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PubMed1998

Membrane current noise in dark-adapted and light-adapted isolated retinal rods of the larval tiger salamander.

1. Low-frequency light-sensitive membrane current noise in isolated rod photoreceptors of the larval tiger salamander was recorded using suction electrodes, in the dark, and during light adaptation by backgrounds or by bleaching visual pigment. 2. In background light, noise variance increases and then decreases. For rods desensitized to similar levels by bleaching visual pigment, the noise variance either does not change (weak adaptation) or decreases (with stronger adaptation). 3. The power spectral density of the current noise in dark-adapted rods shows a component with half-power cut-off frequency at about 0.1 Hz, attributed to spontaneous single events and continuous noise from dark phosphodiesterase activity. A second component, with half-power cut-off frequency at about 1 Hz, may be due to slow components in the light-sensitive channel gating. 4. The power spectral density of the noise in background light is dominated by noise generated by the background. Background light adapts at least the first component of the noise seen in dark-adapted cells. For cells desensitized by bleaching, light adaptation of both components of the dark-adapted noise is observed. 5. The results confirm that the low-frequency noise in dark-adapted cells arises from the transduction mechanism of the rod, in that both components can be light adapted, and show that, for rods permanently desensitized by bleaching, the desensitization is not due to the presence of active visual pigment molecules similar to those produced by background light.

Adaptation, Ocular↗

PubMed2004

Preserved prism adaptation in bilateral optic ataxia: strategic versus adaptive reaction to prisms.

To date the anatomical substrate(s) of prism adaptation remain(s) particularly debated, with two main candidates emerging from the literature: the posterior parietal cortex (PPC) and the cerebellum. The functional processes involved in the acquisition of the adaptive aftereffects also remain largely unknown. The main result shown here is that a patient with a bilateral optic ataxia can adapt to an optical deviation, which allows us to make a step forward on these two issues. First, it demonstrates that the corresponding part of the PPC is not a necessary substrate for prism adaptation. Second, since this patient exhibits deficit for fast visuo-motor guidance, it provides direct evidence for a dissociation between on-line visuo-motor control and visuo-motor plasticity. Since the intermanual transfer rate of adaptation is larger in this patient than in control subjects, the PPC may still have an influence on adaptation under normal conditions. We propose a model of the relative contribution of the PPC and the cerebellum during prism exposure, associating these two structures with the two interacting behavioural components of prism adaptation described by previous psychophysical experiments: the strategic component would be linked to the PPC and the adaptive component to the cerebellum. In this model, the strategic component enters in conflict with the development and the generalisation of the adaptive aftereffects. This idea is compatible with the fact that a lesion of the PPC increases the transfer rate and the generalisation of the adaptation, as is also observed in unilateral neglect.

Adaptation, Physiological↗

PubMed1985

Effect of localized grating adaptation as a function of separation along the length axis between test and adaptation areas.

Aftereffect following adaptation to localized gratings was measured as a function of the separation along the length axis between test and adaptation gratings. When the adaptation gratings were located on or near the retinal area occupied by the test grating, contrast sensitivity greatly decreased. When the adaptation gratings were spatially separated from the test grating, contrast sensitivity significantly increased. This property is similar to that which was observed in our previous study, in which the adaptation gratings were displaced from a test grating along the modulation axis. The facilitatory aftereffect of the grating adaptation can be accounted for by assuming that there may exist two mechanisms involved in the adaptation process; one is a center mechanism responsible for the detection of a test pattern, its adaptation producing a reduction in responsiveness; the other is a surround mechanism which tonically inhibits the center mechanism, its adaptation resulting in an increase in the sensitivity of the center mechanism by releasing the tonic inhibition. The spatial property of the adaptation effect may reflect the nature of spatial integration process of the center and surround mechanism.

Adaptation, Ocular↗

PubMed2001

Bioaccumulation of copper(II) and nickel(II) by the non-adapted and adapted growing Candida sp.

The effect of copper(II) and nickel(II) ions on the growth and bioaccumulation properties of non-adapted and adapted growing cells of a non-pathogenic Candida sp. has been tested under laboratory conditions as a function of initial pH and initial metal ion concentration. Optimum pH value for maximum metal ion accumulation was determined as 4.0 for both the metal ions. Although the copper(II) adapted Candida sp. was capable of removing of copper(II) with the maximum specific uptake capacity of 36.9 mg g-1 at 783.6 mg dm-3 initial copper(II) concentration, non-adapted Candida was only capable of bioaccumulating copper(II) with 23.1 mg g-1 maximum uptake capacity from aqueous solution at 578.7 mg dm-3 initial copper(II) concentration. The non-adapted and nickel(II) adapted Candida cells also showed the highest nickel(II) uptake capacities (46.8 and 30.8 mg g-1, respectively) at 321.5 and 300.6 mg dm-3 initial nickel(II) concentrations, respectively. For both the non-adapted and nickel(II) adapted Candida sp., the growth of cells was totally inhibited by 500 mg dm-3 of nickel(II) ions. The results also indicated that copper(II) adapted Candida sp. has been found to be more efficient to accumulate larger amounts of copper(II) than that of nickel(II) bioaccumulated by nickel(II) adapted Candida at higher initial metal ion concentrations without loosing its biological activity.

Adaptation, Physiological↗

PubMed2003

Adaptive and cross-adaptive responses of persistent and non-persistent Listeria monocytogenes strains to disinfectants.

Persistent and non-persistent Listeria monocytogenes strains were tested for initial resistance and adaptive and cross-adaptive responses towards two quaternary ammonium compounds, alkyl-benzyl-dimethyl ammonium chloride and n-alkyldimethyl ethylbenzyl ammonium chloride, one tertiary alkylamine, 1,3-propanediamine-N-(3-aminopropyl)N-dodecyl, sodium hypochlorite and potassium persulphate. The initial resistance of two persistent and two non-persistent L. monocytogenes strains was observed to differ. Both types of strains adapted after a 2-h sublethal exposure to the quaternary ammonium compounds and the tertiary alkylamine, the highest increase in the minimum inhibitory concentration (MIC) being 3-fold. Progressively increasing disinfecting concentrations at 10 and 37 degrees C resulted in adaptation of L. monocytogenes to all disinfectants except potassium sulphate. The highest observed increase in MIC was over 15-fold, from 0.63 to 10 microg/ml of n-alkyldimethyl ethylbenzyl ammonium chloride. All strains reached approximately similar MICs. Stability of the increased resistance was tested by measuring MICs every seventh day for 28 days. The increased resistance to sodium hypochlorite disappeared in 1 week, but the quaternary ammonium compounds and the tertiary alkylamine showed increased resistance for 28 days. These results suggest that cellular changes due to adaptive responses continue to have an effect on the resistance some time after the exposure. All disinfectants were shown to cause cross-adaptation of L. monocytogenes, the highest increase in MIC being almost 8-fold. The only agent that L. monocytogenes could not be shown to cross-adapt to was potassium persulphate which did, however, cause cross-adaptation to the other disinfectants. The mechanism behind these adaptive responses seemed to be non-specific as cross-adaptation was observed not only between related but also unrelated disinfectants. These findings suggest that sustaining high disinfectant effectiveness may be unsuccessful by rotation, even when using agents with different mechanisms of action.

Adaptation, Physiological↗

PubMed2006

Molecular adaptation during adaptive radiation in the Hawaiian endemic genus Schiedea.

BACKGROUND: "Explosive" adaptive radiations on islands remain one of the most puzzling evolutionary phenomena. The rate of phenotypic and ecological adaptations is extremely fast during such events, suggesting that many genes may be under fairly strong selection. However, no evidence for adaptation at the level of protein coding genes was found, so it has been suggested that selection may work mainly on regulatory elements. Here we report the first evidence that positive selection does operate at the level of protein coding genes during rapid adaptive radiations. We studied molecular adaptation in Hawaiian endemic plant genus Schiedea (Caryophyllaceae), which includes closely related species with a striking range of morphological and ecological forms, varying from rainforest vines to woody shrubs growing in desert-like conditions on cliffs. Given the remarkable difference in photosynthetic performance between Schiedea species from different habitats, we focused on the "photosynthetic" Rubisco enzyme, the efficiency of which is known to be a limiting step in plant photosynthesis. RESULTS: We demonstrate that the chloroplast rbcL gene, encoding the large subunit of Rubisco enzyme, evolved under strong positive selection in Schiedea. Adaptive amino acid changes occurred in functionally important regions of Rubisco that interact with Rubisco activase, a chaperone which promotes and maintains the catalytic activity of Rubisco. Interestingly, positive selection acting on the rbcL might have caused favorable cytotypes to spread across several Schiedea species. SIGNIFICANCE: We report the first evidence for adaptive changes at the DNA and protein sequence level that may have been associated with the evolution of photosynthetic performance and colonization of new habitats during a recent adaptive radiation in an island plant genus. This illustrates how small changes at the molecular level may change ecological species performance and helps us to understand the molecular bases of extremely fast rate of adaptation during island adaptive radiations.

Adaptation, Physiological↗

PubMedDate not supplied

[Change in adaptability and kinetics of T-lymphocyte adaptation to hypotonia in pathological states of mammals].

The kinetics of adaptation of the volume of T-lymphocytes and their membrane potential in a hypotonic medium is investigated. It is shown to have a quasiperiodic character. The shortest adaptation period T = 2 min characterizes the adaptation of T-lymphocytes test animals, the most complete adaptation of the volume and the membrane potential in hypotonic medium. Upon adaptation their values are only 6% higher than respective values in an isotonic medium. If an aseptic inflammatory process develops in a mammalian organism, the adaptation period increases to T = 2.5 min, while the volume and the membrane potential remains 28% higher than in an isotonic medium. In the course of development of induced cancerogenesis, 10 min after the cells have been placed in a hypotonic medium, their size is equal to that at the point of maximal swelling, while the membrane potential is 20% lower than that in an isotonic medium. The reason for the varying adaptability of T-lymphocytes is, in our opinion, that, as the inflammation develops, the concentration of corticosteroids increases, the concentration of intracellular K+ decreases, the concentration of macromolecules increases and the potential of the plasmatic membrane of the cell rises, thus leading to the slowing down of the process of adaptation and its decreased extent. The lack of regulation of the volume by T-lymphocytes of mammals in the organisms of which cancerogenesis develops, testifies to the fact that, in such a case, cells lose their adaptability to changing external conditions. Therefore, the disappearance of adaptability of T-lymphocytes on the third day of development of cancerogenesis represents an early test of the process.

Adaptation, Physiological↗

PubMed1982

The acute regulation of mitochondrial proton conductance in cells and mitochondria from the brown fat of cold-adapted and warm-adapted guinea pigs.

Cells and mitochondria were prepared from the brown adipose tissue of adult guinea-pigs adapted to either 4-7 degrees C or 22-25 degrees C. The cold-adapted cells displayed noradrenaline-stimulated, propranolol-sensitive respiration, but noradrenaline failed to increase the respiration of the warm-adapted cells. Purine-nucleotide-sensitive proton conductance was greater in cold-adapted mitochondria than in warm-adapted controls. At the same time cold-adapted mitochondria were extremely sensitive to the uncoupling effect of endogenous and infused fatty acids, and resembled the mitochondria from the brown adipose tissue of cold-adapted hamsters. Warm-adapted mitochondria were ninefold less sensitive, and resembled liver mitochondria. With cold-adapted, but not warm-adapted mitochondria, respiration increased proportionately to the rate of fatty acid infusion. It is concluded that the presence of the 32000-Mr proton conductance pathway is necessary for the expression of a high sensitivity to fatty acid uncoupling, suggesting that the fatty acids interact directly with this protein to modulate the proton conductance during the acute regulation of thermogenesis.

Acclimatization↗

PubMed1995

Light adaptation of the human photopic oscillatory potentials: influence of the length of the dark adaptation period.

Photopic electroretinograms recorded immediately after a period of dark adaptation show a regular increase in amplitude with time spent in light. The retinal mechanisms at the origin of this light adaptation effect remain obscure. The purpose of this study was to investigate the duration of the dark adaptation period needed to produce an optimal light adaptation effect as demonstrated by photopic oscillatory potential recordings. Our results indicate that the light adaptation effect can be separated into two distinct processes. The first one, activated early in the dark adaptation process, reduces the amplitude of the fourth oscillatory potential to 32% of control after less than 5 min of dark adaptation, while the second process, activated after more than 10 min of dark adaptation, appears to impact solely the amplitude of the earlier oscillatory potentials 2 and 3. Our results suggest that the light adaptation effect is mediated by two distinct retinal pathways or mechanisms.

Adaptation, Ocular↗

PubMed2004

Attention enhances adaptability: evidence from motion adaptation experiments.

Several previous psychophysical and neurophysiological studies have investigated the separate effects of attention and adaptation on visual processing. Here, we investigated the combined effects of attention and adaptation on motion processing by measuring the effects of spatial attention on the duration of the motion after-effect (MAE) over a wide range of stimulus contrasts. MAE duration was compared between two conditions: full-attention, subjects were required to pay attention to the adapting motion stimulus, and poor-attention, subjects performed a difficult vowel detection task at the center of gaze and ignored the adapting motion stimulus. Attention was found to increase the MAE duration by a factor of 1.4, which was approximately constant over a wide range of stimulus contrasts (3.22-80.6%). Notably, this included contrasts for which the MAE duration had reached its asymptotic value. We show that a quantitative model based on known properties of directionally selective MT neurons can explain these results by assuming that attention enhances the effects of adaptation, a phenomenon we refer to as "adaptation gain". Specifically, attending to an adapting motion stimulus shifts the semi-saturation point (C50) of the underlying contrast response function (CRF) of motion detectors roughly 1.4-fold more to the right than does ignoring that same stimulus. By enhancing the effects of adaptation in this fashion, attention is predicted to enhance the adaptability of the visual motion system.

Adaptation, Physiological↗

PubMed1994

Understanding adaptive processes in a developmental context. A reappraisal of Hartmann's problem of adaptation.

Hartmann's theory of adaptation introduced the metapsychology of ego as an agent of adaptation to external reality as well as a defense against internal conflict. His notions of autonomous ego functions serving adaptation and of the child's biological preparedness for adaptation made a significant contribution to psychoanalytic developmental theory. However, the study of children developing in the midst of environmental discord and violence who enter such environments with or without an adequate endowment encourages a reappraisal of three issues in Hartmann's view of adaptation: (1) the developmental vicissitudes of adaptation, (2) the notion of an average expectable environment; and (3) the distinction between adaptation as state and as process. These issues are reviewed to outline factors that may preserve and foster adaptation for children in the face of adversity and chronic trauma. It is suggested that adaptation is better understood as the individual's reaching a relative state of autonomy vis-à-vis deviations from average expectable endowment, experience, or environment and as one that occurs not in spite of but in the context of adversity.

Adaptation, Psychological↗

PubMed1981

Adaptation problems with nursing home application for elderly persons: an application of the Roy adaptation nursing model.

This study sought to identify adaptation problems on the part of elderly persons and significant others that were associated with nursing home applications for elderly persons. Within the framework of the Roy Adaptation Nursing Model, an ex post facto research design was utilized to identify these adaptation problems. The four adaptive modes in this model are: physiological, self-concept, role function, and interdependence. The study group (n = 22) and a control group of elderly persons living in Calgary, as well as their significant others, were administered a structured questionnaire. Five hypotheses relating to overall adaptation problems, powerlessness, role reversal, guilt, and knowledge and utilization of services were formulated and tested. Only the hypothesis indicating role reversal on the part of the significant others was accepted. Adaptation problems encountered by the elderly which were associated with nursing home applications occurred in the self-concept and interdependence adaptive modes. The adaptation problems perceived by the significant others, which were associated with nursing home applications for their elderly, occurred in the self-concept, role function, and interdependence modes. Adaptation problems from the significant others' perception rather than from the elderly persons' perception appear to be more significantly associated with nursing home applications.

Adaptation, Psychological↗

PubMed1983

Light adaptation in cells of macaque lateral geniculate nucleus and its relation to human light adaptation.

Responses of macaque lateral geniculate nucleus (LGN) cells to stimuli of different incremental intensities and wavelength compositions were studied at different levels of light adaptation from scotopic to low photopic levels. Stimuli were large in comparison with receptive-field size. Human increment thresholds were measured for comparison. The strength of responses grew in many cells from threshold up to a saturation level as a logarithmic function of incremental intensity. More complex intensity-response functions were also obtained, particularly from parvocellular layer (PCL) cells, but the shape and slope of the intensity-response function changed as a function of adaptation level only with chromatic backgrounds. As a function of adaptation level, the intensity-response functions shifted along the logarithmic abscissa but not sufficiently for a complete contrast constancy. Thus responses to any constant contrast became smaller when adaptation level decreased. The change from cone to rod responses, when possible, took place without noticeable change in shape of intensity-response functions, and much of the adaptive shift of the functions could be attributed to the change-over between rods and cones. Differences between different cells in light adaptation and dark-adapted sensitivity were large, mostly because of variation in the strength of rod input. The strongest excitatory rod inputs were found in PCL cells activated by short-wavelength light, so that the highest sensitivity at low levels of illumination occurred in blue- and blue-green-sensitive cells. The lowest increment thresholds based on cones matched the thresholds of macaque cone late receptor potentials recorded by Boynton and Whitten (3). They were also similar to human cone thresholds measured psychophysically but only for small stimulus sizes that may approximate the size of the receptive-field centers. Human sensitivity was much higher when measured with large stimulus sizes, indicating integration at post-geniculate neural levels. Light adaptation, as evaluated with respect to contrast constancy and Weber law behavior, was similarly incomplete in monkey single cells and human perception. A few cat LGN cells were studied in a control experiment; results agreed with previous findings. The light adaptation of cat cels was more complete and sensitivity higher than those observed under comparable conditions in macaque single cells and human. The maintained activity level of cells was little affected by the intensity of steady backgrounds. Thus, the steady-state hyper-polarisation of receptors was not transmitted to LGN cells.

Adaptation, Ocular↗

PubMed1998

Pre-adaptation, adaptation and de-adaptation to high altitude in humans: hormonal and biochemical changes at sea level.

High altitude residence is known to modify body biochemistry and hormone status. However, the effects of such a sojourn on these status observed at sea level both immediately and later after return are not as well established as are the effects of an intermittent acclimation. The aim of this study was therefore to investigate these changes. To achieve our objectives, nine subjects received intermittent acclimation at low pressure in a barometric chamber (8 h daily for 5 days, day 1 at 4500 m, day 5 at 8500 m) before an expedition to the Himalayas. Hormonal and biochemical changes were studied using samples of venous blood taken at sea level before and after acclimation, after return from the expedition and 1 and 2 months after descent. Concentrations of thyroid hormones, adrenaline, noradrenaline (NA), hormones of hydromineral metabolism (aldosterone, renin, arginine vasopressin, atrial natriuretic peptide) as well as prolactin, cortisol, insulin and endothelin 1 were measured. Biochemical measurements made were plasma osmolality, and concentrations of glucose, total cholesterol, total proteins, pre-albumin, transferrin, complement 3C, apolipoproteins A1 and B and serum iron. Acclimation induced no alteration in hormone (except for NA with increases of about 1.5, fold P < 0.05) and biochemistry data. After the expedition, hormone responses were characterized by a higher total triidothyronine concentration (+18%, P < 0.05) while other hormones did not vary. A linear relationship was found between thyroid-stimulating-hormone and body mass changes after the expedition (r = 0.67, P < 0.05). The observed increased concentrations of plasma proteins and total cholesterol (P < 0.05) could be related to the restoration of lean body mass. At 1 and 2 months after return, no changes in hormones were observed but a significant decrease in transferrin concentration was noticed. The higher serum iron concentration reported after 1 month (P < 0.05) could have been the result of a physiological haemolysis. It was concluded that both acclimation and the expedition in the Himalayas affected hormone status and body biochemistry status even though the observed changes were slight and rapidly reversed.

Adaptation, Physiological↗

PubMed2005