Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “ADAPTATION”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,693 records · Page 94Linked to original sources
PubMed1981

Abnormal adaptation of visual contrast sensitivity in multiple sclerosis patients.

Some multiple sclerosis patients with 20/20 acuity complain of poor vision. In a previous report we accounted for this in our patient group by showing that multiple sclerosis had caused a depression of contrast sensitivity while sparing visual acuity. In this study we investigated whether some of this measured depression might be due to abnormally rapid or severe adaptation during the test procedure rather than a true permanent loss. Our finding was opposite to this supposition: adaptation was normally slight and/or slow. Depressed contrast sensitivity was not well correlated with abnormal adaptation to contrast. In patients whose contrast sensitivity losses were restricted to a band of spatial frequencies, we found no evidence that abnormalities of contrast adaptation were restricted to this same spatial frequency band. Further evidence of dissociation between abnormal contrast sensitivity and abnormal contrast adaptation is that some patients with normal contrast sensitivity showed abnormally small adaptation.

Adaptation, Ocular↗
PubMed1991

Involvement of glycinergic neurons in the diminished surround activity of ganglion cells in the dark-adapted rabbit retina.

Previous studies have reported that the surround responses of retinal ganglion cells weaken or disappear upon dark adaptation. The mechanism(s) by which this occurs is largely unknown, although changes in activity of retinal dopaminergic neurons have been implicated. In the light-adapted rabbit retina, the surround ON responses of OFF-center ganglion cells have been shown to be markedly reduced or abolished by a dopamine antagonist. This effect of a dopamine antagonist was recently shown to be reversed by the glycine antagonist strychnine and by compounds that elevate intracellular cAMP levels. The present study was conducted to determine whether strychnine and cAMP-elevating compounds could bring out the surround ON responses in OFF-center ganglion cells that are diminished upon dark adaptation. Extracellular recordings of OFF-center brisk ganglion cells were made from isolated, superfused retinal preparations. During the course of dark adaptation, the surround ON responses of many cells decreased markedly. Application of low micromolar concentrations of strychnine to the bathing solution brought out the surround ON responses in both brisk-transient and brisk-sustained OFF-center ganglion cells. The center OFF responses of these cells, on the other hand, were not enhanced by strychnine. Of the cAMP-elevating compounds tested, 8-(4-chlorophenylthio) cyclic AMP was the most effective in bringing out the surround ON responses in dark-adapted OFF-center ganglion cells. The effects of bath application of this cAMP analog were very similar to those of strychnine. The findings from this study suggest that under dark-adapted conditions glycinergic neurons inhibit the surround component of OFF-center ganglion cells. The release of glycine from these neurons is suggested to be regulated by a cAMP-dependent mechanism.

Aminobutyrates↗
PubMedDate not supplied

Characterization of the rod photoresponse isolated from the dark-adapted primate ERG.

The a-wave of the human dark-adapted ERG is thought to derive from activity of rod photoreceptors. However, other sources within the retina could potentially perturb this simple equation. We investigated the extent to which the short-latency dark-adapted rod a-wave of the primate ERG is dominated by the rod photoresponse and the applicability of the phototransduction model to fit the rod a-wave. Dark-adapted Ganzfeld ERGs were elicited over a 5-log-unit intensity range using short bright xenon flashes, and the light-adapted cone responses were subtracted to isolate the rod ERG a-wave. Intravitreal 4-phosphono-butyric acid (APB) and cis-2,3-piperidine-dicarboxylic acid (PDA) were applied to isolate the photoreceptor response. The Hood and Birch version of the phototransduction model, Rmax[1 - e(-I x S x (t-t(eff)))2], was fitted to the a-wave data while allowing Rmax and S to vary. Three principle observations were made: (1) At flash intensities > or =0.77 log sc-td-s the leading edge of the normalized rod ERG a-wave tracks the isolated photoreceptor response across the first 20 ms or up to the point of b-wave intrusion. The rod ERG a-wave was essentially identical to the isolated receptor response for all intensities that produce peak responses within 14 ms after the flash. (2) The best fit of sensitivity (S) was not affected by APB and/or PDA, suggesting that the inner retina contributes very little to the dark-adapted a-wave. (3) APB always reduced the maximum dark-adapted a-wave amplitude (by 15-30%), and PDA always increased it (by 7-15%). Using the phototransduction model, both events can be interpreted as a scaling of the photoreceptor dark current. This suggests that activity of postreceptor cells somehow influences the rod dark current, possibly by feedback through horizontal cells (although currently not demonstrated for the rod system), or by altering the ionic concentrations near the photoreceptors, or by neuromodulator effects mediated by dopamine or melatonin.

Aminobutyrates↗
PubMedDate not supplied

Effects of light adaptation on contrast processing in bipolar cells in the retina.

Effects of light adaptation on contrast processing in the outer retina were investigated over nearly four decades of background illumination by analyzing the intracellular responses of 111 bipolar cells, 66 horizontal cells, and 22 cone photoreceptors in the superfused eyecup of the tiger salamander (Ambystoma tigrinum). Light adaptation had striking and similar effects on the average contrast responses of the hyperpolarizing (Bh) and depolarizing (Bd) classes of bipolar cells: Over the lower two decades of background illumination, the contrast gain increased 7-fold to reach values as high as 20-30, the dynamic range and the half-maximum contrast decreased by about 60%, the total voltage range increased some 40%, and contrast dominance changed from highly positive to more balanced. At higher levels of background, most aspects of the contrast response stabilized and Weber's Law then held closely. In this background range, the contrast gain of bipolar cells was amplified some 20X relative to that of cones whereas the corresponding amplification in horizontal cells was about 6X. Differences in the growth of contrast gain with the intensity of the background illumination for cones versus bipolar cells suggest that there are at least two adaptation-dependent mechanisms regulating contrast gain. One is evident in the cone photoresponse such that an approximately linear relation holds between the steady-state hyperpolarization and contrast gain. The other arises between the voltage responses of the cones and bipolar cells. It could be presynaptic (modulation of cone transmitter release by horizontal cell feedback or other mechanisms) and/or postsynaptic, that is, intrinsic to bipolar cells. Contrast gain grew with the background intensity by a larger factor in horizontal than in bipolar cells. This provides a basis for the widely held view that light adaptation increases the strength of surround antagonism in bipolar cells. On average, the effects of light adaptation and most quantitative indices of contrast processing were remarkably similar for Bd and Bh cells, implying that both classes of bipolar cells, despite possible differences in underlying mechanisms, are about equally capable of encoding all primary aspects of contrast at all levels of light adaptation.

Adaptation, Ocular↗
PubMed2003

Flash-induced relaxation changes of the EPR signals from the manganese cluster and YD reveal a light-adaptation process of photosystem II.

By exposing photosystem II (PSII) samples to an incrementing number of excitation flashes at room temperature, followed by freezing, we could compare the Mn-derived multiline EPR signal from the S2 oxidation state as prepared by 1, 5, 10, and 25 flashes of light. While the S2 multiline signals exhibited by these samples differed very little in spectral shape, a significant increase of the relaxation rate of the signal was detected in the multiflash samples as compared to the S2-state produced by a single oxidation. A similar relaxation rate increase was observed for the EPR signal from Y(D*). The temperature dependence of the multiline spin-lattice relaxation rate is similar after 1 and 5 flashes. These data are discussed together with previously reported phenomena in terms of a light-adaptation process of PSII, which commences on the third flash after dark-adaptation and is completed after 10 flashes. At room temperature, the fast-relaxing, light-adapted state falls back to the slow-relaxing, dark-adapted state with t(1/2) = 80 s. We speculate that light-adaptation involves changes necessary for efficient continuous water splitting. This would parallel activation processes found in many other large redox enzymes, such as Cytochrome c oxidase and Ni-Fe hydrogenase. Several mechanisms of light-adaptation are discussed, and we find that the data may be accounted for by a change of the PSII protein matrix or by the light-induced appearance of a paramagnetic center on the PSII donor side. At this time, no EPR signal has been detected that correlates with the increase of the relaxation rates, and the nature of such a new paramagnet remains unclear. However, the relaxation enhancement data could be used, in conjunction with the known Mn-Y(D) distance, to estimate the position of such an unknown relaxer. If positioned between Y(D) and the Mn cluster, it would be located 7-8 A from the spin center of the S2 multiline signal.

Adaptation, Physiological↗
PubMed2004

Adaptation of soil biological nitrification to heavy metals.

The adaptive response of soil biological nitrification to Zn and Pb was assessed using an in situ method we have developed. The method is based on reinoculating a sterilized metal contaminated soil with the same soil that is either uncontaminated or has been incubated with metal. This approach excludes the potentially confounding effects of metal aging reactions in soils. We found added Zn concentrations which gave rise to a decrease in nitrification to 50% that of the uncontaminated soil (i.e. EC50) of 210 mg/kg for communities not previously exposed to Zn and 850 mg/kg for communities exposed to Zn for 17 months, indicating that significant adaptation of the community to Zn had occurred. Similarly, this protocol was able to demonstrate adaptation of soil biological nitrification to Pb, with EC50 values of 1960 and 3150 mg/kg for the unexposed and exposed treatments, respectively. Exposure of unadapted and adapted microbial communities to a combination of Zn and Cd showed that the presence of Cd did not lead to greater toxicity in either community. Adapted communities were not more sensitive to decreases in soil pH than unadapted communities. Prior exposure to Zn was found to confer significantly greater tolerance of the community to Pb. Prior exposure to Pb similarly conferred significantly greater tolerance of the community to Zn. Implications of the adaptive capacity of soil microbes to the development of critical threshold values for heavy metals in soil based on ecotoxicity assessments are discussed.

Adaptation, Physiological↗
PubMed1999

Different induction of adaptive response to ionizing radiation in normal and neoplastic cells.

Since the beneficial effects of low-dose radiation (0.01 Gy) are usually observed in normal cells, we investigated whether the adaptive response was induced by low-dose radiation in neoplastic cells of different origin as well as in normal cells. Cell lines used in this experiment were as follows: mouse lymphocytes (NL); L929 cells established from mouse connective tissue; primary mouse keratinocytes (PK); line 308 from mouse papilloma; X-ray sensitive lymphoma cells, L5178Y-S and EL-4 cells from mouse lymphoma. The adaptive response was determined by cell survival and apoptosis. The involvement of apoptosis in the adaptive response was examined by ELISA and TUNEL assay. Adaptive response was induced by pretreatment with low-dose radiation of 0.01 Gy in normal cells such as NL, L929, and PK, but not in L5178Y-S, EL-4, and line 308 cells. In addition, the reduction of apoptosis by pretreatment with low-dose radiation was observed in NL, L929, and PK, but not in L5178Y-S, EL-4, and line 308 cells. These results suggested that the adaptive response could be induced by pretreatment with low-dose radiation and the phenomena were observed in normal cells, not in neoplastic cells. In addition, pretreatment with low-dose radiation reduced apoptosis, suggesting that an anti-apoptotic pathway may be involved in the adaptive response.

Adaptation, Physiological↗
PubMed1999

Adaptation to a starch environment and regulation of alpha-amylase in Drosophila.

The adaptation to glucose and starch foods in six species, D. melanogaster, D. virilis, D. saltans, D. funebris, D. levanonensis and D. americana, was studied by measuring productivity. D. melanogaster and D. virilis adapted more to the starch environment than to the glucose environment, while D. saltans adapted more to the glucose environment than to the starch environment. D. funebris, D. levanonensis, and D. americana did not distinctly adapt to either environment. In addition, the regulation of amylase in the six species was investigated by measuring the levels of amylase activity with glucose and starch food environments. The levels of amylase activity in D. levanonensis and D. saltans were substantially low, indicating that these species cannot utilize starch as a carbon source. The starch-adapted species, D. melanogaster and D. virilis, showed higher levels of amylase activity with the starch environment and higher inducibility. These results suggest that changing the regulation of amylase is important for the adaptation to a starch environment in Drosophila.

Adaptation, Physiological↗
PubMed1999

Damage-repair kinetics and early adaptive response induced by gamma rays in murine leukocytes in vivo.

The kinetics of damage induction and repair at different doses, and the adaptive response induced by gamma ray exposure were determined in murine leukocytes in vivo. The adaptive response was determined after an adaptive dose of 0.01 Gy and a challenge dose of 1.0 Gy administered 60 min later. DNA damage was measured by the single cell gel electrophoresis. Results indicate there is an early and efficient repair process that acts even during the exposure to radiation, which is able to reduce 80% of damaged cells. Later, an increase in damaged cells occurs, which seems to represent the breaks induced during the repair of other kinds of lesions. This suggests that mouse cells are genetically adapted to repair this kind of damage. It was found that the adaptive pretreatment reduces the percentage of damaged cells caused by the challenge dose to one third, and diminishes the damage produced during the late repair. This indicates that the early adaptive response is caused by the induction of a process that protects DNA from damage induction, i.e., synthesis of substances that scavenge free radicals.

Adaptation, Physiological↗
PubMed2002

The relation between general cognitive level and adaptive behavior domains in individuals with autism with and without co-morbid mental retardation.

This study examined the association between adaptive behavior and general cognitive level in individuals with autism or PDD-NOS with and without comorbid mental retardation. Data from the screening version of the Vineland Adaptive Scales and the Wechsler Intelligence Scales were analysed in a sample of 67 subjects. While in the higher functioning individuals (IQ > 70, n = 34) IQ and adaptive behavior level differed significantly, performances were fairly comparable in subjects showing lower cognitive functioning (IQ < 70, n = 33). Regression models revealed a higher correlation between IQ and single adaptive behavior domains in the non-mentally retarded participants, with the domain Communication reaching the highest predictive power of the single adaptive behavior areas. Findings indicate, the relationship between adaptive and cognitive function in autistic disorders is mediated by the presence of a qualitative reduction of intelligence. Methodological limitations of the study are discussed.

Adaptation, Psychological↗
PubMed2003

Genetic adaptation controlled by methylations and acetylations at the nuclear and cytosolic levels: a hypothetical model.

Metabolic sensors related to the maturation of metabolism seem to control a process of generic adaptation involving the silencing of genes and the expression of their copies more adapted to environmental changes. Nuclear methylases and histone deacetylases control the gene silencing process. Nuclear methylases compete with cytosolic methylases for the same methyl donnors, this will favor the expression of unmethylated more adapted gene copies, when cytosotic methylases take over. Methylated cytosolic compounds may then represent an index of this adaptation. If a more adapted gene copy is mutated, the regulatory ligand of the gene product that does not find its target may induce a reexpression of the silenced gene. The hypothetical model proposed considers that gene silencing and expression of a more adequate copy involves a non-specific gene silencer switch that depends on the histone status; the silencer switch is counteracted by the ligand of the adapted gene copy product acting like an inducer.

Acetylation↗
PubMed2003

Relationship between motion VEP and perceived velocity of gratings: effects of stimulus speed and motion adaptation.

The N200 amplitude of the motion-onset VEP evoked by a parafoveal grating of variable speed (0.25-13.5 degrees/s), constant spatial frequency (2 cpd), contrast (4%), and direction (horizontally rightward) was studied before and after adaptation to a stationary or drifting grating (1 or 4 degrees/s). Psychophysical measurements were made simultaneously of the perceived speed. In the unadapted condition the slope of the N200 amplitude versus speed function is positive, but lower for high compared to low speeds. The N200 amplitude increases slightly after stationary adaptation. An increase in perceived speed is also evident after stationary adaptation. This increase is more pronounced for low compared to high speeds. Motion adaptation reduces N200 amplitudes over the entire speed range, whereas perceived speeds change from under-estimation to over-estimation when the speed exceeds 1.8 degrees/s after 1 degree/s adaptation and 4.5 degrees/s after 4 degrees/s adaptation. The simultaneous evaluation of motion VEP and psychophysical results supports the view that the neurons generating the N200 component are also involved in speed perception. The data suggest the existence of a limited number (three or more) speed channels.

Adaptation, Physiological↗
PubMed2000

Impact of FK506 and steroids on adaptation after intestinal resection or segmental transplantation.

Segmental small intestinal transplantation (SIT) using living related donors (LRD) is being evaluated as a therapy, clinically. Advantages of this technique include an increase in the donor pool, optimization of the timing of transplants, and potential immunologic benefits. However, the ability of a short segment of intestine to function after transplantation has not been investigated in large animal models. This study evaluates the impact of immunosuppression on the adaptive process and the ability of a transplanted segment of intestine to adapt. A pig model of segmental SIT was used. Animals were resected, leaving 150 cm of distal ileum (n = 5), resected and treated with FK506 (n = 4), or steroids (n = 4), or with FK506 + steroids (n = 7), or transplanted using a similar segment of ileum and treated with FK506 + steroid immunosuppression (n = 9). Animals undergoing resection, or resection plus steroid treatment, did well, gaining weight post-operatively (37% and 15% of preoperative weight, respectively). However, animals undergoing resection and treated with FK506 or FK506 + steroids did poorly, losing weight (-14% and -22% of preoperative weight, respectively) and showing significant impairment of intestinal adaptation, morphologically and functionally. Furthermore, FK506-treated animals developed inflammatory changes in the intestinal mucosa, mimicking rejection. Segmental SIT animals had a high rate of rejection (66%) and showed a similar impairment in adaptation. Hence, segmental SIT is a stringent physiological test of intestinal adaptation. FK506 appears to impair gut function after resection, either directly, or by interfering with the adaptive process. In this model of segmental SIT, FK506 and steroids at the doses tested did not provide adequate immunosuppression to prevent rejection and the graft did not function adequately to allow growth. Further studies are required to evaluate the mechanisms underlying these findings, and to determine if similar effects occur in humans.

Adaptation, Physiological↗
PubMed2000

Impaired dark adaptation in polycythemia. Improvement after treatment.

PURPOSE: To determine if dark adaptation is reduced in individuals with polycythemia and if so whether there is any improvement in dark adaptation after treatment. METHODS: Dark adaptation was recorded monocularly by automatic dark adaptometry in ten consecutive patients with polycythemia before and after treatment. Analogue investigations were performed in 31 healthy control subjects. RESULTS: Dark adaptation was markedly impaired in the patients as compared with the control subjects. After reduction of the red cell count and normalization of the hematocrit and hemoglobin the dark adaptation was markedly improved. There was no significant change in dark vision in the control subjects negating a confounding learning effect. CONCLUSION: The findings indicate a sustained but reversible neuronal hypofunction secondary to polycythemia. As the rheological abnormality was normalized, dark adaptation was improved, probably secondary to normalized microcirculation within the retina or the brain, or both, possibly with reactivation of formerly inactive neuronal cells.

Adult↗
PubMed2000

Cone electroretinogram amplitude growth with light adaptation in patients with retinitis pigmentosa.

PURPOSE: It has been hypothesized that the increase in the b-wave during light adaptation is directly related to the level of cone malfunction in patients with retinitis pigmentosa (RP). Because this hypothesis has important bearing on the mechanism for the increase in the electroretinogram (ERG), we examined the increase in the amplitude of the cone ERG during light adaptation in patients with typical RP. METHODS: Cone ERGs were recorded to Ganzfeld white flash stimuli in the presence of white background illumination in 51 RP patients and in 27 normal subjects. RESULTS: In the normals, the increase in the b-wave amplitude during light adaptation ranged from 14-92% of the dark-adapted amplitude. All RP patients showed an amplitude increase that ranged from 5 to 100% of the baseline amplitude. This increase was not significantly different from that of the normals (p = 0.71, unpaired t-test). The baseline amplitudes and the increase in the relative amplitude were weakly correlated in the RP patients (r = 0.31; p = 0.029). No significant difference was observed in the amplitude increase between patients with near normal b-wave implicit times and those with delayed times (p = 0.17, unpaired t-test). Changes of the b-wave implicit time were not significantly different from those in the controls. CONCLUSION: These findings that the changes in the cone ERG with light adaptation in the RP patients were very similar to those in normal subjects do not support the proposed hypothesis that the increase in the b-wave amplitude during light adaptation was directly related to the level of cone malfunction.

Adaptation, Ocular↗
PubMed1998

Trajectories of adaptation in pediatric chronic illness: the importance of the individual.

This study used individual growth modeling to examine individual difference and group difference models of adaptation. The adaptation of 27 children with juvenile rheumatoid arthritis (JRA) and 40 children with insulin-dependent diabetes mellitus (IDDM) was tracked for 18 months from diagnosis. A control group of 62 healthy children was followed over the same time period. Clustering procedures indicated that child and family adaptation could be described by a number of distinct adaptation trajectories, independent of diagnostic group membership. In contrast, parental adaptation trajectory was associated with diagnostic group membership and control over disease activity for the JRA group and with diagnostic group membership for healthy controls. The observation of common patterns across trajectory sets, as well as the finding that trajectories were differentially related to a number of variables of interest, support the use of trajectories to represent adaptation to chronic disease.

Adaptation, Psychological↗
PubMed1999

Perceptual depth synthesis in the visual system as revealed by selective adaptation.

Selective adaptations was used to determine the degree of interactions between channels processing relative depth from stereopsis, motion parallax, and texture. Monocular adaptations with motion parallax or binocular stationary adaptation caused test surfaces, viewed either stationary binocularly or monocularly with motion parallax, to appear to slant in the opposite direction compared with the slant initially adapted to. Monocular adaptations on frontoparallel surfaces covered with a pattern of texture gradients caused a subsequently viewed test surface, viewed either monocularly with motion parallax or stationary binocularly, to appear to slant in the opposite direction as the slant indicated by the texture in the adaptation condition. No aftereffect emerged in the monocular stationary test condition. A mechanism of independent channels for relative depth perception is dismissed in favor of a view of an asymmetrical interactive processing of different information sources. The results suggest asymmetrical inhibitory interactions among habituating slant detector units receiving inputs from static disparity, dynamic disparity, and texture gradients.

Adaptation, Physiological↗
PubMed2005

Adaptation of teams in response to unforeseen change: effects of goal difficulty and team composition in terms of cognitive ability and goal orientation.

Halfway through a 3-hour experiment in which 64 3-person teams needed to make a series of decisions, a communications channel began to deteriorate, and teams needed to adapt their system of roles in order to perform effectively. Consistent with previous research, team composition with respect to members' cognitive ability was positively associated with adaptation. Adaptation was also influenced by interactions of team goal difficulty and team composition with respect to team members' goal orientation. Teams with difficult goals and staffed with high-performance orientation members were especially unlikely to adapt. Teams with difficult goals and staffed with high-learning orientation members were especially likely to adapt. Supplemental analyses provided insight into the observed effects in that the difficulty of team goals and members' goal orientation predicted interpersonal, transition, and action processes, all of which predicted team adaptation.

Adaptation, Psychological↗