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PubMedDate not supplied

[The autoregulation of intracellular oxygen tension and the modification of cellular radiosensitivity. The development of an adaptation hypothesis].

A hypothesis is reported postulating that the range within which the intracellular oxygen content varies with changes in the external oxygenation conditions is responsible for the oxygen-dependent radiosensitivity modification that may be controlled by the diffusion resistance of a cytoplasmic membrane. The adaptation mechanism of intracellular Po2 autoregulation is involved when drastic changes in the oxygen content of the environment occur. As the oxygen content decreases this mechanism provides maximal values of the intracellular Po2 required for optimizing cell viability; the increased oxygen content prevents cells from oxygen intoxication.

Adaptation, Physiological↗
PubMed2005

Lower-extremity gait kinematics on slippery surfaces in construction worksites.

PURPOSE: The purpose of this study was to investigate the lower-extremity kinematics when walking on potentially slippery surfaces in simulated construction worksite environments. METHODS: A survey was conducted to select two types of footwear, two floorings, and four contaminants to represent the local construction worksite environments, making 16 simulated conditions. A mechanical slip-resistance test was conducted to evaluate the slipping potential of the 16 conditions by the value of the dynamic coefficient of friction. The 16 conditions were classified into three groups by slipping potential. Fifteen harnessed Chinese male subjects were instructed to walk and avoid slips on each of the 16 simulated 5-m walkways 10 times at their natural cadence. The movements in the sagittal plane were videotaped, digitized, and analyzed by a motion analysis system. Gait pattern parameters were obtained. Lower-extremity kinematic data were time-normalized from foot strike (0% stance) to take-off (100% stance) and were extracted from foot strike to midstance (50% stance) at 10% stance intervals. RESULTS: ANOVA showed that with increased slipping potential, changes in gait pattern parameters included increased stance and stride time, shortened stride length, decreased propagation speed, and gentle heel strike. In lower-extremity kinematic parameters, significant differences were found mainly at the ankle joint rather than the knee joint. CONCLUSION: Strategies to prevent slips included increased stance and stride time, shortened stride length, decreased propagation speed, and gentle heel strike. The ankle joint played the most important role in adaptation strategy. Such strategy included reducing range of motion, maintaining a stiff joint, and achieving flatfoot landing or a plantarflexed ankle joint during the first 10% stance.

Accidental Falls↗
PubMed1978

[Adaptation and disadaptation of the myocardium of rats trained to hypoxia].

Adaptation to oxygen deficit resulted from training of rats to hypoxia (8--9% O2) at the normal atmospheric pressure, during 3 weeks. Subsequent 2-week training decreased the resistance to hypoxia (disadaptation). Perfusion of the isolated hearts of adapted and disadapted animals at anoxic regimen together with the recording of the systolic pressure in the left ventricle, the rhythm, glucose uptake, lactate excretion, coronary blood flow, and the histochemical data on SDH, MDH, LDH, and hydroxibutyric DH, as well as the electron microscopy of the left ventricle mitochondria, indicate that the range of compensation reactions increases in adapted rats and decreases in disadapted ones.

Adaptation, Physiological↗
PubMed1997

Mechanoelectrical transduction and adaptation in hair cells of the mouse utricle, a low-frequency vestibular organ.

Hair cells of inner ear organs sensitive to frequencies above 10 Hz adapt to maintained hair bundle deflections at rates that reduce their responses to lower frequencies. Mammalian vestibular organs detect head movements at frequencies well below 10 Hz. We asked whether hair cells of the mouse utricle adapt, and if so, whether the adaptation was similar to that in higher frequency organs such as the frog saccule. Whole-cell transduction currents were recorded from hair cells in the epithelium of the mouse utricle. Hair bundles were deflected by a fluid jet or a stiff probe. The transduction currents evoked by step deflections adapted over 10-100 msec. The mean operating range was 1.5 micron (deflection of the tip of the bundle), approximately threefold larger than in frog saccule. Taller and more compact bundles of the mouse utricle account for this difference. As in frog saccular hair cells, adaptation shifted the current-deflection (I(X)) relation along the deflection axis. These adaptive shifts had time constants of 10-20 msec and reached 60-80% of stimulus amplitude. The adaptive shift and voltage-dependent bundle movement are consistent with the motor model of adaptation. When the fluid jet was used, adaptation also broadened the I(X) relation and reduced the maximum current. Adaptation attenuated the transduction currents evoked by sinusoidal bundle deflections below 5 Hz, within the frequency range of the utricle, but because it was incomplete, substantial responses remained. Moreover, the adaptive shift mechanism preserves sensitivity even in the presence of large stimuli that would otherwise saturate transduction.

Adaptation, Physiological↗
PubMed1996

Suppression of first pain and slow temporal summation of second pain in relation to age.

BACKGROUND: Thermal stimuli delivered to skin of the arms or legs can produce a sensation of two distinct pains. These pains have been associated with activity in A-delta (first pain) and C-fiber (second pain) nociceptive fibers, respectively. Under appropriate conditions first pain decreases in intensity (adaptation) while second pain increases in intensity (slow temporal summation). Change in first and second pain to repeated stimulation of skin has not been assessed in relation to age. METHODS: Ten younger (M = 25 years) and ten older (M = 65 years) subjects participated in a study of first and second pain intensity elicited by nociceptive range heat pulses (.7 second pulses; adapting temperature 39 degrees C to a stimulus temperature of 51 degrees C) delivered to skin of arms and legs. Response times to sensations of first and second pain were assessed to provide evidence that subjects were responding to first and second pain. RESULTS: Age groups did not differ on pain intensity ratings of initial stimuli to previously unstimulated skin for either first or second pain. Older subjects failed to evidence slow temporal summation of second pain at the leg. Response times to first, but not second pain from the leg were delayed in the elderly. Response times to first and second pain at the arm did not differ with age. Auditory response times were slower in the older group. CONCLUSIONS: Age did not influence pain intensity to unadapted and unsensitized skin. Slow temporal summation of second pain was not observed at the leg in the older group, suggesting that mechanisms subserving C-fiber mediated sensitization of second order nociceptive neurons may fail with age. Longer response times to first, but not second pain in older subjects may represent an age effect on myelinated (A-delta; first pain) and not unmyelinated (C-fiber; second pain) nociceptive afferents and may represent a type of small fiber peripheral neuropathy.

Acoustic Stimulation↗
PubMed1975

Accommodative reactions of medullary respiratory neurons of the cat.

In most of the bulbospinal respiratory neurons, threshold depolarization increased during the early period of their spontaneous burst discharge but decreased again at the end of a burst. In some vagal respiratory neurons, however, threshold depolarization increased steadily until the very end of their discharge period. These changes generally were accompanied by changes in the rate of depol1rization of the spikes, the amplitude of their overshoot, and their discharge frequency. For a given synaptic input, as indicated by the constancy of the interspike membrane potential trajectories, threshold depolarization of bulbospinal neurons remained constant or even decreased. Only in some vagal neurons was an increase in threshold deplarization observed under these conditions. With the exception of some vagal neurons, most of the respiratory neurons did not show a pronounced accommodative behavior when stimulated with linear rising currents. When stimulating with current pulses, all neurons discharged repetitively with only slight adaptation, which was already complete by the first few spike intervals. The current-frequency relationship was linear and revealed a primary and secondary range. The results support neither accommodation nor adaptation as important mechanisms in the genesis of the rhythmic activity of respiratory neurons.

Adaptation, Physiological↗
PubMed2004

Integron-associated mobile gene cassettes code for folded proteins: the structure of Bal32a, a new member of the adaptable alpha+beta barrel family.

The wide-ranging physiology and large genetic variability observed for prokaryotes is largely attributed, not to the prokaryotic genome itself, but rather to mechanisms of lateral gene transfer. Cassette PCR has been used to sample the integron/gene cassette metagenome from different natural environments without laboratory cultivation of the host organism, and without prior knowledge of any target protein sequence. Since over 90% of cassette genes are unrelated to any sequence in the current databases, it is not clear whether these genes code for folded functional proteins. We have selected a sample of eight cassette-encoded genes with no known homologs; five have been isolated as soluble protein products and shown by biophysical techniques to be folded. In solution, at least three of these proteins organise as stable oligomeric assemblies. The tertiary structure of one of these, Bal32a derived from a contaminated soil site, has been solved by X-ray crystallography to 1.8 A resolution. From the three-dimensional structure, Bal32a is found to be a member of the highly adaptable alpha+beta barrel family of transport proteins and enzymes. In Bal32a, the barrel cavity is unusually deep and inaccessible to solvent. Polar side-chains in its interior are reminiscent of catalytic sites of limonene-1,2-epoxide hydrolase and nogalonic acid methyl ester cyclase. These studies demonstrate the viability of direct sampling of mobile DNA as a route for the discovery of novel proteins.

Amino Acid Sequence↗
PubMed2000

Adaptation of the phase of the human linear vestibulo-ocular reflex (LVOR) and effects on the oculomotor neural integrator.

The phase of the translational linear VOR (LVOR) can be adaptively modified by exposure to a visual-vestibular mismatch. We extend here our earlier work on LVOR phase adaptation, and discuss the role of the oculomotor neural integrator. Ten subjects were oscillated laterally at 0.5 Hz, 0.3 g peak acceleration, while sitting upright on a linear sled. LVOR was assessed before and after adaptation with subjects tracking the remembered location of a target at 1 m in the dark. Phase and gain were measured by fitting sine waves to the desaccaded eye movements, and comparing sled and eye position. To adapt LVOR phase, the subject viewed a computer-generated stereoscopic visual display, at a virtual distance of 1 m, that moved so as to require either a phase lead or a phase lag of 53 deg. Adaptation lasted 20 min, during which subjects were oscillated at 0.5 Hz/0.3 g. Four of five subjects produced an adaptive change in the lag condition (range 4-45 deg), and each of five produced a change in the lead condition (range 19-56 deg), as requested. Changes in drift on eccentric gaze suggest that the oculomotor velocity-to-position integrator may be involved in the phase changes.

Adaptation, Physiological↗
PubMed1981

Non-surgical factors in the correction of aphakia.

72 unselected patients wearing aphakic spectacle correction were examined more than 6 months postoperatively. Approximately one third had poor adaptation in spite of satisfactory acuity. No correlation with age was found in the 60-85 year range. Binocularity appeared to play no part in adaptation but a significant sex difference was found, females predominating in the non-adapted group. Tests of eye movements showed defects in vestibulo-ocular suppression, smooth pursuit, and saccadic accuracy in the non-adapted group. This may indicate floccular dysfunction as a reason for failure to adapt to aphakic spectacles. This suggests the possibility of a useful preoperative assessment test to predict adaptation difficulties.

Adaptation, Ocular↗
PubMed2005

Two realms of dark adaptation.

The recovery of rod responsiveness after saturating flashes is greatly retarded above a certain critical level of rhodopsin bleaching (approximately 0.1%). A mathematical description of the process of turn-off of the phototransduction cascade allows attributing different phases of the recovery to specific products of rhodopsin photolysis. The fast phase is determined by quenching of metarhodopsin II and activated transducin. The slow phase is controlled by decay of partially inactivated (phosphorylated and arrestin-bound) metarhodopsins, and by regeneration of rhodopsin. The transition between the two regimes of adaptation is rather abrupt, occurring within a few-fold range of stimulus intensity. This marks the border between reversal of light adaptation and dark adaptation, as it is commonly defined.

Adaptation, Ocular↗
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

Development and evolution of adaptive polyphenisms.

Phenotypic plasticity is the primitive character state for most if not all traits. Insofar as developmental and physiological processes obey the laws of chemistry and physics, they will be sensitive to such environmental variables as temperature, nutrient supply, ionic environment, and the availability of various macro- and micronutrients. Depending on the effect this phenotypic plasticity has on fitness, evolution may proceed to select either for mechanisms that buffer or canalize the phenotype against relevant environmental variation or for a modified plastic response in which some ranges of the phenotypic variation are adaptive to particular environments. Phenotypic plasticity can be continuous, in which case it is called a reaction norm, or discontinuous, in which case it is called a polyphenism. Although the morphological discontinuity of some polyphenisms is produced by discrete developmental switches, most polyphenisms are due to discontinuities in the environment that induce only portions of what is in reality a continuous reaction norm. In insect polyphenisms, the environmental variable that induces the alternative phenotype is a token stimulus that serves as a predictor of, but is not itself, the environment to which the polyphenism is an adaptation. In all cases studied so far, the environmental stimulus alters the endocrine mechanism of metamorphosis by altering either the pattern of hormone secretion or the pattern of hormone sensitivity in different tissues. Such changes in the patterns of endocrine interactions result in the execution of alternative developmental pathways. The spatial and temporal compartmentalization of endocrine interactions has produced a developmental mechanism that enables substantial localized changes in morphology that remain well integrated into the structure and function of the organism.

Adaptation, Physiological↗
PubMed2006

Radioadaptive response revisited.

Radiation-induced adaptive response belongs to the group of non-targeted effects that do not require direct exposure of the cell nucleus by radiation. It is described as the reduced damaging effect of a challenging radiation dose when induced by a previous low priming dose. Adaptive responses have been observed in vitro and in vivo using various indicators of cellular damage, such as cell lethality, chromosomal aberrations, mutation induction, radiosensitivity, and DNA repair. Adaptive response can be divided into three successive biological phenomena, the intracellular response, the extracellular signal, and the maintenance. The intracellular response leading to adaptation of a single cell is a complex biological process including induction or suppression of gene groups. An extracellular signal, the nature of which is unknown, may be sent by the affected cell to neighbouring cells causing them to adapt as well. This occurs either by a release of diffusible signalling molecules or by gap-junction intercellular communication. Adaptive response can be maintained for periods ranging from of a few hours to several months. Constantly increased levels of reactive oxygen species (ROS) or nitric oxide (NO) have been observed in adapted cells and both factors may play a role in the maintenance process. Although adaptive response seems to function by an on/off principle, it is a phenomenon showing a high degree of inter- and intraindividual variability. It remains to be seen to what extent adaptive response is functional in humans at relevant dose and dose-rate exposures. A better understanding of adaptive response and other non-targeted effects is needed before they can be confirmed as risk estimate factors for the human population at low levels of ionising radiation.

Adaptation, Physiological↗
PubMed2006

Performance of a dose-defining insulin infusion protocol among trauma service intensive care unit admissions.

BACKGROUND: Among critically ill patients, glycemic control reduces mortality and morbidities, but the use of intravenous insulin infusion is complicated by hypoglycemia. Having a standardized algorithm increases the likelihood of effective and safe utilization of intravenous insulin therapy. A tabular dose-defining protocol for intravenous insulin infusion is described, containing design elements intended to minimize risk for hypoglycemia while seeking control in a narrow target range, and performance is evaluated among critically ill trauma service patients. METHODS: The protocol assigns insulin infusion rate (IR) for ranges of blood glucose (BG). The columns are arranged in order of increasing maintenance rate (MR) for insulin infusion. Patient column assignment is determined according to rate of change of BG. During stable column assignment, the IR is a function of column MR and BG. Within-column, the protocol formula provides that (a) for BG between 70 mg/dL and target BG, the IR increases exponentially to the column MR; and (b) for BG above upper target BG range, the IR increases linearly as an adaptation of the rule of 1800, with slope determined by the column MR. Values for IR calculated by formula are rounded to correspond to BG ranges of the table. Performance was assessed in 27 sequential runs among 24 trauma service patients admitted to a surgical intensive care unit (2004-2005). RESULTS: Using point-of-care measurements, mean preinfusion BG was 230.0 +/- 67.9 mg/dL. BG < 140 mg/dL was reached during all 27 runs (median time 5.0 h), and target BG was < 110 mg/dL during 25 runs (median time 11.0 h). For the group of runs attaining target before interruption of insulin infusion, the average +/- SD of the principal measure of glycemic control, the within-run mean BG, was 113.7 +/- 14.8 mg/dL (coefficient of variation 13%, n = 25 runs). After attaining target, the average within-run SD for BG was 22.9 mg/dL. The within-run frequency of hypoglycemic measurements (BG < 70 mg/dL) as a percentage of BG determinations was 2.4%. In this series, no instance of BG <50 mg/dL was seen. CONCLUSIONS: This report describes a nurse-implemented tabular protocol for intravenous insulin infusion having the advantages of efficacy, safety, and simplicity of use. Wide variability of IR in the neighborhood of BG 110 mg/dL is associated with stable BG response, and protection against hypoglycemia is achieved by rapid decline of IR at BGs in or below the target range.

Adult↗
PubMed1996

Temporal and spatial frequency tuning of the flicker motion aftereffect.

The motion aftereffect (MAE) was used to study the temporal and spatial frequency selectivity of the visual system at supra-threshold contrasts. Observers adapted to drifting sine-wave gratings of a range of spatial and temporal frequencies. The magnitude of the MAE induced by the adaptation was measured with counterphasing test gratings of a variety of spatial and temporal frequencies. Independently of the spatial or temporal frequency of the adapting grating, the largest MAE was found with slowly counterphasing test gratings (at approximately 0.125-0.25 Hz). The largest MAEs were also found when the test grating was of similar spatial frequency to that of the adapting grating, even at very low spatial frequencies (0.125 c/deg). These data suggest that MAEs are dominated by a single, low-pass temporal frequency mechanism and by a series of band-pass spatial frequency mechanisms. The band-pass spatial frequency tuning even at low spatial frequencies suggests that the "lowest adaptable channel" concept [Cameron et al. (1992). Vision Research, 32, 561-568] may be an artifact of disadvantaged low spatial frequencies using static test patterns.

Adaptation, Ocular↗
PubMed2003

Adaptive crystal structures: CuAu and NiPt.

We discover that Au-rich Cu1-xAux and Pt-rich Ni1-xPtx contain a composition range in which there is a quasicontinuum of stable, ordered "adaptive structures" made of (001) repeat units of simple structural motifs. This is found by searching approximately 3x10(6) different fcc configurations whose energies are parametrized via a "cluster expansion" of first-principles-calculated total energies of just a few structures. This structural adaptivity is explained in terms of an anisotropic, long-range strain energy.

Journal Article↗
PubMed2002

Two temporal phases of light adaptation in retinal rods.

Vertebrate rod photoreceptors adjust their sensitivity as they adapt during exposure to steady light. Light adaptation prevents the rod from saturating and significantly extends its dynamic range. We examined the time course of the onset of light adaptation in bullfrog rods and compared it with the projected onset of feedback reactions thought to underlie light adaptation on the molecular level. We found that adaptation developed in two distinct temporal phases: (1) a fast phase that operated within seconds after the onset of illumination, which is consistent with most previous reports of a 1-2-s time constant for the onset of adaptation; and (2) a slow phase that engaged over tens of seconds of continuous illumination. The fast phase desensitized the rods as much as 80-fold, and was observed at every light intensity tested. The slow phase was observed only at light intensities that suppressed more than half of the dark current. It provided an additional sensitivity loss of up to 40-fold before the rod saturated. Thus, rods achieved a total degree of adaptation of approximately 3,000-fold. Although the fast adaptation is likely to originate from the well characterized Ca(2+)-dependent feedback mechanisms regulating the activities of several phototransduction cascade components, the molecular mechanism underlying slow adaptation is unclear. We tested the hypothesis that the slow adaptation phase is mediated by cGMP dissociation from noncatalytic binding sites on the cGMP phosphodiesterase, which has been shown to reduce the lifetime of activated phosphodiesterase in vitro. Although cGMP dissociated from the noncatalytic binding sites in intact rods with kinetics approximating that for the slow adaptation phase, this hypothesis was ruled out because the intensity of light required for cGMP dissociation far exceeded that required to evoke the slow phase. Other possible mechanisms are discussed.

3',5'-Cyclic-GMP Phosphodiesterases↗
PubMed2004

The cutaneous contribution to adaptive precision grip.

Only after injury, or perhaps prolonged exposure to cold that is sufficient to numb the fingers, do we suddenly appreciate the complex neural mechanisms that underlie our effortless dexterity in manipulating objects. The nervous system is capable of adapting grip forces to a wide range of object shapes, weights and frictional properties, to provide optimal and secure handling in a variety of potentially perturbing environments. The dynamic interplay between sensory information and motor commands provides the basis for this flexibility, and recent studies supply somewhat unexpected evidence of the essential role played by cutaneous feedback in maintaining and acquiring predictive grip force control. These examples also offer new insights into the adaptive control of other voluntary movements.

Adaptation, Physiological↗