escherichia coli, nuclease and polymerase activities of the large fragment of that polymerase, and polymerization by the T4 DNA polymerase. For all of these reactions, high concentrations of nonspecific polymers increased enzymatic activity under otherwise inhibitory conditions resulting from relatively high ionic strength. The primary mechanism of the polymer effect seems to be to increase the binding of polymerase to DNA. We suggest that this effect on protein-DNA complexes is only one example of a general "metabolic buffering" action of crowded solutions on a variety of macromolecular interactions.

Binding Sites↗
PubMed1993

Differences in adaptation between on- and off-centre ganglion cells and rod-mediated cone sensitization in cat retina.

1. Response properties of on- and off-centre retinal ganglion cells were investigated in cats. The stimulus parameters were selected so as to demonstrate interactions between the rod and the cone systems. 2. Response versus log stimulus intensity (R-log I) functions were determined for the receptive field centres while both test stimulus irradiance and the background illumination were varied over a range up to 7 log units. In order to determine the course of adaptation to chromatic stimuli, threshold versus intensity (t.v.i.) functions were measured over a wide range of adaptation levels. 3. An increase in background illuminance produced a shift of the R-log I functions to higher irradiances of test stimuli in most ganglion cells, indicating a desensitization of the centre response in the presence of background lights. Using test stimuli which most efficiently stimulate the rods (501 nm), clear differences could be seen in the adaptation behaviour of on- and off-centre ganglion cells. Chromatic backgrounds (blue-green and orange) reduced the responses of off-centre cells more than those of on-centre cells (the difference between them amounting to as much as 2 log units). Simultaneously, equivalent t.v.i. functions had significantly steeper slopes (0.94 and 1.1) in the linear proportions of off-centre cells compared to on-centre cells (0.76 and 0.75) under light levels mediated by rods. Such differences were not observed when a test stimulus of 575 nm was used which resulted primarily in stimulating the long-wavelength cone (L-cone) system. 4. In a subpopulation of off-centre cells (20% of the total number of off-centre cells recorded), a strikingly different adaptation behaviour was observed. Here, the presentation of a dim short-wavelength background produced a shift of R-log I functions to lower test stimulus irradiances. The receptive field centre became even more sensitive, by up to 1.5 log units, in the presence of dim adapting backgrounds rather than in the dark-adapted state. Accordingly, the t.v.i. function did not increase monotonically but showed a 'dip' in the presence of dim backgrounds. Only at photoic levels, the t.v.i. functions revealed a response behaviour similar to the other ganglion cells. The sensitization with dim backgrounds was only observed in the case of test stimuli designed to stimulate the cone system (575 nm) and in the presence of a rod-adapting blue-green background.(ABSTRACT TRUNCATED AT 400 WORDS)

Adaptation, Physiological↗
PubMed2005

Measuring physical function in patients with complex medical and postsurgical conditions: a computer adaptive approach.

OBJECTIVE: To examine whether the range of disability in the medically complex and postsurgical populations receiving rehabilitation is adequately sampled by the new Activity Measure--Post-Acute Care (AM-PAC), and to assess whether computer adaptive testing (CAT) can derive valid patient scores using fewer questions. DESIGN: Observational study of 158 subjects (mean age 67.2 yrs) receiving skilled rehabilitation services in inpatient (acute rehabilitation hospitals, skilled nursing facility units) and community (home health services, outpatient departments) settings for recent-onset or worsening disability from medical (excluding neurological) and surgical (excluding orthopedic) conditions. Measures were interviewer-administered activity questions (all patients) and physical functioning portion of the SF-36 (outpatients) and standardized chart items (11 Functional Independence Measure (FIM), 19 Standardized Outcome and Assessment Information Set (OASIS) items, and 22 Minimum Data Set (MDS) items). Rasch modeling analyzed all data and the relationship between person ability estimates and average item difficulty. CAT assessed the ability to derive accurate patient scores using a sample of questions. RESULTS: The 163-item activity item pool covered the range of physical movement and personal and instrumental activities. CAT analysis showed comparable scores between estimates using 10 items or the total item pool. CONCLUSION: The AM-PAC can assess a broad range of function in patients with complex medical illness. CAT achieves valid patient scores using fewer questions.

Activities of Daily Living↗
PubMed1993

Vitamin B12 and folate. Pediatric reference ranges.

Pediatric reference ranges were obtained for vitamin B12 and folate (Quantaphase radioimmunoassay, BioRad, Hercules, Calif) using a large hospital population. Data were analyzed employing the Hoffman approach, which was computer adapted. For folic acid, the range for subjects aged 1 to 12 years averaged 5.7 to 31.3 nmol/L for female subjects and 4.5 to 27.0 nmol/L for male subjects. There was a significant decrease in folic acid concentrations after 13 years, the upper limit being 16.5 nmol/L in female subjects and 19.9 nmol/L in male subjects. For vitamin B12, the values in the 0- to 1-year age group were nearly double those in the 13- to 18-year age group. For female subjects, the values in the 0- to 1-year age group were 168 to 1116 pmol/L and in male subjects were 216 to 891 pmol/L. At 13 to 18 years, for female subjects the values were 158 to 637 pmol/L and for male subjects, 134 to 605 pmol/L.

Adolescent↗
PubMed1997

Sexual signalling in bladder grasshoppers: tactical design for maximizing calling range.

Pair formation in the bladder grasshopper (Bullacris membracioides) is by duetting and male phonotaxis. Low-frequency stridulatory signals are emitted by an abdominal resonator in the male and are answered by females using a species-specific time delay. Acoustic transmission in the natural environment was studied using playback of sexual signals over distances of 450m under two atmospheric conditions (day and night). Upward-refracting sound conditions and a sound shadow zone beyond approximately 50m prevailed during the day. Acoustic enhancement was demonstrated at night when downward-refracting temperature inversions created a tunnel effect with sound caught between the ground and zones of different temperatures. Transmission conditions are almost ideal at night when the species actually calls; calling distances of 150m for the male signal in the afternoon increased to 1.5-1.9km at night, arguably the largest calling distance yet reported for insects. In contrast, female calls transmit over a maximum of 50m, signifying a marked discrepancy in the active space of sex-specific signals. Transmission distance may, however, be profoundly affected by levels of masking noise. Adaptations to increase the signal range may variously be found in the signal itself, in behaviour patterns or in the sensory system. Here we demonstrate aspects of the first two types of adaptation in the sexual signalling system of a grasshopper in which maximizing the calling range appears to be the major selection pressure, with lesser effects imposed by inter- and intraspecific pressures and by the transmission channel.

Animals↗
PubMed2002

A distinctive form of congenital stationary night blindness with cone ON-pathway dysfunction.

PURPOSE: To characterize a distinctive form of congenital stationary night blindness (CSNB). DESIGN: Observational case report. PARTICIPANTS: A 30-year-old male with a history of night blindness, several members of his family, a patient with "complete" congenital stationary night blindness (CSNB1), and groups of age-similar control subjects. METHODS: Rod-system function was evaluated by measuring psychophysical dark-adapted thresholds, by recording dark-adapted electroretinograms (ERGs), and by fundus reflectometry. Cone-system function was evaluated by recording light-adapted ERGs, including those to sawtooth flicker, and by recording light-adapted visually evoked potentials (VEPs) to luminance increments and decrements. MAIN OUTCOME MEASURES: Dark-adapted thresholds, ERGs, rhodopsin double densities, Goldmann visual fields, and VEPs. RESULTS: The patient's visual acuity, visual fields, and color vision were normal. His peripheral dark-adapted thresholds were rod-mediated but elevated by approximately 3 log units above normal. Rhodopsin double density and bleaching recovery were normal. His dark-adapted maximal-flash ERG showed a "negative" waveform, in which the b-wave was more reduced in amplitude than the a-wave, although the a-wave amplitude was also reduced. The rod photoreceptors contributed to the patient's dark-adapted ERGs, as illustrated by the unequal responses to cone-matched stimuli. The patient's cone-mediated thresholds for long-wavelength stimuli were within the normal range. However, his light-adapted brief-flash b-wave was abnormal in amplitude and implicit time. Selective abnormalities of the ON responses of the cone system were apparent in the patient's reduced b-wave amplitude to rapid-on flicker with a normal response to rapid-off flicker, and his prolonged VEP latencies to increments but not to decrements. CONCLUSIONS: The overall pattern of findings distinguishes this patient from previously described forms of CSNB. The results suggest that two factors likely contribute to the patient's night blindness: (1) a rod phototransduction defect and (2) a postreceptoral defect. The results also indicate dysfunction within the cone ON pathway.

Adult↗
PubMed1998

Adaptation in the processing of interaural time differences revealed by the auditory localization aftereffect.

Two experiments were conducted involving the auditory localization aftereffect, in which the perceptual lateralization of a test sound having an interaural time difference (ITD) shifts away from that of a prior adapting sound having a different ITD. First, the frequency selectivity of the aftereffect was examined for sinusoids presented through headphones, with various combinations of adapter and test frequencies below 800 Hz, using the method of constant stimuli. The magnitude of the aftereffect was found to be largest when the frequencies of the two tones were similar, and virtually disappeared at a frequency difference of one-half octave. Second, the ITD selectivity of the aftereffect was examined for 400-Hz sinusoids. Subjects' judgments of lateralization were measured directly in terms of the perceived azimuth of the test tone for various combinations of adapter and test ITDs in the range of +/- 625 microseconds. The magnitude of the aftereffect was found to be largest when adapter and test ITDs differed by approximately 250 microseconds. These results were successfully simulated by an interaural cross-correlation model having gain control. The results are consistent with the idea that the gain of ITD-selective units, located after binaural interaction but before across-frequency integration, is changed by recent input.

Humans↗
PubMed1988

Adaptation for growth at various saline concentrations by the archaebacterium Methanosarcina thermophila.

We report the ability of Methanosarcina thermophila TM-1 to adapt and grow in media containing NaCl concentrations of 0.005 to 1.2 M. When adapted to marine NaCl concentrations, this species ceased to produce the heteropolysaccharide outer layer typically formed by species of nonmarine origin. concomitant with this adaptation, M. thermophila ceased to grow as multicellular aggregates and existed solely in single-cell form. The sodium ion concentration was critical for the adaptation process, although magnesium ion appeared to contribute to the cell wall stability of single cells. The results suggest that these archaebacteria possess regulatory systems that enable them to adapt to environments with a wide range of saline concentrations.

Adaptation, Physiological↗
PubMed1988

[The heart and catecholamines from the viewpoint of the adaptive-trophic function of the sympathetico-adrenal system].

Basal excretion of DOPA, dopamine, noradrenaline and adrenalin and its variation in response to oral administration of L-DOPA, a catecholamine precursor, were measured in 491 patients with essential hypertension, cardiomyopathy and myocardial infarction to assess catecholamine synthesis reserves at the systemic level. It is suggested that the development and progress of these diseases is associated with initial activation of the system, accompanied by increased noradrenaline release, which is followed by a gradual decrease in mediator synthesis reserves. The physiologic noradrenaline/adrenalin constant hypothesis, based on clinical and experimental evidence, is supported by the results of catecholamine studies in the heart and the central nervous system in cases of sudden human cardiac death, demonstrating an abrupt drop in noradrenaline. A conclusion is made that adaptive-trophic adrenosympathetic function is linked with biochemical events maintaining noradrenaline content within a normal range.

Adaptation, Physiological↗
PubMed2003

Adaptation to disability in chronic obstructive pulmonary disease: neglected relationships to older adults' perceptions of independence.

PURPOSE: This study extends understanding of the relationship between disability and independence in older adults with COPD. METHODS: An interviewer-administered questionnaire was used to examine disability, adaptation, perceptions of independence, and self-efficacy in a sample of 50 community-dwelling older adults. Odds ratios were used to investigate relationships between variables. RESULTS: Participants used a wide range of behavioural strategies to adapt to their disability including: limiting activities, optimizing performance (e.g. taking rests), compensating for lost function (e.g. using equipment), and obtaining help from others. The relative use of these adaptations varied across five domains of activity: personal care, in-home mobility, household activities, community mobility, and valued activities. Most participants felt very or extremely independent in all domains. In personal care, those who reported greater disability (O.R. = 0.26), more frequent attempts to optimize performance (O.R. = 0.57), or greater reliance on help from others (O.R. = 0.79) were significantly (p < 0.05) less likely to feel very or extremely independent. CONCLUSIONS: The relationship between disability and perceptions of independence depends on the nature of the activity and is influenced by factors that are amenable to study and intervention. In particular, the vast array of behavioural strategies available to older adults with COPD enables them to feel highly independent despite disability.

Activities of Daily Living↗
PubMed1975

Safe protein-calorie ratios in diets. The relative importance of protein and energy intake as causal factors in malnutrition.

There has been up to now a lack of agreement as to the way in which protein and energy requirements could be combined to give estimates of adequate dietary protein-energy ratios. In particular, the relevance of the simple ratio, average protein--average energy requirement as a basis for assessing diets, has been questioned on the grounds that it fails to take account of individual variability in needs for energy, and of the extent to which these may be independent of variability in protein requirements. The main problem is to evaluate the range over which individuals can adapt either energy intake to suit expenditure, or expenditure to suit intake, without detriment to health or growth. One solution adopted by Beaton and Swiss in a recent paper is to accept the range of observed variability of energy intakes in normal populations as a measure of this. An alterative is to make use of experimental evidence for the minimum energy intake for maintenance of body energy content. These two approaches are compared, and are shown to give quantitatively similar results. The method based on minimum maintenance requirements offers the further advantage that it allows an assessment of dietary situations in relation to the likelihood of occurrence of different forms of protein--energy malnutrition; those situations in which protein deficiency is a secondary consequence of low energy intake are differentiated from those in which the primary cause is an inadequate level of protein in the diet. The adequate "safe" level of protein-energy ratio in the diets of 2- to 3-year old children is close to 5% and since most varieties of cereal grains appear to provide utilizable protein levels of close to this amount, this lends further support to the view that primary protein deficiency is unlikely to be the main factor causing protein-energy malnutrition in communities for which cereals are the cheapest source of energy.

Breast Feeding↗